NTT Technical Review

March 2023 Vol. 21 No. 3

View from the Top

Masaaki Moribayashi, Representative Member of the Board, President and CEO, NTT WEST

Front-line ResearchersTatsuaki Okamoto, NTT Fellow, NTT Social Informatics Laboratories

Rising ResearchersAtsushi Nakamura, Distinguished Researcher, NTT Access Network Service Systems
Laboratories

Feature Articles: Keynote Speeches at NTT R&D Forum—Road to IOWN 2022
Akira Shimada, President and Chief Executive Officer, NTT Corporation

Atsuko Oka, Executive Vice President, Head of Research and Development Planning
Department, NTT Corporation

Regular Articles
Over 100-Tbit/s Ultra-wideband Wavelength Division Multiplexed Transmission Technologies
for Future Optical Transport Network Systems

Global Standardization Activities


Report of the ITU Plenipotentiary Conference 2022 (PP-22)

Information


Report on NTT R&D Forum—Road to IOWN 2022

External Awards/Papers Published in Technical Journals and Conference Proceedings

View from the Top

Let’s Focus on the Now Regardless ofHistory or Background and Take on
New Challenges with ICT from a
Global Perspective
Masaaki Moribayashi
Representative Member of the Board,
President and CEO, NTT WEST
Abstract

NTT WEST is striving to solve social issues in the region where it operates by supporting the digital transformation of regional industries andcommunities. The company is also taking on challenges in new areas andcreating innovations by using cutting-edge information and communication
technologies toward building a sustainable society of well-being. We asked
Masaaki Moribayashi, CEO of NTT WEST, about his vision and attitude as
top management.
Keywords: ICT, DX, co-creation

2023 will be a critical year
—It’s been two years since our last interview, and thisis your third time in total. The last interview waswhen you were in London during the COVID-19 pandemic. How does it feel to be back to Japan?
Although remote work has taken root in society
after the COVID-19 pandemic, people are also
returning to the office as an option, and opportunities
to meet face-to-face with customers and partners aregradually increasing. Considering that trend, I feelthat society has changed from what it was before thepandemic.
After returning to Japan in June 2022, I’ve beenworking in western Japan for the first time in 30
years. I was with NTT Communications from 1999,
the year it was founded, until 2019. With the exception of the years from 2016 to 2018, I was consisNTT Technical Review

Vol. 21 No. 3 Mar. 2023

tently engaged in international business, including
secondments to overseas companies. From 2019 to2022, I was working in London for NTT Ltd. andmore than half of my life at NTT has been spent
involved in international business mainly related tooverseas bases. For that reason, some people might
be concerned about whether I am able to fit into
domestic business, particularly, for a reginal company like NTT WEST, but I assure you that I’m working
without any sense of discomfort or resistance.
Of course, I realize that business in the westernJapan region has changed dramatically over the past
30 years, and our customers have changed as well.
However, from a global perspective, Japan is one
region of the world, and regarding information andcommunication technology (ICT), the issues faced bydomestic companies such as NTT EAST and NTT
WEST are almost the same as those faced globally interms of networks, security, cloud computing, digital
1View from the Top

transformation (DX), and so on. Therefore, I think I
can make use of my experience. For example, we cancollaborate directly with global partners by taking
advantage of the relationships that I have formed during my time at NTT Ltd. and NTT Communications.
In 2022, with the completion of the new headquarters of NTT WEST, NTT WEST i-CAMPUS, we
opened an open-innovation facility called
QUINTBRIDGE, for solving social issues and creating a future society with our partner companies.
Since the opening of QUINTBRIDGE, more than
50,000 people have visited and more than 240 events
have been held. We have also started a future co-creation program, called “Future-Build,” and received
more than 100 proposals from domestic and foreign
ventures in the four fields of health, lifestyle, economy, and environment and are investigating the commercialization of six of such proposals. We plan toprovide the partner companies at QUINTBRIDGE
business-matching opportunities with NTT WEST
Group companies, NTT Group companies inside andoutside of Japan, venture companies in the West
Coast of the USA and Israel, and major IT companies
to facilitate collaboration and co-creation.

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Vol. 21 No. 3 Mar. 2023

—The knowledge you have acquired while working in
the global market and your solid personal network
are very reassuring. Could you tell us about the current business environment and your vision for 2023?
Social conditions have changed significantly suchas semiconductor shortages and soaring energy prices. In the field of information and telecommunications, the importance of the infrastructure supporting
information and telecommunications is increasing associal life is transformed in light of the COVID-19
pandemic, and the trend toward digitization andonline access is accelerating and taking root in all
aspects of business and daily life.
With such a business environment as a backdrop, atmy presidential inaugural press conference in June
2022, I raised the slogan 伝新人輪 (den-shin-jinwa), which is composed of the Japanese kanji characters mimicking the sound of the words 電信電話
(den-shin den-wa, i.e., “telegraph and telephone”).
The first character, 伝 (den, i.e., “tradition”), represents our desire to preserve and refine NTT’s traditions and technologies. The second character, 新(shin, i.e., “new”), represents taking on new challenges viewed from a global perspective. The third
character, 人 (jin, i.e., “people”), represents our connections with all types of people, including employees, customers, and the local community, and theimportance we place on people. The fourth character,
輪 (wa, i.e., “circle”), expresses our desire to expand2

View from the Top

the circle of co-creation with partners.
The year 2023 will be a critical year for NTT
WEST—as we transform from our past image as atelephone, optical, and telecommunications company
to an advanced, innovative, and attractive company
that leverages artificial intelligence (AI), Internet ofThings, and other technologies. We are aiming tokeep the information and telecommunications infrastructure—the backbone of our business—connected
in a stable and high-quality manner while continuing
to improve the infrastructure by increasing efficiency
through DX. As a pioneer in solving social issues, wewill also promote regional revitalization through connections with local communities and partners.
With those aims in mind, we will further strengthen
our business in growth areas. Strengthening the businesses of our group companies, such as the infrastructure business, which capitalizes our expertise in
infrastructure facilities, e-book business, and contact
center business, will also be essential for our future
growth. Specifically, we focus on (i) the “regional
revitalization cloud” to address issues such as industrial revitalization, job creation, and aging populationthat local governments are facing and improve work

NTT Technical Review

Vol. 21 No. 3 Mar. 2023

efficiency required by local companies, which areoften short of labor; (ii) the platform “L. ID” to helptransform uniform education into personalized education and improve the convenience of education(including student life) for promoting educational
DX for universities in accordance with the concept of“digital education”; (iii) multiple-solution packages
for small and mid-size companies; (iv) new co-creation through the use of electric vehicles as a carbonneutral initiative; and (v) the carrier-infrastructurebusiness, which is becoming more sophisticatedthrough the analysis and use of our data.
Pursuing well-being and solving social issues withthe power of ICT—All of the businesses in the growth areas are indispensable and important in today’s society. In ourdaily lives, ICT is becoming more and more convenient and widely used.
As our daily lives become increasingly digitalized,
we are also becoming increasingly oriented toward
well-being. With that trend in mind, we are also
focusing on the development of ICT-based services inthe entertainment area. Have you heard of “Comic
C’moA,” a comprehensive e-book service that celebrated its 18th anniversary in 2022? In March 2022,
as a first step to deliver this service to customers
around the world, we began offering a digital manga
store for overseas customers called “MangaPlaza.”
Entertainment service is a dynamic area in which newservices are born one after another along with theevolution of information terminals, and together with
our partners, we want to take on the challenge of creating a new culture.
Prevention and early detection of illness and promotion of health are important issues for all people.
These issues are deeply correlated with sleep habits.
We have therefore established NTT PARAVITA, ajoint venture with Paramount Bed Corporation,
which has the largest market share in Japan for medical and nursing care beds and mat-type sleep sensors.
The purpose of this venture is to support the early
detection of illness and provide information for
health promotion by using ICT from the perspectiveof sleep. Specifically, the venture provides a service
for visualizing sleep information using high-precision sensors and providing advice by experts toimprove sleep and a health support service at dispensing pharmacies. We will work on early detection of
diseases in the pre-disease stage by combining our3

View from the Topexpertise in an AI engine for analyzing sleep datawith the expertise of Paramount Bed on sleep.
Be comfortable with change and alteration—What has been important to you as a top executive?
I consider “people” and “human connections” to be
the most important. Although remote work has
become a common practice in Japan, I want to value
human connections and communication in our hybrid
work environment while taking advantage of the benefits of both remote work and face-to-face work.
The relationships we have with our employees aswell as our customers and partners are important.
Even though I have opportunities to interact withexecutives and department heads on a daily basis, I
don’t have many opportunities to talk with other
employees, so I visit branches in 30 prefectures inwestern Japan to communicate with employees andhold dialogue meetings over lunch. NTT WEST
employs approximately 50,000 people, so it is notpossible to hold a dialogue with all of them. Even so,
I’m planning to communicate with as many employees as possible.
As a top executive, I value the outside perspective
when making decisions. For example, one may feelthat something is not quite right with the work that isbeing done at one’s new assignment. That unease
usually signifies an issue that needs to be addressed,
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and such perception is often correct. In that case, I ask
employees, “Isn’t this strange?” I understand that it isdifficult for them to argue against me, the president,
so I carefully observe their facial expressions andnuances during conversations and try to listen to theiropinions before making decisions.
When I ask such questions, I often hear a reply saying “This is the way it is because of what we havedone up to now.” When I ask, “What would it be like
without that background?”, the answer is often, “Inthat case, as you say, it would appear strange.” We
don’t have a rule that you have to carry on what was
decided 10 years ago. So throw away your ties ofobligation and do what you think is right and optimalon the basis of your judgment at the moment.
—Finally, what would you like to say to our partners,
researchers, and employees?
I expect researchers to create something that NTT
can add value to, something that does not exist in theworld. As a world-leading technology, the Innovative
Optical and Wireless Network (IOWN) is a major
vision for the NTT Group. We will promote IOWN at
Expo 2025 Osaka, Kansai, Japan in two years. I wantto encourage all our bright-minded researchers toapproach their research with a global mindset.
We look forward to collaborating with our partners.
Our doors are open such as at QUINTBRIDGE. We
want to create new business and provide services
4View from the Top

with as many people as possible, whether it be one
person or one company.
To our employees. The key to solving social issues
and growing as a company is people. We promoterespect for human rights, diversity and inclusion, safe
labor, health management, and a new work style
based on remote work, and we promote a “work-inlife” style that allows employees to choose where andwhen they work. I’ll say it again, 2023 is a criticalyear for us. We have many things to do to grow businesses in growth areas in parallel. I encourage you tolook at the “now” and propose what you think is best,
without regard to history or background. My own
positivity will never change. Let’s continue being
positive.

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Vol. 21 No. 3 Mar. 2023

Interviewee profile
Career highlights
Masaaki Moribayashi joined Nippon Telegraphand Telephone Public Corporation in 1984. He
became president and managing director of NTT
Europe Ltd. in 2009, senior vice president andhead of the Cloud Services Department of NTT
Communications in 2016, senior executive vicepresident of NTT Communications in 2018, andboard director and senior executive vice presidentof NTT Ltd. in July 2019. He has been in his current position since June 2022.

5

Front-line Researchers

Researchers Value Passion andKnowledge, and Seek to Solve
Problems at Hand and Those That
Have Remained Unsolved forMany Years
Tatsuaki Okamoto
NTT Fellow, NTT Social Informatics
Laboratories
Abstract

One of the most fundamental problems in science is quantitatively defining the complexity of organized things. Over the past
several decades, many quantitative definitions of complexity havebeen proposed, but a single definition has not been agreed upon.
Tatsuaki Okamoto, an NTT Fellow at NTT Social Informatics
Laboratories proposed a quantitative definition that simultaneously captures all three key features of complexity for the firsttime. We interviewed him about the progress of his research
activities and the research environment in Japan and the UnitedStates.
Keywords: organized complexity, probability distribution, deterministic strings

The world’s first quantitative definition thatsimultaneously captures all three key featuresof complexity—It has been two years since our last interview. I
heard that you have returned to Japan from Silicon
Valley.
Yes, the previous interview took place in 2020. At
that time, I was in Silicon Valley as the director of
Cryptography and Information Security Laboratories(CIS Lab) of NTT Research, and I talked about the
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Vol. 21 No. 3 Mar. 2023

research themes in cryptography and blockchains
pursued at the CIS Lab and what kind of research
institute NTT Research is. After returning to Japan in
July 2022, I have been researching cryptography
theory at NTT Social Informatics Laboratories.
While at NTT Research in the summer of 2021, I
managed the CIS Lab while also providing researchguidance for internship students on the topic of adaptor signatures, a cipher used in blockchain transactions.
The research I’ll discuss today is related to cryptography in a broad sense, but it is more specifically6Front-line Researchers

about the field of complexity. If we follow the microscopic world, such as the cells that make up organisms such as animals and plants, we will see they
have extremely complicated structures. We also
know that the universe has evolved from its simple
form immediately after the Big Bang to a more complex form. When we look around us in this way, we
see that we are in fact surrounded by an abundance ofcomplex things. Complexity is the topic of scientificstudy through which the complexity of those things
that are said to be complex in the world is defined andquantified from a unified viewpoint. The research
field of complex systems has been around for morethan 30 years, and many excellent research results
have been reported; however, not much progress has
been made in regard to the study of the underlying
complexity of those systems. I have been thinking
about this research field while researching cryptography and recently published a paper on a quantitative
definition of complexity in the journal Complexity[1]. It is the world’s first definition that simultaneously captures all three key features of complexity(described later).
The ideas and concepts behind cryptography havealso been helpful for me to study complexity; forexample, the concept of knowledge complexity introduced in connection with the theory of zero-knowledge proof used in cryptography provided one clue inderiving this definition.
—You have proposed a world’s first in research that
could be considered your life work. Would you tell us
more about it?
First, let me explain the essence of the problem ofcomplexity. Warren Weaver, an American scientist,classified scientific problems into three categories:
problems of simplicity, problems of disorganizedcomplexity, and problems of organized complexity(OC). A typical problem of simplicity is one in which
the motion of a few balls on a billiard table is accurately analyzed and predicted using dynamics. A
typical problem of disorganized complexity is one inwhich millions of balls are rolling around on a giant
billiard table and randomly colliding with one another and the cushions of the table, and their average
motions are analyzed and predicted using statisticalmechanics. A problem of OC is defined as one
involving organized and complex things such as living organisms and ecosystems in which many cells
are interrelated and form a single living organism aswell as artificial objects. Problems of complexity are
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Vol. 21 No. 3 Mar. 2023

thus categorized as “organized” or “disorganized.”
In problems of complexity, the most fundamental
and important notion—from a scientific perspective—is the quantitative definition of complexity.
The quantitative definition of disorganized complexity (randomness) of physical systems was established
to be entropy, which appears in thermodynamics andstatistical mechanics. Moreover, the quantitative
definition of the disorganized complexity (randomness) of information sources (a probability distribution) was established as Shannon entropy. These two
entropies are essentially the same except for a constant.
Despite many attempts to give a quantitative definition of OC, there is no definition that is widely agreed
upon. The difficulty with this definition lies in thefact that OC depends heavily on our senses—or canbe perceived by intelligent creatures like humans—
and is very different from the randomness of objects.
Those previous attempts have covered either deterministic strings or probability distributions, and there
was no definition that covered both simultaneously.
Capture all three key features of complexity(descriptive, computational, anddistributional) simultaneously—So, it is necessary to establish a definition that covers both deterministic strings and probability distributions at the same time.
I considered what should be the object of the definition of OC. The object of complexity is everythingaround us, which includes the stars and galaxies in
the universe, living organisms, ecosystems, artificial
things, and even human societies. The only way for
us to recognize those things is observation via telescopes, microscopes, various instruments, and electronic devices. We directly recognize the existence ofan object by actually holding it in our hands; however, this recognition is also a result of observation;that is, our brain processes the observed data obtained
through our five senses (sensors) to interpret and recognize the existence of the object. In other words, weperceive everything on the basis of observed data.
In general, the source (information source) ofobserved data (i.e., a deterministic string) of physicalphenomena is a probability distribution, and theobserved data are values randomly selected in accordance with that distribution. It is therefore natural toassume that the object of OC is not the observed data
(i.e., deterministic values) selected by chance from7

Front-line Researchers

the source but the source itself (i.e., probability distribution). Accordingly, I considered that the object ofOC should be a probability distribution (i.e., thesource). Since a deterministic string may be a special
case of a probability distribution (in which only one
value occurs with probability of 1), it is also an eligible object.
—What were the problems with the existing quantitative definitions of OC?
Let’s take two cases as an example. First, we give a
chimpanzee a computer keyboard and allow it topress keys freely and generate a character string of1000 letters of the alphabet. Second, we take a character string of 1000 letters of the alphabet from one of
Shakespeare’s plays. Both cases are deterministic
strings; however, comparing the two sources of information clearly reveals the difference in complexity ofthe two strings.
The information source of the chimpanzee’s stringis almost a uniform distribution (i.e., a simple distribution) of 1000 random letters, so its OC is at thelowest level. On the contrary, the information sourceof Shakespeare’s string is the probability distributionof several candidate expressions in Shakespeare’s
mind. Regardless of whether Shakespeare chooses
from several expressions that come to mind (i.e., acomplex probability distribution of several candidate
expressions) or he chooses one expression without
hesitation (i.e., a probability distribution of one complex string occurring with probability of 1), both
distributions are complex, so their level of OC is veryhigh.
If we consider OC in Shakespeare’s strings, we
notice that complexity has several different features.
Since the object (information source) of OC is a probability distribution, one feature of complexity is thecomplexity of the pattern of probability distribution(distributional feature). Another feature of complexity is the complexity of the amount of description(descriptive feature) such as the knowledge required
to write a play (language, history, culture, etc.) andthe play’s story. Moreover, when Shakespeare decided what he wanted to write, he would have thought
deeply to choose the appropriate literary expressions
to express that decision. Choosing such linguistic
expressions can be regarded as a graph problem, andchoosing an appropriate expression has a computational complexity (computational feature) that isequivalent to solving a graph problem. Therefore, OC
has three features: distributional, descriptive, and
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computational, and to define it, all of these features
must be captured simultaneously. Of course, valuesof complexity should be computable, and the complexity of problems of disorganized complexity (as in
the above-mentioned example of a chimpanzee) or
problems of simplicity should be low.
The problem with the existing definitions is fourfold: first, they capture only one of these three features of complexity (distributional, descriptive, andcomputational); second, they target either deterministic strings or probability distributions and cannot
seamlessly target both at the same time; third, thecomplexity of some definitions is incomputable;
fourth, some definitions are not rigorously specified(Table 1).
Accordingly, I set out to and successfully established a new quantitative definition of OC that would
solve all four of those problems.
You need to have enough energy and passion tokeep pursuing your research—whether you areasleep or awake—You have overcome a longstanding issue. Pleasetell us about your definition of OC.
The basic idea of my quantitative definition of OC
is that OC is defined by using the smallest stochastic
automaton-form of a circuit (oc-circuit) that simulates an object, i.e., information source (probability
distribution). (Making the oc-circuit the “smallest”
means my definition accords with the principle called
Occam’s razor.) While some computational models
must be used to capture the descriptive and computational features of complexity, the existing definitions
use a Turing machine (a computer). Instead, my definition uses a circuit (oc-circuit). The reason for using
a circuit is that the three features of OC can beobtained simultaneously. Moreover, a definition
using a circuit is computable, whereas a definition
using a Turing machine is incomputable.
Therefore, my quantitative definition of OC satisfies all the requirements and overcomes all the problems of existing definitions: (i) the three features ofcomplexity (distributional, descriptive, and computational) can be obtained simultaneously, (ii) probability distributions and deterministic strings can beseamlessly covered as objects, (iii) the definition iscomputable and (iv) rigorously specified, and (v) thecomplexity of problems of disorganized complexityand problems of simplicity is low (Table 1).
My definition can be applied to theoretical8

Front-line Researchers

Table 1. Comparison with existing definitions.
Definition

Object(probabilistic anddeterministic)

Simplyregular

SimplyrandomOC
Descriptive

Computational

Distributional

Computable

Kolmogorov complexity
Effective complexity
Logical depth
Effective measure complexity
Statistical complexity
My definition of OC
Definition

Approach

Rigorously
specifiedComputational models

Computable

Kolmogorov complexity
Effective complexity
Logical depth
Statistical complexity
My definition of OC
Effective measure complexity
Natural complexity
Thermodynamics depth

Descriptive

Turing machine
Occam’s razor

Computational
Stochastic finite-state
automata (-machine)

Distributional

Stochastic automaton form ofcircuit (oc-circuit)All

Information theoretic
Framework

Features

Distributional
None

—

—
—

—: Difficult to evaluate

foundations for machine learning and artificial intelligence, algorithms with OC, networks, analysis ofamounts of computational and communication limits
and averages, and semantic information theory. I
believe that, for example, in contrast to Shannon’s
information theory, which treats entropy (disorganized complexity) as the amount of information forthe problem of signal transmission (syntactics), a
semantic information theory that deals with the problem of conveying meaning (semantics) can be constructed using my definition of OC as the amount of(semantic) information (Fig. 1).
—The impact you have academically and socially isimmeasurable. Finally, please tell us what you value
as a researcher and what you would like to say toJapanese researchers who are aiming to work
abroad.
I believe that a researcher is someone who values
passion and knowledge, and attempts to solve problems at hand and problems that have remained
unsolved for many years. With the spread of the Internet, the world has become borderless. It is thus
important for researchers to approach their research
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with a global perspective.
As I mentioned, I have worked with some of thebest and brightest researchers at the CIS Lab, NTT
Research in Silicon Valley. The CIS Lab is full ofenergy since the world’s best and brightest researchers are stimulating and competing with each other.
Some of the researchers are enrolled in doctoral programs and are quite enthusiastic. I believe it is important for young Japanese researchers and graduate
students who aspire to become researchers to possess
such enthusiasm for research. If you want to competewith powerful researchers around the world andaccomplish research that will have an impact on theworld, you will need to have enough energy and passion to keep pursuing your research—whether you
are asleep or awake.
If we want to produce world-class researchers fromJapan, we may have to reform our research systemand structure that supports them. For example, in the
U.S., PhD researchers usually start as postdoctoral
fellows. A postdoctoral fellow is not positioned as an
assistant researcher, but rather as an independent
researcher with their own research theme. When theirtenure is up, if their results are good, they will continue to research as a researcher in an upgraded9Front-line Researchers

Shannon’s information theory
Disorganized complexity(randomness) (entropy)

Problem of signaltransmission (syntactics)

Amount of (syntactic)
information

to some extent as they get used to life in anothercountry. I hope that when they determine to researchabroad, they will bring enough enthusiasm that overcomes such stress.
Reference

Semantic information theory
Organized complexity(OC)

Problem of semantictransmission (semantics)

Amount of (semantic)
information

Fig. 1. Application to semantic information theory.

position (obtained through competition). (Although
this is the case for theoretical research, it seems todiffer in the case of experimental research.) As an
independent researcher, you are more likely to develop yourself through competition with your peers thanby learning from your professors. I therefore think it
is necessary to create an environment in which outstanding researchers from around the world cangather so that young researchers can develop theircareer as researchers without depending on where
they do their research.
Nevertheless, it is important for researchers andthose who aspire to become researchers to choose
where they can conduct research and where they can
engage in competition—without blaming the environment if they make the wrong choice. One choice
is to work at a research institute abroad. In that case,living abroad can be stressful owing to differences inlanguage and culture. Such a situation could be adisadvantage, although time may solve that problem

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[1]

T. Okamoto, “A New Quantitative Definition of the Complexity ofOrganized Matters,” Complexity, Vol. 2022, Article ID 1889348.
https://doi.org/10.1155/2022/1889348

Interviewee profile
Tatsuaki Okamoto received a B.E., M.E., andPh.D. from the University of Tokyo in 1976,
1978, and 1988. He has been working for NTT
since 1978 and is an NTT Fellow. He is engaged
in research on cryptography and information
security at NTT Social Informatics Laboratories.
He served as the director of Cryptography andInformation Security (CIS) Laboratories at NTT
Research in USA from 2019 to 2022. He also
served as president of the Japan Society for
Industrial and Applied Mathematics (JSIAM),
director of International Association of
Cryptology Research (IACR), and a program
chair of many international conferences. He
received the best and life-time achievement
awards from the Institute of Electronics,
Information and Communication Engineers(IEICE), the distinguished lecturer award fromthe IACR, the Purple Ribbon Award from theJapanese government, the RSA ConferenceAward, and the Asahi Prize.

10

Rising Researchers

Spatial-mode Optical Measurement
Technology to Support Diverse
Global Services in the Future
Atsushi Nakamura
Distinguished Researcher, NTT AccessNetwork Service Systems Laboratories
Abstract

Communication traffic continues to increase each year and tocontinue to support this demand in the future, it will be necessary
to shift from conventional single-mode fiber to next-generation
optical fiber lines, utilizing multi-core and multi-mode fiber.
However, to implement high-quality next-generation optical fiberlines requires consideration of different physical phenomena thanthose considered in the past. We spoke with Distinguished
Researcher Atsushi Nakamura about his spatial-mode opticalmeasurement technology, which can visualize and grasp suchphenomena.
Keywords: optical measurement technology, spatial modes, optical-fiber transmission line

Spatial-mode optical measurement technology isessential for high-quality, next-generation
optical-fiber transmission lines—Can you tell us what “next-generation optical-fibertransmission lines” are?
Communication traffic has continued to increase inrecent years, and society’s demand for more capacity
on optical fiber networks is increasing. Transmission
methods on conventional optical fiber networks haveused single-mode fiber, meaning a single optical fiber
carried only one optical signal. However, we areapproaching the limits of per-fiber transmission
capacity for single-mode fiber, which will make it
difficult to increase transmission capacity in the
future. As such, new transmission methods that overNTT Technical Review

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lap multiple signals spatially will be needed in order
to continue to meet the increasing demand for communication capacity in the future.
The simplest method for spatially overlap signals is
to build multiple conventional single-mode fibertransmission systems in parallel. However, with thismethod, increasing the transmission capacity by afactor of N would also increase the cost by a factor ofN, which would not be practical or economically feasible. Thus, to continue increasing transmission
capacity, methods incorporating multiple cores within a single optical fiber, and methods that create multiple optical signal paths (spatial modes) within asingle core (space-division multiplexing) are being
studied (Fig. 1).

11

Rising Researchers

Current

Next-generation

Increase
capacity

Transmission
line
Single-core/single-mode

Multi-core/multi-mode(using spatial modes)

Fig. 1. Next-generation optical fiber technology using spatial modes.

Connections• Spatial modes are susceptible to external factors.
• It is not easy to maximize the potential of nextgeneration optical-fiber technology.

Physical deformations(bending/lateralpressure/strain)

Environmental changes(temperature/vibration)

Fig. 2. External factors when constructing optical-fiber transmission lines in real environments.

—Can you tell us about any difficulties encounteredin implementing next-generation optical-fiber transmission lines?
Next-generation optical fiber is a promising technology for dramatically increasing the transmission
capacity of a single optical fiber, but it is not easy to
implement transmission lines that can maximize thispotential. With conventional single-mode fiber, communication uses only a single spatial mode, so whencreating a transmission line with single-mode fiber,quality could be ensured mainly by evaluating losses
in the optical signal. However, multiple spatial modes
are used for communication in next-generation optical fiber, so in addition to optical signal losses, it isnecessary to consider complex optical characteristics
such as interference and loss differences between thespatial modes. These characteristics are susceptible toexternal factors, so even the smallest changes canalter their behavior. To maximize the potential of
next-generation optical-fiber technology, it is important to evaluate how these complex optical characteristics change due to external factors, and to create
optical-fiber transmission lines that minimize theeffects of such changes. For these reasons, it is
NTT Technical Review

Vol. 21 No. 3 Mar. 2023

extremely important to have optical measurement
technology that can visualize the quality of transmission lines.
Additionally, creating optical-fiber transmission
lines in real environments introduces various external
factors, including physical deformation due to bending, lateral pressure, and strain; optical fiber connections; and environmental factors such as temperatureand vibration (Fig. 2). For example, when the two
communication buildings on the left and right in Fig.
2 are connected, an optical-fiber transmission line iscreated by installing several kilometers of opticalcable through conduits, with successive connections
between them. If there are any quality issues withconnections or other factors when building this transmission line, it will need to be rebuilt to ensure communication quality. If any issues are detected after theentire transmission line has been built, manual work
to re-connect, or to remove and reinstall opticalcables will be required. To avoid the additional effortof redoing this work requires testing the quality every
time a connection is made.
The difficulty here is the need to evaluate characteristics at any point along the transmission line fromone end of an optical fiber cable, while the transmission
12

Rising Researchersline is being built. This is because optical cables andconnection points are on outdoor and undergroundsegments when building a transmission line and it is
not operationally practical to transport measurement
equipment to each location. As such, we require measurement equipment that can be placed within thecommunication facility buildings and can evaluate
the quality of the line being built at any distance fromthe building. Establishing this sort of optical measurement technology will enable us to build and operate next-generation optical-fiber transmission lines
with a thorough understanding of spatial-mode characteristics and will contribute to taking the lead globally in implementing next-generation ultra-highcapacity optical communication services.
—Specifically what sort of research are you conducting to implement these next-generation optical-fibertransmission lines?
A specific area of research has involved devisingand verifying testing methods to be used when building optical-fiber transmission lines with multi-core
fiber, which has multiple cores within a single opticalfiber. If the spacing between cores becomes too narrow, optical signals can leak between the cores (causing “crosstalk”) and can degrade communication
quality when creating multi-core fiber transmission
lines. The effects of such crosstalk on communication
quality can vary greatly depending on the quality ofwork when performing construction in real environments, so it is necessary to evaluate such effects atevery stage of transmission line construction. If suchtests are not done and poor quality is identified only
after construction is completed, the line may have tobe rebuilt, as mentioned earlier, incurring great additional time and expense. However, directly measuring crosstalk requires very expensive equipment,
which is a major obstacle for businesses. Existing
single-mode fiber will continue to be used even after
multi-core fiber is introduced, so new equipment will
also need to be compatible with single-mode fiber.
For these reasons, we also devised and verified amethod to evaluate changes in crosstalk characteristics based on loss values that can be measured using
an ordinary optical-pulse tester, which is also used fortesting single-mode fiber. This enables us to use
existing equipment to ensure construction quality
when building next-generation optical-fiber transmission lines using multi-core fiber in real environments.

NTT Technical Review

Vol. 21 No. 3 Mar. 2023

Explaining spatial-mode characteristics,
establishing methods to evaluate
transmission-line quality, and creating new
added value—Could you tell us about your research objectives
and vision for the future?
Next-generation optical-fiber transmission line
technology is an important technology for achieving“125x transmission capacity,” which is one of theperformance objectives for the All-Photonics Networks (APN), as part of the Innovative Optical andWireless Network (IOWN) plan. The optical measurement technology that I am currently researching
to visualize spatial-mode characteristics and behavior
will contribute to building and operating next-generation optical-fiber transmission lines with highcapacity and stable communication quality. In future
research, we hope to realize a world in which nextgeneration optical-fiber transmission lines are used
continuously as indispensable social infrastructure to
support all kinds of services around the world.
In a future initiative, I would like to be able to fully
control spatial modes so that they can be used for
optical measurements. I do not have concrete ideas
for this technology yet, but I think we should be able
to create new optical measurement technologies
using the characteristic of spatial modes that they aresensitive to minute changes. For example, no changes
can be observed before an earthquake using existing
optical measurement technologies, but it may be possible to use spatial modes to take measurements andvisualize phenomena that could not be observed earlier. Using spatial-mode characteristics could contribute to early detection of disasters in this way, or tosolving other societal issues (Fig. 3).
—What are some important aspects of research foryou?
I conduct research with the idea that technology
does not produce any value until it is used by someone. Research is the first step, and I am careful toconsider where what I am researching will ultimately
be used, what it will be useful for, what approach willachieve it, and what impact all of these will have on
my final objectives. Research also involves competition with other institutions, so a sense of momentum
and urgency is important. Of course, we want to takethe time needed to produce good technology, butthere is always the chance of being second to themarket, which reduces the value of the technology. To
13

Rising Researchers(1) Explain spatial-mode behavior

Mode behavior observation,
scattering mechanisms, etc.
Short-term objective(2) Evolve into method for evaluatingtransmission-line quality

Remotely visualize transmission-line
quality at any location(3) Create added value using spatialmode technology

Detect disaster indicators, evaluate
infrastructure conditions

Mid-to-long-term objective

Final objective

Fig. 3. Initiatives and objectives in spatial-mode optical measurement technology.

avoid such an outcome, I set objectives and priorities
to be the first to achieve them. I also approach
research with the intention of always producing a
result in the form of a patent or published paper on thesubject being studied. Including other group companies, NTT is a large corporation, so what we research
can be made into something that is actually put to use
within the group. This makes it possible to accumulate results that have been implemented, which gives
me a sense of the value of my efforts and experience.
The ability to produce good results is not something
we are born with, but is determined by our knowledge
and experience. Especially now, technology and conditions in society are changing quickly, and what isneeded changes accordingly. Under such conditions,insufficient preparation and effort can result in
missed opportunities, so I try to maintain steadyeffort in my studies. Even for business or events that
initially seem unrelated to my research, I always try
to find something that I can get from them, becausechanging my perspective can provide a chance togain a new way of thinking or new experience.

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Vol. 21 No. 3 Mar. 2023

—Dr. Nakamura, please leave us with a message forother researchers, students, and business partners.
NTT Access Network Service Systems Laboratories, where I work, has wide ranging initiatives frombasic research to applications, mainly in communications infrastructure technology. There are many
excellent researchers, each with different knowledge
and experience, so I have strong connections in many
fields, and by conducting research as a team in suchan environment, I can achieve things I could not do as
an individual. I feel this is a real strength of NTT. As
I continue my research, I always feel that it would be
difficult for me to produce major results by myself,
and my social connections are extremely important
for the smooth progress of my research. As an example, for research it is important to collaborate withpeople in many fields, but if I have no relationshipwith someone and suddenly try to ask them to dosomething new, they basically would not listen to me.
For starting new research, it is very important to build
a broad network. When someone has a network inanother laboratory within or outside of NTT, it canalso help to make connections through them. Having
people with many connections around me in this way
also helps me to steadily advance my research.
When research advances to a completed product ortechnology, no matter how good it is, the result will
be meaningless if we cannot describe it to users in a
way that makes them want to use it. Someone withexperience in business will have better skills in thisarea than a researcher like me. I am also very thankfulthat I can collaborate with people around me who areskilled at tasks that I cannot do myself.
I suppose there may be young researchers reading
this who would like to stay inside their own world
doing their research. When I was a student, I don’t
think I was very courteous with people that seemed
14

Rising Researchers

unrelated to my research either. However, after entering the work-force, we sometimes meet people that
do not seem to have anything to do with our research,or even have to work with them on research, and thiscan lead to new and different opportunities. I hopethat you will always value the connections you havewith the people you meet, to find as many opportunities as possible and not miss any.

NTT Technical Review

Vol. 21 No. 3 Mar. 2023

Interviewee profile
Atsushi Nakamura completed a master’s degree
at Osaka Prefecture University in 2012 and joined
NTT the same year. He completed a Ph.D. at
Osaka Prefecture University in 2018. He has beena distinguished researcher at NTT AccessNetwork Service Systems Laboratories since2022, conducting research on optical measurement technology and contributing to realizing
next-generation optical-fiber transmission lines.
He has received awards including a 2018 IEICE
Young Researcher’s Award.

15

Feature Articles: Keynote Speeches at NTT R&D
Forum—Road to IOWN 2022

IOWN1.0—Start of IOWN Service
Akira Shimada
President and Chief Executive Officer,
NTT Corporation
Abstract

This article introduces the Innovative Optical and Wireless Network(IOWN) service that is due to launch in March 2023. It is based on the
keynote speech given by Akira Shimada, president and chief executive
officer of NTT Corporation, at the “NTT R&D Forum—Road to IOWN
2022” held from November 16th to 18th, 2022.
Keywords: IOWN, APN, Digital Twin Computing

1. The future is a data-driven societyWith the spread of Internet of Things (IoT) and new
digital services, we are rapidly transforming into a
data-driven society, where analysis and actions are
based on data. In addition to the vast increase in volumes of data handled in this data-driven society, it isanticipated that the power consumption required fordata processing will increase significantly.
In terms of data volume, to watch a video in fullhigh definition, for example, requires broadband
speeds of 1.5 Gbit/s, but to watch the same video in
16K requires speeds approximately 750 times faster.
It is anticipated that the extended reality of the metaverse will grow rapidly, and the move from twodimensional (2D) to 3D data will necessitate an
approximately 30-fold increase in data volume. Moreand more aspects of our lives will also be networked
as part of IoT. It is projected that the number of IoT
devices in use will increase 5-fold, from approximately 27 billion in 2017 to 125 billion by 2030
(Fig. 1).
Let’s take a look at the expected increase in energy
consumption. Datacenter energy consumption in2018 stood at 14 TWh in Japan and 190 TWh globally. However, as more data migrates to the cloud, by
2030 it is anticipated that energy consumption will
increase significantly, increasing 6-fold in Japan to
90 TWh and 13-fold globally. When we factor in the
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Vol. 21 No. 3 Mar. 2023

various new services that will begin to appear, alongwith the existing services such as large-volume storage and video streaming which today can be usedwithout problems on current high-speed communication networks, extremely lower latency will be essential to enable, for example, the adoption of virtual
reality and augmented reality (VR/AR) robots andautonomously driven drones. In VR, unless latency ofless than 20 ms is achieved, images appear slower
than human movement, causing VR motion sickness.
Looking at all the statistical data it is clear that data
volumes and energy consumption are anticipated toincrease significantly (Fig. 2).
The Innovative Optical and Wireless Network(IOWN) will resolve the challenges relating to data
volume, energy-consumption increases, and network
latency. Specific performance targets for IOWN are
100 times more energy efficiency and have 125 times
more transmission capacity and 1/200 end-to-end
latency.
2. All-Photonics Network services (low latency
and high capacity)
In the first phase of IOWN services (i.e., IOWN1.0),
we will launch All-Photonics Network (APN) services in March 2023. They will be 100-Gbit/s leased
line services that will provide users with exclusive
end-to-end access to optical wavelengths. The service
16Feature Articles

Shift to superhigh-definition video

Adoption of 3D video andimmersive experiences

Full high-definition video

Acceleration of connected
IoT devices
Increase in the number of devices
connected to the Internet
2017
27 billion

2D data

1.5 Gbit/s
Metaverse(VR)

1147 Gbit/s

16K video

2030

125 billion

750-times

30-times

5-times* Theoretical value for uncompressed video

Source: Cisco Annual Internet Report (2018–2023)* For compressed ultra-high-definition video

Source: IHS Markit

Fig. 1. Why will data volume increase?

Estimated volume of Internet traffic

Increase in data volume(Times)200(Zeta
bytes)
180

Increase in traffic

150

190-times

100
50
0

121 Tbit/s

2010

2015

2020

2025

Source: Ministry of Economy, Trade and Industry, “Green IT Initiative,”
Dec. 2007.

Estimated power consumption of IT devices (Japan)
(TWh)
500

12-times

90-times

60

637 Gbit/s
2006

175 ZB

120

0

2010

470
0

2006

Limits to performance improvement achievable Transistors(thousands)
by miniaturization of semiconductors
Single-thread
performance
Barrier from operating(SpecINT x 10 )frequency
3

10 0

2400

Barrier from power
consumption

100
2025

2025

Limits to technological evolution

250

5-times

2020

2015

Source: IDC White Paper, sponsored by Seagate, “Data Age 2025:
The Digitization of the World from Edge to Core,” Nov. 2018.

107

5500

2 ZB

2050

1970

Source: Ministry of Economy, Trade and Industry, “Green IT Initiative,”
Dec. 2007.

2000

Frequency(MHz)
Typical Power(Watts)Number of
Logical Cores

2020

Source: K. Rupp, “42 Years of Microprocessor Trend Data,”
https://www.karlrupp.net/2018/02/42-years-of-microprocessor-trend-data/

Fig. 2. Statistical data.

specifications are shown in Fig. 3. The key featuresof IOWN1.0 APN services are low latency and highcapacity. In terms of capacity, a 1.2-fold increase will
be provided. Because of transmission as optical
wavelengths, latency can be reduced to just 1/200thof current services. In other words, IOWN1.0 willachieve the performance targets initially set for
IOWN. Latency fluctuations will also be eliminated.
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Vol. 21 No. 3 Mar. 2023

With Internet protocol (IP) and Ethernet service
latency fluctuations, it is difficult to predict latency
with any certainty, which in turn presents challenges
for conducting detailed and complex operations
remotely. With IOWN1.0 APN services, latency fluctuations will be eliminated, making it possible topredict a consistent level of latency, and this predictability can be applied to many different services. The
17

Feature Articles• 100-Gbit/s leased line
• Users exclusively use an optical wavelength end-to-end.
• APN terminal devices enable visualization and adjustment of delay.
Network
APN-G(gateway)

APN-G
Wavelength
path

APN-T
(transceiver)
User

Exclusive useof wavelength

APN-T

NTT EAST, NTT WEST

Communication mode

Point-to-point (to be expanded topoint-to-multipoint*1)

Unit of service area

Within prefecture (to be expanded tocover areas spanning prefectures*1)

InterfaceOTU4 (100 Gbit/s)(to be expanded to other interfaces*1)

Basic
Guaranteed (exclusive use ofBandwidth quality
functionality
wavelength)

APN
Delay adjustment
APN
terminal device
function
terminal device(in ms)User terminal

ProviderUser terminal

Frame transparent
Unlimitedtransfer
Link disconnection
AvailabletransferDelayadjustment*2
Fault report
Operation
reception andandmonitoring
maintenance
Fault notification

Available
24/7
Available (by e-mail)*1 The required devices are installed on the basis of service applications.
*2 Provided by terminal device

Fig. 3. IOWN1.0 APN services start in March 2023.

capability to visualize and adjust latency means thateven when connecting between remote locations it ispossible to synchronize timing.
I would now like to give four examples of the ways
APN services can be used. First is the field of remote
medicine. Low and unfluctuating latency enables thestable operation of precision robots. We believe that
this will significantly expand opportunities forremote surgery. We are currently engaged in joint
experiments with Medicaroid Corporation, which
manufactures and sells the hinotoriTM surgical robot
system, and together we plan to contribute to thedevelopment of community medicine.
Let’s take a look at another example involving theuse of robots, i.e., a smart factory. We are looking into
the possibilities for operating chemical plants
remotely. Chemical plants are enormous and maintenance is very demanding in terms of staffing requirements. It is in these plants that we are planning to use
APN services to conduct detailed operations remotely, such as checking equipment and fine-tuning
valves in elevated locations and explosion-proof
areas.
The third example is in e-sports. In e-sports games,
where split seconds make the difference between
winning and losing, using the low and unfluctuating
NTT Technical Review

Vol. 21 No. 3 Mar. 2023

latency of APN services will make it possible forplayers in remote locations to enjoy stress-free andfair play.
The fourth example is connectivity between datacenters. Using APN services to connect regional
datacenters and hyperscale datacenters with highcapacity and low-latency connectivity will make itpossible for all locations to be handled as if they werea single datacenter.
3. Photonics-electronics convergence devices(low power consumption of the APN and servers)
Next, let me explain the status of the developmentof a photonics-electronics convergence device thatwill help achieve low energy consumption. Our APN
services will ensure low latency, but perhaps the mostsignificant point about IOWN is improvement inenergy efficiency. The key element behind this efficiency boost is the photonics-electronics convergence device. Photonics-electronics convergence isthe fusion of optical and electrical circuits to improve
performance in various ways, including miniaturization and efficiency as well as boosting speed andlowering energy consumption. By applying photonics-electronics convergence to networks as well as
18

Feature Articles

IOWN1.0
FY2022
APN
services

Photonicselectronics
convergencedevices

FY2023–Ultra-low-latency services

Compact/low-powerdevices for networks

Servers(SWB)

IOWN2.0

IOWN3.0

IOWN4.0(Optical inter-board connection)(Optical inter-chip connection)(Optical intra-chip connection)

FY2025–Ultra-low-latency, highcapacity, low-powerconsumption services

FY2029–After FY2030–

Ultra-low-latency, ultra-highcapacity, ultra-low-powerconsumption services

Further low-powerconsumption
services

Inter-board connection devices

Inter-chip connection devices

Optical Intrachip connection

Ultra-low-powerconsumption servers

Further low-powerconsumption
servers

Low-powerconsumption servers

SWB: super white box

Fig. 4. Services for photonics-electronics convergence devices.

the world of computing, we are seeking to achieve
major reductions in energy use.
In our roadmap to the implementation of photonicselectronics convergence devices, by FY2023 we aim
to have a miniaturized, low-power-consumption
device for networks ready for commercial use. We
are seeking to reduce power consumption by incorporating what used to be multiple devices into a single,
significantly miniaturized package. Specifically, weare planning to have a commercial 400-GB device
ready in FY2023 and 800-GB device available in
FY2025. Additionally, as devices become smaller,
this will enable the miniaturization of network devices, such as transmission equipment, which will leadto simplified operations.
In FY2025, we plan to commercialize board-connecting devices that will enable the use of optics forboard-to-board and board-to-external interface connections. These advances will make it possible to use
photonics-electronics convergence in computing. By
FY2029, we aim to use photonics-electronics convergence technology to connect chips within boards, andfrom FY2030 onwards achieve in-chip connectivity.
By applying such photonics-electronics convergencedevices to APN services and servers, we will further
refine and improve IOWN. In FY2023, we will
launch a miniaturized and low-power-usage networked device in our APN services, further helping
to boost their energy efficiency (Fig. 4).
As part of IOWN2.0, from FY2025 we plan toexpand the scope of application of board connection
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devices to include not just APN services but also
servers. Under our current schedule, by FY2026 theplan is to develop a commercially feasible low-energy-consumption server using such a photonics-electronics convergence device. As part of IOWN3.0, by
FY2029 the aim is to have developed chip-to-chip
devices, and from FY2030 or thereafter, as part of
IOWN4.0, to achieve optical intra-chip connection,
thus significantly reducing power consumption.
In addition to these photonics-electronics convergence devices, and taking into account anticipatedimprovements in wavelength and optical fiber technologies, for IOWN2.0 from FY2025, we plan toachieve a 13-fold increase in energy efficiency in the
APN sector, an 8-fold increase in efficiency in theserver sector, as well as a 6-fold increase in capacity.
From FY2029, with IOWN3.0 we anticipate further
performance improvements and predict that we will
be able to achieve a 125-fold increase in capacity.
Although energy efficiency depends on the rollout oftechnology to devices, from IOWN2.0 we expect tobe able to improve performance, achieving a 20-foldincrease in the server sector compared with current
levels. What is more, from FY2030 and beyond, with
IOWN4.0 we are seeking to boost energy efficiency
100 times overall, enhance capacity 125 times, andachieve our target for latency of 1/200th of current
levels.

19

Feature Articles

Control for comfortable andefficient air conditioning

Food loss reduction

Scenario
calculation
Interworking digital twins
Data collection, automatic control
and monitoring
Lunch recommendation

Robotic delivery

Display ofrecommended
restaurant andmenu items

Order in mobile
situation
Urbannet Nagoya Nexta Building
Automatic delivery
Receipt of goods

Fig. 5. Urban development using Digital Twin Computing.

4. Digital Twin Computing
Next, let me say a few words about Digital Twin
Computing, which is another IOWN technology. The
IOWN framework consists of the APN and server
infrastructure, of which photonics-electronics convergence devices are a component, as well as Cognitive Foundation and Digital Twin Computing technologies. Cognitive Foundation means the optimization of all information and communication technology resources and their operation and control. Digital
Twin Computing is the ability to predict the futureand optimize by combining digital twins in the realand digital worlds. Digital Twin Computing is theprocess of taking various digital copies of people,
objects, and things in real space and expressing these
digital copies in cyberspace, using them to perform
data analysis and simulations such as predictions
about the future. On the basis of the results, the optimal methods and actions are then fed back to the realworld to help improve processes and decisions toaddress challenges in real situations. For example, by
linking data on people flows and traffic volumes withbasic data on the urban environment, it will become
possible to create conditions for controlling an optimal transportation environment.
Let me introduce a real example of how Digital
Twin Computing is being put to use in urban develop-

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Vol. 21 No. 3 Mar. 2023

ment. Since FY2022, we have been conducting anurban development pilot project at Urbannet Nagoya
Nexta Building using Digital Twin Computing(Fig. 5). At Urbannet Nagoya Nexta Building, we are
testing a new initiative to link four services, i.e., airconditioning control, food loss reduction, robotic
delivery, and lunch recommendation, and optimize
them on the basis of predictions using Digital Twin
Computing.
As you can see, urban development using Digital
Twin Computing has already begun. Although currently still in the pilot stages, we plan to commercialize solutions for air-conditioning control and foodloss reduction by the end of FY2022. By further
expanding our services and deploying them in various urban environments, we aim to contribute tourban development that benefits both people and theglobal environment.
5. Concluding remarks
Finally, let me share with you that at Expo 2025
Osaka Kansai, Japan, NTT plans to present a realworld pavilion and virtual platform to be called“Floating Yumeshima” where every life shines. We
hope to be able to announce the launch of IOWN2.0
services at the Expo, so please keep following ourprogress.

20

Feature Articles: Keynote Speeches at NTT R&D
Forum—Road to IOWN 2022

Road to IOWN – Light Up –Atsuko Oka
Executive Vice President,
Head of Research and Development
Planning Department,
NTT Corporation
Abstract

This article introduces research and development efforts and the latest
results on the Innovative Optical and Wireless Network (IOWN). It isbased on the keynote speech given by Atsuko Oka, executive vice president, head of the Research and Development Planning Department of
NTT Corporation, at the “NTT R&D Forum—Road to IOWN 2022” heldfrom November 16th to 18th, 2022.
Keywords: IOWN, APN, photonics-electronics convergence

1. Welcome to NTT R&D ForumAt this NTT R&D Forum titled “Road to IOWN
2022,” more than 90 exhibits and 5 lectures werestreamed. The exhibits were divided into three categories: “IOWN Now,” “IOWN Evolution,” and“IOWN Future.” The respective exhibits introduced
the Innovative Optical and Wireless Network(IOWN) available now, the world and related technologies envisioned by 2030, and the technologies
beyond that.
We again held the exhibits virtually as part of ourmeasures against COVID-19. However, some exhibits were shown in-person by reservation and invitation only. This was our third year holding the forum
online. Many participants from previous forums
commented that the long list of exhibits made it difficult to find those of interest to them. Many people
also asked us to summarize the key points of thetechnologies. Therefore, we asked someone who is
not in the research and development (R&D) field tocreate illustrations that will help to visualize andunderstand the content. Therefore, participants wereable to find exhibits close to their interests more
quickly.
Before I discuss the highlights of this forum, I
NTT Technical Review

Vol. 21 No. 3 Mar. 2023

would like to recap the IOWN initiative. The key element is optical technology. The concept is to create asmart world that promotes well-being through Digital
Twin Computing (DTC). DTC adopts a new networkand computing infrastructure using high-speed andlow-power-consuming optical devices to process,analyze, and use massive data.
Let me explain the All-Photonics Network (APN)that uses optical technology. You may be asking,aren’t we already using optical fiber for communications? The answer is ‘yes,’ but it requires many electro-optical conversions along the communication
path. It is like changing trains (Fig. 1). We are changing this to a direct optical path. It will be like taking a
direct train. This will enable the creation of a higher
capacity, lower latency, and more secure network
than what currently exists.
By changing the wavelength, i.e., the color, of light,
separate networks can also be created within a single
fiber. One network may be for traditional Internet
protocol, another for medical protocol. Therefore,
function- and role-specific networks can be created.
Optical communications go inside the computer.
By connecting the card level with optical waveguides, we can get rid of the server chassis. Opticallines have extremely low distance attenuation,21

Feature Articles

Currently

Adapter

Electric circuit
Local
edge

Hub

Hub
PacketswitchPacketswitchTransfer

Opticaltransceiver

Optical fiber
backbone

Transfer

OpticaltransceiverPacketswitchTransfer

Local
edge

Optical device

PacketswitchAdapter

Transfer

APN

Adapter
Opticaltransceiver

Local
edge

Hub

WSS

WSS

Hub
Optical fiber
backbone

Straight through

WSS

Local
edge
WSS

Adapter
Opticaltransceiver

Straight through

WSS: wavelength-selective switch

Fig. 1. All-Photonics Network (APN).

allowing for greater parallel computing and memory
sharing than before. By creating intra-board opticalwaveguides, we can also eliminate the board walls
and achieve a powerful computing system. We callthis photonic disaggregated computing.
2. Where did IOWN actually originate from?
I am often asked, “When did NTT consider the
IOWN initiative?” It was prompted by NTT’s development of an optical transistor, announced in April
2019. This instantly sped up the discussion on IOWN
and led to its announcement. However, the idea oflight impacting not only communications but evencomputing is not a new one. Believing in its feasibility, NTT has continued to research light since the1960s. When I was reviewing this history, I found aninteresting article from 1988, more than 30 years ago,
the year I joined the company. It was included to ajournal of the Institute of Electrical Engineers ofJapan (IEEJ) for their 100th anniversary issue by our
researchers at the time. Chapter 3.1 of the article istitled “Optical interconnection,” which refers toboard-to-board and chip-to-chip connections by light,
and embodies the very idea of photonic disaggregated computing. Chapter 3.2, “Computing with coherent optics,” is about building a physical machine.
This led to the IOWN initiative’s LASOLVTM coherNTT Technical Review

Vol. 21 No. 3 Mar. 2023

ent Ising machine for solving optimization problems.
Chapter 3.3, “Parallel digital optical computing,” isabout fabricating optical processors. The development of the optical transistor was a part of this. Chapter 3.4, “Optical neurocomputing,” is about constructing neural networks using light. Therefore, theidea had been around even when no one knew about
the significant social impact that neural networkbased artificial intelligence (AI) would have. Whenthe IOWN initiative was announced in 2019, I imagine many people wondered if NTT had lost its senses
and if it was even possible. However, NTT researchers had long predicted the heralding of such an era
and proceeded with their research. We have now
finally reached the stage when the research findings
can be shared.
3. Development plan for photonics-electronics
convergence devices
I will explain our development plan for photonicselectronics convergence devices, which will be central to the actualization of the IOWN initiative. Our
R&D classifies devices into five generations (Fig. 2).
The first generation is current networks with higher
performance. The second generation is devices
focused on easy handling for inter-datacenter transmission. In the third generation, light enters the22

Feature Articles

IOWN1.0
1st generation
For relay devices

2nd generation

For pluggable transceivers

IOWN2.0

IOWN3.0

IOWN4.0

3rd generation

4th generation

5th generation

For board connection

For chip connection

Fiber-less

ASIC
Optical fiber

SiPhAnalog IC

Optical engine

Transmission
device between
datacenters

Telecom relay device(long-distance, metro
networks)• Ultrafast switch• SmartNIC

Network

Photonic disaggregatedcomputerComputing

ASIC: application specific integrated circuit
SiPh: silicon photonics
SmartNIC: smart network interface card

Fig. 2. Evolution of photonics-electronics convergence devices and application areas.

computing domain. Rather than computer-to-computer connections, the devices are designed for connecting their parts, board-to-board, using light. The
fourth and fifth generations are respectively interchip and intra-chip devices where light penetrates
deep into the computer. While there are still technicalhurdles to overcome, we are working hard to developthese devices.
4. Light Up
I would like to move on to the progress of ourresearch. The APN will be available as a service at theend of FY2022 (March 2023). Since the announcement of the IOWN initiative to today, we have been
studying use cases and discussing necessary technicalrequirements with IOWN Global Forum members
and other partners. Equipment compliant with the
IOWN method have already been launched by member companies. The ideas that we have been brainstorming with IOWN Global Forum members havebeen translated into tangible form, and we are entering the phase of full-scale demonstration. The subtitleof this lecture is “Light Up.” I chose this subtitle
envisioning the light of IOWN being lit up and its
infrastructure becoming available to you.
NTT Technical Review

Vol. 21 No. 3 Mar. 2023

4.1 IOWN “Datacenter × APN”
First, I will explain IOWN “Datacenter × APN.”
The APN will connect NTT’s laboratories in Japan
and NTT Group companies’ datacenters, among otherfacilities. Datacenters will be installed with photonic
disaggregated computing, data hubs that enable data
sharing, the latest security technologies, and other
IOWN capabilities, in a stepwise manner. We will be
conducting testing in this large, practical environment and developing services at an accelerated pace.
One of the goals of connecting datacenters with the
APN is decentralization of datacenters. Datacenters
are becoming increasingly larger. For large datacenters, securing land and power is a major challenge.
Looking ahead to the future, a key question will be
how to meet the large power requirements withrenewable energy alone. To address this issue, we aim
to decentralize datacenters. By connecting small andmedium-scale datacenters with the APN, we aim to
make computers run as if the datacenters are a single
datacenter. It is inefficient to transmit valuable powerover long distances. Decentralizing datacenters willbe essential for the local production and local consumption of energy.
The core infrastructure for decentralizing datacenters is high-speed, high-capacity, low-latency
23

Feature Articles

Decentralization of datacenters while conserving energy: commercial use in 2023
1st generation

EO response (dB)

Digital coherent signal processing circuit with the world’s highest capacity: 1.2 Tbit/s per wavelength

3-db bandwidth: 80 GHz

Frequency (GHz)The world’s widest-class electrooptic (EO) bandwidth

Optical signal with theory-achieving
coded modulation• Comparison with current commercial systems: transmission capacity 12-fold; energy efficiency 10-fold• 2 Tbit/s is achieved in the laboratory.

Fig. 3. Digital coherent signal processing circuit capable of optical fiber transmission at 1.2 Tbit/s per wavelength.

communications, or the APN. Let me mention two
APN-related achievements.
The first is the successful development of a digital
coherent signal processing circuit capable of opticalfiber transmission at 1.2 Tbit/s per wavelength(Fig. 3). The mainstream commercial capacity is currently 100 Gbit/s. Therefore, our circuit instantly
increases capacity by 12 times and improves energy
efficiency per bit by 10 times. This system will becommercially available in 2023. As we announced in
our press release in September 2022, we haveachieved 2 Tbit/s in the laboratory. There is still muchroom for improvement. We will continue our researchof this platform technology, which will support nextgeneration ultra-high-capacity communications.
Our other achievement is the successful creation of
a 400-Gbit/s co-packaged optics prototype for transceivers (Fig. 4). This is a small, low-power-consumption device that integrates everything from signal
processing circuits to optical transmission and reception functions. It is currently under development andis expected to be commercially available in 2023. We
are also conducting R&D to deliver an 800-Gbit/s
version, which will contribute to further energy savings in datacenters. Connecting the high-speed APN
to datacenters will significantly change the way customers design future services. You have probably
seen many times the picture of “AI and Internet ofThings,” where only mechanical and other devices
NTT Technical Review

Vol. 21 No. 3 Mar. 2023

are at the sites and the AI part is cloud-based. However, is this really the case? With the exception ofsmartphone apps, the edge is also often equippedwith GPGPUs (general-purpose computing on graphics processing units) or other fairly large computing
units. This is because there were many problems on
the network side. We will address this issue by using
the APN to connect datacenters as well as the sites
and create a genuine industrial infrastructure environment. We will demonstrate that it is truly possible to
make advances in AI and foster an environment thatcan continue to provide high-value services.
4.2 The APN transfers reality & skills
The APN is more than just an infrastructure platform for datacenters. One of the main benefits of the
APN is high transmission capacity for conveying
reality. For a person to perform an activity in a simulated reality, that person must be able to demonstrate
their skills, which are transmitted through the APN.
Information is needed to reproduce reality. This may
be visual or acoustic information, or in some cases,
verbal or tactile information or their combination. To
reproduce reality, high-capacity communications andultra-low latency are extremely important, which aresupported by the APN next-generation network. If
people can fully demonstrate their skills and theseskills can be transmitted, new ways of working andengaging with society will emerge, creating new24

Feature Articles

Decentralization of datacenters while conserving energy: commercial use in 2023
2nd generation
400-Gbit/s co-package for pluggable transceivers

400G co-package prototype• Device designed for short distances (100 km) boasting high capacity, lowpower consumption, and small size
• 800-Gbit/s transceivers are also under development.

Fig. 4. 400-Gbit/s co-packaged optics prototype for transceivers.

value. We will proactively implement such initiatives
to create services as quickly as possible.
The most typical use case is remote surgery, which
was presented at this forum. The remote operator of
the machine needs real information about the patient.
In remote medicine, there are physicians, both on theside operating the machine and with the patient. Even
if they are separated physically, they need to be able
to communicate smoothly as one team. Whether it istransmission of clear voices or panoramic images,
two-way transmission is critical to realistically convey the situation of the entire operating room, i.e., theonsite environment. The APN’s high-capacity communications and low latency make it possible forpeople in different locations to work together as if
they are in the same place.
4.3 Perspectives on the “Now” exhibits
I mentioned that the exhibits of this forum weredivided into three categories and that “IOWN Now”
introduced technologies that are available now. They
were centered around the decentralized datacenters aswell as technologies that support the APN and use
cases that I have discussed. If you viewed the exhibits
from this holistic perspective, I believe you gained adeeper understanding of our initiatives. In this forum,
we announced that IOWN will be taking off. These
are services that we have been discussing together
with the members of IOWN Global Forum. The
NTT Technical Review

Vol. 21 No. 3 Mar. 2023

members discussed the activities of the Global Forumin a panel discussion, which was streamed during thisforum. The title was “Have your ticket ready.
– IOWN is taking off NOW!” As the title suggests,
the members presented IOWN’s initiatives that areabout to get off to a flying start.
4.4 Other notable exhibits
Next, I would like to introduce other noteworthy
exhibits. Since announcing IOWN, light has been the
keyword of our various announcements. However,sound is another area NTT has long researched. Somepeople may still think of us as a telephone company.
Delivering clear sound has value even now. NTT has
an advantage in acoustics and voice technologies,
both in conference presentations and intellectual
property. I would like to mention two applications, aswell as one basic research project that looks ahead tothe future.
The first is acoustic communication technology.
Did you know that there are drones that can maneuverunderwater? There are no means of communication
capable of high-capacity, long-distance transmissions
underwater. Therefore, most underwater drones
needed to be connected to a cable to control remotely.
Sometimes they get entangled or harm organisms andthe environment. We applied acoustic technology tocommunications and achieved 1-Mbit/s communication at a 300-m distance (Fig. 5). Underwater drones
25Feature Articles

Wired underwater drones become wireless: controllable from a remote location

Antenna for receiving underwater signals

Underwater drone filming

Achieving 1-Mbit/s communication (300 m) underwater (sea)SD-quality video transmission is possible*.
*Depends on the object and other conditions

Fig. 5. Acoustic communication technology.

can now be controlled wirelessly over long distances.
Technically, the shallower the water, the harder communication becomes due to sound waves bouncing
off the seafloor and due to marine life. However,high-speed communications are now possible even inshallow water. At 1 Mbit/s, standard definition (SD)quality movies can be transmitted. Since clear images
can be produced, underwater drones are expected tohave a variety of uses, such as inspecting underwaterequipment and checking shellfish and fish being cultured.
Next is Personalized Sound Zone (PSZ) technology. Our goal is to create a sound space that lets you
hear only the sounds you want to hear and not thesounds you do not want to hear. The PSZ technology
exhibit presented two achievements. The first is atechnology to contain the reproduced sound in asmall area. Using this technology, we have created a
new type of earphones. Open-ear earphones that are
not placed inside the ear usually leak sound into thesurroundings. With our earphones, leakage is kept toa minimum. Such earphones have been commercialized by NTT Sonority. I understand they havereceived very positive reviews. I use them for myonline meetings. They are lightweight, so your ears
do not get tired even after long use. Because they are
open-ear type, you can also hear surrounding sounds,
which is great. PSZ has also succeeded in cancellingout ambient noise. This technology is the active noise
cancellation feature, which is available with manyearphones inserted into the ear. At this forum, we

NTT Technical Review

Vol. 21 No. 3 Mar. 2023

showed speakers with this feature.
I would like to mention a study by NTT Research,
Inc., which is based out of the West Coast of the U.S.
It has been published in the scientific journal, Nature.
The AI boom is supported by deep learning technology. Its many layers of neural networks learn from avast amount of data and make outstanding predictions. Although this is usually done by computation
inside a computer, the study showed that various
physical systems can become multi-layered neuralnetworks. This exhibit introduced some systems,
including an interesting system that uses a microphone and speaker to create a neural network which
can recognize handwritten numbers. The researchfindings are extremely interesting. I urge you to takea look at them.
5. Closing remarks
Today, in my presentation entitled, “Road to IOWN
– Light Up –,” I discussed IOWN’s broad applications. The IOWN initiative may have been just a
concept to you. This concept is becoming tangible inthe current phase. We are now ready to put the ideas
into action. We are committed to deepening collaboration with our partners to create concrete products
and services. I invite people from the telecommunications and many other industries, academia, and government agencies to join us in creating a new future
together. Stay tuned to what the future holds for
IOWN.

26

Regular Articles

Over 100-Tbit/s Ultra-wideband
Wavelength Division Multiplexed
Transmission Technologies for Future
Optical Transport Network Systems
Fukutaro Hamaoka, Kohei Saito, Akira Masuda,
Hiroki Taniguchi, Takeo Sasai, Masanori Nakamura,Takayuki Kobayashi, and Yoshiaki Kisaka
Abstract

This article reviews trends in ultra-wideband wavelength-division multiplexing (WDM) transmission
techniques for expanding the capacity of optical transmission systems. It also presents NTT’s recent
research and development results on ultra-wideband WDM transmission for over 100-Tbit/s transmission
capacities in a triple-band (S, C, and L bands) WDM configuration.
Keywords: digital coherent, wavelength division multiplexing, digital signal processing

1. Introduction
To cope with the rapid increase in communication
traffic, it is necessary to increase the transmission
capacity per optical fiber while reducing the cost per
bit of optical transmission systems. Innovative technologies, such as wavelength-division multiplexing(WDM) transmission with optical amplifiers anddigital coherent technology with digital signal processing (DSP) [1], have continuously been expanding
the system capacities for optical transmission. DSP
application-specific integrated circuits (ASICs) for
digital coherent technology support multi-rate andmulti-modulation formats to meet the demand for
multiple applications: long-haul, metro, and shortreach (particularly datacenter interconnects) networks. For example, a DSP-ASIC can execute ~32GBaud polarization-division multiplexed (PDM)
quadrature amplitude modulation (QAM) formats
with modulation orders from 4 to 16 for from 100 to
200 Gbit/s/carrier [2]. Up to 600-Gbit/s/carrier with
64QAM transmission experiments have also been
NTT Technical Review

Vol. 21 No. 3 Mar. 2023

reported with a real-time transponder including a
64-GBaud-class DSP-ASIC [3]. NTT has recently
developed a cutting-edge DSP and an optical device
supporting 1.2 Tbit/s/carrier with 140-GBuad-classcoded 64QAM for digital coherent systems [4].
To further increase system capacity, expanding the
WDM bandwidth is effective along with high spectral
efficiency (SE) signals with digital coherent technology using high-order QAM formats. A transmissionof 102.3-Tbit/s with PDM-64QAM signals has been
demonstrated under the 11.2-THz dual-band (C and L
bands) WDM condition with an SE of 9.1 bit/s/Hz[5]. NTT has also successfully demonstrated the firstever greater than 150-Tbit/s transmission with
272-channel PDM-128QAM signals under the 13.6THz triple-band (S, C, and L bands) WDM condition
with an SE of 11.05 bit/s/Hz [6]. Both experiments
were conducted using the offline evaluation technique in which DSP is carried out on workstations fortransmitted and captured received signals. The offline
evaluation enables detailed signal analysis of DSP
methods toward ASIC implementation.
27

Regular Articles

120

F. Hamaoka et al.
(OECC/PSC2022)

Capacity (Tbit/s)

100
80

D. L. Gac et al.
(ECOC 2021)

T. Kato et al.
(ECOC 2019)60

H. Zhang et al.
(ECOC 2019)
K. Yonenaga et al.
B. Zhu et al.
(OECC 2016)(ECOC 2019)

40
20

2015

2017

>100 Tbit/s

X. Zhao et al.
(ECOC 2022)

B. Zhu et al.
P. Kumar et al.
(ECOC 2021/OFC 2022)(OFC 2020)
T. Kato et al.
(ECOC 2022)

2019

2021

2023

2025

Year

Fig. 1. T rends in capacity growth in digital coherent experiments for real-time transmission with DSP-ASIC-integrated opticaltransponders.

S : TDFAWDM signal

C

S

L

: EDFAS

GEQ
WSS

Real-time transponder for S band
(1467.233–1524.304 nm)

S

LD Signal
S

IQM

WDM signal
C

WSS

WSS

400-Gbit/s 16QAM
500-Gbit/s 32QAM

LO LD
HB-ICR

S

WSS

S

C

Real-time transponder for C band
(1530.529–1567.133 nm)

C

WSS

C

L

Real-time transponder for L band
(1570.005–1607.897 nm)

L

WSS

L

WDM signal
L

DRV

DSPASICDSP-ASIC: 16-nm CMOS

WDM coupler

WDM coupler

Forward Raman pump:
1370 nm

101 km(Aeff: 125 µm2)

Backward Raman pump:1390 & 1430 nm

Fig. 2. Experimental setup for triple-band WDM transmission with DSP-ASIC-integrated real-time optical transponders.

In this article, we present real-time triple-band
transmission with a WDM bandwidth of 16.95 THz
using DSP-ASIC-integrated optical transponders. We
transmitted total capacities of 102.7 and 112.8 Tbit/s
using 226-channel WDM signals with 400-Gbit/s
PDM-16QAM and 500-Gbit/s PDM-32QAM [7]. As
can be seen in Fig. 1, we achieved, for the first time,over 100-Tbit/s capacity in real-time transmission
experiments.

NTT Technical Review

Vol. 21 No. 3 Mar. 2023

2. Experimental setup for ultra-wideband WDM
transmission using DSP-ASIC-integrated
optical transponders
Figure 2 shows the setup for triple-band WDM
transmission experiments with real-time optical transponders. We used three real-time optical transponders having DSP-ASICs based on 16-nm complementary metal oxide semiconductor (CMOS) technology [3, 8]. The transponders were also implemented driver (DRV) amplifiers, a lithium niobate
in-phase and quadrature modulator (LN-IQM), and ahigh-bandwidth intradyne coherent receiver (HBICR). Signal and local oscillator (LO) laser diodes
28

Optical power(10 dB/div.)

Regular Articles

1450

S: 103 
7.725 THz

C: 62 L: 61 4.650 THz 4.575 THz

75-GHz gridMainsignal
1500

1550

1600

Wavelength (nm)Fig. 3. WDM signal spectra of 16.95-THz bandwidth.

(LD) sources were external cavity lasers for the S
band and integrable tunable laser assemblies for the
C and L bands. The modulation formats of the main
signal were 67-GBaud PDM-16QAM with a net rateof 400 Gbit/s and 66-GBaud PDM-32QAM with a
net rate of 500 Gbit/s, which were generated in the
optical transponder for each WDM band. The carrier
frequency of the main signal was set to 1467.233–
1524.304 nm in the S band, 1530.529–1567.133 nm
in the C band, and 1570.005–1607.897 nm in the Lband.
The WDM signals in the S, C, and L bands weregenerated using amplified spontaneous emissions
from the thulium-doped fiber amplifiers (TDFAs)and erbium-doped fiber amplifiers (EDFAs). The
power level of the WDM signal was equaled using again equalizer (GEQ) on the basis of flexible-gridwavelength selective switches (WSSs) with liquid
crystal on silicon (LCOS). TDFAs for the S band andEDFAs for the C and L bands were used in thisexperiment. The main signal from the real-time optical transponder and WDM signal for each band were
multiplexed in a LCOS-based flexible-grid WSS. The
WDM grid in this experiment was set to 75 GHz. The
WDM signals in the S, C, and L bands were thenmultiplexed in a WDM coupler with a total bandwidth of 16.95 THz (7.725, 4.650, 4.575 in the S, C,
and L bands, respectively), as shown in Fig. 3. The
total number of WDM signals was 226 channels (103,62, and 61 channels in the S, C, and L bands, respectively). The triple-band WDM signal was transmitted
through the transmission line of a 101-km large-core
low-loss fiber, which is compliant with ITU-T (International Telecommunication Union - Telecommunication Standardization Sector) G.654.E, with aneffective area (Aeff) of 125 μm2. We used a forward(FW)-pumped distributed Raman amplifier (DRA) ata wavelength of 1370 nm and a backward (BW)NTT Technical Review

Vol. 21 No. 3 Mar. 2023

pumped DRA at 1390 and 1430 nm.
The triple-band WDM signal was divided into each
S-, C-, and L-band WDM signal after 101-km opticalfiber transmission. The WDM signals were thenamplified using a TDFA for the S band and EDFAs
for the C and L bands at the receiver side to compensate for the transmission losses. After filtering themain signal for each S, C, and L band using a LCOSbased flexible grid WSS, the signal was coherently
detected with the HB-ICR with the optical LO.
Finally, the received signal was equalized, demodulated, and decoded in the DSP-ASIC [3].
3. Experimental results of over 100-Tbit/s
real-time transmission
In the ultra-wideband WDM configuration, interband stimulated Raman scattering (SRS) affects the
WDM signals. A nonlinear interaction is caused byinter-band SRS in bands with a gap of around 100 nm
for ultra-wideband transmission systems; inter-band
SRS causes a signal power transition from S- to
L-band signals in triple-band transmissions [6].
Therefore, we evaluated the effect of inter-band SRS
with the 16.95-THz triple-band WDM configuration.
The fiber loss at 101 km and transmission loss withinter-band SRS are shown in Fig. 4. The signalpower transition was mainly observed from the S
band to the L band.
Figure 5 shows the experimental results in 101-km
real-time triple-band WDM transmission. The FWand BW-pumped DRA were applied for the transmission line to compensate for the excess power loss in
the S band caused by the inter-band SRS. As Fig. 5(a)shows, the WDM signal power in the S band was
drastically increased by the Raman amplifiers with
sufficient Raman amplification gain. To evaluate thesignal performance, we used the pre-forward error
collection (FEC) quality (Q) margin, which is definedby the difference between the measured pre-FEC Q
factor in the experiments and the required pre-FEC Q
factor to achieve an error-free post-FEC bit error rate
(BER). We observed that the pre-FEC Q margins of
all measured 226-channel WDM signals showed
more than zero, as shown in Fig. 5(b). We also confirmed that the post-FEC BER of all signals were
error-free in this case. That is, in this setup, weachieved 112.8-Tbit/s (= 500 Gbit/s × 224 λ + 400
Gbit/s × 2 λ) transmission using real-time opticaltransponders.
The long-term signal performance under the 16.95THz triple-band WDM condition was evaluated29Regular Articles

Loss (dB)30
Fiber loss at 101 km
Transmission loss with inter-band SRS

25

20

15
1460

1500

1540
Wavelength (nm)

1580

1620

Fig. 4. 1
 01-km fiber loss and transmission loss with inter-band SRS.

(a)
Optical power(10 dB/div.)

w. FW- (1370 nm) and BW-pumped DRA (1390 & 1430 nm)
w.o. Raman amp.

1460

1480

1500

1520

1540

1560

1580

1600

1620

1600

1620

Wavelength (nm)2.5
Pre-FEC Q margin (dB)

(b)

2.0

500 Gbit/s
400 Gbit/s

1.5
1.0

500 Gbit/s

0.5
0.0
1460

1480

1500

1520
1540
1560
Wavelength (nm)1580

Fig. 5. E xperimental results: (a) WDM optical spectra with and without FW- and BW-pumped DRA and (b) pre-FEC Q margin
after 226-channel triple-band WDM transmission through 101-km fiber transmission with FW- and BW-pumped
DRA.

during transmission in 101-km fiber when applying
the FW- and BW-pumped DRA. As shown in Fig. 6,
we obtained stable signal-transmission performanceat the center channels of S-, C-, and L-band signals
with small pre-FEC Q-factor fluctuations of less thanor equal to 0.036, 0.025, and 0.037 dB, respectively,
within continuous measurements for 60 min. During
the stability test, we also confirmed error-free operation after FEC decoding.

NTT Technical Review

Vol. 21 No. 3 Mar. 2023

4. Conclusion
We reviewed trends in ultra-wideband WDM transmission techniques to expand the capacity of opticaltransmission systems and NTT’s latest R&D in thefield. With the combination of ultra-wideband WDM
transmission and digital coherent technology using
the state-of-the-art DSP-ASIC, we successfully demonstrated the first ever over 100-Tbit/s real-timetransmission. This technology is promising for use in30

Regular Articles

Pre-FEC Q margin (dB)

1.3

C band

0.025 dB

L band

0.037 dB

S band

0.036 dB

1.1
0.9
0.7
0.5
0

10

20

30

40

50

60

Time (min.)Fig. 6. S tability test for signal performance at center channels of S-, C-, and L-band signals with FW- and BW-pumped DRA
during 101-km fiber transmission under 16.95-THz triple-band WDM condition within continuous measurements for
60 min.

future optical transport network systems.
Acknowledgments
This work was supported by the Ministry of Internal Affairs and Communications, “The research anddevelopment project for the Tera-bit optical network
technologies towards big data era” and “Researchand Development of innovative optical network technology that bears new social infrastructure (Technological Theme I) (JP MI00316).”

[4]

[5]

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[2]

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E. Yamazaki, S. Yamanaka, Y. Kisaka, T. Nakagawa, K. Murata, E.
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Nakashima, T. Mizuochi, K. Kubo, Y. Miyata, H. Nishimoto, S.
Hirano, and K. Onohara, “Fast Optical Channel Recovery in Field
Demonstration of 100-Gbit/s Ethernet over OTN Using Real-time
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S. Okamoto, K. Yonenaga, K. Horikoshi, M. Yoshida, Y. Miyamoto,
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Kametani, K. Kubo, and T. Sugihara, “400 Gbit/s/ch Field
Demonstration of Modulation Format Adaptation Based on Pilotaided OSNR Estimation Using Real-time DSP,” IEICE Trans.
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F. Hamaoka, T. Sasai, K. Saito, T. Kobayashi, A. Matsushita, M.

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[6]

[7]

[8]

Nakamura, H. Taniguchi, S. Kuwahara, H. Kawahara, T. Seki, J.
Ozaki, Y. Ogiso, H. Maeda, Y. Kisaka, and M. Tomizawa, “Dualcarrier 1-Tb/s Transmission over Field-deployed G.654.E Fiber Link
Using Real-time Transponder,” IEICE Trans. Commun., Vol. E103-B,
No. 11, pp. 1183–1189, Nov. 2020.
NTT press release, “World’s largest capacity of 1.2 Tbit/s per
wavelength by newly developed digital coherent signal processing
circuit and optical device - For larger capacity, longer transmission
distances, and lower power consumption in optical networks -,” Sept.
5, 2022.
https://group.ntt/en/newsrelease/2022/09/05/220905a.html
A. Sano, T. Kobayashi, S. Yamanaka, A. Matsuura, H. Kawakami, Y.
Miyamoto, K. Ishihara, and H. Masuda, “102.3-Tb/s (224 × 548-Gb/s)
C- and Extended L-band All-Raman Transmission over 240 km Using
PDM-64QAM Single Carrier FDM with Digital Pilot Tone,” Proc. ofthe 35th Optical Fiber Communication Conference and Exposition
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Matsushita, E. Yamazaki, and Y. Kisaka, “Ultra-wideband WDM
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F. Hamaoka, K. Saito, A. Masuda, H. Taniguchi, T. Sasai, M.
Nakamura, T. Kobayashi, and Y. Kisaka, “112.8-Tb/s Real-time
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CA, USA, Paper W3G.3, Mar. 2016.

31

Regular Articles

Fukutaro Hamaoka

Senior Research Engineer, NTT Network Innovation Laboratories.
He received a B.E., M.E., and Ph.D. in electrical engineering from Keio University, Kanagawa, in 2005, 2006, and 2009. From 2009 to 2014,
he was with NTT Network Service Systems
Laboratories, where he was engaged in the R&D
of high-speed optical communication systems,
including digital coherent optical transmission
systems. His research interests include highcapacity optical transport systems with ultrawideband WDM and high-symbol rate techniques. He is a member of the Institute of Electronics, Information and Communication Engineers (IEICE) of Japan and the Institute of Electrical and Electronics Engineers (IEEE). He hasserved as a program sub-committee member of
the Optical Communication Systems and Networks category for the 15th Pacific Rim Conference on Lasers and Electro-Optics (CLEO-PR)
in 2022. He was the recipient of the Japan Society of Applied Physics Young Scientist Presentation Award in 2007 and IEICE Communications
Society Optical Communication Systems (OCS)Best Paper Award in 2022.

Kohei Saito

Research Engineer, NTT Network Innovation
Laboratories.
He received an M.S. in electronics and applied
physics from Tokyo Institute of Technology in2013. In the same year, he joined NTT Network
Service Systems Laboratories, where he wasengaged in development on optical communication systems. In 2020, he moved to NTT Network
Innovation Laboratories and has been investigating high-capacity optical transmission systems.
He is a member of IEICE.

Akira Masuda

Research Engineer, NTT Network Innovation
Laboratories.
He received a B.E. and M.E. in electrical engineering from Tokyo University of Science in2011 and 2013. In 2013, he joined NTT Network
Innovation Laboratories, where he was engaged
in research on optical technologies for highspeed short-reach transmission. From 2019 to
2021, he was with NTT Communications Corporation, where he was engaged in the development
of beyond 100-Gbit/s/ch optical WDM transmission systems. Since 2021, he has been with NTT
Network Innovation Laboratories, where he isengaged in research on optical transmission
technologies for high-capacity optical transport
networks. He received the Young Researcher’sAward from IEICE in 2019.

Takeo Sasai

Researcher, NTT Network Innovation Laboratories.
He received a B.E. and M.E. in electrical engineering from the University of Tokyo in 2015
and 2017. Since 2021, he has been working
toward a Ph.D. in applied physics at the same
university. In 2017, he joined NTT Network
Innovation Laboratories. He is engaged in themodeling of optical fiber communication systems from both behavioral and data-driven
approaches, particularly optical fiber nonlinearity and transceiver nonlinearity. He is a memberof Optica, IEICE, and IEEE. He was a recipientof the IEICE Communications Society OCS
Young Researchers Award in 2021 and the IEICE
Young Researcher’s Award in 2021.

Masanori Nakamura

Research Engineer, NTT Network Innovation
Laboratories.
He received a B.S. and M.S. in applied physics
from Waseda University, Tokyo, in 2011 and2013, and Ph.D. in electrical, electronic, andinfocommunications engineering from Osaka
University in 2021. In 2013, he joined NTT Network Innovation Laboratories, where he isengaged in research on high-capacity opticaltransport networks. He is a member of IEICE andIEEE. He received the IEICE Communications
Society OCS Young Researchers Award in 2016
and IEICE Communications Society OCS Best
Paper Award in 2022.

Takayuki Kobayashi

Distinguished Researcher, NTT Network Innovation Laboratories.
He received a B.E., M.E., and Dr. Eng. fromWaseda University, Tokyo, in 2004, 2006, and2019. In April 2006, he joined NTT Network
Innovation Laboratories, where he was engaged
in the research on high-speed and high-capacity
digital coherent transmission systems. In April
2014, he moved to NTT Access Network Service
Systems Laboratories and was engaged in fifthgeneration mobile optical network systems. In
July 2016, he moved back to NTT Network
Innovation Laboratories and has been working
on high-capacity optical transmission systems.
His current research interests are long-haul optical transmission systems using spectrally efficient modulation formats enhanced by digitaland optical signal processing. He is a member of
IEICE and IEEE. He has served as a technicalprogram committee (TPC) member of the Electrical Subsystems’ Category for the Optical Fiber
Communication Conference (OFC) from 2016 to2018. He has been serving as a TPC member of
the Point-to-Point Optical Transmission Category for the European Conference on Optical Communication (ECOC) since 2018.

Hiroki Taniguchi

Researcher, NTT Network Innovation Laboratories.
He received a B.E. and M.E. in electrical engineering from Tokyo Institute of Technology in2014 and 2016. In 2016, he joined NTT Network
Innovation Laboratories. His research interests
include photonic transport network systems. He
is a member of IEICE. He was a recipient of the
IEICE Communications Society OCS Young
Researchers Award in 2019 and the IEICE Young
Researcher’s Award in 2020.

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32

Regular Articles

Yoshiaki Kisaka

Senior Research Engineer, Supervisor, Transport Innovation Laboratory, NTT Network Innovation Laboratories.
He received a B.E. and M.E. in physics from
Ritsumeikan University, Kyoto, in 1996 and1998. In 1998, he joined NTT Optical Network
Systems Laboratories, where he was engaged in
R&D on high-speed optical communication systems including 40-Gbit/s/ch WDM transmission
systems and mapping/multiplexing scheme in the
Optical Transport Network (OTN). From 2007 to
2010, he was with NTT Electronics Technology
Corporation, where he was engaged in the development of 40/100-Gbit/s OTN framer large-scale
integrated circuits. His current research interests
are in high-speed and high-capacity optical transport network using digital coherent technology.
From 2010, he has been contributing to the R&D
of digital coherent signal processers at 100 Gbit/sand beyond. He is a member of IEICE.

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33

Global Standardization Activities

Report of the ITU Plenipotentiary
Conference 2022 (PP-22)
Memiko Otsuki and Noriyuki Araki
Abstract

The Plenipotentiary Conference 2022 (PP-22) of the International Telecommunication Union (ITU)
was held in Bucharest, Romania, from 26 September to 14 October 2022. This article gives an overview
of the conference and its major deliberations.
Keywords: ITU, PP, election, ICT, development

1. Introduction​The Plenipotentiary Conference 2022 (PP-22) of
the International Telecommunication Union (ITU)
was held in Bucharest, Romania, from 26 September
to 14 October 2022. About 2500 people from 193
countries participated in the conference, and the Japanese delegation consisted of about 90 people from thegovernment and private sectors, led by Mr. Yoshifumi
Tsuge, State Minister for Internal Affairs and Communications, and Mr. Hiroshi Yoshida, Vice Minister
for Policy Coordination (International Affairs) of the
Ministry of Internal Affairs and Communications.
2. Overview of PP-22
The PP is the highest decision-making body of ITU,
which meets once every four years. Representativesof all member countries (Member States) participate
in the conference for the elections of senior officials
and the Member States of the ITU Council (Council
Member States) for the next period and for the discussion of important documents such as PP resolutions.
The PP-22 established six committees (COMs) and a
Working Group of the Plenary (WG-PL) under the
Plenary. COM1 was a Steering Committee, COM2
dealt with credentials, COM3 with budget control,
COM4 with editing, COM5 with policy and legal
matters, COM6 with administration and management, and WG-PL with the reports and proposals andrecommend appropriate actions with regard to issues
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related to public policies, including Internet, andother general matters. Mr. Sabin Sărmaș, a memberof the Romanian Parliament and a Chairman of the
IT&C Commission within the Chamber of Deputies,
was appointed the Chair of the conference.
3. Results of the elections of senior officials andCouncil Member States
The PP-22 held elections of ITU senior officials
and Council Member States for the period 2023–
2026. The Japanese candidate Seizo Onoe (Chief
Standardization Strategy Officer, NTT) was elected
as the next Director of the Telecommunication Standardization Bureau (TSB). He will serve one term offour years, with a maximum of two terms. In addition
to Mr. Onoe, there were two other candidates runningfor the post of the TSB Director: Dr. Thomas Zielke(Germany) and Dr. Bilel Jamoussi (Tunisia), a current TSB staff member. Mr. Onoe was elected on thefirst ballot with a majority of the votes cast by the
PP-22 participating Member States entitled to vote.
This is the first time a Japanese national has been
elected as the Director of TSB, and he is expected tobe responsible for the standardization of next-generation telecommunications networks.
In addition to the next TSB Director, the PP-22 also
saw the election of the next Secretary-General, thenext Deputy Secretary-General, the next Director ofRadiocommunication Bureau, the next Director of
the Telecommunications Development Bureau, the34Global Standardization Activities

next member of the Radio Regulations Board, and thenext Council Member States, with Ms. Doreen Bogdan-Martin (USA) elected as the Secretary-Generaland Mr. Tomas Lamanauskas (Lithuania) as the
Deputy Secretary-General. Mr. Mario Maniewicz(Uruguay) was re-elected for his second term as the
Director of Radiocommunication Bureau, and Dr.
Cosmas Zavazava (Zimbabwe) was elected as the
Director of Telecommunications Development
Bureau.
In the election for the next Council Member States,
Japan also stood for Region E (Asia and the Pacific)(13 seats) and was elected with 146 votes (180 valid
votes). This is the 13th consecutive time since 1959
that Japan has served on the Council. For more information on the election results, see Election Results[1] on the ITU PP-22 website.
4. Major resolutions discussed at PP-22
Fifty-seven resolutions and two decisions wererevised, one resolution was deleted, and six new resolutions were approved at the PP-22. The following isa summary of the main discussions and outcomes.
4.1 Policy and legal matters(1)	Resolution 208: Appointment and maximum
term of office for chairmen and vice-chairmen of
sector advisory groups, study groups, and othergroupsBased on the Japanese proposal, it was agreed toreport the attendance rate of the chairmen and vicechairmen to the relevant assemblies or conferences.
The Russian region proposed that the candidates
agreed upon by each region for the appointment of
the chairmen and vice-chairmen be approved at theassembly level meeting, but this proposal was notreflected due to the opposition from the U.S., European countries, and Japan. The author of this article,
Ms. Memiko Otsuki, chaired the ad hoc meeting
including this resolution.
(2)	Proposed resolution: Encouraging the participation of industry in the work of the Union
Concerned about the declining participation ofindustry in ITU, a new resolution to enhance theengagement of industry in the work of ITU had been
proposed by the Europe and Americas regions andAustralia. However, since China, Africa and Arabcountries insisted on limiting the definition of “industry,” the conflict could not be resolved, and it wasagreed to insert a recommendation to continue toencourage the enhanced participation of entities and
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organizations in the activities of ITU in the plenary
report.
(3)	New resolution: Use of frequency assignments
by military radio installations for national
defense services
A new resolution includes the following points: afrequency assignment for which Article 48 of the ITUConstitution has been invoked is used only for military radio installations, and the Secretariat may seek
clarification from the Member State regarding possible misuse of this article.
4.2 Administrative and operational matters(1)	Resolution 71: Strategic plan for the Union for
2024–2027
New strategic goals and priorities were set underthe vision and mission for the 2024–27 strategic plan.
After discussion on whether cybersecurity should bea stand-alone priority, it was agreed to merge it withanother priority.
(2)	Decision 5: Revenue and expenses for the Union
for the period 2024–2027
Although the contributions from Member States
increased by 12 1/4 units from the previous period,
the financial plan for 2024–2027 was agreed to beabout 652 million Swiss francs (CHF). It was decided
to maintain the contributory unit for ITU’s annual
budget at 318,000 CHF per year for the period 2024–
2027.
4.3 Matters related to public policies(1) Resolution 130: Cybersecurity
The African, Arab, and Russian regions proposed to
expand the activities of ITU, including enhancing its
role in the United Nations (UN)-wide cybersecurity
discussions, while the Western countries argued that
ITU’s activities should be limited to sharing bestpractices and capacity building. In the latter half ofthe negotiations, the review and revision of the ITU
Global Cybersecurity Agenda (GCA) became themost contentious issue. It was finally agreed to delete
the reference to the GCA in the resolution, but a recommendation that “the ITU Council will consider
proposals from Member States on the GCA and its
possible future elaboration” will be included in theplenary report.
(2) Resolution 139 and proposed new resolution:
Open Radio Access Network (RAN)
Brazil proposed a new resolution including thestandardization of Open RAN, and the Arab region
proposed to include a reference to Open RAN in several resolutions. However, due to the opposition from35

Global Standardization Activities

Europe, the U.S., Canada, and other countries, it wasagreed to include a reference to the promotion andinformation sharing of Open RAN and other activities in Resolution 139, which aims at bridging thedigital divide.
(3) Resolution 206: Over the top (OTT)The Americas region proposed “no change” and theAfrican region proposed a new text to encourage
OTT companies to contribute financially to infrastructure development and instruct the Secretary
General to support the establishment of regulatory
frameworks for OTTs in developing countries.
Although Europe and the U.S. compromised on thechange during the ad hoc discussions, the text was notrevised as a result of the lack of agreement on thecontent of the revised text until the end of the meeting.
(4) New resolution: Artificial intelligence (AI)Two proposals had been submitted for the adoptionof a new resolution on AI, which was rejected by thelast PP (PP-18). The African region emphasized theneed to introduce AI in developing countries toachieve the Sustainable Development Goals, but after
discussion, the European region’s proposal, which
included the continuation of existing work on AI
within the mandate and core competence of ITU andcontinued collaboration with other UN bodies, wasreflected. It was agreed that the title of the resolution
would be “AI technologies and telecommunications/information and communication technologies(ICTs)” to reflect this.
(5)	New resolution: Role of telecommunications/
ICTs in mitigating global pandemics
Several regions proposed a new resolution on therole of ICTs and ITU in pandemic preparedness,
which included working with the World Health Organization and other agencies and organizations within
the mandate of ITU, and support projects and otheractivities that enable the deployment and use of tele-

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communications/ICTs.
4.4 Other topics
The candidacy of India for the 2024 World Telecommunication Standardization Assembly (WTSA24), Thailand for the 2025 World Telecommunication
Development Conference (WTDC-25), and Qatar forthe 2026 Plenipotentiary Conference (PP-26) wereapproved as the host countries for the next major
conferences. Rwanda has also announced its intention to host the 2027 Radiocommunication Assemblyand World Radiocommunication Conference (RA/WRC-27). The exact location and dates will bedecided at a future Council meeting.
5. Conclusion
The PP-22 was held with a sense of tension due to
COVID-19 and Russia’s invasion of Ukraine. However, the meeting proceeded very efficiently andfruitfully, thanks to the scheduled preparatory meetings in each region and inter-regional coordination,
including online, as well as the fact that several resolution proposals were packaged for discussion in thead hoc meetings during the conference. In the election, Japan was elected as a Council Member Statefor the 13th consecutive time since 1959, and Mr.
Seizo Onoe, the candidate for the TSB Director, waselected with a majority of the first ballots cast. The
NTT Group will continue to make efforts to enhance
its presence in the ITU and actively engage in activities related to the development of telecommunications and ICTs and their deployment around theworld.
Reference[1]

ITU PP-22, Election Results, https://pp22.itu.int/en/elections/elections-results/

36

Global Standardization Activities

Memiko Otsuki

Manager, Tariff and Regulatory Affairs Office/Spectrum Planning Office, NTT DOCOMO,
INC.
She received an MPP from the Australian
National University (Canberra, Australia), andB.A. in business management from the International Christian University (Tokyo, Japan). She
is currently serving as a manager of the Tariff andRegulatory Affairs Office and the Spectrum
Planning Office at NTT DOCOMO, where she
has been actively involved in policy and standardization work at ITU and Asia-Pacific Telecommunity (APT). Most recently, she wasappointed as the Vice-Chair of the ITU Telecommunication Development Sector Study Group(SG) 1 and the rapporteur of Question 12 of ITU
Telecommunication Standardization Sector(ITU-T) SG3. Prior to her current position, she
was the assistant director of the Global Strategy
Division at the Ministry of Internal Affairs andCommunications, Japan. In her role, she had
been contributing to a number of ITU activities
including the Council, the Council Working
Group, the Expert Group on the International
Telecommunication Regulations, the Informal
Experts Group on World Telecommunication/
ICT Policy Forum (WTPF-21), the World Summit on the Information Society (WSIS) Forum,
the ITU Telecom, the Broadband Commission,and preparatory meetings for WTSA-20, WTDC22, and PP-22. She has over 15 years of professional experience in the telecommunications/ICT
field and has expertise in policy and regulatory
issues. She received the ITU-AJ Encouragement
Award from the ITU Association of Japan in2017 for her contributions over the years. She isa member of the Japan Society of Information
and Communication Research (JSICR).

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Vol. 21 No. 3 Mar. 2023

Noriyuki Araki

Director, Standardization Office, Research andDevelopment Planning Department, NTT Corporation.
He received a B.E. and M.E. in electrical andelectronic engineering from Sophia University,
Tokyo, in 1993 and 1995. He joined NTT AccessNetwork Service Systems Laboratories in 1995,
where he researched and developed operationand maintenance systems for optical fiber cable
networks. He has been contributing to standardization efforts in ITU-T SG6 since 2006. He was
the rapporteur of Question 6 of ITU-T SG6 from2006 to 2008 and rapporteur of Question 17 of
ITU-T SG15 from 2008 to 2012. He also served
as the chairman of the ITU-T Focus Group on
Disaster Relief Systems and Network Resilienceand Recovery. He was the vice-chairman of
ITU-T SG15 from 2013 to 2022. He also contributes to the activities of International Electrotechnical Commission (IEC) Technical Committee
86 (fiber optic systems). He received the ITU-AJ
award from the ITU Association of Japan in
2017. He is a member of the Institute of Electronics, Information and Communication Engineers(IEICE).

37

Information

Report on NTT R&D Forum—
Road to IOWN 2022
NTT R&D Forum Secretariat
Abstract

NTT R&D Forum—Road to IOWN 2022 was held from November 16th to 18th, 2022. The following
is an introductory overview of the Forum.
Keywords: R&D Forum, IOWN, latest technology

1. Forum overview
With the commercialization of Innovative Opticaland Wireless Network (IOWN)1.0 services close athand, NTT R&D Forum 2022 introduced the latest
achievements of NTT research and development(R&D) toward the further evolution of large-capacity,
low-latency, and low-power communication technologies. It featured keynote speeches by Akira Shimada, president and chief executive officer (CEO) of
NTT Corporation, and Atsuko Oka, executive vicepresident, head of the Research and Development
Planning Department of NTT Corporation, and three
special sessions by members of the IOWN Global
Forum as well as more than 90 research exhibits. The
technology roadmap that has been under consideration is finally taking shape and the light of IOWN isabout to shine. We report on this NTT R&D Forumsuccessfully held online under the theme of “Road to
IOWN 2022.”
2. Keynote speeches/special sessions
2.1 Keynote Speech 1
Under the theme of “IOWN1.0—Start of IOWN
Service,” Akira Shimada, president and CEO of NTT
Corporation, delivered a keynote speech centered on
IOWN services scheduled for launch at the end of
FY2022 (Photo 1).
President Shimada first touched upon key issues
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that arise in a “data-driven society” in which actions
are taken on the basis of data generated by a wide
variety of devices making up the Internet of Things(IoT). These include a significant increase in datacapacity and power consumption as well as communication delays. He announced the commercializationof All-Photonics Network (APN) services by March2023 as the first round of IOWN services (i.e.,
IOWN1.0) to address these issues. He then went on todescribe how APN services could be applied to avariety of services such as remote medicine, smart
factories, and e-sports among remote players byachieving communications that satisfy IOWN performance targets, i.e., a delay 1/200 the current levelwith no flicker. He also presented the possibility oftreating multiple datacenters as a single datacenter byinterconnecting them with high-capacity, low-latency
circuits.
Next, President Shimada talked about “photonicselectronics convergence devices” that merge opticaland electronic circuits as key power-efficient devices
that represent the most outstanding feature of IOWN.
The plan is to apply these devices not only to networking but also to computing to achieve a drastic
reduction in power consumption. He also announced
a detailed plan for service development that, while
applying and expanding these photonics-electronics
convergence devices to APN services and servers,
IOWN would increase communication capacity by
125 times in IOWN3.0 in 2029 and increase power38

Information

Photo 1. K eynote Speech 1 delivered by NTT President
and CEO Akira Shimada.

efficiency by 100 times in IOWN4.0 and beyond as
performance targets.
Finally, President Shimada introduced the urban
development of Urbannet Nagoya nexta Building as
an example of Digital Twin Computing that represents diverse digital copies of real space in cyber
space to conduct data analysis and simulations forpredicting the future. He described how services for
air conditioning control and reduction of food waste
would be commercialized and implemented in
FY2023 and how such a development would “contribute to people-friendly and earth-friendly urban
development” while promoting service enhancement
and expansion. With a view to Expo 2025 Osaka,
Kansai, Japan, President Shimada also declared that
NTT would be announcing pavilion exhibits and thecommercialization of IOWN2.0 services. For details,
please see the article titled “IOWN1.0—Start of
IOWN Service” in this issue.
2.2 Keynote Speech 2
Atsuko Oka, executive vice president, head of
Research and Development Planning Department of
NTT Corporation, also delivered a keynote speech
under the theme of “Road to IOWN – Light Up –.”She described how the actual provision of IOWN
services would begin at the end of FY2022 and that
IOWN would finally shine its light on users (Photo 2).
Though currently at the conceptual level, IOWN isabout to enter a practical phase, and with this in mind,
Executive Vice President Oka announced a variety of
research findings as the first round of research resultsof the IOWN initiative.
In the first topic of her speech, “IOWN Datacenter× APN,” Executive Vice President Oka described theneed for interconnecting NTT datacenters by the
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Photo 2. K eynote Speech 2 delivered by NTT Executive
Vice President and Head of Research andDevelopment Planning Department Atsuko Oka.

APN and accelerating service development in a largescale and practical environment. To deal with thetrend toward increasingly larger datacenters, she
explained a plan to make operations more efficientthrough the APN while decentralizing datacenters.
This approach has the potential of solving the problem of securing land and power. She also introduced
two examples of APN-related achievements. One isthe development of a digital coherent signal processing circuit that can achieve an optical-fiber transmission capacity of 1.2 Tbit/s per wavelength. The otheris the creation of a 400-Gbit/s co-package prototype
for transceivers. She revealed that these technologies
should be commercialized in 2023 and that researchwould continue on basic technologies for supportingnext-generation ultra-high-capacity communications.
Executive Vice President Oka also pointed out that“the current environment that combines AI [artificial
intelligence] and IoT has a network problem,” andthat NTT would solve this problem by interconnecting datacenters by the APN to create a “true industrial infrastructure.”
Given that “high transmission performance for conveying reality” is an intrinsic property of the APN,
Executive Vice President Oka presented remote surgery as a use case of the APN that supports the transmission of visual, acoustic, verbal, and even tactile
information essential to reproducing reality. Then,from among a variety of acoustic and voice technologies that NTT has long been researching, sheannounced the development of advanced acoustic
technology for wirelessly controlling underwater
drones. She also introduced the world’s first earphones and speakers using Personalized Sound Zone
(PSZ) technology that generates only the sound that
39

Information

Photo 3. S pecial Session 1: (from left) Dr. Brent Waters
and NTT Research CEO Kazuhiro Gomi.

you want to hear and cancels out unwanted ambient
noise. For details, please see the article titled “Roadto IOWN – Light Up –” in this issue.
2.3 Special Session 1
In Special Session 1, “Protocols for Post Quantum
Cryptography,” Dr. Brent Waters, director of Cryptography & Information Security Laboratories (CIS
Lab), NTT Research, Inc., spoke with Kazuhiro
Gomi, president and CEO of NTT Research, about
the current research in this field (Photo 3).
Dr. Waters began the discussion by talking about
the problem of using quantum computing to breakpublic-key encryption, one of the encryption systems
now in use. Learning with error, which adds error
during inner-product computation, is a lattice-based
encryption scheme that can withstand even calculations by a quantum computer, and Dr. Waters
explained that this function has various benefits apartfrom post-quantum cryptography.
Next, in response to the question: “Can public-key
encryption be protected against malicious acts?” Dr.
Waters replied “Definitely yes!” In support of his
answer, he touched upon a method that can avoid therisk of security breaches, citing fully homomorphic
encryption technology proposed by Craig Gentry in2009. This method “enables computations to be performed on received data despite knowing nothing
about that data.” Additionally, as a deeply interesting
encryption technology, Dr. Waters talked about attribute-based encryption, which he invented, as ascheme that executes “encrypting toward an accesspolicy,” and gave examples of advanced versions of
this function developed in succession by fellow
researchers. In the second half of the session, theNTT Technical Review

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Photo 4. S pecial Session 2: (Top) Gonzalo Camarillo;(from bottom left) Andres Arjona, Ian A. Hood,
Katsutoshi Itoh, and Masahisa Kawashima.

NTT Belgium team introduced a method using attribute-based encryption to protect portions of images
that include highly confidential information.
Finally, with respect to risks in post-quantum cryptography, Dr. Waters said “While we don’t know how
many years it will take for large-scale quantum computers to appear, we must devise countermeasures inadvance,” and emphasized the importance of being
cautious about those risks.
2.4 Special Session 2
Special Session 2 titled “Have your ticket ready.
IOWN is taking off NOW!” brought together fivemembers of the IOWN Global Forum to discuss
proof of concept (PoC) activities (Photo 4). Moderator Gonzalo Camarillo, chair of the Marketing Steering Committee, talked with panelists Andres Arjona,editor of IOWN GF Vision 2030 White Paper, Ian A.
Hood of Red Hat, Katsutoshi Itoh, chair of the Use
Case Working Group, and Masahisa Kawashima,
head of IOWN Development Office and chair of theTechnology Working Group.
Mr. Arjona began the session by sharing his vision.
Mr. Itoh then introduced use cases implemented in
2022 while Mr. Kawashima introduced the APN and
Data Centric Infrastructure (DCI) as key IOWN technologies along with their role in PoC activities. Mr.
Camarillo then opened the discussion by sharing hisview of the “importance of reiterations in developing
and further evolving paper specifications and use
cases based on PoC implementations.”
Starting with the topic of “study items in PoC
activities and activities now being focused on,” eachpanelist reported on specific PoC activities that40

Information

IOWN Global Forum commenced in 2022, indicating
technical specifications that had been discussed since2021 are finally breaking through into an implementation phase.
First, Mr. Hood introduced PoC activities forachieving use cases on Red Hat’s platform and demonstrating the advantages of the APN. He described
how technologies such as remote direct memory
access and remote information management security
could be used to eliminate some of the technology
gaps that are needed to implement those use cases. He
also presented a plan for demonstrating the advantages of the APN in the mobile field and accelerating
the introduction of new services. Next, Mr. Arjonadescribed a plan to develop a PoC regarding use of
the APN in the mobile fronthaul. Continuing on, Mr.
Itoh reported on activities using sensing and robotic
solutions in the entertainment and industry-management fields. Finally, Mr. Kawashima reported on thebuilding of an IOWN testbed that will use the APN toconnect current NTT datacenters in major cities andon the development of use cases, the feasibility andviability of which will be tested in 2023.
Turning to the second topic of “what comes next
after PoC,” Mr. Arjona shared his idea of promoting
global alliances and collaborative activities withother standards bodies to open up new horizons in
optical communications. Mr. Hood then announced aplan for achieving targets at standards bodies andwithin open source projects and Mr. Itoh reported on
activities for bringing service providers into an open
ecosystem. Finally, Mr. Camarillo concluded the session by sharing his outlook for the future, saying “Iwould like to make it a tradition of NTT R&D Forumto explain our work on realizing and popularizing
IOWN and what advances we were able to make eachyear.”
2.5 Special Session 3
In Special Session 3, “The Era of Space Voyages: A
Compass for Carving a Path to the Future,” celebrity
Harry Sugiyama served as Master of Ceremonies inwelcoming Koichiro Matsufuji and Shigehiro Hori,
representative directors and Co-CEOs of Space Compass Corporation, to talk about the future of the spaceindustry (Photo 5).
The Space Integrated Computing Network concept
promoted by Space Compass Corporation is a planfor “connecting all people and things on the ground,on the sea, in the air, and in outer space by opticalcommunication at high speeds.” To achieve the
Beyond fifth-generation (5G)/6G mobile network
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Photo 5. S pecial Session 3: (from left) Harry Sugiyama,
Shigehiro Hori, and Koichiro Matsufuji.

envisioned by NTT, this plan aims to construct newhigh altitude platform stations (HAPS) to cover terrestrial communication bands throughout Japan fromthe stratosphere and low Earth orbits in space and toobserve Earth in real time. Mr. Matsufuji explainedthat the benefit of this plan is “the ability to objectively capture the true conditions and appearance ofEarth by observing it from space.”
Next, Mr. Hori and Mr. Matsufuji talked about thethree business pillars of the Space Integrated Computing Network concept: space sensing, space datacenter, and space radio access network. They
explained that the Space Integrated Computing Network will make possible what heretofore has been
impossible, such as the “reliable implementation ofdisaster-prevention measures, transmission of economic information, and ensuring of national security”
by collecting data through observations of what cannot be seen with the human eye. Among these developments, they introduced experiments currently
being conducted on eagerly anticipated non-terrestrial infrastructure HAPS with a view to achieving
practical communications by 2025.
Finally, as visions of the future, Mr. Hori talked
about the need for people to undertake “business andchallenges that will pave the way to the new era ofspace voyages,” while Mr. Matsufuji stressed theneed for “constructing a network that can support
technologies such as robots, drones, and self-driving
for the coming aging society.”
3. Research exhibits
NTT’s latest technologies and research achievements were introduced through virtual exhibit booths
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Information

Fig. 1. Use case of surgical robot using IOWN APN.

Fig. 2. Photonic and electronic device technology for the APN.

divided into six categories. We report on research that
attracted particular attention.
3.1 Network
In the “Network” category, we introduced a varietyof optical/wireless network technologies centered on
IOWN APN services to be provided from March
2023.
In “Use case of surgical robot using IOWN APN,”
we introduced technology for supporting surgicalrobots as an example of applying the APN (Fig. 1). A
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Vol. 21 No. 3 Mar. 2023

service using this technology will be provided from
2023. We anticipate that medical treatment from evenmore remote locations will become possible byachieving robot operations and video transmission
with low latency and no flicker through the APN and
implementing a high-security surgery environment
by adding encryption technology.
In “Photonic and electronic device technology for
APN,” we introduced a variety of advanced functional devices for supporting high-speed and largecapacity optical paths in the APN (Fig. 2). These
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Fig. 3. Personalized Sound Zone (PSZ).

Fig. 4. Metaverse in the IOWN era.

include an optical device that achieves the world’s
largest capacity of 1.2 Tbit/s and a next-generation
high-density interface, both of which contribute tomeeting the IOWN performance targets of large
capacity, low latency, and low power consumption.
3.2 XR (UI/UX)
In the “XR (UI/UX)” category, we exhibited technologies for supporting the convergence of the realworld and cyber world and for supporting a remoteworld that enables experiences that transcend thereal-world environment.
In “Personalized Sound Zone (PSZ),” we introduced research on controlling the ambient sound
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Vol. 21 No. 3 Mar. 2023

space and creating a sound space appropriate for theuser (Fig. 3). Using technology for blocking ambient
sound and technology for hearing the sounds desiredby the user, we exhibited a comfortable-and-safe
sound space inside a vehicle and the world’s first
open-ear earphones.
In “Metaverse in IOWN era,” we held a demonstration of future communication in which the real andvirtual are intermixed using “3D [three-dimensional]
spatial media processing technology” to achieve real
space and “Another Me technology” to enable anavatar having a real identity to behave in an autonomous manner in cyber space (Fig. 4). The aim is toheighten connections between people and society and43

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Fig. 5. Secure optical transport network for quantum computer age.

NG: not goodFig. 6. Verification of AI’s identity by its profile.

create a sustainable society receptive to diversity.
3.3 Security
In the “Security” category, we presented technologies for achieving safe and secure communications
using encryption technology.
In “Secure optical transport network for quantum
computer age,” we introduced secure cryptographic
technologies in anticipation of quantum computersthat are expected to become a reality from 2030 on(Fig. 5). For example, “elastic key control technoloNTT Technical Review

Vol. 21 No. 3 Mar. 2023

gy” that combines multiple algorithms and key-sharing protocols will eliminate security breaches inencrypted communications, digital signatures,
authentication and approval, etc.
In “Verification of AI’s identity by its profile,” weintroduced technology for preventing damage caused
by impersonating AI as AI comes to be widely used
(Fig. 6). It will be possible to identify inappropriate
AI by paying attention to those locations focused on
by AI and examining output results. The aim is topromote the safe use of AI in business and enable44

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Fig. 7. Real-time translation technology to break the language barrier for business.

Fig. 8. Signal-free mobility: distributed traffic coordination without traffic signals.

people and AI to coexist and prosper together.
3.4 AI/Computing
In the “AI/Computing” category, we introduced
services using AI in diverse fields and presented
exhibits using AI.
In “Real-time translation technology to break thelanguage barrier for business,” we introduced highaccuracy Japanese-English simultaneous translation
technology as an alternative to interpretation (Fig. 7).
This technology achieves natural translation of conversations in real time by combining technology for
automatically removing words, pauses, etc. deemed
unnecessary for conveying the meaning of a sentence, technology for automatically inferring theposition of sentence delimiters, and a machine-translation engine.
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Vol. 21 No. 3 Mar. 2023

In “Signal-free mobility: distributed traffic coordination without traffic signals,” we demonstrated andpresented “signal-free mobility” in which vehicles
can run without colliding with each other on streetswith no traffic signals by using digital twins (Fig. 8).
In a demonstration using digital twins in the virtualworld and miniature cars in the real world, we
showed that optimal traffic control could be achieved
through mutual feedback between these two worlds.
Therefore, we expect signal-free mobility to put an
end to existing traffic problems such as congestion at
traffic intersections.
3.5 Environment and Energy
In the category of “Environment and Energy,” weexhibited technologies for achieving a comfortableenvironment on Earth with a view to achieving the45

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DBR laser: distributed Bragg reflector laser

Fig. 9. Semiconductor laser diode for carbon dioxide gas sensing.

Fig. 10. Biological conversion technology to reduce CO2 in the ocean.

Sustainable Development Goals (SDGs) and carbon
neutrality.
In “Semiconductor laser diode for carbon dioxide
gas sensing,” we described sensing technology thatuses a semiconductor laser to accurately measure thestate of carbon dioxide (CO2) gas (Fig. 9). This technology can measure CO2 concentrations in real timeeven in environments with large state changes such as
thermoelectric power stations, which has not beenpossible with conventional lasers. It can contribute toa decrease in environmentally harmful gases and the
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easing of global warming.
In “Biological conversion technology to reduce
CO2 in the ocean,” we introduced genome-editing
technology to enhance carbon fixation in algae, fish,and shellfish that absorb CO2 in the ocean and technology for evaluating the annual amount of carbon
fixation (Fig. 10). Decreasing the amount of CO2 in
the ocean will help reduce its impact on the marine
ecosystem, solve a variety of global environmental
problems, and achieve carbon neutrality.

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Information

Fig. 11. Social well-being to enhance employee experience and create customer experience.

Fig. 12. Assessing one’s physical performance through mobile sensing and bioinformatics.

3.6 Basic Research
Finally, in the category of “Basic Research,” weintroduced basic research in diverse fields to foster
innovation in society as in the R&D of physical neural networks and bio digital twins. In “Social wellbeing to enhance employee experience and createcustomer experience,” we exhibited research focusing on values (well-being) that do not depend only on
economic rationality (Fig. 11). This research treats“Self-as-We”—a view of self based on East Asian
traditions of thought—as a key concept and establishes technologies for supporting and measuring
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engagement between the individual and the group
together with methodologies to achieve both individual well-being, or employee experience, and thecreation of group achievements, or customer experience.
In “Assessing one’s physical performance throughmobile sensing and bioinformatics,” we presented
research on preventing cardiovascular disease—forwhich the number of patients is increasing yearly—
by using an individual’s Bio Digital Twin to generatecoronary and other physical conditions in cyber spacefrom the biological data of that person (Fig. 12).
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Thus, measurement of cardiopulmonary functions bya simple examination and effective rehabilitation
proposals will contribute to enhanced health maintenance and the prevention of serious illnesses formany people, giving hope for tomorrow.
4. NTT R&D Forum comes to a close
NTT R&D Forum 2022, which was held online forthe third time in a row, introduced a variety of
research projects, and to present exhibits that werevisually easy to understand, we used illustrations thatmade it easy to imagine the content of research andpanels that enabled key technical points to be understood at a glance. With an eye to the launch of IOWN

services, we used examples of specific systems andinitiatives to convey to everyone cutting-edge technologies that will brighten up the future in a multitudeof ways.
Going forward, the NTT Group will continue thework of technology development to solve a wide
variety of social problems. It is our wish to deliver
new experiences and emotions and create a new
future together with everyone. Please follow the evolution of IOWN in the years to come!
The keynote speeches (videos) and exhibitions areposted on the special website “Report on NTT R&D
Forum─Road to IOWN 2022” (https://www.rd.ntt/e/
forum/2022/index.html).

Members of NTT R&D Forum Secretariat: (from left)
Yoshifumi Shiraki, NTT Science and Core Technology
Laboratory Group; Hirofumi Abe, NTT Service Innovation
Laboratory Group; Keita Takahashi, NTT Information
Network Laboratory Group/NTT IOWN Integrated
Innovation Center; Shunsuke Mori, Research andDevelopment Planning Department, NTT Corporation;
Tokinobu Mitasaki, Research and Development Planning
Department, NTT Corporation; Takayuki Onzuka, Researchand Development Planning Department, NTT Corporation;
Hironari Yokoi, Research and Development Planning
Department, NTT Corporation; and Taeko Tamada,
Research and Development Planning Department, NTT
Corporation.

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Vol. 21 No. 3 Mar. 2023

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External Awards
SIGGRAPH Asia 2022 Emerging Technologies Best DemoAward
Winners: Kengo Sato, Tokyo Institute of Technology; Hiroki Tera‑shima, NTT Communication Science Laboratories; Shin’ya Nishida,
Kyoto University/NTT Communication Science Laboratories; Yoshi‑
hiro Watanabe, Tokyo Institute of Technology
Date: December 9, 2022
Organization: Special Interest Group on Computer Graphics andInteractive Techniques (SIGGRAPH) Asia 2022

Published as: A. A. Hasegawa, N. Yamashita, M. Akiyama, and T.
Mori, “Experiences, Behavioral Tendencies, and Concerns of Nonnative English Speakers in Identifying Phishing Emails,” Journal of
Information Processing, Vol. 30, pp. 841–858, 2022.

For “E.S.P.: Extra-sensory Puck in Air Hockey Using the Projec‑
tion-based Illusion.”
Published as: K. Sato, H. Terashima, S. Nishida, and Y. Watanabe,“E.S.P.: Extra-sensory Puck in Air Hockey Using the Projectionbased Illusion,” Proc. of SIGGRAPH Asia 2022, Article no. 3,
Daegu, South Korea, Dec. 2022.

For research on quantum supremacy of measurement-based quan‑tum computation and its verification.
Published as: Y. Takeuchi, A. Mantri, T. Morimae, A. Mizutani, andJ. F. Fitzsimons, “Resource-efficient Verification of Quantum Com‑puting Using Serfling’s Bound,” npj Quantum Information, Vol. 5,
Article no. 27, 2019.
Y. Takeuchi and T. Morimae, “Verification of Many-qubit States,”
Phys. Rev. X, Vol. 8, 021060, 2018.
Y. Takeuchi and Y. Takahashi, “Ancilla-driven Instantaneous Quan‑tum Polynomial Time Circuit for Quantum Supremacy,” Phys. Rev.
A, Vol. 94, 062336, 2016.

Best Paper Award
Winners: Masahiro Kohjima, NTT Human Informatics Laborato‑
ries; Yuta Nambu, NTT Human Informatics Laboratories; Yuki Kura‑uchi, NTT Human Informatics Laboratories; Ryuji Yamamoto, NTT
Human Informatics Laboratories
Date: December 13, 2022
Organization: The 29th International Conference on Neural Infor‑
mation Processing (ICONIP 2022)
For “General Algorithm for Learning from Grouped Uncoupled
Data and Pairwise Comparison Data.”
Published as: M. Kohjima, Y. Nambu, Y. Kurauchi, and R. Yama‑
moto, “General Algorithm for Learning from Grouped Uncoupled
Data and Pairwise Comparison Data,” ICONIP 2022, Nov. 2022.
Specially Selected Paper
Winners: Ayako A. Hasegawa, National Institute of Information andCommunications Technology; Naomi Yamashita, NTT Communica‑tion Science Laboratories; Mitsuaki Akiyama, NTT Social Informat‑
ics Laboratories; Tatsuya Mori, Waseda University
Date: December 15, 2022
Organization: Information Processing Society of Japan (IPSJ)
For “Experiences, Behavioral Tendencies, and Concerns of Nonnative English Speakers in Identifying Phishing Emails.”

NTT Technical Review

Vol. 21 No. 3 Mar. 2023

Young Scientist Award of the Physical Society of Japan
Winner: Yuki Takeuchi, NTT Communication Science Laboratories
Date: March 22, 2023
Organization: The Physical Society of Japan

Japanese Society of Crop Science Young Scientist Award
Winner: Kazuma Sakoda, NTT Space Environment and Energy
Laboratories
Date: March 29, 2023
Organization: Crop Science Society of JapanFor his physiological and genetic study on leaf photosynthesis incrops in fluctuating environments.
Published as: K. Sakoda, Y. Tanaka, S. P. Long, and T. Shiraiwa,“Genetic and Physiological Diversity in the Leaf Photosynthetic
Capacity of Soybean,” Crop Science, Vol. 56, pp. 2731–2741, 2016.
K. Sakoda, S. Suzuki, H. Fukayama, Y. Tanaka, and T Shiraiwa,“Activation State of Rubisco Decreases with the Nitrogen Accumula‑tion during the Reproductive Stage in Soybean [Glycine max (L.)
Merr.], Photosynthetica, Vol. 57, No. 1, pp. 231–236, 2019.
K. Sakoda, A. Kaga, Y. Tanaka, S. Suzuki, K. Fujii, M. Ishimoto, andT. Shiraiwa, “Two Novel Quantitative Trait Loci Affecting the Varia‑
tion in Leaf Photosynthetic Capacity among Soybeans,” Plant Sci‑ence, Vol. 291, 110300, 2019.

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Papers Published in Technical Journals andConference Proceedings
Topological Thouless Pumping in Arrays of Coupled Spin
ChainsV. M. Bastidas
Physical Review B, Vol. 106, No. 22, L220308, December 2022.
Thouless pumping is a mechanism to perform the topologicallyprotected transport of particles by adiabatically modulating the Ham‑
iltonian. The transported current is a topological invariant that is
intimately related to the integer quantum Hall effect. Most of theprevious works focus on topological pumping in linear and squarelattices. In this Letter, we theoretically propose a mechanism to per‑form topological pumping in arrays of spin chains with complex
geometries. To achieve this, we consider an array where the spin
chains are coupled through their edges, which allows us to split the
populations to generate superpositions of spin excitations in different
spin chains. We show that due to the topological protection, the quan‑tum superpositions can be transported through the array against theeffect of disorder. This approach will open another avenue to trans‑
port excitations and correlated states with potential applications inquantum technologies and information processing. Our ideas can berealized in state-of-the-art quantum simulators such as cold atoms
and superconducting qubit arrays.

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Vol. 21 No. 3 Mar. 2023

Finite-key Security Analysis of Differential-phase-shift
Quantum Key Distribution
A. Mizutani, Y. Takeuchi, and K. Tamaki
arXiv:2301.09844, January 2023.
Differential-phase-shift (DPS) quantum key distribution (QKD) is
one of the major QKD protocols that can be implemented with asimple setup using a laser source and a passive detection unit.
Recently, an information-theoretic security proof of this protocol has
been established in [npj Quant. Inf. 5, 87 (2019)] assuming the infi‑
nitely large number of emitted pulses. To implement the DPS proto‑
col in a real-life world, it is indispensable to analyze the security withthe finite number of emitted pulses. The extension of the security
proof to the finite-size regime requires the accommodation of thestatistical fluctuations to determine the amount of privacy amplifica‑tion. In doing so, Azuma’s inequality is often employed, but unfortu‑
nately we show that in the case of the DPS protocol, this results in a
substantially low key rate. This low key rate is due to a loose estima‑tion of the sum of probabilities regarding three-photon emission
whose probability of occurrence is very small. The main contributionof our work is to show that this obstacle can be overcome by exploit‑
ing the recently found novel concentration inequality, Kato’s inequal‑
ity. As a result, the key rate of the DPS protocol is drastically
improved. For instance, assuming typical experimental parameters, a
3 Mbit secret key can be generated over 77 km for 8.3 hours, whichshows the feasibility of DPS QKD under a realistic setup.

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