NTT Technical Review
April 2014 Vol. 12 No. 4
Feature Articles: Keynote Speeches at NTT R&D
Forum 2014
Hiroo Unoura
President & CEO, NTT
Hiromichi Shinohara
Director and Executive Vice President
Director of Research and Development Planning
Department, NTT

Feature Articles: Cutting-edge Device and Materials
Technologies for Creating New Business
Innovative Services in Medicine, Healthcare, and Environment with
Advanced Device and Materials Technologies
Electrocardiogram Monitoring Simply by Wearing a Shirt––
For Medical, Healthcare, Sports, and Entertainment
200-kHz Swept Light Source Using a KTN Deflector and a
High-speed Optical Coherence Tomography System
Terahertz Spectroscopic Identification of Pharmaceutical
Crystals: Cocrystals and Polymorphic Forms
Highly Sensitive Laser Based Trace-gas Sensor Technology and
Its Application to Stable Isotope Ratio Analysis
GaN-on-Si Technology for High-power Transistors

Global Standardization Activities
Standardization Activities on EMC for Telecommunication in
ITU-T SG5

Practical Field Information about
Telecommunication Technologies
Case Studies of Insulation Failures in Outdoor Facilities andCountermeasures against Failures

New NTT Colleagues
We welcome our newcomers to the NTT GroupPapers Published in Technical Journals
and Conference Proceedings
Papers Published in Technical Journals and Conference Proceedings

Feature Articles: Keynote Speeches at NTT R&D Forum 2014

Accelerating Innovation and
Collaboration for the Next Stage
Hiroo Unoura
President & CEO, NTT
Abstract

This article introduces a vision for new services to be achieved by
2020 and the technical challenges taken on by the NTT Group to provide behind-the-scenes support. The content of this article is based on
the keynote lecture presented by NTT President and CEO Hiroo
Unoura at NTT R&D Forum 2014 held on February 13–14, 2014.
Keywords: innovation, collaboration, cloud

1. Towards the Next Stage
NTT’s Medium-Term Management Strategy
announced in the fall of 2012 can be summarized byits subtitle “Towards the Next Stage.” In this regard,
we are all delighted that Japan will host the “Big
Event” in 2020, and I believe that this Big Event ismaking the “next stage” easier to visualize whileclarifying targets for our business development
schedule.
The key concept of our Medium-Term Management Strategy is “value partner.” For NTT, the time
has come to shift from a business-to-consumer (B2C)
model of selling lines and terminals to a cloud-based
business model. In this shift, we aim to support abusiness-model transformation among our corporate
customers and the creation of enriched lifestyles
among our individual customers. It is in this sensethat we use the term “value partner.”
There are a number of major currents in the field of
information and communication technology (ICT) in
relation to global, cloud, and mobile technologies,
and there are many and varied players in this field.
While it may appear to be a highly competitive era, I
personally believe that we have entered an era of

cooperation and collaboration.
In a cloud or global era, customers can freely selecttheir services. It therefore stands to reason that being
competitive in such an era means the ability to becontinually selected by our customers. In short, theessence of being competitive is not getting a customer to buy something just once but in retaining that
customer for a long period of time.
To become the value partner that customers continue to select, I believe it is extremely important that
we have cooperative and collaborative abilities topromote new businesses with a variety of players.
2. The year 2020
A number of interesting forecasts have been madein relation to 2020, as shown in Fig. 1. First of all,while the gross domestic product (GDP) looks as if itwill pick up steam in China and emerging countries,
Japan at the center of this figure is marked with asmall circle. This forecast was made by a variety of
researchers before the decision was made about the2020 Big Event. I would therefore like to use the Big
Event as an opportunity to do what we can to makeJapan’s circle a bit larger.
NTT Technical Review

Feature Articles

GDP

Population demographics
World
65+
10%

Devices connected to the Internet

30–50 billion(Japan: 1–2 billion)

100–
90–94
80–84
70–74
60–64
50–54
40–44
30–34
20–24
10–14
0–4

Japan
30%

Travellers- Worldwide: 1.8 billion/year- Visitors to Japan: 20 million/year(twice that of 2013)

Quasi-zenith satellite system

Fig. 1. Forecasts for the year 2020.

In addition, Japan is predicted to lead the world asan aging society. The number of terminals connectedto the Internet, meanwhile, is expected to reach 30–50
billion, which is 10 times the current number. It isalso said that Japan’s quasi-zenith satellite system
will be in full-scale operation by 2020. The first satellite of this system was launched in 2010, and the plan
is to launch three more satellites by 2019. This system will make it possible to achieve highly accurate
positioning as fine as several centimeters. I would
like to consider with everyone here how these changes in the present might affect business in the future.
3. Smart life and smart work 2020
In the world of 2020, a variety of services will bebuilt on and enabled by clouds (Fig. 2). I believe thatlinking and coordinating multiple clouds will lead tonew services and business models.
Take transportation, for example. Linking theclouds of the bus, subway, airplane, and taxi industries could lead to an advanced intelligent transportsystem (ITS). In other words, linking clouds in thisway can open up a new world in a certain sector, butwhat would happen if transportation is linked withthe clouds of other industries? I will address thisquestion next.
3.1 Tourism: navigation × translation
Here, I will introduce services that come about byVol. 12 No. 4 Apr. 2014

linking technologies associated with transportation
with those of tourism, navigation, and translation. To
begin with, we can envision a travel service thatbegins when you use a smartphone to take a pictureof your train station’s symbol or mark and then a picture of your destination from a travel magazine orsimilar. You could then receive information on thistrip from the station to the destination in the languagethat you previously set as well as information onsightseeing spots, restaurants, etc., at the destination.
It was recently reported in the news that the Japanese
government has issued guidelines calling for the
installation of multilingual information boards intrain stations. This could result in the preparation ofrelatively large boards in many languages, but usinga smartphone would make such multilingual boards
unnecessary since receiving information in yourmother tongue could be achieved by simply taking a
picture. I think a world with such services will be areality by 2020.
Let me introduce such a service that has alreadybeen achieved within the NTT Group. This is PictuAR,
which was developed and commercialized by NTT
COMWARE (Fig. 3). With this service, a user who
uses his or her smartphone to capture a photo that
includes the PictuAR symbol will see that photocome alive as a video on the smartphone screen. For
example, capturing a photo of a restaurant with thePictuAR symbol results in a video display of recommended menu items or views of the restaurant’s interior.
Feature Articles

Transportation
Intelligent transportation systems

Environment
Smart housing/smart buildings,
demand response

Healthcare
Telemedicine, regional medical
collaboration

Train and subway
system cloud
Aeronauticalsystem cloud
Bus operation
system cloudHome entertainment
Head mount display
with 360 degree view

Tourism
Multilingualization, barrier-free

Stadiums
Highly realistic/ultrahigh definition
video, public viewing

Fig. 2. Smart life & smart work 2020—Enabled with clouds.

PictuARNTT COMWARE

Fig. 3. Smart life & smart work—tourism ‘navigation × multilingualization’.

3.2 Entertainment: video × sports
I would now like to take a look at a world of entertainment that links sports and video. For sports suchas soccer or baseball, a service could make it possible
for the viewer to observe play from an athlete’s view,
from the manager’s or coach’s view, or from an overhead position, or to combine a view with data on
individual athletes. This kind of service could be

implemented on smartphones and tablets. It is alreadybeing tested in the United States, and steps are being
taken toward its commercialization.
There has been much talk about the convergence ofcommunications and broadcasting, but if we consider
the potential of collaboration between broadcasters
and stadium owners or baseball teams, perhaps thatconvergence will evolve in unexpected ways.
NTT Technical Review

Feature Articles

Entertainment
Tourism
Navigation
Translation

Video

Sportsmanagement

Sport

ApparelBus stop
No. 4
Bound For
Stadium

Sport

Medical care forforeigners
Translation
MedicalHealthApparelMedicalBus stop
No. 4
Bound For
Stadium

Supported by cloud collaboration

Fig. 4. Innovation through service collaboration.

3.3 Innovation through service collaboration
As I mentioned, new services can be developed bytying together a variety of services (Fig. 4). It was justannounced the other day that Toray Industries andNTT had collaborated on the development of a smart
shirt that can be used to obtain an electrocardiogramof the wearer. This is a good example of a collaborative effort between the apparel and IT (information
technology) industries the likes of which have notbeen seen before. Imagining that such tie-ups andcollaborative efforts continue to take place, I think
new worlds will be drawn, which will lead to the creation of a new Japanese business model for the
future.
Japan and the United States have often been compared with reference to the word “innovation.” In the
United States, old legacy systems can be replaced
relatively easily, but in Japan, it is more difficult. For
this reason, I believe that innovation through collaboration provides a convenient shortcut for Japanesestyle innovation, service development, and businessmodel creation. Looking forward, technologies andservices that support the linking of ICT infrastructures and the linking of clouds will be needed topromote various types of collaboration between services and enterprises. I believe that NTT R&D canmake a contribution to this end and that a new business-to-business (B2B) model of NTT Group can beapplied here.
Vol. 12 No. 4 Apr. 2014

4. NTT Group challenges toward 2020
I have talked about the possibility of creating a new
business model through collaboration. Of course, wewill continue to face a number of challenges both asa player participating in new markets and as a value
partner opening up new markets. In the following, I
would like to introduce two major challenges for
NTT as a telecommunications carrier toward 2020.
4.1 Challenge 1: Network controls
Various predictions have been made, but I think I
can safely say that the volume of information passing
through our network and those of other players will
increase substantially by 2020. By the way, a reportfrom British Telecom stated that network traffic in thevicinity of venues of the London Olympics increased
by seven times over that of the Beijing Olympics held
four years earlier, so we can only wonder how traffic
might further increase at the Rio de Janeiro Olympics, and for that matter, at the Tokyo Olympics four
years after that. If traffic simply continues to increaseby seven times in this way, we would get 7 × 7 = 49
times the amount of information.
How can such an ever-increasing amount of traffic
be controlled? This is the first challenge for the NTT
Group, and I introduce here four technologies that weplan to deploy to meet this challenge.

Feature Articles

Carrier aggregation allows a larger overall transmission bandwidth through concurrent
utilization of multiple spectrum allocations.

Aggregation of non-contiguous
spectrum allocations
Collaboration

800 MHz

3.5 GHz

Small
cell

800 MHz

Macro cell

Speed up

Speed
Concurrent
utilization** Utilizing both FDD(frequency division duplex)
and TDD (time division duplex).

Fig. 5. Challenges—carrier aggregation.

(1) Carrier aggregation
Carrier aggregation technology will enable thesimultaneous use of multiple spectrum allocations(Fig. 5) while accommodating both time division
duplex (TDD) and frequency division duplex (FDD)
wireless communications. In the future, we expect
carrier aggregation to enable even higher transmission speeds by simultaneously using a number ofspectrum allocations including Wi-Fi.
(2) Software-defined wireless network
If we were to attempt to deal with an increase intraffic that is several tens of times the current levels
by simply adding more hardware, we would need anenormous number of new facilities. Likewise, if wewere to simply increase the number of Wi-Fi basestations at stadiums and other venues, the resulting
high-density configuration would generate mutualinterference among those stations. In short, relying
solely on a hardware solution has its limits. In contrast, base-station coordination by using software
controls can reduce mutual interference and provide
a comfortable wireless communications environment(Fig. 6).
(3) Edge computing
Edge computing is a technology that can reduce
traffic in the relay network by placing cloud servers
closer to users and performing distributed processing(Fig. 7). It can also minimize delay by shortening thedistance between servers and terminals. Let’s consider traffic conditions at the opening ceremony forthe 2020 Big Event, when about 80,000 people will
be walking around with their smartphones and tabletsin the main stadium. To handle this traffic, we willneed to implement distributed processing by edge
computing and direct the flow of traffic through storage facilities at locations close to terminals.
(4) Proactive wide-area traffic controls
Wide-area traffic controls provide a means ofadjusting bandwidths to control the overall traffic on
the network (Fig. 8). Let’s assume, for example, thata datacenter hosting cloud systems related to the 2020
Big Event is located in Sapporo. We can expect thetraffic to be heavily concentrated during the period of
the 2020 Big Event. This technology will predict that
traffic at the Sapporo datacenter will become congested at that time and will automatically perform
distributed processing at a backup datacenter inFukuoka. In other words, it will proactively respond
before that congestion has a chance to negatively
affect overall cloud services. I believe that this kindof technology for achieving wide-area traffic controls
will be an absolute necessity by the time of the Big
Event.

NTT Technical Review

Feature Articles

From hardware-intensive to software-defined efficient network controls

Interference

Cooperation

Interference prevention
based on software-defined
network controls

Wi-Fi frequency interference caused
by increase in number of access points

Fig. 6. Challenges—software-defined wireless network.

Edge computing pushes cloud servers away from centralized points to the logicalextremes of a network and reduces the core network traffic.

App

App

App

App

Offloadthe traffic.
Process at logicalextremes ofa network(close to users)

Network

App

App
App

App

App

App: application

Fig. 7. Challenges—edge computing.

4.2 Challenge 2: Integrated security
About 210 million attacks were mounted on theofficial website of the 2012 London Olympics, andwhile British Telecom managed to fight off those
attacks without incident, we can imagine that by
2020, attacks will be mounted on a more sophisticated level.
In a world in which almost all services are migrating to clouds, including those provided by financial
Vol. 12 No. 4 Apr. 2014

institutions and smart cities, the risk to society is
increasing (Fig. 9). We can assume that attackers will
mount attacks by taking advantage of various vulnerabilities in networks and clouds. How then can wedeal with the increased risk to society? This is also amajor challenge for the NTT Group.
The NTT Group is developing world-leading technologies to counter these increasingly sophisticatedattacks (Fig. 10). For example, NTT Communications
Feature Articles

Control overall traffic by adjusting bandwidths.
Forecast traffic with big-data analysis and maximize total network
capacity (proactive handling).

Sapporo

Backupdatacenter

Datacenter

Fukuoka

Datacenter

SapporoFukuoka
Osaka

Osaka
Tokyo

Tokyo

Overall traffic control through forecasting and bandwidth adjustment

Fig. 8. Challenges—wide-area traffic controls.

Smart city
Social infrastructureinterconnectivity
e-Government

Increasedrisk

toward…
2012 London Olympic
210 million attacks

2012 Japan
Concerted attack on agovernment organization2009 USA, Korea
Concerted attacks on
government and bankorganizations

governments,social infrastructures

Corporations

Individuals
2000

2010

2020

Fig. 9. Cyber attacks on social infrastructure.

is already coordinating security operations on a
global scale, but coordinated operations that include
overseas carriers and IT vendors will also be necessary. We can think of this as collaboration between
security operations. As clouds become increasingly
linked in the future, it will become impossible for the
NTT Group to implement a complete set of security
measures by itself. It will therefore be necessary to
defend against increasingly sophisticated attacks bycoordinating operations with a variety of players andeven other competitors in the same industry. NTT

R&D has a strong security team for dealing with suchattacks, and NTT Innovation Institute, Inc. (NTT I3),
founded in the spring of 2013, is also preparing a
range of products that incorporate advanced security
technologies developed in the United States.
5. NTT Group future activities
Trusted relationships between partners are a major
source of collaborative abilities. For this reason, Ichanged the words “total solutions” to “trusted
NTT Technical Review

Feature Articles

World-leading technology
Proactive security countermeasures
SIEM engine, secure
dispersion/computation

Operation advancement
Global collaboration(Intelligent information collection etc.)

Operation
collaboration

Monitoring
information

Threatinformation- Sophistication of global-scale cyber attacks- Increase in security threats to clouds and new
devices such as smartphones and sensors- Integrated security(applications x clouds x devices)
SIEM: security incident and event management

Fig. 10. Challenges—integrated security.

solutions,” so that “Next Value Partner for Transformation by Total Solutions” became the more meaningful “Next Value Partner for Transformation by
Trusted Solutions.” Instead of being a corporategroup that simply functions as a provider as we havebeen so far, the NTT Group has its eye on collaborating with diverse companies and industries and assisting in the creation of new business models. I would
like to shift the company toward B2B in this sense.
I believe that NTT R&D has the power to function

Vol. 12 No. 4 Apr. 2014

well as a catalyst for collaboration among various
industries, enterprises, and services. The year 2020
will be a time when the fundamental strengths of the
NTT Group are put to a test in the areas of network
controls and security management. Going forward,
my aim is to plan the further growth of the NTT
Group by overcoming all sorts of trials and challenges through the power of NTT R&D and the business-development abilities of the group companies.

Feature Articles: Keynote Speeches at NTT R&D Forum 2014

Co-innovation Challenges
Hiromichi Shinohara
Director and Executive Vice President
Director of Research and Development Planning
Department, NTT
Abstract

NTT aims to enhance the comfort and quality of life of people byexploiting information and communications technology (ICT). This
article introduces NTT’s research and development (R&D) activities
to achieve innovation through various collaborations. It is based on the
keynote speech delivered by Hiromichi Shinohara, Director and Executive Vice President, Director of Research and Development Planning
Department, NTT, at the NTT R&D Forum 2014 held on February
13–14, 2014.
Keywords: co-innovation, ICT, R&D

1. NTT R&D (research and development)
design for tomorrow’s world
1.1 Advances in ICT and the role of the NTTGroup
The role of telecommunication carriers used to beconnecting people to people. The goal was primarily
to provide connections rapidly at any time. However,in the last two decades, the role of connecting people
with information has been added. It has become
important to deliver vast amounts of information tocustomers at high speed. The NTT Group believes
that it needs to take this trend a step further. It wishes
to transform its role to one of enabling those in a variety of fields and industries to enhance their value,
through the provision of information and communications technology (ICT) (Fig. 1).
Before we look to the future, let us first look backat how technology and everyday life have evolved.
The computing power of super computers in the
1980s was roughly equivalent to that found in today’s
CPU for mobile devices. A 20-GB storage unit
weighed 2 tons then and cost about 100 million yen.
Today, the same amount of storage can be provided
with a device weighing 0.5 g for just a few thousand
yen. While technology has advanced dramatically,
our everyday life and social activities do not seem tohave kept pace. Instead of looking at progress in technology and thinking how it can change society, it istime to undertake technical development with the aimof realizing the forms of everyday life and the kindsof social activities that we want to create.
1.2 Activities that look to the future
In the years to come, Japan will see both its total
population and productive population shrink. The
decline in the birthrate and the aging of the population will continue unabated. It is necessary to create asociety in Japan that empowers foreigners, women,
and the elderly. Everyone at the NTT laboratories
believes that it is important to harness ICT to promote
the comfort and quality of life of society at large.
Allow me to introduce the activities that the
researchers at the NTT laboratories believe theyshould undertake in order to realize a prosperous andhealthy society, using the Japanese characters 安(safety), 報 (inform), 健 (health), 癒 (medical care),etc. as keywords (Fig. 2).
NTT Technical Review

Feature Articles

XX × ICT
Enhances the value of various industries

Content
EnergyInformation
communication
connects people
with information.

Big data
Clouds
Machine learning
Security
UI, UX
Compression coding
MachineMedia processing
translation

Information
processing
technology

Rapid connection
anytime

Medical andhealthcare

Markets, technologies,
institutions, etc.
in other fields

High-speed transmissionof vast amounts of
information

Telecommunication
connects people.

Transport

Creation of
new values

M2M, sensor networks
5G, collaborative wireless LAN

Telecommunication technology
Past

Present

LAN: local area network
M2M: machine-to-machine

SDN/NFV

Optical transmission, nanophotonics
From now on

SDN-NFV: software-defined networking – network function virtualization
UI: user interface
UX: user experienceFig. 1. Advances in ICT and the role of the NTT Group.

働く

援ける

Work

SupportInformTransmit

HealthSafety

Move

伝える

健やかに
かに 省く

安らぐ
動く

報せる
る

癒す
Medical care

Energy産む

観る

Produce

View

Fig. 2. Concepts and activities required for the future.

(1) 安 (Safety)
Let us look at ICT application examples from theviewpoint of safety and security (Fig. 3). These days,
cyber-attacks have become a serious social problem,
Vol. 12 No. 4 Apr. 2014

and it is therefore becoming increasingly important toprevent attacks in cyberspace. At the NTT laboratories, it is regarded as vital to find ways of preventing
various actions that threaten our lives. These include
Feature Articles

安Prediction and prevention of accidents and crimes based on big data

Safe

Robot

Crim

e pre

ventionnntio
Functional
paralysis

eve

pr
eud

Serviceinfrastructure

F

Physical space

Accident prevention
Fraud
Drugs
MaliceArson
Theft

Structure
Malfunction

War
Cyberspace

Traffic accident
人

Vehicles,machines
Detects signs of malicious intent, malfunction, or attack from all
devices and other sources

Fig. 3. ICT that supports safety.

not only attacks that take place in cyberspace but also
those that alter real structures or cause them to fail or
malfunction. It is therefore necessary to develop predictive security technology that detects early signs ofaccidents and other problems by, for example, using
sensors or similar devices installed in structures toavert problems before they actually occur.
Another example of ensuring 安 (safety) is to use
ICT applications to reinforce disaster response capabilities. In March 2011, Japan experienced an unprecedented disaster. At the NTT laboratories, we believethat more ICT can be usefully employed in implementing various measures in situations in the futuresuch as those for disaster prevention, mitigation of
the damage caused by disasters, and restoration
through reconstruction. For example, if a large number of people take the same route to go to a shelter inthe event of a disaster, bottlenecks may arise at somepoints. To reduce the potential harm to people, it isimportant to be able in the future to rapidly selectappropriate shelters and routes for individual residents and send the information to them. Therefore,
we need a technology that will provide globally optimized and integrated guidance rather than guidance
that has been optimized for a limited area.
(2) 報 (Inform)
A service has been developed from the viewpoint of

報 (inform) as an information service that enables
everyone to receive signage in their own language(Fig. 4). It is important to enable people from abroad
to live safely and comfortably in Japan, and we therefore need to develop a technology that makes it possible to send information displayed on digital signage
to individual smartphones in the user’s own language
by using an electronic watermark or similar technology to specify the required language. This is essential
in the event of a disaster and will be used during thebig event in 2020.
(3) 健 (Health)
ICT applications can also be used for health management. As the number of elderly people increases,
a rise in the level of medical expenditure is inevitable.
Preventive medicine is important in keeping medical
costs to a minimum. In particular, we need to develop
a technology to measure vital signs such as pulse rate
and respiration, and store the data in a cloud so that
health can be managed on a daily basis.
(4) 癒 (Medical care)
An ICT application example of a comprehensive
family doctor service can be set up to expand 癒(medical care) (Fig. 5). The international exchange ofdigital health records and telemedicine will enablepeople to receive medical services with confidence
from anywhere, thereby eliminating the regional
NTT Technical Review

Feature Articles

報

Wi-Fi access
point

Public digital signage

InformArtificial cloud screen

Earth ake detected!
qud!
Be prepare

Bulletin

Earthquake damage info
Signage content can bebrowsed in own language
on any mobile terminal

Nearby shelterd on digital
Selected basewatermark etc.

Traffic info
Latest news

Earthquake detected!
Be prepared!

Fig. 4. Service enabling people to receive messages in their own language.

癒Medical/health informationsharing cloud
Sharing of medical
information between
remote sites

Medical care
Remote site

Specialist or
family doctor

Medical images
Electronic(CT, MRI)
health record

Current site

Doctor at thecurrent site

High-definition
videoconferencing
system 4K/8K video)
Use of electronicstethoscope

Patient

CT: computed tomography
MRI: magnetic resonance imaging

Fig. 5. Family doctors anywhere.

disparities in the level of service provision. NTT
EAST provides a remote medical support service in
Hinoemata Village, Fukushima. The village residents
Vol. 12 No. 4 Apr. 2014

used to have to travel several hours if they needed tosee medical specialists. Now, they visit a local clinicand can get support from medical specialists over theFeature Articles

network. We plan to strengthen this type of activity.
(5) 援 (Support)
From the viewpoint of 援 (support), I would like tointroduce a crowdsourcing service used in an urbansocial plan as an example. Crowdsourcing needs to be
expanded to harness the resources of the general public using ICT in order to make life more comfortablefor people in wheelchairs, etc. It is necessary todevelop technology that automatically collects datasuch as road surface conditions and human traffic
from privately owned smartphones and sensors,
makes the data available on a cloud, and outputs
requests for rapid road repairs or provides a barrierfree map.
Another example conceived from the viewpoint of
援 (support) is sensory assistance intended to enable
the elderly and people with disabilities to participate
in social activities. We hope to help people maintaintheir health and live independently. To achieve this,
we are developing an aid that produces a sensory
stimulus that is perceived as a sense of the hand being
tugged to indicate direction. We are also analyzing
the characteristics of sounds that the elderly and disabled find hard to understand and using that knowledge to develop a special hearing aid that compensates for their poor ability to discriminate thosesounds.
(6) 働 (Work)
From the viewpoint of 働 (work), I would like tooutline a form of ICT application that gives people
more freedom in choosing their workplace and working hours. The shrinking of the population is expectedto accelerate a shift to more compact cities. An everincreasing number of people will have to telework or
work in satellite offices. One downside of teleworking is that workers may experience a sense of isolation from their colleagues. Therefore, it will be necessary to develop technology that enables people toretain a subtle sense of being connected to remotecolleagues instead of trying to solve the problem byconnecting people constantly via videoconferencing.
(7) 省 (Energy)
An example of using ICT from the viewpoint of 省
(energy) is an ICT infrastructure that can operate
without consuming much power. It is known that
intra-LSI (large-scale integrated circuits) electricalconnections account for most of the power consumed
by servers in today’s datacenters. Power consumption
can be slashed dramatically by replacing electricalconnections in LSIs with optical connections. In thefield of power generation, it will be possible to develop solar cells that fit into the landscape. NTT labora

tories have developed a transparent thin film made ofgallium nitride (GaN) that absorbs only ultraviolet
rays. In principle, the thin film can be fabricated on a
glass window pane and used as a solar cell. In thisway, power can be generated without marring thetownscape.
(8) 産 (Production)
From the viewpoint of 産 (production), ICT can beapplied to increase agricultural productivity. Today,
methods to measure growth conditions with sensors
and to control the yield accordingly are well established. We believe that in addition to these, we needto develop, for example, technology that analyzes big
data and uses the results to improve crop varieties andto manage cultivation efficiently. It is important thatpractices adopted in forestry and agriculture ensurebiodiversity. ICT can be a valuable tool in this area.
2. R&D activities looking to the future andco-innovation challenges
We are reinforcing our activities in six technicalfields along with their underlying basic technologies:
improvement of UI/UX (user interface/user experience); big data; easy-to-use cloud; security; highcapacity, high-reliability network; and a flexible network to build a prosperous and healthy society (Fig. 6).
First, I will outline R&D management.
2.1 R&D management
In managing R&D, we would like to actualize innovation through collaboration in a variety of ways
instead of sticking to developing everything within
the NTT laboratories as we used to. For this purpose,
we are promoting three concepts: cohesion, whichmeans that NTT researchers cooperate with eachother to achieve a common vision, and fusion, whichmeans that NTT researchers in different fields work
together to create new value. In addition, we arestrengthening boundary crossing, which refers toopen innovation in which NTT researchers cooperatewith those in external organizations.
(1) Cohesion
Three virtual organizations were created within
NTT laboratories last year to promote cohesion: theNanophotonics Center, the Machine Learning & Data
Science Center, and the Innovative Photonic Network
Center. The employees working in these centers span
a number of laboratories.
A representative example of what the Nanophotonics Center was able to accomplish in fiscal 2013 is thedevelopment of a current-injected photonic crystal
NTT Technical Review

Feature Articles

Solve social problems.

Improve
UI/UX

Big data
Easy-touse cloud

Quantum/
nano-devices

Leading-edge
materials
Cryptography

Security

High-capacity, highreliability network

Basic technologies

Machinelearning
Audio/video

Flexible
network
Human
information
scienceTechnologies

Fig. 6. Building the society we are aiming for.

laser. As was mentioned earlier, it is necessary toreplace the present electrical connections with opticalconnections in order to achieve a major reduction in
the power consumption of servers. A laser that can beused for optical communication within or between
LSI chips has been fabricated on a nanocrystal. Thishas made it possible to transmit data with the world’s
lowest power consumption (5.5 femtojoules per bit).
(2) Fusion
A representative example of advances made as aresult of fusion is technology that allows a silk fiber
to be coated with a conductive polymer. This wasdeveloped by the Polymer Material Group of NTT
laboratories last year. Moreover, this research result
was combined with the system implementation technology developed by the Interface Design Group to
create a T-shirt that can obtain an electrocardiogram
simply by having the user wear it.
(3) Boundary crossing
NTT laboratories are seeking to approach open
innovation from four perspectives (Fig. 7). The first isincreased speed, which means that we incorporate
external technologies into our innovation cycle. The
second is market-in, which means that we alreadypossess necessary technologies and have incorporated them into developments carried out by NTT operating companies or vendors in order to accelerate theintroduction of these technologies into the market.
The third is missing link, where NTT laboratories
compensate for the technologies they lack by importing technologies from outside. The fourth perspectiveis entry into new markets, whereby we introduce ourVol. 12 No. 4 Apr. 2014

technologies into other industrial fields in order toenable NTT to expand its business into new non-telecommunication fields.
Naturally, this open innovation must not be confined to Japan but should be implemented on a global
level. For this purpose, we established the NTT Innovation Institute, Inc. (NTT I3) in North America in
April 2013 as a global promotion site.
2.2 Technical fields
The activities of NTT laboratories are introduced
below from the above-mentioned viewpoints andperspectives.
(1) Improvement of UI/UX
In the field of high-definition video delivery, we
have proposed a powerful error correction technology
called LDGM (low-density generator matrix). Thishas been incorporated into the next generation transport standard. It is now possible to transmit 8K highdefinition videos over a long distance on an IP (Internet protocol) network based on this standard. We
have also developed an HEVC (high efficiency videocoding) encoder, which is implemented with a mix of
hardware and software. The use of this encoder isbeing studied by the Next Generation Television &Broadcasting Promotion Forum (NexTV-F).
At the end of July 2013, we formed a business alliance with Dwango Co., Ltd. and are running a number of projects that make use of each other’s expertise. In the field of UI/UX, we are working to developinteractive viewing technology for whole-sky video,
which enables a user wearing a head-mountedFeature Articles

Non-telecommunication
areas, such as
Innovation
medical care

Ventureetc.

Otherindustries

Cloud,
software,etc.

Innovation

Innovation
Entry into new markets

Increased speed
NTT
R&D

Innovation

Businessvalue

Missing link

Market-in*
Innovation
Innovation

Innovation
Other
industries

Operatingcompanies*Rapid development of products that satisfy market needs

Fig. 7. Objectives of open innovation.

display to view “nicofarre,” a video service provided
by Dwango (Fig. 8). Conventional technology transmits all of the video data to the user, but the newtechnology reduces data traffic by transmitting inhigh quality only the part focused on by the viewer,with the remaining part being transmitted in low or
medium quality.
We have also worked with NTT DOCOMO todevelop a chat technology that can ascertain thepredicate structure of what did what in a speech, andgenerate a speech response that is relevant to the subject of the chat. This technology has been incorporated into the Drive Net Info service provided by NTT
DOCOMO.
We have started trials to provide an any-device
environment by using edge computing technology,
which is characterized by distributed computing
resources that are brought into close proximity withusers. It offloads part of the terminal processing toedge computers allocated near users so that the user
can enjoy stress-free browsing of rich content evenwith a low-end terminal. In the field of statisticalmachine translation, we have demonstrated that our
syntax analysis and word-order conversion technology can dramatically improve the accuracy of transla

tion from English to Japanese, which has been conventionally difficult because of differences in word
order between the two languages.
We have also initiated another language activity
that looks to the future. It is technology to make theEnglish spoken by a Japanese speaker closer to theEnglish spoken by a native speaker. This technology
separates English speech into pronunciation andspeech rhythm and adjusts only the rhythm so that the
speech has the same rhythmical characteristics as
those of a native speaker. This is expected to makeEnglish spoken by Japanese people easier to understand even though the pronunciation is unchanged.
(2) Big data
In cooperation with NTT DATA, we have developed high-speed graph clustering technology. This
technology dynamically changes the congestion
analysis area in accordance with changes in the volume of vehicle traffic (Fig. 9). It has been applied to
NTT DATA’s system that forecasts congestion fromdata sent from vehicles, and it controls traffic signals
in a sophisticated manner to prevent congestion. It is
now possible to process data for one million vehicles
within several milliseconds and at low cost.
We have jointly developed Jubatus, a data analysis
NTT Technical Review

Feature Articles

観

View

by ICTnicofarre

Compression ofwhole-sky video
Whole-sky
video stream

Recording of awhole-sky video

Delivery of only the partselected for viewing
HMD
HMD

Intuitive viewing
using HMD
nicofarre(live music venue)

Interactive viewing technology
HMD: head-mounted display

Fig. 8. Interactive viewing technology for whole-sky videos.

動 by ICT

Move

Data from 1 million
vehicles can beprocessed in milliseconds(at 1/3 of conventionalcost).
Allocate a server
to each mesharea in a traffic
network.

Simulatemovement ofeach car.

Rapid processing using dynamic mesh partitioning

Increasein traffic

Processing of ahuge amountof data

Simulation
scenario

Information onroad andintersection
connections

Optimally and rapidly
partition traffic network
into mesh areas bydynamicallyunderstanding traffic
conditions.

GPS
probe

Congestion prediction and control simulator

High-speed graph clustering
technology: Grapon

Fig. 9. High-speed graph clustering technology.

Vol. 12 No. 4 Apr. 2014



Feature Articles

IaaS platform

PaaS platform

OpenFlow

We are participating in and contributing to communities
on clouds, virtual networks, etc.

OpenFlow
control platform

Big data processing
platform

Storage cluster
management

Tool for migrating
existing applications

NTT is also making a contribution by creating communities of its own.
IaaS: infrastructure as a service
Paas: platform as a service

Fig. 10. Open source activities.

platform, with Preferred Infrastructure, and we provide it as open source software. We have hosted
hands-on sessions (workshops) for it as part of efforts
to expand its market. This has led to its adoption in 評
Ban, an information analysis service provided by
NTT IT.
We are also working on the anonymization of personal data. While big data are expected to create newvalues, there are concerns about how personal data
are handled. A current solution to this is k-anonymity
technology, which processes data in such a way thatit guarantees that the number of people with the given
attributes cannot be narrowed down to a value smaller
than k. Conventional anonymization methods areoften associated with a problem in which large errors
occur in the analysis results. In contrast, NTT laboratories has developed pk-anonymity technology that
ensures both k-anonymity and high analysis accuracy
by bringing the data close to their original state using
Bayesian estimation after having processed the data.
(3) Easy-to-use cloud
In cooperation with the former Nicira, we havedeveloped technology that automates the work ofchanging network configurations. This is necessitatedwhen a server installed on premises, that is, at thecustomer site, is to be migrated to a cloud. NTT Communications launched a service using this technology
in June 2013. Since IP addresses can be reused after
migration, the service lowered the barrier to migra

tion to clouds.
To support the use of clouds, we have combined
NTT laboratories’ test item generation tool with NTT
DATA’s automatic execution tool, and developed anengine that automatically generates test items and test
data from a design specification. This is expected tolead to the development of a tool that will automate
the testing of a mobile terminal environment.
One method to accelerate the speed of development
is the use of open source software. NTT laboratories
not only participate in communities such as OpenStack, Cloud Foundry, and OpenFlow, but they havealso created communities such as Ryu, Jubatus,
Sheepdog, and TUBAME, and are pressing ahead
with open source activities (Fig. 10).
(4) Security
In the field of information security, we have developed secure computation technology that makes it
possible to analyze secret data without having torestore it with information theory-backed security.
The technology allows secure analysis of personal
data—in particular, highly confidential patient information—and is therefore expected to facilitate thediscovery of new treatments and drugs. In this fiscal
year, we have improved the technology to make theprocessing fast enough for commercial application.
We have improved traceability technology, which
traces the history of operations in a cloud service. It
is now possible to trace not only operations involving
NTT Technical Review

Feature Articles

Phone
The unit can betransported and installed
in disaster-stricken
areas.

email…

Wide-area network

Wi-Fi-APThe unit makes Wi-Fi
communication andphone calls possible.

Portable ICT unit
- Can operate for up to 5 days onfull tank of gas- Wi-Fi: Covers 500-m radius area withmultiple APs.
- Telephone: 5000 extensions; 140 simultaneous calls(IP-PBX)

Centralized control of
Wi-Fi APs using sensor
network technology

Portable
Attaché case-type ICT box- Can operate for 10 hours
on batteries- Wi-Fi: APx1

Battery
Small exchange(IP-PBX)

Fits into an attaché case

Wireless LAN
access point

Mobileterminals

AP: access point
IP-PBX: Internet protocol – private branch exchange
LAN: local area network

Fig. 11. Portable ICT unit.

files but also operations involving copying or deleting
virtual machines. In addition, we have developed ananalysis engine that focuses on data flow sequences
to detect security threats. This engine has been incorporated into a security platform provided by NTT
Communications.
(5) High-capacity, high-reliability network
As mobile network traffic increases, optical fibersthat connect base stations to telecommunicationbuildings are growing in number. NTT laboratories
are working on technology to multiplex mobile signals on a single fiber and technology to compress
signals. We are also studying technology to conduct
big data analysis of network device data in order todetect signs of possible faults before they occur.
Since network growth brings about an increase inpower consumption, we are studying technology tointerlock the control of virtual servers and air conditioners in such a way that the total power consumption will be minimized.
Additionally, a portable ICT unit has been developed for use as a disaster prevention tool based onVol. 12 No. 4 Apr. 2014

lessons learned from the Great East Japan Earthquake(Fig. 11). Various information devices are mounted
on a vehicle to enable phone calls, emails, and applications of municipalities to be promptly put into service in the field, even during a blackout, by combining Wi-Fi environments. We have also developed anattaché case-type ICT Box. We have limited its functionality to make it more portable.
One example of our activities to compensate for a
missing link in our expertise is software error testing
technology, which has been jointly developed with
Hokkaido University. Researchers at NTT laboratories studied faults affecting telecommunication
devices and found that some faults are due to software errors attributable to neutrons coming fromspace. However, we have been unable so far to replicate an environment in which this type of fault actually occurs. This time, we constructed a software
error replication environment by utilizing the neutron
generation environment at Hokkaido University andascertained that faults detected in the replication
environment matched those in the field. The next step10

Feature Articles

Linear scale-out while
ensuring reliability

Internet
services

Network
services
Resources can be flexibly
exchanged between services
to suit the demand.
Autonomous restoration
when a fault occurs

Joint research initiatedby Alcatel-Lucent
Japan, Fujitsu, and NTT

General-purpose server resource poolSite #A

Redundancy is incorporated
into distributed resources
at multiple sites to prepare
for a large disaster.

Site #C
Site #B

Fig. 12. Distribution platform that enables creation of high-reliability systems.

will be to study how to avoid software errors fromhappening.
(6) Flexible network
Quality of experience (QoE) optimization technology is another project we are pursuing in conjunction
with Dwango. If the network becomes congested during the delivery of a high-quality video requiring ahigh delivery rate, the transmission capacity may
become too constrained to deliver the video, and theplaying of the video can be interrupted. We have analyzed the relationship between the state of network
congestion and the user’s QoE and developed a quality application programming interface (API) thatrecommends the optimal delivery rate. It enables
Dwango to optimize the user’s QoE in the niconico
video and other services by optimally controlling thedelivery rate on the basis of this API.
To facilitate the application of virtual networks tocarrier networks, we have developed service tuning
technology that enables the user to select which virtual network functions, available on a cloud, to use
based on the history of how he/she has been using
them. We have proposed a use case of this to the NFV(Network Functions Virtualisation) Working Groupof ETSI (European Telecommunications Standards
Institute) together with Cisco, Juniper Networks, andHP Japan.
11

Because network services require highly reliable
servers, they conventionally use expensive dedicatedservers. We have developed a distributed platformthat makes it possible to satisfy requirements related
to both economy and reliability (Fig. 12). Our aim is
to implement a mix of network services with different
reliability requirements on general-purpose servers
by utilizing distributed processing technology. Whena server fails, for example, other servers autonomously take over the services being provided. In the eventof a disaster, computing resources can be flexibly
adjusted to reduce the number of servers providing
Internet services and to increase the number of servers providing network services. We have started joint
research on this platform with Alcatel-Lucent Japanand Fujitsu.
(7) Entry into new markets
In the field of materials technology, we have jointly
developed with Toray Industries, Inc. a T-shirt
embedded with electrodes for taking an electrocardiogram (Fig. 13). It is already commercially available. By combining our conductive fiber technology
and clothing design technology with Toray’s nanofiber
material and compression control technology, it has
become possible to stably record someone’s vital
signs over a long period. We will collaborate withusers to expand its application to medical care and
NTT Technical Review

Feature Articles

癒・健by ICT

Medical care/health
Health promotion/sports

Medical field

Biosignals can becollected stably overa long period.

Biodata-measuring clothing using a
conductive functional material: hitoe

Back

Front

Nanofiber

Biodata-measuring clothing design technology

Compression control material design technology

Conductive fiber technology

Nanofiber material/advanced 3D processing

Fig. 13. Bio-electrode made of conductive polymer/fiber materials, developed with Toray.

support for the elderly.
In the audio field, we have developed technologythat separates an audio sound into a direct sound andreverberation. This will make it possible, for example,
to separate musical sounds in this way so that a car
audio user can obtain an acoustic effect similar to thatin a concert hall. It will also be possible to record only
the clear direct sound in an IC (integrated circuit)recorder.
In the field of optical technology, we have developed
KTN (potassium tantalum niobate: KTa1-XNbXO3)
crystal technology, which deflects (bends) light.
Originally developed for optical communication, thistechnology is now considered to be applicable to lightsources for optical coherence tomography in the
medical field. By combining this technology with
Hamamatsu Photonics’ optical design technology, it
has become possible, for example, to examine thefundus oculi (interior of the eye), blood vessel walls,
and skin at high speed. In addition, we are exploring
the possibility of using the crystal as a high-speed
Vol. 12 No. 4 Apr. 2014

varifocal lens, which can be used as a biosensor formeasuring neurotransmission.
We also have a super-high-purity laser light source
technology. By combining this technology with thelaser spectroscopic technology of Picarro (USA), we
have developed isotope ratio analysis technology thatuses laser gas sensing. This will make it possible, forexample, to determine where an item of produce wasgrown or where a gas leak is occurring by identifying
the origin of a methane gas leak. We hope to use thistechnology to make society at large more secure.
Next, I would like to discuss our collaboration with
the Japan Aerospace Exploration Agency (JAXA). If
the efficiency of an ion engine used in rockets is to beenhanced, we must be able to measure the electricfield distribution inside an ion engine accurately, but
JAXA initially had no means of doing this. However,
JAXA solved this problem by using NTT laboratories’ electro-optic probe, which was originallydesigned to measure electromagnetic waves from a
mobile phone, and discovered a mechanism for12

Feature Articles

boosting the engine’s propulsive power.
(8) Cutting-edge technology
In the field of basic research, which is the foundation of our open innovation, we are focusing on technology for easily delaminating and transferring thinfilm elements, technology related to quantum computing and for producing high-purity phonons, andtechnology for human information science.
3. Conclusions
The NTT Group has declared itself to be a value
partner. In the context of NTT R&D, this means that
we need to be regarded by potential partners as a coinnovator worthy of their selection.
Researchers tend to do everything by themselves,
which is good in general. However, we should accelerate our co-innovation initiatives to drive home the13idea that far better achievements can be obtained bycooperating with others.
The objective of research is to produce excellent
results. However, when these results are to be incorporated into products and introduced to the market, it
will be necessary to reduce costs even if it means
removing some of the good aspects of the results.
Even if an excellent technology has been developed,
it may not assume a commercially marketable form if
it lacks something no matter how small this deficit
might be. What this tells us is that researchers need toconsciously shift gears when their research advances
to the commercialization phase.
NTT R&D will press ahead with co-innovation to
expand and develop the future vision of ICT by combining ICT with other fields instead of sticking to ICT
alone.

NTT Technical Review

Feature Articles: Cutting-edge Device and Materials
Technologies for Creating New Business

Innovative Services in Medicine,
Healthcare, and Environment with
Advanced Device and Materials
Technologies
Koji Fujii, Tadashi Sakamoto, and Yoshihisa Sakai
Abstract

Device and materials technologies originally developed for the telecommunications industry can beapplied to implement creative and competitive information and communications technology services.
This article introduces some research and development activities we are pursuing for the creation of new
business fields.
Keywords: device, material, services

1. Introduction
Solving social problems

Science and technology have progressed andmatured greatly over the years, and many of theachievements in these areas have motivated researchers to create tools or systems for solving various
existing social problems. These problems include, forexample, many wrongdoings that have been exposed
recently in the food and environment industries,
whose operations should be subject to the highest
standards because they are fundamental for safe andsecure daily living. Another urgent issue is theincrease in atmospheric carbon dioxide density
caused by human activities, which is causing rises intemperature as well as unprecedented abnormal
weather patterns around the world. There is also theaging society, which threatens the sustainability of
our society because the ever increasing welfare andmedical-care expenses for the elderly occupy a significant portion of the national budget.
At the NTT laboratories, we are working to develop
solutions to these social problems by employing ourmost advanced human- or environment-centric technologies. Our research and development (R&D) flow
for solving the social problems is shown in Fig. 1.
Human-oriented technologies- Medical devices- Human-data processing

Eco-friendly technologies- Ultralow power devices- Highly efficient devices- Environmental
measurement

World’s most advanced scienceand technologies- Devices and materials technologies- Physical science- Communication scienceFig. 1. Research flow for solving social problems.

Our research fields include physical science, communications science, and device and materials engineering. Together, they provide a solid foundation on
NTT Technical Review

Feature Articles

Exploiting external cooperation
NTT’s originaltechnologies

NTT’s originaltechnologies

Company B’s
technologies

Company A’s
technologies

NTT

Company B

NTT

Company A

Product

Fig. 2. R&D scheme utilizing external organizations.

which to develop human-centric technologies such as
medically oriented devices and data processing of
human biomedical signals and environment-centric
technologies such as highly efficient and ultralowpower-consumption devices.
We are ready to license our intellectual property(IP) that has been created through our research. The
effort to promote our IP to as many people as possible
contributes not only to the telecommunications market but to other markets as well.

cooperation as early as possible to ensure there is sufficient time to establish a collaborative work relationship with outside organizations. This expedites theintroduction of products and services with more value
added to the market.
This research attitude or practice that we are seeking is schematically shown in Fig. 2. We plan to continue this research practice strategically to create new
business fields that expand our overall telecommunications business.

2. Exploiting external cooperation

3. Sensing technologies and highly efficientelectronic materials

Competitive devices and materials produced fromresearch in the fields of smart living and life assistance can bring us many opportunities to create new
business and expand our current business further. The
expertise necessary for this kind of research, however,is quite diverse since it involves a deep technologicalhierarchy and broad application fields. This makes itmuch harder to complete the entire research process––from coming up with a concept to implementing an actual business framework––by ourselves.
Exploiting outside technical resources is a key way
to tackle this difficulty. We need to define what we
can do by ourselves, spot technical elements that arelacking, and exploit outside resources effectively tocompensate for the missing technical elements. Openinnovation is a key practice, or attitude, for expediting the commercialization of products and services
since it helps us use outside technologies whenevernecessary without persisting in the use of our own
technologies. A rule of thumb is to start external
Vol. 12 No. 4 Apr. 2014

Sensing technologies are crucial for creating attractive services in the smart-life and life-assistancedomains. Highly efficient electronic materials arevital for making energy-saving electronic appliances
and thereby for supporting or sustaining our daily life
with limited natural resources. We are creating new
information and communications technology (ICT)
services that employ novel sensing data acquired in
the fields of medicine, healthcare, and the environment. This special issue highlights some of our sensing technologies and electronic materials, and provides detailed descriptions in individual articles.
Those technologies and materials with links to theircorresponding applications and ICT services are outlined in Fig. 3.
Future sensing technologies will be capable of integrating sensing data acquired from separate sources
and as a result will be able to extract larger amounts
of useful information than can be obtained byFeature Articles

Life log

Vital/mental
Cloud computing
environments

Environment

Expansion of businesses

M2M

Digitize everything.

Create new business.

Smart life

Life assistance

Environmental
sensing

Highly efficient electronicmaterials

Medical and drug sensing
Health support services

CO2

OCT light source with
KTN crystal

CH4
GaN on Si

Laser gas sensing

CH4: methane
CO2: carbon dioxide
GaN: gallium nitride
KTN: potassium tantalite niobate

Wearableelectrodes

Drug inspection withterahertz waves

Application of advanced devices and materials M2M: machine-to-machine
OCT: optical coherence tomography
Si: siliconFig. 3. Sensing technologies and highly efficient electronic materials for ICT services.

Cloud
computingSensorCoverage area
Sensing
Coverage
Interdependence
of information

Local
Self-contained

GlobalComposite,
complementary

Fig. 4. Integration of sensing technologies and cloud computing for innovative services.

analyzing sensing data from a single source. Other
physical phenomena that correlate with an original
sensing source could add value to the analyzed information. From this viewpoint, cloud services will playa crucial role in creating innovative services in thefields of medicine, healthcare, and the environment.
In these fields, various kinds of sensing data need tobe easily exchanged, analyzed, and enhanced withadditional values online in order for such services tobecome more feasible to general customers. Integrat

ing sensing data with cloud services will help us
advance related services, as illustrated in Fig. 4.
This special issue features five articles, each ofwhich deals with promising technologies that cancontribute to solving social problems in the fields of
medicine, healthcare, and the environment. The first
four articles describe sensing technologies, while thelast one explains highly advanced electronicmaterials technologies.

NTT Technical Review

Feature Articles

4. Articles in this special issue
The first article, entitled “Electrocardiogram Monitoring Simply by Wearing a Shirt––For Medical,
Healthcare, Sports, and Entertainment [1],” describes
a sensing technology intended for measuring bioelectrical signals generated by the human body. NTT’s
proprietary fabrication technique for bioelectrodes
makes them flexible, durable, and biocompatible atthe same time. These properties were once difficult toimplement in conventional bioelectrodes. However,by wearing a compression shirt affixed with thesebiocompatible electrodes on the inside, the wearers
can easily and continuously measure their own bioelectrical signals for long periods of time. The shirt
has various applications, especially in the ICT
domain, such as online advisory services in sports,
healthcare, and medicine.
The second article, entitled “200-kHz Swept Light
Source Using a KTN Deflector and a High-speed
Optical Coherence Tomography System [2],” explainsa sensing technology for a medical diagnosis instrument. The medical diagnosis method called opticalcoherence tomography (OCT) is drawing a lot of
attention these days because of its ability to quickly
obtain cross-sectional images of biological tissue.
NTT laboratories have successfully accelerated therate at which a cross-sectional image can be captured
by using a high-speed wavelength-swept light source
fabricated with NTT’s proprietary KTN (potassium
tantalite niobate) crystal. The acceleration can shorten the OCT procedure and thereby reduce the burden
on patients. OCT cross-sectional images of biologicaltissue can be shared among hospitals over the Internet
and can be analyzed with the help of cloud services tocreate new ICT services in medicine.
The third article, entitled “Terahertz Spectroscopic
Identification of Pharmaceutical Crystals: Cocrystals
and Polymorphic Forms [3],” introduces a sensing
technology intended for use in a drug inspection
apparatus. In drug inspection, it is highly desirable tobe able to observe the manner in which moleculesbond to each other since such information can be used
to determine a drug’s effectiveness. NTT’s proprietary terahertz-wave technologies enable us to observe
molecular bonding, which has not been possible withconventional technologies. This inspection technique
is attracting much attention for its use in clarifying
how pharmaceutical crystals are dissolved andabsorbed in the human body.
The fourth article, entitled “Highly Sensitive Laser
Based Trace-gas Sensor Technology and Its ApplicaVol. 12 No. 4 Apr. 2014tion to Stable Isotope Ratio Analysis [4],” explains asensing technology applicable to the analysis of foodand atmospheric gasses. With NTT’s proprietary laser
diode, we can analyze a tiny amount of an isotopic
component with high sensitivity and cost effectiveness. The tiny amount of the isotopic component canbe used as a signature for determining the origin ofthings, such as where or how they were produced.
The signature can be obtained by investigating theratio of the isotopic element contained in the targeted
object. New ICT services such as preventing food
fraud or monitoring sources of greenhouse gases
could be implemented with this sensing technology
in the near future.
The fifth article, entitled “GaN-on-Si Technology
for High-power Transistors [5],” describes a highly
efficient electronic materials technology. NTT’s proprietary fabrication technique for growing GaN thinfilms on Si substrates makes it possible to produce
more efficient and cost-effective electronic devices ormore energy-efficient power devices than ever. This
technology is attracting a great deal of interest
because of its potential to reduce the environmental
impact of our daily activities, particularly the impactof our use of electrical appliances.
5. Future prospects
The technologies dealt with in this special issue
vary in their development phase. Some are at an earlystage where they are being tested to prove their applicability to their targeted fields. To refine such immature technologies for practical use, we need to simultaneously solve a lot of issues associated with reliability, safety, and cost.
In this regard, cooperative work with other departments, laboratories, companies, and/or organizations
is very effective and efficient since they can compensate for each other’s elements that are lacking. We
have just started this cooperative research in somefields and are trying to expand it to other fields to
expedite our competitive technologies for use in real
products or services in the marketplace.
References
[1]

[2]

S. Tsukada, N. Kasai, R. Kawano, K. Takagahara, K. Fujii, and Koji
Sumitomo, “Electrocardiogram Monitoring Simply by Wearing a
Shirt––For Medical, Healthcare, Sports, and Entertainment,” NTT
Technical Review, Vol. 12, No. 4, 2014.
https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr2014
04fa4.html
J. Kobayashi, Y. Sasaki, M. Ueno, T. Sakamoto, and S. Toyoda, “200kHz Swept Light Source Using a KTN Deflector and a High-speedFeature Articles[3]

Optical Coherence Tomography System,” NTT Technical Review,Vol. 12, No. 4, 2014.
https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr2014
04fa5.html
K. Ajito, J. Kim, Y. Ueno, and H.-J. Song, “Terahertz Spectroscopic
Identification of Pharmaceutical Crystals: Cocrystals and Polymorphic Forms,” NTT Technical Review, Vol. 12, No. 4, 2014.
https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr2014
04fa6.html

Koji Fujii

Senior Research Engineer, Research Planning
Department, NTT Science and Core Technology
Laboratory Group.
He received the B.S. and M.S. degrees inphysical electronics from Tokyo Institute ofTechnology in 1991 and 1993, respectively. In
1993, he joined NTT LSI Laboratories, where heengaged in research on low-voltage digital circuits. In 2005, he was involved in a research
project on a wireless sensor network. Since then,he has been working on the design of VLSI circuits and a system for a low-power wirelesstransceiver. He is currently working on activities
promoting the commercialization of researchoutcomes achieved in his laboratory group. His
current interests include wireless transceivers,
biomedical sensors and their signal processing
circuits. He served as an editor of the Institute ofElectronics, Information and Communication
Engineers (IEICE) Electronics Express from2011 to 2012. He currently serves on the Technical Program Committee of the VLSI Circuits
Symposium.

[4]

[5]

R. Yoshimura, M. Kohtoku, K. Fujii, T. Sakamoto, and Y. Sakai,“Highly Sensitive Laser Based Trace-gas Sensor Technology and Its
Application to Stable Isotope Ratio Analysis,” NTT Technical
Review, Vol. 12, No. 4, 2014.
https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr2014
04fa7.html
N. Watanabe, “GaN-on-Si Technology for High-power Transistors,”
NTT Technical Review, Vol. 12, No. 4, 2014.
https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr2014
04fa8.html

Yoshihisa Sakai

Executive Research Engineer, R&D Produce
Group, Research Planning Department, NTT
Science and Core Technology Laboratory
Group.
He received the B.E. and M.E. degrees in electronics engineering in 1986 and 1988, respectively, and the D.E. degree from Kanazawa University, Ishikawa, in 1995. Since joining NTT in
1988, he has been engaged in researching frequency stabilization of semiconductor lasers and
WDM optical networks. From 1997 to 1999, healso worked at Photonic Integration Research
Incorporation (PIRI), which was a venture company manufacturing PLC-based devices inColumbus, OH, USA. From 2009 to 2012, he
was a Director of Mining, Information, Communication and Monitoring (Micomo) in Santiago,
Chile. He has been an Executive Research Engineer of NTT Science and Core Technology Laboratory Group since 2010.

Tadashi Sakamoto

Senior Manager, R&D Produce Group,
Research Planning Department of NTT Science
and Core Technology Laboratory Group.
He received the B.E. and M.E. degrees in electronic engineering from Waseda University,
Tokyo, in 1990 and 1992, respectively. In 1992,
he joined NTT Photonics Laboratories, where hehad been engaged in research on optical devices
and their applications to optical communication
until 2011. Then he started working as a producer to search new applications of R&D outputs
in the fields such as medicine, healthcare, andenvironment. He is a member of IEICE and
IEEE.



NTT Technical Review

Feature Articles: Cutting-edge Device and Materials
Technologies for Creating New BusinessElectrocardiogram Monitoring
Simply by Wearing a Shirt––
For Medical, Healthcare, Sports,
and Entertainment
Shingo Tsukada, Nahoko Kasai, Ryusuke Kawano,
Kazuhiko Takagahara, Koji Fujii, and Koji Sumitomo
Abstract

We developed a conductive fiber by coating the surface of silk or synthetic fiber with a conductive
polymer and fabricated wearable electrodes to achieve long-term biosignal monitoring. This new bioelectrode made of a complex conductive material is flexible, biocompatible, and hydrophilic and allows
stable recording equivalent to that obtained with conventional medical electrodes but without the needfor any electrolyte paste, which can irritate the patients’ skin. We can expect this wearable electrode to
be utilized in various applications related to sports, health improvement, and early medical diagnosis byproviding long-term biosignal monitoring without patient discomfort or irritation.
Keywords: wearable electrodes, electrocardiogram, smart textiles

1. Introduction
1.1 Biosignal monitoring in daily life
The need for early detection and treatment of diseases is increasing as the aging of Japanese society
accelerates. Specifically, concern has been rising
about the need for continuous, long-term monitoringof electrocardiogram (ECG) data with a view to
reducing the risk of sudden death and critical healthincidents such as heart attacks. Moreover, people intheir 30s or 40s who are in the prime of life are often
exposed to excessive stress at the office and/or athome, and monitoring the heart rate (HR) and ECG
data is thought to be effective in allowing this groupto recognize the state of their physical and mental
health in order to maintain it in the optimal condition.
However, conventional medical electrodes used forrecording ECG signals use electrolyte paste*1, which
can cause rashes and irritation. These electrodes are
therefore unsuitable for continuous long-term use indaily life. Bioelectrodes based on a conductive fiberthat is coated with metal, for example, silver, areoften used for measuring HR and have attracted agreat deal of interest lately, especially for use during
participation in sports since people are becoming
increasingly health conscious. However, metal-based
conductive fiber, which is usually used without electrolyte paste, can result in a higher noise level becauseof its instability when it is in contact with skin, andthus, ECG measurement using the conventional electrodes has been difficult for medical applications.
1.2 Newly developed wearable electrodes
We have succeeded in developing flexible, stretchable, and highly breathable (air-permeable)*1	 Electrolyte paste: A paste or gel containing electrolyte that is applied to the skin surface and on which a metal electrode is affixedin order to obtain ECG measurements at medical facilities. The
electrolyte is applied between the electrode and the skin surface
and reduces contact resistance. Conductive adhesive gel is also
used for Holter ECG measurements.

NTT Technical Review

Feature Articles

50 µm
Silk fiber

Complex conductive material
SEM image

PEDOT-PSS
SEM: scanning electron microscope

Fig. 1. Complex conductive material using conductive polymer and fiber.

bioelectrodes by coating non-conductive fibers with aconductive polymer material called poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOTPSS). This material makes it possible to obtain a stable ECG measurement equal to that obtained with a
medical electrode without having to use electrolyte
paste. This is possible because of the material’s highhydrophilicity, whereby the electrode becomes betterattached to the skin by absorbing sweat and steam.
We have succeeded in developing wearable electrodes that enable long-term recording of both HR
and ECG signals simply by having users wear anelectrode-equipped shirt, thus positioning the textile
electrodes on the body. These wearable electrodes
can greatly reduce the burden imposed on patients orusers, and they enable monitoring of everyday biological signals.
2. Complex conductive material made of
PEDOT-PSS and textile/fiber
PEDOT-PSS is one of the most commonly usedcommercially available conductive polymers, and it
is important in industry as an anti-electrostatic material, an organic photovoltaic material, and a transparent conductive material that is used as an alternative
to indium tin oxide (ITO) for touch-panel and flexible
LED displays. Moreover, PEDOT-PSS is expected tofind use as bioelectrodes because of its high hydrophilicity and biocompatibility. However, its use todate has been limited because of its poor processability and instability in highly humid environments. Our
Vol. 12 No. 4 Apr. 2014group has used PEDOT-PSS in biosensors to coatmetal microelectrode arrays (MEAs)*2 for monitoring in-vitro neuronal activity, and in electrodes for
implantation in order to confirm its high biocompatibility and its excellent electrical properties [1].
In our most recent work, we successfully developed
a new material by coating textiles or fibers with
PEDOT-PSS. This smart-textile, complex conductive
material is stable in water and has good processability, thus solving the aforementioned problems. Furthermore, it maintains conductivity, hydrophilicity,and biocompatibility. Coating PEDOT-PSS uniformly onto a silk thread (Fig. 1) gives this compoundmaterial the characteristics of both silk fiber and
PEDOT-PSS. The base material is not limited to silk
fiber, and fibers or textiles made of synthetic material
can be coated with the polymer. Thus, we have developed a conductive textile that is flexible, elastic, andair-permeable.
The ECG of laboratory animals (rats) was measured using this complex conductive material (Fig. 2).
In the measurement, electric waves were obtainedthat were as clear and stable as those provided by aconventional medical electrode but without the need
to use electrolyte paste [2]. Metal-coated fiber without electrolyte paste gives an unstable ECG baseline
due to breathing-related body movement, and it
induces noticeable noise as a result of contact
resistance with the body surface. By contrast, we*2	 Microelectrode array (MEA): Patterned microelectrode device
used to stimulate nerve cells and detect nerve signals.

Feature Articles

Complex conductive material(PEDOT-PSS/fiber)(pasteless)This report

Medical electrode,commercially available(with electrolyte paste)
Silver-coated textile,commerciallyavailable

Baseline fluctuation caused by breathing

Fig. 2. Stable monitoring of electrocardiogram using complex conductive material made of PEDOT-PSS/fiber.

Electrodes

Shirt with electrodes(The transmitter is shown at theshoulder.)Long-term ECG (10 minutes of data extracted from 24 hours of monitoring)

Fig. 3. Wearable electrodes and long-tem ECG.

were able to obtain a stable measurement using thiscomplex conductive material consisting of PEDOTPSS and a textile/fiber, because it was effective inabsorbing sweat and steam from the body due to its
high hydrophilicity, and it adhered gently to the skinthanks to its flexibility.
3. Electrocardiography using
wearable electrodes
We took advantage of the characteristics of conductive fibers/textiles to develop wearable electrodes,
which enabled us to measure biosignals such as HR
and ECG simply by having the patient wear an electrode-equipped shirt.
An electric potential distribution is induced in allparts of the body by the electromotive force caused
by cardiac activity. An ECG is a wave pattern of thepotential difference between two points on the bodysurface. When the electrode-equipped-shirt is worn,it can provide an ECG because the textile electrodeadheres to the skin.
The wearable electrodes were jointly developedwith Toray Industries, Inc. (Toray), one of the largest
fiber manufacturers in Japan. A sample ECG obtained
from the shirt in a 10-minute period during 24 hours
of monitoring is shown in Fig. 3. This newly developed textile electrode is flexible and air-permeable,
does not require electrolyte paste, and is thus capableof monitoring HR or ECG signals over long periods
NTT Technical Review

Number of participants

Feature Articles

Did you experience any skin problems?
(78)
80
70
60
50
40
30
20
10
0

Irritation at transmitter position
Irritation near electrode due to tight fit
Irritation all over
Irritation in abdominal region due to tight fit(All types of irritation disappeared after
volunteers removed their undershirt.)
No electrode-induced irritation was reported.

(4)
No

Yes
Skin irritation test
Uncoated
Coated textile(control)(electrode)

Cell viability

98.3%

96.2%

Result

No irritation

No irritation

Fig. 4. Subjective examination of wearable electrodes.

without discomfort or irritation to the wearer.
Before undertaking the joint development with
Toray, we fabricated our original wearable electrodes
to examine the effect of the material on human skinand the capacity for performing electrical biosignal
measurements. We used 82 healthy male volunteers
employed at the NTT Atsugi R&D (research anddevelopment) Center for our study. We investigatedtheir HRs (R-R intervals) for up to 24 to 48 hours,
except when they were showering or bathing. We
confirmed that the HR was successfully recorded formore than 10 hours for most subjects, and that theelectrode material itself caused no irritation or rash
(Fig. 4). In addition, this experiment confirmed thatthe wearable electrodes provided stable and longterm HR monitoring even during sleep. Thus, theresults can also be analyzed to determine sleep quality to promote better health.
In addition, we carried out a skin irritation examination in accordance with OECD (Organization for
Economic Co-operation and Development) Test
Guideline TG439. We conducted a comparative
examination of the survival rate of cultured cells withor without a PEDOT-PSS coating, and found thatboth survival rates were slightly less than 100%, andthat the PEDOT-PSS coating caused no skin irritation. The results revealed that the complex conductive
material we have developed makes it possible toundertake long-term electrical biosignal monitoring
without safety problems, and the material can be used
for wearable electrodes.
This experiment indicated that reduced adhesion of
the electrode (due to clothing pressure), and dryness
Vol. 12 No. 4 Apr. 2014of the skin caused noise and signal interception,
which had previously prevented long-term HR measurements. The aim of the joint development with
Toray of the wearable electrodes was to optimize thematerial specifications in order to improve the retention of moisture in the skin to ensure adherence of theelectrode.
4. Transmitter for ECG monitoring
The electrical biosignals that show the changes inthe electric potential of the body surface, measured
with the wearable electrode using PEDOT-PSS, aretransmitted wirelessly (e.g., using Bluetooth) to asmartphone or personal computer by our own smalltransmitter attached to the shirt. The device and asample ECG obtained using the device are shown in
Fig. 5. We obtained a high quality ECG with low
noise and a high S/N (signal to noise) ratio, and weclearly observed sharp QRS waves*3 as well as P and
T waves. The HR is calculated from the intervals
between the two peaks of the R waves (R-R intervals). The device is equipped with a lithium-ion
rechargeable battery, and the wave pattern can betransmitted continuously for around 12 hours. The
electrocardiographic information can be sent to aserver via a smartphone from anywhere via the Internet, thus enabling data analysis. We will continue toimprove the quality of the wearable electrode system*3 QRS wave: Electrical waveform obtained during ventricular excitation, whose shape can demonstrate an irregular pulse (arrhythmia) or myocardial infarction.

Feature Articles

Front

75
m
m

35

mm

74 bpmR-wave11 mm
Electrocardiogram

P-waveT-waveHeart rate

Rear
Q-waveS-waveAlert for electrode removal
25 g(including batteries)

bpm: beats per minuteFig. 5. Transmitter for ECG monitoring and smartphone display.

Chronic diseases
Deconditioning
Diagnosis

SportsGuide for exercise level
Guide for rehydration
Database for
emergency contacts

Early detection
Early treatment

Stress check;
Guide forrest/exercise

Detection of
dehydration,
deconditioning

Early morning
wakingHealthpromotion

Detection of stress,
lifestyle diseases,
dysautonomia

Fig. 6. Future applications of wearable electrodes.

to create new value by combining it with cloud services or big data analysis by further downsizing andreducing energy consumption, and by adding multiple functions to the system.



5. Future applications
HR and ECG signals can be measured simply by
wearing the electrode-equipped-shirt described in
section 3. The shirt is soft, flexible, and air-permeableand does not require electrolyte paste. As a result, theshirt can be used to record electrical biosignals
NTT Technical Review

Feature Articles

without irritating or imposing a burden on the person
wearing it. We expect it to be used to support diagnosis leading to early detection and early treatment of
illnesses through regular ECG monitoring (Fig. 6).
As one key medical ICT (information and communications technology) device application, the device
can be studied or used in such medical fields as home
medical care or telemedicine. Additionally, the medical quality level provided by wearable electrodes isbeing studied in cooperation with the medical departments of hospitals and universities with a view toexpanding its applications.
The complex electrode material incorporating conductive polymer and fiber/textile that we developed
can also be applied to fields other than ECG and HR
monitoring. For example, we have examined its
applicability to electroencephalographic measurements and to implantation at the research level.
The monitoring of changes in HR is also useful inunderstanding and controlling exercise levels and for
improving health care. The wearable electrodes canbe used in various settings while the wearer enjoys
participating in sports. In addition, the HR normallyfluctuates even while a person is resting quietly in
bed, and this HR fluctuation can reveal both auto-Vol. 12 No. 4 Apr. 2014

nomic nerve functions and stress levels. Thus, HRchanges measured with precision by employing anelectrocardiographic QRS wave can be useful for
calculating the appropriate exercise load as well as
for evaluating mental aspects of users quantitatively.
These wearable electrodes are effective in supporting
mental health care for people of all ages who facevarious stresses by enabling the daily monitoring of
HR changes even while the subject is asleep.
Thus, the wearable electrodes can be used for awide variety of applications ranging from the healthand medical field to the sports/entertainment field.
We will continue our development with the aim of
putting the wearable electrode to practical use while
extending our collaborative work both inside andoutside the NTT Group companies.
References[1][2]

T. Nyberg, A. Shimada, and K. Torimitsu, “Ion Conducting Polymer
Microelectrodes for Interfacing with Neural Networks,” Journal of
Neuroscience Methods, Vol. 160, No. 1, pp. 16–25, 2007.
S. Tsukada, H. Nakashima, and K. Torimitsu, “Conductive Polymer
Combined Silk Fiber Bundle for Bioelectrical Signal Recording,”
PLoS ONE, Vol. 7, No. 4, e33689, 2012.

Feature Articles

Shingo Tsukada

Senior Research Scientist, Supervisor, Materials Science Laboratory, NTT Basic ResearchLaboratories.
He received the M.D. Diploma and Licensefrom Toyama University in 1990, and the Ph.D.
degree from the University of Tsukuba in 2003.
He joined NTT Basic Research Laboratories as
Research Specialist in 2010 and has been in his
present position since 2013. He is engaged inwork on human-machine interfaces, including
wearable electrodes and their systems, both invivo and in vitro, especially in the neurosciencefield. He is a member of the Japan Neuroscience
Society (JNS), the Physiological Society ofJapan, the Japanese Circulation Society, and theSociety for Neuroscience.

Nahoko Kasai

Senior Research Scientist, Materials Science
Laboratory, NTT Basic Research Laboratories.
She received the Ph.D. degree in applied chemistry from Tohoku University, Miyagi, in 1996.
She joined NTT Interdisciplinary Laboratories in
1996. She has been based at NTT Basic ResearchLaboratories since 1998. She was a guest
researcher at the University of Oxford in 2006.
She is currently engaged in a wearable electrodeproject and is also working on neuronal growth
control using nanostructured substrates for artificial synapse applications. She is a member of
JNS, the Electrochemical Society of Japan, andthe Chemical Society of Japan.

Ryusuke Kawano

Senior Research Engineer, Network Hardware
Integration Laboratory, NTT Microsystem Integration Laboratories.
He received the B.E. and M.E. degrees in electronic engineering from Osaka Prefecture University in 1987 and 1989, respectively. He
received the Ph.D. degree in electrical engineering from Tokyo University of Science in 2007.
He is currently engaged in R&D of wearable
devices. He is a member of the Institute of Electronics, Information and Communication Engineers (IEICE) and IEEE.



Kazuhiko Takagahara

Engineer, Innovative Life-care Devices
Research Group, NTT Microsystem Integration
Laboratories.
He received the B.E. and M.E. degrees inmechano-informatics from the University ofTokyo in 2006 and 2008, respectively. He joined
NTT Microsystem Integration Laboratories in2008 and studied MEMS devices for RF and
optical communication applications. He is currently studying biosensing devices and systems
for life-care services. He is a member of theJapan Society of Applied Physics (JSAP).

Koji Fujii

Senior Research Engineer, Research Planning
Department, NTT Science and Core Technology
Laboratory Group.
He received the B.S. and M.S. degrees inphysical electronics from Tokyo Institute ofTechnology in 1991 and 1993, respectively. In
1993, he joined NTT LSI Laboratories, where heengaged in research on low-voltage digital circuits. In 2005, he was involved in a research
project on a wireless sensor network. Since then,he has worked on the design of VLSI circuits anda system for a low-power wireless transceiver. He
is currently working on activities promoting thecommercialization of research outcomesachieved in his laboratory group. His current
interests include wireless transceivers, biomedical sensors and their signal processing circuits.
He served as an editor of IEICE Electronics
Express from 2011 to 2012. He currently serveson the Technical Program Committee of the
VLSI Circuits Symposium.

Koji Sumitomo

Senior Research Scientist, Group Leader,Supervisor, Materials Science Laboratory, NTT
Basic Research Laboratories.
He received the B.E., M.E., and Ph.D. degrees
in electronics from Osaka University in 1986,
1988, and 1991, respectively. He joined NTT
Basic Research Laboratories in 1991. Since then,he has been engaged in research on the characterization and control of nanostructures on semiconductor surfaces. He is currently focusing on
nanobioscience and nanobiodevice fabrication.
He is a member of JSAP, the Physical Society ofJapan, the Surface Science Society of Japan, theBiophysical Society of Japan, and the Biophysical Society.

NTT Technical Review

Feature Articles: Cutting-edge Device and Materials
Technologies for Creating New Business

200-kHz Swept Light Source
Using a KTN Deflector and a
High-speed Optical Coherence
Tomography System
Junya Kobayashi, Yuzo Sasaki, Masahiro Ueno,
Takashi Sakamoto, and Seiji Toyoda
Abstract

Optical coherence tomography (OCT) using a swept light source can acquire cross-sectional imagesof tissue with micrometer resolution for biomedical applications. High-speed OCT imaging is important
for achieving advanced volume rendering and for reducing the number of undesirable artifacts. Here, wereport the development of a 200-kHz swept light source (SS) using a KTN (potassium tantalite niobate:
KTa1-xNbxO3) deflector and a high-speed SS-OCT system, which we used to successfully obtain OCT
images of a human finger.
Keywords: optical coherence tomography, swept light source, KTa1-xNbxO3 (KTN)

1. Introduction
Optical coherence tomography (OCT) has attracted
attention because of its potential use as a medical
imaging technology [1]. OCT is an optical interferometry technique for acquiring cross-sectional
images of tissue and other scattering materials withmicrometer resolution. The resolution of OCT ishigher than that of conventional imaging. Many studies related to two-dimensional (2D)-OCT imaging
have been done. Three-dimensional (3D) OCT also
promises to provide a more complete characterizationof tissue structures on a par with those obtained withother medical imaging technologies [2]. However,
3D-OCT requires extremely high imaging speeds anddata processing rates, in addition to the control of two
scanning mirrors.
OCT using a swept light source (SS-OCT) offers
the potential for high-speed data acquisition. SSOCT reduces the quality degradation of in-vivo OCT
images of moving artifacts caused by movement ofthe body, and it also achieves rapid imaging with 3DOCT [3].
SS-OCT detects wavelength-resolved interference
fringes generated by a wavelength-scanning laser. A
key component of the SS-OCT system is the lightsource. The desirable output characteristics of aswept light source include high power, a high repetition rate, and a broad sweep wavelength range. As therepetition rate of the light source is increased, theduration of the laser irradiation decreases and thequantity of data obtained within a fixed measurement
duration increases. Thus far, such light sources haveused mechanical actuators for wavelength scanning[4]. In contrast, we are developing a new light sourcethat incorporates an electro-optic deflector that weplan to employ in a high-speed SS-OCT system.
The deflector is based on a potassium tantalite niobate (KTa1-xNbxO3 (KTN)) single crystal. KTN has avery large electro-optic effect, which changes therefractive index by an applied voltage and bends thepath of a light beam in a certain direction [5]. The
NTT Technical Review

Feature Articles

deflection effect of the KTN is caused by a nonuniform electric field generated by injected carriers,
and it exhibits a fast response and a fairly large lightdeflection angle [6]. The KTN deflector is useful fora fast repetition rate swept source.
We have taken the advantages of KTN crystal into
consideration in developing a new swept light source
using the KTN deflector (Fig. 1). Furthermore, weare developing a high-speed SS-OCT system using
the light source in order to achieve advanced image
rendering.
2. Swept light source with KTN deflector
The setup of a swept light source equipped with a
KTN deflector, which is based on a Littman-Metcalf
cavity configuration, is shown in Fig. 2 [7]. The cavity consists of a 1.3-μm semiconductor optical amplifier (SOA) module, a collimator, a KTN deflector
with electrodes, a cylindrical concave lens, a grating,and a high reflector (HR). The SOA module has a

10% reflector coupled to an optical fiber through an
optical isolator on one side. The cavity length between
the 10% reflector and the HR is about 60 mm. The
KTN crystal is precharged by applying ± DC (direct
current) voltage; then we scan the laser wavelength
by applying a ±350-V sinusoidal voltage.
The light emitted from the SOA is collimated by thecollimator, and it reaches the HR through the KTN
deflector and the grating. The filter is constructedusing the KTN deflector, the grating, and the HR.
Light of a certain wavelength is selected according to
the deflection angle of the KTN deflector, and it
returns to the SOA.
The 200-kHz voltage is applied to the KTN deflector, and the corresponding interference fringe signal
is successfully obtained (Fig. 3). We also measured
point-spread functions (PSFs), namely, the relative
OCT signal intensity for a single-layer reflection at
various optical delays between the sample and reference arms. The PSFs were obtained by fast Fouriertransforming (FFT) the interference fringe signals.
We observed a decrease in the interferometry fringe
amplitude (or the peak height of its FFT) as we
increased the optical delay. The measured coherence
length in air was approximately 7 mm for a 200-kHz
scan. This indicates that a depth range of several millimeters can be covered using this frequency swept
light source.
3. High-speed SS-OCT systemusing KTN swept light source

Fig. 1. 200-kHz swept light source using a KTN deflector(Hamamatsu Photonics K.K).

The high-speed OCT system is shown in Fig. 4. The
setup consists of a swept light source with a KTN
deflector, an optical fiber interferometer with aHR

Diffraction

Voltage source
OC (10%)KTN

SOA

Fiber out

Grating
Cylindricalconcave lensCollimator

Fig. 2. Setup of swept light source equipped with KTN deflector.

Vol. 12 No. 4 Apr. 2014



Feature Articles

Applied voltage (V)Signal (Arb. unit)

1.0
0.5
0.0
−0.5
−1.0
400
200
0
−200
−400
−600
−5.0

5 µs (200 kHz)

−2.5

0.0
Time (µs)

2.5

5.0

Fig. 3. Lower: voltage applied to the KTN deflector; upper: corresponding interference fringe signal.

KTN swept
light source

A-scan trigger

Function
generator

Sample arm

Synchronizing signal

x-GalvanomirrorPC withA/D converter

Collimator
Light

Pol. Control.

Objectivelensy-GalvanomirrorSampleDisplay

Circulator
Pol. Control.
90%

Coupler(90/10)10%

Circulator

Coupler(50/50)Pol. Control.

Reference arm
Collimator

ReferencemirrorSignalBalancedphotodetector

A/D: analog to digital
PC: personal computer
Pol: polarization

Fig. 4. High-speed SS-OCT system configuration.

Mach-Zehnder configuration, galvano mirrors, and acomputer for signal processing. The source outputs
light at 20 mW around a center wavelength of 1.33 µm,
with a wavelength scanning range of over 100 nm.
Light from the source is split by a 90/10 coupler
into a sample arm and a reference arm. The lightreflected from the reference mirror and from thesample is separated by respective optical circulators.
Polarization controllers in both arms are used toadjust their polarization states. Light through the twoarms interferes at a 50/50 coupler, the outputs ofwhich are detected by a balanced photodetector.
The light source also outputs an A-scan trigger insynchronization with a wavelength sweep. The ANTT Technical Review

Feature Articles

Sweat gland

Skin surface
Epidermis

an

B-sc

A-scanDermis

A-scanSweat glandB-scan(b)(a)

Fig. 5. (a) 2D and (b) 3D OCT images of human finger.

scan triggers generate triggers of the galvano mirrors
via a function generator. Interference fringe signals
and synchronizing signals are recorded on a channelof a 10-bit data acquisition board at a sampling rate of
1-G sample/s. A depth profile, as a single A-scan, isobtained by the FFT of the interference fringe signal.
In the 2D imaging, the x-galvano mirror of thesample arm is driven in synchronization with a Bscan trigger from the function generator. The beamscans a sample surface in the axial direction. All thesignals for a single B-scan are detected and stored in
the data acquisition board. A 2D image is constructedby mapping a transversal set of A-line scans.
Furthermore, in the 3D imaging, in addition to theoperation of the x-mirror, the y-galvano mirror of thesample arm is driven in synchronization with a Cscan trigger from the function generator. The beam
performs an in-plane scan of the sample surface. A
typical single C-scan consists of 200 sheets as Bscans, or 60,000 lines as A-scans. All of the data for asingle C-scan are stored in the data acquisition board.
A 3D image is constructed by post-processing thecollected data.
We acquired a 2D image of a human finger using
the high-speed SS-OCT system. The image resolution was 200 × 200 pixels, and the image area wasapproximately 2 mm (horizontal) × 3 mm (depth), as
shown in Fig. 5(a). The 2D image acquisition time
was about 1.5 ms, which is several times faster thanconventional SS-OCT systems. A 3D OCT image ofthe human finger with a 300 × 200 × 200 voxel resolution and a volume image area of 2 mm (horizontal)
× 3 mm (vertical) × 3 mm (depth) is shown in Fig. 5(b).
Here, the microstructures of the human skin including the epidermis, dermis, and a sweat gland areclearly visible as bright structures.
Vol. 12 No. 4 Apr. 2014

4. Conclusion
We have developed a high-speed swept light source
using a KTN deflector for OCT. A 200-kHz scan rate
was obtained with a 20-mW average output power ata wavelength scanning range exceeding 100 nm. The
coherence length measured by using the relative signal decay from a different path delay was longer than
7 mm. We obtained 2D and 3D OCT images of ahuman finger using the OCT system equipped with
the KTN swept light source.
References
[1]
[2]

[3]
[4]

[5]

[6]

[7]

S. R. Chinn, E. A. Swanson, and J. G. Fujimoto, “Optical Coherence
Tomography Using a Frequency-tunable Optical Source,” Optics Letters, Vol. 22, No. 5, pp. 340–342, 1997.
D. C. Adler, Y. Chen, R. Huber, J. Schmitt, J. Connolly, and J. G.
Fujimoto, “Three-dimensional Endomicroscopy Using Optical
Coherence Tomography,” Nature Photonics, Vol. 1, No. 12, pp. 709–
716, 2007.
S. H. Yun, G. J. Tearney, J. F. de Boer, N. Iftimia, and B. E. Bouma,“High-speed Optical Frequency-domain Imaging,” Opt. Exp., Vol. 11,
No. 22, pp. 2953–2963, 2003.
R. Huber, M. Wojtkowski, and J. G. Fujimoto, “Fourier Domain Mode
Locking (FDML): A New Laser Operating Regime and Applications
for Optical Coherence Tomography,” Opt. Exp., Vol. 14, No. 8, pp.
3225–3237, 2006.
K. Nakamura, J. Miyazu, M. Sasaura, and K. Fujiura, “Wide-angle,
Low-voltage Electro-optic Beam Deflection Based on Space-chargecontrolled Mode of Electrical Conduction in KTa1-xNbxO3,” Appl.
Phys. Lett., Vol. 89, No. 13, 131115-1-3, 2006.
J. Miyazu, Y. Sasaki, K. Naganuma, T. Imai, S. Toyoda, T. Yanagawa,
M. Sasaura, S. Yagi, and K. Fujiura, “400 kHz Beam Scanning Using
KTa1-xNbxO3 Crystals,” Proc. of the 2010 Conference on Lasers andElectro-Optics (CLEO) and Quantum Electronics and Laser Science
Conference (QELS), San Jose, CA, USA.
Y. Okabe, Y. Sasaki., M. Ueno, T. Sakamoto, S. Toyoda, S. Yagi, K.
Naganuma, K. Fujiura, Y. Sakai, J. Kobayashi, K. Omiya, M. Ohmi,and M. Haruna, “200 kHz Swept Light Source Equipped with KTN
Deflector for Optical Coherence Tomography,” Electronics Letters,Vol. 48, No. 4, pp. 201–202, 2012.

Feature Articles

Junya Kobayashi

Senior Research Engineer, Supervisor,
Advanced Opto-electronics Laboratory, NTT
Photonics Laboratories.
He received the B.S. and M.S. degrees inchemical process engineering from Hokkaido
University and the Ph.D. degree in materials
chemistry from Tohoku University, Miyagi, in
1986, 1988, and 1999, respectively. He joined
NTT LSI Laboratories in 1988. He is currently
engaged in research on KTN crystals and polymer waveguides for optical device applications.
He is a senior member of the Institute of Electronics, Information and Communication Engineers (IEICE) and a member of the Japan Institute of Electronics Packaging.

Yuzo Sasaki

Senior Research Engineer, Advanced Optoelectronics Laboratory, NTT Photonics Laboratories.
He received the B.E., M.E., and Ph.D. degrees
in electronic engineering from Tohoku University, Miyagi, in 2000, 2003, and 2005, respectively.
He joined NTT Photonics Laboratories in 2005.
Since then, he has been engaged in research on
the material properties of KTN crystal and development of optical devices based on KTN crystal.
He received the IEICE Best Paper Award in2005.

Masahiro Ueno

Senior Research Engineer, Advanced Optoelectronics Laboratory, NTT Photonics Laboratories.
He received the B.E. and M.E. degrees in electrical engineering from Chiba University in 1987
and 1989, respectively and the Ph.D. degree from
Tokyo University of Science in 2010. He joined
NTT Applied Electronics Laboratories in 1989
and studied mass storage systems using opticaldisks, disaster tolerant storage systems, holographic storage systems, ion flow printers, threedimensional imaging systems, and cloud computing systems during 1989–2008. He was also
active in developing small computer systeminterface (SCSI) specifications. He is currently
studying optical coherence tomography (OCT)systems using KTN crystal in NTT Photonics
Laboratories. He is a member of IEICE.



Takashi Sakamoto

Senior Research Engineer, Advanced Optoelectronics Laboratory, NTT Photonics Laboratories.
He received the B.A. degree in liberal arts andthe M.S. degree in multidisciplinary sciencesfrom the University of Tokyo in 1994 and 1996,
respectively and the Ph.D. degree from Tohoku
University, Miyagi, in 2008. In 1996, he joined
NTT Opto-electronics Laboratories (now NTT
Photonics Laboratories), where he engaged inresearch on optical interconnections and opticalpacket switching. From 2004 to 2008, he studied
scanning nonlinear dielectric microscopy(SNDM) and device applications of KTN crystals. Since 2011, he has been working on KTN
deflectors and their application to optical coherence tomography (OCT). He is an associate
member of IEEE.

Seiji Toyoda

Senior Research Engineer, Advanced Optoelectronic Device Research Group, NTT Photonics Laboratories.
He received the B.S., M.S., and Ph.D. degrees
in chemistry from the University of Tokyo in
1990, 1992, and 2005, respectively. He joined
NTT Basic Research Laboratories in 1992 andstudied low-dimensional Si polymers. He moved
to NTT Opto-electronics Laboratories (now NTT
Photonics Laboratories) in 1996 and studied
thermo-optic and electro-optic waveguide technologies. In 2004, he was a visiting scholar at
Stanford University, CA, USA. He is currently
studying KTN electro-optic devices in order tocommercialize them. He received the 2001
IEICE Lecture Encouragement Award and the2003 MOC Best Paper Award. He is a member of
IEICE and the Japan Society of Applied Physics.

NTT Technical Review

Feature Articles: Cutting-edge Device and Materials
Technologies for Creating New Business

Terahertz Spectroscopic
Identification of Pharmaceutical
Crystals: Cocrystals andPolymorphic Forms
Katsuhiro Ajito, Jae-Young Kim, Yuko Ueno,
and Ho-Jin Song
Abstract

Terahertz radio waves have about the same energy level as the non-covalent bonds between molecules,
so they can be used in a spectroscopic technique for identifying differences in molecular networks. We
introduce terahertz spectroscopy as a revolutionary technique for visualizing the molecular bonds invarious forms of pharmaceutical crystals such as cocrystals and polymorphic forms that are closely
related to crystal properties that have not yet been understood. Examples of such properties include
solubility and systemic absorption rate.
Keywords: terahertz spectroscopic identification, cocrystals and polymorphic forms, pharmaceuticalcrystals

1. Introduction
The simple reactions of dissolving a crystal inwater and forming a crystal from a solution are very
important features of pharmaceutical crystals. Terahertz (THz) spectroscopy can clarify changes in noncovalent bonds of the molecules (Fig. 1), whichmakes it possible to understand the dynamics of crystal dissolution and crystallization. Pharmaceuticalmolecules are extracted from solution as pharmaceutical crystals and then formed into pills, tablets, etc.
The pharmaceutical crystals must be dissolved inwater to be absorbed in the body; otherwise the drug
will have no effect. Pharmaceutical crystals that havegreater molecular complexity are being developed
every year, so the proportion of drugs that do not dissolve easily is presumably also increasing. Although
the network of non-covalent bonds on the crystal surface is considered to be closely related to solubility,that network is described by data on hydrogen bonds,
van der Waals interactions, or other such interactions


between molecules rather than by data on the periodic structure of the crystal obtained by x-ray diffraction measurement. It is currently difficult, therefore,
to observe this network directly, and this difficulty iseven greater with ultra-fine particles.
We have approached the problem of elucidating the
crystal dissolution mechanism by using THz (THz =1012 Hz) spectroscopy, which can measure a spectrum in the energy band of molecular interaction.
THz light frequency is in between the light and radio
frequencies (Fig. 2) and can be used to investigate
various molecular properties through resonance, suchas the phonon mode of crystals, the low-frequency
vibration mode of molecules, and the rotation modeof gases. Many amino acid and sugar crystals haveTHz resonance peaks for the hydrogen bonds between
molecules in the crystal. The advantage offered by
THz spectroscopy is that it can provide informationon the non-covalent bond networks from the hydrogen bonds of biomolecules, organic molecular crystals, protein molecules that have higher-order
NTT Technical Review

Feature Articles

Crystal dissolution

Crystallization

THz spectroscopy

Observation of changes in non-covalent
network on the molecular level

Fig. 1. Clarification of the dissolution and formation of crystals by THz spectroscopy.

Relaxationof orientation

Inter-molecule
vibration

Plasma vibration

Microwaves

Intra-molecule
vibration

Electrontransition

Near-andintermediateinfraredTHz

X-ray diffraction

Ultraviolet, x-ray
Visible

109

1010

1011

1012

1013

1014

1015

1016

(Hz)

Inter-molecular hydrogen bond vibration mode
Molecular distortion mode

Low-frequency molecular vibration mode

Crystal phonon vibration mode

Rotation mode (gas molecules)

Fig. 2. THz and specific chemical absorption frequencies.

Vol. 12 No. 4 Apr. 2014



Feature Articles

THz generatorySamplez

Femtosecond laser

Delay
stage

x
Environment control chamberTHz detector

Three-axis movable stage

Fig. 3. TCI analysis system.

structures, double-helix DNA (deoxyribonucleicacid), and other such molecules that dissolve in aqueous solution. [1], [2].
2. TCI analysis method
Terahertz chemical imaging (TCI), which visualizes the THz optical spectrum in two or three dimensions, differs from ordinary x-ray imaging in that it
identifies molecules from the spectra of molecular
networks. TCI can be used to investigate the noncovalent bond network of molecules as well as themolecular distribution, so it may provide a means ofevaluating new medical diagnostics and pharmaceuticals. Systems for production process design, analysis,
management, and final product quality assurance,
generally referred to as process analytical technology(PAT), have already been introduced in the petroleum
and chemical industries, and FDA (U.S. Food andDrug Administration) guidance calls for introductionof that technology to improve the quality of pharmaceuticals. The applicability of THz spectroscopy to
PAT is also attracting attention. TCI analysis systems
used in THz time-domain spectroscopy (THz-TDS)
systems include those that use pulsed light, which cancover a wide frequency band, and those that use continuous light with frequency scanning [3].
A TCI analysis system that uses THz-TDS with anenvironment control chamber is illustrated in Fig. 3.
An ultrashort-pulse laser beam is split into two
beams, one of which is input to a THz wave generator
and the other to a THz detector. The most typical THz
wave generators and detectors are photoconductive
antennas. The sample is illuminated with coherent
sub-picosecond THz pulse waves, and the electricfield strength of the passing waves is changed. Insteadof measuring the strength of the light in the frequency
domain, a delay stage is used to measure the electricfield strength in the time domain. The THz pulse
waves are measured repeatedly and converted tostrength and phase values by Fourier transform. The
waveform of the THz pulse wave is measured andrecorded while scanning the stage, and the Fouriertransform is used to convert the data to an image foreach frequency. A feature of this system is that it canmeasure the images of the sample in an environmental control chamber. The temperature and pressure
within the chamber can be controlled, so it is possible
to change the non-covalent bond network of the molecules inside the crystal. As a result, the applicationsof TCI analysis now include investigating multi-component analysis, distinguishing active pharmaceuticalingredients (APIs) in diluents, and identifying differences in degree of hydration.
3. Identification of pharmaceutical crystals
using TCI analysis system
An example of using a TCI analysis system to distinguish between pharmaceutical crystal polymorphs
and diluents is shown in Fig. 4 [4]. Crystal polymorphs consist of the same molecules but differ in
how the molecules are linked. They thus can havelarge differences in solubility and other chemical
properties that affect drug efficacy. Also, diluents
such as cellulose and/or sugars, which themselves
have no drug efficacy, are used when pressing pharmaceutical crystals into pills or tablets. Those diluents also often have high absorbance in the THz band,making identification difficult. Famotidine, a component of stomach medicines, has two crystalline forms,
type A, which has low solubility, and type B, which
NTT Technical Review

Feature Articles

Famotidine A

Famotidine B

D-mannitol
Polyethylene(b) 220 K

Test tablet

1.62 THz

1.05 THz

1.13 THz

AbsorbanceLow(a) Room temperatureHigh

1.62 THz

1.05 THz

1.10 THz

Fig. 4. Example of distinguishing pharmaceutical crystal polymorphs.

has high solubility. Only the highly soluble famotidine B has drug efficacy. These two crystal polymorphs exhibit entirely different THz spectra and are
therefore easily distinguished, but it is often difficult
to distinguish the drug from the diluent. In this example of a test tablet, the peaks for D-mannitol andfamotidine B are very close and cannot be distinguished in the image acquired at room temperature(Fig. 4(a)). However, if a low temperature of 220 K is
maintained within the environmental control chamber, we can see clear separation of famotidine A,
famotidine B, and D-mannitol as shown in Fig. 4(b).
This is due to the differences in structural changes
such as the distance between molecules in the crystals
at different temperatures.
4. Analysis of crystal distribution
An example analysis of pharmaceutical cocrystals
is shown in Fig. 5 [5]. An advantage of cocrystallization is the discovery of functions and properties thatcannot be obtained with single-compound crystals. In
particular, because improved solubility can lead torelaxed constraints on dose absorbability and selection of formulation, it is very important in exploratory
research on drug development. TCI analysis has beenVol. 12 No. 4 Apr. 2014

attracting attention as an effective method for distinguishing high clarity cocrystals and the pharmaceutical molecules that constitute them, and additives as
well, in the analysis of pharmaceutical cocrystals
whose structure is stabilized by hydrogen bonds, andother interactions between and within molecules. In
this example, we created a tablet model with anuneven distribution in which readily soluble oxalic
acid is used as an additive for cocrystallization withinsoluble caffeine, a drug that has a stimulating
effect. We used a TCI system to analyze the cocrystal
distribution in test tablets formed from a mixture of
the active compound with polyethylene powder.
Comparison of the THz spectra showed that the single
compound caffeine or oxalic acid crystal exhibited
almost no absorption, but the caffeine and oxalic acidcocrystal exhibited a particularly strong absorption
peak at low temperature. We know from this resultthat it is possible to clearly distinguish a cocrystal andits constituent API and diluent. We also learned thatthe component distribution in a non-uniform tablet
model can be visualized as a two-dimensional image
by applying TCI analysis and using the characteristic
absorbance peak data.

Absorption

Feature Articles

1

Caffeine-oxalic
acid cocrystal

2 THz

Cocrystal

Test tablet

Absorption+
Caffeine Oxalic acid
1

2 THz

Crystal modelTHz spectra and
THz imageFig. 5. Example of distribution analysis of a pharmaceutical cocrystal.

5. Conclusion
We described THz spectroscopy as a revolutionary
technique for visualizing the molecular bonds invarious forms of pharmaceutical crystals such as
cocrystals and polymorphic forms. THz spectroscopy
and TCI analysis have not come into widespread use
because of the high equipment cost, but differences inmolecular non-covalent bond networks can only be
identified in the THz energy band. We can therefore
expect further development of THz spectroscopy as arevolutionary technique for visualizing the molecularbonding that is closely related to pharmaceuticalcrystal solubility and systemic absorption rate butthat has not previously been understood, and as atechnique for carrying out early diagnosis of cancer
and other such diseases.

References
[1]

[2]
[3]

[4]

[5]

K. Ajito, Y. Ueno, and H.-J. Song, “Visualization of Pharmaceutical
Drug Molecules by Terahertz Chemical Imaging,” NTT Technical
Review, Vol. 10, No. 2, 2012.
https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr2012
02fa6.html
K. Ajito and Y. Ueno, “THz Chemical Imaging for Biological Applications,” IEEE Trans. Terahertz Sci. Technol., Vol. 1, No. 1, pp. 293–
300, 2011.
J.-Y. Kim, H.-J. Song, K. Ajito, M. Yaita, and N. Kukutsu, “Continuous-wave THz Homodyne Spectroscopy and Imaging System with
Electro-optical Phase Modulation for High Dynamic Range,” IEEE
Trans. Terahertz Sci. Technol., Vol. 3, No. 2, pp. 158–164, 2013.
K. Ajito, Y. Ueno, H.-J. Song, J.-Y. Kim, E. Tamechika, N. Kukutsu,
W. Limwikrant, K. Yamamoto, and K. Moribe, “Terahertz Chemical
Imaging of a Multicomponent Tablet in Pharmaceutical Applications,” ECS Trans., Vol. 50, No. 12, pp. 109–116, 2013.
D. M. Charron, K. Ajito, J.-Y. Kim, and Y. Ueno, “Chemical Mappingof Pharmaceutical Cocrystals Using Terahertz Spectroscopic Imaging,” Analytical Chemistry, Vol. 85, No. 4, pp. 1980–1984, 2013.

NTT Technical Review

Feature Articles

Katsuhiro Ajito

Senior Research Scientist, Distinguished Technical Member, Smart Devices Laboratory, NTT
Microsystem Integration Laboratories, NTT Science and Core Technology Laboratory Group.
He received the Ph.D. degree in applied chemistry from the University of Tokyo in 1995. He
joined NTT Basic Research Laboratories in
1995. From 1995 to 2007, he studied glutamate
in single synapses using Raman spectroscopy
and laser tweezers. His current research interests
include the study of nano- and biochemistry
using terahertz spectroscopy and imaging techniques. He received the Young Scientist Awardfor the Presentation of an Excellent Paper fromthe Japan Society of Applied Physics (JSAP) in
1999 and the Tatsuo Itoh Award from IEEE
Microwave Theory and Techniques Society in
2014. He has been the Executive Director and the
Chair of the Terahertz Spectroscopy Division of
the Spectroscopical Society of Japan (SPSJ)
since 2005 and was the Secretary of the Terahertz
Interest Group in IEEE 802.15 Working Groupfor wireless personal area networks from 2011 to2013 and the Chair of the Micro/Nano Electromechanical Systems and Bio/Medical Analyses
Area of the International Conference on Solid
State Devices and Materials in JSAP from 2012
to 2013. He is a member of JSAP, SPSJ, theChemical Society of Japan (CSJ), the American
Chemical Society, and IEEE.

Jae-Young Kim

Post-doctoral Researcher, Smart Devices Laboratory, NTT Microsystem Integration Laboratories, NTT Science and Core Technology Laboratory Group.
He received the B.S., M.S., and Ph.D. degrees
in electrical and electronic engineering fromYonsei University, Seoul, Korea, in 2004, 2006,
and 2011, respectively. For his Ph.D. dissertation, he investigated integrated circuits andoptoelectronics for millimeter-wave wirelesscommunication. In 2011, he joined NTT Microsystem Integration Laboratories, Atsugi, Kanagawa, Japan, as a post-doctoral researcher. His
research interests are millimeter-wave and THz
systems for wireless communication, and sensing and imaging applications based on photonic
and high-speed electronic technologies. He is amember of IEEE.

Vol. 12 No. 4 Apr. 2014

Yuko Ueno

Senior Research Scientist, Materials Science
Laboratory, NTT Basic Research Laboratories,
NTT Science and Core Technology Laboratory
Group.
She received the B.S., M.S., and Ph.D. degrees
in chemistry from the University of Tokyo in
1995, 1997, and 2002, respectively. She joined
NTT Integrated Information & Energy Systems
Laboratories in 1997. She was a post-doctoral
fellow at the University of California at Berkeley
and at Lawrence Berkeley National Laboratory,
Berkeley, CA, USA, from 2004 to 2005. She
received the Encouragement Award (award for ayoung scientist) from the Japan Society for Analytical Chemistry in 2008. She is a member of
JSAP, SPSJ, CSJ, and the Japan Society for Analytical Chemistry.

Ho-Jin Song

Senior Research Scientist, Smart Devices
Laboratory, NTT Microsystem Integration Laboratories, NTT Science and Core Technology
Laboratory Group.
He received the B.S. degree from Kyungpook
National University, Korea in electronics engineering in 1999 and the M.S. and Ph.D. degree in
information and communications engineeringfrom Gwangju Institute of Science and Technology (GIST), Korea, in 2001, and 2005, respectively. From 2005 to 2006, he was involved in theCenter for Hybrid Optical Access Networks(CHOAN) at GIST, Korea, as a research professor, where he engaged in research on millimeterwave communications systems utilizing radioover-fiber technologies. Since joining NTT
Microsystem Integration Laboratories, Atsugi,
Kanagawa, Japan, in 2006, he has been working
on the development of millimeter-wave and subterahertz wave systems for communications,sensing, imaging, and measurement applications
using photonic technologies and high-speed
electronics. He is a member of IEEE and theInstitute of Electronics, Information and Communication Engineers.

Feature Articles: Cutting-edge Device and Materials
Technologies for Creating New BusinessHighly Sensitive Laser Based
Trace-gas Sensor Technology and
Its Application to Stable Isotope
Ratio Analysis
Ryoko Yoshimura, Masaki Kohtoku, Koji Fujii,
Tadashi Sakamoto, and Yoshihisa Sakai
Abstract

Laser based trace-gas sensor technology has been used in various fields such as greenhouse gas
monitoring. It has attracted a lot of attention in recent years due to its use in stable isotope analysis. This
form of analysis is expected to have many applications, including verifying the geographic origin of foodand determining the emission sources of greenhouse gases. These applications are promising for theirrole in overcoming various social problems.
Keywords: laser-based trace gas sensor technology, isotope analysis, semiconductor laser

1. Introduction
Laser based trace-gas sensor technology [1] has
attracted a lot of attention because it is an extremely
effective tool for detecting and quantifying gases
such as carbon dioxide and methane with a view to
reducing global warming and air pollution and contributing to a safe and secure society. NTT Photonics
Laboratories has been developing laser light sources
for gas sensing along with the corresponding application technology, which are expected to be useful inresolving various social problems.
The principle of laser based trace-gas sensor technology is illustrated in Fig. 1. Gas molecules absorb
the energy of light at a particular wavelength andgenerate molecular vibration. These molecules canabsorb many light wavelengths, which are calledabsorption lines because the wavelengths are very
narrow. When we sweep the wavelength of a laser
light whose emission wavelength is about the same as
the absorption line of the gas to be measured, we finda dip around the absorption line in the detected light
power, as shown in Fig. 1. We can find the type anddensity of the gas to be measured from the position(wavelength) and the depth of the dip. This is thefundamental principle of laser based trace-gas sensor
technology.
2. Technology to increase sensitivity of laser
based trace-gas sensors
One of the most important advantages of laser
based trace-gas sensor technology is that it is highly
sensitive compared with other sensor technologies.
We describe in this section the factors that increase
the sensitivity of laser based trace-gas sensors.
One of the simplest ways to increase sensitivity is
to lengthen optical path L. This is the path by which
the laser light passes through the gas to be measured,as shown in Fig. 2(a). This method is often used inopen path measurement techniques such as remotesensing. One problem, however, is that the apparatus
becomes too large for L to be lengthened because
most conventional trace-gas sensors have gas cells
inside them. Therefore, the limit for this method isusually from tens of centimeters to several meters.
NTT Technical Review

Feature Articles

Detector
Wavelength

Gas

Opticalintensity

Molecular vibration

Laser source
Gas absorption lines

Fig. 1. Principle of laser based trace gas sensor technology.

(a) Long path
Laser source

Optical path: L

Detector
Laser source(b) Multipath

Detector
Highly reflective mirrors(c) Optical cavity

Laser source

Optical resonance

Detector

Fig. 2. Technology to increase sensitivity of laser based trace gas sensing.

Another method is shown in Fig. 2(b). We canincrease the sensitivity and reduce the size of theapparatus by using a multipath cell. The laser lightenters the gas cell and is reflected many times by mirrors that are located at either end of the cell. The lightthen exits the cell and is sensed by a detector. We canobtain a long effective light path of tens to hundredsof meters with a gas cell whose actual length is lessthan 1 m if we use multiple (from a few dozen to
several hundred) reflections.
Another method that uses an optical cavity is shownin Fig. 2(c). This approach greatly improves sensitivity and has attracted a lot of attention in recent years.
Vol. 12 No. 4 Apr. 2014

Several techniques fall into this category, including
cavity ring-down spectroscopy (CRDS) [2] and cavity enhanced absorption spectroscopy [3]. Thismethod utilizes optical resonance with highly reflective mirrors and traps laser light in a cell. We canobtain a very long effective light path that exceeds
several kilometers by using optical resonance.
3. Application of laser based trace-gas
sensor technology
Laser based trace-gas sensor technology is useful invarious fields. Application examples in which NTT’sFeature Articles

Table 1. Example applications using NTT’s laser technology.
Environmental protection- Real-time monitoring of GHG to prevent global warming- In-situ monitoring of exhaust gas to prevent environmental pollution- Real-time gas monitoring for surveillance and optimization of DeNOx process- Global and environmental studies (water cycle, carbon cycle, methane emission from freezing tundra, etc.)
Ensuring safety of work environment- In-vehicle gas leak detection system- Remote methane leak detector- Hazardous gas (toxic gas, inflammable gas) detectors used in oil fields, coal mines, petroleum refineries, etc.
- Fire/smoke detector
Industrial fields- Real-time gas monitors for combustion control in coal-fired power plants- Real-time gas monitors for engine development- Process gas monitors in metal industry (steel and aluminium manufacturing)- Highly sensitive moisture analysis for semiconductor process gases
Safety and security; medical and health- Technology to prevent the disguising of geographic origin or production history of foods and beverages- Medical diagnosis by expiration analysis (study phase)
DeNOx: removal of nitrogen oxide
GHG: greenhouse gases

laser technology is used are listed in Table 1.
Greenhouse gas monitors designed to help prevent
global warming are representative examples. Many
global organizations including the World Meteorological Organization and the Japan Meteorological
Agency use laser based trace-gas sensors because of
their many advantages such as providing quick,highly sensitive measurements with high resolution.
Furthermore, they make it possible to reduce operating costs because they are easier to calibrate andmaintain than conventional monitors.
Hazardous gas detectors that ensure a safe andsecure work environment are another important
example. Laser based trace-gas sensors can detect asmall amount of hazardous gas even if its source is far
away. Therefore, they are often used for detecting
toxic gases such as hydrogen fluoride and hydrogensulfide or inflammable gases such as methane in oil
fields or coal mines. Furthermore, laser based tracegas sensors have another important advantage in thatthey are more compact than other analyzers with thesame high level of performance. Therefore, they arealso used as portable sensors, for example, as a portable remote methane leak detector [4] and an invehicle gas leak detection system [5], which enables
us to investigate gas leaks while driving a vehicle.
These detectors have been used for inspection workby gas companies.
High-precision isotope analyzers have been developed using highly sensitive laser technology such as
CRDS, and they have attracted increased attention inrecent years.
Stable isotope ratio analysis has been used for along time in various fields including earth science,
environmentology, and archaeology because it is a
useful technology for detecting or estimating the origin of a material. However, it is necessary to use large
analytical equipment such as an isotope ratio mass
spectrometer or a nuclear magnetic resonance spectrometer, which require a large laboratory room and acomplicated operating procedure. This creates difficulties in expanding the areas of application. Newly
developed laser based isotope analyzers have many
advantages including a more compact size and excellent portability and operability, and we can therefore
expect the application fields of stable isotope analysis
to expand greatly.
4. Stable isotope analysis of water anddetermination of geographic origin of foodMany atoms have different mass numbers, whichindicate the weight of the atom, despite being atomsof the same element and having the same number ofprotons. These atoms are called isotopes. A lot of
information can be obtained about the origin of amaterial if we can precisely measure its isotope ratio.
In this section, we give a concrete example of how thegeographic origin of a water sample can be determined.
NTT Technical Review

Feature Articles

Table 2. Water molecules including isotopes.
Light water
Molecular
structure

Heavy water

O

O

16

H

H

H

18

D

H

H

Molecular
formula

H216O

HD16O

H218O

Mass number(weight)

18

19

20

Abundance ratio(standard water)

99.75%

0.02%

0.20%

The molecular formula of water is expressed as
H2O. This formula means that a water molecule consists of two hydrogen atoms (H) and one oxygen atom
(O). The mass numbers of most hydrogen and oxygen
atoms are 1 and 16, respectively. Therefore, themolecular formula of most water molecules can be
expressed as H216O, which means it consists of twohydrogen atoms whose mass number is 1 (H) and one
oxygen atom whose mass number is 16 (16O). However, since there is also an isotope of hydrogen called
deuterium whose mass number is 2 (D), as well as an
isotope of oxygen whose mass number is 18 (18O),
there are isotopic water molecules that include theseisotopes (DH16O and H218O), although their abundance is low (see Table 2). The abundance ratios ofthese isotopic water molecules are closely related totheir geographic origin [6]. Since DH16O and H218O
are slightly heavier molecules than H216O, we callwater with a relatively high content of these isotopic
water molecules heavy water, and that with a low
content light water. The rainwater that falls in hot
areas, for example tropical regions, is known to beheavy water, whereas the rain or snow that falls incold areas, for example, the polar regions, is lightwater. The origin of river water and groundwater israinwater. Animals and plants consume the rainwaterthat falls in the region they inhabit. Therefore, theiroxygen and hydrogen isotopic ratios are related tothose of the rainwater that falls in the region. We cantherefore expect to apply isotope analysis technology
to determine or estimate the geographic origin offoods and beverages.
We measured the isotope ratios of eight types ofwater available in Japan: seven bottled waters samVol. 12 No. 4 Apr. 2014

O

16

pled from various places in Japan, and one tap-water
sample from Atsugi, the location of our laboratory,
using a laser based water isotope analyzer. The measurement results are shown in Fig. 3(a), and the sampling locations and their latitudes are in Fig. 3(b).
The horizontal axis indicates the oxygen isotopic
composition δ18O, and the vertical axis indicates thehydrogen isotopic composition δD in Fig. 3(a). The
isotopic composition is usually denoted δ, as definedby the following equation:
δX (‰) = ( Rsample/Rstandard – 1 ) × 1000
where X represents 18O or D, and R represents theisotope ratio of each element, that is, 18O/16O or D/H
for oxygen or hydrogen, respectively. The isotopic
composition δX is defined by the difference between
the isotope ratio of the sample (Rsample) and the standard material (Rstandard), and is expressed in per milleunits (‰), as shown in the above equation. For oxygen and hydrogen, Vienna Standard Mean Ocean
Water (VSMOW), which is managed by the International Atomic Energy Agency, is usually used as theinternational standard material. The solid line in Fig. 3(a)indicates the Global Meteoric Water Line, which
gives the average relationship between hydrogen andoxygen isotopic compositions in natural terrestrial
waters, expressed as a worldwide average.
Although A and B are both examples of water
sampled in Kumejima, Okinawa, there is a big difference between them. A is deep ocean water, and B isspring water sampled on the island. Since VSMOW
was composed of ocean water collected from different locations around the globe as the standard mean
ocean water, the oxygen and hydrogen isotopicFeature Articles

Hydrogen isotopic compositionδD (‰)
20
Global meteoric water line
δD = 8 × δ18O + 10 (‰)

0

H: Yoteizan, Hokkaido(43˚N)

Heavy water

G: Shirakami-Sanchi,
Aomori(40˚N)
F: Hakushu, Yamanashi(36˚N)

A

B

−20
−40
G D

−60

E

C

D: Ryugadake, Tokushima(34˚N)

H
F−80

Light water

δ O (‰)−10 −8−6−4−2
0
2
Oxygen isotopic composition(a) Oxygen and hydrogen isotopic compositionof water in Japan

−100
−14

18

−12

E: Atsugi, Kanagawa(35˚N)

A: Kumejima, Okinawa(deep ocean water)

C: Ikoma-Kogen, Miyazaki(32˚N)
B: Kumejima, Okinawa(26˚N)(b) Sampling location and latitudeFig. 3. Isotope analysis of water in Japan.

compositions (δ18O, δD) of the deep ocean water A
are both nearly zero. We denote the lower to higher
latitude order as B to H. We found that as the latitudeof the sampling place became higher, the isotopic
composition became lower, with two exceptions,
namely Ryugadake, Tokushima (D) and Hakushu,
Yamanashi (F). We believe this is because the water
sources are at a higher altitude than in the other locations.
The isotope ratio of precipitation is related to thegeographic characteristics because light water molecules are easier to vaporize and harder to condense
than heavy water molecules. Therefore, the watermolecules in the atmosphere are lighter than those in
the ocean. First, the relatively heavy light-water molecules in the atmosphere condense into liquid waterand cause rain in hot regions near the equator, andthen, the water molecules, which become lighter andlighter, move to colder regions and condense andbring light rain or snow.
The oxygen and hydrogen isotope ratio of the wateris closely related to such geographic information as
the latitude and altitude of its source, and we can
expect to determine or estimate the geographic originof different types of water by using this property.
Furthermore, the isotope ratio of water affects that of
the material composition of animals and plants,
which consume the rainwater that falls in the region.
Therefore, a lot of research has been done on the useof isotope analysis technology to detect the geographic origin of various foods including agriculturaland livestock products.
The material composing food contains not only
oxygen and hydrogen but also carbon and nitrogen,so we can also measure the isotope ratio of carbon or
nitrogen to achieve a more precise determination. For
instance, the carbon isotopic composition (δ13C) is
known to be related to certain species of plants andtheir growing environment or the kind of feed used
for livestock. Therefore, it is also useful for determining or estimating the geographic origin of food.
5. Future developments
We have mainly focused in this article on the use of
isotope analysis technology to determine the geographic origin of food, but we can also expect thistechnology to be applied to various other fields
including quality inspection of manufacturing methods, the production history of food (e.g., as a screening method to reveal the adulteration of honey or fruit
juice with lower cost sweeteners and for discriminating between straight fruit juice and concentrated fruit
juice), and the determination of the source of greenhouse gases such as carbon dioxide (e.g., fossil fuels,
biomass, animal exhalation), which will be a very
useful technology for maintaining food safety andimproving the global environment. NTT Photonics
Laboratories will promote the research and development of laser source technology and its corresponding application technology in line with efforts toresolve various social problems.
NTT Technical Review

Feature Articles

References
[1]

[2]
[3]

Y. Kondo, M. Asobe, and H. Oohashi, “Light Source Technologies for
Sensing Applications,” NTT Technical Review, Vol. 7, No. 1, 2009.
https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr2009
01sf1.html
A. O’Keefe and D. A. G. Deacon, “Cavity Ring-down Optical Spectrometer for Absorption Measurements Using Pulsed Laser Sources,”
Rev. Sci. Instrum., Vol. 59, No. 2544, 1988.
H. R. Barry, L. Corner, G. Hancock, R. Peverall, and G. A. D. Ritchie,“Cavity-enhanced Absorption Spectroscopy of Methane at 1.73 μm,”

Ryoko Yoshimura

Senior Research Engineer, Photonics Device
Laboratory, NTT Photonics Laboratories.
He received the B.S. and M.S. degrees in physics and the Ph.D. degree from Keio University,
Kanagawa, in 1987, 1989, and 2001, respectively. In 1989, he joined NTT Basic Research Laboratories, where he engaged in R&D of polymeric
optical waveguides for optical communicationand optical interconnection. In 2000, he moved
to NTT Photonics Laboratories, where he hassince been engaged in R&D of optical semiconductor devices and their application technologies. He is a member of the Japan Society ofApplied Physics (JSAP) and the Institute of Electronics, Information, and Communication Engineers (IEICE).

[4]

[5]
[6]

Chem. Phys. Lett., Vol. 333, No. 3-4, pp. 285–289, 2001.
M. B. Frish, R. T. Wainner, J. Stafford-Evans, B. D. Green, M. G.
Allen, S. Chancey, J. Rutherford, G. Midgley, and P. Wehnert, “Standoff Sensing of Natural Gas Leaks: Evolution of the Remote Methane
Leak Detector (RMLD),” Proc. of LEO/QELS 2005, Vol. 3, pp.
1941–1943, Baltimore, MD, USA.
Environmental Defense Fund.
http://www.edf.org/energy/innovation/gas-leak-detection-innovation
WaterIsotopes.org.
http://www.waterisotopes.org

Tadashi Sakamoto

Senior Manager, R&D Produce Group,
Research Planning Department of NTT Science
and Core Technology Laboratory Group.
He received the B.E. and M.E. degrees in electronic engineering from Waseda University,
Tokyo, in 1990 and 1992, respectively. In 1992,
he joined NTT Photonics Laboratories, where heengaged in research on optical devices and theirapplications to optical communications until
2011. He is currently working as a producer tosearch for new applications of R&D outputs infields such as medicine, healthcare, and the environment. He is a member of IEICE and IEEE.

Yoshihisa Sakai

Masaki Kohtoku

Senior Research Engineer, Group Leader of the
Crystal Growth and Fabrication Process ResearchGroup, NTT Photonics Laboratories.
He received the B.E., M.E., and Ph.D. degrees
from Tokyo Institute of Technology in 1989,
1991, and 2006, respectively. In 1991, he joined
NTT Photonics Laboratories, where he has since
been engaged in research on InP-based monolithic integrated circuits and silica-based PLCs.
His work mainly involves the design, fabrication,
trimming, and characterization of AWGs andtheir integrated devices. He is a member of JSAP
and IEICE.

Koji Fujii

Senior Research Engineer, Research Planning
Department, NTT Science and Core Technology
Laboratory Group.
He received the B.S. and M.S. degrees inphysical electronics from Tokyo Institute ofTechnology in 1991 and 1993, respectively. In
1993, he joined NTT LSI Laboratories, where heengaged in research on low-voltage digital circuits. In 2005, he was involved in a research
project on a wireless sensor network. Since then,he has worked on the design of VLSI circuits anda system for a low-power wireless transceiver. He
is currently working on activities promoting thecommercialization of research outcomes achievedin his laboratory group. His current interests
include wireless transceivers, biomedical sensors
and their signal processing circuits. He served asan editor of IEICE Electronics Express from2011 to 2012. He currently serves on the Technical Program Committee of the VLSI Circuits
Symposium.

Vol. 12 No. 4 Apr. 2014

Executive Research Engineer, R&D Produce
Group, Research Planning Department, NTT
Science and Core Technology Laboratory
Group.
He received the B.E. and M.E. degrees in electronics engineering in 1986 and 1988, respectively, and the D.E. degree from Kanazawa University, Ishikawa, in 1995. Since joining NTT in
1988, he has been engaged in researching frequency stabilization of semiconductor lasers and
WDM optical networks. From 1997 to 1999, healso worked at Photonic Integration Research
Incorporation (PIRI), which was a venture company manufacturing PLC-based devices inColumbus, OH, USA. From 2009 to 2012, he
was a Director of Mining, Information, Communication and Monitoring (Micomo) in Santiago,
Chile. He has been an Executive Research Engineer of NTT Science and Core Technology Laboratory Group since 2010.

Feature Articles: Cutting-edge Device and Materials
Technologies for Creating New Business

GaN-on-Si Technology for
High-power Transistors
Noriyuki Watanabe
Abstract

Group-III nitride semiconductors are very promising materials for high-power electronic devices. The
physical properties of these semiconductors make it possible to develop devices that show better performance than the silicon (Si)-based devices that are currently used for integrated circuits. In particular,
replacing Si-based devices in inverters, which are widely used in home appliances, with gallium nitride(GaN)-based devices is an effective way to reduce electric power consumption in homes. In this article,
a technique for forming GaN and related materials on Si substrates is introduced. This technique is suitable for low-cost mass production techniques because Si substrates have the largest size and lowest costamong various substrates.
Keywords: GaN, Si substrate, epitaxial growth

1. Overview of nitride semiconductors
Nitride semiconductors are a type of compound
semiconductor that are composed of a group-III element and nitrogen, for example, gallium nitride(GaN), aluminum nitride (AlN), indium nitride (InN),
or a combination of these materials. These semiconductors have a band gap corresponding to shortwavelength light, and they are chemically andmechanically very stable. This gives them highpotential strength even in high-temperature environments. Recently, light-emitting diodes (LEDs) havecome to be widely used as lighting devices in place ofincandescent light bulbs or fluorescent lamps. These
LEDs are made with nitride semiconductors. Nitride
semiconductors are thus widely used in many familiar applications.
2. Promising applications of
nitride semiconductors
The use of LEDs made of nitride semiconductors
can contribute to reducing electric power consumption, and this is one reason why nitride semiconductors are promising materials. Another large energysaving effect is achieved when nitride semiconduc

tors are applied to devices used in power supply units
in home appliances. One such example is the circuitthat drives the motor in compressors used in refrigerators and air conditioners. In Japan, a circuit called
an inverter is used in most home appliances. The
inverter generates an AC (alternating current) signal
with an arbitrary frequency by using the switching
function of transistors, and it can control the amountof electric power that is supplied by changing thefrequency. The power consumption of the inverter ismuch lower than that of the power unit that controls
the supplied power by simply switching the electric
power on and off. As described above, most refrigerators and air conditioners in Japan already have power
units that include an inverter. However, the use of
inverters is not as widespread in other developed anddeveloping countries. An extremely large reductionin power consumption around the world could beachieved by replacing non-inverter products withinverter ones (Fig. 1). The power-saving effect from
replacing all non-inverter type power units in refrigerators and air conditioners throughout the world
with inverter ones is estimated to equal the amount ofelectric power produced by eight thermal power
plants [1]. Moreover, the use of GaN-based transistors instead of silicon (Si)-based transistors, which
NTT Technical Review

Feature Articles

Air conditioners

Refrigerators
Inverter10%

Refrigerator
14.2%
Illumination
13.4%

Non-inverter
60%

Television
8.9%

Water heater
5.4%
Hot-water supply machine
3.8%
Toilet flush system
3.7%(a) Distribution of power consumption in the home inJapan (2009)
Dishwasher
3.7%(b) Ratio of non-inverter and inverter appliances in theworld (2012)

Refrigerators

Air conditioners
kWh/y
3000
Power consumption

Air conditioner
7.4%

Non-inverter
90%(from data of Agency for Natural Resources and Energy [1])

kWh/y
1000
Non-inverter

2000
Inverter
1000

0Power consumption

Others
39.5%

Inverter
40%

500

Non-inverter
Inverter

0(c) Reduction in power consumption using inverter

Fig. 1. Electric power saving effect using inverter.

are included in inverters, is estimated to result in a
one-third to one-half reduction in power consumption. Therefore, GaN-based transistors are considered
to be very promising devices for saving power.
3. Mechanism of achieving low power
consumption with GaN-based transistors
I discuss here the mechanism in which power consumption can be reduced using GaN-based transistors[2]. There are two main factors in the power loss that
occurs because of the characteristics of transistors in
the inverter circuit. One is the conduction loss, whichcorresponds to the power loss when current is flowing
through transistors. Conduction losses increase as theon-resistance increases. This refers to the resistanceof the current path between terminals when the transistor is in the on-state. The other factor is the switching loss that occurs when transistors are switchedfrom the on-state (in which current flows throughtransistors) to the off-state (in which current does not
Vol. 12 No. 4 Apr. 2014flow) and vice versa (as shown in Fig. 2(a)). These
are described in more detail in the following subsections.
3.1 Conduction loss
Si-based devices called insulated gate bipolar transistors (IGBTs) are typically used in the inverter circuit. The IGBT has three terminals consisting of agate, emitter, and collector. Current flows from thecollector to the emitter; we can switch the IGBT fromthe on-state to the off-state by applying bias voltage
to the gate. The electron density in the area where
current flows in the IGBT is relatively low in order toavoid breakdown during high-voltage operation. Thisis one reason why the on-resistance of IGBTs is large.
Moreover, no current flows below a certain voltage(called offset voltage) between the emitter and collector because of this operating principle. This is anotherreason for the large on-resistance in IGBTs. In turn,transistors called high-electron mobility transistors(HEMTs) are widely used in GaN-based transistors.
Feature Articles

Gate signal
TimetCollector (drain) voltage
Vm
Collector (drain) current
Power loss

Si-IGBT

GaN-HEMT

Collector current

Drain current

Im
Time

Switchingloss

OffsetvoltageTime

Collector voltage

Conduction loss

A steeper slope of the line indicates lower
on-resistance. GaN-HEMT shows lower
on-resistance than Si-IGBT because of the larger
gradient of GaN-HEMT and the lack of offset voltage.

(a) Conduction loss and switching loss in transistor

Si-IGBT

Drain voltage

GaN-HEMT(b) Comparison of current-voltage characteristics of
Si-IGBT and GaN-HEMT

Gate signal
Time
Collector (drain) voltage

Collector (drain) current

TimePower loss
The power loss can be reduced in GaN-HEMT, which has a shorter
switching time than Si-IGBT.
(c) Comparison of switching properties of Si-IGBT and GaN-HEMT

Fig. 2. Reduction in transistor power loss using GaN.

The HEMT has a channel layer with a very high density of electrons, which is known as two-dimensional
electron gas (2DEG). The electron mobility of 2DEG
is very high, as the device name suggests. HEMTs
also have three terminals consisting of a gate, source,and drain. Current flows from the drain to the source,
and we can switch the HEMT from the on-state to theoff-state by applying bias voltage to the gate in thesame manner as the IGBT. Consequently, because
nitride-based semiconductors have higher breakdown
strength than Si, a GaN-based HEMT can be operated
under higher voltage. In addition, the HEMT has
essentially no offset voltage (Fig. 2(b)). Therefore,
GaN-based HEMTs have much smaller on-resistancethan Si-based IGBTs. As a result, using GaN-based
HEMTs instead of IGBTs can reduce the conductive
power loss to half or less.
3.2 Switching loss
In the inverter circuit, transistors are switched from

the on-state to the off-state, or vice versa, by changing the gate bias voltage. In the on-state, the current
flowing from the collector to the emitter (IGBT) orfrom the drain to the source (HEMT) shows the
maximum value (Im) when the voltage between thecollector and emitter or the drain and source is verysmall (limited by the on-resistance). On the contrary,in the off-state, a certain voltage (Vm) between thecollector and emitter or the drain and source isapplied while the current from the collector to theemitter or from the drain to the source is almost zero.
Therefore, the power loss per unit time in the on- or
off-state itself is very small. The power loss during
the switching between the on-state and the off-state iscalled the switching loss. Power consumption in transistors is approximately given by the product of thecurrent, voltage, and duration time. If the switchingfrom the on- to off-state or from the off- to on-state is
fast enough, the switching loss is negligible. However, the switching time in actual devices is not zero but
NTT Technical Review

Feature Articles

a finite value. As a result, switching loss occurs. The
switching loss can be reduced by shortening theswitching time. The operating speed of GaN-based
HEMTs is much higher (about 10 times higher) thanSi-based IGBTs. Therefore, the switching loss can be
reduced by replacing Si-based IGBTs with GaNbased HEMTs.
4. Low-cost GaN-based HEMTs using
GaN-on-Si technology
With Si-based transistors, devices are fabricateddirectly on Si substrates using various process technologies such as thin film deposition, impurity diffusion, ion implantation, or electrode formation. On thecontrary, in the case of GaN-based transistors, thetransistors cannot be fabricated until nitride semiconductor films are first formed on the substrate using an
epitaxial growth technique. This section focuses on
the epitaxial growth of GaN-based materials.
4.1 G rowth of semiconductor materials
on substrates
The first process in fabricating III-V compound
semiconductors, including nitride semiconductors, isthe epitaxial growth of semiconductor materials on
substrates. There are various methods of growing
semiconductor materials; the vapor phase epitaxial
technique is one widely used method. Substrates
made of the same material or made with other materials that have similar properties are commonly used
for epitaxial growth because high quality semiconductors can be obtained using such substrates. However, substrates consisting of nitride semiconductors
are currently very expensive, and their size is rather
small because of the difficulty in producing nitride
substrates. Because GaN-based HEMTs are used inhome appliances, it is essential to achieve cost competitiveness. In view of this, GaN-on-Si technology,
by which nitride semiconductor materials are grownon Si substrates, has attracted a lot of attention. Thatis, nitride semiconductors are grown on a large scaleon high-quality and low-cost Si substrates that areeasily obtained.
4.2 T echnical problems related to growthof materials
Many technical problems first need to be solved,
however, in order to successfully grow GaN-basedmaterials on Si substrates. The most serious issue tobe solved is the mismatch in material properties
between GaN and Si. The process of growing semiVol. 12 No. 4 Apr. 2014

conductors is greatly affected by the properties ofsubstrates. One of the most important properties isthe lattice constant, which is the unit size of the crystal structure of the material. Individual materials havedifferent lattice constants. The mismatch in the lattice
constant between a substrate and a material grown on
the substrate should generally be less than 0.1%.
However, the lattice mismatch between GaN and Si isover 14%. Therefore, we have to overcome a latticemismatch that is 100 times larger in order to develop
effective GaN-on-Si technology.
Another important property is the thermal expansion coefficient. The lattice of the material expands
and shrinks as the temperature increases and decreases.
The thermal expansion coefficient is defined as theratio between the change in the lattice constant due toa temperature change of 1 K and the lattice constantitself. The growth temperature of GaN and relatedmaterials is very high at about 1000˚C. When thesubstrate is cooled down to room temperature after
growth, both the GaN layer and the Si substrateshrink. Because GaN has a larger thermal expansion
coefficient than Si, the Si substrate with the GaN
layer has a concave shape. If the curvature of the substrate exceeds the limit of the mechanical strength ofthe material, the GaN layer will crack over the entire
substrate (Fig. 3(a)). Therefore, it is also necessary to
overcome the mismatch in the thermal expansion
coefficient between GaN and Si. A buffer layer thatcan compensate for the mismatch between material
properties such as the lattice constant and the thermal
expansion coefficient is usually grown between the Si
substrate and the GaN layer. At NTT Photonics Laboratories, we have been investigating the structure of
the buffer layer and have successfully obtained highquality GaN-based HEMT structures on Si substrates[3] (Fig. 3(b)). We are now planning to develop GaNon-Si technology that is even more cost-effective.
Until now, we have been able to successfully grow
GaN-based HEMT structures more than 4 µm thickon large Si substrates up to 6 inches in diameter byusing an improved buffer structure. This has resulted
in electrically robust properties in which the fabricated structure does not crack even if subjected tovery high voltage exceeding 1000 V (Fig. 4). The
GaN-based HEMTs fabricated using GaN-on-Si
technology are expected to be widely used in green
devices that will contribute to achieving an energysaving society in the near future.

Feature Articles(a) Conventional method
During growth

Cooling

Room temperature

GaN
Nucleation
Si substrate
Crack(b) Improved method
During growth

Cooling

Room temperature

GaN
BufferNucleation
Si substrate

Fig. 3. Growth of GaN and related materials on Si substrate [3].

Breakdown@ < 500 V(A/cm2)100

A
AlGaN barrier
GaN channel
AlGaN-based buffer(conventional)
Nucleation
Si substrate

10−2

Buffer leakage current

No breakdown@ 1000 V

10−4
A

Improved

Conventional

AlGaN barrier
GaN channel> 4 µm10−6

AlGaN-based buffer(improved)
Nucleation
Si substrate

10−8
0

200

400

600

800

(V)
1000

VoltageFig. 4. Current-voltage curve of GaN HEMT on Si substrate.

NTT Technical Review

Feature Articles

5. Conclusion
This article described a technique for forming GaN
and related materials on Si substrates. This technique
is suitable for low-cost mass production because substrates fabricated from Si are the largest in size andlowest in cost among various substrates. However,some issues remain to be solved. One of the mostserious issues is current collapse, a phenomenon inwhich the on-resistance of a transistor gradually
increases during transistor operation. These issues are
now under investigation. Nevertheless, the GaN-onSi technology is expected to lead to the developmentof devices that are indispensable for an energy-savingsociety.

References
[1]

[2]

[3]

“Survey on Energy Saving Measures of Machinery and Appliances,”
Acceleration of Rationalization of Energy Usage, Structural Improvement 2011, by Energy Efficiency and Conservation Division, Energy
Conservation and Renewable Energy Department, Natural Resources
and Energy, Ministry of Economy, Trade and Industry (in Japanese).
http://www.enecho.meti.go.jp/policy/saveenergy/save03/h23_gaiyou.pdf
T. Morita, S. Tamura, Y. Anda, M. Ishida, Y. Uemoto, T. Ueda, T.
Tanaka, and D. Ueda, “99.3% Efficiency of Three-phase Inverter for
Motor Drive Using GaN-based Gate Injection Transistors,” Proc. ofthe 26th Annual IEEE Applied Power Electronics Conference andExposition (APEC 2011), Fort Worth, TX, USA, pp. 481–484.
Y. Oda, N. Watanabe, and T. Kobayashi, “Crystal Growth Technologyof Nitride Semiconductors on Si Substrate,” NTT Technical Journal,
Vol. 20, No. 7, pp. 55–56, 2008 (in Japanese).
http://www.ntt.co.jp/journal/0807/files/jn200807055.pdf

Noriyuki Watanabe

Senior Research Engineer, Supervisor, HighSpeed Devices and Technology Laboratory, NTT
Photonics Laboratories.
He received the B.E., M.E., and Ph.D. degrees
in applied physics from the University of Tokyoin 1989, 1991, and 1997, respectively. In 1991,
he joined NTT LSI Laboratories, Kanagawa,where he engaged in R&D of epitaxial growth ofelectronic devices consisting of III-V compound
semiconductors using metalorganic chemical
vapor deposition. Since 2004, he has been
engaged in R&D of epitaxial growth of GaNbased high electron mobility transistors (HEMTs)
at NTT Photonics Laboratories. His current
research interests include epitaxial growth of
nitride-based semiconductor devices such as
GaN-based HEMTs on Si substrates and InGaNbased solar cells. He is a member of the Japan
Society of Applied Physics. He received the 2003
Gallium Arsenide Application Symposium(GAAS®) (now the European Microwave Integrated Circuits Conference) Best Paper Award.

Vol. 12 No. 4 Apr. 2014



Global Standardization Activities

Standardization Activities on
EMC for Telecommunication in
ITU-T SG5
Yuichiro Okugawa, Yasuhiro Honma,
and Kazuhiro Takaya
Abstract

The NTT Group participates in the development of electromagnetic compatibility (EMC)-related
standards as part of its effort to provide safe and secure telecommunication services. This article reportson the latest standardization activities on EMC for telecommunication. Specifically, it presents an overview of the first meeting of ITU-T SG5 (International Telecommunication Union, Telecommunication
Standardization Sector, Study Group 5) in its new study period (2013–2016), including details of discussions held.
Keywords: EMC, ITU-T, standardization

1. Introduction
The NTT Group aims to enhance the quality andreliability of telecommunication services and has
therefore defined an internal standard on electromagnetic compatibility (EMC) called Requirements for
EMC of Telecommunication Systems, which specifies
technical requirements that must be met in formulating specifications for the development or procurement of telecommunication systems (Fig. 1). The
technical requirements for EMC define permissible
values of electromagnetic interfering waves radiatedby telecommunication systems, requirements forresistance to overvoltages generated by electromagnetic interfering waves from other systems, lightning,etc., and test methods related to these requirements.
These requirements conform to international standards on IT (information technology) systems or
telecommunication systems defined by the IEC(International Electrotechnical Commission), CISPR(International Special Committee on Radio Interference), and ITU-T (International Telecommunication
Union, Telecommunication Standardization Sector).
Therefore, activities in these international standard

ization organizations greatly affect the quality andreliability of telecommunication services provided by
the NTT Group. This article introduces international
standardization activities related to EMC, particularly
the activities of ITU-T.
2. Overview of ITU-T SG5 WP1/WP2
ITU-T is headquartered in Geneva, Switzerland andissues recommendations in the field of telecommunications. ITU-T has ten Study Groups (SGs). Recommendations on EMC are developed by SG5 (Environment and climate change). SG5 consists of three
Working Parties (WPs), of which WP1 (Damage prevention and safety) and WP2 (Electromagnetic fields:
emission, immunity, and human exposure) are working on standards related to EMC.
In the current study period (2013–2016), WP1 and
WP2 are addressing the questions shown in Fig. 2.
The first meeting of SG5 was held in Geneva fromJanuary 29 to February 7, 2013. Discussions held onthese questions in the first meeting are introduced
below.

NTT Technical Review

Global Standardization Activities

EMC 1.1 Standards on EMC for Telecommunications Equipment
4th edition, September 2012

Technical Requirements for Electromagnetic Disturbance Emitted from
Telecommunications Equipment
TR No. 550004, 4th edition December 18, 2009
Technical Requirements for Immunity of Telecommunications Equipment
TR No. 549001, 3rd edition May 11, 2005
Technical Requirements for Resistibility of Telecommunications Equipment toOvervoltage and Overcurrent
TR No. 189001, 2nd edition June 29, 2012
Technical Requirements for the Electrical Safety of External Power Supplies
for On-Premises Information and Communications Equipment
TR No. 177001, 2nd edition March 15, 2013
Technical Requirements for Electromagnetic Disturbances Emitted from
Lighting Equipment Installed in Telecommunications Centers
TR No. 174001, 1st edition March 10, 2011
TR: technical requirement

Fig. 1. NTT Group’s requirements related to EMC in telecommunication equipment.

ITU-T SG5WP1 (Damage prevention and safety)
Q1 (Copper cables, networks and fibre-optic connection hardware for broadband access)
Q2 (Protective components and assemblies)
Q3 (Interference to telecommunication networks due to power systems and electrified railway systems)
Q4 (Resistibility and safety in telecommunications)
Q5 (Lightning protection and earthing of telecommunication systems)
WP2 (Electromagnetic fields: emission, immunity and human exposure)Q6 (EMC issues arising from the convergence of IT and communication equipment)
Q7 (Human exposure to electromagnetic fields (EMFs) due to radio systems and mobile equipment)
Q8 (EMC issues in home networks)
Q9 (Generic and product-family EMC recommendations for telecommunication equipment)
Q10 (Security of telecommunication and information systems concerning the electromagnetic environment)
Q11 (EMC requirements for the information society)Fig. 2. Questions (Qs) discussed by WPs 1 and 2.

2.1 Discussions in WP1
WP1 is studying how to protect telecommunication
systems from overvoltages generated by lightningand other sources, and from electromagnetic interferVol. 12 No. 4 Apr. 2014ence due to electromagnetic induction from powersystems, electrified railway systems, and other sources.
In particular, in view of the fact that reports of lightning damage have begun to come from areas that

Global Standardization Activities

have conventionally seldom been hit by lightning andthat the extent of damage from localized lightning has
been increasing in recent years owing to global climate change, WP1 is studying new and additional
recommendations to protect telecommunication systems from overvoltages generated by lightning.
Discussions on each question are summarized
below.
Question 2 concerns test methods, requirements,and methods of use related to components and assemblies that protect against overvoltage such as fuses,
varistors, surge arresters, and transformers. In thecurrent study period, WP1 is focusing on developing
recommendations on the basis of K.appl4, a new draft
recommendation on the application of isolation transformers in telecommunication systems, and K.LIT, a
new draft recommendation on requirements for isolation transformers.
In the first meeting, in order to advance discussions
on K.appl4, NTT proposed a method of increasing
the dielectric strength of telecommunication systems
by using isolation transformers in both the telecommunication system and the associated power supply
system. Whether the proposed method should be
included in the new proposed recommendation will
be discussed at the next meeting. China proposed asurge protective device (SPD) to be applied to 400-V
direct current (DC) systems. Discussions on this proposal will continue in subsequent meetings.
Question 3 relates to the issue of how to protect
telecommunication systems from electromagnetic
induction from power systems and electrified railway
systems, and the safety of workers in the event ofground faults. In the first meeting, NTT submitted theresults of an experiment on measuring the voltagethat rises in the metallic tension member of an opticalfiber cable when a ground fault occurs in the powerline. It was decided to study the need for protection
from such voltages. At the next meeting, a questionnaire will be distributed to collect information aboutsuch cases in other countries. Greece submitted acontribution concerning protective measures taken
when installing telecommunication devices at thetops of poles. It was decided to study this issue undera new draft recommendation, K.tup.
Under Question 4, WP1 studies requirements forovervoltage resistibility at interfaces of telecommunication systems that are installed in telecommunication centers, outdoors, or in customers’ premises,
methods of protection against overvoltage, and electrical safety. WP1 also keeps existing relevant ITU-T
recommendations up to date. In the first meeting,NTT submitted a contribution that reports on the
results of an overvoltage test in which high-voltage
pulse transformers were used to raise the overvoltage
resistibility at the Ethernet port of devices connected
to a home network. The contribution showed that an
overvoltage resistibility of 7 kV can be provided at
the Ethernet port. This has given Japan a strong position to drive the discussion on Ethernet ports with theaim of developing an overvoltage protection guideand a new draft recommendation K.lit (Question 2) atthe next meeting.
Question 5 addresses methods of risk management
related to lightning protection and the earthing of
telecommunication systems. At the first meeting it
was agreed to study during this study period theearthing of 400-V DC systems, a new draft recommendation, K.dbs, concerning lightning protection of
power transformers near wireless base stations, andlightning protection of concrete poles installed near
wireless repeater stations to protect these stations
from lightning. At the next meeting, we will submit a
proposal on the earthing of 400-V DC systems basedon studies done by ETSI (European Telecommunications Standards Institute).
2.2 Discussions in WP2
WP2 is studying emissions from telecommunication systems and devices, immunity to such emissions, and protection against human exposure toelectromagnetic fields. Owing to the widespread use
in recent years of electrical appliances and power
converters that use inverter control to save energy,
there is an increasing number of reports of telecommunication failures caused by electromagnetic disturbance waves at low frequencies (up to 150 kHz),
which are problems not covered by existing ITU-T
recommendations. WP2 will study EMC problems
that arise from such electromagnetic disturbancewaves, discuss new draft recommendations, andrevise existing recommendations as necessary. The
main questions that WP2 is discussing are introduced
below.
Question 6 concerns EMC problems that arise fromthe mutual use of telecommunication networks bydifferent providers, which has resulted from the liberalization of telecommunication policies, and themaintenance of existing relevant recommendations.
At the first meeting it was agreed to study the newdraft recommendation, K.eun, which addresses methods of estimating the leakage of broadband signals
from cables and which had been discussed in the previous study period (2009–2012), and to treat it as a
NTT Technical Review

Global Standardization Activities

draft revision to the existing recommendation, K.60
(Emission levels and test methods for wireline telecommunication networks to minimize electromagnetic disturbance of radio services). Similarly, WP2
decided to discuss the new draft recommendation,
K.mit, which is intended to define methods of reducing the effects on next-generation access systems, as
draft revisions to K.58 (EMC, resistibility and safety
requirements and guidance for determining responsibility under co-located telecommunication installations) and K.59 (EMC, resistibility and safety
requirements and procedures for connection to
unbundled cables).
Question 7 deals with human exposure to electromagnetic fields near antennas of radio systems andmobile equipment. WP2 is studying methods andprocedures for estimating, calculating, and measuring electric field strength. In the first meeting, a rapporteur proposed a revised version of the software
program for calculating equivalent isotropically radiated power (attached to the existing recommendation,
K.52: Guidance on complying with limits for human
exposure to electromagnetic fields (EMFs)), and arevised version of the software program for calculating the EMF (attached to the existing recommendation, K.70: Mitigation techniques to limit human
exposure to EMFs in the vicinity of radiocommunication stations). WP2 approved the addition of theserevised programs to the Appendix of each of theserecommendations.
Question 8 covers immunity specifications, overvoltage and electrical safety specifications, and electromagnetic environments for communication devices that make up a home network. The first meeting
included a discussion of the policy for revising theexisting recommendation, K.74 (EMC, resistibility,
and safety requirements for home network devices).
Additionally, a new draft recommendation, K.mhn(Version 3) was studied, which concerns how to mitigate disturbances caused by radio signals in cables ordevices connected to broadband cables. WP2 agreed
to develop a recommendation on the basis of K.mhn
by collecting further information about cases of interference between CATV (community access television) and wireless devices, which are referred to in
the Appendix to K.mhn, and by exchanging information with ITU-R.
Question 9 relates to the study of EMC specifications for new telecommunication equipment and services, and the maintenance of existing relevant rec-Vol. 12 No. 4 Apr. 2014

ommendations. In the first meeting, NTT submitted
cases of telecommunication service failures caused
by a sub-150-kHz conducted disturbance wave emitted by inverters. The meeting participants recognized
the need to specify emission immunity in sub-150kHz frequency bands, and they agreed to develop a
new recommendation on this subject. In addition,
NTT reported on the results of its tests of a radiation
immunity testing method. This method assumes theuse of wireless devices near telecommunication systems, and it was studied in order to meet the growing
demand for using wireless devices in NTT’s telecommunication equipment rooms. The meeting agreed toincorporate this issue in revising the existing recommendation, K.80 (EMC requirements for telecommunication network equipment (1 GHz–6 GHz)).
Question 10 focuses on issues pertaining to theelectromagnetic security of telecommunication systems. WP2 is studying methods of protecting electronic systems from the electromagnetic effects of
HEMP (high altitude electromagnetic pulse) and
HPEM (high power electromagnetic) attacks, andmeasures to prevent information leaks in attacks thattake advantage of electromagnetic properties. At thefirst meeting, a new draft recommendation, K.secmiti(Version 3) was discussed, which has been developedsince the previous study period. It defines a methodof mitigating threats to electromagnetic security.
WP2 agreed to incorporate NTT-developed technology for preventing information leaks via electromagnetic waves as one of the countermeasures.
3. Conclusion
This article introduced standardization activities in
ITU-T SG5 WP1/WP2. The main issues to beaddressed in this study period are the development of
new recommendations to prevent lightning-derived
failures of telecommunication systems and finding
solutions to new EMC problems arising from a conducted disturbance wave emitted by inverters, alongwith the revision of existing recommendations. These
are important issues for telecommunication services
in Japan, so NTT will be active in submitting proposals, thereby contributing to solving EMC problems.
NTT will also enhance the quality and reliability oftelecommunications by incorporating useful test
methods and countermeasure technologies adopted in
ITU recommendations into its technical requirements.

Global Standardization Activities

Yuichiro Okugawa

Research Engineer, EMC Technology Group,
Energy Systems Project, NTT Energy and Environment Systems Laboratories.
He received the B.E. and M.E. degrees in electrical engineering from Tokyo University of Science in 2002 and 2004, respectively. He joined
NTT Energy and Environment Systems Laboratories in 2004 and studied EMC technology fortelecommunication. He is currently studying
radiation immunity test methods for vicinity useof wireless devices. He is a member of the Institute of Electronics, Information and Communication Engineers (IEICE).

Kazuhiro Takaya

Senior Research Engineer, Supervisor, Group
Leader of EMC Technology Group, Energy Systems Project, NTT Energy and Environment
Systems Laboratories.
He received the B.E. and M.E. degrees in electrical and electronic engineering from Okayama
University in 1993 and 1995, respectively. He
joined NTT Telecommunication Network Laboratory in 1995. He has studied electromagnetic
interference in wireless and wired communication systems, and disaster prevention countermeasures using communication systems. He is amember of IEICE.

Yasuhiro Honma

Research Engineer, EMC Technology Group,
Energy Systems Project, NTT Energy and Environment Systems Laboratories.
He received the B.E. and M.E. degrees in electrical and electronic engineering from Kitami
Institute of Technology, Hokkaido, in 1998 and
2000, respectively. He joined NTT EAST in
2000. He moved to NTT Energy and Environment Systems Laboratories in 2008. He has been
engaged in R&D of lightning protection andgrounding for telecommunication systems. He isa member of IEICE.

NTT Technical Review

Practical Field Information about
Telecommunication Technologies

Case Studies of Insulation Failures in
Outdoor Facilities andCountermeasures against Failures
Abstract

In this article, we introduce failure cases in outdoor access equipment and a countermeasure to them.
This is the twenty-second in a bimonthly series on the theme of practical field information on telecommunication technologies. This month’s contribution is from the Materials Engineering Group, Technical
Assistance and Support Center, Maintenance and Service Operations Department, Network Business
Headquarters, NTT EAST.
Keywords: countermeasures, access equipment, outdoor facilities

1. Introduction
NTT EAST has been developing and deploying
outdoor optical access equipment that accommodates
multiple lines (referred to below as remote terminal(RT) equipment) in order to economically upgrade
the metallic cable network. Compact RT equipment
can be installed in small spaces such as in the cornersof public sites and facilities and under pedestrian
bridges, and many units have been installed throughout Japan (Fig. 1).
However, more than ten years have passed since thedevelopment and deployment of this equipment
began, and in recent years, the number of requests for
consultation regarding problems in compact RT
equipment has increased. At the Technical Assistanceand Support Center, we have analyzed the cause of
insulation failures throughout the country that havebeen brought to our attention in these consultations
and have studied countermeasures to prevent such
failures. We report here on our investigation into thecause of insulation failures in compact RT equipment
and also describe a preventive measure.
2. Insulation failures in compact RT equipment
Compact RT equipment has been designed for outdoor installation and the need to maintain communi

cation functions even when the equipment is exposed
to wind and rain. However, equipment that has beenin the field for more than ten years is inevitably
affected by the installation environment (rain, humidity, corrosive gases, etc.) over the long term. Suchequipment is at greater risk for problems as deterioration progresses.
Consultations on insulation failures in compact RT
equipment have been requested from all regions ofJapan from Okinawa to Hokkaido. These failures,moreover, have been reported in all seasons, fromJapan’s relatively long rainy season and severe
typhoon season to its dry winter season.

RSBM-F

O-PW

O-PW: Outdoor Cabinet with Power
RSBM-F: Remote SuBscriber Module-Feeder

Fig. 1. Examples of outdoor RT equipment.

NTT Technical Review

Practical Field Information about Telecommunication Technologies

Condensation
Water

Condensation in MDF chamber

Water penetration in
power supply chamber

MDF: main distribution frameFig. 2. Examples of water penetration in equipment.

Instances of rainfall(a) Degraded rubber sealing

Relative humidity,
temperature

100 Relative humidity
90
Fluctuation
80
range
70
60
50
40
30
20
Temperature
100(%,°C)
2011/5/13 2011/7/2 2011/8/21 2011/10/10 2011/11/29 2012/1/18
Date of measurement(b) Normal rubber sealing

Instances of rainfall

Relative humidity,
temperature

100
90
Relative humidity
80
70
60
50
40
30
20
(%,°C) 10
Temperature0
2011/4/22 2011/6/21 2011/8/20 2011/10/19 2011/12/18 2012/2/16
Date of measurement

Fig. 3. Temperature/humidity inside compact RT equipment before and after rainfall.

Similar characteristics have been found in compact
RT equipment in which insulation failures haveoccurred. Condensation has been observed inside theequipment on the inner side of the door and on theunderside of the top panel, and traces of water havebeen found on the inspection sheet inside the equipment. In the worst cases, water has been found tocollect on the floor of the power supply chamber (Fig. 2).
These conditions led us to infer that external environmental factors such as rain and humidity contributed
to the insulation failures in the equipment.
Vol. 12 No. 4 Apr. 2014

The Technical Assistance and Support Center conducted a survey on the causes of individual failures inorder to develop countermeasures against them.
3. Causes of severe condensation
inside equipment
Humidity inside compact RT equipment tends torise whenever the equipment doors are opened andclosed in rainy weather when deploying new circuits
or carrying out maintenance. Most equipment,Practical Field Information about Telecommunication Technologies

MDF door

MDF door
RubbersealingTop
Raindrops surface
Housingside

MDF door
Conductive
sealing

Drainage
ductFig. 5. Penetration of rainwater through equipment door.
Fig. 4. Clogged drainage duct.

Missing sealing

Damaged section

Fallen leaves

Sand/dust

CracksFig. 6. Examples of problems in rubber sealing.

however, does not develop problems when exposed tosuch conditions, which led us to believe that equipment in which insulation failures occur are subjectedto particular conditions.
The changes in temperature and humidity insideequipment were measured when there were cases ofnormal and degraded rubber sealing. The results areshown in Fig. 3. These graphs show that after a rainfall, the internal relative humidity rises remarkably inequipment with degraded rubber sealing, whereas it
shows little change in equipment with normal rubber
sealing. In other words, it can be inferred that the
housing is not airtight in equipment with degradedrubber sealing, and that the equipment can consequently be affected by moisture in the outside air or
can be penetrated by rainwater.
A drainage duct is installed in each door of thecompact RT equipment in order to lower the risk ofrainwater penetration. However, if fallen leaves clog
the drainage duct (Fig. 4), or if the amount of waterflowing into the drainage duct is excessive due toheavy rain, the rubber sealing may come into contact
with rainwater as the drainage duct overflows. This
raises the risk of rainwater penetrating the equipment
through gaps in the rubber sealing (Fig. 5). Surveys
that we have conducted to date have revealed that rubber sealing often deteriorates and cracks when equipment doors are frequently opened and closed during
circuit-deployment or maintenance work. They havealso shown that it is not unusual for rainwater to penetrate the equipment when leaves and branches
become wedged between the door and the housing
when the door is opened and closed (Fig. 6).
4. Mechanism behind insulation failure
The interior of compact RT equipment is always ina warm state due to heat generated by the power
NTT Technical Review

Practical Field Information about Telecommunication Technologies

supply section and other areas. At night, the outside
surface of the housing can be cooled by cold outside
air, and if the warm air inside the equipment comes
into contact with the cooled inner side of the housing
under such conditions, condensation can occur due tothe temperature difference. However, the occurrenceof condensation does not necessarily mean that an
insulation failure will occur. We examined problem
equipment in various regions and found that insulation failures had occurred under severe condensationin which many water droplets formed on the inside of
the top panel. With this in mind, we postulated that
insulation failures occur by the following mechanism(Fig. 7).
(1)	Rainwater and humidity (moisture) penetrate
the equipment through gaps between the rubber
sealing and housing.
(2)	Temperature inside the equipment rises when
the penetrated rainwater vaporizes due to heatinside the equipment.
(3)	The temperature difference between the insideand outside of the equipment causes condensation (water droplets) to form on interior parts ofthe equipment at relatively lower temperatures(such as the top panel).
(4)	The water droplets drop into the gaps between
terminals of the equipment, causing an insulation failure to occur.

Cold area

Raindrops

Condensation
conditions
Vaporization
Temperature rises
Power
meter
Warm area
Vaporization

Fig. 7. Mechanism behind insulation failure.

5. Overview of preventive measure
Here, we introduce a preventive measure for the
RSBM-F (remote subscriber model-feeder) model ofcompact RT equipment. In the past, the response
taken when insulation failures occurred was to ask
the equipment manufacturer to replace the rubber
sealing. This approach, however, was costly and time
consuming and did not guarantee that an insulation
failure would not occur again. Given these problems,
the Technical Assistance and Support Center proposed a countermeasure commonly referred to as awaterproof roof to prevent water penetration (Fig. 8)
instead of replacing the rubber sealing. The idea
behind this waterproof roof was to prevent the penetration of rainwater that can trigger an insulation
failure. In addition, we collaborated with the manufacturer to (1) give the roof a structure tailored to thepart of the equipment that was most susceptible towater penetration, thereby lowering costs, and to (2)optimize the structure for more efficient maintenance
operations.
Vol. 12 No. 4 Apr. 2014

Waterproof roof

Fig. 8. C ountermeasure to prevent penetration of
rainwater.

The features of the developed waterproof roof arelisted in Table 1, and the half-year result of a test caseusing the roof on actual equipment throughout Japanis shown in Fig. 9. This graph indicates the relative
humidity before and after installation of the waterproof roof. It is clear from these results that installingthe waterproof roof suppresses the fluctuation in relative humidity when rainfall occurs. Consequently,
installation of a waterproof roof has the effect of preventing the penetration of rainwater and suppressing
a rise in humidity within the equipment, which meansthat this countermeasure is effective in preventing
insulation failures.
Practical Field Information about Telecommunication Technologies

Table 1. Features of waterproof roof.
Location of waterproof roof

Ease of installation

Ease of maintenance work

- Equipment door (MDF chamber)- Compact design, stacked storage, portable- Installation time: about 5 min- Technicians required for installation: 2- Equipment side door can be opened/closed by
opening waterproofing door

Without waterproof roof

Relative humidity,
temperature

Instances of rainfall
100
With waterproof roof
90
80
Relative humidity
70
60
50
40
30
20
(%,°C) 10
Temperature0
2011/9/16 2011/10/26 2011/12/5 2012/1/14 2012/2/23
2012/4/3
Date of measurement
Fluctuation in relative humidity is suppressed

Fig. 9. Temperature/humidity before and after installation of waterproof roof.

6. Conclusion
In this article, we introduced case studies of insulation failures in compact RT equipment and a preventive measure. Our findings can be summarized asfollows.
-	Insulation failures frequently occur in equipment
within which rainwater has penetrated throughrubber sealing. Attention should be paid not only
to cracks in the sealing and sealing that is missing due to aging but also to cases in which fallen
leaves and sand and dust become wedged
between the sealing and housing when the equipment door is opened and closed.
-	Preventing the penetration of rainwater throughthe rubber sealing can suppress a rise in humid-

ity within the equipment; therefore, installing awaterproof roof can be expected to prevent theoccurrence of insulation failures.
Looking forward, we consider the possibility thatthe number of insulation failures in compact RT
equipment will increase as equipment continues toage. To prevent failures from happening in the firstplace or to at least reduce the occurrence of failures,
it is essential that equipment be adequately maintained as a preventive measure.
The Technical Assistance and Support Center
works continuously to improve the reliability of all
NTT facilities. We ask those having a difficult timewith equipment-related problems and countermeasures to feel free to contact us.

NTT Technical Review

New NTT Colleagues––We welcome our newcomers to the NTT Group
Here, we welcome newcomers to the NTT Group. This is a new corner of the NTT Technical
Review where we introduce our new affiliate companies.

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integration, application management, and outsourcing services worldwide. It serves over 1,000 clientsprimarily in the banking, insurance, telecommunications, public, industry, and utilities sectors.
everis began its operations in Madrid in 1996. It reached a turnover of EUR 591 million in fiscal year 2012
and a headcount of more than 10,000 consultants worldwide, purely through organic growth.
For further information please visit: everis Group (www.everis.com)
Contacts
everis Groupwww.everis.com
Optimal Solutions Integration, Inc.
Optimal Solutions Integration is a new breed of consulting firm dedicated to driving business transformation
for companies and public sector organizations of all sizes. As an award-winning SAP® services partner,
Optimal provides a comprehensive offering of SAP solutions and services, a proven methodology foraccelerated delivery of SAP solutions, deep industry expertise, and a flexible onsite/offshore delivery modelthat accommodates the reality of business today. Optimal specializes in helping companies maximize theROI (return on investment) of their SAP applications by planning, deploying, and maintaining world-classsolutions in a timeframe the companies require, and at a cost they demand. In April 2014, Optimal started
doing business under the NTT DATA brand name.
For more information about Optimal Solutions Integration, visit http://americas.nttdata.com/
Contacts
NTT DATA, Inc.
http://americas.nttdata.com/

NTT Technical Review

Papers Published in Technical Journals andConference Proceedings
Outdoor AP Measurement in Tokyo
T. Aoki, T. Adachi, M. Kubota, R. Okada, K. Mizutani, M. Morikura, M. Matsui, M. Mizoguchi, Y. Inoue, and A. Yamada
IEEE 802.11 HEW SG, Vol. IEEE11–14, No. 0086, Los Angeles,
CA, USA, 2014.
We conducted outdoor access point (AP) measurements aroundTokyo. The results indicated that the outdoor inter-AP distance wasabout 50 m.

The New Public Phone Service––Non Contact Ultra High
Speed Contents Download
M. Shimizu, K. Hiraga, K. Sakamoto, T. Seki, T. Tsubaki, H.
Toshinaga, and T. Nakagawa
IEEE 802.11 WNG SC, Los Angeles, CA, USA, 2014.
This contribution presents the non-contact ultrahigh speed transmission service over the 60-GHz band. The 60-GHz band is expected
to be useful in non-contact file download kiosk systems with up to 24
Gbit/s and with over 100 Gbit/s using MIMO (multiple input multiple
output).

An SD Method Utilizing Null Dependency on Transmission
Distance Due to Two-ray Fading
K. Hiraga, K. Sakamoto, M. Arai, T. Seki, T. Nakagawa, and K.
UeharaAntennas and Wireless Propagation Letters, IEEE, Vol. 13, No. 1,
pp. 126–129, 2014.
A spatial division (SD) transmission method utilizing the characteristics of two-ray fading due to ground reflection with linear
antenna arrays horizontal to the ground is proposed. Formulations of
the optimum array arrangements as functions of the transmission
distance and achievable channel capacity are clarified. For two- andthree-element arrays, channel capacity is respectively doubled andtripled over that of free-space propagation. The proposed method
provides increased capacity without the extra signal processing cost
incurred when using conventional MIMO (multiple-input and multiple-output) transmission.

A Study of Home Measures for Children’s Safe Internet
Use
N. Chiba, Y. Seki, Y. Horikawa, and Y. Hashimoto
IPSJ Journal, Vol. 55, No. 1, pp. 311–324, 2014 (in Japanese).
With the spread of smartphones, the degree of Internet usage has
increased even more, and Internet safety is an urgent problem facing
young people. Our research focuses on parents and the home situation of young Internet users. We constructed a hypothetical modelthat provides a framework for discussing how to lessen the risk foryoung people using the Internet at home based on our qualitative
analysis. Furthermore, we tested the hypothetical model based on aquantitative investigation of 300 smartphone-using junior and seniorhigh school students and their mothers. The investigation results
clarify the correlation model considering such factors as parenting
concepts, family relations, in-home rules and measures as domesticelements that control the risk when children use the Internet. In addition, we clarify that home measures are related to family relations, theparents’ learning experience regarding the risk of Internet use, and theimplemented parenting concepts.

Compact Optical Devices for High-speed Digital Coherent
Link
S. Kamei
Photonics West 2014, SPIE, Vol. 9008, No. 1, p. 900805-, San
Francisco, CA, USA.
This paper describes recent progress in relation to the key opticaldevices for high-speed digital coherent transmission, namely coherent receivers and advanced-format modulators. Miniaturization andhigher performance have been achieved on a silica-based PLC (planar lightwave circuit) platform and it has been integrated with otherkey materials.

A Study of Short-range MIMO Transmission Utilizing Polarization Multiplexing for the Simplification of Decoding
K. Hiraga, K. Sakamoto, K. Nishimori, T. Seki, T. Nakagawa, andK. Uehara
IEICE Trans. on Communications, Vol. E97-B, No. 2, pp. 459–
468, 2014.
One of the procedures for increasing the number of multiple-input
and multiple-output (MIMO) branches without increasing the computational cost for MIMO detection or multiplexing is to exploit
parallel transmissions by using polarization multiplexing. In thispaper, the effectiveness of using polarization multiplexing is confirmed under the existence of polarization rotation, which is inevitably present in short-range multiple-input and multiple-output (SRMIMO) channels with planar array antennas. It is confirmed that an
8 × 8 SR-MIMO transmission system with polarization multiplexinghas 60 bit/s/Hz of channel capacity. This paper also shows a modelfor theoretical cross polarization discrimination (XPD) degradation,
which is useful for calculating XPD degradations on diagonal paths.

MulDiRoH: A Multi-view Human Representation System
Using a QDA Screen with Multiple Cameras
S. Ozawa, S. Mieda, Y. Yao, M. Date, H. Takada, T. Kawakami, S.
Nasu, T. Ishinabe, M. Kano, M. Sasai, and T. Uchida
IEEE Journal of Display Technology, Vol. 10, No. 2, February
2014.
We have developed a human representation system we call
MulDiRoH. It consists of a multiview display that uses a quantizeddiffusion-angle (QDA) screen and multiple cameras. The QDA
screen has a large, wide viewing area that enables observers to comfortably watch the display. It is also convenient in that accurate projector orientation is unnecessary; this makes easy system construction possible. In this paper, we describe the MulDiRoH system andpropose a Tiled Image Method to achieve shorter projection distancewith it and a Perspective Transform Method to correct views obtainedwith it.

NTT Technical Review

Papers Published in Technical Journals and Conference Proceedings

Structural and Electrical Transport Properties of MOVPEgrown Pseudomorphic AlAs/InGaAs/InAs Resonant Tunneling Diodes on InP Substrates
H. Sugiyama, A. Teranishi, S. Suzuki, and M. AsadaJapanese Journal of Applied Physics, Vol. 53, 031202, 2014.
We report metal-organic vapor-phase epitaxy (MOVPE) growth ofpseudomorphic AlAs/InGaAs/InAs resonant tunneling diodes(RTDs) on InP substrates for the first time. XRD (X-ray diffraction)measurements and TEM (transmission electron microscopy) observations reveal that a uniform strained InAs subwell is coherently
grown in the double-barrier (DB) structure. The AlAs/InGaAs/InAs
RTDs exhibit excellent current–voltage characteristics with a highpeak current density (JP) of around 2 × 105 A/cm2 and peak-to-valley
ratio (PVR) of around 6. A comparison with control RTDs consistingof AlAs/In0.8Ga0.2As DB confirms the effectiveness of InAs subwell
insertion for the improvement of PVR.

Proposal and Evaluation of Agent-based Service Platformby Applying on BMI-enabled Services
S. Takeuchi, R. Banno, K. Umakoshi, A. Kanemura, M. Kawanabe, T. Kawano, T. Kambayashi, M. Takemoto, M. Matsuo, and R.
KakinumaIPSJ Journal, Vol. 55, No. 2, pp. 681–694, 2014.
Real world services that affect entities in the real world throughactuators deployed by extracting the environmental context based onsensing data will be available in the future. These real world services
are expected to be provided by combining dynamic and diverse

Vol. 12 No. 4 Apr. 2014devices, processes, and varieties of data, and therefore, a flexible andscalable service platform is essential. Thus, an agent-based service
platform that represents a service as a series of agents is proposed.
While the overhead is generally larger than that of integrated systems,
the feasibility of an agent-based system in the real environment is notclear. Therefore, the proposed platform was applied on BMI (brainmachine interface)-enabled services that should be provided in realtime and evaluated through simulation and in a real environment. As
a result, the latency on the platform is less than a few hundreds ofmilliseconds, so the platform can be applied to a practical service.

Pedestrian Navigation System Utilizing Effectiveness of
Dynamic Exploration for Force Direction Perception
T. Amemiya and H. Gomi
IEICE Trans. on Information and Systems, Vol. J97-D, No. 2, pp.
260–269 (in Japanese).
Integration of an information presentation device and a positionand orientation tracking system is required for effective indoor pedestrian navigation. We developed a pedestrian navigation system with amobile haptic display. The haptic display creates a sensation of being
pulled using asymmetric oscillation and provides precise angularresolution of force direction with a rotation mechanism. The experimental result showed that actively moving the hand facilitated understanding of the directional cue. We discuss the feasibility of the system for indoor pedestrian navigation.

