NTT Technical Review

June 2021 Vol. 19 No. 6
View from the TopHiroshi Tanabe, Senior Executive Vice President and Senior Executive Manager of Digital
Transformation Headquarters, NTT EAST

Front-line ResearchersMasaaki Nagata, Senior Distinguished Researcher, NTT Communication Science Laboratories

Feature Articles: Challenges of NTT Space Environment and Energy Laboratories toward
Ultra-resilient Smart Cities

Research and Development on Technologies for Transforming the Global Environment from aSpace PerspectiveNext-generation Energy-utilization and CO2-conversion Technologies Contributing to Zero
Environmental Impact

Energy-distribution Platform Technologies toward Zero Environmental Impact



ESG Management Science and Technology for a Sustainable and Inclusive SocietyProactive Environment Adaptation Technology for Living Safely and Securely

Feature Articles: Healthcare Devices and Infrastructure-maintenance Technology that
Support People and Society

The Future Pioneered by Device Technology for a Sustainable SocietyPhysical-condition Management Technology for Creating More Comfortable Work Sites



Non-invasive Biological-information Sensing Using Photoacoustic Measurement Technology



Derusting Technology Using High-power Laser DeviceTechnology for Predicting Hydrogen Embrittlement in Reinforcing Bars of Concrete Poles

Feature Articles: Encryption and Security Technologies for Creating a Safe and Secure
SocietySecurity R&D Initiatives for Creating a Safe and Secure SocietyData Sharing and Utilization Technologies for Safe and Secure Value-creation ProcessesEstablishment and Development of Cybersecurity Technologies to Solve Problem of Increasing
Operation Costs and to Minimize Damage

Security Based on Quantum Information Technology and Data Protection of Quantum
Information

Regular Articles

Neutron-energy-dependent Semiconductor Soft Errors Successfully Measured for the FirstTime

Global Standardization Activities


Recent Standardization Activities of Optical Connectors in IEC

Practical Field Information about Telecommunication Technologies


Sulfur Damage and Its Countermeasures in Telecommunication Equipment and Facilities

External Awards

View from the Top

Passing on Expertise and Enthusiasm
in the New Era through IOWN
Initiatives and Making Front-line
Employees Shine
Hiroshi Tanabe
Senior Executive Vice President and Senior
Executive Manager of Digital Transformation
Headquarters, NTT EAST
Overview

In today’s society, in which technological innovation and market changes
are accelerating, NTT EAST is committed to solving problems of local
communities while valuing the ties that it has cultivated with those communities over the more than 100 years in the telephone business. We interviewed Hiroshi Tanabe, senior executive vice president of NTT EAST,
about his thought on the use of technology to solve social problems and why
he has been focusing on helping front-line employees shine.
Keywords: ICT, digital transformation, front line

Meet the expectations of local communities byconsidering changes in ways to use informationand communication—A little over a year has passed since you wereappointed senior executive vice president. How doyou feel about the unprecedented situation sincethen?
First of all, I would like to thank all our employees
and partners for their support and cooperation during
this difficult period of the novel-coronavirus (COVID19) pandemic. Looking back on this unprecedented
situation from a technological perspective, tremendous achievements in medical technology have beenmade. It took only about a month after COVID-19
was identified to pinpoint the causative virus and its
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Vol. 19 No. 6 June 2021

genome sequence. After that, PCR and other testing
methods were established, and within a year of
COVID-19 identification, vaccines were being manufactured. Another example of the extremely highlevel of technology was the impact of droplets
exhaled on other people was simulated using a supercomputer. Although my knowledge of pandemics isbased on novels, such as “The Plague” and “The Red
Zone,” I am reminded of today’s advances in medical
technology in light of the fact that during past pandemics, medical workers on the front line had nochoice but to wait for the disease to end without
knowing how to fight it. Regarding the present pandemic, I express my heartfelt gratitude to the medical
personnel who are struggling to cope with increasingcases caused by the spread of variants of COVID-19.
In this environment, as exemplified by the spread of1

View from the Top

teleworking, the ways to use information and communication technology (ICT) have changed dramatically over the past year. To support this dramaticchange, we have invited a researcher, who also
belongs to the University of Tsukuba, the Informationtechnology Promotion Agency, Japan, and other institution, to join our company, and developed and provided a virtual private network-based remote desktop
service called “thin telework system” as a support
tool for teleworking, which has been well received.
Many local governments have chosen NTT EAST
as a partner in the GIGA School Initiative of the
Ministry of Education, Culture, Sports, Science andTechnology, which aims to create an educational and
ICT environment that nurtures children’s creativity inSociety 5.0. I am grateful that we can be of service tosociety during this difficult period.
—It must have been hard for the front-line employees
to take countermeasures against COVID-19 infection.
Until March 2020, since we did not know the
impact of the COVID-19 pandemic on our customers,
we carried out repairs and construction work to
enable telework. As I mentioned above, as the realityof COVID-19 has gradually become clearer, we havebeen able to take countermeasures to ensure thesafety of our customers, all persons concerned, andour employees.
Furthermore, the outbreaks and clusters of infection in call centers have been reported worldwide.
Our business is supported by many people at our call
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centers, which respond to telephone-service breakdowns and general inquiries about products and services, and we have been able to suppress cluster outbreaks and minimize infections among our call-center
workers by taking countermeasures using our pastknowledge.
Taiwan has succeeded in containing the COVID-19
pandemic by using digital technology. I believe that
we can contribute to prevent the spread of virus in
Japan by further using our technology in cooperation
with medical facilities. One example is the use of our
Digital Twin Computing to connect the real world
with cyberspace. I think that by using this technology
to perform calculations, such as simulating infection
routes and identifying the source of clusters, and feed
the results back to the real world, it will be possible
to prevent the next pandemic. Such technology has
great potential, and I want us to contribute to society
by implementing it.
We want to be firmly rooted in the community in
new areas—Even in the face of the COVID-19 pandemic, NTT
EAST continues to take on challenges, doesn’t it?
About three years ago, to establish firm roots in thelocal community in new areas, we started an initiativein which branch managers and area business managers visit customers to listen to their problems andrequests. The majority of the comments we received
were issues related to the primary industries of agriculture, forestry, and fisheries.
2

View from the Top

With those comments in mind, we are striving tocontribute to solving the problems faced by local
companies and governments by making full use of
our strength in ICT. Specifically, to support agriculture, which is a major industry in many regions, wehave started various businesses. NTT AgriTechnology
was established in July 2019 to revitalize the local
economy and advance urban development by using
advanced technology to discover new possibilities
and value in the agricultural industry. Biostock
was established in July 2020 to build a sustainableregional recycling ecosystem in the livestock and dairy
industries. NTT e-Drone Technology was establishedin February 2021 to develop industrial drones initiallyfor agricultural use.
—The term “digital transformation (DX)” hasbecome familiar, and expectations for ICT to solve
social issues are rising.
In addition to the businesses described above, wehave launched several companies that use our ICT tosolve customers’ problems.
It is expected that working styles that use cloudtechnology, including teleworking during the COVID19 pandemic, will become the standard rather thanbeing transient. Although the needs to improve business operations and promote DX by introducing pub-lic cloud services are becoming apparent, many customers are hesitant to introduce cloud services
because they do not know much about them. To solve
this problem, in July 2020, Nextmode was established to support our customers’ sustainable growththrough our network and cloud-computing capabilities.
What’s more, to create new connections and experiences as well as new cultures and societies while
contributing to regional revitalization throughe-sports (the domestic market for which will reachabout 10 billion yen in 2022), NTTe-Sports waslaunched in January 2020. NTT ArtTechnology was
also established in December 2020 to contribute toregional revitalization and economic circulation bydisseminating valuable culture and art of regions
through digitalization and connecting region toregion and connecting regions to the world.
I believe that we can leverage our strengths in various fields. In collaboration with universities, we have
had quite a few collaborations with faculties of engineering, however, we are also promoting collaborations with researchers in other fields, and I want tofurther strengthen those collaborations from now
onwards. Universities are rooted in the local community, and many professors are not only experts but arealso active as hubs for solving local problems. Theremay be some fields that require ICT, so I want to
combine our strengths with those of these experts tosolve local problems.
Passing on expertise and enthusiasm—You have been with NTT for 34 years. What’s thejourney been like?
I am very attached to NTT Technical Journal (original Japanese version of NTT Technical Review).
One year after I joined NTT, I was assigned to theTechnology Development Department, where I wastold to gather all the back issues of “Tsuuken Geppou”(“The Monthly Journal of the Electrical Communica­tion Laboratory,” the predecessor of NTT Technical
Journal) and “Shisetsu” (Facilities) and create adetailed chronology of various communication technologies and the ideas of the people in charge of thosetechnologies. Therefore, I dug up those dusty issues
from the library of the NTT Hibiya Building andtabulated them in chronological order. When I was
asked to be interviewed for this issue, the first thingthat sprung to mind was the file containing those backissues.

NTT Technical Review

Vol. 19 No. 6 June 20213

View from the Top

I was then engaged in developing structures aroundcables and optical-related systems. At the time, I wasdoing basic research at NTT laboratories, writing
specifications at the Technology Development
Department to introduce those research results inbusiness, and discussing specifications with manufacturers and persons in charge at the site of introduction every day to make them tangible. On one occasion, I was told by a senior colleague to read a vast
amount of documents in the library before a meeting.
Those documents described discussions about costs
and technologies that had been held over the previous
few years. By reading those documents before themeeting, I learned the background of the discussion,and I understood what was being discussed. I was
reminded of my naivety every time I read those documents—which my seniors had left behind as proof of
their exhaustive pursuit of their mission to provide
high-quality services to customers. This custom canbe described as having established a mechanism forpassing on—from seniors to juniors—backgroundand enthusiasm related to the development of technology.
However, we live in an age that demands speed, andunlike the days that I described above, NTT-driven
technology is no longer dominant, so we are not necessarily at the center of technology. It is important
how quickly we can put technologies and services
from around the world into an easy-to-use form forcustomers. The Innovative Optical and Wireless
Network (IOWN) will allow NTT to take the lead in
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creating partnerships, and I believe that NTT’s expertise and enthusiasm for research and development in
the new era will be handed down from generation to
generation through this initiative.
—What have you valued when passing on your expertise and enthusiasm?
When I look back on my life journey as an engineer,I think my main concern over the past ten years has
been how to polish the front-line employees’ skills sothat they can shine at work. Thirteen years ago, I wastransferred to Iwate Prefecture as a branch manager.
At that time, the front-line work was not the first
focus of attention, namely, new employees had notbeen assigned to positions, and existing employees
were struggling to do their jobs. To overcome these
difficult circumstances, even after returning to theheadquarters, I was thinking of a system for supporting and training front-line employees.
Although ten years have passed since the Great East
Japan Earthquake, I still recall how our employees at
the Iwate branch worked with the spirit of “We willprotect the communications in this area ourselves”
after the disaster struck. Since many problems in
disaster sites often have to be dealt with manually, it
is vital to have that kind of spirit. In fact, I want todraw attention to the fact that front-line employees
deal with customers with pride and outstanding productivity not only in the event of disasters but also innormal times.
4View from the Top

Given those circumstances, I have been focusing on
productivity, changing the work style and culture in
the field, and upgrading work through DX. Throughthese activities, I have tried to get people to understand that change is required, even on the front lines,
so that those on the front lines can shine. Currently,
I am the head of the Digital Transformation Head­quarters, and I believe that this kind of effort is necessary regardless of whether you are working in thefield or at the headquarters. By embracing DX, wehope to further strengthen our ability to connect our
diverse technologies and expertise with the needs ofour customers throughout Japan and provide solutions to customers’ problems.
—You’ve been through a lot of intense situations. Do
you have any unforgettable experience?
Even today, I feel the anguish caused by the Great
East Japan Earthquake. On the day of the earthquake,
I was at NTT EAST’s headquarters in Hatsudai inTokyo while on a business trip, and immediately after
the earthquake had struck, I had no way to return to
the Iwate branch. In the early morning of the day that
I was finally able to return to Iwate via Akita airport,
I got a phone call from an employee at the disastersite. The employee said, “When people see us wearing NTT work clothes, they ask us to convey theirmessages to their families that they are safe,” andasked me if it is OK to meet such requests. When I
replied, “First you must restore the facilities,” thecaller said, “Do you know what is going on at thesite? You are always telling us to work for the community!” and hung up the phone. I still remember
how proud I was of the employees when I returned tothe branch and saw not only the employee who had
conveyed the message of the victims but also all theother employees working hard on site to restore thedamaged facilities and support our customers. What’smore, the employees who were due to retire at the endof March 2011, shed tears when they said, “I cannot
retire at this time. I want to be allowed to work until
this crisis is over.” Even now, my heart aches at thefact that the only thing I could do was to say “Thankyou for your tremendous efforts” to the employees

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who worked so desperately to contribute to the community and complete their mission to connect communications as social infrastructure.
This experience has led me to focus on highlighting
the front lines and helping front-line employees
shine; however, if I feel strongly that things are fine
the way they are, we won’t be able to meet the expectations of our customers. Just as the means of communications has changed from fixed-line telephones
to cell phones, the expectations of customers havealso changed over time. I also think it is important toexpand the spirit of pride in one’s work that has supported these front lines in new directions. I want tomake the front lines shine by multiplying new fields
and communications.
—What is your message to those who are engaged inresearch and development?
I think that NTT’s research labs can now be given
clear direction on the basis of IOWN, and I feel theenthusiasm and momentum of researchers towardthat goal. I hope our researchers will lead the NTT
Group—and society as a whole—with confidence
and pride in the fact that nothing is wasted in researchand development.

Interviewee profile
Career highlights
Hiroshi Tanabe joined Nippon Telegraph andTelephone Corporation in 1987. In his career at
NTT EAST, he became manager of the Iwate
branch office in 2008; senior manager of the Plant
Department, Network Business Headquarters, in
2011; executive manager of the Engineering
Department, Network Business Headquarters, in
2013; board of director in 2015; executive vicepresident in 2018; senior executive vice president, senior executive manager of the Digital
Transformation Headquarters, president of NTT
E-Asia, and president of NTT e-Drone Technology
in 2000.

5

Front-line Researchers

Being Different Is a Compliment.
Practice Talking Logically about
Future Plans
Masaaki Nagata
Senior Distinguished Researcher, NTT
Communication Science Laboratories
Overview
Research on machine translation using neural networks has
made rapid progress, and the accuracy of machine translation has
improved considerably. Although websites and smartphone apps
providing machine translation have become more popular, issues
with accuracy remain. To address such issues, researchers are
studying more advanced translation technology that reflects context, situation, and culture. We interviewed Masaaki Nagata,senior distinguished researcher at NTT Communication Science
Laboratories, who is researching context- and situation-basedneural machine translation, about the progress of his research andwhat it means to be a researcher.
Keywords: natural-language processing, machine translation, neural network

Our research has been highly appreciated at oneof the top international conferences onnatural-language processing—Please tell us about your current research.
Since 2013, when I was interviewed last time, I
have been researching technology for translating one
language into another. During this time, the target of
my research changed from statistical machine translation based on translating words and grammar toneural machine translation based on context and situation (Fig. 1). Artificial intelligence (AI) technology
has advanced rapidly since around 2014, for example,
AI beat humans in the game of Go. As a result, majorchanges have emerged in each research field related
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to AI. In speech recognition, AI can not only recognize speech, which was considered difficult, but can
do so with dramatically improved quality. In machinetranslation, in which I have been researching, translation accuracy has rapidly improved since 2016, andhuman parity, namely, human-like translation, has
become possible. The time has come when we cansuddenly do what was previously thought impossible.
In the course of searching for future research themes
while considering these trends, I realized that many
issues remain to be addressed. One such issue is thefact that the meaning of a translated sentence may
change in accordance with the preceding and following sentences. To address such issues, I arrived at thetheme of context- and situation-based neural machinetranslation.
6

Front-line Researchers

Sentence-by-sentence translation is
at a practical level.

Daily conversation

Short sentences
and phrases

Translation based on context and situation

Video-conference interpretation

Document
translation

Neural networks (deep learning) have greatly improved translation accuracy, and sentence-by-sentence translation has reacheda practical level. The challenge for the future is to take context and situation into account.

Fig. 1. Current and near-future goals of machine translation.

If you use the translation function of a website or
smartphone app, the accuracy of the translation is sohigh that you might think that machine translation isbetter than humans for composing, for example, English for student homework. At a bicycle rental shop, I
encountered a situation in which a Japanese shopkeeper and non-Japanese speaker were communicating via the translation function of a smartphone. As I
watched the exchange, I was so impressed that I
thought to myself, “Wow, translation technology hascome this far!” However, the conversation between
them was not smooth. This is because subtle phrases
and nuances could not be translated.
This lack of smoothness is a slightly troublesomefeature of neural machine translation. While thetranslated text might be as grammatically accurate asa native speaker’s text, it may not faithfully reproduce
the meaning of the source text. Conventional
machine-translation systems use a sentence as thebasic input unit. Accordingly, even if the translation
accuracy of each sentence equates to sentences produced by humans and if a target text consists of multiple sentences, such as a document or conversation,
is machine translated, the translated anaphoric relationships do not match the source text because context and situations are not taken into account. In otherwords, the translations are inconsistent.
—You are advancing research to further evolve suchcurrent technology.
To deal with the above translation inconsistency,
we must address the following three issues. The firstissue is that the subject and object are often omitted
in Japanese conversation; therefore, they should be
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identified from the context and translated. The second
issue is to make sure that the translation reflects thecharacters of the persons in question. This includes,for example, gender bias, as in associating the word
“neurosurgeon” with men, even though there arefemale neurosurgeons. The third is to find and reflectappropriate meanings and expressions of those having multiple meanings.
Let me give an example of translation consideringcontext and situation when translating Japanese into
English (Fig. 2), where the English translation of thesecond Japanese sentence is determined in accordance with the first Japanese sentence.
In the example shown in Fig. 2, “I’m afraid that thedoctor is running a bit late this afternoon. It might beabout 20 minutes before he can see you.” is the correct translation from Japanese. However, because thesubject “doctor” is omitted from the second Japanese
sentence, the machine translation often determines
the subject is “we” and presents “It might be about 20
minutes before we can see you.” There is also a problem of gender bias. In English, when choosing apronoun, it is often necessary to specify the gender.
Judging that “the doctor is a man,” the machine translation is likely to choose the pronoun “he” for the
doctor.
When Japanese is translated into English in thisway, if the subject and object (which are often omitted in Japanese) are not properly interpreted, themeaning will change, and the translated words will
not match the context. For example, in the Japanese
sentence “昨日、渋谷に行った。すごい人だった。” (“Kinou, Shibuya ni itta. Sugoi hito datta.”(Romanized version) or “I went to Shibuya yesterday.
There were a lot of people.”), the nuance of “すごい”
7Front-line Researchers

Preceding sentence

Input sentence

Source language
Target language
申し訳ありませんが、先生は午後
I’m afraid that the doctor is running a bit late
少し遅れているんです。
this afternoon.
(Moushiwake arimasen-ga, Sensei
wa gogo sukoshi okureteirun-desu.)
診察するまでに 20 分ほどかかると思います。
(Shinsatsu suru madeni 20-pun
hodo kakaru to omoimasu.)
Source language

Preceding sentence

昨日、渋谷に行った。
(Kinou, Shibuya ni itta.)

Input sentence

すごい人だった。
(Sugoi hito datta.)

Correct answer: It might be about 20 minutes before
he can see you.
Wrong answer: It might be about 20 minutes before
we can see you.
Target language
I went to Shibuya yesterday.
Correct answer: There were a lot of people.
Wrong answer: He was a great man.

Because gender distinction applies to English pronouns, the problem of gender bias also affects
translations of “doctor” and “person.”Fig. 2. Example of translations that require contextual consideration.

(“Sugoi” or “great”) should be translated into English
as “a lot of people” in this context. However, if thesentence “Sugoi hito datta” is interpreted in a different way, without reflecting the context from the preceding sentence, it will end up being translated into
English as “He was a great man.” Although that translation is also correct on a sentence-by-sentence basis,
it does not correspond to the preceding sentence, “Iwent to Shibuya yesterday.”No matter how high the accuracy of the translation,
it will never be perfect, so it is important to identify
mistranslations. In statistical machine translation, if
you want to find the source (Japanese) text that corresponds to the mistranslated (English) text, you can
see the internal correspondence between the source
and target texts by holding the cursor over the mistranslated text. However, neural machine translationinterprets the entire text to create a semantic vector
then translates in accordance with that vector, so it is
impossible to specifically identify the correspondingtext.
To solve this problem, I proceeded with myresearch with the goal of identifying the correspondences of the input and output sentences, which iscalled “word alignment” and “sentence alignment.”
In 2020, at the Conference on Empirical Methods in
Natural Language Processing (EMNLP), one of theworld’s largest international conferences in the fieldof natural-language processing and computational
linguistics, we announced that we can identify pairsof words that are translations of one another by conNTT Technical Review

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sidering their context in the sentences [1] (Fig. 3).
This “cross-language span prediction” method wasrecognized as pioneering and remarkably accurate.
Do something different and be as controversial
as possible—You have achieved outstanding research results.
What do you value in your research activities?
I try to do things differently from other people andbe as controversial—in a good way—as possible. I
consider it a problem and very inconvenient that neural machine translation cannot identify word alignment. To solve this problem, I searched for and trieda different method from those of other researchersand discovered by chance that it is easy to train aneural network on whether one word and anotherword are semantically close, even if the words are indifferent languages. In fact, word alignment can beobtained with high accuracy if enough data, namely,
correct word alignment between about 300 sentences,
are available. During the process leading up to that
discovery, I first looked at the semantic vectors ofwords learned by multilingual BERT (Bidirectional
Encoder Representations from Transformers)*. I
noticed that despite not using the so-called bilingual*

BERT: A semantic representation model of a language (developedby Google) that has been pre-trained from a large amount of text
by using a deep learning method called Transformer. Multilingual
BERT is a single model trained from text in 104 languages.

8

Front-line Researchers

language

is

言語

は

コミュニケーション

の

道具

で

ある

Gengo

wa

communication

no

dougu

de

aru

a

means

of

communication

language is a means of communication
Q. 言語
A. Language
Q. は
A. No_Answer
Q. コミュニケーション
A. communication…
For each word (span) in the Japanese sentence, find the word sequence (span) that is atranslation of each other in the English sentence. The correspondence is determined fromthe semantic vector representation of the two spans.

Fig. 3. An example of word alignment based on cross-language span prediction.

corpus, which is a database of multilingual bilingual
sentences, in the trained model, similar words exist ina relatively close place in the vector space.
The reason for that finding is twofold. First, even if
the languages are different, some parts are written incommon notations such as numbers and alphabets.
Second, there are commonalities that exists between
languages that have similar characteristics. For example, Japanese and Chinese overlap because both languages use Chinese characters. When I looked at thatreason in more detail, I thought that there might be asituation in which common notations and words
become pivots, and each language expands its own
world around those pivots. From that idea, I deduced
that it is actually very easy to train a neural networkon whether a word and another word in the vector
space are semantically close, and if there are correctanswer data for word correspondences between about
300 sentences, word alignment can be obtained withhigh accuracy.
This groundbreaking discovery was made possible
through repeated trial and error, as well as my desire
to do something different and controversial. This wayof thinking may have come from my experience ofstudying in the United States in my early thirties. I
went to the United States for research twice. I was
first a visiting researcher at Carnegie Mellon University (CMU), where I learned that when they say “Heis different,” they use “different” as a compliment. I
then spent time at AT&T, and Dr. Kenneth Church,
who was my supervisor, said, “I do things differently
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and try to be controversial,” and I deeply related withhis attitude as a researcher. Those experienceschanged my view that “being different” is a goodthing.
I also learned the importance of self-review after
researching in the United States those two times. To
do something different, you have to understand what
other people do, so I am still diligently reviewing
where my research stands and what I do not understand.
—Your experience in the United States has greatly
influenced your career as a researcher.
CMU also taught me the mindset of a researcher.
During the summer and fall, when new semesters
start at universities in the United States, guidance sessions on research and other topics are held. At thattime, I learned that research is to be at the forefront of
human intelligence and use one’s wisdom to elucidate things that are not yet understood. I was fortunate to have the opportunity to learn at the early stageof my research career about the basic concepts ofwhat research entails and how I should contribute. I
also remember that in the United States, the evaluation criteria for a doctoral degree, such as researchmethods, results, and level of achievement, were
specifically indicated, so it became easier for me toset my own goals and approach to research.
NTT has an outstanding tradition called “theme
planning.” It involves presentations of research
9Front-line Researchers

projects by researchers in their first and second years
after joining the company. During these presentations, the speakers present their research plans in a
logical manner for the next three to four years. It issimilar to the thesis proposal adopted at graduate
schools in the US. Talking about what you haveresearched is something that you will naturally learn
by gaining experience as a researcher; however, logically talking about future plans requires training. I
think it is very beneficial to give that opportunity toyoung researchers in a systematic manner. I also
think that understanding your own foothold andclarifying your mission through such activities willlead to research that is different from that of others
and will produce research results worth discussing.
On the basis of the approach that I described above,
I always try to look at my research objectively andwork on something new. I recently started studying
graph neural networks to reflect real-world circumstances beyond language in neural machine translation. Graph neural networks have been put to practical use in a variety of applications such as predicting
arrival times via Google Maps. This function measures the movement of people between all road intersections and road links and predicts the time it willtake to move from point A to point B at each time ofday. Similarly, the recommendation function provided by Uber Eats associates information on the person
placing the order with ordered items, etc. to predict
what the person will order next time. I believe that theaccuracy of machine translation can be further
improved by reflecting information about real-world
circumstances that cannot be verbalized by applying
graph neural networks.
My unprecedented “I’m giving up!” declaration—Looking back on your research career to date, what
has left an impression on you, and what will you be
working on in the future?
The declaration that I made in the summer of 2016,“I’m giving up research on statistical machine translation,” left a lasting impression on me. I have been
researching machine translation for about 30 years,
and the technological changes brought about by theadvent of neural machine translation have had a profound impact on the study of machine translation; infact, its impact was so huge that it has cancelled out
past research. As a result, researchers in the field ofneural machine translation are all at the same starting
line. Under these circumstances, I declared at a meetNTT Technical Review

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ing announcing my research policy that “Statisticalmachine translation cannot beat neural machinetranslation, so I’m giving up researching it.” In hindsight, saying that would have been unheard of.
I had been the leader of my team’s research on statistical machine translation, so I felt as if I wasretreating from the front line. However, with technological innovation, I could conduct research individually instead of in a team and was able to go back tobeing a researcher. It was a very emotional experience for me to be able to publish a paper as the firstauthor again at the age when I was in a position tolead a team as a manager.
Going forward, I want to leave something behindthat will serve as a foundation for research. I thinkthat since data is the key to any research, that foundation is a bilingual corpus or translation database forresearch on machine translation. A bilingual corpus isa database of bilingual sentences, and a data source isnecessary to create it. In the early 2000s, documentsfrom international organizations were used as data
sources; however, today, Google Translate, a typicalexample of an online machine-translation service,uses the web as its data source. Some people argue
that it is unacceptable for a single company like
Google to accumulate information exclusively.
Accordingly, several attempts to create a bilingual
corpus by extracting bilingual sentences on a large
scale from the web archive of Common Crawl, a nonprofit organization that aims to “crawl” the web andprovide data to the public, have been made.
According to ParaCrawl, a project to create a largescale bilingual corpus between European languages
and English using data of Common Crawl, the accuracy of machine translation became equivalent to thatof translation by humans when 40 million pairs ofsentences were accumulated. That number of sentences in the Japanese language has not been accumulated, and if the current trend continues, the machinetranslation industry in Japan will be left behind bythat in Europe. For that reason, I want to enrich
JParaCrawl, a Japanese-English bilingual corpus created by NTT, and contribute to the development ofJapanese research on machine translation.
I witnessed a university professor who was about toretire organize his students in an attempt to create alarge-scale database of Japanese-English sentencepairs called Tanaka Corpus, which was later incorporated into the “tatoeba” project [2]. At the time, I
couldn’t understand the passion of Professor Tanaka
as I wondered what the point of starting something
like this was when he was so close to retirement.
10Front-line Researchers

However, now that I am approaching retirement age,
I understand the feeling. I also want to continue to be
involved in activities to create a database that can beaccessed by many people.
—Do you have any advice for young researchers?
The longer you pursue a topic of interest, the betteroff you will be. To that end, I want you to value two
behaviors: to acquire the ability to explain yourresearch to others in an easy-to-understand mannerand to evaluate your research activities on a regularbasis.
Skills to evaluate your research activities on a regular basis can also be developed through writing a
research plan. At NTT, you are required to submit a
one-year research plan every year. At that time, I
review my research plan from the previous year, eventhough it was my “best effort” plan, I found that mypredictions did not come true. However, after repeating the review a few times, you will learn what you
can do and what you did as predicted and, conversely,
what you cannot do and what you do not predict. As
you gain experience, you will be able to formulate
research plans on the basis of more-realistic predictions and develop the skills you need to communicate
them clearly to a third party.
To work on a long-term project, the theme must be
interesting. I was not so sure about my future prospects when I was younger. In the past, I tried to lookahead five or ten years, but it was in the first one or
two years that the prospects held some reality. In thisage of rapid change, it is extremely difficult to predict
the future five or ten years down the line. Even undersuch circumstances, I think it is important to try to

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Vol. 19 No. 6 June 2021

imagine as far as possible what you want to be in yourimagined future.
Young researchers, there may be no other job inwhich you can stay active as long as a researcher.
Therefore, find themes that you can research for along time and continue your research activities
focused on those themes.
References[1][2]

M. Nagata, K. Chousa, and M. Nishino, “A Supervised Word Alignment Method based on Cross-language Span Prediction Using Multilingual BERT,” Proc. of EMNLP 2020, pp. 555–565, Nov. 2020.
Tatoeba Project, https://tatoeba.org/eng/

Interviewee profile
Masaaki Nagata
Senior Distinguished Researcher, GroupL e a d e r, N T T C o m m u n i c a t i o n S c i e n c eLaboratories.
He received a B.E., M.E., and Ph.D. in information science from Kyoto University in 1985,
1987, and 1999. He joined NTT in 1987. His
research interests include morphological analysis, named entity recognition, parsing, andmachine translation. He is a member of theInstitute of Electronics, Information andCommunication Engineers, the Information
Processing Society of Japan, Japanese Society for
Artificial Intelligence, the Association for Natural
Language Processing, and the Association for
Computational Linguistics.

11

Feature Articles: Challenges of NTT Space Environment
and Energy Laboratories toward Ultra-resilient Smart Cities

Research and Development on
Technologies for Transforming the
Global Environment from a Space
Perspective
Yuji Maeda
Abstract

NTT Space Environment and Energy Laboratories was established in July 2020 to develop innovativetechnologies for regenerating the global environment and achieving a sustainable and inclusive society.
We are the first NTT laboratories with “space” in our name, but our purpose is not to conduct researchon space itself. Rather, we study the Earth from the perspective of the space environment, including theSun, and take on challenging studies with the aim of transforming the future of the global environment
from dynamic viewpoints.
Keywords: space, environment, energy

1. Introduction
NTT embarked on new smart energy business ventures on the basis of NTT Group’s Medium-termManagement Strategy “Your Value Partner 2025”
announced in November 2018. Next-generationenergy technologies, such as nuclear fusion, are
beginning to look feasible. There are also growing
expectations for the development of technologies,
such as the Innovative Optical and Wireless Network(IOWN), that will break through the limitations ofcurrent technologies and contribute to the restorationof the global environment. Environmental, social, andgovernance (ESG) management with efforts to meet
the United Nations’ Sustainable Development Goals
has a significant impact on the sustainable growth ofcorporations. It is in this context that the NTT Groupannounced its Environmental and Energy Vision:
Zero Environmental Impact in May 2020, and established NTT Space Environment and Energy Laboratories in July of that year to implement this vision.
The purpose of the Laboratories is to develop technologies that will enable innovation in smart energy
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Vol. 19 No. 6 June 2021

and transform the future of the global environment.
NTT Space Environment and Energy Laboratories
aims to contribute to the regeneration and innovationof the global environment by re-examining the Earthand society from the higher and broader perspectiveof space without being restricted by conventional
technologies.
2. The Laboratories’ vision
NTT Space Environment and Energy Laboratories
has the following vision: to regenerate the global
environment and achieve a sustainable and inclusive
society to develop next-generation energy technologies that adapt to the environment and contribute to
the elimination of environmental impact, i.e., zero
impact.
The specific type of society that we aim for throughthis vision is an ultra-resilient smart city, as shown in
Fig. 1. Our objective is not just to eliminate theimpact of our society on the global environment but
to bring about a society in which the impact of changes in the global environment becomes acceptable, in
12Feature Articles

Ultra-resilient smart city(regeneration of the global environment and a sustainable and inclusive society)Zeroenvironmental
impactCarbon-free

Weather control

Decentralized autonomous cooperative society
Local production ofDisaster green
clean energy for local
energyZero power
consumption
outagesZero damage fromnatural disasters

Environmental adaptation

Fig. 1. Image of ultra-resilient society.

Society

Impacts: CO2/waste emissions, resource
consumption, environmental destruction, etc.

Global environment

Zero impact on the global environment

Adaptation to changes in the global environment
Impact: extreme weather, e.g., typhoons.

Fig. 2. Future image of the relationship between society and global environment.

which a zero power-outage state is achieved throughlocal production of clean energy for local consumption, use of decentralized autonomous cooperative
energy networks, and harnessing the power of severe
weather conditions such as typhoons (Fig. 2). To
achieve such an ultra-resilient smart city, we are conducting research and development of innovative technologies such as for the utilization of overwhelmingly clean next-generation energy, sustainable technologies including carbon dioxide (CO2) conversion,
ESG management, and proactive environmental
adaptation.
3. Research topics
A list of our research topics is shown in Fig. 3. The
Laboratories is currently focusing on two research
projects: Zero Environmental Impact Research Project and Resilient Environmental Adaptation Research
Project. This article presents only an overview ofthese projects because the details of each aredescribed in separate articles in this issue [1–4].

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Vol. 19 No. 6 June 2021

3.1 Zero Environmental Impact Research Project
As shown in Fig. 3, the Zero Environment Impact
Research Project is working on three topics: technology to produce overwhelmingly clean next-generation energy [1], energy network technology to enableefficient distribution of energy [2], and sustainablesystem technology to reduce CO2 in the air and water[1].
For next-generation energy, we are focusing on
fusion energy and space solar power generation.
Fusion energy is power generation using nuclear
fusion. In May 2020, NTT concluded a cooperative
agreement with the ITER International Fusion Energy Organization (ITER Organization). In November
2020, a collaboration agreement was concluded with
the National Institutes for Quantum and Radiological
Science and Technology, which is the domestic organization of the ITER Organization. We are seeking tosupport successful application of the ITER nuclear
fusion reactor using IOWN. The ITER Tokamak
Fusion Test Reactor is scheduled to begin operationin 2025. This is an attempt to create a “mini-Sun”
with the plasma temperature inside the reactor reaching
13

Feature Articles

Zero environmental
impactResilient environmental
adaptation

Next-generation energy technologies

Sunlight  Laser

ESG management science and technologies• Optimal operation of
nuclear fusion reactors• Space solar power©ITER Organization
generation

Transmission
36,000 km(geostationary
orbit)Laser
 electricity, hydrogen

Proactive responses totransform the future• Predictive simulation of ESG integration• Evaluation of future corporate value

Energy network technologies• Next-generation energyDCmicrogrid
supply• Virtual energy demand andLocal production of renewablesupply control
energy for local consumption

Achieve a sustainable
and inclusive society

Naturally derived
photonic/
electromagnetic
energySustainable system technologies• CO2 conversion/application(electrochemical/biologicalapproaches)• Environmental impact
reduction/application

Regenerate the global
environment

Rawmaterial

Conversion energy
generation

Secondaryuse

CO2

CO2 conversion

Organic
substance

Proactive environmental adaptation technologies• Geo-information analysis platform• Weather forecast/control(weather control, lightning conduction,lightning charging)• Electromagnetic barriers (cosmic rays, EMP)

DC: direct current
EMP: electromagnetic pulse

Fig. 3. List of research topics.

150 million degrees Celsius. IOWN’s ultra-lowlatency, high-speed, high-capacity network will be
used to transmit the huge volume of sensor data coming from the test reactor to the operation center. We
will also contribute to achieving optimal operation byusing our Digital Twin Computing (DTC) to predict
future outcomes from the collected data.
Space solar power generation is an ambitious
research project in which a satellite in geostationary
orbit at an altitude of 36,000 km above the groundwirelessly transmits energy from sunlight to the Earth
24 hours a day, 7 days a week. Several mechanisms
have been conceived for wireless power transmission.
We are focusing on using laser light. We will build on
our photonics and photoelectric conversion technologies developed for telecommunications to achieve
high-efficiency, ultra-long-distance wireless powertransmission in the very near future.
Regarding energy network technology, we will
apply the indoor direct-current (DC) power supply
technology, in which we have considerable expertise,to the outdoors. We are aiming to build highly resilient, decentralized, autonomous cooperative energy
networks by setting up DC transmission links
between NTT buildings (central offices) and electricpower consumers’ premises in their surrounding
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Vol. 19 No. 6 June 2021

regions. The network will enable the participatingcompanies to give and take power flexibly and efficiently. It will also enable power to be supplied stably
in the event of a disaster. We are studying technology
for simulating energy demand, generation, and storage in an integrated manner in cyberspace and reflecting the resultant optimal solution in the actual field tobalance power supply and demand. We are also working on technology for flexibly reallocating information-processing loads for communications traffic andcomputation among multiple sites to efficiently use
renewable energy, the generation of which is affectedby weather conditions.
Sustainable systems technology is aimed at reducing CO2 in the air and water. We intend to take two
approaches. One (electrochemical) is to produce artificial photosynthesis using semiconductor and catalyst technologies. The other (biological) is to fully
exploit the abilities of plants and algae. With the former, we use materials informatics *1 to identify*1 Material informatics: A method for achieving efficient material
development. It uses information-processing technology, including artificial intelligence, to identify candidates for compounds
that have desirable characteristics, on the basis of a huge volumeof chemical compound data, experiment results, and simulation
results.

14

Feature Articles

combinations of materials that cannot be discovered
with conventional approaches on the basis of experimental rules and existing concepts. With the latter, we
will use DTC to reproduce a wide range of plantgrowing environments in cyberspace and reflect theresults in real space after verifying the effects ofgenome editing and environmental control.
3.2 R esilient Environmental Adaptation
Research Project
The Resilient Environmental Adaptation Research
Project is working on two research topics: ESG management science [3] and proactive environmental
adaptation [4].
ESG management has recently become one of theimportant criteria for investment decisions, prompting many corporations to adopt it. However, most
corporations have difficulty in effectively linking thethree ESG elements. To solve this problem, we areworking on ESG management science and technology with a focus on minimizing risk in ESG management by using future prediction and future transformation. Specifically, we draw on DTC to analyze data
about the environment and society and predict the
future of both on the basis of scientific evidence. We
aim to transform the future of the global environmentand human society by taking proactive actions on thebasis of those predictions. For example, the corporate
value and well-being of a company can be evaluatedon the basis of its future prediction results. We are
studying methods of predicting what actions will
enhance corporate value and presenting a future scenario.
In proactive environmental adaptation, we areworking on four research topics to enable aggressive
and physical adaptation to weather patterns and environmental conditions, which are becoming increasingly extreme. Enhancing prediction of weather conditions and disaster damage is most critical for environmental adaptation. NTT currently predicts potential damage to telecommunications equipment fromforecasts provided by the Japan Meteorological
Agency.
The first of the four topics is studying geo-information-analysis platform technology for enhancing suchprediction. The key to this technology is an entirely
new sensing technology whereby a satellite orbiting
at about 500 km collects data from Internet-of-Things
sensors (920-MHz band), bundles the data, and transmits them back to Earth [5]. We are using this sensing
technology to collect and analyze data from sensors
on and beneath the sea and in mountainous areas,
NTT Technical Review

Vol. 19 No. 6 June 2021

none of which are currently well monitored. We are
seeking to enhance the degree of accuracy of weather
forecasts and disaster-damage prediction using theanalysis results.
The second topic is studying technology for proactively controlling the weather on the basis of accurate
weather forecasts. For example, water mass replacement*2 can be used to lower the temperature of theJapanese coastal waters that supply energy for
extreme weather events such as typhoons and trainings (line-shaped rainfall systems), thereby weakening their power. We are investigating disaster green
energy. For example, typhoon power can be harnessed to generate electricity. However, it is also
necessary to study the potential impact of such
weather control. Therefore, we plan to simulate andevaluate such impact by exploiting DTC to reproduce
the global environment in cyberspace. This will
include socio-economic systems, as referred to in the
explanation of ESG management science and technology. We will also predict the future in cyberspace
to derive optimal solutions and implement them in thereal world.
The third topic is studying lightning as one of thetargets of weather control. We already have advanced
measures to protect telecommunications equipmentfrom lightning strikes. We will build upon this to
study lightning control and lightning charging. Specifically, we are investigating lightning-control technology that will predict the lightning-strike area witha high degree of accuracy and induce lightning to
strike a drone and lightning-charging technology forstoring lightning-generated energy. We are aiming todevelop an airborne lightning-energy-absorption system that will operate autonomously using lightning
energy and absorb energy before a lightning strikeoccurs.
The fourth topic is studying measures against cosmic rays, which can be considered a “weather problem in space.” Malfunctions of semiconductors
caused by cosmic rays emanating from the Sun andother stars in the galaxy are called soft errors. We are
expanding our conventional technology for evaluating
soft errors, not only to prevent soft errors on Earth but
also to predict the impact of cosmic rays and electromagnetic pulses on devices and human bodies, which
are directly exposed to them in outer space, and todevelop electromagnetic-barrier technology, which*2 Water mass replacement: Technology to replace warm seawaterin the surface layer with cold seawater in the deep sea for coolingand power generation. There is a temperature difference of morethan 30 degrees in some sea areas.

15

Feature Articles

will proactively protect devices and human bodies
against those phenomena. Since there are overheating
risks and cosmic rays in space, it is difficult to use
sophisticated electronic devices in that environmentand difficult for humans to remain in space over an
extended period. Once further progress is made ontechnology and IOWN, such facilities as space-based
datacenters will become feasible.

forcing our resources and collaborating with partners
in various industries. Stay tuned to follow the growthof our Laboratories as it works to develop innovativetechnologies in the environment and energy fields
from a space perspective.
References[1]

4. Conclusion
The research projects introduced in this article arestill in the embryonic stage. They have only just been
initiated with modest resources, but our dreams are
far more ambitious. We will strengthen our resources
to take on challenges in new fields that we currently
cannot undertake and work to contribute to the regeneration of the global environment and transformationof our future.
The resumption of economic activities after
COVID-19 should move toward achieving a resilient
society that solves problems such as climate change
and marine pollution. This movement is acceleratingin governments and industries around the world.
Therefore, we will accelerate our research while rein-

[2]

[3]

[4]

[5]

K. Akiyama and K. Takaya, “Next-generation Energy-utilization andCO2-conversion Technologies Contributing to Zero Environmental
Impact,” NTT Technical Review, Vol. 19, No. 6, pp. 17–21, June 2021.
h t t p s : / / n t t - r ev i ew. j p / a r c h ive / n t t t e c h n i c a l . p h p ? c o n t e n t s =ntr202106fa2.html
T. Tanaka, H. Minami, T. Tanaka, N. Nakamura, T. Hayashi, M.
Kozai, Y. Higuchi, N. Hanaoka, and M. Iwamoto, “Energy-distribution Platform Technologies toward Zero Environmental Impact,” NTT
Technical Review, Vol. 19, No. 6, pp. 22–29, June 2021.
h t t p s : / / n t t - r ev i ew. j p / a r c h ive / n t t t e c h n i c a l . p h p ? c o n t e n t s =ntr202106fa3.html
Y. Tanaka, X. Zhang, and M. Shinozuka, “ESG Management Scienceand Technology for a Sustainable and Inclusive Society,” NTT Technical Review, Vol. 19, No. 6, pp. 30–36, June 2021.
h t t p s : / / n t t - r ev i ew. j p / a r c h ive / n t t t e c h n i c a l . p h p ? c o n t e n t s =ntr202106fa4.html
J. Kato, “Proactive Environment Adaptation Technology for Living
Safely and Securely,” NTT Technical Review, Vol. 19, No. 6, pp.
37–41, June 2021.
h t t p s : / / n t t - r ev i ew. j p / a r c h ive / n t t t e c h n i c a l . p h p ? c o n t e n t s =ntr202106fa5.html
NTT press release issued on May 29, 2020 (in Japanese), https://www.
ntt.co.jp/news2020/2005/200529a.html

Yuji Maeda

Vice President of NTT Space Environment andEnergy Laboratories.
He received a Ph.D. in systems information
science from Future University Hakodate, Hokkaido, in 2013. He joined NTT Telecommunication Networks Laboratories in 1991. He has been
engaged in managing projects related to generalemergency management such as those concerning natural disaster response and cybersecurity.
He received the Scholarship Encouragement
Award from the Institute of Electronics, Information and Communication Engineers (IEICE) in1998. He is a senior member of IEICE and amember of the Institute of Electrical and Electronics Engineers (IEEE).

NTT Technical Review

Vol. 19 No. 6 June 2021

16

Feature Articles: Challenges of NTT Space Environment
and Energy Laboratories toward Ultra-resilient Smart Cities

Next-generation Energy-utilization
and CO2-conversion Technologies
Contributing to Zero Environmental
ImpactKazuya Akiyama and Kazuhiro Takaya
Abstract

This article outlines next-generation energy technologies to enable the use of overwhelmingly clean
and inexhaustible energy sources, which are expected to be put to practical use, and carbon dioxide(CO2)-conversion technologies to effectively fix CO2 and reduce the total CO2 emissions of businessactivities to zero or less.
Keywords: fusion energy, space solar power, CO2 conversion

1. Initiatives to use next-generation energy
To achieve a sustainable society, the Next-Generation Energy Technology Group in NTT Space Environment and Energy Laboratories is working on twothemes: technology related to fusion energy, which isan overwhelmingly clean and inexhaustible energy
source, and space solar-power-generation technology.
1.1 O ptimal operation technology for fusion reactors
The fusion energy technology will be used to optimize fusion reactor operations by using the Innovative Optical and Wireless Network (IOWN). In May
2020, we concluded a comprehensive cooperationagreement with the ITER International Fusion Energy Organization (ITER Organization, where “ITER”
means “the way” in Latin) [1]. In November 2012, we
also entered into a partnership agreement with the
National Institutes for Quantum and Radiological
Science and Technology to develop innovative environmental energy technologies ahead of the rest of
the world [2]. Fusion energy is produced by the sun
and other stars in the universe. It is a nuclear reaction
NTT Technical Review

Vol. 19 No. 6 June 2021

in which light nuclei fuse to form heavier nuclei. For
example, in DT nuclear fusion reaction*1 in which thenuclei of deuterium (D), which is an isotope of hydrogen, and tritium (T) are fused, helium and neutrons
are produced, and the energy generated from thenuclear fusion reaction of only one gram of deuterium and tritium is equivalent to the heat generated
from burning about 8 tons of petroleum (a full lorry).
The ITER project is a very large international project(Fig. 1) with the goal of using fusion energy for
power generation. The seven regions of Japan,
Europe, the United States, Russia, South Korea,
China, and India are promoting the project, andpreparations are underway at Saint-Paul-les-Durance
in southern France to commence operation in 2025.
Fusion energy, combined with more distributed
renewable energy sources such as solar and wind, is
expected to provide a safe and reliable energy for theworld for millions of years.
In the ITER experimental nuclear fusion reactor,
deuterium and tritium, which are forms of hydrogen*1 DT nuclear fusion reaction: D + T = He (3.52 MeV) + n (14.06
MeV). To overcome the repulsive force of electric charge and tocollide D and T, a speed of 1000 km/s or more and heating temperature equivalent to 100 million degrees or more are required.

17

Feature Articles

Thermonuclear fusion reactor
DTC

ITER worksite

30 m

Data rate 50 Gbit/s
APN

Controlroom

Weight of the main body: 23,000 t
Thermal power: 500,000 kW

Predicting the future of fusion
reactors in cyberspace

Data sharing(EB/day)

Scientific Data
Center©ITER Organization, http://www.iter.org/

Research institutes around the world

APN: All-Photonics Network

Fig. 1. Overview of ITER worksite and optimal operation technology for fusion reactors.

that serve as fuel, are confined in a doughnut-shaped
magnetic field, heated to a plasma state, and further
heated to 150 million degrees Centigrade to generate
a nuclear fusion reaction. The ability to stably produce such plasma for extended periods is essential if
we are to extract energy from a hydrogen fusion reactor. This requires an enormous volume of sensor data,
up to 50 Gbit/s, obtained from the fusion reactor to betransferred to the control center, where optimal values for controlling the plasma shape must be instantaneously calculated and sent back to the reactor. To
facilitate this, it is vital to further increase the speed
and reduce the latency of the control network. In
addition to the high-quality, large-capacity, and lowlatency All-Photonics Network, which is one of theelemental technologies of IOWN, our goal is toachieve this by using disaggregated computing,which is a new computing architecture that enables
high-speed and high-efficiency data processing.
When a fusion reactor is put into full operation,
experimental data at the exabyte (EB) level are generated per day. We believe that IOWN can contribute to
the storage of such data in datacenters around theworld and the high-speed replication between datacenters. We plan to further improve control technology by using Digital Twin Computing (DTC) torealistically reproduce a hydrogen fusion reactor incyberspace, conducting highly advanced simulations,and predicting the future performance of a hydrogenfusion reactor.
1.2 Space solar-power-generation technology
Space solar-power-generation technology generNTT Technical Review

Vol. 19 No. 6 June 2021

Sunlight → Laser
Intensity

Wavelengths

Transmission
36,000 km(geostationary
orbit)

~1 GW

Laser
→ electricity, hydrogen

Fig. 2. Space solar-power-generation technology.

ates solar power on a satellite in geostationary orbit
36,000 km above the ground, transmits the energy to
the ground by lasers or microwaves, and converts itback to electric power or other energy on the ground(Fig. 2). A satellite in geostationary orbit can receive18

Feature Articles

energy from the sun almost 24 hours a day, 365 daysa year, and because the satellite is not affected by theabsorption or scattering of energy by Earth’s atmosphere, it can stably receive about 10 times moreenergy per unit area than on the ground. The Japan
Aerospace Exploration Agency and other organizations are conducting research and development(R&D) with the aim of putting this technology into
practical use after 2030, and if it is achieved, clean
and inexhaustible energy can be used. Since thewavelength of lasers is about 3–4 orders of magnitude
shorter than that of microwaves, we are investigating
an approach using lasers because the beam divergence angle is small and it is easy to transmit overlong distance.
There are three major technologies for generating
space solar power. The first is effeciently converting
sunlight into a laser on a satellite in geostationary
orbit. Unlike the conventional method of laser oscillation using power generated from solar cells, we areconducting research on a system that executes laser
oscillation with high efficiency by directly irradiatinga special crystal with sunlight to excite a laser. The
second technology accurately irradiates a target on
the ground with a laser beam. Although the laser canbe easily transmitted over long distance, a direction
control accuracy of 0.3 μrad (2 × 10–6 degrees) is
required to irradiate a laser beam with an accuracy of± 10 m from a satellite in geostationary orbit. The
effects of atmospheric turbulence must also be
removed. Therefore, we are conducting research on
optical systems with deep focal depths such as theBessel beam*2 and beam transmission systems thatuse adaptive optics*3 used in astronomy to eliminate
fluctuations in light propagating through the atmosphere. The third technology converts lasers into
energy with high efficiency. Since laser light is asingle wavelength, unlike sunlight in which light ofvarious wavelengths is mixed, we are researchingsolar cells with high conversion efficiency at specificwavelengths. When a laser is converted into electric
power using a solar cell, about half the energy
becomes heat. Therefore, we are studying methods ofstoring energy in different forms such as hydrogenand ammonia using thermochemical reactions insteadof converting lasers directly into electricity. We
believe that this technology can be key to achieving ahydrogen-based society.

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Vol. 19 No. 6 June 2021

2. Efforts to reduce carbon dioxide (CO2)emissions to zero or less
To contribute to the restoration of the global environment and achieve a sustainable society, the Sustainable Systems Group is engaged in the R&D ofsustainable systems that reduce all environmentalloads to zero or less and their implementation in society. Below zero means not only reducing emissions
but also reducing what already exists. There are various factors in terms of environmental impact, and one
is CO2. Under the Paris Agreement, reduction of CO2
emissions is required. Therefore, the Sustainable Systems Group has been conducting R&D on two
approaches to reduce CO2 (Fig. 3).
2.1 C
 O2-conversion technology (electrochemical
approach)
One approach is an electrochemical approach thatapplies the semiconductor technology used in communication devices and the catalyst technology usedin fuel cells. This involves the R&D of CO2-conversion technology for generating hydrocarbon fuelssuch as methane and formic acid, which is a storablehydrogen carrier, from water (H2O) and CO2 using
light and electromagnetic energy such as solar light,
as well as reducing the amount of atmospheric CO2.
This is also called artificial photosynthesis*4 because
it mimics the photosynthesis of plants that use sunlight and other light energy to synthesize carbohydrates from H2O and CO2. An advantage of the electrochemical approach is that it enables the productionof storable fuel (source of energy) from natural energy sources such as solar light, which can be used in avariety of applications, and is expected to be a carbon
neutral energy source.
There are still problems regarding practical application. For example, a semiconductor device (material) that generates hydrogen ions and electrons using
the energy of sunlight is installed in water as an electrode, which ionizes (corrodes) the surface of thedevice and degrades its performance. Since the wavelengths of light that can be used as energy are limited*2 Bessel beam: A type of non-diffracted beam in which the beam
does not expand because of diffraction phenomena.
*3 Adaptive optics: A technique to improve image quality by measuring the fluctuation of an image caused by the atmosphere witha wavefront sensor and correcting it dynamically.
*4 Artificial photosynthesis: This technology imitates the action ofplants to produce starch and oxygen from carbon dioxide andwater using solar energy and generates organic substances fromcarbon dioxide and water by chemical reaction using solar energy
and water used as raw materials.

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Feature Articles

CO2-conversion technology(electrochemical approach)CO2-conversion technology(biological approach)Light orelectromagnetic energy
H2O
Material

Energy-conversion
generator(semiconductor &catalyst)

CO2

CO2-conversion
component (catalyst)

Secondary use
material

Carboncompounds

Photoreaction

OxygenH+
CO2

CO2 conversion

StarchRemove the function that inhibits
photosynthesis and growth
Add a function that is
effective for CO2 fixation
Genome editing

Fig. 3. Two approaches of CO2-conversion technology.

depending on the physical properties of semiconductor devices, a wide bandwidth that can absorb energyof various wavelengths is required. It is also necessary to establish a technology to extend the life ofcatalysts for reducing CO2 by reducing performancedegradation due to repeated chemical reactions.
Therefore, the group is collaborating with NTT
Device Technology Laboratories, which has experience and skills in semiconductor devices and catalysts.
There are also operational and safety issues for thepractical application of CO2-conversion technology
using the electrochemical approach. For example,
many artificial photosynthesis systems currently
under development are evaluated for their performance in laboratories and other environments that are
relatively easy to control. For example, althoughhighly pure and highly concentrated CO2 is often
added from gas cylinders in the laboratory, it is necessary to act on approximately 0.04% of the atmospheric concentration of CO2 with high efficiency.Therefore, R&D on a technology called direct air capture(DAC) for directly recovering low concentrations of
CO2 from the atmosphere is being promoted. However, if the combination of an artificial photosynthesis
system with DAC becomes essential, the cost
becomes even higher, and an optimal design isrequired so that either one does not become a bottleneck. In addition, hydrogen and carbon monoxide areincluded in the gases used as raw materials for electrochemical reactions, and strong safety designs are
NTT Technical Review

Vol. 19 No. 6 June 2021

required to prevent these gases from being released
into the atmosphere in the event of an emergency. For
practical application of CO2-conversion technology
using this electrochemical approach, it is not enoughto simply pursue efficiency, it is also essential tosearch for optimal solutions that simultaneously
solve operational and safety issues.
2.2 C
 O 2 -conversion technology (biologicalapproach)
The other approach to CO2-conversion technology
is the biological approach that maximizes the photosynthetic function of plants and algae throughgenome editing*5 and optimal control of breeding andgrowth environments. Over the past 30 years, the areaof forests around the world has been increasing, but it
has been reported that the diversity and soundness offorests have been decreasing due to global warming
and logging. This may indicate that the natural division of roles necessary for the symbiosis and coexistence of the vegetation forming the forest and theorganisms and microorganisms living there are not
optimum. Therefore, we are carrying out R&D for
maximizing the photosynthetic capacity per plant bymaking full use of genome-editing technology andgrowing-environment control technology by accelerating the time when plants activate photosynthesis*5 Genome editing: The technology to change the characteristics ofan organism by editing a specific base sequence (DNA sequence)in the genome of the organism.

20

Feature Articles(early growth) and maintaining that time for a long
period (long-term soundness). If we can increase theforest area where photosynthesis is enhanced per tree,
we can achieve long-term carbon fixation throughplants. If we focus on vegetables and trees, which arefood and industrial resources, we can absorb more
CO2 during the growing season by promoting early
growth while maintaining high quality, and after harvesting and felling, we can use vegetable and tree
wastes for other carbon cycles. Regarding algae, we
believe it is possible to efficiently absorb CO2 dissolved in water and improve the environment of wetlands and seagrass beds by using genome-editing
technology and environmental-control technology to
proliferate algae within a short period.
The issues with CO2-conversion technology using
the biological approach are as follows. Trees, which
can fix carbon over a long period and have a highphotosynthetic capacity, have a large number ofgenes, and it takes a great deal of time to analyze
genome and identify the genes that determine early
growth and long-term health. Even if genome editing
is carried out, it is not easy to confirm the effects ofsuch editing because it takes many years for trees togrow.
Although genome analysis and editing are relatively easy regarding algae due to the small numberof genes, a large amount of energy is required forresource recovery (machining) to increase added
value after growth and for disposal of the parts ofalgae that cannot be used effectively.
Therefore, we are studying using DTC, one of theelemental technologies of IOWN, as a time-saving
means to verify the effect of genome editing on trees.
If an analytical model of plants and growing environments can be constructed in a virtual space and virtual growth simulations can be conducted, the effects
of genome editing should be predicted in a short

Kazuya Akiyama

Senior Research Engineer, Supervisor, NTT
Space Environment and Energy Laboratories.
He received a B.S. and M.S. in astrophysics
from Nagoya University, Aichi, in 1995 and1997. He joined NTT in 1997 and engaged inenvironmental and energy research (seconded to
NTT WEST Technology Innovation Department
from 2009 to 2013). In 2015, he assumed theposition of general manager, Corporate Planning
Department, ENNET Corporation. In 2017, he
was assigned to the NTT Technology Planning
Department and was involved in the establishment of joint ventures. In 2018, he was assigned
to NTT Facilities and engaged in solution sales.

NTT Technical Review

Vol. 19 No. 6 June 2021

period without real verification such as cultivation. If
it is possible to select genetic characteristics with low
disease risk at the seed and seedling stages, selective
breeding can be achieved. Regarding the issue ofalgal waste, we believe that it is important to efficiently link a number of carbon cycles such as providing algal waste as food and resources to other organisms.
3. Future developments
The challenges we are taking on concerning nextgeneration energy-utilization and CO2-conversion
technologies were outlined in this article. Technologies developed through optimization of fusion-reactor operation will be applied to other industries as ause case of cooperation among cyber-physical systems through real-time control. We plan to commercialize the space solar-power-generation technology
by introducing it on the ground for supplying power
to devices such as drones for long-term operation andsupplying emergency power to evacuation centers
and isolated islands.
To address these issues with the CO2-conversion
technology at an early stage, we will promote R&D
focusing on where the effects of information andcommunication technology can be expected, such as
physical properties of electrochemical materials, useful genomes of plants and algae, and virtual growthsimulation.
References[1][2]

NTT press release, “Conclusion of a Cooperation Agreement with
ITER,” May 15, 2020.
https://group.ntt/en/newsrelease/2020/05/15/200515c.html
NTT press release issued on Nov. 6, 2020 (in Japanese).
https://www.ntt.co.jp/news2020/2011/201106a.html

Kazuhiro Takaya

Senior Research Engineer, Supervisor, NTT
Space Environment and Energy Laboratories.
He received a B.E. and M.E. in electrical andelectronic engineering from Okayama University
in 1993 and 1995. He received a Ph.D. in electrical engineering from Kyoto University in 2019.
He has been engaged in research on carbon
dioxide conversion technologies using electrochemistry and biology.

21

Feature Articles: Challenges of NTT Space Environment
and Energy Laboratories toward Ultra-resilient Smart Cities

Energy-distribution Platform
Technologies toward Zero
Environmental Impact
Toru Tanaka, Hiroya Minami, Toshimitsu Tanaka,
Naomichi Nakamura, Toshihiro Hayashi, Masaki Kozai,
Yuji Higuchi, Naoki Hanaoka, and Miho Iwamoto
Abstract

The use of renewable energy has been increasing, but further adoption will require effective distribution of energy and energy resilience. The Energy Network Technology Group of NTT Space Environment and Energy Laboratories is researching and developing virtual energy demand/supply control
technology to enable full use of renewable energy and next-generation energy-supply technology basedon direct current microgrids to provide a stable supply of power to regional areas even if the supply ofcommercial power is interrupted. This article introduces these technologies.
Keywords: virtual energy demand/supply control, DC microgrid, renewable energy

1. Introduction of renewable energy anddisaster response
A growing sense of crisis with respect to resource
depletion and global warming has been driving the
introduction of renewable energy, but additional factors such as environmental, social and governance(ESG) investing*1 and use of renewable energy as aregion’s main power supply are dramatically changing the situation surrounding energy. While highcosts have historically made the widespread use ofrenewable energy difficult, national policies, such as
feed-in tariffs, have dramatically lowered costs bypromoting the introduction of large-scale renewableenergy such as mega solar power plants and massive
wind power generation. These policies have helped
reduce price-related barriers to the introduction ofrenewable energy. Recent advances in investing andmanagement with respect to the environment, such as
ESG investment and the Task Force on Climaterelated Financial Disclosures (TCFD)*2, have also
become essential elements in corporate activities, and
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Vol. 19 No. 6 June 2021

at the national level, initiatives toward the expanded
use of renewable energy, such as its use as a country’s
main power supply, have already become a matter ofcourse.
The amount of power generated from renewableenergy fluctuates greatly with weather, so it will bedifficult to balance the amount of power consumed
the more that renewable energy will be used. There
has been much effort in controlling demand, but there
is still the need for a large-scale and high-speedmeans of absorbing such fluctuations.
A large-scale power outage that occurred in September 2019 due to a direct hit by a typhoon in Chiba
Prefecture followed by another large-scale power
outage in the Tokyo metropolitan area due to the
Fukushima Prefecture Offshore Earthquake in February*1 ESG investing: A type of investing that places importance on andselects companies that give serious consideration to environment,
society, and corporate governance.
*2 TCFD: A framework established by the Financial Stability Board(FSB) at the request of G20 to promote information disclosureson corporate initiatives with respect to climate change.

22

Feature Articles

2021 have again raised awareness of the importanceof a stable power supply. Resilience measures centered about the national government in Japan haveconsequently been promoted such as constructing
backup systems at evacuation centers.
However, when commercial power becomes
unavailable, power from renewable energy cannot betransmitted, and there are concerns that the backup
facilities will be difficult to maintain continuously. In
addition to disasters that have already been experienced, it will be necessary to deal appropriately withnew risks such as electromagnetic pulses (EMPs) andcosmic radiation accompanying the expanded use ofelectronic equipment.
In this article, we introduce virtual energy demand/
supply control and next-generation energy supply astechnologies for solving these problems.
2. Virtual energy demand/supply
control technology
A variety of measures are being taken to absorb
large changes in the power generated from renewableenergy. These include predicting the amount of power
generated; adjusting the amount of power generated
in conjunction with thermal power generation,
pumped-storage hydropower, etc.; controlling theamount of power consumed by air conditioning,lighting, etc. on the consumer side; and storing surplus power in storage batteries. There have been
recent developments in and introduction of new
demand/supply control systems, such as virtual
power plants that group and control many small-scale
power generation facilities and multiple consumer
devices much like a single electric power plant, andsystems that use storage batteries in electric vehicles(EVs).
However, if renewable energy in large quantities is
introduced to a specific region, there is still the possibility that controlling power fluctuation at the timeof a surplus or shortage will be quantitatively or temporally difficult in that region. There is therefore aneed for large-scale and high-speed control of theamount of consumed power so that no surplus orshortage of power occurs in the power system of any
region even for a moment. The NTT Group consumes
approximately 1% of the power consumed in Japan,
and since NTT telecommunication buildings anddatacenters are scattered throughout the country, it
has the potential of modifying power consumption
between regions. This modification of consumed
power can be achieved by controlling the volume of
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Vol. 19 No. 6 June 2021

communication traffic and amount of information
processing of computational data, etc. For example,
information processing can be transferred from atelecommunication building in a region where rainfall has caused a drop in solar power generation and ashortage of power to a telecommunication building ina region where fine weather has resulted in a surplusof power. Therefore, the region with rainfall can
lower power consumption and avoid tight supply/
demand conditions while the region with fine weather
can increase power consumption and make full use of
the power generated by solar power generation. To
achieve such a transfer of information processing
across regions, the aim of our research and development efforts is to make the amount of information
processing follow the amount of power generated
from renewable energy, enhance tracking of theamount of information processing and the amount of
power consumed by information and communication
technology (ICT) equipment, and optimize theamount of information processing to transfer and thetiming of such transfers to achieve a supply/demandbalance in each region. To achieve such optimization,
our research and development is also aimed at performing such control so as not to affect communication service quality and facility stability (Fig. 1). It
must also be considered that a large number of storage batteries are installed in NTT telecommunicationbuildings as backup power supplies for communication services, so making use of these batteries as well
as EV batteries at the right time in conjunction withEV operation information should make it easier tocontrol the charging/discharging of even greater
amounts of power.
As an initial step toward establishing the above
technology, we constructed a container-type test bed
at NTT Musashino R&D Center, installed a rectifier,solar array simulator, storage batteries, information
processing servers, etc., and began testing energy
demand/supply control (Fig. 2). The plan is to use
this test bed to test demand/supply control with distant telecommunication buildings and datacenters.
3. Next-generation energy supply technology
Various regions in Japan have been establishingresilience measures to reduce power supply interruptions brought on by disasters such as large-scale
earthquakes. NTT is also promoting measures tostrengthen the earthquake resistance of its buildings,
defend against flooding, and fortify backup systems.
However, in addition to extreme weather, it is thought
23

Feature Articles

Capture changes in demand/
supply by predicting renewableenergy power and consumed
power from weather, people’s
behavior, etc.

Determine destination
and amount of traffic/datatransfer on basis ofchange in demand/supply

Virtual space
DC microgridAi

AC power
systemAC power
system

DC microgrid

Processing: increase

Select appropriate
communication pathconsidering QoSProcessing: decrease

AC: alternating current
DC: direct current

Ai: artificial intelligence
QoS: quality of service

Fig. 1. Virtual energy demand/supply control technology.

External view
Container for power
generationand storage

System configuration
Container for power
Solar arraygeneration and storage simulator

Container for power
consumption

Container for power
consumption
PDF

Server rack

DC/DC
AC
RectifierDC/DC

380 VDC

DC/DC
Storagebattery
PDF: power distribution frameFig. 2. Container-type test bed.

that the risk of damage, interruption, or erroneous
operation of electronic equipment and power supply
equipment still exists due to, for example, EMP irradiation resulting from a high-altitude nuclear explosion attack or cosmic rays emitted during solar flares.
Such events are considered rare, but taking into
account the further miniaturization and integration ofsemiconductor devices from here on and the further
spread of electronic equipment and devices, damage
to systems involving the power supply can have direconsequences for society. To solve this problem, theEnergy Network Technology Group has undertaken
the development of an energy supply system thatNTT Technical Review

Vol. 19 No. 6 June 2021

enables a stable power supply in the face of all typesof events.
The power supply system used in NTT telecommunication buildings had been a direct current (DC)system based on –48 VDC, but the recent increase in
the power consumed by ICT equipment is prompting
the introduction of a high voltage direct current(HVDC) power supply system that increases the voltage to 380 VDC. This HVDC power supply system(Fig. 3(b)) supplies DC power directly to ICT equipment that operates on DC, decreasing the number ofconversion steps and reducing conversion loss compared with an alternating current (AC) power supply
24

Feature Articles(a) AC power supply system

200
VAC

Conversion (1)

200
VAC

(b) DC power supply system
ICT equipment

200
VAC

CircuitConversion Conversion Conversion (4)(3)(2)
Storage

ICT equipment

380
VDC

Conversion (1)CircuitConversion (2)Storage battery

battery

Fig. 3. AC and DC power supply systems.

(a) Normal case(b) Disaster/abnormal caseEV

Achieve independent
operation within the DC
microgrid even if commercial
power is interrupted

Power supply continues
even under the risk of an
EMP, etc.
EMP

EV

Cosmic rays
(solar flare)EV
DC microgridStore surplus power in storage
batteries to achieve efficient
power interchange

Power supply using
storage batteries
and EVs

Inducedlightning

Power supply prioritized where needed -> demand control

Fig. 4. Next-generation energy supply technology.

system (Fig. 3(a)). This makes for a high-efficiency
system as well as an extremely reliable system since
the storage battery used as backup is directly connected to the DC bus. We expect that this high-efficiency, high-reliability system can be used as a basis
for constructing a DC microgrid that connects an
NTT telecommunication building and local consumers to a 380 VDC network (Fig. 4). This would
achieve a power supply system with efficient powerinterchange and no outages. In normal times, when asurplus amount of power is generated by renewableenergy in the neighboring area, that power can be
stored with good efficiency in storage batteries at the
NTT telecommunication building (Fig. 4(a)). Furthermore, during a disaster or other abnormal occurrence, storage batteries for stationary use and thosefor EV use can be combined with renewable energy
to enable power interchange even if the power supNTT Technical Review

Vol. 19 No. 6 June 2021

plied by a power company is interrupted (Fig. 4(b)).
However, this DC microgrid has a configuration thatconnects multiple units of power-generating equipment and multiple consumers, which means thatevents, such as short circuits, grounding, and lightning, can have far-reaching effects. There is therefore
a need for a stable power supply that is robust to eventhese types of events.
The Energy Network Technology Group is proceeding with a three-step study as shown in Fig. 5.
Step 1 will involve connecting the supply side withthe demand side in a one-to-one format, Step 2 will
involve connecting multiple units of equipment andexecuting power interchange in a bidirectional format, and Step 3 will involve stabilizing the power
supply by extending the DC microgrid in which thepower is networked. In Step 1, which is now in progress, we are studying technology for connecting an
25

Feature Articles

Steps toward a bidirectional DC microgrid
FY2020: Step 1(outdoor DC power supply
between 2 points)

FY2021: Step 2(bidirectional and extended length)

Test (≈ 400 m)
Nearby building (elementary/
middle school, local government)

Power(380 VDC)
Unidirectional

EV charger/
discharger
EV

PV

Telecommunicationbuilding

PV

Power (380 VDC)
Microgrid

Storagebattery

NTT powerline

EV charger/
discharger

Photovoltaic (PV)power connection

Actual deployment(microgrid)

PV

Storage battery

PV

Nearby building

PV

Bidirectionaland extended
lengthNTT power
line
Storage battery

Actual deployment(≈ 2 km)

FY2022–FY2023: Step 3(bidirectional DC microgrid)

PV

EV

Power
EV charger/(380 VDC)
discharger
Bidirectional
EV
Transform
intoPV
microgrid

Telecommunicationbuilding

EV charger/
discharger

Telecommunicationbuilding

Storagebattery

PV

EV

PV

PV
PV

PV

PV

Telecommunication building

Fig. 5. Test steps toward a DC microgrid.

Short-circuit protection
Power supply
equipment

Distribution board

Power
line
380 VDC

Gate block

Power feeddestination building

Power line impedance
R

L

R

L

Fuse

Short
circuitTechnique to determine characteristics
of gate block and fuse to power line
impedance

Telecommunication building

Directlightning
strikeLightning protection
Distribution board

DC/DC converterSPD(built-in)

SPD(Class I)
R

TelecommunicationbuildingIndoorequipment

L
Ground-line
impedance

380 VDCPower line
Lightning surge current
Solar panel

R
L

Technique to determine SPD coordination
conditions and ground line wiringconditions

Fig. 6. Schematics of short-circuit protection and lightning protection.

NTT telecommunication building to an elementary or
middle school acting as an evacuation center during adisaster in a one-to-one format (power supply distance: ≈ 400 m). Since we are extending 380 VDC
power to an outdoor environment in this study, as
shown in Fig. 6, we are giving priority to developing
power quality technology involving electrical safety
to prevent major accidents such as system fires or
NTT Technical Review

Vol. 19 No. 6 June 2021

electric shock to workers. During a short circuit, theshort circuit current decreases as the power supply
distance from indoors to outdoors becomes longer,
and since the current is DC, it is difficult to detectsuch an accident on the telecommunication-building
side, which results in risk of failing to cut off the current safely. To solve this problem, we developed amechanism that detects a short circuit with high26

Feature Articles

accuracy and cuts off the current by incorporating an
overcurrent protection function (gate block) inside
DC power supply equipment in addition to the use of
conventional fuses. Though a telecommunicationbuilding, in particular, requires high reliability, therisk of a penetrating lightning surge increases when atelecommunication building draws in power generated by a solar power generation system or othersources, so there is a need for technology for suppressing voltage. For this reason, we developed atechnique that can significantly reduce the voltage
accompanying a lightning surge by optimizing thewiring setup of surge protection devices (SPDs) andgrounding wires. The provision of the above technologies is centered about NTT Anode Energy Corporation [1], which specializes in the energy business. It is currently expanding the testing of a backup
power supply business in Chiba City [2].
On the basis of these technologies, we are also
addressing the additional risks of EMP and cosmic
radiation. In an AC system, the occurrence of suchphenomena can lead to software errors in the control
system that executes synchronization control,*3
increasing the risk of an interrupted power supply due
to poor synchronization. A DC system, in contrast,
directly connects the storage batteries to the DC bus,which lowers this risk. We will make maximum useof this feature of DC systems to establish a systemthat is robust to a variety of risk events that could
otherwise interrupt the power supply.

4. Future developments
We will work to further develop the two technologies introduced in this article and take up the challenge of researching and developing a new network
system that merges the information and energy networks. To this end, we will link these technologies to
the All-Photonics Network in the Innovative Opticaland Wireless Network (IOWN) proposed by NTT anddisaggregated computing for high-speed and highefficiency data processing through decentralized
coordination of diverse, geographically distributed
computing devices in accordance with the application. We will also improve the quality of the DCmicrogrid power network through optical-type highspeed cutoff devices and work to integrate renewableenergy and computing devices.
By migrating from the existing centrally managed
energy network system to a new energy network system based on autonomous and decentralized cooperative control, we plan to contribute to the implementation of local production for local consumption thatmakes full and efficient use of renewable energy andto the creation of ultra-resilient smart cities that can
supply power without interruption despite the occurrence of a variety of events.
References[1][2]

NTT Anode Energy, https://www.ntt-ae.co.jp/en/
Joint press release issued by TNcross, NTT Anode Energy, NTT, andTokyo Electric Power Company, “Joint Experiment toward Smart
Energy City in Chiba City,” Apr. 23, 2020 (in Japanese). http://tncross.
co.jp/information/detail20200423.html*3 Synchronization control: The voltage of an AC system repeats
positive and negative values periodically. The role of synchronization control is to match the timing of this repetition between
systems.

NTT Technical Review

Vol. 19 No. 6 June 2021

27

Feature Articles

Toru Tanaka

Senior Research Engineer, Supervisor, Energy
Network Technology Group, Zero Environment
Impact Research Project, NTT Space Environment and Energy Laboratories.
He received a B.E. and M.E. in quantum science and energy engineering from Tohoku University, Miyagi, in 1996 and 1998. He joined
NTT Integrated Information and Energy Systems
Laboratories in 1998, where he was engaged inresearch on the evaluation of DC power supply
system stability and voltage fluctuations. He also
developed HVDC power supply systems fortelecommunication buildings and datacenters.
From 2009 to 2012, he was a manager at NTT
FACILITIES, where he developed power supply
systems and smart community. He is currently
researching energy networks. He received the2003 and 2009 Shibusawa Award of the Japan
Electric Association. He is Professional Engineer, Japan (Electrical & Electronics Engineering).

Hiroya Minami

Senior Research Engineer, Energy Network
Technology Group, Zero Environmental Impact
Research Project, NTT Space Environment andEnergy Laboratories.
He received a B.E. and M.E. from Seikei University, Tokyo, in 1994 and 1996. He joined NTT
in 1996 and has been engaged in research on
traffic technologies of communications systems,
ubiquitous systems, and service delivery platforms. He received the Young Engineer’s Award
from the Institute of Electronics, Information andCommunication Engineers (IEICE) in 2003. He
is a member of IEICE.

Toshimitsu Tanaka

Senior Research Engineer, Energy Network
Technology Group, Zero Environmental Impact
Research Project, NTT Space Environment andEnergy Laboratories.
He received a B.E., M.S., and Ph.D. in electronic engineering from Chiba University in
2001, 2004 and 2007. He joined NTT in 2007,
where he has mainly been engaged in R&D of
DC microgrid systems. He received the Young
Researcher’s Award from IEICE in 2006. He is amember of IEICE.

Naomichi Nakamura

Senior Research Engineer, Energy Network
Technology Group, Zero Environmental Impact
Research Project, NTT Space Environment andEnergy Laboratories.
He received a B.E. in physics from Nihon
University, Tokyo, in 2004 and an M.E. in nanoscience and nanoengineering from Waseda University, Tokyo, in 2006. He joined NTT in 2006
and studied electromagnetic compatibility technology for telecommunication. He has been
researching and developing methods of lightning
protection and grounding for telecommunication
systems.

NTT Technical Review

Vol. 19 No. 6 June 2021

Toshihiro Hayashi

Senior Research Engineer, Energy Network
Technology Group, Zero Environmental Impact
Research Project, NTT Space Environment andEnergy Laboratories.
He received a B.E. and M.E. in geosystemengineering from the University of Tokyo in
2004 and 2006. He joined NTT in 2006, and his
research interests are energy control technologies
and optimization techniques.

Masaki Kozai

Senior Research Engineer, Energy Network
Technology Group, Zero Environmental Impact
Research Project, NTT Space Environment andEnergy Laboratories.
He received a Ph.D. in engineering from Tokyo
Institute of Technology in 2010 and joined NTT
the same year. His research interests are energy
demand forecast and energy control technologies.

Yuji Higuchi

Research Engineer, Energy Network Technology Group, Zero Environmental Impact Research
Project, NTT Space Environment and Energy
Laboratories.
He received a B.E. and M.E. in electrical engineering at Shinshu University, Nagano, in 2007
and 2009. He joined NTT FACILITIES in 2009and engaged in the maintenance of power systems for telecommunication facilities. He subsequently joined NTT Space Environment andEnergy Laboratories and is currently researching
electrical safety of DC microgrid.

Naoki Hanaoka

Research Engineer, Energy Network Technology Group, Zero Environmental Impact Research
Project, NTT Space Environment and Energy
Laboratories.
He received a B.S. in physics from Shinshu
University, Nagano, in 2010 and M.S. in particle
and astrophysical science from Nagoya University, Aichi, in 2012. He joined NTT in 2012 andstudied 380 V power supply systems. From 2015
to 2019, he was a researcher at NTT FACILITIES, where he researched circuit analysis andevaluation of 380 VDC equipment. He is currently researching the electrical safety of DC
microgrids. He is a member of IEICE and theInstitute of Electrical Engineers of Japan.

28

Feature Articles

Miho Iwamoto

Researcher, Energy Network Technology
Group, Zero Environmental Impact Research
Project, NTT Space Environment and Energy
Laboratories.
She received an M.S. in physical chemistry ofsoft matters from Kyushu University, Fukuoka,
in 2019 and joined NTT Space Environment andEnergy Laboratories the same year. Her researchinterests are electrical energy demand forecast
technologies and energy optimization techniques.

NTT Technical Review

Vol. 19 No. 6 June 2021

29

Feature Articles: Challenges of NTT Space Environment
and Energy Laboratories toward Ultra-resilient Smart Cities

ESG Management Science andTechnology for a Sustainable andInclusive Society
Yuriko Tanaka, Xiaoxi Zhang, and Machiko Shinozuka
Abstract

We introduce ESG (environmental, social, and governance) Management Science and Technology forachieving a sustainable and inclusive society with respect to recent climate changes and problems
related to human rights. We also analyze the relationship between the global environment and socioeconomic systems to predict the future and identify long-term corporate risks as well as opportunities
for corporations to generate new revenue and enhance their corporate value.
Keywords: ESG, future prediction, corporate value

1. Overview of ESG Management Scienceand Technology
Increasing attention has been paid to the Sustainable Development Goals adopted by the United
Nations and how to respond to problems caused bychanges in the natural environment (including climate change), poverty, and other social problems.
Amid the global COVID-19 pandemic, we are facedwith the need to re-examine how society and theeconomy operate. Solving these problems requires anapproach that integrates environmental, social, andeconomic aspects and identifies correlations andcausal relations among them [1]. As shown in Fig. 1,
which presents a global view, the Earth and humans
are closely and intricately related, as evidenced byclimate change and social problems, such as poverty,
caused by the concentration of wealth particularly incapitalist societies and the exploitation of natural
capital*1. These problems could result in an unprecedented crisis in 5 to 10 years [2]. Due to changes indemographics and economic growth, social changes
through science and technology and changes in people’s values and behavior, the future is not necessarily
an extension of the present. Corporate activities arealso impacting the environment and society. Businessstrategies and actions developed from a long-term
NTT Technical Review

Vol. 19 No. 6 June 2021

perspective are critical for ensuring a sustainablebusiness environment. Therefore, corporations areattaching importance not only to their financial information but also their non-financial information, suchas environmental, social, and governance (ESG)
information. However, they still fall short of evaluating and verifying the impact of their ESG strategies
and actions.
An overview of the ESG Management Science andTechnology we are developing is shown in Fig. 2.
Future prediction simulation uses environmental andsocial information as input data. Such data include
the sense of value and situations of individual stakeholders in a corporation and is an important element
in formulating an ESG strategy. Such simulation will
use a model that represents causal relations among
various environmental and social events, such as U.S.
presidential elections, decarbonization strategies,
disasters, and corporate performance. We will develop simulation systems as part of global-scale Digital
Twin Computing (DTC) [3] and combine these systems with existing integrated evaluation models andnew models to predict the future. We will evaluate theprediction results to make further predictions by*1 Natural capital: A capital produced by nature, such as forest, soil,
water, atmospheric air, and natural resources.

30

Feature Articles

Changes in human society
Advances in scienceand technology

Changes in sense ofvalue and behavior

Long-term
warming

Future generations

Social issues,
such as poverty

Exploitation ofnatural capital

Capitalists Stockholders Employees
Corporation

Concentrationof wealth

Climate change

Corporation Corporation

Community

NationEconomic
systems

Community

UnusualweatherSocialsystems

The Earth and the natural environment

Note: Created by the authors based on References [1] and [2]Fig. 1. Challenges and changes in the global environment and socio-economic systems.

Analysis ofenvironmental/social data

Future prediction simulation

Naturalenvironment

CusNGOs
tomersStockFuture
holders Employ- generations
ees
Government
Stakeholders

Digital Twin
Computing

Human society
Economic systems
EnergyEnvironment

Presentation of
forecasts andscenarios

Ecosystem

Integrated evaluation model, etc.
Evaluation of future
corporate value

Financial

Financial information
Non-financial information
Economic valueSocial valuet
Short-term profitLong-term profit
Non-financial

NGO: non-governmental organization

Fig. 2. Overview of ESG Management Science and Technology.

using DTC and identify ways to achieve future transformation. We aim to indicate forecasts and futurescenarios that will help corporations formulate their
ESG strategies with a clear picture of their future. For
this purpose, we will undertake research and developNTT Technical Review

Vol. 19 No. 6 June 2021

ment of future evaluation methods that will help
enhance corporate value and reinforce the concept ofcorporate value from viewpoints that involve nonfinancial information, social value, and long-term
profit. We intend to evaluate corporate well-being*2
31

Feature Articles<Viewpoints for measuring corporate value>[Factor]Financialinformation+

Non-financial
information

Economic value+

Social value

Short-term profit+

Long-term profit

ESG
in business management and investment

Causal relation?
[Effects]

Corporate value

Real effects onenvironmentand society

Fig. 3. Corporate value and ESG.

by clarifying the causal relations between factors incorporate actions and their effects on the environmentand society (Fig. 3). In the next section, we describe
future-prediction technology focusing on ESG for
enabling future prediction simulation.
2. Future-prediction technology focused on ESG
One of the potential approaches to making a future
prediction is to first predict social changes at thecountry level, then, on the basis of the previous prediction, predict changes that can affect corporate
management. To predict social changes at the country
level, our ESG Management Science Group began tocollaborate with National Institute for Environmental
Studies and four other research organizations*3 fromfiscal year 2020. Taking climate change and the aging
population, coupled with the declining birthrate faced
by Japan, into consideration, we are developing several future visions that reflect various aspects of Japanese society and technology for predicting social,economic, and environmental changes quantitatively.
One of the important visions we are developing is “ahuman-centered society that balances economic
advancement with the resolution of social problems
by a system that highly integrates cyberspace andphysical space,” as stated in the government’s Society
5.0 [4] document. By determining changes in theeconomy, the environment, and people’s lives before
they occur, we will formulate NTT’s ESG management strategy to maximize positive effects on society
and the global environment while avoiding as many
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Vol. 19 No. 6 June 2021

negative effects as possible. By reflecting predicted
macroscopic social, economic, and environmental
changes in NTT’s management strategy, we can formulate an even more proactive strategy.
With the aim of predicting what the future will look
like with information and communication technology(ICT) including the Innovative Optical and Wireless
Network (IOWN)*4, the following section describes
prediction technology focused on production andconsumption.
3. Predicting the impact of the environment andeconomy on societyFirst, we introduce the prediction method from theviewpoint of production. It goes without saying thatICT boosts the economy by improving productivity
and substituting human labor. Though it has a negative environmental effect because the use of ICT
devices produces environmental loads (such as greenhouse gas emissions through electric power consumption), improved efficiency in production andconsumption leads to dematerialization and a reductionin the use of raw materials, which lower environmental*2 Well-being: A state of being well physically, mentally, and socially, or a concept related to spiritual richness or satisfaction.
*3 This study is supported by the Environmental Research and Technology Development Fund of the Environmental Restoration andConservation Agency of Japan (JPMEERF20201002).
*4 IOWN: The concept of a next-generation communication infrastructure being pursued by NTT with the aim of commercial implementation around 2030.

32

Feature Articles

Table 1. Evaluated ICT and direct effects of their introduction.
Evaluated ICT

BAUFarming robots/
self-driving tractors—

Plant factories/sensors——

Food-distribution platform

—

—

Note:

,

, and

Case 1Case 2

Case 3

Direct effects of theirintroduction
Substitution for human labor
Improved productivity
Stable production
Reduced transport distance(local production for local
consumption), reduction infood waste—

indicate that the penetration level is respectively low, medium, and high.

14

Production value in agriculture(trillion yen)

12
10
8
6
4
2
0
Rice
BAU

Wheat

Other edible crops

Case 1Case 2Non-edible crops

Case 3Fig. 4. Production value in each case (2050).

loads. This method simulates the macroscopic economic state (production and consumption), energy
consumption, and greenhouse gas emissions of afuture scenario using a computable general equilibrium model [5] based on Japan’s input-output table[6]. First, we simulate the state in a baseline scenario
on the basis of basic pre-conditions, such as thechanges in population and gross domestic product(GDP) growth ratio. We then consider the direct
effects of ICT penetration in industries (reduction in
the use of raw materials, reduction in movement,
improvements in productivity, etc.). We reflect theseeffects into the model and simulate the macroscopic
economic state, energy consumption, and greenhousegas emissions in the ICT-accelerated scenario.
The effects of introducing several types of ICT inagriculture up to 2050 are described as an example.
Table 1 shows the ICT we are focusing on, its peneNTT Technical Review

Vol. 19 No. 6 June 2021

tration levels, and the direct effects of its introduction. We conducted calculations for four cases. In thebaseline scenario (BAU), the penetration of ICT isassumed at current levels. To evaluate the effects ofintroducing further ICT, we considered three cases inwhich the penetration of farming robots/self-driving
tractors, plant factories, and food-distribution platforms is set at different levels (low, medium, andhigh). Figures 4 and 5 show the simulation results on
the effects (change in production value and greenhouse gas emissions) due to the introduction of ICT.
In Case 1, in which the ICT-penetration level is low,
the production value in the agriculture sector isalmost the same as that in BAU, while the greenhousegas emissions slightly decrease. In Cases 2 and 3, in
which the ICT penetration level is higher, production
increases, boosting the country’s food self-sufficiency, but the greenhouse gas emissions are also likely to33

Feature Articles

Greenhouse gas emissions (MtCO2e)

12
10
8
6
4
2
0
BAU

Case 1Case 2

Case 3−2−4

Fig. 5. Difference in greenhouse gas emissions of each case in comparison to BAU in 2050.

increase.
We will apply this analysis and prediction to awider range of industries and not only evaluate greenhouse gas emissions and GDP but also use DTC toevaluate other indicators, such as resources, land use,
and water utilization in an integrated manner and ona global scale.
4. Predicting environmental changes caused bychanges in people’s lifestyles
We now focus on the behavior of consumers. The
use of ICT brings about changes in people’s lifestyles
and affects the production activities of industries andenvironmental loads. For example, when teleworking
enables people to work at home, the use of private
cars and public transportation systems will decrease,
reducing environmental loads. On the other hand, theuse of lighting and home appliances at home increases electric power consumption, generating environmental loads. Since commuting time is saved, time
for new activities, such as hobbies, will increase.
Therefore, the use of ICT can reduce environmentalloads through reductions in travel time but can also
increase them through changes in people’s activities
that result from changes in their locations and reduction in commuting time.
As an example of using the prediction of socialchanges caused by lifestyle changes, the following
describes the analysis of how the penetration of ICT
services, such as teleworking, online shopping, andonline education, into consumers’ lives affects environmental loads. We focus on how people use their 24
NTT Technical Review

Vol. 19 No. 6 June 2021

hours. On the basis of statistical data and survey
reports, we specifically consider how ICT penetration
changes time-usage patterns of consumers. Whenpeople switch from commuting to the office to working at home, they increase the time they spend on
cooking and leisure activities. Taking changes in theiractivity locations and the use of ICT tools for reading
and learning into consideration, we calculate theduration of their activities and the amount of greenhouse gas emissions per unit of time, as shown in
Table 2. We calculate the environmental loads interms of greenhouse gas emissions using the lifecycle assessment method [7]. The amounts of energy
and physical material consumed are calculated fromthe details and durations of activities. We analyze thecontribution of each ICT usage (component) tochanges in greenhouse gas emissions after ICT penetration and identify those components that are critical in accelerating the decrease of emissions or in
slowing the increase of emissions. Since the environmental loads arising from human activities are affected by social conditions, such as lifestyle and the typesof electric power sources, it is necessary to reflect in
the analysis the relations between such social conditions and the effects of using ICT. We pay attention to
the negative effects of ICT penetration, such as people’s weariness from working at home, in creating
options that will lead to corporate actions to resolve
social problems, thereby helping to build a better
society.
As part of DTC initiatives, NTT aims to create afuture in which a harmonious relationship can beestablished among the Earth, society, and individuals
34

Feature Articles

Table 2. Examples of impact of ICT penetration.
Activity

Changes after ICT penetration
Activity duration

Greenhouse gas (GHG) emissions per unit time (GHG intensity)

CommutingDecreases as a result of Since commuting methods remain unchanged, the GHG
telework
intensity remains unchanged.

Shopping

Travel time is reduced

The GHG intensity increases because electronic devices
consume electric power.

Hobbies

Increases as a result of
reduction in commuting

Since hobbies remain unchanged, the GHG intensity remains
unchanged.

…

[3]. To achieve it, we are enhancing the purpose oflife and the richness of the spirit of the individual
expressed as well-being, in a future in which thediversity, opportunities, and possibilities of individuals are expanded and the complexity of the social
structure and global uncertainty increase throughtechnologies for exploring the shape of a future society and deriving an inclusive equilibrium solution
between the Earth and socio-economic systems.

we aim to achieve a sustainable global environmentand sustainable and inclusive human society as wellas enhance corporate value.
References[1][2]

5. Conclusion[3]

Looking forward, we will build a firm technicalfoundation for future prediction on the basis of thetechnologies mentioned above and develop a method
for evaluating corporate value and corporate wellbeing. We will predict a future society in which social
structures will become increasingly complex and theuncertainty on a global scale will increase. We will
identify the impact of ICT on climate change andother problems and reflect the results in corporate
ESG strategies so that corporations can proactively
solve the problems identified. Through these efforts,[4]

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Vol. 19 No. 6 June 2021

[5]

[6]
[7]

Annual Report on the Environment, the Sound Material-Cycle Society and Biodiversity in Japan, https://www.env.go.jp/en/wpaper/
index.html
K. Saito, “‘The Capital’ in Anthropocene,” Shueisha, 2020 (in Japanese).
NTT press release, “NTT Announces New R&D Projects of Digital
Twin Computing,” Nov. 13, 2020.
https://group.ntt/en/newsrelease/2020/11/13/201113c.html
Cabinet Office, Government of Japan, Society 5.0,
https://www8.cao.go.jp/cstp/english/society5_0/index.html
National Institute for Environmental Studies, “Asia-Pacific Integrated
Model 2: Economic Model,” NIES Research Booklet, Vol. 74, p. 9,
2019 (in Japanese). http://www.nies.go.jp/kanko/kankyogi/74/
column4.html
Ministry of Internal Affairs and Communications, Input-Output
Tables for Japan, https://www.soumu.go.jp/english/dgpp_ss/data/io/
index.htm
Japan Environmental Management Association for Industry, “Method
to Develop Environmentally Friendly Products and Services: Life
Cycle Assessment,” 2004 (in Japanese).
https://www.meti.go.jp/policy/recycle/main/3r_policy/policy/pdf/
text_2_3_a.pdf

35

Feature Articles

Yuriko Tanaka

Senior Research Engineer, Supervisor, ESG
Management Science Group, Resilient Environmental Adaptation Research Project, NTT Space
Environment and Energy Laboratories.
She received a B.S. and M.S. in physics from
Keio University, Kanagawa, in 1992 and 1994.
Since joining NTT in 1994, she has been engaged
in research on micromachining and sensing andassessment of environmental impact. She is amember of the Institute of Electronics, and Communication Engineers (IEICE) of Japan.

Machiko Shinozuka

Research Engineer, ESG Management Science
Group, Resilient Environmental Adaptation
Research Project, NTT Space Environment andEnergy Laboratories.
She received a B.S. and M.S. in medical engineering from Keio University, Kanagawa, in2013 and 2015. Since joining NTT in 2015, she
has been engaged in research on assessment of
the environmental impact of ICT use. She currently specializes in environmental and social
future prediction simulations in terms of lifestyle. She is a member of IEICE.

Xiaoxi Zhang

Senior Research Engineer, ESG Management
Science Group, Resilient Environmental Adaptation Research Project, NTT Space Environment
and Energy Laboratories.
She received a B.S. and M.S. in social engineering from Tokyo Institute of Technology in2007 and 2009. Since joining NTT in 2009, she
has been engaged in research on risk-based management of telecommunication infrastructures
and assessment of the environmental impact of
ICT use. She currently specializes in environmental and social future prediction simulations.
She won TTC (the Telecommunication Technology Committee) Distinguished Service award in2020. She is a member of IEICE.

NTT Technical Review

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36

Feature Articles: Challenges of NTT Space Environment
and Energy Laboratories toward Ultra-resilient Smart Cities

Proactive Environment Adaptation
Technology for Living Safely andSecurely
Jun Kato
Abstract

Changes in the Earth’s environment are expected to have a significant impact on our social life. In thisarticle, environmental adaptation technologies (technology to develop a platform for collecting and analyzing all types of information on the Earth, meteorological forecasting/control technology, lightning
control technology, and electromagnetic barrier technology) for predicting various effects of changes inthe Earth’s environment, responding to such effects proactively, and achieving a resilient society byenabling humans to adapt to such changes are introduced.
Keywords: resilience, weather prediction, cosmic rays

1. Introduction
The frequency of extreme weather*1 has increasedaround the world [1]. In Japan, heavy rains andtyphoons are common extreme-weather events but
are difficult to observe and predict, causing severe
damage. For this reason, highly accurate weather
forecasting is important. Weather-forecasting technology has made significant progress from technology based on the experience and subjectivity of forecasting engineers to observation technology such as
weather radar and numerical analysis using supercomputers. However, typhoon predictions, especiallyregarding intensity, are still done using satellite photographs.
Meteorological observations are carried out on aregular basis using an observation and forecasting
system that uses observation data from land and sea
on a global scale as well as from space. Since it takes
only about 15 minutes from cumulonimbus formation
to maturity and fluctuation occurs rapidly within alimited area of several square kilometers [2], observations, such as with satellites and AMeDAS (Automatic Meteorological Data Acquisition System), arenot sufficient to respond to such extreme weather.
The rise in sea-surface temperature due to global
NTT Technical Review

Vol. 19 No. 6 June 2021

warming and the meandering of mid-latitude westerlies increase the water vapor supply to typhoons [3].
Such climate change is caused by human activities aswell as natural climate change of the Earth over thelong term [4]. Examining, understanding, and diagnosing the state of the Earth’s climate is crucial to thelong-term prediction of climate change and theimplementation of policies to curb the effects ofanthropogenic causes. Wide-area observations areneeded to assess the state of the Earth’s climate. Suchobservations can be carried out using satellites, butthere is a problem regarding observation accuracy(vertical components of the atmosphere, observation
below the sea surface, etc.).
Therefore, we are investigating the technologies
described in this article for making high-precisionpredictions on changes in the global environment,such as extreme weather and climate change, andmaking the impact less severe by implementing countermeasures in advance.

*1 Extreme weather: A phenomenon that exceeds a specific index,
such as extremely high or low temperatures or heavy rain.

37

Feature Articles

TyphoonProcessing
and applicationof real data

MaturedDeveloping
Land Ocean

Formation

Typhoon, heavy rain

Meteorological
Seawater temperature/geomagnetic sensor/current sensor

Fig. 1. Image of Earth-information analysis using satellite IoT platform.

2. Technology to develop a platform forcollecting and analyzing all types of informationon the Earth
We are conducting studies on predicting weather
and disasters in real time and with high accuracy bymaking extensive use of information from areas thathave not been extensively observed such as the sea
surface, underwater, and mountains. NTT’s proposalof “In-orbit demonstration of 920 MHz band satellite
Internet of Things (IoT) platform utilizing satellite
multiple-input and multiple-output (MIMO) technology” was selected as an innovative satellite-technology demonstration theme by the Japan Aerospace
Exploration Agency (JAXA) in May 2020 [5]. In thisdemonstration theme, we are currently investigating asystem to cover areas where information cannot becollected using terrestrial communication infrastructure.
This system is a new sensor-network system thatsimultaneously acquires information from various
IoT sensors on the ground with satellites over 550 km
above the Earth then bundles, transmits, and analyzes
it on the ground.
With this system, IoT sensors can be installed atdesired positions to enable detailed meteorologicalobservations for data acquisition and data assimilation*2, which will enable predicting extreme weather
that changes drastically, such as local heavy rains andtyphoons (Fig. 1).

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3. Meteorological forecasting andcontrol technology
We will collect meteorological information byusing the basic technology of Earth information
analysis, construct a digital twin*3 of meteorologicalphenomena of the whole Earth from the data, andenable the simulation of meteorological prediction
and meteorological control on a digital twin.
In meteorological forecasting, we will investigate
how to enable high-precision meteorological observation. In particular, we are designing a system forobserving meteorological data and measuring data
related to typhoons from the ocean and air. We will
also study typhoon weather models in collaboration
with universities.
We now discuss typhoons and lightning as examples of weather control. Regarding typhoon control,
we are studying technologies such as for lowering thetemperature of the nearby sea by exchanging water
masses in the deep sea and shallow water to weaken
the force of a typhoon and a technology for converting the energy of a typhoon into electricity (Fig. 2).
Regarding lightning control, we are developing atechnology that guides lightning strikes to a safe
*2 Data assimilation: This is mainly done in Earth science to improve the reproducibility of numerical models. Simply put, it involves inputting actual observation data into a model to obtain
more realistic results.
*3 Digital twin: A technology that reproduces various data collectedfrom the real world on a computer as if they were twins. It is possible to conduct physical simulations that are as close to reality
as possible from the enormous amount of data collected, which isan effective means for further improving the manufacturing process and services of products.

38

Feature Articles

Technology for predicting
the future environment

Technology for sensing the Earth

Technology for controlling the weather

Extreme weather
Vulnerability
High-precision simulation
Converting typhoon into electricity
Current: The accuracy of weather anddamage prediction has not improved due
to insufficient sensing data.
Task: Establishment of new sensing
method and methods for real-time typhoonobservation and vulnerability sensing forsocial infrastructure, etc.

Current: Due to lack of high-precision
simulation, weather control and energyconversion efficiency have not improved.
Task: Necessary to develop a modelingmethod using Digital Twin Computing toincorporate complex elements such as
weather + infrastructure, people, and things.

Current: Damage will increase due to theinability of society to adapt to extreme
weather.
Task: Necessary to achieve anenvironment-adaptive society by converting
extreme weather into energy by using
electromagnetic waves and lasers.

Fig. 2. Overview of weather prediction and control technology.

Lightning-control drone

Lightning charge car
Operates with only lightning energy
EVFig. 3. Image of lightning control and lightning charging system using drone.

place using an air vehicle, such as a drone, with functionality to maintain flight even if it is struck by lightning, as shown in Fig. 3. Figure 4 shows photographsof a drone with a grid-like Faraday cage*4 attached to
it at the moment of a lightning strike that continued to
fly and of the same model without the Faraday cage,
which lost control after being struck by lightning andcrashed. This confirms that the drone with the FaraNTT Technical Review

Vol. 19 No. 6 June 2021

day cage had high lightning resistance. We will also
consider methods, such as that illustrated in Fig. 3,
for collecting and using lightning energy and construct*4 Faraday cage: A space surrounded by conductors, or a conductor
cage or vessel used to create such a space. Since electric lines offorce cannot enter the space surrounded by conductors, the external electric field is blocked and all the internal potentials areequal. It is also called a Faraday shield.

39

Feature Articles

Lightning
strikeLightning
strikeDrone(flying)

Ground cableWith cage (no damage)Drone(damaged)
Without cage (damaged after lightning strike)Fig. 4. Drone lightning-strike performance test (effectiveness of Faraday cage).

a lightning-control system for charging electric vehicles (EVs) that operate autonomously using only
lightning energy to achieve a safe and secure society.
4. Electromagnetic barrier technology
The Proactive Environmental Adaptation Technology Group is also engaged in research and development for technologies that will innovate the future ofsociety and the environment from a space perspective. For humans to advance into space, create living
spaces, and live for a long time in space, the impact
of powerful cosmic rays*5 from the sun and otherstars on the human body and precision equipment
must be reduced. Therefore, we are investigating theevaluation of cosmic rays and the development ofbarrier technology to reduce their impact.
The impact of cosmic rays on the ground is mainly
derived from neutrons, but in space, protons are themain source. Since protons have an electric charge,
they can form an electromagnetic barrier (Fig. 5) thatblocks and refracts cosmic rays with strong magnetic
and electric fields.
Verification in space is required to study this technology, but it is not easy to transport experimental
materials into space. Therefore, we are developing atechnology for designing electromagnetic barriers in
virtual space by digitally twinning spacecraft, spacestations, and lunar bases in cyberspace. To do this, wewill first conduct simple experiments and simulations
using a proton accelerator.
If this research progresses, not only will we be able
to live in space for a long time but manned planetary
exploration and lunar bases will no longer be dreams.
It will also be possible to build an ultra-high security
and highly reliable datacenter in outer space.
5. Conclusion
We are developing an IoT network platform using
satellite MIMO to carry out more detailed weather
observations to make highly precise predictions andtake countermeasures regarding extreme weather andclimate change, which are expected to have a greater
impact in the future. We will develop a weather-prediction technology that uses analysis data from digital twins and work on achieving the goal of prediction/control of extreme weather. We will also study
electromagnetic barriers that block and refract cosmic rays and create an environment where people cansafely and securely live and work in space.

*5 Cosmic rays: High-energy radiation that travels through space.
The main component of cosmic rays is protons, which originate
from the sun and other stars. There is concern about the effects
on electronic devices and living organisms due to long-term cosmic ray exposure.

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40

Feature Articles

Datacenter in space
Cosmic rays
(mainly protons)

Spacecraft outer wall

NeutronSemiconductor device
Bend the orbit of
the particles

Barrier to cosmic rays(by magnetic andelectric fields)

Fig. 5. Electromagnetic barrier system in space.

References
[1]
[2]

[3]

T. Toyoda, “Extreme Weather and Observation/Prediction Technology,” Forecast and Response to Extreme Weather, pp. 5–15, 2019 (inJapanese).
E. Nakakita, H. Sato, and K. Yamaguchi, “Studies on Formation
Mechanism of Vertical Vortex Tube inside Cumulonimbus Cloud for
Accuracy Improvement of Guerrilla-heavy Rainfall Prediction,”
DPRI Annuals, Vol. 60, No. B, pp. 539–558, 2017 (in Japanese).
S. C. Herring, N. Christidis, A. Hoell, J. P. Kossin, C. J. Schreck III,and P. A. Stott, “Explaining Extreme Events of 2016 from a Climate
Perspective,” Special Supplement to the Bulletin of the American

[4]

[5]
[6]

Meteorological Society, Vol. 99, No. 1, pp. S1–S157, 2018.
The Intergovernmental Panel on Climate Change (IPCC): “Climate
Change 2007: The Physical Science Basis,” Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental
Panel on Climate Change, Cambridge University Press, 2007.
NTT press release issued on May 29, 2020 (in Japanese), https://www.
ntt.co.jp/news2020/2005/200529a.html
Press release issued by NTT, Nagoya University, and Hokkaido University, “Neutron Energy Dependence of Semiconductor Soft Errors
Was Successfully Measured for the First Time,” Nov. 25, 2020.
https://group.ntt/en/newsrelease/2020/11/25/201125a.html

Jun Kato

Project Manager, NTT Space Environment andEnergy Laboratories.
He received a B.E. from Shizuoka University
in 1992 and joined NTT the same year. He is currently engaged in research and development ofproactive environmental adaptation technologies.

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Vol. 19 No. 6 June 2021

41

Feature Articles: Healthcare Devices and Infrastructuremaintenance Technology that Support People and Society

The Future Pioneered by Device
Technology for a Sustainable Society
Masato Tomizawa and Akira Okada
Abstract

The research and development NTT is conducting to create a sustainable society, specifically regarding human health and aging infrastructure, is outlined in the following Feature Articles in this issue. Afterthe trends toward solving social issues in Japan and overseas are briefly described, the direction of smarthealthcare and infrastructure-maintenance technologies—which use device technology cultivated by
NTT laboratories—is discussed. Research results and cutting-edge technologies that are about to be put
into practical use and be used for prevention and maintenance by grasping and estimating the conditionsof people and infrastructure are also introduced.
Keywords: healthcare, infrastructure maintenance, sustainability

1. Challenges facing creation of asustainable society
Problems, such as declining birthrates and aging
populations, global warming, energy problems, andfood crises, are becoming apparent across the world,
and it is said that 2030 will be the turning point for thecontinuous economic growth that humankind has
enjoyed as civilizations have developed. The Sustainable Development Goals (SDGs) were established by
the United Nations with the aim of creating a sustainable society [1], and in Japan, efforts toward creatinga people-centered super-smart society called “Society 5.0” have been positioned as important issues [2].
Under such circumstances, we have entered an era ofreorganization of the economic and geopoliticalworld order, and how to revise the information society has become a major issue. To address such issues,
it is necessary to develop technologies to promote
continuous business while understanding the needs ofsociety and expanding the horizons of the entire
social system. In other words, simultaneously achieving business continuity and solutions to social issues
is the key to the creation of a truly sustainable society.
We believe that people-centered efforts will be amajor first step when addressing the above issues. If
we want to think in a people-centric manner, we
NTT Technical Review

Vol. 19 No. 6 June 2021

should focus on two aspects: (i) the health of individuals and healthcare provided for them and (ii) theenvironment surrounding them. We believe thatdeveloping technology that takes into account people
and their environment will significantly contribute tosolving social issues while achieving business continuity.
Regarding human health, the economic effect ofachieving a lifelong active society is 33 trillion yen,and the health-technology market is worth over 50
billion yen [3] (Fig. 1). It is thought that the time will
come when we will take the initiative in managing
our own health, such as early intervention throughdaily monitoring and pre-illness care and prevention
through personalized guidance. The above awarenessof issues has been pointed out for some time; however, the need for digital transformation (DX) of
health is increasing at a rapid pace due to the recent
spread of infectious diseases.
Regarding environment-friendly technology, how
to efficiently maintain infrastructure equipment, themost-basic element of the information society, needs
to be addressed. The cost of infrastructure maintenance and renewal in Japan is estimated to be enormous, 5 to 7 trillion yen per year [4] (Fig. 2). Infrastructure maintenance is an extremely difficult technical area because infrastructure is used for a long42

Feature Articles(100 million yen)
700

Sports/healthcare

Medical/long-term care

Healthcare in Society 5.0
Toward a lifelong active society• Pre-illness care and prevention• Personalization• Proactively manage one’s health Accelerated due to COVID-19
pandemic

600
500
400

581

408
445

300

235

200
100

64

0

80

6

99
10

16

162

125
29

281

119

56

58

71

84

97

107

116

126

136

2017

2018

2019

2020

2021

2022

2023

2024 (Year)

Source: Nomura Research Institute, materials for the 273rd NRI Media Forum (issued on December 6, 2018).
The graph is created by NTT utilizing data from Nomura Research Institute.

Fig. 1. Trends in domestic market size of healthcare technology.

(Trillion yen)
12

10

8

5.2 trillion yen

6.0 trillion yen(1.2 times)

6.6 trillion yen(1.3 times)

6.4 trillion yen(1.2 times)

7.1 trillion yen(1.4 times)

6.5 trillion yen(1.3 times)

6

4

2

0
2018

2023
Roads

2028

2033

Rivers, dams, erosion
control, and coastlines

2038

SewersHarbors

2043(Year)
2048

Six other areas*Since the estimated value is a value with a width, the graph is created using the maximum value.
Source: Ministry of Land, Infrastructure, Transport and Tourism, “Estimation of Future Maintenance andRenewal Costs of Social Capital in Fields under the Jurisdiction of the Ministry of Land, Infrastructure,
Transport and Tourism,” 2018 (in Japanese).

Fig. 2. Changes in infrastructure maintenance and renewal costs.

time in various environments, and it is necessary toevaluate and elucidate physical phenomena in unitsof ten-years. Infrastructure maintenance currently
involves a large amount of manual work; therefore,
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Vol. 19 No. 6 June 2021

DX conversion including automation of inspection isrequired by using the power of technology. Against
this background and to create a sustainable society,NTT is focusing on research and development (R&D)
43

Feature Articles

Smart-healthcare technology

Creation of a sustainable societythat focuses on people andthe environment

Infrastructure-maintenancetechnology

Added-value feedback
Safe and secure life

Contribution to asustainable society

Medical/healthcare

Easily create new data without
being aware of the device

Safe and economical infrastructure
Datacenter

Communication

End user
IOWN

IoT-edge

Edge devices(which provide theinput of IOWN)
Data provision

Communicationinfrastructure equipmentthat supports IOWN

Infrastructure
management

IoT: Internet of Things
IOWN: Innovative Optical and Wireless Network

Fig. 3. Smart-healthcare and infrastructure-maintenance technologies for a sustainable society.

of smart-healthcare and infrastructure-maintenancetechnologies (Fig. 3).
2. Direction of smart-healthcare andinfrastructure-maintenance technologies
2.1 Smart-healthcare technology
To support people’s health and provide healthcare
to them on a daily basis, it is necessary to (i) acquire
the information necessary of their daily lives without
them being aware the devices being used to collectsuch information and (ii) present the appropriate
information in accordance with the circumstances
concerning each person. Accordingly, it is necessary
to develop devices that naturally blend into as well as
enrich our lives. Portable devices and smartwatches
for measuring heartbeats and pulse have been commercialized, and their usefulness in various situations
is beginning to be recognized. From the perspectiveof addressing social issues and creating a market, thesituation is on the verge of great change. Such devices have begun to evolve from their utilization at thepersonal-fitness level to true healthcare in the form of
medical applications. NTT has developed low-power
multi-sensor data-processing and high-precision
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Vol. 19 No. 6 June 2021

sensing technologies. In addition to conventional
electrocardiographic measurement and acceleration
sensors, we have put into practical use a wearable,compact low-power transmitter with a built-in temperature and humidity sensor as our first wearable
device [5]. By using this device, it is possible to estimate fluctuations in body temperature and body load,
and that information will make it possible to develop
high-value-added services by obtaining body information that was previously unknown in real time. We
are also researching and developing photoacousticsensing and molecular-labeling technologies thatenable non-invasive, highly selective, and highly
sensitive monitoring. Targeting previously unmeasurable vital-sign information and biomarkers in relation
to lifestyle-related and chronic diseases, for which
the number of patients is increasing yearly, we areaiming for a simpler biosensor device that does not
require the collection of samples such as saliva andblood.
2.2 Infrastructure-maintenance technology
Infrastructure facilities, which are used for long
periods of time (several decades) in a variety of harshenvironments, are supported by a large amount of
44

Feature Articles

Photoacoustic measurement
technology
Sensor Sound fieldEarhitoeTM wear

SensorLight

Transmitter

Derusting laser
technology

Hydrogen-embrittlementprediction technology

EarTime to fracture

Physical-conditionmanagement technology

Infrastructure maintenanceMicrophone

Smart healthcare

A future pioneered by device
technology that focuses on
people and the environmentNofracture

Fracture
Time to fractureTime until one
rebar breaks

ThresholdAmount of bending

Diffractive optical element

Fig. 4. Technology NTT is developing that is focused on people and the environment.

labor and experience, and the development of technologies that contribute to efficient work is still insufficient. Moreover, many unknowns, such as thedegree of deterioration of the materials that make up
the infrastructure over a period of ten years, must be
considered. It will be paramount to achieve sustainable conservation of infrastructure that is both safeand economical. Infrastructure maintenance mainly
consists of four steps: (i) maintenance planning, (ii)inspection, (iii) diagnosis, and (iv) repair and reinforcement. For more efficient and safer infrastructure
maintenance, it is important to plan in advance as
precisely as possible and streamline manual repair
work.
Infrastructure facilities are mainly made of steel
and concrete, so it is no exaggeration to say that infrastructure maintenance is the maintenance of steel andconcrete. Accordingly, from the viewpoint of preventive maintenance of infrastructure, NTT is focusing
on steel and concrete poles and researching anddeveloping technologies that contribute to making
rust removal more efficient and estimating deterioration, which are extremely difficult challenges toaddress with current technologies. It is important toremove rust from telecommunication towers andother steel infrastructure facilities as they age. By
using the diffractive-optical-element technology
developed by NTT and combining it with a highpower laser, the weight of a rust remover is expected
to decrease by several times compared to commercial
products, significantly improving work efficiency.
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The degradation of reinforcing bars (rebars) in concrete poles is caused by hydrogen embrittlement, but
the details of this phenomenon are still unknown.
NTT is promoting R&D to establish hydrogenembrittlement-prediction technology using core technologies such as electrochemistry and materials.
3. Topics and composition of the
Feature Articles
The following Feature Articles in this issue focus
on smart-healthcare and infrastructure-maintenancetechnologies that are close to practical application
and are medium- to long-term, and the following four
technologies are introduced as the latest research
results (Fig. 4).
3.1 P
 hysical-condition-management technology
using wearable biological and environmental-sensor technology
NTT has commercialized wearable biological andenvironmental-sensor technology that can acquire
and transmit not only biological data (such as heart
rate and electrocardiograms) but also environmental
data (such as temperature and humidity underneathclothing) by using the functional fabric hitoeTM* aselectrodes. This technology enables efficient signal
processing of data from three sensors (electrocardiogram, acceleration, and temperature/humidity),
which result in a low-power, compact wearable
device. It will make it possible to comfortably and45

Feature Articles

easily obtain biological information and personalenvironmental information from various daily activities. For example, it will enable the development ofsmart-healthcare applications such as those to counter heat stroke. A method based on this technology
was developed that involves workers in hot environments wearing sensors to manage their physical conditions. This makes it possible to understand realtime physical information that was previously
unavailable. Its effectiveness and practicality wereverified at a network-construction site [6].
3.2 N on-invasive biological-information sensing
using photoacoustic-measurement technology
A technology for non-invasive sensing of biologicalinformation without damaging the body—by using aphotoacoustic method for measuring ultrasonicwaves generated when a specific light is irradiatedonto biological components in the body—is introduced. Compared with other methods such as opticalcoherence tomography and ultrasonography, photoacoustic technology is superior in measurement depth
and spatial resolution as well as the potential in
responding to various biological components. It istherefore expected to enable monitoring of various
biological components related to lifestyle-relateddiseases. Since a non-invasive method enables continuous measurement of biological data, it is expected
to be used in medical and healthcare applications tomonitor biological data that change daily. To establish the technology for such a biological-sensing
device, we are constructing a biophysical model ofthe penetration of a probe into the skin and its effecton biological mechanisms. We are also pursuing
R&D on measuring biological components on thebasis of the correlation between biological mechanisms and electrical and optical parameters concerning the regions from the surface of the skin to theinterior of the body [7].
3.3 C ompact and lightweight rust remover incorporating a high-power laser device that uses a
diffractive optical element
Infrastructure facilities made of steel, such as communication towers, are subject to aging due to rusting. The first step in maintaining a steel tower is toremove the rust, and the second step is to paint the
tower to protect the surface. To maintain the performance of coating and increase the durability of thesteel tower, the surface condition of the underlying
steel is important, and the key is how to effectively
remove the rust. Rust is removed by irradiating a
NTT Technical Review

Vol. 19 No. 6 June 2021

high-power laser beam onto the steel surface. By
combining NTT’s optical device technology with acompact and lightweight diffractive optical element,
it is possible to fabricate a rust remover that is several
times lighter than other products on the market forcontrolling the laser profile and efficiently removing
rust. At current work sites, metal brushes are used toremove rust in narrow spaces; however, using thedeveloped technology is expected to reduce work
load and shorten work time [8].
3.4 H ydrogen-embrittlement-prediction technology for rebars of concrete poles
A technology for predicting hydrogen embrittlement, which is a degradation phenomenon of steel
rebars in concrete poles will enable safer and more
economical maintenance and management of concrete poles, which are one of the key infrastructure
facilities that support telecommunications services.
Concrete is strong in compression but weak in tension; thus, tensile stress is applied to the internal
rebars so that compressive stress can be applied to theconcrete. However, steel rebars subjected to tension
undergo deterioration called hydrogen embrittlement, which can lead to facility failure. However,such rebars cannot be visually checked, so it is difficult to determine the deterioration status of concrete
poles, which poses a challenge for maintenance.
From the viewpoint of preventive maintenance, by (i)establishing evaluation methods (such as conducting
an accelerated hydrogen-embrittlement test andevaluating hydrogen amount), (ii) using analysis
methods such as statistical data analysis, and (iii)
elucidating and modeling the hydrogen-embrittlement mechanism, we are working on a formula for
estimating hydrogen embrittlement [9].
4. Future developments
We will accelerate the practical development of thesmart-healthcare and infrastructure-maintenance*hitoeTM: A functional fabric developed by Toray and NTT. It isfabricated by specially coating nanofiber fabric, which is themost-advanced fiber material, with a highly conductive resin. It
has excellent durability and can detect biosignals with high sensitivity even though it is a non-metallic material. Having hitoe adhere to the skin surface makes it possible to obtain biological
data, such as heart rate, electrocardiograms, and sleep data, estimated from R-wave intervals. Using nanofibers makes it possible
to acquire more-sensitive measurements of biological signals inclose contact with a person’s body (e.g., through clothing andhats) because the nanofibers are durable enough to be washed athome and have an increased degree of adhesion to the skin.

46

Feature Articles

technologies introduced in this article. We will also
promote R&D on challenging themes from a medium-to-long-term perspective to contribute to creatinga sustainable society that focuses on people and theenvironment.
References
[1]
[2]
[3]
[4]

[5]

Website of the United Nations, Sustainable Development Goals,
https://www.un.org/sustainabledevelopment/
Website of Cabinet Office, Government of Japan, Society 5.0,
https://www8.cao.go.jp/cstp/english/society5_0/index.html
Nomura Research Institute, materials for the 273rd NRI Media
Forum, Dec. 2018.
Ministry of Land, Infrastructure, Transport and Tourism, “Estimationof Future Maintenance and Renewal Costs of Social Capital in Fields
under the Jurisdiction of the Ministry of Land, Infrastructure, Transport and Tourism,” 2018 (in Japanese).
h t t p s : / / w w w. m l i t . g o . j p / s o g o s e i s a k u / m a i n t e n a n c e / _ p d f /research01_02_pdf02.pdf
NTT press release issued on Nov. 8, 2019 (in Japanese).

Masato Tomizawa

Vice President, Head of NTT Device Innovation Center.
He received an M.S. and Ph.D. in applied physics from Waseda University, Tokyo, in 1992 and2000. From 2003 to 2004, he was a visiting scientist at Massachusetts Institute of Technology,
USA. He has been engaged in R&D of highspeed optical transmission systems. Since 2009,he has been a project leader of the 100G Centerof-Excellence (CoE) Consortium consisting ofseveral manufacturing companies and is responsible for the development and marketing strategies of 100G coherent digital signal processors.
In 2013, he received the Minister’s Award of the
Ministry of Internal Affairs and Communicationsof Japan from the Telecommunication Technology Committee for his contributions and leadership of the consortium in the 100G digital coherent CoE project. In 2015 and 2016, he received
Fellow-grade memberships from the Institute ofElectronics, Information and Communication
Engineers (IEICE) and the Optical Society(OSA), respectively.

NTT Technical Review

Vol. 19 No. 6 June 2021

[6]

[7]

[8]

[9]

https://www.ntt.co.jp/news2019/1911/191108a.html
K. Takagahara, Y. Hashimoto, K. Matsunaga, Y. Higuchi, N. Matsuura, K. Kuwabara, H. Togo, T. Kawahara, A. Hirata, H. Tanaka, and T.
Miyazawa, “Physical-condition Management Technology for Creating More Comfortable Work Sites,” NTT Technical Review, Vol. 19,
No. 6, pp. 48–54, June 2021.
h t t p s : / / n t t - r ev i ew. j p / a r c h ive / n t t t e c h n i c a l . p h p ? c o n t e n t s =ntr202106fa7.html
Y. Tanaka, T. Tajima, and M. Seyama, “Non-invasive Biologicalinformation Sensing Using Photoacoustic Measurement Technology,”
NTT Technical Review, Vol. 19, No. 6, pp. 55–60, June 2021.
h t t p s : / / n t t - r ev i ew. j p / a r c h ive / n t t t e c h n i c a l . p h p ? c o n t e n t s =ntr202106fa8.html
S. Kawamura, T. Sakamoto, M. Ueno, and S. Oka, “Derusting Technology Using High-power Laser Device,” NTT Technical Review,Vol. 19, No. 6, pp. 61–65, June 2021.
h t t p s : / / n t t - r ev i ew. j p / a r c h ive / n t t t e c h n i c a l . p h p ? c o n t e n t s =ntr202106fa9.html
T. Kamisho, R. Ishii, and M. Tsuda, “Technology for Predicting
Hydrogen Embrittlement in Reinforcing Bars of Concrete Poles,”NTT Technical Review, Vol. 19, No. 6, pp. 66–70, June 2021.
h t t p s : / / n t t - r ev i ew. j p / a r c h ive / n t t t e c h n i c a l . p h p ? c o n t e n t s =ntr202106fa10.html

Akira Okada

Vice President, Head of NTT Device Technology Laboratories.
He received a B.S. and M.S. in physics in 1988
and 1990, and a Ph.D. in materials science in1993 from Keio University. He joined NTT in
1993 and conducted research on polymer-based
waveguide devices, full-mesh wavelength division multiplexing networks, optical packet
switching, and optical modules for access networks. From October 1997 to October 1998, he
was a visiting scholar at Stanford University, CA,
USA. He is a member of the Institute of Electrical and Electronics Engineers (IEEE), IEICE,
and the Japan Society of Applied Physics(JSAP).

47

Feature Articles: Healthcare Devices and Infrastructuremaintenance Technology that Support People and Society

Physical-condition Management
Technology for Creating More
Comfortable Work Sites
Kazuhiko Takagahara, Yuki Hashimoto,Kenichi Matsunaga, Yuichi Higuchi, Nobuaki Matsuura,
Kei Kuwabara, Hiroyoshi Togo, Takashi Kawahara,
Akimasa Hirata, Hideto Tanaka, and Taiki Miyazawa
Abstract

Physical-condition management is becoming more important to improve the safety of work sites, suchas preventing heat stroke caused by intense heat. We at NTT Device Innovation Center have developed
a physical-condition management technology for creating more comfortable work sites by using thewearable-device sensors and data-analysis technology we have developed thus far, and the knowledge ofthermal and exercise physiology in collaboration with specialists. This article introduces the problems
with physical-condition management, how our technology can solve these problems, and the results fromverifying our technology at an actual work site.
Keywords: wearable sensor, physical-condition management, heat countermeasures

1. Introduction

2. Technical problems

The number of emergency transports and deaths
due to heat stroke has increased, and reducing themhas become a major social issue in Japan. According
to a survey by the Fire and Disaster Management
Agency, 64,770 people were transported by emergency due to heat stroke from June 1st to October 4th,
2020. According to the Ministry of Health, Labor andWelfare (MHLW), there were 829 casualties (deathand leave of absence 4 days or more) due to heatstroke in the workplace in 2019, of which 25 died.
MHLW has published guidelines and manuals forheat-stroke prevention measures in the workplace [1].
We at NTT Device Innovation Center have been
engaged in research and development of physicalcondition management technology using wearable
biological/environmental sensors to solve such social
issues and create more comfortable work sites.

We developed our physical-condition management
technology to make work sites more comfortablefrom two aspects: real-time control of the risk of poor
physical condition due to heat and reduction of accident risk by short- and medium-term operation management.
Figure 1 shows a schematic of the cause of poor
physical condition due to activities in a hot environment [2]. When the body temperature rises due toexercise in normal environments, the heat is dissipated to the outside air due to sweating and increasein skin temperature, regulating body temperature.
However, in a hot environment, it is difficult for heatto dissipate to the outside air. If the water and salt lost
due to sweating are not sufficiently replenished,blood flow will also be impaired and heat will easily
accumulate in the body, causing poor physical condition.

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Feature Articles

NormalNormalbody temperature
Exercise and activities
in a hot environment

Heat dissipation(sweating, increased
skin temperature)

Increased bodytemperature

AbnormalHeat production >Heat dissipation(body temperature
increased further)

Task (1)Estimate the risk of poor
physical condition in real time

Task (2)Determine the high risk ofpoor physical condition andtake an appropriate break

Fig. 1. Cause of poor physical condition in a hot environment.

We have found two requirements to mitigate suchconditions. One is that it is necessary to estimate therisk of poor physical condition for each individual inreal time because the environment, such as outside
temperature and humidity at the work site, and theintensity of work and exercise vary from person toperson and change from moment to moment. The
other is that it is necessary to determine the high riskof poor physical condition from the estimation results
to properly encourage breaks and water intake before
poor physical condition occurs.
To reduce accident risk by short- and medium-term
operation management, we applied the acute chronic
workload ratio (ACWR), which is attracting attention
as being effective in reducing the risk of injury andpoor physical condition of athletes, to workers. The
ratio of short-term work load of about one week tolong-term work load of about one month is defined as
the ACWR. The risk of injury increases if the ACWR
is too high or too low, so daily operation is managed
so that the ACWR is in the low risk area. One of the
problems is quantifying the work load caused bydaily work.
To solve these problems, we developed a wearable
sensor for acquiring biological/environmental information and a sensor-data-analysis technology basedon thermal and exercise physiology.

each worker in real time, it is necessary to acquirevarious biological and environmental information
without interfering with work, and we believe wearable sensors are effective for this purpose.
Figure 2 shows our wearable biological/environmental sensor. It consists of a transmitter (TX02),
which is commercialized by NTT TechnoCross basedon the wearable biological/environmental sensor
technology researched and developed at NTT Device
Innovation Center [4], a hitoeTM*1 shirt, hitoe belt
from Toray Industries, Inc., or C3fit IN-pulse*2 shirt
from GOLDWIN INC. Figure 3 shows a schematicof data acquisition. The user wears the garment as
underwear so that the hitoe electrode is in direct contact with the skin, and the TX02 is attached to thegarment via the connector. The weak bioelectric signal generated from heart beats is acquired from thehitoe electrode, input to the TX02 via the connector,
and recorded as electrocardiographic data by the bioelectric signal sensor. In addition to the bioelectric
signal sensor, the TX02 has a built-in temperature/humidity sensor and acceleration/angular velocity
sensor. Therefore, it is possible to measure data on anelectrocardiogram, temperature and humidity insideclothes, and acceleration and angular velocity of theupper body. Various features such as heart rate, heartrate interval, number of steps, and upper body tilt, are

3. Key technologies*1 hitoeTM: The functional fabric hitoe is a fiber material jointly developed by Toray Industries, Inc. and Nippon Telegraph andTelephone Corporation, and is a trademark of the two companies.
*2 C3fit IN-pulse: A clothing line that monitors physiological information using hitoe offered by GOLDWIN INC.

3.1 Wearable biological/environmental sensor
To estimate the risk of poor physical condition for
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Feature Articles

hitoeTM transmitter(TX02)

hitoeTM garment group

hitoeTM shirt

C3fit IN-pulse shirt

hitoeTM belt

*Wear one of the above

Fig. 2. Wearable biological/environmental sensor.

hitoe wear

Connector

Human body
TX02
(built-in bioelectric signal sensor,
temperature and humidity sensor,
acceleration and angular velocity sensor)

Hearthitoe electrode

Outerwear

Fig. 3. Schematic of data acquisition.

also analyzed from the measured data.
3.2 Core-temperature-fluctuation estimation
Body-core temperature*3, heart rate, and subjective
symptoms of dizziness and nausea are listed as indicators of poor physical condition in hot environments[5]. Conventionally, the body-core temperature ismeasured by inserting a thermometer into the esophagus or rectum, which requires specialized skills, andis difficult to measure it in real time during activities
such as work and exercise.
Therefore, we developed a technology for estimating core-temperature fluctuations in real time during
activity through joint research with Nagoya Instituteof Technology. With this technology, body-temperature fluctuation is estimated by inputting the information acquired from the wearable sensor into a newly
constructed calculation model. The overview of thismodel is shown in Fig. 4. The human body is divided
into a core layer and skin layer, and the heat exchange
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Vol. 19 No. 6 June 2021

between each layer and the outside air is formulated.
The formula uses an algorithm developed by Nagoya
Institute of Technology that takes into account factors
such as heat production from human activities, thermoregulatory function due to sweating etc., andclothing. Heart rate, temperature/humidity insideclothes, and personal information (age, height,
weight, gender, clothes, etc.) are input to this model
to calculate fluctuations in core temperature. With
this model, it has become possible to calculate coretemperature fluctuations in real time even with theprocessing power of smartphones.
To confirm the usefulness of this estimation technology, we conducted a joint clinical experiment*4
with NTT, Yokohama National University, Shigakkan
University, and Nagoya Institute of Technology. This
*3 Body-core temperature: Temperature inside the head or trunk.
*4 Shigakkan University Research Ethics Review Committee No.
124.

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Heat exchange between coreand outside air(breathing, etc.)

Outside air

Core

Heat exchange between
core and skin

Heat production(muscle activity, etc.)
Heat exchange between
Skinskin and outside air(sweating, etc.)
Human body model (2 layers)

Fig. 4. Calculation model of core-temperature fluctuation.

4. Verification in the workplacea verification experiment*5 targeting construction
workers in the Tokyo, Kanagawa, and Hokkaido
regions from August to September 2020 with thecooperation of NTT EAST. Figure 5 shows a schematic diagram of this experiment. We implemented
our core-temperature-fluctuation-estimation technology, algorithm for determining the risk of poor-physical condition, and work-load-estimation techniqueas smartphone applications and built a demo systemthat remotely monitors the physical condition of eachworker wearing wearable biological/environmental
sensors via the cloud (this demo system is not for
medical use). Alerts were sent to workers who were
determined to be at high risk.
To confirm the usefulness of the core-temperaturefluctuation-estimation technology and work-loadestimation technique at the work site, we evaluatedthe relationship between the subjective information(warm/cold feeling, rate of perceived exertion)
obtained from the workers and the estimation results.
We confirmed that there is a correlation between theestimated core-temperature fluctuation and warm/
cold feeling and between the estimated work load andthe rate of perceived exertion. These results indicate
the possibility of visualizing the subjectivity of workers without using questionnaires and the usefulnessof core-temperature fluctuation estimation and workload estimation based on wearable biological/environmental sensor data.
Risk cases were comprehensively detected during
the verification by the three indicators and the algorithm
for determining the risk of poor physical condition.

To verify the usefulness of our physical-conditionmanagement technology at work sites, we conducted*5 The Japanese Society for Wellbeing Science and Assistive Ethics
Review Committee No. 286.

experiment was conducted in the artificial weather
room of Shigakkan University to simultaneously estimate body-temperature fluctuations using this technology and with a rectal thermometer. We confirmedthat the estimation accuracy of our technology was
sufficient to determine the risk of poor physical condition.
3.3 Determine risk of poor physical condition
Indicator criteria and algorithms are required todetermine the high risk of poor physical condition foreach worker. On the basis of the knowledge obtained
from the joint experiment and from thermal physiology, we set criteria for three indicators: heart rate,estimated core-temperature fluctuation, and subjective information. We also constructed an algorithm
that determines the overall risk of poor physical condition from the state of the three indicators and issues
an alert in the case of high risk.
3.4 Work-load estimation
To quantify the workload caused by daily work, it
was conventionally necessary to obtain the rate ofperceived exertion from questionnaires as soon as
possible after the work. We developed a technique toestimate the rate of perceived exertion through heartrate analysis based on exercise physiology without
using a questionnaire and confirmed its effectivenesswith the cooperation of the Waseda University Rugby
Club [6].

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Feature Articles

This technology
Heart rateCore-temperature-fluctuation estimation

Temperatureinside clothes

Determine poor physical condition risk

Humidity
inside clothes

OutdoorworkingWork-load estimation

Subjective
information
Physical conditionof each worker

Sato

Koizumi

Kato

Saito

YamanoSato

SuzukiEto

Remote monitoring

Alert
Indoorworking

Order to take a break

Fig. 5. Schematic of verification experiment at the work site.

Alerts were sent to remotely monitoring managers
and workers. Since no serious cases of poor physicalcondition, such as heat stroke, occurred during thisverification experiment, we consider our technology
useful.
5. Summary
To make work sites more comfortable, we developed a physical-condition-management technologythat involves wearable sensors and verified it at awork site. We will continue to deepen our knowledge
by introducing our technology at more work sites andpromote further improvements.

NTT Technical Review

Vol. 19 No. 6 June 2021

References
[1]
[2]
[3]
[4]

[5]
[6]

Ministry of Health, Labor and Welfare, “Heat Stroke Prevention Measures in Workplace” (in Japanese), https://www.mhlw.go.jp/stf/
seisakunitsuite/bunya/0000116133.html
Ministry of the Environment, Heat Illness Prevention Information,
Heat illness prevention/countermeasures, https://www.wbgt.env.go.
jp/en/doc_prevention.php
T. J. Gabbett, “The Training-injury Paradox: Should Athletes Be
Training Smarter and Harder?”, Br. J. Sports Med., Vol. 50, No. 5, pp.
273–280, 2016.
Focus on the News: “Development of Low-power and Compact Wearable Sensor for Measuring Electrocardiographic, Acceleration, Temperature/Humidity Data for Use in Smart Healthcare,” NTT Technical
Journal, Vol. 32, No. 3, pp. 57–58, 2020 (in Japanese).
American Conference of Governmental Industrial Hygienists,“Threshold Limit Values and Biological Exposure Indices,” 2019.
Focus on the News: “Development of Technology for Supporting
Scientific Training in Sports and Demonstration of the Feasibility for
Rugby Players,” NTT Technical Journal, Vol. 32, No. 7, pp. 60–62,
2020 (in Japanese).

52

Feature Articles

Kazuhiko Takagahara

Senior Research Engineer, NTT Device Innovation Center.
He received a B.S. in mechanical engineeringand M.S. in information science and technology
from the University of Tokyo in 2006 and 2008.
He joined NTT Microsystem Integration Laboratories in 2008, where he has been engaged inresearch and development (R&D) of optical andwireless telecommunication devices and vitalsensing devices. He is a member of the Japan
Society of Applied Physics.

Yuki Hashimoto

Engineer, NTT Device Innovation Center.
He received a B.E., M.E., and Ph.D. in engineering from Tokyo Institute of Technology in2014, 2016, and 2018. He joined NTT Device
Innovation Center in 2018 and is currently
researching wearable healthcare devices for
management of heat stress. He is a member of theJapan Society of Mechanical Engineers and theInstitute of Electrical Engineers of Japan.

Nobuaki Matsuura

Senior Research Engineer, NTT Device Innovation Center.
He received a B.S. in applied physics and M.E.
in energy science from Tokyo Institute of Technology in 1990 and 1992. He joined NTT in 1992
and has been conducting research on opticalinterconnection technology. He is a member of
IEICE.

Kei Kuwabara

Senior Research Engineer, Project Planning
Section, NTT Device Innovation Center.
He received a B.E. and M.E. in electronics
engineering from Keio University, Kanagawa, in2002 and 2004. He joined NTT Microsystem
Integration Laboratories in 2004 and studied
micro electro-mechanical systems for wirelessand optical networks. Since 2013, he has been
engaged in R&D of wearable devices for healthcare, such as wearable blood-flow sensors andhitoe, and in 2015, was responsible for promoting open collaboration of hitoe in the R&D planning department. He is currently in charge ofpromoting R&D of NTT Device Innovation
Center. He is a member of IEEE and IEICE.

Kenichi Matsunaga

Research Engineer, NTT Device Innovation
Center.
He received an M.E. in electronics from Tokyo
Institute of Technology in 2010 and joined NTT
Microsystem Integration Laboratories the same
year, where he studied low-power complementary metal oxide semiconductor (CMOS) circuits
design for wireless sensor nodes. Since 2015, hehas been with NTT Device Innovation Center,
where he is currently developing Internet ofThings devices. His research interests include
CMOS circuits and sensor networks. He is amember of the Institute of Electronics, Information and Communication Engineers (IEICE) andthe Institute of Electrical and Electronics Engineers (IEEE).

Yuichi Higuchi

Manager, Digital Twin Business Department,
NTT TechnoCross Corporation.
He received a B.E. and M.E. from Kyoto University in 2006 and 2008. He joined NTT Microsystem Integration Laboratories in 2008, where
he was engaged in R&D of optical telecommunication devices and vital sensing devices. In 2020,
he moved to NTT TechnoCross, where he iscurrently in charge of the healthcare service
development. He is a member of IEICE and theJapan Society for Precision Engineering.

NTT Technical Review

Vol. 19 No. 6 June 2021

Hiroyoshi Togo

Senior Research Engineer, Supervisor, NTT
Device Innovation Center.
He received an M.Sc. and Ph.D. in applied
physics and electronic engineering from the
University of Tsukuba, Ibaraki, in 1996 and2010. He joined NTT Musashino Opto-electronics Laboratories in 1996. Until 2001, he wasinvolved in the development of the thermo-capillary waveguide-based optical switch and from2001 to 2002 endeavored to commercialize it for
NTT Electronics. From 2003 to 2015, he developed ultrawideband impulse radio systems using
photonic techniques and millimeter-wave tomography with electro-optic probing at NTT Device
Technology Laboratories. Since 2016, he has
been leading a wearable-device development
project to contribute to smart healthcare at NTT
Device Innovation Center. He is a senior memberof the IEEE Photonics, Antenna and Propagation,and Microwave Theory and Techniques Society,and IEICE of Japan. He was a finance director of
the Council of Technical Committee Representatives and a director of the Technical Committee
on Photonics-applied Electromagnetic Measurement in the IEICE Communications Society. He
is also an expert member of the Technical Committee on Microwave Photonics in the IEICEElectronics Society and an expert member of theJapan Electronics and Information Technology
Industries Association wearable electronics standardization. He received the 2006 Asia PacificMicrowave Photonics Conference AP-MWP
Award, the 2010 European Conference on
Antenna and Propagation Award, and The Japan
Wood Research Society Best Paper Award 2013.

53

Feature Articles

Takashi Kawahara

Research Professor, NTT.
He graduated Medical School, the Universityof Tokyo in 1976. After his medical internship,
he specialized in cardiology and worked at the
Hospital, the University of Tokyo. He became
lecturer at the Department of Physical Educationand Sport Sciences, College of Arts and Sciences, the University of Tokyo in 1985, associate
professor in 1989. He became director of Sport
Medicine, Japan Institute of Sport Sciences in
2001, general director of Japan Institute of Sport
Sciences in 2014, and retired in 2017. He joined
NTT as research professor in 2019. His main
research areas were prevention of disorders
caused by sport (such as heat stroke, overtraining
syndrome, anemia) and hypoxic training. He
participated in the Olympic Games six times as
the Japanese delegation doctor. He is currently
vice president of the Japan Association for University Athletics and Sport, chairman of Sport
Medicine and Science Commission, Japan Sport
Association.

Akimasa Hirata

Professor and Research Director, Nagoya Institute of Technology.
He received a B.E., M.E., and Ph.D. in communications engineering from Osaka University
in 1996, 1998, and 2000. From 1999 to 2001, he
was a research fellow of the Japan Society for the
Promotion of Science (JSPS) and a visiting
research scientist at the University of Victoria,
Canada, in 2000. In 2001, he joined the Department of Communications Engineering, Osaka
University, as an assistant professor. In 2004, hejoined the Department of Computer Science andEngineering, Nagoya Institute of Technology as
an associate professor where he is currently a full
professor. His research interests include electromagnetic safety, risk management system forheat-related illness, methods in neuroscience,
antennas, and related computational techniques.
He is an editorial board member of Physics in
Medicine and Biology, a member of the maincommission and a chair of project group of International Commission on Non-Ionizing Radiation
Protection, a member of administrative committee and a subcommittee (EMF Dosimetry Modeling) chair of IEEE International Committee on
Electromagnetic Safety, and an expert of theWorld Health Organization. He received several
awards including Young Scientists’ Prize (2006)
and Prizes for Science and Technology (Research
Category 2011, Public Understanding Promotion
Category 2014, 2020) by the Commendation for
Science and Technology by the Minister of Education, Culture, Sports, Science, and Technology,
Japan, and IEEE EMC-S Technical Achievement
Award (2015), and the Japan Academy Medaland JSPS Prize (2018). He is a fellow of IEEE,
Institute of Physics, and IEICE.

NTT Technical Review

Vol. 19 No. 6 June 2021

Hideto Tanaka

Professor, Graduate School of Education,
Yokohama National University.
He received a Bachelors of Health and Sports
Science and an M.A. in health education fromthe University of Tsukuba, Ibaraki, in 1981 and1983 and a Ph.D. in medical science from Osaka
University in 1988. He has been an assistant at
the School of Medicine, Osaka University since
1983, conducting research on thermal physiology, especially thermoregulation during exercise.
He then became a lecturer at the Faculty of Education, Yokohama National University in 1990,
associate professor in 1991, and professor in
2004. From 1994 to 1995, he was appointed as avisiting researcher at the Faculty of Psychology,
University of Delaware, USA. His research areas
are exercise physiology and environmental
physiology, with a focus on thermal physiology.
His current main research themes are thermoregulation during exercise, the living environment and thermoregulatory function, and prevention of heat stroke. In 2002, he received the 5th
Chichibunomiya Memorial Sports Medicine andScience Encouragement Award for “Study ofHeat Stroke Prevention (Principal Investigator:
Dr. Kawahara).” His main academic societies are
the Japanese Society of Physical Fitness andMedicine, the Japan Society of Exercise Physiology, the Japanese Society of Biometeorology,
and the Physiological Society of Japan.

Taiki Miyazawa

Associate Professor, Department of Health andSports Science, Faculty of Wellness, Shigakkan
University.
He received a B.E. in mechanical engineeringfrom Osaka City University in 2004, M.E. inphysics system of machine from the Graduate
School of Engineering, Osaka City University, in
2006, and Ph.D. in medical science from the
Graduate School of Medicine, Osaka City University, in 2010. He was a postdoctoral fellow
with the University of Toyo, Saitama, from 2010
to 2012, the National Institute of Advanced
Industrial Science and Technology, Ibaraki, from2012 to 2013, and Kyorin University, Tokyo,
from 2013 to 2015. He is currently an associate
professor with Shigakkan University, Aichi. His
current research interests include body-temperature regulation and cerebral blood-flow regulation during exercise.

54

Feature Articles: Healthcare Devices and Infrastructuremaintenance Technology that Support People and Society

Non-invasive Biological-information
Sensing Using Photoacoustic
Measurement Technology
Yujiro Tanaka, Takuro Tajima, and Michiko Seyama
Abstract

Biological-information sensing technology for simplifying the measurement of blood components
without drawing blood has been attracting attention. NTT has been researching and developing biological-information sensing using photoacoustic measurement technology that combines the ability of light
to selectively measure specific biological components and the ability of sound (ultrasound) to propagate
through the human body. In this article, we introduce non-invasive biological-information sensing technology using photoacoustic measurement technology with the aim of collecting various types of information from within the body.
Keywords photoacoustic, non-invasive, sensor

1. Advances in biological-information sensing
through non-invasive measurement technologies
Recent progress in information and communications technology (ICT) and growing awareness ofhealth management has made personalized healthcare services that use biological information obtained
from wearable devices increasingly popular. Information that is monitored during an individual’s daily
life shows promise for application to systems that
promote behavior modification or use healthcareoriented big data (Fig. 1). However, biological information obtained from current wearable devices consists mostly of data such as amount of activity, heartrate, respiration, body temperature, and blood pressure obtained from physical sensors. Consequently,
when one is not feeling well, for example, such biological information cannot be used to describe thecause or suggest a countermeasure even if one’s state
can be objectively presented. It would therefore be
desirable if wearable devices could also provide biochemical information such as data on blood components. The current method of obtaining such information is to draw blood at a hospital or medical clinic
and analyze that sample using various types of test
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Vol. 19 No. 6 June 2021

equipment on an item-by-item basis. Alternatively, toobtain blood-component information from wearable
devices, it would be necessary to establish technology that could easily obtain data in a continuous andnon-invasive manner without harming the body. In
this regard, biological imaging technology using thephotoacoustic effect has recently been investigated asa non-invasive biological sensing technique. This is a
powerful technique for learning about the body’s
interior by combining two key features: the ability oflight to measure biological components selectively
and the ability of sound to propagate well through the
body. In other words, the strongpoint of photoacoustic measurement technology is the ability to makemeasurements deep into the body that light cannot
easily penetrate. There is a great need to look inside
the human body at healthcare facilities, and this iscurrently done through the use of diagnostic imaging
equipment such as X-ray computed tomography,
magnetic resonance imaging, and positron emission
tomography. In contrast to such diagnostic imaging
equipment, photoacoustic equipment consisting of alight source and microphone has the advantage ofbeing simple and portable with little burden placed on
the user. We have been researching and developing
55

Feature Articles

Physical information
Cloud dataprocessing
Physical and biochemical
information• Heart rate
• Blood pressure
Home
Biochemical information

Wearable device• Blood sugar• Lipids

Applications• Sports• Healthcare• Medical treatment

Healthcare facility

Fig. 1. Advances in biological-information sensing through non-invasive measurement technologies.

the application of the photoacoustic effect to biochemical information measurements from the viewpoint of establishing technology that enables measurements to be conducted anytime and anywhere. In
this article, we first provide a basic description of theprinciple behind the photoacoustic effect then introduce the current state of photoacoustic research at
NTT.
2. Measurements using the photoacoustic effect
The photoacoustic effect was discovered in 1880 byAlexander Graham Bell, the inventor of the telephone, as a phenomenon in which the intermittent
irradiation of a substance with light generates sound.
In 1965, Mark Leonidovitch Veingerov proposed theapplication of the photoacoustic effect to the analysis
of gaseous components at concentrations on the ppm(parts per million) level (one-ten-thousandth of 1%),since then, techniques have been established forusing the photoacoustic effect to analyze chemical
structures on a molecular level.
We describe the photoacoustic effect in easy-tounderstand terms. As shown in Fig. 2(a), the absorption of light by matter is followed by the conversionof that optical energy to heat and the thermal expansion of that substance due to this thermal energy. Ifsuch optical irradiation should be applied in an intermittent manner, thermal expansion will occur repeatNTT Technical Review

Vol. 19 No. 6 June 2021

edly giving rise to elastic waves, that is, sound (ultrasonic waves). These are called photoacoustic waves.
Recent advances in ICT have also led to amazing
benefits from a variety of devices and technologies
such as light sources and optical switches that cangenerate optical pulses with high temporal controllability, acoustic technologies that can detect soundwith high sensitivity, and electronics technologies
that can perform diverse signal processing. Suchdevices and technologies have been applied in a wide
range of fields including material analysis, gas analysis, and imaging. In biological measurements using
the photoacoustic effect, the amount of light absorbedby the target substance within the body is converted
to ultrasonic waves that propagate well through thebody, and the concentration of that substance is estimated by detecting those waves as photoacoustic
waves. Substances have optical colors (wavelengths)that are easy to absorb due to individual characteristics. This feature can be used to learn about biologicalcomponents and their distribution in the human body.
For example, as shown in Fig. 2(b), blood cells, lipids, and glucose/proteins absorb light well in the 500nm (visible light), 1000-nm (near-infrared light), and1500-nm (near-infrared light) regions, respectively.
Making use of this property, information on biological components can be obtained by irradiating the
body with various colors and measuring how much ofthat light is absorbed. It is well known that more than56

Feature Articles

Ultrasonic waves

Light

TargetOptical absorption

Heating

Thermal expansion/contraction

Absorption intensity(a) Outline of photoacoustic effect

1st

Blood
cells
500

2nd

3rd

4th

Sugars, protein
Lipids
1000
1500
2000
Wavelength (nm)(b) Diagram of biological components and optical absorption spectrum

Fig. 2. Relationship between light and matter.

half of a living body is composed of water, which also
has the property of absorbing light. Consequently,
when using light to conduct measurements, it is generally necessary to select optical wavelengths that are
not greatly absorbed by water. This is because nowavelength absorption by water makes it easier for
light to enter the body without attenuation. This range
of optical wavelengths is called the “optical window.”
At the same time, there are limits to the depth atwhich light can penetrate the body for conducting
measurements, and it is extremely difficult to determine by what path and in what way light is absorbed
as it passes through our bodies intricately composedof diverse components. Despite this problem, photoacoustic measurements are conducted to detect theamount of absorbed light by converting it to ultrasonic waves that propagate well through the body,which means that the effects of reflection in the bodycan be suppressed. It is also possible to investigate theinterior of the body in a non-invasive manner by measuring not only the intensity of photoacoustic waves(sound pressure) from light absorption by the target
substance but also their propagation time and frequency characteristics.

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3. Non-invasive approaches for measuring
biological components using thephotoacoustic effect
There are two approaches for measuring biologicalcomponents in a non-invasive manner using the photoacoustic effect. One involves irradiating the bodywith a light pulse of extremely short duration (pulse
width: several nanoseconds), having the target substance absorb that light, and measuring both the time
taken for the generated photoacoustic wave to returnand the position of the component absorbing the lighton the basis of the sound pressure of that wave. With
this approach, a photoacoustic wave is obtained asshown in Fig. 3(a), and the depth of the target substance is determined from the time spent by the soundpropagating through the body and its speed. A demonstration of three-dimensional imaging of the letter“N” embedded in material simulating the humanbody is shown in Fig. 3(b). The second approach, asshown in Fig. 3(c), involves irradiating the body withlight that is periodically turned ON/OFF, letting thephotoacoustic wave generated from the target substance reflect any number of times to generate astanding wave, and measuring the concentration of
the target from the sound pressure of that wave.
The former approach can be used to obtain
57

Distance totarget

5 mm

Ear

Optical intensity

Optical intensity

Feature Articles

5 mm
5 mm

SensorTime(a) Optical irradiation andphotoacoustic waveTime(b) Photoacoustic
imaging

Sound field

MicrophoneLight

Photoacoustic
wave intensity

Photoacoustic
wave intensity

Sensor(c) Repeated optical irradiationand standing wave

Ear(d) Sensor interface

Fig. 3. Biological measurements using the photoacoustic effect.

information on a substance and its position. For
example, knowing that many fine blood vessels form
near cancer cells that require a considerable amountof nutrition to survive, much applied research has
been conducted on imaging that situation. Such
research, however, generally requires equipment thatis large and expensive. Another problem is that signals that include information on biological components are weak and easily affected by noise.
The latter approach, while not able to obtain positional information of the target substance, can obtaina relatively large signal-to-noise ratio with just a lowintensity, inexpensive light source and one microphone, which makes it advantageous for measuringcomponent concentrations or downsizing equipment.
However, component measurements cannot provide
clear contours such as those of blood vessels obtainedby imaging. Since irradiated light is absorbed in a
graduated manner in accordance with that component’s concentration, the propagation waveform of
the photoacoustic wave can collapse. To solve thisproblem, NTT proposed a sensor structure that confines the sound wave to reflect the photoacoustic
wave many times. To give an example, a person’s
earlobe can be sandwiched by a clip with an irradiating light source on one side and a microphone embedded on the other side. A method for generating astanding wave and obtaining a strong signal by
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reflecting a photoacoustic wave many times between
a light-irradiating surface and a sound-receiving surface is shown in Fig. 3(d). Although the frequency ofthe photoacoustic wave is determined by the frequency of the irradiating light, selection of that frequency is important. This is because low frequencies
are easily affected by human voices or everyday
sounds (up to several tens of kilohertz), while highfrequencies (up to several megahertz) suffer fromsignificant attenuation within the body. As a result,researchers at NTT conduct measurements using
photoacoustic waves in a frequency band (several
hundred kilohertz) between those frequencies.
4. Application example:
biological measurements
Finally, we introduce an example of applying thephotoacoustic effect to the measurement of biologicalcomponents. The sensor used in this example was one
that sandwiches the earlobe as in the clip introduced
above. We asked a healthy person to drink a beveragecontaining a large amount of glucose and measured
subsequent change in the concentration of glucose inthat person’s interstitial fluid [1, 2]. Glucose concentration in interstitial fluid differs from that in the
blood (so-called blood-sugar level) in that it indicatesthe concentration of glucose in interstitial fluid exuded
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Light

Drawing

0.21
DCW PAS (–)

Skin

Subcutaneous tissue

0.14

Glucose−0.07

Blood vessel(a) Behavior of glucose in tissue

150

SMBG

0.07
0.00

200
FGM (L)FGM (R)DCW PAS
Taking liquid glucose
0:00

0:30
1:00
Time (h)

1:30

100

Blood glucose level (mg/dL)

Correlation: 0.9450(b) Comparison of photoacoustic and invasive technologies

FGM: flash glucose monitoring tool
SMBG: self-monitoring blood glucose toolFig. 4. Example application for measuring blood-sugar level.

from blood vessels and supplied to cells, as shown in
Fig. 4(a). It is known that the glucose concentration
in interstitial fluid changes in nearly the same manneras the blood-sugar level. A comparison of measured
values by using photoacoustic measurement technology with those by using various types of invasive
blood-sugar-level sensors is shown in Fig. 4(b). The
blue plot represents values from differential continuous-wave photoacoustic spectroscopy (“DCW PAS”
in the figure), and the other plots represent values
measured by drawing blood and carrying out an intravenous procedure, i.e., invasively. With the invasive
technologies, the blood-sugar level increased byabout 60 mg/dl 15–30 min after drinking the glucose
beverage and began to decrease gradually one hourlater. These results indicate that the photoacoustic
method could enable measurements that conform
well to this 60-mg/dl change in the blood-sugar level.
By matching a target substance with an appropriate
optical wavelength, this technology holds promise forapplication to a variety of biological components ofgreat interest such as cholesterol, neutral fats, andother types of lipids.
5. Future work
This article introduced the potential of biologicalinformation sensing using the photoacoustic effect

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and its application to technology for measuring biological components. Up to now, biochemical-information sensing has not been a target of continuous
monitoring in everyday life, but if it can be madepractical, we can expect it to be applied in a variety ofways. It could be used, for example, as a technology
supporting online diagnostics, which have become
increasingly popular during the COVID-19 pandemic. To achieve such continuous monitoring in everyday life, device size and usability will be importantfactors in addition to non-invasive features. Goingforward, we will take up the research and development of technology that uses photoacoustic measurements to enable high accuracy analysis regardless ofgas, liquid, or solid targets and that enables the continuous monitoring of biochemical information suchas biological and respiratory components in everyday
life.
References
[1]

[2]

Y. Tanaka, T. Tajima, M. Seyama, and K. Waki, “Differential Continuous Wave Photoacoustic Spectroscopy for Non-invasive Glucose
Monitoring,” IEEE Sensors Journal, Vol. 20, No. 8, pp. 4453–4458,
2020.
Y. Tanaka, T. Tajima, and M. Seyama, “Acoustic Modal Analysis of
Resonant Photoacoustic Spectroscopy with Dual-wavelength Differential Detection for Noninvasive Glucose Monitoring,” IEEE Sens.
Lett., Vol. 1, No. 3, 3500704, 2017.

59

Feature Articles

Yujiro Tanaka

Researcher, NTT Device Technology Laboratories and NTT Bio-Medical Informatics
Research Center.
He received a B.S. and M.S. in engineeringfrom Tohoku University, Miyagi, in 2011 and2013. He joined NTT Microsystem Integration
Laboratories in 2013. He has been with NTT
Device Technology Laboratories and NTT BioMedical Informatics Research Center, where heis currently engaged in photoacoustic technology
for biosensing. He is a member of the Japan
Society of Applied Physics (JSAP).

Takuro Tajima

Senior Research Engineer, NTT Device Technology Laboratories.
He received a B.S. and M.E. from the University of Tokyo in 2000 and 2002, and a Ph.D. from
Tokyo Institute of Technology in 2017. In 2002,
he joined NTT Telecommunication Energy Laboratories, where he has been engaged in the
research and development of laser photoacoustic
spectroscopy for biomedical sensing, sub-terahertz antenna-in-packages for ultrafast wirelesscommunication, and broadband dielectric spectroscopic system using photonic integration
technologies. His current research involves
multi-modal biomedical analysis using microwave, terahertz-wave, optics, and ultrasonics. He
is a member of the Institute of Electronics, Information and Communication Engineers.

NTT Technical Review

Vol. 19 No. 6 June 2021

Michiko Seyama

Senior Research Engineer, Supervisor, NTT
Device Technology Laboratories and NTT BioMedical Informatics Research Center.
She received a B.S., M.E., and Ph.D. fromWaseda University, Tokyo, in 1995, 1997, and2004. In 1997, she joined NTT and worked on an
odor sensing system based on a plasma-polymerized organic film for environmental contamination and biogas and a one-dimensional-surface
plasmon resonance biosensor combined with amicrofluidic device for on-site immunologicalsensing. Her current interest is the developmentof biosensing platforms for blood components
and blood coagulation, including both invasive
and non-invasive technologies. She is a memberof JSAP, the Electrochemical Society of Japan,
and the American Chemical Society.

60Feature Articles: Healthcare Devices and Infrastructuremaintenance Technology that Support People and Society

Derusting Technology Using Highpower Laser Device
Sohan Kawamura, Takashi Sakamoto, Masahiro Ueno,
and Soichi Oka
Abstract

Rust removal in narrow spaces that are inaccessible to human hands or electric tools is a challenge inderusting operations essential in prolonging the life of steel towers and other communication infrastructure facilities supporting communication services. We are developing technologies for efficient derusting
using high-power laser devices developed by NTT. In this article, we introduce a compact and lightweight derusting technology incorporating a high-power laser device called a diffractive optical element.
Keywords: high-power laser, derusting, diffractive optical elements

1. Issues surrounding derusting technologies forcommunication infrastructure facilities
Steel towers and other communication infrastructure facilities are important in safely and securely
providing communication services essential in modern life. Exposure to sunlight and weather elements
deteriorates the strength of these facilities, which are
not easy to replace. Therefore, they need to undergo
regular inspection and repair to enable continued use
over a long period. There are approximately 20,000of these steel towers, including small ones, owned by
the NTT Group across Japan. Most were built during
the high-economic-growth period in the 1960s and1970s and are now in an advanced state of deterioration; thus, costs and human resources needed for theirinspection and repair have increased yearly. Reducing costs and labor is, therefore, critical in making
future inspection and repair sustainable. NTT is currently developing various painting materials to control rusting, as well as technologies to test paintdeterioration, predict corrosion of steel products, andremove rust.
Prolonging the life of steel towers requires methodsof controlling rusting as well as removing rust. Electric tools and metallic brushes are usually used inderusting, but it is difficult to remove rust from narrow spaces or around bolts. Sand blasting, a method
NTT Technical Review

Vol. 19 No. 6 June 2021

with which sand particles are propelled at high speed
onto surfaces, is one such method but is difficult touse because removing the sand takes time. Derusting
tools using high-power lasers have, therefore, drawn
attention. Commercially available rust removers
using high-power lasers, however, have large andheavy handheld laser-emission heads, making it difficult to use by workers who have to climb steel towers to carry out derusting. We, therefore, developed
an affordable, light-weight diffractive optical element(DOE) for a compact, lightweight, and field-friendly
rust remover we are developing.
2. Technology of DOEs used inhigh-power lasers
A DOE is a device that applies holographic techniques for phase modulation of incident light in substrate microstructures. It enables the transforming of
the incident laser-beam into any desired shape, as
shown in Fig. 1. This characteristic is exploited inmetal and resin processing.
Figure 2 is a schematic diagram of the DOE wedeveloped for high-power laser processing. To prevent the increase in temperature due to the absorptionof laser light and the damage it causes, we used asilicon carbide substrate, which has high thermal
conductivity, and designed a reflection-type device,61

Feature Articles

Fig. 1. Example of laser-beam shaping using a DOE.

Reflection-type DOE

Galvanometer mirror
2m

Coolant
Incident laser light

Increase in temperature
Reflected laser lightDeflection
angle 2

ang 1
Deflection angle
Galvanometer mirror 1
Galvanom

Fig. 2. S chematic diagram of a 10-kW reflection-type DOE
for processing.

Incident light

Fig. 3. E xample of a beam-scanning method using
galvanometer mirrors.

which is easier to cool, making it possible to carry out
laser processing at 10 kW [1]. This DOE is not only
light at only a few grams but also simple in structure.
We used this DOE to develop the compact and lightweight rust remover described below.

DOE

Manualscanning

3. Rust remover that NTT is developing
As shown in Fig. 3, in commercially available rustremovers using lasers, laser-beam scanning is carriedout either one-dimensionally or two-dimensionallyusing a mirror and motor to enable workers to remove
rust over a fixed surface area without moving theirhands. The handheld laser-emission head, however, islarge and weighs several kilograms, making it burdensome for the worker and difficult to use on steel
towers. To address these issues, we developed themethod shown in Fig. 4 for shaping light into a thinstraight line using our DOE and carrying out manual
scanning without the need for a motor. Derusting,therefore, can be carried out with the same efficiency
as with the conventional method.

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Vol. 19 No. 6 June 2021

Laser source

Fig. 4. Conceptual drawing of derusting laser using a DOE.

4. Towards affordable DOEs
As mentioned above, we used silicon carbide for
DOEs in high-power lasers, but it is an expensive
62

Feature Articles

100

Reflectance (%)

90
Experimental value
80

Theoretical value

70

60
10

1000

100
Film thickness (nm)Fig. 5. Correlation between thickness and reflectance of gold film.

material. Due to the high likelihood that a DOE
would become dirty or damaged during derusting, itis preferable to use more inexpensive DOEs. We,
therefore, devised methods of replacing silicon carbide with less expensive materials to promote the useof rust removers that use DOEs.
Silicon is a material for which micro-processing
techniques are well established in the semiconductor
industry. Aside from its relatively low cost, it is alsoeasily available, making it an ideal substitute as aninexpensive material. However, due to absorption oflight at a wavelength of 1.07 μm used in rust removal,
there is risk of damage due to increase in temperature.
Although reflectance can be increased by applying a
metal film on the surface to minimize light absorption, a thicker coating would result in the rounding of
the corners of the DOE surface’s microstructure,
leading to errors in laser-beam shapes. In otherwords, it is critical to find the right metal with theproper thickness to achieve sufficient reflectance
while reducing laser-beam-shape errors.
We, therefore, considered gold, which has highreflectance and high thermal conductivity, as a coating material and calculated and measured the relationship between its film thickness and reflectance.
As shown in Fig. 5, reflectance reaches its peak at
50-nm thickness. Therefore, we determined the optimum thickness that results in sufficiently low laserbeam-shape error at around 50 nm. We were able toachieve laser processing at 10 kW, which far exceeds
the power needed for rust removal. This demonstrates
that costs can be feasibly reduced by using silicon as
the diffraction grating material [2].
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Vol. 19 No. 6 June 2021

5. Development of a compact and easy-to-use
rust remover
Figure 6 shows a prototype of the laser-emission
head of the rust remover we are developing. By using
our DOE, we demonstrated the possibility of fabricating a laser-emission head that weighs only 500 g,
which is not possible with commercially available
devices. The laser head is as small as a conventional
electric tool, and being light and easy to use, it has
potential for widespread use in derusting. Figure 7
shows the results of an experiment to remove rustfrom narrow spaces that are difficult to reach withelectric tools. Since laser light is used, there are no
vibrations and restrictions in applicability inherent
with electric tools, reducing the burden on workers.
These results indicate that using our DOE eliminates the need for motors, which are a limiting factor
in the size and weight of commercially available
devices, demonstrating the feasibility of using compact and lightweight rust removers for steel-tower
cleaning.
6. Future prospects
As mentioned in the introduction, prolonging thelife of steel towers and other communication infrastructure facilities requires technologies for rustremoval and for maintaining surface conditions thatprevent paint from peeling off.
The conditions needed in the irradiation of laser
light affect surface conditions and the strength ofpaint adhesion. Therefore, research on the surface
63

Feature Articles

Fig. 6. C onventional electric tool (far right) and prototype of the laser-emission head of the rust remover we are developing(left).

Fig. 7. Example of derusting experiment using our prototype laser-emission head of the rust remover we are developing.

conditions after rust removal using laser and on-paintadhesion are crucial in prolonging the life of communication infrastructures. Going forward, we willcontinue to conduct research on these areas to create
new value by developing rust removers that contribute to improving paint adhesion and are easy to use in
the field.

the size and weight of commercially available devices
and demonstrated the feasibility of an affordable,compact, lightweight, and user-friendly rust remover.
Going forward, we will conduct research on surface
conditions to improve paint adhesion and create newvalue in infrastructure maintenance.
References

7. Conclusion[1]

In this article, we introduced the derusting technology we are developing to contribute to a sustainable
society. We were able to reduce the cost of a device
by replacing the silicon carbide of our DOE with silicon. We also resolved the problems associated withNTT Technical Review

Vol. 19 No. 6 June 2021

[2]

Y. Akage, T. Imai, S. Kawamura, S. Oka, Y. Fujitani, and T. Okuda,“Development of Beam Shaping Device for 10-kW-class Laser Processing,” 94th Japan Laser Processing Society Conference, Online,
Nov. 2020 (in Japanese).
S. Kawamura, S. Toyota, and S. Oka, “Reflection-type Diffractive
Optical Element Employing SiC and Si for Application to High Power
Laser Material Processing,” Proc. of SPIE, Vol. 11273, San Francisco,
CA, USA, Mar. 2020.

64

Feature Articles

Sohan Kawamura

Engineer, Smart Maintenance and Management Technology Development Project, Health& Environmental-Sensing Device Project, NTT
Device Innovation Center.
He received a B.E., M.E., and Ph.D. in engineering science from Hokkaido University in
2004, 2006, and 2009. At Hokkaido University,
he studied on-single crystal growth and scintillation properties of Ce-doped gadolinium pyrosilicate. He joined the Advanced Opto-electronics
Device Research Group in NTT Photonics Laboratories in 2009, where he studied on-crystal
growth of electro-optic materials, nonlinear optical devices, and diffractive optical elements forhigh-power laser machining.

Takashi Sakamoto

Senior Research Engineer, Smart Maintenanceand Management Technology Development
Project, Health & Environmental-Sensing
Device Project, NTT Device Innovation Center.
He received a B.A. and M.S. (multidisciplinarysciences) from the University of Tokyo in 1994
and 1996 and a Ph.D. in engineering fromTohoku University, Miyagi, in 2008. He joined
NTT in 1996, where he researched optical packet
switching, wavelength conversion, scanning
nonlinear dielectric microscopy, and the development of high-speed optical scanning devices withpotassium tantalate niobate crystals. He is now
investigating rust removal from metal surfaces
with laser irradiation. He is an associate memberof the Institute of Electrical and Electronics
Engineers.

NTT Technical Review

Vol. 19 No. 6 June 2021

Masahiro Ueno

Senior Research Engineer, Health & Environmental-Sensing Device Project, NTT Device
Innovation Center.
He received a B.E. and M.E. in electrical engineering from Chiba University in 1987 and 1989
and a Ph.D. from Tokyo University of Science in2010. He joined NTT Applied Electronics Laboratories in 1989 and studied mass storage systems using optical disks, disaster tolerant storage
systems, holographic storage systems, ion flow
printers, three-dimensional imaging systems,
cloud computing systems, and optical coherence
tomography systems from 1989 to 2018. He wasalso active in developing small computer systeminterface specifications. He is currently studying
LiDAR (light detection and ranging) systems anddiffractive optical elements at NTT Device Innovation Center. He is a member of the Institute ofElectronics, Information and Communication
Engineers.

Soichi Oka

Senior Research Engineer, Supervisor, NTT
Device Innovation Center.
He received a B.E. in environmental information and an M.E. and Ph.D. in media and governance from Keio University, Kanagawa, in 1996,
1998, and 2001. From 2002 to 2003, he wasengaged in research and development of evanescent microwave imaging at Wright Patterson Air
Force Research Laboratories and the Universityof Cincinnati in Ohio, USA. Since joining NTT
in 2004, he has been researching and developing
civil engineering technologies.

65Feature Articles: Healthcare Devices and Infrastructuremaintenance Technology that Support People and Society

Technology for Predicting Hydrogen
Embrittlement in Reinforcing Bars ofConcrete Poles
Takuya Kamisho, Ryuta Ishii, and Masayuki Tsuda
Abstract

A concrete pole, which is an important part of the communication infrastructure supporting communication services, requires significant maintenance costs to ensure its safety. If hydrogen embrittlement,a phenomenon by which reinforcing bars in concrete poles deteriorate, could be accurately predicted, itwould be possible to maintain and manage concrete poles more safely and economically. A technology
for predicting hydrogen embrittlement in reinforcing bars inside concrete poles that involves using an
accelerated-hydrogen-embrittlement test and statistical data analysis is introduced.
Keywords: hydrogen embrittlement, deterioration prediction, concrete pole

1. Maintenance of concrete poles
A concrete pole is an important part of the communication infrastructure supporting communication
services in Japan. If a concrete pole breaks, it may
lead to property damage or personal injury; accordingly, all concrete poles are systematically maintained and managed so that they do not deteriorate.
Maintaining concrete poles in this manner incurs ahuge cost, so an economical maintenance technologythat also ensures safety is required.
Pre-stressed concrete is used to suppress cracks inconcrete poles. Such concrete is formed by applying
tensile stress to the reinforcing bars (rebars) inadvance. This shrinks the rebars and applies compressive stress to the concrete, which suppresses crack
generation. Rebars used in pre-stressed concrete do
not exhibit any problems under normal usage conditions. However, a deterioration phenomenon calledhydrogen embrittlement can progress when various
adverse conditions are combined [1–3]. Since thestrength of concrete poles is secured by the internal
rebars, deterioration of the rebars could lead to breakage of the concrete poles. If hydrogen embrittlementof rebars in concrete poles could be accurately predicted, inspections and repairs based on the predicted
NTT Technical Review

Vol. 19 No. 6 June 2021

risk of deterioration would be possible; as a result,concrete poles could be maintained and managed
more safely and economically. Given this possibility,
we are pursuing research and development to establish a technology for predicting hydrogen embrittlement of rebars in concrete poles.
2. Hydrogen-embrittlementprediction technology
Hydrogen embrittlement is a phenomenon in which
atomic hydrogen (i.e., individual hydrogen atoms)
penetrates a metallic material under tensile stress,
reducing its strength and causing cracks and fracturesin the material. It is sometimes called delayed fracture because the metallic material breaks after a certain period after hydrogen invades it under a constantload. Since the rebars used in pre-stressed concrete
are constantly subjected to tensile stress, hydrogen
embrittlement due to intrusion of hydrogen is a constant risk. The interior of concrete is normally an
alkaline environment, so corrosion of rebars rarely
occurs; however, when cracks occur in concrete, theconcrete around the cracks are neutralized by carbon
dioxide in the air, and rainwater that has penetrated
the concrete via the cracks can corrode the rebars.
66

Feature Articles

Tensile-stress application
Current
controller

Thermometer

Referenceelectrode
Counter
electrode

Water circulation

Test solution
Test cell
Reinforcing bar(rebar)

Water circulation

Tensile-stress application

Fig. 1. External appearance and schematic of accelerated-hydrogen-embrittlement test.

When rebars corrode in this manner, hydrogen is generated, penetrating the rebars and causing hydrogen
embrittlement. Therefore, the environmental factorsthat cause hydrogen embrittlement of rebars in prestressed-concrete are being investigated.
The mechanism of hydrogen embrittlement remains
unclear. It is therefore considered difficult to predicthydrogen embrittlement by using a deductive method
based on the hydrogen-embrittlement mechanism. By
conducting tests to reproduce hydrogen embrittlement in a neutralized concrete environment andinvestigating the behavior of hydrogen embrittlement, we are attempting to predict hydrogen embrittlement by using an inductive method based on data
analysis. In the future, it will be possible to makepredictions with deductive methods by deepening ourunderstanding of the hydrogen-embrittlement mechanism; in other words, we are aiming for a virtuous
cycle in which the prediction accuracy of an inductive
method is further improved using the results from adeductive method.
When reproducing hydrogen embrittlement, it isassumed it takes a long time to occur in an actual
environment. To shorten that time, we are using an
accelerated test that increases hydrogen concentration in a rebar to quickly cause fracture by hydrogen
embrittlement. The external appearance and a schematic diagram of the accelerated-hydrogen-embrittlement test are shown in Fig. 1. In the test, hydrogen
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embrittlement in a neutralized concrete environment
is simulated as follows: (i) a rebar is immersed in a
weak-alkaline test solution inside a test cell (to reproduce a neutralized concrete environment); (ii) a tensile tester is used to apply a pre-determined tensilestress to the rebar (to reproduce the pre-stress applied
to the rebar); and (iii) an electric current is passed
through the rebar to generate hydrogen by electrolysis of water (to reproduce hydrogen generation due tocorrosion). Since the amount of hydrogen generated
can be controlled by adjusting the magnitude of theelectric current, the hydrogen concentration in therebar is increased by generating a sufficiently larger
amount of hydrogen than that in an actual environment, accelerating hydrogen embrittlement. By conducting the accelerated-hydrogen-embrittlement test
to determine the relationship between hydrogen concentration and fracture time/probability and extrapolating that relationship to the hydrogen concentrationin an actual environment, we are attempting to predicthydrogen embrittlement in an actual environment.
3. Estimating time to fracture and fracture
probability by conducting theaccelerated-hydrogen-embrittlement test
Hydrogen embrittlement of rebars is known to vary
greatly in time to fracture even under uniform environmental conditions. For general regression analysis,
67

Feature Articles

Predicted averagetime to fracture

Prediction of probability distribution
Fracture probability
density

Prediction of average value only

Distribution of predicted
fracture probability

Time
Actualtime to fracture

Time
Actualtime to fracture

Prediction of average time to fracture alone
cannot be used to detect short-term fracturesthat occur randomly.

By predicting the fracture-probability distribution,
it is possible to take measures in accordancewith the risk.

Fig. 2. Results of predicting time to fracture (including probability distribution).

only the average time to fracture can be predicted,
and predicting only this average cannot be done todetect short-term fracture that occurs randomly. If theprobability distribution of time to fracture could be
predicted, it would be possible to detect fractureswith shorter times to fracture than the average inaccordance with the risk fracture (Fig. 2). Accordingly, we are attempting to predict time to fracture(including its probability distribution) by using statistical modeling for a large amount of time-to-fracture
data acquired from the accelerated-hydrogen-embrittlement test.
Two conclusions can be drawn from the results of
the accelerated-hydrogen-embrittlement test: (i) the
relationship between hydrogen concentration on thesurface of a rebar and the average time to fracture canbe approximated by an exponential function and (ii)the variation in time to fracture at uniform hydrogenconcentration follows the Weibull distribution. By
creating a statistical model from these results andusing the maximum-likelihood method for the timeto-fracture data, the relationship between hydrogenconcentration and the probability distribution of time
to fracture can be estimated. The maximum-likelihood method is used to estimate the parameters ofprobability distributions other than normal distributions such as a Weibull distribution. Regarding the
maximum-likelihood method, the parameters are
estimated from the acquired data by searching for theparameters that maximize the infinite product (likelihood) of the probability density of the acquired data.
Examples of time-to-fracture data obtained from theaccelerated-hydrogen-embrittlement test, estimatedNTT Technical Review

Vol. 19 No. 6 June 2021

average values only from regression analysis, andestimation results (including the probability distribution) obtained using statistical modeling are shown in
Fig. 3. It is clear from these results that using statistical modeling makes it possible to estimate not only
the average time to fracture but also its probability
distribution.
When exposed to a certain environmental condition, some rebars fracture due to hydrogen embrittlement after a certain time and others do not no matter
how much time passes, and the occurrence or nonoccurrence of future fracture can be expressed as afracture probability. When the tensile stress applied toa rebar or the hydrogen concentration on the surfaceof the rebar increases, the fracture probability
increases. When the tensile stress or hydrogen concentration becomes sufficiently low, however, thefracture probability becomes almost zero. When considering the maintenance of concrete poles, we mustalso consider the importance of the fracture probability of rebars due to hydrogen embrittlement.
It is understood from the results of the acceleratedhydrogen-embrittlement test that the relationshipbetween hydrogen concentration on the surface of arebar and fracture probability can be approximatedwith a sigmoid curve. It thus follows that the relationship between hydrogen concentration and fracture
probability can be estimated using logistic regression
analysis, which is a means of estimating the probability of an event occurring when a binary variable(namely, whether a certain event occurs) is taken as
the objective variable. A logistic function is used inlogistic regression analysis as a regression model,
68

Feature Articles

Unpredictable variation in time to fractureTime to fracture

Experimental
result

sio

res

g
Re

Time to fracture

sis

aly

n
na

Averagevalue

Hydrogen concentration on surfaceof the rebar
Prediction of variation in time to fracture

tist

ica

Hydrogen concentration on
surface of the rebar

lm

od

elin

g

Average value
50% prediction
interval
90% prediction
interval

Time to fracture

Sta

Hydrogen concentration on surfaceof the rebar

Fig. 3. Estimating the probability distribution of time to fracture by using statistical modeling.

1

Logistic regression
analysis

0.5
Experimental result

0

Hydrogen concentration on the surfaceof the rebar

Fracture probability

Fracture probability

1

0.5
Regression curve
95% confidence
interval
0

Hydrogen concentration on surfaceof the rebar

Fig. 4. E xperimental results of fracture occurrence or non-occurrence from accelerated-hydrogen-embrittlement test andestimated fracture probability.

and the parameters of the logistic function are estimated using the maximum-likelihood method.
We conducted the accelerated-hydrogen-embrittlement test under variable tensile stress, hydrogen concentration on the surface of a rebar, and temperatureand estimated the fracture probability from theacquired data on occurrence or non-occurrence of
fracture. The relationship between hydrogen concenNTT Technical Review

Vol. 19 No. 6 June 2021

tration on the surface of a rebar and fracture probability when tensile stress and temperature were fixed isshown in Fig. 4. In this analysis, the case in which therebar fractures during the accelerated-hydrogenembrittlement test is defined as “1” and that in which
it does not fracture is defined as “0,” and the regression curve of fracture probability and the 95%-confidence intervals are estimated from logistic regression
69

Feature Articles

analysis. Therefore, the relationship between hydrogen concentration on a rebar surface and future fracture probability can be estimated from the fracture
occurrence or non-occurrence data obtained from theaccelerated-hydrogen-embrittlement test.
4. Future developments
By extrapolating the relationship between hydrogen concentration, time to fracture, and fracture probability obtained from the accelerated-hydrogenembrittlement test to include the hydrogen concentration in an actual environment, it will be possible topredict the time to fracture and fracture probability ofrebars in concrete poles. The estimated surfacehydrogen concentration of rebars in a standard realenvironment will be used for extrapolation, and byconstructing a new measurement system for detecting

Takuya Kamisho

Research Engineer, Advanced Infrastructure
Maintenance Technology Research Group, NTT
Device Technology Laboratories.
He received a B.S. and M.S. in meteorology
from Hokkaido University in 2008 and 2010. He
joined NTT Environment and Energy ResearchLaboratories in 2010. He has been with NTT
Device Technology Laboratories since 2018,
where he is currently working on developing
prediction technology for hydrogen embrittlement.

Ryuta Ishii

Researcher, Advanced Infrastructure Maintenance Technology Research Group, NTT Device
Technology Laboratories.
He received a B.S. and M.S. in condensed matter physics from Osaka University in 2012 and2018. He joined NTT Device Technology Laboratories in 2018, where he is currently working
on developing prediction technology for hydrogen embrittlement.

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Vol. 19 No. 6 June 2021

hydrogen that has entered a rebar, we plan to acquire
the surface-hydrogen-concentration data for rebars
that are required for estimation. To verify the prediction results, we also plan to continue research—incollaboration with universities—on modeling thehydrogen-embrittlement mechanism from the viewpoint of materials science.
References
[1]
[2]

[3]

S. Matsuyama, “Delayed Fracture,” pp. 45–48, The Nikkan Kogyo
Shimbun, Tokyo, 1989.
T. Shiraga and S. Mizoguchi, “Present State of Steel Bars for Prestressed Concrete as Civil Engineering and Construction Materials,”
Bulletin of the Iron and Steel Institute of Japan, Vol. 13, No. 9, pp.
611–615, 2008.
M. Elices, A. Valiente, L. Caballero, M. Iordachescu, J. Fullea, J.
Sanchez-Montero, and V. López-Serrano, “Failure Analysis of Prestressed Anchor Bars,” Engineering Failure Analysis, Vol. 24, pp.
57–66, 2012.

Masayuki Tsuda

Senior Research Engineer, Supervisor, andGroup Leader, Advanced Infrastructure Maintenance Technology Research Group, NTT Device
Technology Laboratories.
He received an M.E. and Ph.D. in mechanicalengineering from Tokyo Institute of Technology
in 1998 and 2005. He joined NTT Integrated
Information and Energy Systems Laboratories in
1998, where he developed materials for lithiumion batteries and environmental impact assessment of information and communication technology services. From 2013 to 2018, he worked at
the NTT Environment Promotion Office. He wastransferred to NTT Device Technology Laboratories in 2018, where he is currently working on
developing technology to visualize infrastructure
deterioration.

70

Feature Articles: Encryption and Security Technologies
for Creating a Safe and Secure Society

Security R&D Initiatives for Creatinga Safe and Secure Society
Shinichi Hirata
Abstract

To talk about the future vision of security research and development (R&D) that NTT is working on,
it is important to think not only about the problems in front of us but also about the future of society andsecurity. This article introduces security R&D initiatives for the future.
Keywords: security, cyber attacks, data utilization

1. Introduction
The novel coronavirus has had varying impact on
our society and lives. Various events, including the
Olympic and Paralympic Games, were postponeddue to the transition of social activities and lifestyles
premised on the securing of social distance.
As the impact of the coronavirus has spread worldwide and the situation is expected to continue for along time, the world’s transformation (adoption of a
new way of life and reconstrucion of social order in a
post-coronavirus world) is being accelerated; accordingly, various efforts towards digitization andenhancement of connectivity to the Internet are rapidly advancing. The supply chain, which was basedon conventional social activities, has become dysfunctional, and major changes are occurring not onlyat the individual level but also at the social-frameworklevel.
Security and privacy concerns are spreading, andthe damage caused by cyber attacks aimed at telework/telecommuniting, which is increasing rapidly,
and attacks that take advantage of people’s anxiety
are becoming increasingly serious. Sufficient consideration must also be given to privacy in monitoring
and behavior tracking to identify infected persons andthose suspected of being infected for preventing the
spread of coronavirus infection.
In the supply chain, wide-area attacks taking
advantage of the rapid digitization and enhancemnetof connectivity are intensifying, and reconstruction of
NTT Technical Review

Vol. 19 No. 6 June 2021

secure supply chains is necessary.
NTT is conducting research and development(R&D) on security to contribute to a safe and securesociety. As the world changes drastically, it is important to think about the future of society and security
to engage in security R&D looking ahead not only tothe problems that are occurring in front of us but also
to the future.
To create a safe and secure society, we will consider future visions, specifically the Smart World [1]10 years from now, through changes in the social
environment and development of technologies surrounding information and communication technology.
2. What will be the Smart World 10 years
from now?
The society in which innovative technologies, suchas artificial intelligence (AI), Internet of Things,
robots, and big data, have penetrated is the fifth newsociety (Society 5.0 [2]) in the history of social development, following the development into an industrialized society due to the industrial revolution and into
an information society due to the development ofcomputer technology, and is expected to be a futureideal way (Smart World) to enrich lives.
In the Smart World, where cyberspace (virtual
space) and the physical space (real space) are highly
integrated by various innovative technologies, anenormous amount of data, such as sensor information
71

Feature Articles

Industry

Responding to flexible
diversification
Economic development despite
declining birthrate and aging

Life

Cyberspace

Personalized customization of
everything

Big data• Mass customization• Supply chain efficiency• Agritech

Cross-domain
analysis• Decision support• Custom-made service

Higherintelligence

Autonomy

Socialinfrastructure

Optimal and sustainable as awhole by anticipating the future• Automatic city updates• Sharing service

Flexibility

IOWN/DTC

Domaincooperation

Cyberspace and physical spaceinteraction

Separation ofownership and use

Evolution of things

Healthcare

Multifunctionalization

You can live safely andhealthily where you like.

• Custom-made medicine• Power assist• Autonomous vehicle
control• Evolve even after buying

DTC: Digital Twin Computing
IOWN: Innovative Optical and Wireless Network

Fig. 1. The Smart World 10 years from now.

accumulated from physical space, is used for data
analysis and prediction in highly intelligent cyberspace and fed back autonomously to the physicalspace. As a result, both the optimization of individual
users and that of society as a whole will progress invarious services and social infrastructures, and a society in which everyone can live safely and independently (a true Smart World) will be possible.
For example, when it comes to personal life andliving, people will be able to enjoy ultimate customized services tailored to their individual circumstances. In terms of social infrastructures, AI predictions
will enable us to take proactive measures to optimize
the entire society and provide sustainable services. In
terms of economy and industry, it will be possible toflexibly respond to diversification and develop the
economy even in a society with a declining birthrate
and aging population (Fig. 1).
There is also concern that the exposure to cyberattacks and the extent of such damage will intensify
due to the increase in higher intelligence, autonomy,
flexibility, and domain cooperation of technologies
and infrastructures that support such an ideal world(Fig. 2). When analyzing or using huge amounts ofdata, privacy may not be sufficiently considered,unethical use may occur, or information may be uninNTT Technical Review

Vol. 19 No. 6 June 2021

tentionally leaked.
The threat of malicious tampering with data-analysis algorithms is also becoming more real. In the past,
it was difficult to tamper with a program that was
created in accordance with a pre-designed algorithm
without directly modifying or replacing it. However,in a situation in which AI has become widespread,
there are risks of attacks that do not involve direct
tampering, such as causing malfunctions in AI learning and AI decisions. Specifically, we can think of
new attacks, such as an attack in which an attacker
makes an intended decision by mixing illegal values
into data learned by AI or an incorrect decision bycrafting data recognized by AI or a new attack inwhich data that could violate privacy are illegallyobtained by inferring data learned from AI operations.
Alteration of the algorithm can not only result in theintentional leakage of data but can also change theanalysis results to malicious ones. Malicious analysis
results are fed back into the physical space, which has
a significant impact on various services and social
infrastructures.
To achieve a true Smart World, it is necessary toconsider that a new threat will be created by theadvanced fusion of cyberspace and the physical space72

Feature Articles

Industry

Heavy blow tothe economy
Incorrect
data processing

Leakage of
trade secrets

Big data

Cross-domain
analysis

Attacking a wide areawith the same techniqueAutonomy

Attacks from
unpredictable routes

Higherintelligence

Attacks by
IoT device bots

An attack catchingpeople off guard
Pinpoint attack

Flexibility
IOWN/DTC
Cyberspace and physicalspace interaction

Indirect damage
to human life
Separation ofownership and use

City malfunction

Unintentional
information leak

Leakage of
personal information

Attacks on AI

Domaincooperation
Socialinfrastructure

Life

Cyberspace

Helpless situation
Healthcare

Physical space
direct attack
Evolutionof things

Unnoticed escalationof damageMultifunctionalization

Permanent attack risk

Direct damage
to human life

Fig. 2. Security threats in Smart World 10 years from now.

and focus on security R&D that can simultaneously
improve convenience while resisting attacks thatgrow in size and sophistication.
3. Approach to security R&D froma long-term perspective
Security risk depends on the threat of an attack (ina broad sense involving people and society), vulnerability of the system, and size of the assets that must
be protected (including not only information andmoney but also human life). As cyber attacks grow insize and sophistication and we become more exposed
to various threats due to the advanced fusion of cyberspace and the physical space, security risks will
increase dramatically.
There is a limit to how much a company can spend
on security measures because it is expensive tostrengthen security measures. It is difficult to implement countermeasures against all threats only byextending or simply enhancing existing security measures. Therefore, it is necessary to drastically improve
defense and countermeasures against cyber attacks.
Security R&D from a long-term perspective must
(1) focus on technologies that respond to new threatsand protect the environment to support the creation ofvalue in the Smart World; and (2) create technologies
NTT Technical Review

Vol. 19 No. 6 June 2021

that change the situation in which attackers dominate,such as technologies that reduce the vulnerability risk
to zero and that predict and proactively respond to
attacks.
The NTT Group will strengthen its response systems to major sporting and cultural events, and thedevelopment of new fields (urban development,
energy, and healthcare) on the basis of its mediumterm management strategy will require the safe use ofdata and the security necessary to implement theInnovative Optical and Wireless Network (IOWN).
Therefore, the following points will be important insecurity R&D (Fig. 3).
(1)	Development and deployment of data distribution and utilization technologies that secure thevalue-creation process
Develop technology for flexible and safe sharing
and analysis of data and capable of using data acrossfields to solve problems of data encirclement, privacy
infringement, and illegal use of data [3].
(2)	Development of technologies to solve operational-cost problems and minimize damage
Develop technology to autonomously and automatically respond to cyber attacks while responding
to new threats so that humans will be able to focus onconfirming responses and responding to new threatsthat require creativity, thereby strengthening their73

Feature Articles

Development and deployment of data
distribution and utilization
technologies that secure thevalue-creation process

Development of technologies to solve
operational-cost problems andminimize damage

Development of advanced technologies
for the future to support security R&D

Fig. 3. Viewpoints required for security R&D.

comprehensive response capabilities [4].
(3)	Development of advanced technologies for the
future to support security R&D
As a security Center of Excellence, develop basic
technologies for the future such as cryptography andinformation theory and quantum information security
technology [5].
To sustain the safe and secure communication
demanded by the NTT Group into the future, we will
engage in R&D to meet the medium- and long-term
objectives of safe data distribution and utilization andminimize damage including cutting-edge technologies for the future and those that make use of IOWN.
References[1]

NTT Technology Report for the Smart World, https://www.rd.ntt/e/

[2]
[3]

[4]

[5]

techreport/
Cabinet Office, Government of Japan, “Society 5.0,” https://www8.
cao.go.jp/cstp/english/society5_0/index.html
T. Washio, Y. Orime, T. Morita, K. Chida, K. Morimura, and Y. Oshima, “Data Sharing and Utilization Technologies for Safe and Secure
Value-creation Processes,” NTT Technical Review, Vol. 19, No. 6, pp.
75–80, June 2021.
h t t p s : / / n t t - r ev i ew. j p / a r c h ive / n t t t e c h n i c a l . p h p ? c o n t e n t s =ntr202106fa12.html
Y. Koga, Y. Nakajima, N. Chiba, J. Miyoshi, T. Koyama, H. Shito, and
A. Miyajima, “Establishment and Development of Cybersecurity
Technologies to Solve Problem of Increasing Operation Costs and to
Minimize Damage,” NTT Technical Review, Vol. 19, No. 6, pp.
81–87, June 2021.
h t t p s : / / n t t - r ev i ew. j p / a r c h ive / n t t t e c h n i c a l . p h p ? c o n t e n t s =ntr202106fa13.html
Y. Tokunaga, Y. Suzuki, S. Endo, R. Nishimaki, F. Kitagawa, and S.
Tamechika, “Security Based on Quantum Information Technology
and Data Protection of Quantum Information,” NTT Technical
Review, Vol. 19, No. 6, pp. 88–93, June 2021.
h t t p s : / / n t t - r ev i ew. j p / a r c h ive / n t t t e c h n i c a l . p h p ? c o n t e n t s =ntr202106fa14.html

Shinichi Hirata

Vice President, Head of NTT Secure Platform
Laboratories.
He received a B.S. from Hokkaido University
in 1990 and joined NTT in the same year. He has
been engaged in R&D of cryptography, smart
card technology, and authentication systems.

NTT Technical Review

Vol. 19 No. 6 June 2021

74

Feature Articles: Encryption and Security Technologies
for Creating a Safe and Secure Society

Data Sharing and Utilization
Technologies for Safe and Secure
Value-creation Processes
Tomoaki Washio, Yoshinori Orime, Tetsushi Morita,
Koji Chida, Kazuo Morimura, and Yoshihito Oshima
Abstract

To achieve Society 5.0, a vision of a future society that achieves both economic development andresolution of social issues, it is essential to use data across organizations and industries, but this is not as
widespread as it should be. This article outlines the risks associated with data utilization and their causes
and introduces a new paradigm of data sharing and the platform and key technologies to achieve it.
Keywords: data sharing, security, trust

1. Society 5.0 and cross-domain data sharing
The Japanese government proposed “Society 5.0,”
as a vision of the future society that achieves both
economic development and resolution of social
issues [1], and efforts to achieve it are actively being
made. In Society 5.0, cyberspace and the physicalspace will be highly integrated, and by making fulluse of various data, it will become possible to understand the situation at that time, discover issues, predict the future, and derive optimal solutions, which
will lead to economic development and solve social
problems. In other words, the success of Society 5.0
depends on how much data across organizations andindustries (i.e., cross-domain data sharing) can beused.
2. Barriers to cross-domain data sharing
and its causes
However, cross-domain data sharing, especially thesharing of sensitive and rare data, has not progressed
as much as expected. The largest barrier is the risk toboth the data provider and data user.
Data providers take the risk that the data they provide may be leaked or used in an unexpected way,
NTT Technical Review

Vol. 19 No. 6 June 2021

causing damage to themselves or others. Data users,
on the other hand, take the risks associated with confidentiality management of the data provided and therisks associated with the legality of such data.
From another perspective, data users take the riskthat the data they receive will not produce the desired
results or value or may not meet the conditions
imposed for receiving the data (for example, the payment for receiving the data). Data providers take therisk that the data they provide will create more value
than expected (i.e, the payment they receive is undervalued) or may not fulfill the purpose of providing
data for the data provider (for example, not receiving
the obtained results from data utilization) when the
expected results are not obtained.
The root cause of the above risks is that traditional
methods of data sharing involve passing on or receiving the data. Data can create different values andproblems depending on how the data are used; therefore, it is difficult to determine all values and problems beforehand. With all this uncertainty, crossdomain data sharing cannot be actively carried out.

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Feature Articles

Conventional: Data-passing management and control
DatapassedData

Dataprocessed

Data

Data provider

Processing
results

Proposed: Data-processing management and control

Valueobtained

Value

Data user

High risk• Data leakage• Unexpected use• Unusable data

Data
processed

Data

Results
only passed

Processing
results

Data provider(Same)
value obtained

Processing
results

Value

Data user

Low risk• No data leakage• Expected use only
• Minimum required data

Fig. 1. Paradigm shift in data-sharing methods.

3. Toward a new paradigm of data-processing
management and control
To solve this problem, it is necessary to shift fromthe conventional to a new paradigm of data-processing management and control. In this new paradigm,
on the basis of the principle of data minimization,
data users are only given the results of agreed processing (the processing data users request and theprocessing data providers approve) of the data, notthe original data. By doing this, the value and problems that can arise from the use of those data arelimited and predictable, and the risks mentioned
above are greatly reduced (Fig. 1).
4. Overview of cross-domain
data-sharing platform
Our goal is to create a trustworthy*1 cross-domain
data-sharing platform based on the above new paradigm so that all data providers and data users participating in the platform can share and use all data withconfidence. The platform’s three main requirementsare (1) to be able to execute the necessary processing
for the purpose while protecting the data, (2) to beable to control the processing of the data in accordance with the agreements and laws between the data
provider and data user, and (3) to be transparent andaccountable about the data handled and their processing (Table 1).
We believe the platform should consist of the folNTT Technical Review

Vol. 19 No. 6 June 2021

lowing three mechanisms (Fig. 2):(1) Data protection and utilization mechanism•	Executes various processes such as analysis ortransformation required by the data user on thedata while keeping the data (containing derived
data*2) confidential.
•	Ensures that only the processing permitted by thedata-processing-authorization mechanism is
executed as permitted and proves the facts ofdata processing, processing history for certain
data, and origin of the derived data.
(2) Data-processing-authorization mechanism•	When a request for data processing is made to
the data protection and utilization mechanism, it
is determined whether to accept the request on
the basis of the data usage policy*3 specified by
the data provider, agreement between the data
provider and data user, and legality of therequest.
•	Prior to determining the above, the data provider,*1 Trustworthy (platform): To earn the trust of data providers anddata users, the platform should be able to demonstrate that it isdoing exactly what data providers and data users expect it to do.
*2 Derived data: The result of processing data entrusted to the platform by the data provider. Includes the results of processing derived data.
*3 Data usage policy: The policy specifies what kind of data usage
shall be permitted. The target of authorization is specified using
the attributes of the target data and the requesting entity, how to
use the data (method for processing), etc. Permitted/prohibited,or conditions to be satisfied to permit, are also specified to eachtarget.

76

Feature Articles

Table 1. Key requirements for cross-domain data-sharing platform.
Classification
Protect data storage andprocessing

Key requirements
Executes various analysis, transformation and other processing requested by data users while keeping theconfidentiality and integrity of data at a high level.
Also handles the results of data processing (derived data) as described above.
Restricts platform operators from viewing or modifying data or derived data.

Managing and controlling
data processing

Executes only data processing agreed between the data provider and data user.
Depending on the target data, executes only processes that conform to laws (Personal Information Protection Law, etc.)
Authorizes after confirming the propriety of data providers, data users, and target data involved in therequested data processing accurately and in detail.

Ensure transparency of dataprocessing

Enables data users to confirm the characteristics and origin of data and derived data.
Enables data providers and data users to confirm the fact and history of processing performed on data andderived data.
Enables data providers and data users to confirm the operation of platforms regarding data storage andprocessing.

Cross-domain data-sharing platform
Data protection and utilization mechanism
Data provider

Executes various processes on the data
while keeping them confidential
Data-processing-authorization mechanism
Determines whether to accept the dataprocessing request on basis of the datausage policy, agreements, and legality

Data provider

Data user

Data user

Trust-data-management mechanism
Manages trust data (various attributes related
to data providers, data users, and data)

Data provider

Data user*Functions such as data retrieval, matching, billing, and settlement are omitted.

Fig. 2. Cross-domain data-sharing platform architecture.

data user, and target data are confirmed on thebasis of accurate and detailed information onthem from the trust-data-management mechanisms.
(3) Trust-data-management mechanism•	Manages various attributes related to data providers, data users, and target data (i.e., trust data)and provides them to the data-processing-authorization mechanism and those who need them.
•	Manages information that proves the fact andhistory of data processing by the data protection
and utilization mechanism and the origin of
derived data as trust data as well and provides
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those trust data to those who need them.
5. Key technologies for cross-domain
data sharing
The following is an overview of the key technologies for implementing the above mechanisms.
5.1 Secure computation
Secure computation is a technology that enables
computation while keeping data encrypted. This
enables secure use of sensitive data such as personal
data or corporate trade secrets. It also should enable77Feature Articles

the analysis of such data to extract new value by
increasing the types and amounts of data to be analyzed. In secure computation technology, not only
safety but also performance and diversity of processing are important. NTT Secure Platform Laboratories
developed a secure computation system with theworld’s fastest statistical processing [2]. We are currently developing secure computation artificial intelligence (AI) technology for executing learning andprediction processing in deep learning while keeping
the input data and neural networks encrypted [3]. We
are also working on increasing the speed of processing and expansion of the AI algorithms needed toprocess large amounts of data such as high-definition
images.
5.2 E
 nhancing confidentiality and authenticity
when data processing
Because cross-domain data sharing processes data
in a variety of stakeholder computing environments,
it is not easy to ensure data access control (ensuringconfidentiality) or the authenticity of data-processing
results. However, as mentioned above, cross-domain
data-sharing platforms must meet these requirements
to be trusted and widely used. Specifically, we believe
the following two requirements are particularly
important: (1) the data provider can check whether
the provided data are being used only within the permitted operations and (2) the data user can check
whether the data-processing results are correct asrequested.
5.3 Attribute-based authorization
Because large amounts of data are registered continuously on the platform and it is not known inadvance who is going to use the registered data,
attribute-based authorization is effective for crossdomain data sharing. Regarding attribute-based
authorization, data-usage policies are defined in theform of conditions for what kind of subject can use
what kind of data using the attributes of the subject
and data. When authorization decisions are made, theattribute values of the data users and target data areapplied to the conditions and evaluated. For example,
a data user’s qualification (e.g., Information Security
Management Systems Certification) is specified as arequired attribute in the data-usage policy.
Attribute-based authorization is not a new concept,
but there are technical challenges when applying it tocross-domain data sharing. To make authorization
decisions that take legality into account, it is necessary to check and determine the existence or value of
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specified attributes in accordance with the characteristics of the data, regardless of the data-usage policy,
as described later. To avoid making an incorrect
authorization decision, it is necessary to strictly
determine the existence of the attribute specified in
the data-usage policy and its authenticity (whether it
has been certified by a third-party organization, etc.).
It is also necessary to have flexibility in authorization
decisions, such as conditionally allowing data usagein addition to permitting or prohibiting it. For example, the requested data may not be used as is but may
be used after being anonymized. We believe thatmaking flexible authorization decisions while coordinating the requirements of both data providers anddata users will contribute to expanding data-sharing
opportunities (Fig. 3).
5.4 Trust-data management
The trust-data-management mechanism collects
and manages attributes of platform users (qualifications, achievements, reputation, etc.) and attributes ofdata processed on the platform (data characteristics
such as type, items, collection method, origin, andprocessing history). It then provides them to the dataprocessing-authorization mechanism, data providers,and data users as “trust data” that can be relied onwhen users and data are confirmed (Fig. 4).
Because trust data are the basis of trust, it is necessary to be able to verify that such data have beenguaranteed by various entities regarding the data’s
authenticity and correctness. However, trust data may
be confidential; thus, it is necessary to appropriately
determine when, to whom, and to what extent to disclose trust data. It is also required for the data to beavailable whenever needed. We will develop trustdata-management technologies and mechanisms thatmeet these various requirements.
5.5 Implementing legal requirements for trust
data and authorization decisions
Data providers and data users must also consider
the legality of the data they share. It is difficult fordata users to understand how the data were obtained
and might not notice that illegally obtained data were
included. The Act on the Protection of Personal Information prohibits the use of data that constitute personal information outside the scope of the purpose ofuse indicated to the person at the time of acquisition
and the provision of such data to third parties without
the person’s consent.
To reduce the burden of legal compliance, we are
studying a method of assigning attribute data that78

Feature Articles

Data protection and utilization mechanism
Data registration

Data

Processing request
Data processing

Data provider

Data user

Decision resultge
Data-usa
condition
Authorization
decisionge

Data-usa
policyData-processingauthorization mechanism

in,stics, orig
Characteri istory, etc.
hginprocess

ns,
Qualificatio t,
enachievem, etc.
reputation

Trust data
(data attributes)

Trust data
(user attributes)

Trust-data-management mechanism

Fig. 3. Attribute-based authorization.

Data protection and utilization mechanism
Data
Origin, processing
history, etc.
Data processing
Data-processingauthorization mechanism

Characteristics, origin,processing history, etc.

Processing
history, etc.

Authorization decision

Credentials, achievements,
reputation, etc.

Acquisition method, characteristics, quality, origin, etc.
Data user

Data provider
Trust data
(data attributes)

Trust data
(user attributes)

Acquisition method,characteristics, etc.

Qualifications, achievements,
reputation, etc.

Characteristics, quality, etc.
Trust-data-management
mechanism

Attribute certifierCollection and verification of trust data

Provision and certification of trust data

Fig. 4. Flow of trust data.

implements legal requirements together with data,
managing the data as trust data, and checking the data
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when making authorization decisions.

79

Feature Articles

6. For the future
We believe that a trustworthy cross-domain datasharing platform will accelerate collaboration andco-creation among the same or different industries,
which were previously difficult, and enable the creation of new value and resolution of major social
issues such as those regarding food, health, and theenvironment.
To achieve this, we will accelerate not only researchand development of key technologies but also proof
of concept in cooperation with partners aiming at

Tomoaki Washio

cross-domain data sharing, international standardization, and activities to foster social acceptability.
References
[1]
[2]
[3]

Cabinet Office, Government of Japan, “Society 5.0,”
https://www8.cao.go.jp/cstp/english/society5_0/index.html
NTT press release, “Trial Service of Secure Computation System SanShi®,” Aug. 8, 2018.
https://www.ntt.co.jp/news2018/1808e/180808a.html
NTT press release “Secure Computation for a Typical Training Algorithm of a Deep Neural Network,” Sept. 2, 2019.
https://www.ntt.co.jp/news2019/1909e/190902a.html

Koji Chida

Senior Research Engineer, NTT Secure Platform Laboratories.
He received a B.E. and M.E. in systems andinformation engineering from Hokkaido University in 2000 and 2002. Since joining NTT in
2002, he has been engaged in research and development (R&D) of authentication systems andsecure data-sharing technologies.

Senior Research Engineer, Supervisor, NTT
Secure Platform Laboratories.
He received a B.S. and M.S., and Dr.Eng. fromWaseda University, Tokyo, in 1998, 2000, and2006. Since 2000, he has been engaged inresearch on cryptography and privacy-enhancing
technologies at NTT. He is a member of theInstitute of Electronics, Information and Communication Engineers (IEICE) and Information
Processing Society of Japan (IPSJ). He received
the IPSJ Best Paper Award in 2012.

Yoshinori Orime

Kazuo Morimura

Senior Research Engineer, NTT Secure Platform Laboratories.
He received a B.E. in computer science from
Saitama University in 1998 and joined NTT thesame year. Since 2020, he has been engaged inresearch on incorporating legal and social
requirements into technical requirements.

Senior Research Engineer, Supervisor, NTT
Secure Platform Laboratories.
He received a B.A. from Aichi University of
Education in 1993 and M.E. from Nara Instituteof Science and Technology in 1996. He joined
NTT in 1996 and is currently conducting R&D
on data protection technologies centered on cryptography.

Tetsushi Morita

Yoshihito Oshima

Senior Research Engineer, Supervisor, NTT
Secure Platform Laboratories.
He received a B.E. and M.E. from Kyoto University in 1996 and 1998 and a Ph.D. in engineering from University of Tsukuba, Ibaraki, in 2010.
Since joining NTT Software Laboratories in
1998, until 2012, he was engaged in research on
information retrieval and personalization systems. His current research interests include
secure data-sharing technologies.

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Executive Research Engineer, Supervisor,
NTT Secure Platform Laboratories.
He received a B.E. and M.E. in electrical engineering from Hokkaido University in 1994 and1996. He joined NTT in 1996 and is currently
conducting R&D on secure data-sharing technologies. He is a member of IPSJ.

80

Feature Articles: Encryption and Security Technologies
for Creating a Safe and Secure Society

Establishment and Development ofCybersecurity Technologies to Solve
Problem of Increasing Operation
Costs and to Minimize Damage
Yuzo Koga, Yoshiaki Nakajima, Naoko Chiba,
Jun Miyoshi, Takaaki Koyama, Hidehiro Shito,
and Asami Miyajima
Abstract

While responding to new cybersecurity threats such as cyber attacks, we will radically improve theefficiency of security operations by developing technologies for autonomous and automated security
measures. Such technologies will enable operators to concentrate on countermeasures against advanced
threats that cannot be handled mechanically and enhance overall security-response capabilities.
Keywords: cybersecurity, security operation, security measures

1. Background
Cyber attacks are increasing yearly and becoming
more complicated and sophisticated. In particular,
there has been a significant increase in cyber attacks
that directly target humans, which has dramaticallyincreased the cost of cybersecurity measures forenterprises.
When users have diverse requirements and enterprises need to cope with long tail customers, a variety
of applications should be provided through a combination of servers and software on ultrahigh-speed
optical communication networks connecting various
communication equipment, terminals, and devices. In
such a situation, the efficiency of security measures tohandle each cyber attack is too low, which can be afactor hindering the digital transformation and business-value creation of enterprises.
2. Goal of our research and development(R&D) on technologies for automatically and proactively implementing security measures against cyberattacks and various vulnerabilities that are targets ofthem.
Through such technologies, we will provide an
information and communication technology (ICT)
environment capable of preventing damage caused bycyber attacks and resolving the shortage of humanresources in security operations that restrict enterprise management, enabling users to use services
with peace of mind. This environment eliminates theneed for enterprises to respond to security vulnerabilities each time (whack-a-mole game), after an incident (cat-and-mouse game), or respond to businessloss due to damage (Fig. 1).
By reducing the total cost of security operations, wewill enable enterprises to focus on development andoperations and support them in creating business values in short cycles in a Smart World of smart factories, buildings, mobility, etc. (Fig. 2).

We are conducting research and development
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81

Feature Articles

10 yearsfrom now

Currently

Cost at the time of the incident(For example, data loss)

Business loss

se

Incident responsSecurity service
T
provided by NTsponseVulnerability re
Cost incurred eachtime a vulnerability
is discoveredce
Corporate servi
ons
ati
er
op
nt/
me
developce
Corporate servi
erations
development/op

terprises

Total cost for en

Fig. 1. Total cost reduction of security operations.

Reduce the burden on security measures,and encourage enterprises to continue creating
diverse business values as Smart World services.
Delivery ofbusiness values

Provide a variety of business values in a timely mannerand shorten the cycle of development and testingby combining componentized security functions.

Minimize security operations
that have to be responded toevery time requirements change.

Smart World
services
Development

Through research on cyber-attack methods andhuman vulnerability, actively nip vulnerabilities in the bud
and fundamentally reform application development.

Operation

Feedback from operations

Drastically improve cost efficiency
by automating and upgrading
the conventional manual response.

Outcome of
R&D
Target of our R&D

Fig. 2. Purpose of our R&D.

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82

Feature Articles

Large amount oflogs fromapplications
and servers

Services
Platform for always taking proactive and automatic security measures

Monitoring

Keep track ofchanges inevery situation

Analysis

Derivecountermeasuresby simulating
vulnerabilities

Automatic incorporationof new function block
into a service system
to cope withvulnerabilities or
automatically prevent
users from being harmed

Implementation

Response of measuresIntelligence
Excessive logs andtraffic informationfrom communication
nodes and control
servers

Infrastructure (communication nodes and control servers)

Automatic reconfiguration
to a system thatincorporated new
countermeasures against
vulnerabilities,
configuration changes ofcommunication nodes, etc.

Fig. 3. Platform as a result of our R&D.

3. Platform as a result of our R&D
In security operations, many security measures,such as monitoring, analysis, and response, areimplemented manually, so the ability to carry themout depends heavily on human skills.
By implmenting a platform with our technologies,
we will constantly monitor the status of devices andapplications that make up infrastructure and services
and automatically execute security measures on systems in advance as soon as a vulnerable situation isfound. The platform provides an environment to conduct stable, effective, and efficient security measures(Fig. 3).
4. Challenges in implementing the platform
To automatically and proactively implement security measures, we will conduct R&D on the following
three technologies (Fig. 4) and create intelligence, as
shown in Fig. 5.
(1)	Technologies for actively visualizing and minimizing vulnerabilities, and implementing automatic correction cycles
To provide robust security, we will conduct R&D
on visualizing and minimizing vulnerabilities, andalso on implementing automatic correction cycles toenable shift-left security measures that can nip vulnerabilities in the bud and drastically improve efficiency of security operations.
(2)	Technologies for generating and using intelligence that follows environmental changes
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Security measures are continuously and autonomously implemented in a wide variety of ICT environments through technologies for automaticallygenerating intelligence unique to telecommunication
carriers and automatically using intelligence that
does not require awareness.
(3)	Technologies for countering human-inducedrisks
We will conduct R&D on security technologies thatcan respond to risks arising from humans and drastically reduce risks related to human errors, fraudulent
attacks targeting humans, internal fraud by employees, etc., which can lead to security damage.
In the following section, we introduce our major
R&D efforts.
5. Current activities(1)	Configuration and status analysis technology(Fig. 6)
We are currently conducting R&D on software
agents and communication-analysis engines that analyze the configuration and status of Internet of Things
devices for people and things as a security technology
to protect complex cyber-physical systems composedof various elements such as smart cities. We will conduct R&D on crossing-analysis technology for multiple domains to detect signs of security anomalies
and estimate probable causes and measures, whichhave been difficult in the past, by analyzing the correlation between elements across systems and services in addition to configuration and status.
83Feature Articles

Subject to respond

To become more numerous, diverse,and distributed(g 2)
in en Teen telli era chn
vir ge tin olo
on nc g a g
m e t nd ies
en ha u fo
ta t f si r
l c ol ng
ha lowng s
es

Things(1) Tevis chno
vulne ualizing logies foraraa
auto bilities a nd minim ctivelymati
c cor nd imple izingmrecti
on c enting
ycles

Infrastructure

DesignDevelopment /Testing

for ediesclog nduhno an-i
Tec um(3) ring h ks
ris
nte

cou

Application
HumanIntelligence utilization areas thatwere primarily “ex post response”(conventional)
Operations /Utilization

Attack /Identification

Phases of security
measuresResponse /RecoveryTake more proactive approaches

Fig. 4. Three technical issues.

Intelligence
For more efficient operations (reduce operationalcosts through automation)• Blacklists of malicious sites and indicator ofcompromises (IOCs), which extract evidence of
attacks on devices• Security-measure information obtained from
unstructured data
• Operational information held and used as tacitknowledge by analysts at security operations
center

For more advanced operations (enable proactive
security measures)• Information on configuration and status of various
devices that form communication networks• Information on supply chain that makes up theapplication• Information on vulnerabilities and risks attributableto humans

For differentiating from competitors (security measures unique to telecommunications carriers)• Carrier-network risk information• Information on cyber attacks and vulnerabilities that can be analyzed and obtained from large andsmall network-flow data
• Malware information for various terminals/devices connected to the network

Fig. 5. Intelligence created from our R&D.

(2)	Initial-forensic-investigation technology (Fig. 7)
In cyber forensic investigation, a terminal that issuspected of being attacked is preserved, and a security analyst extracts evidence of an attack. Whiledetailed analysis is possible from investigation byhumans, it depends on the analyst’s experience andcan take several days. In the initial investigation
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phase, therefore, its accuracy and speed remain issues
for early clarification of the entire damage. Therefore, we are developing a technology for preserving
only important logs and automatically extracting
traces of attacks. The goal with this technology is tocreate an intelligence database of attack proceduresthat are often used by attackers and processing them84

Feature Articles[Complex cyber-physical system]
Interdomain
collaboration

cyberspace

Monitoring
centerVerification
list

Monitoring
centerIntelligence

AI modelMonitoring
centerIntelligence

Verification Abnormal!
AI modellist

Verification
listIntelligence
AI modelDetailed monitoring of systems in various fields by analyzing configuration and status of devices
Home

Transportation Medical care

Building

EnergyLogistics

Factory

Agriculture

physical space

Normal?
Smart building

Normal?
Smart factory

Local government
related services
Normal?
Smart mobility[Security composite analysis]
Trace using crossing-analysis technology for
multiple domains, detect predictive signs, anddetermine measures.

[Attack detection and analysis for mobility]
Detect anomaly signals in on-vehicle
networks and identify attack pathfor connected cars.

Estimatedattack path

Attack to ECU

ECU: electronic control unit

Fig. 6. Configuration and status analysis technology.

automatically. Initial investigations can be conductedin a few hours, regardless of the skill levels of analysts.
(3)	Technology for detecting web-based socialengineering attacks that exploit human psychological vulnerabilities (Fig. 8)
Attackers use opportunities such as international
sporting events and the spread of COVID-19 infection to attract people’s interests and carry out cyberattacks that deceive users. Attackers can trick users
into visiting a malicious site with interesting content
or fake warning messages, causing malware infections and theft of money and personal information.
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We are conducting R&D on technology that can emulate the browser operations of deceived people, automatically crawl and collect webpages, and detectmalicious sites with high accuracy and speed basedon the image, language, and feature amount of thearrival path with the aim of reducing fraud damage
targeting such people.
6. For the future
Cybersecurity risks can now threaten countries andare one of the most serious social problems. As thesituation continues to be dominated by attackers, we85

Feature Articles

Suspected
attackedterminal

Damage overview
Preservation of terminal
condition (Copy HDD)

Conventional

Investigations by analyst

a few days
Damage overview
Preservation of Extraction ofimportant logs attack traces

Initial forensic
investigation technology*Conventional preservation and investigation
are conducted at the same time.

a few hours

Intelligence DB
DB: database
HDD: hard disk drive

Fig. 7. Initial forensic investigation technology.

Collecting URLs by simulating user’s browsing behavior
Automatic
crawling
Automatic web crawling, recording, and collecting imitating browser operationsof a psychologically influenced user

Install
Click HereWeb
crawling

Download Now!

Detection
Identify malicious pages by extracting features from the content and entire
sequence of webpages

HTML

Crawling result

AH!

A

Extracting features

Machinelearning

Identification ofmalicious websites

Threat intelligence about sites that exploit social engineering
HTML: Hyper Text Markup Language
URL: uniform resource locator

Fig. 8. Technology for detecting web-based social-engineering attacks that exploit human psychological vulnerabilities.

will continue to contribute to the betterment of society
by creating new security technologies that can over-

NTT Technical Review

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come the current severe cybersecurity situation.

86

Feature Articles

Yuzo Koga

Director, Head of Cyber Security Project, NTT
Secure Platform Laboratories.
He received a B.E., M.E., and Ph.D. in instrumentation engineering from Keio University in
1996, 1998, and 2001. He joined NTT in 2001,
and has had several years of experience indesigning, building, and operating various communication services including identity management, cloud computing, the Internet exchange
point, and the Internet access network. He is amember of the Institute of Electronics, Information and Communication Engineers (IEICE).

Yoshiaki Nakajima

Takaaki Koyama

Director, Security Operation Project, NTT
Secure Platform Laboratories.
He received an M.M.G. in media and governance from Keio University in 1996. He joined
NTT in 1996 and has been studying several typesof virtual private networks and software-defined
networking as well as security operation systems
for these network technologies. His researchinterests have recently extended to security
analysis and operation technologies for smart
cities. He is a member of IPSJ.

Hidehiro Shito

Director, Head of Security Operation Project,
NTT Secure Platform Laboratories.
He received a B.S. in information science andan M.S. in mathematical and computing sciencefrom Tokyo Institute of Technology in 1995 and1997. He joined NTT Information and Communication Systems Laboratories in 1997, where heworked on R&D of information security. From2009 to 2013, he was with the Security Strategy
Section of the Technology Planning Department.
He has been involved in R&D of information andcommunication platforms, security platforms,
and other areas. He is a Certified Information
Systems Security Professional (CISSP) and Registered Information Security Specialist (RISS).

Director, Security Operation Project, NTT
Secure Platform Laboratories.
He received a B.E. and M.E. in mechanical andsystem engineering from Yamanashi University
in 1994 and 1996. He joined NTT in 1997. Afterseveral years of experience in R&D, operation,and construction of communications infrastructure, he started his career as a member of computer security incident response teams (CSIRTs)of organizations such as NTT EAST and NTT
DATA. He joined NTT R&D in 2018, and his
current position is a director of NTT-CERT(Computer Security Incident Response andReadiness Coordination Team), the representative CSIRT of the NTT Group.

Naoko Chiba

Asami Miyajima

Director, Cyber Security Project, NTT Secure
Platform Laboratories.
She received a B.S. and M.S. from Tokyo Institute of Technology in 1998 and 2000. She joined
NTT R&D in 2000 and has been working for
more than 20 years in the information security
field. Her research interest lies in high-quality
and usable cybersecurity intelligence. She is a
CISSP and a member of Information Processing
Society of Japan (IPSJ).

Director, Security Operation Project, NTT
Secure Platform Laboratories.
She received a B.S. and M.S. in science andtechnology from Keio University in 1998 and2000. She joined NTT R&D in 2000, and her
research interests include cyber-physical systems
security.

Jun Miyoshi

Director, Cyber Security Project, NTT Secure
Platform Laboratories.
He received a B.E. and M.E. in system sciencefrom Kyoto University in 1993 and 1995. Sincejoining NTT in 1995, he has been researchingand developing network security technologies.
Prior to his current position, he was engaged in
R&D strategy management of the Labs. from2011 to 2015. He is a member of IEICE.

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87

Feature Articles: Encryption and Security Technologies
for Creating a Safe and Secure Society

Security Based on Quantum
Information Technology and Data
Protection of Quantum Information
Yuuki Tokunaga, Yasunari Suzuki, Suguru Endo,
Ryo Nishimaki, Fuyuki Kitagawa, and Sachi Tamechika
Abstract

Quantum information processing is expected to have unique security applications such as communication security and copy protection based on physical principles in addition to high-speed computation.
For the practical use of quantum information processing, fault-tolerant processing is essential to protect
quantum information from noise, and fault-tolerant processing for quantum communication based on
quantum repeaters is the key for networking. We introduce our efforts in this area in this article.
Keywords: quantum information processing, security, fault-tolerant technology

1. Introduction
The possibility of new high-speed computation
using quantum information processing has been
attracting attention, and new security using such processing and data protection of quantum information
are also important research topics. Quantum information is known to be very sensitive to noise, and toprocess information correctly, it is necessary to protect quantum information from noise and errors.
Protecting the availability of such information processing is one of the three elements of security*, andis one of the important roles of security. Without this,no matter how fast the computation is or how many
new security applications there are, the information
cannot be processed correctly. The ability to protect
quantum data from noise is the most important issue
in quantum information processing, and the securityof quantum information processing supports the
backbone of such processing.
The possibility for new security using quantum
information processing is, in a sense, to take advantage of this weakness against noise, but the nature ofquantum states is such that if one touches a quantum
state to eavesdrop or forge it, traces as noise will
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inevitably be left behind. Quantum cryptography
takes advantage of this property to detect eavesdroppers and maintain security in principle. (Quantum
cryptography is also called quantum key distribution
because it is usually used to distribute secret keys.)
The nature of quantum states can also be used to prevent counterfeiting and has potential applications inquantum money and quantum copyright protection,
where counterfeiting by copying is impossible inprinciple. Such functions will become more valuable
when quantum networks are enhanced; therefore, it isnecessary to develop quantum repeaters and construct a large-scale quantum network. Since quantum
communication is also vulnerable to loss and noise,
the ability to protect data from noise in quantum communication can be regarded as the security of such
communication.
In this article, we first introduce quantum error correction and quantum error mitigation, which are two
important technologies for protecting quantum information data. We then discuss copy protection as a
new application possibility and finally introduce*

The three elements of information security: confidentiality, integrity, and availability.

88Frequency

Feature Articles

Distribution
with errors

Ideal
distribution

After error mitigation

Calculation results
Calculation results with errors

Ideal calculation results

Fig. 1. A schematic of how quantum error mitigation works. The near-term quantum algorithm obtains the averagemeasurement results as the calculation results. After quantum error mitigation, the probability distribution will be
distributed around the correct mean value, but the variance will increase, so more measurements are needed.

research on quantum repeaters, which is a fundamental technology for quantum networks.
2. Fault-tolerant technology to protect
quantum information data
In many applications of quantum information processing, error rates during computation must be sufficiently small. Quantum error correction is a technology that can significantly reduce effective error
rates by encoding the information of qubits using
multiple noisy qubits and by detecting and correcting
errors sequentially. Building a fault-tolerant quantum
computer (FTQC) [1], which enables fault-tolerant
quantum information processing using quantum error
correction, is one of the most promising ways to demonstrate practical applications in a scalable manner.
However, it is not easy to build an FTQC with practical performance because quantum error correction
requires many qubits, feedback, and other complicated processing [2]. Therefore, to build a useful
FTQC, it is necessary to research and develop an
efficient architecture from software to hardware byconsidering many trade-off relations and performance bottlenecks. We are working on the researchand development of software infrastructure for building a practical FTQC. Specifically, we are developinga method of quantum error correction for distributed
computing systems [3], method for optimizing
decoding circuits for small codes by machine learning [4], circuit design of peripheral devices for lowlatency decoding algorithms [5], calibration method
for accurate control of integrated qubits [6], framework for high-speed measurements of qubits, and
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Vol. 19 No. 6 June 2021

series of fundamental software to comprehensively
evaluate and improve the accuracy of these methods.
Near-term quantum computation has attracted agreat deal of attention. This is because in October
2019, Google announced that it was able to solve avery specific, impractical problem, which was said totake a very long time to solve with existing computers, by using a 53-qubit quantum computer. Researchers worldwide are studying how to make practical use
of such quantum devices and applications such asmachine learning and chemical calculations. However, to exploit the computational power of suchsmall-scale quantum computers, it is necessary to
suppress computational errors. Quantum error correction has been studied for many years for removing
computational errors, but this method uses qubits as aresource for error suppression, which is incompatible
with small-scale quantum devices that can be fabricated now or in the near future due to the limited
number of qubits. Instead, quantum error mitigation(or quantum noise compensation) has been proposed
as an alternative to suppressing errors without (significantly) increasing the number of qubits, and anumber of papers have been published recently.
Quantum error mitigation is a method for effectively
suppressing computational errors by adding errorsuppression operations to the quantum algorithm thenexecuting existing classical information processing
on the readout measurement results (Fig. 1). In thiscase, the resource required for quantum error mitigation is a larger number of measurements (number ofcalculations). For error mitigation, there is an overhead of larger number of samples, thus it is not scalable. Nevertheless, it has been shown that error
89Feature Articles

Classical technology: copyable

Cryptography and quantum technology: uncopiable

Fig. 2. Uncopiability with quantum technology.

mitigation can effectively suppress errors if the frequency of computational errors is small in the quantum algorithm [7]. Our group has also recently shownthat the number of qubits required for FTQC can be
reduced in a practical manner by incorporating quantum-error-mitigation methods into FTQC, indicatingthat quantum error mitigation is a method with a wide
range of applications [8].
3. Secure copy protection from cryptography
and quantum information technology
There are various topics at the intersection of cryptography and quantum information processing. Technology related to these two fields are roughly categorized into (1) cryptography secure against quantum
computers (post-quantum cryptography) [9], (2)quantum cryptography, which uses quantum information processing to achieve secure communication[10], and (3) cryptography with new functionalities
that can be achieved by using only quantum information processing. The main theme of this section isabout (3), but we briefly explain (1) and (2). Postquantum cryptography does not require the power ofquantum information processing or quantum computers, but it is designed to guarantee its security evenagainst quantum computers. Quantum cryptographyrequires the power of quantum information processing or quantum computers to achieve cryptographic
functionalities, but its functionalities are the same as
those of classical cryptography. For example, we canachieve secure encrypted communication without thepower of quantum information theory, but we canenhance security by using this power. In contrast, (3)is cryptography with new functionalities that cannot
be achieved without using the power of quantum
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information theory. A typical example is data copy
protection or software copy protection (Fig. 2).
We can generate an unbounded number of copies ofdigital data. It is impossible to prevent the copying ofdigital data and software. However, this is the case inwhich we do not consider quantum information technology. In quantum information theory, there exists a
no-cloning theorem that states that copying an
unknown quantum state is impossible [11, 12]. By
applying this theorem to cryptography, we might beable to achieve data copy protection or software copy
protection. Currency is a type of data that we want toprevent from being copied. Quantum money was proposed as currency that can never be copied [13, 14].
Since current software is digital data, it is hard toprevent software piracy in principle and there is no
copy-protection method that guarantees security.
Provably secure software copy protection [14] makes
it impossible to generate a copy of software by using
cryptography and quantum technology. Achieving
secure software copy protection is one of our goals.
Copy-protection techniques have many applications
other than quantum money and secure software copy
protection. For example, it is possible to securely
delete (encrypted) data that were stored in a cloudstorage and prevent the cloud from reconstructing thedata [15]. It might be possible to securely implement
the right to be forgotten (General Data Protection
Regulation [16] Article 17). It is possible to leasesoftware in a limited time and make the functionality
unavailable after the software was returned [17]. Ourgroup is conducting research and development toachieve cryptography with new functionalities above
what can be achieved by using only the power ofquantum information [18].

90Feature Articles

4. Quantum repeater technologies forquantum networks
Current computation and communication technologies are all based on the rules of classical physics andcan only execute computation and communication
within the limits of classical physics. The same is true
for security. We can currently provide only security
within the limits of classical physics, but we can
expand the possibilities of security by using quantum
mechanics. For example, we enable eavesdropper
detection in key distribution [19] and an informationtheoretically secure and simple secure computing
protocol that uses only one server [20].
It is known that the resource for such quantum
mechanical effects as communication is a correlation
unique to quantum mechanics called entanglement.
To make security applications based on quantum
mechanics available on a global scale, it is necessary
to create entanglement and construct quantum networks in which entanglement can be shared over long
distances and in multiple locations (Fig. 3).
If we want to share the entanglement over long
distances, we cannot use conventional relaying methods because simple amplification is not possible dueto the property of quantum states; quantum statescannot be copied. Since the probability of directtransmission becomes exponentially smaller due tolosses, a method of relaying entanglement distribution is required. The following is a brief descriptionof the main points of the method. First, the directtransmission distance can be shortened by placing
repeaters at a distance that does not cause large loss,
thereby reducing the loss. However, a certain amountof loss and error is unavoidable, so multiple communications are executed redundantly at each repeater
point, and a process equivalent to quantum error correction is applied to them to enable transmission with
reduced loss and error. This is a fault-tolerant processing of entanglement communication and is called
entanglement distillation (purification) because it is
the process of extracting near-perfect entanglementfrom multiple noisy entanglements.
Our group is working on constructing quantum
repeaters using ultra-low loss nano-fiber cavities[21]. The ultra-low loss nano-fiber cavity consists of
two elements: an ultra-low loss tapered fiber andultra-low loss fiber Bragg grating. We are investigating methods of improving the performance of thequantum memory by using it as follows. By trapping
atoms, which are used as quantum memory, in thevicinity of a tapered fiber, which is much thinner than
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Entanglement

Measurement

Fig. 3. S chematic of entanglement sharing using aquantum repeater.

an ordinary fiber, we can enable photons through thetapered fiber and atoms to interact. By placing theentire repeater system inside the fiber, it is possible toreduce optical loss by eliminating the lossy process ofemitting photons out into free space to interact withatoms. By using a cavity structure with a fiber Bragg
grating, it is also possible to increase the probability
that photons emitted from the quantum memory will
be coupled into the fiber. This will increase the success probability of write and read operations on thequantum memory, improving the overall performanceof the repeater.
The realization of quantum networks using highperformance quantum repeaters will provide various
security applications, including those for diplomacy
and defense, handling genetic information, and financial institutions.
5. Conclusion
It is important to emphasize once again that faulttolerant and quantum repeater technologies, which
protect the data of quantum information and quantum
communication, are essential for the correct and safe
execution of quantum information processing [22].
There are many unexplored areas of architectures for
fault-tolerant processing in quantum information processing, and breakthroughs are expected throughfuture research. For the security applications of91

Feature Articles

quantum information processing, in addition tosecure secret communication and copy protection,
new applications such as quantum-secure computation and quantum-based reduction of communication
complexity are expected. Near-term quantum security, which is not yet so large in scale, is also a promising research theme.
References[1]

A. G. Fowler and C. Gidney, “Low Overhead Quantum Computation
Using Lattice Surgery,” arXiv:1808.06709, 2018.
[2] P. Das, C. A. Pattison, S. Manne, D. Carmean, K. Svore, M. Qureshi,
and N. Delfosse, “A Scalable Decoder Micro-architecture for Faulttolerant Quantum Computing,” arXiv:2001.06598, 2020.
[3] K. Fujii and Y. Tokunaga, “Fault-tolerant Topological One-way Quantum Computation with Probabilistic Two-qubit Gates,” Phys. Rev.
Lett., Vol. 105, No. 25, 250503, 2010.
[4] A. Davaasuren, Y. Suzuki, K. Fujii, and M. Koashi, “General Framework for Constructing Fast and Near-optimal Machine-learningbased Decoder of the Topological Stabilizer Codes,” Phys. Rev.
Research, Vol. 2, No. 3, 033399, 2020.
[5] Y. Ueno, M. Tanaka, Y. Suzuki, Y. Tabuchi, and M. Kondo, “Quantum
Error Correction with a Superconducting Decoder,” 2nd Workshop on
Quantum and Classical Cryogenic Devices, Circuits, and Systems(QCCC 2020), Dec. 2020.
[6] K. Heya, Y. Suzuki, Y. Nakamura, and K. Fujii, “Variational Quantum
Gate Optimization,” arXiv:1810.12745, 2018.
[7] S. Endo, S. C. Benjamin, and Y. Li, “Practical Quantum Error Mitigation for Near-future Applications,” Phys. Rev. X, Vol. 8, No. 3,031027, 2018.
[8] Y. Suzuki, S. Endo, K. Fujii, and Y. Tokunaga, “Quantum Error Mitigation for Fault-tolerant Quantum Computing,” arXiv:2010.03887,
2020.
[9] D. J. Bernstein, J. Buchmann, and E. Dahmen, “Post-quantum Cryptography,” Springer, 2009.
[10] C. H. Bennet and G. Brassard, “Quantum Cryptography: Public Key
Distribution and Coin Tossing,” Proc. of IEEE International Confer-

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Vol. 19 No. 6 June 2021

ence on Computers, Systems and Signal Processing, Bangalore, India,
Dec. 1984.
[11] W. K. Wootters and W. H. Zurek, “A Single Quantum Cannot Be
Cloned,” Nature, Vol. 299, pp. 802–803, 1982.
[12] D. Dieks, “Communication by EPR Devices,” Phys. Lett. A, Vol. 92,
No. 6, pp. 271–272, 1982.
[13] S. Wiesner, “Conjugate Coding,” ACM SIGACT News, Vol. 15, No.
1, pp. 78–88, 1983.
[14] S. Aaronson, “Quantum Copy-protection and Quantum Money,” Proc.
of 24th IEEE Conference on Computational Complexity, pp. 229–
242, Paris, France, July 2009.
[15] A. Broadbent and R. Islam, “Quantum Encryption with Certified
Deletion,” Proc. of 18th Theory of Cryptography Conference (TCC
2020), Nov. 2020.
[16] “Regulation (EU) 2016/679 of the European Parliament and of theCouncil of 27 April 2016 on the protection of natural persons withregard to the processing of personal data and on the free movement ofsuch data, and repealing directive 95/46/EC (General Data Protection
Regulation),” Official Journal of the European Union, Vol. 59, pp.
1–88, 294, 2016.
[17] P. Ananth and R. L. La Placa, “Secure Software Leasing,” CoRR,
abs/2005.05289, 2020.
[18] F. Kitagawa, R. Nishimaki, and T. Yamakawa, “Secure Software Leasing from Standard Assumptions,” CoRR, abs/2010.11186, 2020.
[19] C. H. Bennett and G. Brassard, “Quantum Cryptography: Public Key
Distribution and Coin Tossing,” Proc. of the International Conference
on Computers, Systems and Signal Processing, pp. 175–179, Bangalore, India, Dec. 1984.
[20] T. Morimae, “Measurement-only Verifiable Blind Quantum Computing with Quantum Input Verification,” Phys. Rev. A, Vol. 94, 042301,
2016.
[21] S. Ruddell, K. E. Webb, M. Takahata, S. Kato, and T. Aoki, “Ultralow-loss Nanofiber Fabry–Pérot Cavities Optimized for Cavity Quantum Electrodynamics,” Opt. Lett., Vol. 45, No. 17, pp. 4875–4878,
2020.
[22] Y. Tokunaga, Y. Suzuki, S. Endo, and R. Asaoka, “Fault-tolerant Technology for Quantum Information Processing and Its Implementation
Methods,” NTT Technical Review, Vol. 19, No. 5, pp. 40–44, May
2021.
h t t p s : / / n t t - r ev i ew. j p / a r c h ive / n t t t e c h n i c a l . p h p ? c o n t e n t s =ntr202105fa6.html

92Feature Articles

Yuuki Tokunaga

Distinguished Researcher, NTT Secure Platform Laboratories.
He received a bachelor’s degree from Kyoto
University in 1999, master’s degree from the
University of Tokyo in 2001 and Ph.D. in sciencefrom Osaka University in 2007. He joined NTT
in 2001, where he has been conducting research
toward fault-tolerant universal quantum computing and long-distance secure quantum network.

Yasunari Suzuki

Ryo Nishimaki

Distinguished Researcher, Cryptography
Research Laboratory, NTT Secure Platform
Laboratories.
He received a B.E. and M.I. from Kyoto University and a D.S. from Tokyo Institute of Technology in 2005, 2007, and 2010. He joined NTT
in 2007. His research work focuses on design andfoundation of cryptography. He is currently
researching cryptography and information security at NTT Secure Platform Laboratories.

Fuyuki Kitagawa

Researcher, NTT Secure Platform Laboratories.
He received a Ph.D. in science from the University of Tokyo in 2018 and joined NTT thesame year. He has been focusing on practicalquantum error correction and fault-tolerant quantum computing for achieving reliable quantum
systems. He is currently working on the development of fault-tolerant quantum computing.

Researcher, Cryptography Research Laboratory, NTT Secure Platform Laboratories.
He received bachelor’s, master’s, and Ph.D.
degrees in science from Tokyo Institute of Technology in 2014, 2016, and 2019. From 2016 to
2019, he was a research fellow of Japan Society
for the Promotion of Science. From 2019, he has
been with NTT Secure Platform Laboratories. He
is interested in the research of public key cryptography and provable security.

Suguru Endo

Sachi Tamechika

Researcher, NTT Secure Platform Laboratories.
He received bachelor’s and master’s degrees
from Keio University, Kanagawa, in 2014 and2016 and a Ph.D. from University of Oxford,
UK, in 2019. He joined NTT Secure Platform
Laboratories in 2020. His research interests focus
on hybrid quantum-classical algorithms, quantum error mitigation, and circuit quantum electrodynamics.

NTT Technical Review

Vol. 19 No. 6 June 2021

NTT Secure Platform Laboratories.
She received a B.S. and M.S. from Tokyo Metropolitan University in 2017 and 2019. She
joined NTT the same year, where she is working
on an experiment using cavity quantum electrodynamics.

93Regular Articles

Neutron-energy-dependent
Semiconductor Soft Errors
Successfully Measured for theFirst Time
Hidenori Iwashita, Hirotaka Sato, and Yoshiaki Kiyanagi
Abstract

Problems caused by neutron-induced soft errors in electrical devices are becoming increasingly
common in various applications. The neutron-energy-dependent soft-error rate is indispensable for
evaluating the frequency of such errors in different neutron environments. We observed the energydependent neutron-induced soft-error rates continuously over the energy range of 1–800 MeV at the Los
Alamos Neutron Science Center, USA. This measurement was made possible with a method wedeveloped that uses extremely fast circuits built into field-programmable gate arrays coupled with aneutron time-of-flight technique.
Keywords: soft error, cosmic rays, field-programmable gate arrays (FPGAs)

1. Introduction
Modern society’s infrastructures are becoming
increasingly dependent on digital technologies andare undergoing a digital transformation. Althoughpeople enjoy greater convenience in their everyday
lives, various issues such as software bugs in electrical device logic and security compromises havebecome major social problems. There are also random phenomena called bit errors in semiconductor
devices such as in large-scale integrated circuits(LSIs) including memory chips. Soft errors caused bycosmic rays are a type of bit errors [1], but there aremany cases in which the causes are unknown, making
them very difficult problems to solve. Neutrons generated by cosmic rays are currently the main cause ofsoft errors in semiconductor devices of electricalequipment used on the ground [2, 3]. When cosmic
rays arrive from outer space, they collide with oxygenor nitrogen nuclei in the atmosphere, generating various secondary particles by a spallation reaction(Fig. 1). Neutrons have particularly high penetrating
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Vol. 19 No. 6 June 2021

power because they are uncharged and can passthrough the concrete structures of buildings. Whenneutrons pass through a semiconductor device on anelectrical circuit board, they can interact with a silicon nucleus and generate secondary ionizing particles, though this is very rare. The ionizing particles
can reverse internal logic states in the chip, referred
to as a single event upset (SEU). The rate of SEUs per
device (unit area) becomes non-negligible as thedegree of LSI integration becomes greater. This isbecause the design rule, which is related to the minimum processing line width, becomes narrower eachyear, and the critical charge to cause an SEU lessens
along with the line width. Recent progress in larger
integration and increasingly finer microfabrication
technologies has resulted in a dramatic increase in theoccurrence of soft errors in contrast to hard errors thatpermanently disable semiconductor devices [4].
Figure 2 shows the relationship between the design
rule and failure in time (FIT), which is the number of
failures per billion hours per device, in static random
access memory (SRAM)-based field programmable94Regular Articles

Cosmic rays
Atmosphere(1) Nuclear reaction
in atmosphereHigh-energy particles

Destruction

Oxygen or
nitrogen nuclei

-mesonProtonMuon

Neutron

Neutrons
Building(2) Nuclear reaction
in electric equipment
NeutronSilicon nuclei

Electric
equipment

Secondary ions(3) Soft error(bit reverse)

Fig. 1. Mechanism of soft error.

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Vol. 19 No. 6 June 2021

100,000
Soft error
error
Soft
Failure rate per semiconductor(FIT/Device)gate arrays (FPGAs). The rate of multiple bit upsetsis increasing with narrowing design rules. For example, in a real-world information network consisting of
10,000 communication units, each with 5 of the
10,000 FIT LSIs in stacks, about 12 soft errors will
occur on a daily basis. At this rate, network operators
would not be able to handle all errors. Also, soft
errors may cause network equipment to be hung up,leading to breakdown in some network services. In a
worst case scenario, the breakdown can occasionallybecome widespread. Therefore, SEUs are not limited
to occurring in information network devices but also
in various other electrical devices. Consequently,
SEUs may have a serious impact when such devices
are incorporated into medical instruments, automobiles, airplanes, trains, and personal computers (PCs),
to name but a few.
Therefore, it is crucial to design and fabricate semiconductor devices and systems to minimize the SEU
error rate measured in FIT units to ensure the reliability and safety of these devices and systems. To
calculate the expected number of failures due to soft

Hard error
error
Hard

10,000

1000

100

10

1
350

300

250

200

150

100

50

0

Design rule (nm)Fig. 2. R elationship between the design rule and failure
rate.

95

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SEU cross-section (cm2/Mbit)

10−12

10−13

10−14

1

10
100
Neutron energy (MeV)

1000

section has been measured at only a few points in theneutron energy range from 1 to 176 MeV [5, 6] (Fig.
3). As a consequence, there are no data on SEU crosssections continuously covering a wide range of neutron energy using this method, so the whole picture of
the cross-section is yet to be clarified.
Therefore, we attempted to measure energyresolved SEU cross-sections by using the neutron
time-of-flight (TOF) technique for a wide neutronenergy range. Accordingly, we developed a method of
detecting errors in the desired time resolution using
FPGAs and measured SEU cross-sections using the
TOF technique at the Los Alamos Neutron Science
Center (LANSCE), USA.
2. Measurement methods

Fig. 3. C onventional technology (SEU cross-section
measurement results).

errors in various neutron environments (natural,
space, building, accelerator, nuclear plant, underground, etc.), the number of neutrons per unit time ateach neutron energy, and the SEU cross-section at
this energy are required for a wide energy range of
impinging neutrons. The SEU cross-section depending on the neutron energy σSEU(En) is defined as
σSEU (En) =NSEU(En)
,
Φ(En)

(1)

which identifies a neutron fluence Φ(En) as the total
number of neutrons per unit area impinging on thesemiconductor device and the total number of SEUs,
NSEU(En), generated by these neutrons. Specifically,
σSEU(En) indicates the probability that one neutron
per unit area causes a soft error. Note that the SEU
cross-section for each neutron energy will differ foreach semiconductor device. In addition, neutrons in
the natural environment and those generated byaccelerators have distinct energy distributions. Therefore, the soft error rate (SER) in a specific neutronirradiation environment can be defined as∞

SER = ∫0 σSEU(En)φ(En)dEn(2)using the neutron flux φ(En) (number of neutrons
with En crossing a unit area in a unit time) at eachneutron energy and σSEU(En). Thus, the SEU crosssection is the most important basic datum necessary
for calculating the failure rate of semiconductor
devices due to soft errors. However, the SEU crossNTT Technical Review

Vol. 19 No. 6 June 2021

2.1 TOF technique
The TOF technique makes it possible to determine
the neutron velocity v (i.e., En) by measuring theflight time of a neutron along a flight path with aknown length. In the sub-GeV region, neutrons havevelocities close to the speed of light; thus, we need toconsider the relativistic effects. The En is determined
as
m0 c2
m0 c2
− m0 c2 =− m0 c2 ,
2
v 2
L
1−
1−
c
ct
(3)

En =

()

()

where m0 is the neutron rest mass, v is its velocity, cis the velocity of light, L is the flight path length, andt is the neutron flight time. Using the TOF technique,
it is possible to determine the energy of the neutronthat caused a soft error by measuring the time atwhich the soft error occurred. The TOF of the subGeV is very short, for example 1.4 µs at 1 MeV and
79.3 ns at 800 MeV with the LANSCE L = 20 m
(Fig. 4). Therefore, we chose a duration of 8 ns for
detecting SEUs to obtain a time resolution of Δt/t =10% at 800 MeV (Fig. 5). However, it is impossible
to measure TOF in the desired time resolution using
conventional SRAM. Furthermore, because an ordinary SRAM reads data sequentially, it takes several
milliseconds to scan sufficient data for soft-error
detection. This makes it impossible to conduct nanosecond-order TOF measurements by using SRAM.
Even if many sets of SRAM and memory-readout
circuits are fabricated using on-chip SRAM in an
FPGA, it is impossible to scan several M bits in nanoseconds. Therefore, we designed circuits that can
96

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Detection circuit
Flight distance: 20 m

TargetNeutronSoft error
ProtonDuration of flight: 79.3 ns
Detected neutron
Energy: 800 MeV
Neutron energy can be obtained by measuring the neutron speed.

Fig. 4. Neutron TOF method.

10,000TOF (ns)

1000

100

10

1
1

10
100
Neutron energy (MeV)

1000

Fig. 5. TOF and neutron energy (flight over 20 m).

detect a soft error due to a malfunction in logic circuits composed of configuration random accessmemory (CRAM) that determines the logic of the
FPGA. In this case, determination of a CRAM bit
error is possible at the operating frequency of the
FPGA. It is also possible to monitor a capacity equivalent to several 10-M-bit FPGAs. We devised a circuitthat can detect an SEU in nanoseconds and conducted
SEU cross-section measurements of FPGAs depending on the neutron energy using the TOF technique.
2.2 S oft-error detection in nanoseconds using
FPGAs
We first considered using the cyclic redundancy
check (CRC) circuit, which can detect the CRAM
errors, built into modern FPGAs to obtain TOF information. An FPGA stores circuit design data in an
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Vol. 19 No. 6 June 2021

SRAM-based CRAM and program logic circuits andwiring using bits of the CRAM. When a CRAM bit isinverted by an SEU, it is immediately transmitted toa logic circuit or a wiring, which is not the effectintended by the programmer of the FPGA. Recent
FPGAs can detect bit errors by CRC to detect soft
errors of the CRAM. However, the neutron energy
cannot be specified with the TOF technique from the
CRC of a CRAM because a detection time of several
tens of milliseconds is required to check all the
CRAM bits. Therefore, we focused on any logic malfunction in the circuit caused by CRAM errors. Whena bit error occurs in a CRAM bit related to circuit
operation, the circuit operation changes immediately,
and a logic malfunction occurs. Since FPGA circuits
can operate at several hundred megahertz, a logic
malfunction can be detected in nanoseconds by97

Regular Articles

D Q
CLK

(2)

32bit all ”0”[0x0000_0000]
32bit all ”1”[0xFFFF_FFFF]

(3)

D

1

0

32bit all ”1”[0xFFFF_FFFF]

1

Error

=?

(6)

Equal (5)x 32

Registers 2[32bit]
MUX

32bit all ”0”[0x0000_0000]

Detection

Q

CLK

x 32

Clock
(1)

Registers 1[32bit]0

MUX

Flicker

D

x 32

Q

CLK

(4)

x 32

(a) Register comparator
FPGA(b) FPGA’s internal signals when soft error occurred in CRAM
0

4

8

SEU
12

16

20

Detection
24

28

32

36

Time (ns)(1) Clock(2) Flicker out(3) Registers 1 [32bit] 0x0000_0000 0xFFFF_FFFF 0x0000_0000 0xFFFF_FFFF 0x0000_0000 0xFFFF_FFFF 0x0000_0000 0xFFFF_FFFF 0x0000_0000 0xFFFF_FFFF(4) Registers 2 [32bit] 0x0000_0000 0xFFFF_FFFF 0x0000_0000 0xFFFF_FFFF 0x1000_0000 0xFFFF_FFFF 0x1000_0000 0xFFFF_FFFF 0x1000_0000 0xFFFF_FFFF(5) Equal(6) Error

Fig. 6. High-speed error-detection circuit.

programming user circuits to detect the malfunction.
For this purpose, we programmed a user circuit thathas a large number of registers and monitors.
The basic principle of this measurement is shown in
Fig. 6. This FPGA, which is also a device under test
(DUT), operates at 250 MHz and outputs an error
signal that triggers the TOF signal when a logic error
occurs due to a soft error. As shown in Fig. 6, registercomparator units (Fig. 6(a)) consist of two multiplexer units (MUXs), two 32-bit registers, and a comparator detecting a logic malfunction. Logic malfunction is detected by comparing the two output signalsof the MUXs. Figure 6(b) shows a timing diagram of
the FPGA’s internal logic at signal monitoring points(1) to (6) when a soft error occurred in the CRAM.
The output of the registers repeats all “0”(0x0000_0000) or all “1” (0xFFFF_FFFF) alternately in accordance with the flicker select signal. If noneof the comparison results match, the detection module asserts an error and outputs it as a TOF trigger
signal. The operation of each MUX is controlled by
the look-up table (LUT) in the FPGA. The registers
are all 32-bit ones, but we first focus on only one bitof them. The flicker signal is fed into one of the 4-bit
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Vol. 19 No. 6 June 2021

input lines in the LUT, and all the other three lines are
set to “0”. As a result, one of the two SRAM bits isselected; one is initially set to 1 and the other 0,
resulting in the time series of alternative “1” and “0”.
A corresponding bit pattern of the desired logic isstored in a 16-bit (= 24-bit) CRAM. When a condition is put into the 4-bit input lines, the result is output
to the 1-bit line. The result is then held by a flip-flop
circuit.
When a CRAM bit is inverted, therefore, an incorrect value is written to the register at the next clock
timing. There are two identical 32-bit registers, but
only one register output is affected by the soft error;
therefore, by comparing the two registers, the error is
detected with this circuit. When this circuit is operated with a 250-MHz clock, logic malfunction can bedetected within 8 ns. The neutron energy can then be
specified by obtaining the difference between thetime at which neutrons were generated and the timing((6) in Fig. 6) at which a logic malfunction was
detected in a few-nanosecond resolution.
2.3 Facilities
There are four requirements for an accelerator facility
98Regular Articles

106

ICE-House at LANSCE
Natural environment at New York

Neutron flux (n/cm2/s/MeV)

104
102
100
10−2
10−4
10−6
10−8
1

10
100
Neutron energy (MeV)

1000

Fig. 7. Neutron energy spectrum obtained at LANSCE.

to execute this measurement. The first is a pulsed
neutron source with a short pulse width. To measurehigh-energy neutrons using the TOF technique, theduration of the pulse of the accelerated particles
entering the target is preferably 1 ns or less with aflight path of about 20 m. Note that this requires abeamline through which you can directly view theneutron production target without a neutron moderator from the position of DUTs. The second requirement is a high-energy white neutron source. To measure a wide En range up to hundreds of mega electronvolts, the neutron source driven by a high energy
proton accelerator is indispensable. The third requirement is that the incident neutron energy spectrum
should be available or measurable within a specified
precision. It is crucial to calculate an SEU cross-section. The final requirement is that neutron intensity
should be high enough. In this experiment, it tooktime to obtain data with satisfactory statistical accuracy because the logic malfunction rate with our
method is lower than that of CRAM as a whole. In
addition, to obtain a precise energy-dependent crosssection by using the TOF technique, a very highintensity neutron source is required to obtain highstatistical accuracy in a short time bin for high energy
resolution. The best accelerator facility that satisfies
the above requirements is the ICE-House or ICE-II at
LANSCE [7, 8]. LANSCE is based on an 800-MeV
proton linac with relatively long pulse width but has
a storage ring to compress the beam. It uses a shortproton beam pulse of 125 ps. Figure 7 shows the
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neutron energy spectrum measured in a fission chamber installed 19.7 m from the target at LANSCE,
together with the neutron spectrum in a natural environment [9]. Thus, LANSCE has a neutron energy
spectrum close to that in the natural environment,with about four orders of magnitude higher neutron
flux.
3. Experiment
We conducted the experiment at the ICE-House in
LANSCE involving irradiating DUTs, which were
three types of commercially available FPGAs withdesign rules of 28, 40, and 55 nm. We measured logic
malfunctions as a function of neutron energy. The
experimental setup at the ICE-House is shown in
Fig. 8. The experimental area is separated into two
sections by thick concrete and polyethylene walls.
One of the sections contains the neutron beam (beamarea), in which the DUTs are placed. The yellow line
shows the neutron beam entering from the right andexiting to the left. The other section is equipped withall the monitoring equipment (controller board andPC). The fission chamber was installed at a distanceof 19.70 m from a tungsten neutron production target.
The FPGAs were installed at distances of 20.05,
20.10, 20.15 m.
The controller board calculates the time difference
between the proton pulse and error signal and executes
recovery control of the FPGAs. The controller board
outputs the time difference to the PC.
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Regular Articles

FPGAs for measuring
logical malfunction

20.15 m20.10 m20.05 m19.70 mFission chamber

Length from target

Beam path
FPGAs for measuring
logical malfunction
Shielding blocks

FissionchamberShielding blocks

Controller
board
PC

Fig. 8. Experimental setup at ICE-House.

4. Results and discussion
The TOF spectra of the number of logical malfunctionsof the three FPGAs are shown in Fig. 9. The total
number of logical malfunctions in each FPGA was asfollows: 28-mm FPGA, 12,713; 40-mm FPGA, 2894;
and 55-mm FPGA, 3719.
Figure 10 shows the CRAM SEU cross-sections
calculated from the measured logical malfunction
time distribution, number of CRAM errors, and neutron fluence [10, 11, 12]. The SEU cross-sections
tended to increase rapidly from 3 to 20 MeV andremain almost constant thereafter. There was a difference in the absolute value of the cross-sections
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among the three FPGAs, although they were similar.
In the energy range from 1 to 3 MeV, the differencein the cross-sections was significant. The device type
for the simulation conducted by Abe and Watanabe[13] was not the same as the devices used in thisexperiment, but the trend of the measured SEU crosssections was similar to that in their simulation. Fromtheir simulation, they found that SEUs below 5 MeV
are attributed to elastic recoils of oxygen and siliconions. They also found that the sharp increase in an
SEU cross-section appears near the threshold energies of the (n, p) and (n, α) reactions caused by secondary helium and hydrogen ions. Their simulation
showed that the sharp increase in gradient is enhanced100Regular Articles

Logical malfunction counts / 2.5 ns

250
FPGA 28 nm

200

FPGA 40 nm
FPGA 55 nm

150

100

50

0
0

500

1000
TOF (ns)

1500

Fig. 9. TOF spectra of logical malfunction counts.

Neutron-induced SEU cross section (cm2/Mbit)

10−8

10−9

10−10

FPGA 28 nm
FPGA 40 nm
FPGA 55 nm

10−11

10−12
1

10

100

1000

Energy (MeV)

Fig. 10. SEU cross section of CRAM.

by making the critical charge smaller. Generally, thesmaller the design rule, the smaller the critical charge
tends to be, but the 40-nm FPGA showed the largest
sharp increase. We infer the reason for this is that the
28-nm FPGA uses high-k metal gate (HKMG) technology. An HKMG achieves a high dielectric constant by having metal for the gate. As a result, both
the gate capacitance and critical charge increases, so
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it is speculated that the 28-nm FPGA had a milder
increase than the 40-nm one. To confirm this, it isnecessary to conduct measurements with an HKMG
and silicon dioxide gate devices under the same
design rules.

101Regular Articles

5. Conclusion
We measured the SEU cross-sections with highenergy resolution from 1 to 800 MeV at the ICEHouse of LANSCE with our method of measuring theneutron-induced SEU cross-sections for FPGAs
using the TOF technique. The results clarified thecomplete picture of the SEU cross-sections. The mostimportant contribution of these cross-sections is thatthey enable us to calculate the SERs in any type ofneutron environment.
References
[1]
[2]
[3]
[4]
[5]

E. Ibe, “Introduction,” in Terrestrial Radiation Effects in ULSI
Devices and Electronic Systems, 1st ed., pp. 1–12, Wiley, Hoboken,
NJ, USA, 2015.
J. F. Ziegler, “Terrestrial Cosmic Rays,” IBM J. Res. Dev., Vol. 40, No.
1, pp. 19–39, 1996.
E. Normand, “Single Event Upset at Ground Level,” IEEE Trans.
Nucl. Sci., Vol. 43, No. 6, pp. 2742–2750, 1996.
P. Hazucha and C. Svensson, “Impact of CMOS Technology Scalingon the Atmospheric Neutron Soft Error Rate,” IEEE Trans. Nucl. Sci.,
Vol. 47, No. 6, pp. 2586–2594, 2000.
K. Johansson, P. Dyreklev, B. Granbom, N. Olsson, J. Blomgren, andP. U. Renberg, “Energy-resolved Neutron SEU Measurements from22 to 160 MeV,” IEEE Trans. Nucl. Sci., Vol. 45, No. 6, pp. 2519–
2526, 1998.

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[6]

C. S. Dyer, S. N. Clucas, C. Sanderson, A. D. Frydland, and R. T.
Green, “An Experimental Study of Single-event Effects Induced inCommercial SRAMs by Neutrons and Protons from Thermal
Energies to 500 MeV,” IEEE Trans. Nucl. Sci., Vol. 51, No. 5, pp.
2817–2824, 2004.
[7] B. E. Takala, “THE ICE HOUSE: Neutron Testing Leads to Morereliable Electronics,” Los Alamos Science, pp. 96–103, 2006.
https://permalink.lanl.gov/object/tr?what=info:lanl-repo/lareport/
LA-UR-05-8767[8] P. E. Dodd, M. R. Shaneyfelt, J. R. Schwank, and G. L. Hash,“Neutron-induced Soft Errors, Latchup, and Comparison of SER Test
Methods for SRAM Technologies,” Technical Digest - International
Electron Devices Meeting, pp. 333–336, San Francisco, CA, USA,
2002.
[9] JEDEC Standard, “Measurement and Reporting of Alpha Particle andTerrestrial Cosmic Ray Induced Soft Error in Semiconductor
Devices,” JESD89A, 2006.
[10] H. Iwashita, G. Funatsu, H. Sato, T. Kamiyama, M. Furusaka, S. A.
Wender, E. Pitcher, and Y. Kiyanagi, “Energy-resolved Soft-error Rate
Measurements for 1–800 MeV Neutrons by the Time-of-flight
Technique at LANSCE,” IEEE Trans. Nucl. Sci., Vol. 67, No. 11, pp.
2363–2369, 2020, doi: 10.1109/TNS.2020.3025727.
[11] NTT press release, “Neutron Energy Dependence of Semiconductor
Soft Errors Was Successfully Measured for the First Time,” Nov. 25,
2020.
https://group.ntt/en/newsrelease/2020/11/25/201125a.html[12] NTT video, “Neutron Energy Dependence of Semiconductor Soft
Errors Was Successfully Measured” (long version), https://www.
youtube.com/watch?v=mhQmhzj6Zcg[13] S. Abe and Y. Watanabe, “Analysis of Charge Deposition andCollection Caused by Low Energy Neutrons in a 25-nm bulk CMOS
Technology,” IEEE Trans. Nucl. Sci., Vol. 61, No. 6, pp. 3519–3526,
2014.

102

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Hidenori Iwashita

Senior Research Engineer, NTT Space Environment and Energy Laboratories.
He received a B.S. and M.S. in nuclear engineering from Hokkaido University in 2006 and2008. He has been researching soft errors since2012 at NTT Network Service Systems Laboratories and has been engaged in research on a
mitigation technique of soft errors in space at
NTT Space Environment and Energy Laboratories since 2020.

Hirotaka Sato

Associate Professor, Laboratory of Applied
Neutron Beam Science and Engineering, Division of Applied Quantum Science and Engineering, Faculty of Engineering, Hokkaido University.
He received a B.E., M.E., and Ph.D. in quantum science and engineering from Hokkaido
University in 2006, 2008, and 2011. He was a
research fellow of Japan Society for the Promotion of Science from 2008 to 2011, postdoctoral
fellow in Japan Proton Accelerator ResearchComplex (J-PARC), Japan Atomic Energy
Agency from 2011 to 2012, assistant professor in
Hokkaido University from 2012 to 2020, and has
been an associate professor at Hokkaido University since 2020. He studied particle acceleratordriven neutron sources, neutron optical devices,
neutron detectors, and neutron imaging techniques. He applied neutron imaging techniques
he developed to materials science. He has been amember of several research collaborations forneutron-induced soft errors since 2012. Hereceived internal prizes for best student and best
young professor from Faculty of Engineering,
Hokkaido University, four best presentation
awards from the Atomic Energy Society ofJapan, young scientist award and best paper
award from the Japanese Society for Neutron
Science, best presentation award from the Society of Materials Science, Japan, and two best
paper awards from Japan Institute of Metals andMaterials.

NTT Technical Review

Vol. 19 No. 6 June 2021

Yoshiaki Kiyanagi

Honorable Professor at Hokkaido University
and Honorable Professor at Xi’an Jiaotong University, China.
He received a B.E., M.E., and Ph.D. from Hokkaido University in 1971, 1973, and 1993. He
was a professor at Hokkaido University from1995 to 2012. After retiring, he moved to Nagoya
University as a designated professor from 2013
and retired from that position in 2021. He has
been working on accelerator-based neutron
sources and developed the world’s most efficient
cold neutron source to use at Japan Particle
Accelerator Research Complex (J-PARC). He
constructed two neutron instruments for nuclear
data measurement and neutron imaging at
J-PARC. The imaging instrument is the world’s
first to use the pulsed nature of the neutron
source, which he proposed to J-PARC on thebasis of his pioneer work. He applied this method
to analyze the crystallographic characteristic ofJapanese swords. He engaged in the design ofneutron sources for boron neutron capture therapy and contributed to related activities at International Atomic Energy Agency. He joined a
research program at NTT to measure neutroninduced soft errors by using compact acceleratordriven neutron sources and supported measurements domestically and abroad. He twice
received the Best Paper Award from the Japan
Institute of Metals and Materials and the ScienceAward from Japanese Society for Neutron Science. He is an honorary member of the International Society for Neutron Radiography from
2018.

103

Global Standardization Activities

Recent Standardization Activities of
Optical Connectors in IEC
Ryo Koyama and Yoshiteru Abe
Abstract

Optical communication networks and datacenters worldwide use a huge number of optical connectors
made in many countries. Optical connectors are products that require precise components because adimensional error of only 1 μm can affect the optical signal quality. To ensure the compatibility of connectors, it is essential to internationally standardize the component shapes, connector performance, andthe measurement methods for testing them. This article introduces the standardization activities andrecent trends in optical connectors.
Keywords: optical connector, international standard, optical communication

1. Introduction
International standards for optical connectors aredeveloped by the International Electrotechnical Commission (IEC). The IEC was established in 1906 topromote international cooperation and communication on standardization and related matters in the fieldof electrical and electronic technology. The work
related to the development of the standard is carriedout by the technical committee (TC) and subcommittee (SC) established under it, and the standardizationfor optical connectors is discussed in TC 86 (Fibre
optics)/SC 86B (Fibre optic interconnecting devices
and passive components). As of February 2021, SC
86B published the second largest number of documents in IEC after TC 61 (Household appliancesafety), and the second largest number of documents
in work after TC 82 (Photovoltaic power generation).
Optical connector standardization activities are oneof the most active in IEC.
In the field of optical connectors, the single-fiber
coupling (SC) connector and multi-fiber push-on(MPO) connector developed by NTT have held the
top share of the market for more than 30 years. In
March 2021, both connectors received IEEE Milestone*1 certification [1]. Japan has also made a significant contribution to the standardization of opticalconnectors and has served as the secretariat of SC
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86B since 2003.
IEC TC 86/SC 86B consists of three working
groups (WGs), and standardization documents related to optical connectors are deliberated by WG 4
(Standard tests and measurement methods for fibre
optic interconnecting devices and passive components) and WG 6 (Standards and specifications forfibre optic interconnecting devices and related components). Although the International Telecommunication Union - Telecommunication Standardization
Sector (ITU-T) specifies the performance of opticalconnectors from the viewpoint of system requirements for communication networks, IEC documents
and ITU-T documents are standardized in cooperation to prevent them from becoming double standards.
The IEC standards for optical connectors are divided into four document series, as shown in Table 1:
basic test and measurement procedures, performancestandard, fiber optic connector interfaces, and connector optical interfaces. Figure 1 shows the specification scopes of the connector optical interfaces andfiber optic connector interfaces standards. Optical*1 IEEE Milestone: An award certified by the Institute of Electricaland Electronics Engineers (IEEE) to honor the historical achievements of technological innovation and has been internationallyacclaimed since its inception more than 25 years ago in the fields
of electricity, electronics, information, and communications.

104Global Standardization Activities

Table 1. Standard document series of optical connectors in IEC.
Document series number

Number of documents

Description

IEC 61300 Series

84

Basic test and measurement procedures

IEC 61753 Series

8

Performance standard

IEC 61754 Series

37

Fiber optic connector interfaces

IEC 61755 Series

15

Connector optical interfaces

FerruleOptical fiber(a) Scope of connector optical interfaces
Connector housing

Adapter
Spring(b) Scope of fiber optic connector interfaces

Fig. 1. Difference between connector optical interfaces and fiber optic connector interfaces.

connectors connect optical fibers by aligning andadhering the fiber cores. This connection method iscalled physical contact (PC) connection. An alignment part called a ferrule*2 is used to align the fibercores, and the connector optical interfaces standard
specifies the dimensions of the ferrule necessary forthe fiber cores to adhere to each other. The connector
housings and an adapter are rigidly coupled when theconnectors are connected, and the ferrules are pressedagainst each other using a spring built into the housing. The fiber optic connector interfaces standard
defines the dimensions and spring force of the housing required for this coupling of connector housingsand an adapter. Though PC connection and this coupling structure are adopted in almost all optical connectors, they are independent technologies. For
example, the same SC connector requires different
ferrules for single-mode optical fiber (SMF) and multimode optical fiber (MMF). The same ferrule is used
for different optical connectors such as SC and FC*3
connectors. Considering the actual products, IEC
standardized the PC connection and coupling strucNTT Technical Review

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ture separately as the connector optical interfaces andfiber optic connector interfaces standards, respectively.
2. Trends in standardization of
optical connectors
SC and Lucent (LC) connectors, which are used forconnecting single-core fibers in buildings, have been
widely used for connecting long-distance transmission optical fiber cables and transmission equipment.
MPO connectors, which are multi-core connectors,
have been extensively used for high-speed communication wiring connecting information-processing
equipment in datacenters. Outdoor use of optical connectors is also becoming widespread for connecting
wireless antennas to fiber optic cables. The communication capacity of SMF, which has supported*2 Ferrule: A connector component to align optical fibers. It has
holes of approximately the same size as the outer diameter of thefiber, and the optical fiber is inserted into the hole and bonded.
*3 FC stands for fiber connector.

105

Global Standardization Activities

Ferrule endface
Fiber
endfaceFerruleAlignment
direction

Fiber
Fiber core

Fiber core(a) Endface of SMF connector(b) Cross-sectional view of SMF connector(c) Endface of MCF (4-core) connector(d) Cross-sectional view of MCF connector

Fig. 2. Endfaces and cross-sectional views of optical connectors.

high-speed and large-capacity communication for along time, will reach its limit in the 2020s. The
research and development of optical fiber for space
division multiplexing (SDM), which is expected toenable large-capacity transmission over SMF, hasrecently been conducted. In the standardization of
optical connectors, a new standardization was proposed for use in datacenters and outdoors, and activities related to the standardization of optical fibers for
SDM are ongoing.

characteristics that affect optical signal quality, but
the farther the fiber core is from the center, the more
precise rotational alignment and larger spring force
are required to ensure sufficient signal quality. For
this reason, it is important to evaluate the connection
loss and return loss of optical connectors for MCF
when deciding the core configuration of MCF. NTT
aims to standardize optical fibers, optical cables, andoptical connectors for SDM, but is promoting thestandardization of these two measuring methods first.

2.1 T rends in standardization of test and measurement procedures
The standardization of measuring methods of connection loss and return loss has been promoted since2020 for optical connectors of multi-core optical fiber(MCF), which is one of optical fibers for SDM.
Figure 2 shows the SMF and MCF connector endfaces and their cross sectional views when connected.
Since the optical connector for SMF has a fiber coreat the center of the connector endface, the center axisof the connector is aligned only horizontally and vertically to reduce connection loss. On the other hand,
MCF has a fiber core at the periphery, so the rotational direction must be adjusted. In optical connectors, the endfaces of the connectors are pressedagainst each other using a spring, and the fiber coreadheres to ensure a sufficient amount of return loss.
Connection loss and return loss are important optical

2.2 T rends in standardization of performancestandards
The performance standard for optical connectors
specifies optical characteristics, such as connection
loss and wavelength characteristics, mechanical characteristics, such as tensile resistance and impact resistance, and environmental resistance to temperatureand humidity in the installation environment. Highspeed wireless devices, such as mobile antennas andwireless local area networks, have recently been
installed outdoors, and demand for optical connectors
with environmental resistance for outdoor use isincreasing. Table 2 lists the environmental categories
in the IEC optical connector standardization revisedin 2018. Before the revision, there were four categories, but the category OP+, which assumes outdoor
installation in a more severe climate environment,
and CHD, OPHD, OP+HD, and IHD, which assume electric

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Table 2. Environmental categories for optical connectors in IEC.
Environmental category

Circumstance

Temperature and humidity condition

Category C

Indoor controlled condition

Temperature –10°C to 60°C
Humidity 5% to 93%

Category OP

Outdoor protected by a sealed
closureTemperature –25°C to 70°C
Humidity 0% to 95%

Category OP+

Outdoor protected by a sealed
closure in extreme climate

Temperature –40°C to 75°C
Humidity 0% to 95%

Category I

Industrial condition

Temperature –40°C to 70°C
Humidity 0% to 95%

Category E

Extreme condition

Temperature –40°C to 85°C
Humidity 0% to 100%

Category CHD

Indoor controlled condition settledwith electric devices

Temperature –10°C to 70°C
Humidity 5% to 93%

Category OPHD

Outdoor protected by a sealed
closure settled with electric devices

Temperature –25°C to 85°C
Humidity 0% to 95%

Category OP+HD

Outdoor protected by a sealed
closure in extreme climate settledwith electric devices

Temperature –40°C to 85°C
Humidity 0% to 95%

Category IHD

Industrial condition settled withelectric devices

Temperature –40°C to 85°C
Humidity 0% to 95%

Added in 2018

parts as heat sources in each environment have been
added, now totalling nine categories. Optical connectors had generally been used indoors, so most of theperformance standard adopted the environmental
conditions of category C. However, from 2020, the
new standardization work of connector performancewith the environmental conditions of category
OP+HD, which is the highest temperature, started.

application and the optical characteristics that can beachieved are taken into consideration, and the standardization is carried out by dividing documents into
16 cores, 24 cores, and 32 cores. Twenty-four coresand 32 cores were enacted in 2017 and 2019, and 16
cores are expected to be enacted in 2022. In addition,
standardization work for 36 cores is scheduled to
begin in 2021.

2.3 T rends in standardization of fiber optic connector interfaces
The fiber optic connector interfaces standard mainly specifies the coupling structure of the connector
plug and connector adapter and the spring force thatpresses the ferrule endfaces against each other.
Figure 3 shows the coupling mechanisms of an SC
and MPO connectors. With the recent increase in
speed of communication wiring in datacenters, thestandards with more fiber cores than the conventional
12 cores have been actively standardized for MPO
connectors. As mentioned above, optical connectors
require physical contact between fiber cores to ensurea sufficient amount of return loss, and a larger springforce is required as the number of fiber cores in the
MPO connector increases. Since the MPO connector
has an angled endface, if the spring force is increased,a shear force is generated, the alignment of the fibercore deviates, and connection loss deteriorates.
Therefore, the number of cores required for each

2.4 T rends in standardization of connector optical interfaces
The connector optical interfaces standard mainly
specifies the position of the fiber core relative to thealignment datum of the ferrule. Figure 4 shows theendface of the zirconia ferrule used in an endface SC
connector and mechanical transferable (MT) ferrule
used in the MPO connector. Zirconia ferrules use acomponent called a split sleeve to align the outer
diameter of the ferrule to the same position, thus
defining the range of the fiber core relative to the ferrule center. Since the MT ferrule is aligned by inserting a guide pin into two guide holes, the fiber core
position is defined by the midpoint of the line connecting the two guide hole centers. The connector
optical interfaces standard defines those for standard
connectors used in ordinary optical communications
and those for reference connectors used for highprecision connection measurement of optical connectors. As the use of MPO connectors in datacenters has

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Global Standardization Activities

Guide-pin

Plug

AdapterConnector housing
Zirconia ferrule

MT ferrule
Plug

SpringPlug

MT ferrule
Spring force and angled endface cause
sheering deformation.

Adapter(a) SC connector(b) MPO connector

Fig. 3. Coupling mechanism of SC and MPO connectors.

Range of fiber core position
Ferrule endface

Fiber endface

Fiber core

Ferrule endface
Fiber endface

Fiber core

Datum point(a) Zirconia ferrule

Guide-pin

Datum point

Range of fiber core position(b) MT ferrule

Fig. 4. Fiber core positions of zirconia and MT ferrules.

recently expanded, the number of connector suppliers
has increased, and it has become necessary to accurately measure the loss of MPO connectors. MPO
reference connectors are not currently standardized,
so IEC started to establish new optical compatibility
standards for MPO reference connectors in 2019. In
theory, the maximum error in the fiber core position
for the MT ferrule for the reference connector shouldbe less than 1 μm, but since this error exceeds themeasurement accuracy of the current fiber core position, there is no measurement method to confirm thiseven if it is specified. Therefore, NTT proposed amethod for ferrule specification using fiber hole position with higher measurement accuracy and connector selection through a connection loss test.
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3. Future outlook
The increasing use of optical wiring in datacentersand high-speed wireless devices and efforts to standardize optical connectors for multi-fiber and outdoor use are expected to continue. In the future, optical wiring is expected to be used on substrates in
information equipment and inside automobiles inplace of the conventional metal wiring to further
speed up information processing, so the standardization of a higher density optical connector andimproved environmental resistance optical connector
will become important. In optical communications
applications, the standardization of optical connectors for connecting SDM transmission fibers is
108

Global Standardization Activities

expected to advance due to the development of SDM
transmission technology and the progress of its standardization at ITU-T.

Ryo Koyama

Senior Research Engineer, NTT Access Network Service Systems Laboratories.
He received a B.S. and M.S. in precision engineering from the University of Tokyo in 2001 and2003. In 2003, he joined NTT Access Network
Service Systems Laboratories, where he has been
engaged in research on optical fiber wiring andsplicing techniques for optical access networks.
He is an assistant secretary of the IEC SC 86B
and member of the Institute of Electronics, Information and Communication Engineers (IEICE)of Japan.

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Vol. 19 No. 6 June 2021

Reference[1]

IEEE Milestones: “Physical Contact Push-Pull Technology for Fiber
Optic Connectors, 1986,” http://ieeemilestones.ethw.org/
Milestones:Fiber_optic_connectors

Yoshiteru Abe

Senior Research Engineer, NTT Access Network Service Systems Laboratories.
He received a B.E., M.E., and D.E. in information science and electrical engineering from
Kyushu University, Fukuoka, in 1996, 1998, and2005. In 1998, he joined NTT Photonics Laboratories and has been engaged in the research of
optical connectors. He is a member of the IEC SC
86B and IEICE.

109

Practical Field Information about
Telecommunication Technologies
Practical Field Information about Telecommunication Technologies

Sulfur Damage and Its
Countermeasures in
Telecommunication Equipment
and Facilities
Technical Assistance and Support Center, NTT EAST
Abstract

This article introduces cases of corrosion caused by hydrogen sulfide in telecommunication equipment
and facilities and countermeasures against it. This is the sixty-fourth article in a series on telecommunication technologies.
Keywords: hydrogen sulfide, sulfur damage, corrosion

1. Introduction
Telecommunication facilities, such as utility poles(Fig. 1), are installed throughout Japan and exposed
to various natural phenomena. These facilities arecomposed of various materials, such as metals, plastic, and concrete, and gradually deteriorate due tocorrosion and abrasion caused by the surrounding
environment. In coastal areas, for example, salt damage—which is corrosion caused by particles of sea
salt being blown by strong winds and landing onto
telecommunication facilities containing metal—is awell-known phenomenon. In Japan, salt damage isunavoidable because of the long coastline. Japan is
also a volcanic country, having numerous hot springs.
In many of these areas, hydrogen sulfide (H2S),
which is a gas containing sulfur, is emitted from these
hot springs. Since H2S is highly corrosive, it can deteriorate not only outdoor telecommunication facilities
but also indoor ones. This type of corrosion is called
sulfur damage. Where sulfur damage is severe, terminal equipment fails every few months, so maintenance operations to fix such failures are burdensome.
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In response to on-site requests, the Technical Assistance and Support Center (TASC), NTT EAST, hasinvestigated instances of sulfur damage on outdoor
and indoor equipment and facilities. This article
introduces the mechanism of sulfur damage, actual
cases of sulfur damage to telecommunication equipment and facilities, and countermeasures against it.
2. Mechanism and actual cases of sulfur damage
in telecommunication equipment and facilities
2.1 Mechanism of sulfur damage
The corrosion reaction that causes sulfur damage
occurs when a water film is formed on the surface ofa material by condensation or moisture adsorption.
As shown in Fig. 2(a), when H2S is absent, the corrosion of iron is caused by oxygen in the atmospheredissolving in the water film, followed by reduction of
the dissolved oxygen on the surface of the iron andsimultaneous dissolution of the iron. When sea salt isalso dissolved in the water film, the corrosion rate ofiron will increase due to the increased electrical conductivity of the water film. When there is H2S present
110Practical Field Information about Telecommunication Technologies

Office buildings,
condominiums, etc.

NTT building

Manholes: 700,000

T

Utility poles: 12 million

Fig. 1. Telecommunication equipment and facilities exposed to natural phenomena.

(a) When H2S is absent

Atmosphere(b) When there is H2S*The reaction described in (a) proceeds at thesame time
H2S

Atmosphere

O2
O2 Dissolution

Water film

H2S

Water film

Dissolution
Dissociation

Diffusion
Fe2+ + 2e−
Oxidation(anode reaction)Fe

Fe2+ + 2e−

HS−

H+

S2−

O2 + 2H2O + 4e−
 4OH−
Iron (Fe)

Reduction (cathode reaction)
Iron (Fe)Fig. 2. Corrosion mechanism.

(Fig. 2(b)) in addition to the reactions illustrated inFig. 2(a), the H2S dissolves and dissociates in thewater film to produce H+ ions, which results in anacidic environment in the water film. This acidity
accelerates the dissolution of iron and results in ahigh corrosion rate.
2.2 Actual cases of sulfur damage
2.2.1 Sulfur damage to outdoor facilities
Examples of sulfur damage to outdoor facilities at
a hot-spring area are shown in Fig. 3. Significant rusting (reddish brown) was found on the metal bands at
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the lower part of the guy-line rod and scaffolding
bolts on the utility pole. Thinning can be seen in thecentral part of the guy-line rod, so the rod may breakwhen corrosion progresses. Although this type of corrosion can be caused by either salt or sulfur damage,since this hot-spring area is located in a mountainous
area far from the coast, the effect of salt damage isconsidered small. Moreover, measurements of gas
concentration at the locations shown in Figs. 3(a) and(b) detected H2S at 1.5 ppm (parts per million) and
0.9 ppm, respectively. The above corrosion phenomena are thus considered to be sulfur damage, the main111

Practical Field Information about Telecommunication Technologies(a) Lower part of guy-line rod(b) Concrete utility poleFig. 3. Examples of sulfur damage to outdoor facilities.

factor of which is H2S. The regulation value for atmospheric concentration of H2S stipulated by the Offensive Odor Control Law is 0.06 to 0.2 ppm [1], and theIndustrial Safety and Health Act stipulates that theconcentration of H2S should be less than 1 ppm toensure a safe working environment [2]. Accordingly,
the measured H2S concentrations (1.5 and 0.9 ppm)
at these facilities indicate that H2S exists at high concentrations at those locations.
2.2.2 Sulfur damage to indoor equipment
The corrosion rate of metals in an indoor environment is generally lower than that in an outdoor environment because the intrusion of sea-salt particles
and H 2S is hindered. However, if indoor spaces(rooms, etc.) are not sufficiently sealed, corrosion
may occur due to the intrusion of sea-salt particles or
H2S. Since H2S is a gas, it is difficult to completely
prevent it from entering indoor spaces.
TASC has conducted a number of field investigations of indoor equipment after receiving requests fortechnical consultations from service personnel. An
example of sulfur damage to indoor equipment isshown in Fig. 4, which illustrates sources of H2S(Fig. 4(a)), examples of metal corrosion in indoor
equipment (Fig. 4(b)), and micrographs of a circuitboard inside a piece of terminal equipment (Fig.
4(c)). In this example, the concentrations of H2S near
the hot-spring-water vat and fumaroles, which arethought to be the sources of H2S, were 0.1 and 0.9
ppm, respectively. It was also confirmed that metal
fixtures, such as windows and faucets, were significantly corroded in the indoor environment, and it isconsidered that the corrosion is caused by the intrusion of H2S from outdoors.
In the other case investigated by TASC, a ppb (parts
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per billion, where 1 ppb = 1/1000 ppm) level of H2S
concentration was detected in indoor environments.
From the results of scanning electron microscopy energy dispersive X-ray spectrometry (SEM-EDS)
analysis, the main component of the corrosion depicted in the figure was sulfide, which indicates that areaction between the metal and H2S had occurred.
Black corrosion was found on copper wiring andaround through holes by microscopic observation ofa circuit board collected from a faulty piece of terminal equipment installed in the same indoor space.
SEM-EDS analysis of this black corrosion revealed
that it contained sulfur in a similar manner to theindoor metal fixtures described above, and X-raydiffraction analysis of the corrosion identified themain component as copper sulfide. When the copper
wiring pattern on a circuit board is corroded by H2S
and becomes copper sulfide, it grows on the circuitboard and connects to adjacent wiring, through holes,
etc. It is thought that since the copper sulfide is conductive, a short circuit occurred between the wiring
and through holes, which should not be connected,
causing the equipment failure.
3. Countermeasures against sulfur damage
3.1 B
 asic requirements for countermeasuresagainst sulfur damage
As the installation standard for terminal equipment,
JEITA IT-1004 (Standard for Operating Conditionsof Industrial Computer/Control System) of the Japan
Electronics and Information Technology Industries
Association [3] recommends controlling H2S concentration to 3 ppb or less. There are several methods ofsuppressing corrosion caused by H2S, as listed in112Practical Field Information about Telecommunication Technologies(a) Sources of H2S
Hot-spring-water vat

Fumarole(b) Corrosion under indoor conditions
Metal fittings ofwindow

Water faucet(c) Circuit board surface

Through hole

Wiring and through holes

Fig. 4. Examples of sulfur damage to indoor equipment.

Table 1. M ethods of suppressing corrosion caused by sulfur and their application to telecommunication equipment andfacilities.
Methods of suppressing corrosion

Application to telecommunicationequipment and facilities

Application status and reasons for judgment

Selection of appropriate materials
Difficult(use materials with low reactivity with H2S)

Steel and copper currently in use are very versatile,and it is difficult to select alternative materials.

Isolation from the environment(suppresses contact with H2S)

Applicable

Outdoor facilities: Painting and plating
Indoor equipment: Coating surface of circuit board

Control environmental conditions(reduce H2S concentration)

Applicable

Install equipment in an enclosed space
Use gas adsorbent

Electrochemical control such as using
sacrificial electrodes

Difficult

Difficult to implement for a large number of facilities

Table 1. Taking costs and other factors into consideration, the basic requirements of countermeasuresagainst sulfur damage to telecommunication equipNTT Technical Review

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ment and facilities were determined as suppressing
contact with H2S and reducing H2S concentration.

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Practical Field Information about Telecommunication Technologies

H2S
adsorbent

Fig. 5. E xample countermeasure against sulfur damage tooutdoor telecommunication facilities (metal bands
with powder coating).

3.2 C
 ountermeasures to suppress corrosion due
to sulfur outdoors
Since concentration of H2S is higher outdoors thanindoors, namely, at the ppm level, countermeasures
are required to provide higher corrosion protection
performance. To meet this requirement, it is necessary to ensure that outdoor facilities and equipment
are prevented from coming into contact with H2S.
One way to prevent contact is to coat the surface ofthe base metal with a paint that has stronger adhesion.
By increasing the adhesion between the paint coating
and base metal, it is possible to suppress (i) directcontact between H2S and the metal and (ii) the adhesion of moisture (water film) containing H2S to themetal. Therefore, it is possible to reduce the occurrence of sulfur damage. An example of metal bands
coated with a powder coating, which has stronger
adhesion and higher corrosion resistance than conventional coatings, attached to a concrete utility poleis shown in Fig. 5.
3.3 C
 ountermeasures to suppress corrosion due
to sulfur indoors
An example of a countermeasure against sulfur
damage to indoor telecommunication equipment isshown in Fig. 6. The concentration of H2S can be
reduced by installing the terminal equipment inside asealable acrylic box and placing H 2S adsorbent
inside. In fact, a customer who had been experiencing
failures of terminal equipment every two months or

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Fig. 6. C ountermeasure against sulfur damage to indoor
telecommunication equipment.

so has been free of failures for more than 10 months
after starting to use an acrylic box.
4. Conclusion
Effective countermeasures to protect telecommunication equipment from sulfur damage is to (i) preventthe equipment from coming into contact with H2S
and (ii) reduce the concentration of H2S in the vicinity of the equipment. Housing indoor equipment inacrylic boxes containing H2S adsorbent has been
implemented. For outdoor facilities, a powder coating, which provides better corrosion protection thanconventional zinc plating, can be used. Applying
these countermeasures will extend the life of telecommunication equipment and facilities.
TASC will continue to promote technical-cooperation activities to solve problems in the field, such as
those related to degradation of equipment and facilities due to sulfur and salt damage. Through these
activities, we will contribute to improving the quality
and reliability of telecommunication services.
References
[1]
[2]
[3]

Website of the Ministry of the Environment, Offensive odor control
law (in Japanese), https://www.env.go.jp/hourei/10/000013.html
Website of the Ministry of Health, Labor and Welfare, Laws and regulations concerning chemical substances (in Japanese), https://www.
mhlw.go.jp/content/11303000/000541391.pdf
JEITA IT-1004: Standard for Operating Conditions of Industrial Computer/Control System (in Japanese), https://home.jeita.or.jp/is/
publica/standard/IT-1004.pdf

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External Awards
Activity Contribution Award
Winner: Jun Terada, NTT Device Technology Laboratories and NTT
Device Innovation Center
Date: March 11, 2021
Organization: The Institute of Electronics, Information and Communication Engineers (IEICE) Electronics Society

taxial Ferromagnetic Oxide.”
Published as: K. Takiguchi, Y. K. Wakabayashi, H. Irie, Y. Krockenberger, T. Otsuka, H. Sawada, S. A. Nikolaev, H. Das, M. Tanaka, Y.
Taniyasu, and H. Yamamoto, “Quantum Transport Evidence of Weyl
Fermions in an Epitaxial Ferromagnetic Oxide,” Nat. Commun., Vol.
11, 4969, Oct. 2020.

For his contribution as a director of general affairs in Electronics
Society.

IEEE SSCS Japan Industry Contribution Award
Winner: Jun Terada, NTT Device Technology Laboratories and NTT
Device Innovation Center
Date: March 17, 2021
Organization: IEEE Solid-State Circuits Society Japan/Kansai
Chapter

IPSJ Journal Specially Selected Paper
Winners: Masamichi Hosoda, NTT Smart Data Science Center/NTT
Service Evolution Laboratories; Hiroshi Sakamoto and Tomoki
Murakami, NTT Access Network Service Systems Laboratories;
Tadashi Mouri, NTT Service Evolution Laboratories; Akira Nakayama, NTT Research and Development Planning Department; Tomoaki
Ogawa, NTT Access Network Service Systems Laboratories; Masaru
Miyamoto, NTT Smart Data Science Center/NTT Service Evolution
Laboratories
Date: March 15, 2021
Organization: Information Processing Society of Japan (IPSJ)
For “2D Position Estimation for Wireless LAN Terminals by theAccess Point Using Distributed Antenna System.”
Published as: M. Hosoda, H. Sakamoto, T. Murakami, T. Mouri, A.
Nakayama, T. Ogawa, and M. Miyamoto, “2D Position Estimation
for Wireless LAN Terminals by the Access Point Using Distributed
Antenna System,” IPSJ Journal, Vol. 62, No. 3, pp. 946–958, Mar.
2021.
Research Encouragement Award
Winner: Hiraku Toida, NTT Basic Research Laboratories
Date: March 16, 2021
Organization: Superconductivity Division of the Japan Society ofApplied Physics
For “Electron Paramagnetic Resonance Spectroscopy Using aSingle Artificial Atom.”
Published as: H. Toida, Y. Matsuzaki, K. Kakuyanagi, X. Zhu, W. J.
Munro, H. Yamaguchi, and S. Saito, “Electron Paramagnetic Resonance Spectroscopy Using a Single Artificial Atom,” Commun.
Phys., Vol. 2, 33, Mar. 2019.
Young Researcher Best Presentation Award
Winner: Kosuke Takiguchi, NTT Basic Research Laboratories
Date: March 16, 2021
Organization: The 49th Autumn Meeting of the Japan Society ofApplied Physics

For his contribution to activities of the Solid-State Circuits Society
Japan in promoting outstanding papers written by researchers in thecorporate sector in the International Solid-State Circuits Conference.
The Commendation for Science and Technology by the
Minister of Education, Culture, Sports, Science and Technology, Prize for Science and Technology (Development
Category)
Winners: Hiroyuki Oto and Shinya Hasegawa, NTT DOCOMO;
Yasuyuki Uchiyama, DOCOMO Technology; Kazuaki Obana, NTT
Smart Data Science Center; Yoshihiro Nakajima, NTT DOCOMO
Date: April 14, 2021
Organization: Ministry of Education, Culture, Sports, Science andTechnology
For the commercial deployment of network functions virtualization technology enabling inter-operability with multi-vendor solutions.
ITU-AJ Encouragement Award
Winner: Taiji Sakamoto, NTT Access Network Service Systems
Laboratories
Date: May 17, 2021
Organization: The ITU Association of Japan
Dr. Sakamoto promoted the development of high-speed opticalfiber and submarine optical communication systems under Questions
5 and 8 in ITU-T Study Group 15. He has submitted more than 30
contributions to enable Japanese technologies to be reflected in international standards and led the drafting of three ITU-T Recommendations as the editor. His contributions are especially noteworthy inrecommending G.654.E (High Speed Long-Haul Optical Fiber) andincorporating Japan’s technology into the recommendation. He is
expected to continue to play an important role in international standardization activities in the future.

For “Quantum Transport Evidence of Weyl Fermions in an Epi-

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