NTT Technical Review
December 2012 Vol. 10 No. 12
View from the Top
Kaoru Kato
President and Chief Executive Officer, NTT DOCOMO, Inc.

Feature Articles: Platform Technologies forOpen Source Cloud Big Data
IaaS Platform Using OpenStack andOpenFlow Overlay Technology
PaaS Software Based on Cloud Foundry
NoSQL Database Characteristics and Benchmark System
Efficient Large-scale Data Analysis Using MapReduce
Jubatus in Action: Report on Realtime Big Data Analysis
By Jubatus

Feature Articles: Optical Semiconductor Technologies
for Photonic Networks
High-speed Tunable Distributed Amplification Distributed
Feedback (TDA-DFB) Lasers
Electroabsorption Modulator Integrated Light Sources for
Future High-speed Ethernet
High-speed Photodetector Technologies
InGaAs Metamorphic Laser for
Low-power-consumption Operation
Current-injection Photonic-crystal Laser

Regular Articles
Advertising Effectiveness Measurement Using Crowd
Measurement and Facial Image Processing Techniques

Global Standardization Activities
Report on ITU Radiocommunication Assembly 2012 andITU World Radiocommunication Conference 2012

Practical Field Information about
Telecommunication Technologies
Weather-resistance Tests for Recycled Polyethylene

External Awards
External Awards

View from the Top

Creating New Value in the Spirit of“Speed and Challenge”
Kaoru Kato
President and Chief Executive Officer,
NTT DOCOMO, Inc.
Overview

Competition in Japan’s mobile communications market is becoming
increasingly severe, fueled by the rapidly expanding sales of smartphones
and the appearance of global players. In this environment, NTT DOCOMO
must prove its worth as a leading company in the mobile communications
business, and to do so, it is orchestrating all of its expertise and know-how
to meet the increasingly diverse and advanced needs of its customers. In theaftermath of the Great East Japan Earthquake, we sat down with Kaoru
Kato, President of NTT DOCOMO, to ask him about the role of mobile
communications as a major lifeline for society, recognizing his experiencein spearheading restoration measures at many disaster sites.

Facing the future without a moment to lose––Mr. Kato, congratulations on your appointment as
President of NTT DOCOMO. To begin with, could
you tell us something about your guiding principles
and management policies?
Well, since starting my career at NTT, I have been
involved in the planning and development of mobile
communications systems and mobile phones. I havewitnessed the evolution of mobile communications
and mobile phones from the early days of the industry
and have confronted a wide variety of issues over theyears. The business environment of today is undergoing great change, but we are making an all-out effort
to apply the knowledge that we have accumulated andthe collaborative ties that we have formed both insideand outside the company in order to achieve a management style that can respond swiftly to change.
Keeping the above spirit in mind and adhering to
the policies of my predecessor, I have proposed thespirit of “Speed and Challenge.” When taking up a
new post, some people become rather tense, thinkingthat they must do something different from their predecessor. Although that could also have been the casewith me, I intend to respect the ideas of the former
president in carrying out the company’s management
vision, especially since I worked with him on various
issues over the years. As you know, the mobile communications market is changing at an unprecedented
speed and so are customer needs. To respond to suchan unpredictable environment, I would like to take up
new challenges, knowing that we have not a momentto lose.
To this end, we are implementing the following two
initiatives at NTT DOCOMO: “evolution of services
by pursuing innovation” and “new value creation
through convergence.”
Making smart life a reality
The first initiative “evolution of services by pursuing innovation” means creating new services that link
smartphones with the “DOCOMO cloud”. Let metake Photo Collection as an example of the services
offered through the cloud. This is a storage service
NTT Technical Review

View from the Top

that enables the user to store up to 5 GB of photos andvideo clips free of charge in the personal cloud.
Photos and videos taken with a smartphone or otherdevices or stored on a personal computer can be automatically uploaded to the cloud and then viewed froma smartphone, personal computer, tablet or otherdevice as desired.
The Photo Collection service can be linked with theorganizing function on the cloud, which is capable ofidentifying faces and scenes and automatically grouping those photos and videos according to certain categories such as date, person, event, place, model, andservice. The service can also be linked with external
services such as Evernote, Eye-Fi, and HighCam forenhanced storage, viewing, and organization of photos and videos.
In addition, we are enhancing the functions of
Shabette-Concier, a voice-agent app, Mail-Hon’yaku
Concier, an app for translating text messages, andHanashite Hon’yaku, a speech translation app. We
are also starting to provide the docomo mail anddocomo phonebook services to expand to a full lineupof cloud-linked apps (software applications).
Shabette-Concier now gives more accurate replies bylinking with i-concier, another DOCOMO service.
Mail Hon’yaku Concier translates text messages
composed by the user on their smartphone into theother party’s language in the cloud. This app, whichcurrently supports Japanese-to-English & English-toJapanese, Japanese-to-Korean & Korean-to-Japanese,
and Japanese-to-Chinese & Chinese-to-Japanese, canbe used for text-based communications as in email
and social networking services (SNSs). We take pridein this app because it helps the user to send messages
in a foreign language and facilitates their communication with people who speak other languages.
Finally, the docomo mail and docomo phonebook
services store the user’s email and phonebook data inthe cloud, thereby enabling the user to access the datafrom multiple devices and to recover the data if necessary. These services are making the user’s life safer,smarter and more convenient.
Evolving the mobile phone into
a convenience store in your hand“New value creation through convergence,” thesecond of our new initiatives, means merging thesmartphone with various areas involving the lives andlifestyles of people.
The smartphone, which can fit into your hand,
encapsulates the performance of a supercomputer ofVol. 10 No. 12 Dec. 2012just a few decades ago. Despite its small size, it incorporates functions for enjoying music, TV, movies,
and books and for assisting the user in fields such as
shopping, health, and medical care. For how long are
we separated from our mobile phones during thecourse of a day? We only have to think about ourdaily life to answer this question. The fact is that themobile phone is a device that most users have near athand at all times as a means of receiving a wide arrayof services and products. It is becoming, in a sense, aconvenience store in your hand. We are accelerating
the realization of this vision through our dshopping
service, which enables users to safely and conveniently purchase products that are carefully screened
by NTT DOCOMO. We are also committed to forming alliances with other enterprises to further enhancemobile shopping. Our aim here is to provide our customers with total shopping support.
To implement these two initiatives rapidly, we needto reform our corporate structure and revise our business processes to keep up with the times. Measures
must also be taken to make organizational changes
and enhance personnel training.
Mission and dream arising from personal
experience of the Japan Airlines plane crash
It is my belief that NTT DOCOMO is a company
View from the Top

with a mission to provide its customers with safe andsecure services and with a dream to enhance andenrich the lives of its customers through highly convenient products. This is why I want to create a workplace in which each and every employee can eagerlyand enjoyably take on new challenges. At the sametime, I want to be someone who my subordinates caneasily talk to and feel relaxed around. In particular, I
want to be a person to whom anyone can say anything, even if it concerns difficult situations or bad
news. I don’t mind standing and talking if I can hear
about problems while they are still in the budding
stage.
––From what experiences did this mission and dreamarise?
This dream to enhance and enrich the lives of ourcustomers through highly convenient products hascome about in various ways: from my past involvement in the planning and development of mobile
communications and mobile phones, from my expectations for further evolution and progress of mobile
systems and products, and from my wish to provide
customers with convenient products and thrilling
experiences above and beyond anything that they
have ever seen before. Of course, I realize that NTT

DOCOMO is entering a very difficult period in ourbusiness history, but I also know that there is muchsatisfaction to be gained from doing work that has
great potential for enriching people’s lives.
Though it would be hard to explain the evolution of
our perception of our mission in just a few words, letme say that my past work at actual disaster sites has
had a big influence. In 1985, a Japan Airlines planecrashed into Mount Osutaka in Gunma Prefecture. I
was told to head for the crash site with several mobile
phones. Unlike today’s lightweight models, each ofthese weighed about one kilogram and had a shoulder
strap. I pushed my way up steep mountain paths andeventually arrived at the crash site. It was a horrible
scene that I can hardly put into words. The onlymeans of communications at the site was throughradio equipment, and it took some time to establish
communications even with the incident command
center, but the mobile phones that I brought with me
greatly improved communications between the crashsite and the command center. As a result, I became
more confident about the usefulness of mobile
phones. Last year’s Great East Japan Earthquake
underscored our role as a communications operator toconnect at all times: during emergencies so that people can check on their loved ones and at normal times
so that people can simply communicate with eachother. Our mission to connect people is somethingthat we should never forget.
DOCOMO is the closest to customers
among all NTT Group companies––Could you say a few words to NTT DOCOMO
employees?
Certainly. First, I would emphasize that NTT
DOCOMO must transform itself into an integrated
service company. Continuing to focus our efforts only
on the mobile communications business as we havebeen doing so far can only lower our corporate value.
I would like all of us at NTT DOCOMO to be fearlessand energetic in creating new value and markets.
Here, I would reiterate that communication devices
are first and foremost tools, and to enable them to be
used to their full extent, it is important that we listen
closely to the people using them, namely, our customers. The role of docomo shops and NTT DOCOMO
information centers is not just to sell mobile phones
and network services: they are also places where customers can talk freely to us about their needs. Of
course, there are times when it is technically difficult



NTT Technical Review

View from the Top

to satisfy customer wishes, and requests related toservice quality can sometimes be quite demanding.
Nevertheless, I truly believe that making an effort tosatisfy each and every customer request leads to abeneficial cycle in which the services that we provide
are continuously enhanced and expanded and themobile devices that we offer have increasingly higher
levels of performance.
This endeavor is not limited to projects and activities at NTT DOCOMO headquarters: to become atruly integrated service company, headquarters andall company offices and retail sites in the field mustmove forward as one. My aim is to visit NTT
DOCOMO offices and retail sites throughout thecountry to listen to the ideas and opinions of those
who deal directly with our customers and to bring
their voices back to headquarters. Let’s bring about atrue revolution for the company by working in a unified manner wherever you are: at headquarters,
regional offices, or retail sites.
Furthermore, NTT DOCOMO is closest to customers among companies in the NTT Group in the sensethat we provide communications over the mobile
phone—an item that people keep close at hand day inand day out. We are therefore in a most effective position to listen to customer needs and to convey tocustomers the services and plans of the entire NTT
Group. In short, I want us to be a company that istruly welcoming and hospitable to our customers
while cooperating and collaborating with other NTT
Group companies. Let’s explore new worlds in thespirit of “ONE docomo”!
Facing R&D with a “70% is OK” mindset
while learning from our customers––Mr. Kato, could you also leave us with a message
to everyone in the R&D department?
Yes, I would tell our research and development(R&D) personnel to place importance on speed and to
pursue R&D in the spirit that even 70% is OK. I thinkthat the NTT Group and the R&D department tend tohave the idea that products must be perfect. Although
this is undeniably a noble aspiration, we must make adecision about product or service development atsome point in time even before perfection has beenreached in order to keep up with the rapidly changing
market. I hesitate to say this, but seeking total perfection often makes you lose your sense of time. Services
and products that customers desire should be provided as quickly as possible and anything in those serVol. 10 No. 12 Dec. 2012vices or products that turns out to be inadequate
should then be corrected immediately. In short, I
would like our R&D personnel to adopt the attitude
of “if it’s done wrong, it’s OK to make a course correction and then, redo it” in their work. In this regard,
our customers can assist in making a service even better by giving us feedback.
I believe that success comes after accumulating
many failures. It is not necessary to be 100% successful all the time. What is needed is the ability to ascertain what is of true value, what is truly needed. Of
course, it might be difficult to tell whether what you
have at a certain point in time is 70% of what you
need, but I will continue to talk about the need for this
“70% is OK” attitude until it becomes embedded in
R&D.
A top manager once said to me: “If people say thatyou are saying the same thing again and again, you
can be sure that your words have finally penetrated
their minds.” Fortunately, there have been more
opportunities for me to talk with leaders in various
fields since I became president. From here on, I
would like to share with R&D personnel and other
NTT DOCOMO employees some of the wise adviceof those leaders who have overcome many difficult
situations as well as the words of wisdom that support
my ideas and outlook.
Last but not least, my personal motto is “good cancome out of misfortune.” Good and bad times are theway of the world. Since I entered NTT, it certainly
has not been smooth sailing all the time, and I cannot
say that I have always been highly motivated.
Actually, when I was in charge of achieving apractical in-flight telephone service, I had to conductView from the Top

a very strict airworthiness test that had to be passed.
By making an extreme effort, I was successful incompleting this test in what seemed to be an impossibly short time. This success revealed to me how
hardship and pain are sometimes necessary to getthings done. Even today, I have a vivid memory of
those tough times. Difficult and painful situations cansometimes lead to good results. Furthermore, while
there are only a limited number of things that a person
can complete on his or her own, there are many things
that can be achieved by seeking the cooperation ofpeople around you. Something that has been achieved
through much hardship necessarily becomes a valuable possession of the people involved. Let’s move
forward together without losing heart!

Interviewee profile
Career highlights
Kaoru Kato started his career at Nippon
Telegraph and Telephone Public Corporation(now NTT) in 1977. He has been involved in themobile phone business since the early days of theindustry. He served as Executive Vice President
and Member of the Board of Directors andManaging Director of the Corporate Strategy &Planning Department at NTT DOCOMO Kansai,
Inc. beginning in 2007 and as Executive Vice
President and Member of the Board of Directors
and Managing Director of the Corporate Strategy& Planning Department at NTT DOCOMO from2008. He assumed his current position in June
2012.

NTT Technical Review

Feature Articles: Platform Technologies forOpen Source Cloud Big Data

IaaS Platform Using OpenStack andOpenFlow Overlay Technology
Shintaro Mizuno, Hiroshi Sakai, Daigoro Yokozeki,
Koji Iida, and Takaaki Koyama
Abstract

This article describes how OpenStack and a virtual network controller that uses OpenFlow overlay
technology can be orchestrated to deploy virtual environments with complex network configurations, as
in on-premise systems, in an on-demand manner.

1. Introduction
There is increasing use of infrastructure as a service(IaaS), in which virtual servers, virtual storage, andother such virtual environments are provided, as
exemplified by Amazon Web Services. This situation
has given rise to an open source software (OSS) community whose objectives are reduced cost and open
development in the construction of IaaS platforms.
2. OpenStack
OpenStack [1] is an OSS IaaS platform development project established by NASA and Rackspace in2010. The NTT Group is among the 183 companies
and 3386 individuals that currently make up thatgrowing community. OpenStack version 5 wasreleased in April 2012 under the code name “Essex”.
OpenStack is one of the most prominent of the OSS
IaaS platforms and is now being used in commercial
services as well as for other purposes. In April 2012,19 companies including AT&T, HP, IBM, Rackspace,and Red Hat established the OpenStack Foundation
to promote the development and use of OpenStack,raising expectations for even more widespread adoption of the platform.
OpenStack comprises multiple services (functional
modules), including a virtual server management
function, object storage, and network management.
Users can select the services they need to flexibly
construct an IaaS platform (Fig. 1). This article
focuses on the platform’s virtual server management
and network control functions. We describe a methodof constructing a flexible virtual environment thatcombines virtual servers and virtual networks throughcooperation with those OpenStack functions.
3. Virtual networks
As in hybrid clouds, there are use cases for cloudsystems that include virtual networks as well as virtual servers to constitute virtual systems in a cloudenvironment while maintaining the system configuration and integrity with conventional enterprise systems. The virtual network is one kind of technology
for implementing such use scenarios [2].
4. Technology for implementing
virtual networks
A number of ways of connecting virtual servers toisolated customer virtual networks in the cloud havebeen proposed. One is to allocate a virtual local area
network (VLAN) to each customer to form virtual
networks in units of a VLAN. In the approach using
VMware*1 or other such products, a particular VLAN
is assigned to the virtual server. The virtual servers on
the same VLAN engage in closed communication.
This approach requires the prior setting up of a
VLAN with switches and other communication
devices in the datacenter.
*1	 VMware: A PC/AT compatible emulator that runs on Windows
and Linux.

NTT Technical Review

Feature Articles

Keystone(authentication)

Horizon(web-based user interface)Nova(virtual server
management)

Quantum(network control)Swift(object storage)

Glance(imagemanagement)

Cinder(block storage)(Next version
will correspond.)

Fig. 1. OpenStack services.

Network
controller

Virtualserver

Virtualserver

VirtualserverHypervisor

VirtualserverHypervisor

Virtualserver

Virtualserver

OpenFlow

SoftwareswitchVirtualserver

VirtualserverSoftwareswitchTunnelHypervisor
VLAN 1VLAN 2VLAN 1Hypervisor

VLAN 2(a) Virtual network using VLANs(b) Virtual network using OpenFlow overlay

Fig. 2. Examples of virtual networks.

One method for connecting virtual servers that does
not require control of the settings of communication
devices is the overlay method, which involves extend­
ing tunnels between software switches on a hypervisor to establish communication paths between virtual
servers running on the hypervisors. OpenFlow orother such tools are used to control the software
switches (Fig. 2). Another method is the hop-by-hop
method.
5. Network controller
In OpenFlow, a server referred to as the network
controller manages the creation, setup, and deletionof virtual networks. The network controller manages
the network devices, software switches, and other
Vol. 10 No. 12 Dec. 2012

functions on the hypervisor to construct virtual networks. Network controllers are provided by several
companies (including NEC, Cisco, Nicira, and NTT),and each company has its own approach to network
virtualization, including the methods describedabove.
6. OpenStack network control function
In OpenStack, the network control function isprovided by the Quantum service, which provides anapplication programming interface (API) for creating, setting up, and deleting virtual networks. One
feature of Quantum is a plugin architecture. Quantum
itself provides only common functions such as
authentication and an API for higher-level appli­
Feature Articles

Application
Quantum API
A

BC

PluginPluginPluginNetwork
controller

Network
controller

Network
controller

Quantum
PluginNetwork
controller
Select a plugin to use.
Network appliance/
software switch

Fig. 3. Architecture of Quantum plugins.

Application

Keystone

Quantum

Nova

Authentication
Creation of vitual network
Creation of virtual server(with virtual network information)

Fig. 4. Example of service call procedure.

cations. The virtual network functions are incorporated into the existing network controller. As
described above, network controllers are alreadyavailable from several third-party vendors, and flexible connection to the controllers is possible with
Quantum plugins for the various controllers. Thatmakes it possible to use any network function flexibly
via a unified Quantum API (Fig. 3).

from virtual servers and virtual networks is illustrated
in Fig. 4. When OpenStack is used to provide an IaaS
cloud service, these procedures for calling the various
services are performed according to the use case andcustomer requirements to create the virtual environment.

7. Cooperation between virtual server
management and network control functions

NTT is using OpenStack to construct an environment for verifying IaaS platforms in various use cases(Fig. 5). That environment uses a Nicira network
controller as a network controller attached to a Quantum network controller to implement OpenFlowbased overlay virtual networks. Three typical use
cases that were verified in our laboratory are described
below.
(1) Construction of a flexible virtual environment

In OpenStack, management functions for virtual
servers and networks are individual services that are
called by their respective APIs to construct a virtualenvironment from virtual servers and virtual networks.
A procedure for constructing a virtual environment

8. Work being done at NTT

NTT Technical Review

Feature Articles

User
interface

Cloud controller

PortalNova

Keystone

Customer

GlanceCustomer
control

Network
controller
Quantum
Virtualstorage

NVP plugin
Virtualappliance(LB, FW)

NVP
controller

Virtualappliance(LB, FW)

Virtualserver

FW: firewall
KVM: kernel-based virtual machine
LB: load balancer
NVP: network virtualization platform
OVS: Open vSwitch

Software switch(OVS)

VirtualserverTunnelSoftware switch(OVS)

Hypervisor(KVM)
EuropeLocation A
Asia

Virtualstorage

Hypervisor(KVM)
EuropeLocation B
USA

Fig. 5. NTT’s test environment. Software switches distributed across Japan simulate a global virtual network.

Any number of virtual networks can be created fora customer. Combining them with virtual servers
enables the same configuration flexibility as provided
by on-premises systems, including cascaded multilayer networks and demilitarized zones*2.
Flexible system configuration enables effective useof existing software and other such assets as well as
continuity in the use of firewalls and other network
settings. It can therefore reduce the cost of systemreconfiguration in the case of migration to a virtualenvironment.
Because a virtual environment can be constructedin the cloud while maintaining compatibility withexisting systems, the building of hybrid clouds thatinterwork with existing systems and cloud services
can further expand the range of uses of cloud services. For this use case, a multilayer virtual network is
constructed for each customer, and multiple virtual
servers are placed on each network and assigned arbi*2 Demilitarized zone (DMZ): A network segment that lies between
trusted networks and external networks.

Vol. 10 No. 12 Dec. 2012

trary IP (Internet protocol) addresses. We confirmedthat communication with outside networks is possible
in such a system (Fig. 6).
(2) Office migration
Office migration is a use case that assumes the needto temporarily move a virtual environment to a different location to maintain business continuity during adisaster, pandemic, or other anomalous situation or to
reduce the cost of electrical power.
With the abovementioned overlay virtual network,a tunnel can even be constructed between remote
software switches if IP connectivity is available. It isthus possible to construct a virtual network thatinvolves a remote datacenter and create a single network environment that spans multiple locations.
Doing so enables on-demand migration of virtual
servers between datacenters without the need tochange physical network settings. Previously, thiswould have required constructing individual Layer-2
VPNs and changing network settings within the datacenter.
NTT has constructed an environment in whichFeature Articles

Cloud platform
Virtual environment for customer A
Virtualserver

VirtualserverCustomer B

Customer C

Virtual environment
for customer B

Virtual environment
for customer C

Virtualserver

Virtual network
Virtualfirewall

Virtual network

Virtual network

Fig. 6. Flexible configuration of virtual environment.

Customer

PortalTokyo

USA

Cloud controller(OpenStack)Network controller(Quantum)
NVP controller

NVP controller

Internet
FW

LB
VirtualserverInternet

Virtual environment
migration

FW
Virtualserver

VirtualserverCustomer’s virtual environment
OVS

OVS

OVS

HV

HV

HV

LB
VirtualserverCustomer’s virtual environment
L2-over-L3 tunnel

OVS

OVS

OVS

HV

HV

HV

HV: hypervisor
L2: Layer 2
L3: Layer 3

Fig. 7. Virtual environment migration.

network controllers can be arranged to construct virtual networks between arbitrary datacenters and inwhich virtual servers can be freely placed and moved
to enable unified control of multiple datacenters. We
have confirmed that in this use case the customer canconstruct a virtual environment in any datacenter and

move the entire environment to a different location as
required (Fig. 7).
We demonstrated these results jointly with NTT
Communications at the Open Networking Summit
held in April 2012. The demonstration system wasconstructed at three actual locations in Japan, theNTT Technical Review

Feature Articles(a) Current virtual desktop service

Transfer
desktop.

Internet etc.

(b) Virtual desktop service using virtual network

Deploy office environment
as well as virtual desktops.

Can select which
network to connect to.

Internet etc.

Virtual desktop for users
Virtual network toconnect to internal
LAN

Cloud platform
Virtual desktop for users

Use virtual desktop with astatic configuration.
Virtual servers for internal use
Cloud platform

Fig. 8. Flexible virtual office environment.

USA, and Europe and migration of virtual environments among datacenters in different countries wasverified.
(3) Flexible virtual office environment
In the flexible virtual office environment use case,an IaaS platform is applied as an in-house system toprovide a virtual desktop environment to company
employees. A virtual desktop is a service that provides remote access to the desktop of a virtual server,
thus presenting the same working environment
regardless of the terminal being used.
Combining virtual network technology and a virtual desktop environment allows dynamic network
construction and setup, making it possible to switch
the virtual desktop to a different network without
performing any extra configuration in the physicalnetwork. In this use case, the virtual-desktop users
can switch networks on-demand according to theirassigned tasks. We are now testing the basic operationof this use case and considering the application of
OpenStack (Fig. 8).

Vol. 10 No. 12 Dec. 2012

9. Concluding remarks
We described the use of OpenStack, an OSS IaaS
platform, in the construction of IaaS platforms. Specifically, we have verified use cases that involve interworking with a network controller and we presented
examples of application to cloud services. For thattask, we focused on the network, which is a core competence of the NTT Group. In the two years or sosince the beginning of the OpenStack project, various
proposals have been made by the active OpenStack
community. We intend to continue to cooperate
closely with that community to improve OpenStackfunctionality and raise the quality to the level requiredfor commercial use.
References[1][2]

OpenStack. http://www.openstack.org
H. Kitazume, T. Koyama, T. Kishi, and T. Inoue, “Network Virtualization Technology for Cloud Services,” NTT Technical Review, Vol. 9,
No. 12, 2011.
https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr2011
12fa4.html

Feature Articles

Shintaro Mizuno

Koji Iida

Senior Research Engineer, Cloud System SE
Project, NTT Software Innovation Center.
He received the B.E. and M.E. degrees from
Tokyo Institute of Technology in 1995 and 1997,
respectively. Since joining NTT in 1997, he has
been working on authentication systems, securecommunication systems, and information security. His current research interests include cloud
management system and software defined networks.

Senior Research Engineer, Cloud System SE
Project, NTT Software Innovation Center.
He received the B.E. and M.Sc. degrees from
Keio University, Kanagawa, in 1993 and 1995,
respectively. He joined NTT Information Platform Laboratories in 1995 and studied enterprisecommunication middleware and distributed
object technologies. He moved to NTT Information Sharing Platform Laboratories in 2007 andresearched identity management technology andcloud computing technology. As a result of organizational changes in July 2012, he is now in
NTT Software Innovation Center.

Hiroshi Sakai

Takaaki Koyama

Senior Research Engineer, Supervisor, Cloud
System SE Project, NTT Software Innovation
Center.
Since joining NTT in April 1993, he has contributed to the development of network service
systems including intelligent networks and the
Next Generation Network (NGN). His current
research interests include an OSS-based cloud
management system and software defined networks.

Senior Research Engineer, Cloud System SE
Project, NTT Software Innovation Center.
He received the B.A. and M.M.G. degrees inmedia and governance from Keio University,
Tokyo, in 1994 and 1996, respectively. He joined
NTT Software Laboratories in 1996 and studied
software CALS. Since 1999, he has been studying GMN-CL, which is a kind of IP-VPN technology, and developing some network equipment. Recently, his research interests haveextended to enterprise cloud network systems.
He is a member of the Information Processing
Society of Japan.

Daigoro Yokozeki

Senior Research Engineer, Cloud System SE
Project, NTT Software Innovation Center.
He received the B.E. and M.Sc. degrees fromWaseda University, Tokyo, in 1996 and 1998,
respectively. He joined NTT Information Platform Laboratories in 1998 and studied web middleware and distributed database technologies.
He moved to NTT Software Innovation Center in2012 and is currently researching cloud computing and virtual networking technologies.

NTT Technical Review

Feature Articles: Platform Technologies forOpen Source Cloud Big Data

PaaS Software Based on
Cloud Foundry
Yudai Iwasaki, Shunsuke Kurumatani, Tsutomu Nomoto,
Takahiko Nagata, and Shinichi Nakagawa
Abstract

NTT is developing platform-as-a-service (PaaS) software based on Cloud Foundry, which is opensource PaaS software. We introduce the advantages of developing applications on a PaaS, the features of
Cloud Foundry, and our efforts to put these developments into commercial use.

1. Introduction
The cost and difficulty of developing applications isincreasing. Modern ones are becoming connected to
the network and required to handle a huge number ofusers. They depend on various types of middlewareand may run on more than 100 servers. In addition, toensure that they are kept up to date with the changing
market, they are also required to be flexible.
NTT is developing platform-as-a-service (PaaS)
software*1 based on Cloud Foundry [1], which is a
cloud-computing-based open source software PaaS
(open PaaS), to enable us to develop and manage
applications more easily, quickly, and flexibly at alower cost.
2. Advantages of PaaS for service development
PaaS is a layer on top of the infrastructure-as-a-service (IaaS) layer that provides ready-to-use middleware environments to service developers (Fig. 1).
This middleware includes operating systems, webservers, database management systems (DBMSs),
and application frameworks, and it is essential to run
cloud applications. However, with the functionalityof modern applications becoming much more sophis*1	 In this article, we use “PaaS software” to refer to a stack of technologies (also known as a platform) for constructing a PaaS and“application” to refer to a service application that runs on the
PaaS. A PaaS user is a user that develops and deploys applications on the PaaS; an application user is a person that uses theapplication.

ticated, middleware environments are also becoming
much more complex. This means that efficient management of the middleware is critical to control service costs. However, middleware is commonly sharedby various applications. For example, a middleware
set composed of a Linux operating system, Apache
web server, MySQL DBMS, and Perl (or PHP or
Python) programming language is referred to as
LAMP and is very popular, especially for web applications. Therefore, a PaaS includes the provision ofcommon middleware environments for service developers and their management for users.
The greatest advantage of using a PaaS as a service
environment is the reduced cost and faster speed ofservice development and management. In addition, a
PaaS makes large-scale development easy and does
not require such a large initial investment, so it
enables a small flexible startup with on-demandscale-up.
During a development, cost reductions are achievedby reducing the number of man-hours required to set
up both the hardware and middleware for the ser­vices. Without a PaaS, developers must build theirapplication environments by themselves. For example, they must install servers at their datacenter andset up operating systems, DMBSs, web servers, andany other software they need in each machine. This is
manageable if there are only a few machines, but if
there are over a hundred servers, it becomes a very
labor-intensive task. A PaaS enables such simple
tasks to be offloaded to the PaaS providers. The only
necessary step is to input the required amount of
NTT Technical Review

Feature Articles

Applications

SaaS
Frameworks
PaaS

IaaS

Frameworks
DBMS

Web server

Load balancer
Web server

OS

OS

OS

OS

Virtual machine

Virtual machine

Virtual machine

Virtual machine

Hypervisor

Hypervisor

ServerServer

OS: operating system
SaaS: software as a service

Fig. 1. Technology stack of cloud computing.

resources into the management console. The environment can be set up immediately with fewer manhours and less lead-time.
Another benefit during the development process isthat a PaaS can offer developers mature tools forbuilding high-performance applications. Creating
high-performance scalable applications in a distributed environment generally requires deep and extensive know-how. With a PaaS, however, such knowhow is included in the tools (backend systems andsoftware development kit (SDK) or application programming interface (API)). Users can easily develop
high-level applications using the provided tools.
A PaaS also allows users to reduce the costs ofoperating user services. Such services typicallyrequire system updates such as patches for bugs andsecurity fixes for operating systems and middlewarethat have been in operation for an extended time. In
addition, server hardware and software must be constantly monitored 24 hours a day, 7 days a week toensure correct functioning. The PaaS takes over these
simple tasks and allows the service provider to deliver complex services with minimal monitoring.
Another reason to use a PaaS is flexibility. It allows
computing resources to be consumed on demand.
This means that users do not have to continuously
reserve sufficient resources to handle peak times suchas monthly batch processing or irregular user events.
In addition, providers can start services with a minimum number of servers and add additional resources
step by step. This is a big advantage when an experimental service is being started.
Several commercial PaaS offerings are in operation, for example, Google App Engine, Sales Force’s
Vol. 10 No. 12 Dec. 2012

Heroku and Force.com, and Microsoft Azure. Eachhas its own characteristics in terms of support for
languages, middleware, and frameworks (Table 1).
For example, Google App Engine provides easy-toscale middleware, and Heroku supports many programming languages such as Ruby and JavaScript.
Force.com differs from the other services in providing useful business logic.
3. Cloud Foundry: open-source PaaS software
Cloud Foundry is open source software developed
mainly by VMware in a project that started in 2011.
By contrast, most PaaS software such as Google App
Engine and Heroku uses closed proprietary software.
Since the source code of Cloud Foundry is open, anyone can use it to build their own PaaS. Despite its
newness, Cloud Foundry has become a popular typeof PaaS software. For example, Active State and
AppFog have developed and are selling PaaS solutions based on Cloud Foundry, and Rakuten is using
Cloud Foundry for its in-house PaaS. In the NTT
Group, NTT Communications is planning to launch apublic PaaS based on Cloud Foundry [2].
Cloud Foundry has three main features, which aredescribed below.
(1) No vendor lock-in
PaaS users can avoid vendor lock-in with specific
PaaS vendors by using the open-source Cloud Foundry. In general, PaaS offerings differ in usage such as
in the API that is provided or the process used to
deploy applications. This means that it is difficult tomigrate an application developed for a specific PaaS
to another PaaS. The migration might require theFeature Articles

Table 1. List of existing PaaS offerings.
Name

Vendor

Source code Supported programming languages*

Features

Google App Engine Google

ClosedJava, Python, Go

Easy to develop highly scalable applications
using BigTable and related APIsAWS Elastic
Beanstalk

AmazonClosed.NET, PHP, Java

Supports various other services provided in AWS

Windows Azure(Cloud Services)

Microsoft

Closed.net, JavaScript, Java, PHP, Python

Integrates well with Microsoft’s products including
its integrated development environment

Force.com

salesforce.com Closed

Apex

Provides various types of business logic

Herokusalesforce.com Closed

Ruby, Java, Python, Clojure, Scala,Supports many programming languages
JavaScript

Cloud Foundry

VMWareCloudFoundryJava, JavaScript, Ruby, Scala

Commercial service using Cloud Foundry by
VMwareAppFog

AppFogCloudFoundryJava, Python, JavaScript,.Net, Ruby, PHP

Commercial service based on Cloud Foundry

Stackato

ActiveState

Cloud
FoundryJava, Python, Perl, PHP, Ruby,
JavaScript, Clojure, Scala, Erlang

Private PaaS solution based on Cloud Foundry

OpenShift

Red Hat

OpenShiftJava, Ruby, JavaScript, Python,
PHP, PerlRed Hat’s commercial Paas offering using
OpenShift* Languages listed on official sites. PaaS offerings may support other compatible languages or have restriction for support.

application to be redesigned or rebuilt. This can
impose several risks; for example, PaaS users might
be forced to accept a price increase, or the service
might suddenly be suspended by the provider. In contrast, when PaaS users (i.e., application developers)
use a Cloud-Foundry-based PaaS, all of their developed applications are compatible with each other, sothey can run them with less risk. They can choose thebest PaaS provider at the moment and even build theirown private PaaS environment using Cloud Foundry.
(2) Flexible configuration
Cloud Foundry is designed with sufficient flexibility to satisfy a huge variety of needs for PaaS environments. The Cloud Foundry system consists of several
components, and users can set up their environmentby choosing the necessary combination and numberof components for their needs (Fig. 2). Cloud Foundry supports a wide range of environments—from a
private PaaS on a single server to a huge public PaaS
on a cluster of over a thousand servers—and can be
set up to suit the scale as well as its reliability andsupport features. Moreover, users can add components on demand, so it is possible to start with theminimum configuration and increase the scale as theload grows.
(3) Support for languages and frameworks
Cloud Foundry supports most of the major programming languages such as Ruby, Java, and JavaScript. It also supports a variety of popular frameworks used for building web applications; for example, Ruby on Rails, Sinatra, Spring, and Node.js aresupported as default. DBMS, MySQL, and PostgreSQL are supported, and other modern forms of
DBMS such as MongoDB and Redis are also supported. PaaS users can develop their applications intheir own way even in Cloud Foundry’s PaaS environment. This makes it easy to introduce a PaaS to thedevelopment process with no additional costs.
Another example of an open PaaS is OpenShiftOrigin. Developed by Red Hat as an open-source version of their PaaS called OpenShift, it was announced
on April 30, 2012. At the time of writing, Cloud
Foundry has advantages over the younger OpenShiftOrigin in its more mature quality and market perception. However, Red Hat has a lot of experience andhas made significant contributions to open source
software development, e.g., to Linux and KVM,
which are popularly used for cloud systems. Therefore, we need to monitor further development of
OpenShift Origin.
4. Contributions by NTT
NTT is developing its own PaaS software based on
Cloud Foundry. Although Cloud Foundry is a promising PaaS software solution that has many good features, as described above, it is still not perfect, especially when used for NTT’s PaaS software. For
example, its reliability and convenience in commercial usage were not sufficient in the early phase, and
NTT Technical Review

Feature Articles

DMBSs and other middleware
are run on service nodes.
Applications run on DEAs.
Routing traffic from clients
to DEAs matching the request
MongoDB

Application
Applications that users
access via web browsers

Router

DEA

Servicegateway

PostgreSQL

Application

Service
node

DEA

Web
browser

Servicegateway

Router
Application

Redis
Service
node

DEA
VMC

Service
node

NATS

Cloud
Controller
Application developers
access via command line console

Controls the entire system.
ACM: Access Control Manager
CCDB: Cloud Controller Database
DEA: Droplet Execution Agent
NATS: messaging bus between components
UAA: User Account and Authentication
VMC: virtual machine container

CCDB

HealthManagerStagerACM
UAA

Health check, user authorization & authenticationand co-worker of cloud controller

Fig. 2. Components of Cloud Foundry.

integration with other NTT services was naturally notprovided by other vendors. In addition, Cloud Foundry is still not in wide use, and this is an obstacle thatprevents it from growing as an open source software
solution. Therefore, we have been making efforts toimprove Cloud Foundry.
4.1 Contributions to Cloud Foundry(1) Reliability of Cloud Foundry components
Because Cloud Foundry was a very young project
when we started our development, it did not have sufficient reliability to be used for a commercial service
based on it. Therefore, NTT has been examining theperformance and scalability of Cloud Foundry byconducting various tests and fixing any problems
revealed by them. For example, we solved a problem
involving an important component that was a single
Vol. 10 No. 12 Dec. 2012

point of failure and a problem where some components could not be restored after failures by fixing thesource code and adding additional external systems.
(2) Convenience of Cloud Foundry
Since convenience is important for commercial
services, we created an installer for the virtual
machine container (VMC), which is the console for
PaaS users, and we are now developing a function forlinking the VMC and version control systems such as
Git.
(3) Integration with IaaS software
Although Cloud Foundry has a flexible component
system, as described above, to leverage the features,
it is essential to integrate it with an IaaS layer underCloud Foundry. Therefore, NTT is developing a management system that controls both Cloud Foundry
and the underlying IaaS systems. This orchestrationFeature Articles

system increases competitiveness against other providers because it reduces operating costs andmaximizes datacenter utilization, despite using vendor-lock-in-free open source software.
4.2 Contributions to the community
The presence of active communities is indispensable in the long-term evolution of open source software. We launched the Japan Cloud Foundry Groupin collaboration with NTT Communications and are
fostering a developers’ and users’ community of
Cloud Foundry in Japan [3]. In addition, we haveopened the source code created in the first two of ourabovementioned contributions (component reliability
and convenience) by committing them to the official
repository, and we also provide the know-how inworkshops.

ry as it is, it will be difficult to compete in the cloudcomputing market, which is becoming highly competitive. Therefore, NTT is continuously developing
its own PaaS software by improving upon the featuresof Cloud Foundry. In addition, we are investigating
possible future integration with other NTT products
such as Jubatus [4] and other open source software
such as Hadoop*2.
References

5. Conclusion and future work

Cloud Foundry. http://www.cloudfoundry.com
NTT Communications Press release (in Japanese).
http://www.ntt.com/release/monthNEWS/detail/20120627.html
NTT Press release (in Japanese).
http://www.ntt.co.jp/news2012/1202/120224a.html
K. Horikawa, Y. Kitayama, S. Oda, H. Kumazaki, J. Han, H. Makino,
M. Ishii, K. Aoya, M. Luo, and S. Uchikawa, “Jubatus in Action:
Report on Realtime Big Data Analysis by Jubatus,” NTT Technical
Review, Vol. 10, No. 12, 2012.
https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr2012
12fa5.html

Cloud Foundry is promising open-source PaaS
software that has many good features. It enables us todevelop applications more easily, quickly, and flexibly at a lower cost. However, if we use Cloud Found-*2	 Hadoop: Java software framework that supports distributed processing of big data.



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

NTT Technical Review

Feature Articles

Yudai Iwasaki

Engineer, Platform Technology SE Project,
NTT Software Innovation Center.
He received the B.A. and M.M.G. degrees from
Keio University, Kanagawa, in 2009 and 2011,
respectively. He joined NTT Information Sharing Platform Laboratories in 2009. As a result oforganizational changes in April 2012, he is now
in NTT Software Innovation Center. His research
topics are the Semantic Web and cloud computing technology.

Shunsuke Kurumatani

Researcher, Distributed Computing Technology Project, NTT Software Innovation Center.
He received the B.A. degree in environmental
information from Keio University, Kanagawa, in2009. Since joining NTT Information Sharing
Platform Laboratories in 2009, he has been
engaged in R&D of mobile cloud computing
technology and an application PaaS. His researchinterests include web technology, accessibility,
and mobile cloud computing. As a result of organizational changes in April 2012, he is now in
NTT Software Innovation Center. He is a member of the Institute of Electronics, Information
and Communication Engineers (IEICE).

Takahiko Nagata

Senior Research Engineer, Cloud System SE
Project, NTT Software Innovation Center.
He received the B.E. and M.E. degrees fromthe Faculty of Instrumentation Engineering,
Hiroshima University in 1993 and 1995, respectively. Since joining NTT Information and Communication Systems Laboratories in 1995, he has
been engaged in R&D of high-speed communication processing boards, reliable multicast
delivery systems, secure electronic voting systems, and secure file delivery systems. During
2005–2008, he worked in a department supporting the development of systems in NTT WEST.
He is currently engaged in R&D of cloud computing technology. As a result of organizationalchanges in April 2012, he is now in NTT Software Innovation Center.

Shinichi Nakagawa

Senior Research Engineer, Cloud System SE
Project, NTT Software Innovation Center.
He received the B.S. degree in physics from
Saitama University in 1987 and the M.S. degreein physics from Chiba University in 1989. He
joined NTT in 1989. He is a member of IEICE.

Tsutomu Nomoto

Engineer, Cloud System SE Project, NTT
Software Innovation Center.
He received the B.E. and M.E. degrees in engineering from the University of Electro-Communications, Tokyo, in 2008 and 2010, respectively.
Since joining NTT Information Sharing Platform
Laboratories in 2010, he has been engaged in
R&D of operations management software. As aresult of organizational changes in April 2012, heis now in NTT Software Innovation Center.

Vol. 10 No. 12 Dec. 2012Feature Articles: Platform Technologies forOpen Source Cloud Big Data

NoSQL Database Characteristics andBenchmark System
Kota Tsuyuzaki and Makoto Onizuka
Abstract

The NTT Software Innovation Center has been researching and developing NoSQL (Not Only SQL;
SQL: structured query language) databases as storage platforms for big data. In this article, we discuss
the characteristics of NoSQL databases and their benchmark system. We also report the results of applying the benchmark to MongoDB, a typical example of a NoSQL database.

1. Introduction
The amount of enterprise data has been dramatically increasing, and such large-scale data is referred
to as big data. Many services and analytical applications based on big data have emerged, and users wantto obtain or mine the most recent and useful knowledge from big data. Handling big data requires
advanced technology for data storage. In particular,
NoSQL (Not Only SQL; SQL: structured query language) databases have attracted attention for big data
storage. NoSQL is designed specifically to manage
big data, a task for which commonly used relational
database management systems (RDBMSs) are notwell suited.
We describe the main features and characteristics ofNoSQL databases and report the results of a NoSQL
benchmark using MongoDB [1] as an example.
2. NoSQL
2.1 Features
The three main features of NoSQL databases are
scale-out, replication, and flexible data structure (Fig.
1). We explain these three features below.
Scale-out refers to achieving high performance byusing many general-purpose machines in a distributedmanner. Distributing the data over a large number ofmachines enables scaling of the data set and distribution of the processing load. A common feature ofmany NoSQL databases is that data is automatically
distributed to new machines when they are added tothe cluster, so the performance is also improved.
Scale-out is evaluated in terms of scalability and elasticity.
Replication is the copying of data to achieve data
redundancy and load distribution. Even if data consistency has been lost among the replicas, it is eventually achieved: this is known as eventual consistency.
Replication is evaluated in terms of consistency andavailability.
A flexible data structure means that there is no needto define a structure as a database schema. Traditional RDBMSs require pre-defined schemas, andredefining them carries a high cost. NoSQL, on theother hand, does not require defined schemas, sousers can store data with various different structuresin the same database table. However, most NoSQL
databases do not support high-level query languages
such as SQL, which is used by RDBMSs, so productsthat support either simple relational operations or
indexing have been released. This feature is evaluatedqualitatively.
2.2 Characteristics and benchmark system
Because NoSQL databases feature scale-out andreplication, a NoSQL benchmark should take scalability, elasticity, consistency, and availability into
account as well as performance. We explain eachcharacteristic and describe the benchmarking software design points concerning these characteristics.
Scalability indicates how the performance of a
NoSQL database cluster scales with the number ofphysical machines. If performance improves as
NTT Technical Review

Feature Articles

Flexible data structure

Scale-out

Elasticity:
Machines can be added.

Scalability: Performance increases
as machines are added.

Pre-defined schema are notneeded; simple data accessmodels and languages aresupported product-by-product.

Compatible with various data formats: images (binary),
tweets, geographical data, etc.

Replication

Replica data

Consistency:
Data replicas are identical.

Availability: When a machine goes
down, data can continue to be readfrom replicas on other machines.

Fig. 1. NoSQL database features and characteristics.

machines are added to a NoSQL database cluster, we
can say that the NoSQL product has high scalability.
In scalability benchmarking with many physicalmachines, the load generator, which benchmarks the
NoSQL database cluster, is often a bottleneck. An
effective approach for preventing this is to design
benchmark software as a distributed system runningon the cluster (Fig. 2).
Elasticity enables the addition of physical machines
to a cluster while the NoSQL database is running on
it. Elasticity benchmarking involves measuring theimpact of adding a physical machine to the NoSQL
database cluster. The benchmarking requires the
addition of a machine while the performance is being
measured. The impact of adding a physical machine
has been reported for NoSQL benchmarking with theYahoo! Cloud Serving Benchmark (YCSB) [2]. That
paper [2] also reported a performance instability
issue was arose during several hours of elasticity for
Cassandra, a NoSQL database product.
Vol. 10 No. 12 Dec. 2012

Consistency is a measure of the strength of data
integrity. The parameters used to evaluate it include
the number of replicas and the latency within thecluster. The consistency benchmarking software must
check the consistency among replicas in an updateheavy workload, so data management of that workload, in which data should be updated, is necessary.
The final characteristic, availability, refers to theability of the overall system to continue operating
during a network failure, called a network partition,
or a physical machine failure. High availability meansthat the system can work without interruption andwithout degraded performance, even when somemachines go down and the network is partitioned orboth. In general, network partitioning makes it difficult to ensure both consistency and availability at thesame time, so NoSQL databases are designed to prioritize one or the other in operation. Measuring theeffect on performance in addition to that on operating
continuity is important in the index for availability asFeature Articles

Benchmarking system

Concurrency control ofbenchmarking software(1) Benchmark software should be
distributed and generate an appropriate
load.

BenchmarkAdd or stop machine

Local network

Benchmarking cluster

Database cluster(3) Benchmark software should checkdata consistency.

(2) Benchmark software should add machines tothe database cluster or stop machines during
benchmark testing.

Fig. 2. Important points concerning benchmarking system configuration and benchmarking.

well as that for elasticity. The important points regard­
ing benchmark software are summarized below.
(1)	It should be distributed and should generate an
appropriate load.
(2)	It should add machines to the database cluster orshut down machines automatically during
benchmark testing.
(3)	The benchmark software should check data consistency.
We present selected benchmark results obtainedusing custom benchmark software based on YCSB,
which can automatically execute items (1) and (2).
3. Benchmarking evaluation
3.1 Benchmarking and evaluation of MongoDB
This benchmark test assumed a service in whichuser data is continually increasing, such as blog articles in a social networking service (SNS). The target
software for the benchmarking was MongoDB, whichfeatures scale-out, replication, and a flexible data
structure. Scalability is generally measured in thebenchmarking of NoSQL databases [3] and MongoDB
does not allow eventual consistency. Therefore, we
present the results for elasticity and availability,
which are particularly important when designing asystem such as the SNS described above, by using a
NoSQL database with data having those characteristics.
The performance of MongoDB depends on whetheror not the entire data set resides in physical cachememory; therefore, we used two data sets: a small
data set that could be fully stored in cache memory
and a large data set that was too large to fully residein cache memory, so data swapping was necessary.
3.2 Elasticity benchmark results
The results for elasticity are presented in Fig. 3,
where the horizontal axis is elapsed time from the
beginning of measurement and the vertical axis isperformance relative to the throughput for ideal scaling from the addition of one machine. A physicalmachine was added 600 seconds after the beginningof measurement.
Comparing the results for the small and large data
sets in Figs. 3(a) and (b), we can see that the performance of MongoDB with the large data set became
unstable just after the machine was added and theperformance gradually decreased. This behavior wascaused by the increase in disk access during data
migration of the large data set. Since there was a large
reallocation load on the disks after the machine wasadded, the NoSQL took a lot of time to complete thedata migration.
When the data set was small, as in Fig. 3(a), theimpact of adding the physical machine ended after aminute or two and performance then became stableagain. However, the throughput did not reach theideal value for adding a machine in the case of thesmall data set. This indicates that the added machine
NTT Technical Review

Feature Articles

Timing of adding a physical machine
1.2
0.8
0.6

Performance normalized
to ideal throughput after
a machine was added

0.4
0.2
0

0

600

1200

1800

2400

3000

3600

4200(s)Throughput

Throughput

1

1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0

0

600

1200

1800

2400

3000

Elapsed time

Elapsed time(a) Small data set(b) Large data set

3600

4200 (s)Fig. 3. Effect of elasticity benchmarking process on NoSQL database performance.

Timing of stopping a physical machine
1.2
1

1.1
1.05

Performance normalized to
predicted throughput after
a machine was stopped.

1
0.95

0

600

1200

1800

2400

3000

3600

4200 (s)Throughput

Throughput

1.15

0.8
0.6
0.4
0.2
0

0

600

1200

1800

2400

3000

Elapsed time

Elapsed time(a) Small data set(b) Large data set

3600

4200 (s)Fig. 4. Effect on performance during NoSQL database availability benchmarking.

was used inefficiently.
3.3 Availability benchmark results
The benchmark results for availability are presented
in Fig. 4. The horizontal axis is time and the verticalaxis is the measured throughput for when a machine
had gone down.
Comparing the results for the small and large data
sets in Figs. 4(a) and (b), we see that, after a machine
was stopped, performance took longer to recover forthe large data set than for the small data set. The performance for the large data set did not return to theprevious level, remaining at only about 70% of theideal performance. We believe that this was caused byincreased disk access for reading data on machinesthat had replicas of data on the stopped machine. This
increase in disk access caused a bottleneck in theentire system.
For the small data set in Fig. 4(a), the decrease inperformance with the stopped machine was greater
Vol. 10 No. 12 Dec. 2012

than expected. We believe that this is because there
was almost no effect from the input/output load forthe small data set.
4. Concluding remarks
Our benchmark testing of MongoDB for elasticity
and availability revealed that data size has a significant impact on database performance when the system is extended or machines are taken off-line. However, these characteristics vary with the NoSQL
product. Therefore, when designing the system configuration of actual systems that use NoSQL databases, one should benchmark elasticity and availability as well as performance and scalability. For
example, the trade-off with the impact on performance and recovery time must be estimated andreflected in the system design in terms of the numberof machines and the hardware configuration.
Our future work includes trying to improve theFeature Articles

benchmarking of elasticity and availability to expand
the use of NoSQL for big data. We believe that techniques for controlling the trade-off between performance and features on the basis of such benchmarking results will become more important in the future.
The NTT Software Innovation Center will continue
to engage in research and development of technology
for handling big data.

References
[1]
[2]

[3]
[4]

Kota Tsuyuzaki

Distributed Computing Technology Project,
NTT Software Innovation Center.
He received the M.E. degree in information
science from Waseda University, Tokyo, in 2010.
Since joining NTT in 2010, he has been engaged
in R&D of NoSQL databases. As a result oforganizational changes in July 2012, he is now in
NTT Software Innovation Center.



MongoDB. http://www.mongodb.org/
B. F. Cooper, A. Silberstein, E. Tam, R. Ramakrishnan, and R. Sears,“Benchmarking cloud serving systems with YCSB,” Proc. of the ACM
Symposium on Cloud Computing 2010 (ACM SOCC 2010), Indianapolis, IN, USA.
T. Dory, “Comparing Scalable NOSQL Databases,”
http://www.slideshare.net/ThibaultDory/comparing-nosql-databasesbenchmark
J. Miyazaki and M. Onizuka, “Current trends and techniques on datacloud,” the Information Processing Society of Japan, Vol. 52, No. 6,
pp. 684–692, 2011 (in Japanese).

Makoto Onizuka

Distinguished Technical Member, Distributed
Computing Technology Project, NTT Software
Innovation Center and Visiting Associate Professor at the Graduate School of Information Systems, University of Electro-Communications.
He received the Ph.D. degree in computer science from Tokyo Institute of Technology in 2007.
His primary research interests include systems
and algorithms for data-intensive cloud computing.

NTT Technical Review

Feature Articles: Platform Technologies forOpen Source Cloud Big Data

Efficient Large-scale Data Analysis
Using MapReduce
Rui Kubo, Yoshifumi Fukumoto, and Makoto Onizuka
Abstract

Techniques for efficiently analyzing large-scale collections of data, such as log data or sensor data, areattracting attention as important for improving the operating speed of businesses and enhancing the user
experience. This article outlines MapReduce, which is a typical framework for analyzing big data, andintroduces our techniques for achieving high-speed analytical processing by extending MapReduce.

1. Introduction
1.1 Background of MapReduce
MapReduce is a framework for efficiently processing the analysis of big data on a large number of servers. It was developed for the back end of Google’s
search engine to enable a large number of commodity
servers*1 to efficiently process the analysis of huge
numbers of webpages collected from all over theworld [1].
On the basis of this research, software was developed*2 by the Apache project to implement MapReduce, which was published as open source software(OSS) [2]. Since anyone can use OSS, this enabledmany organizations, such as businesses and universities, to tackle big data analysis [3] in a way that only
a few research institutes could do in the past owing to
the complexity and high cost of the analytical system.
In the NTT Group, there is also an increasing number of cases involving big data analysis in a wide
range of situations such as back-end systems forsearch engines, analysis and reporting systems forcommunications traffic and logs, and advertising recommendation engines.

*1	 Commodity server: An ordinary inexpensive personal-computerbased server using commodity components.
*2 The OSS community is actively advancing development by adding functions and fixing bugs.



1.2 Mechanism of MapReduce
MapReduce provides an application programming
interface (API) and middleware for developers whowant to analyze big data. More specifically, when adeveloper defines processing that is compliant with
two types of APIs, the map and reduce functions,processing is distributed efficiently for execution on
multiple servers (Fig. 1).
The mechanism of MapReduce ensures that thecomplexity involved in developing a system thatworks on numerous servers can be concealed fromthe developer. More specifically, this approach has
the following advantages.
-	Scheduling: The servers that execute the processing defined by the map and reduce functions
are selected automatically by the middleware.
The middleware selects a nearby server in whicha chunk of the data is stored to be the map function execution server. This reduces the volume ofdata transfers and enables efficient processing.
-	Synchronized processing: data transfers between
servers for the map and reduce functions aresynchronized.
-	Fault tolerance: To ensure that processing cancontinue overall even when several servers havefailed, data backups and intermediate processing
results are stored automatically. If a failure actually occurs, servers restart the processing using
the backups and intermediate processing results.
The scheduling and synchronization processing
become more complex as the scale of the data and
NTT Technical Review

Feature Articles

Map function

Reduce function

…

…

…

…

Input data

Distributed file system

Shuffle(data transfer)

Processing
results

Fig. 1. Flow of MapReduce processing.

servers increases; thus, server breakdowns often
occur. Since such complexities are concealed fromthe developer by MapReduce, he or she can focus ondeveloping big data analysis methods.
We have been researching and developing techniques for achieving high-speed analytical processing
by extending MapReduce. Increased efficiency is
extremely important for achieving cost advantages
such as improving the system’s response time andreducing the number of servers. Below, we introduce
the features and suitable usage situations for threetechniques that we have developed: PJoin, Map
Multi-Reduce, and MRFusion.
2. New techniques
2.1 PJoin
There are many developers who have used structured
query language (SQL) when querying a database.
Data manipulations that are frequently used with
SQL include selecting, projecting, aggregating, andjoining. Such data manipulations are frequently usedin various situations. However, if databases that were
designed some time ago are now given big data tohandle, problems arise: the processing time is longand much time is necessary to obtain results. Therefore, there is a demand for techniques that produce
results even more efficiently, even with big data.
PJoin can be used to join data efficiently. For
example, if we analyze the log of an e-commerce site,
we can obtain a best-seller product ranking for eachprofile by joining user data (profiles of all the users,
Vol. 10 No. 12 Dec. 2012

such as their ages and genders) and purchase history
data (purchase histories of all the products), as shownin Fig. 2. PJoin makes it possible to quickly obtainsuch results even more efficiently.
Previously proposed techniques*3 [4] that can beused to perform joining with MapReduce have drawbacks. One drawback is constraints on the size of
input data and another is the large volume of communications *4 generated between servers, whichforms bottlenecks, so the results cannot be obtained
efficiently.
In the preprocessing phase, PJoin creates data that
represent reference information between data to bejoined*5 and rearranges the input data to enable efficient joining. This overcomes the drawbacks of thepreviously proposed techniques and makes it possible
to quickly obtain results efficiently, even when
joining big data (Fig. 3).
Since a feature of PJoin is to perform quick andefficient joining by performing preprocessing, it ismost suitable for use in situations such as querying
repeated joins with large chunks of data.
2.2 Map Multi-Reduce
Map Multi-Reduce can be used to efficiently*3 Typical techniques are Memory-backed Join, Map-side Join, andReduce-side Join.
*4 Processing that hands over generated processing results between
the map and reduce functions.
*5 Only some of the rows, such as a primary key and external keys,
are joined beforehand, as in the semi-join method in distributed
database studies.

Feature Articles

User data
User ID
chono
terauchisakamoto
murata…

GenderMale
FemaleFemale
Male

…

Age
19
45
32
56

Best-seller ranking bygender and generation
Best-seller ranking for males
Best-seller ranking forfemales
1. Handbags
2. Mobile phones
3. Shoes
Users and purchasehistories, joined by user ID

Best-seller ranking forteenagers
1. Pencils
2. Automobiles
3. Baseball gloves

Purchase history data
Purchase date
2012/7/1 13:05
2012/7/1 13:12
2012/7/1 13:20
2012/7/1 13:21…

User ID
sakamotoabeterauchitakahashi

Purchased articles
Hats
Shoes
Beans
Personal computers…

Fig. 2. Example of efficient joining by PJoin.

5

Processing time (minutes)

4* Evaluation environment- Linux (CPU: 2.8 GHz; memory: 8 GB) x 50 servers* Benchmark- Joining of three web access log
tables (150 GB, 75 GB, and 16
GB)

3
Greatly reduced

2

1

0
PJoin

Previous technique

CPU: central processing unit

Fig. 3. PJoin processing time.

perform aggregations in data manipulations such as
SQL. When analyzing the log of an e-commerce site,
this technique makes it possible to perform calculations efficiently to obtain total or average daily orseasonal sales from the purchase histories of all products, as shown in Fig. 4.
To increase the speed of aggregation by MapReduce,
it is common to reduce the volume of data beingtransferred between the map and reduce functions
without changing the overall processing results*6.
Previously proposed techniques*7 have various drawbacks, such as placing a larger load on the developer,
but attempts to reduce this load also reduce efficiency.
Our Map Multi-Reduce is an extension of the MapReduce middleware. It enables the reduction of awider range of data transferred between the map andreduce functions on the middleware side. This overcomes the drawbacks of the previously proposed
techniques, enabling results to be quickly obtained*6 Processing that is equivalent to the reduce function, executed beforehand by the server that executes the map function.
*7 Typical techniques are Combiner and In-mapper Combining.



NTT Technical Review

Feature Articles

Purchase history data
Purchase
date

Purchaseamountsakamotoabeterauchitakahashi¥11,222¥1024¥133,333¥34,333

Sales analyses by day and by season…

…

2012/7/1 13:05
2012/7/1 13:12
2012/7/1 13:20
2012/7/1 13:21…

User ID…
…
…

Daily analysis (2012/7/1)
Total sales: ¥1,210,000
Number of sales: 220
Average sales: ¥5500…

…

Purchase history
aggregation…
…
…

Seasonal analysis (2012/Q1)
Total sales: ¥77,777,777
Number of sales: 1111
Average sales: ¥70,007…

…

Fig. 4. Example of efficient aggregation with Map Multi-Reduce.

7

Processing time (minutes)

6* Evaluation environment- Linux (CPU: 2.8 GHz; memory: 8 GB) x 90 servers* Benchmark- Word frequency calculations
from TREC data (0.5 TB)

54Greatly reduced
32
10
Map Multi-Reduce

Previous techniqueFig. 5. Map Multi-Reduce processing time.

efficiently while keeping the load on the developer
small (Fig. 5). When Map Multi-Reduce is used,
there is an overhead*8 due to the reduction of thetransferred data, so it is most suitable for use withdata and processing where the reduction effect is
expected to be large*9.
2.3 MRFusion
MRFusion is a technique that can be used to repeat
analytical processing of the same data. For example,
to optimize product recommendations on an e-commerce site, such as that shown in Fig. 6, it is necessary to apply various kinds of analytical processing tohistories of past purchases by trial and error. If thetrial and error is not done sufficiently well, accurate
recommendation models cannot be constructed andthe e-commerce site will recommend products thatthe customer does not want. MRFusion ensures thatthe trial and error (iterative processing) for con­
*8 Overhead: Processing time that initially did not exist.
*9 In the example of the e-commerce site discussed in this article,
the reduction effect is larger for the processing to obtain total
sales for each season than that for daily total sales.

Vol. 10 No. 12 Dec. 2012Feature Articles

Purchase history data
Purchase date

User ID

Purchased
articles

2012/7/1 13:05
2012/7/1 13:12
2012/7/1 13:20

sakamotoabeterauchi

Hats
Shoes
Beans

2012/7/1 13:21

takahashi

Personalcomputers…

…

Recommended products
for each user and product

Recommended products for Mr.
Takahashi- Air conditioners- Electric fans
- Hand fans…

Construction ofrecommendation
model from purchase history

Products users want to buy
together with a personal computer- Printers- Liquid-crystal displays- Digital cameras…

Fig. 6. Example of efficient model construction with MRFusion.

18* Evaluation environment- Linux (CPU: 2.6 GHz; memory: 8 GB) x 20 servers* Benchmark- Construction of recognition model for
14
handwritten character
data (20 GB)
12Processing time (minutes)

16

10Greatly reduced

8
6
4
2
0
With MRFusion

Without MRFusion

Fig. 7. MRFusion processing time.

structing valuable models can be done quickly andefficiently.
Usually with MapReduce, when a developer wants
to repeat analytical processing efficiently as de

scribed above, he or she must personally create theprocessing logic to enable acceleration for each variation of the analytical and iterative processing every
time. This imposes a large load on the developer andalso hinders rapid introduction of the latest analysis
algorithms.
As an extended version of the MapReduce middleware, MRFusion provides automatic detection of thesame processing parts among multiple processing
with the same data, combines them, and performs
batch execution. This keeps the load on the developer
small and enables the quick and efficient execution ofmultiple processing such as that described above(Fig. 7). Forcibly expanding the automatic detection
range in this way can sometimes lead to side effects.
Therefore, when MRFusion is being used, the mostsuitable usage method is to first apply it to smallscale data, check for an acceleration effect and anyside effects, and then, if there do not seem to be anyside effects, apply it to big data.

NTT Technical Review

Feature Articles

3. Concluding remarks
Attention is focusing on cloud computing, and theimportance of using big data is now being recognized.
It is also becoming more and more necessary to haveinformation processing systems that are capable ofprocessing big data.
We introduced three techniques that we have implemented to extend MapReduce and increase its speed.
In the future, we plan to research and develop techniques for efficient processing that can be used over a
wider range, as well as various easy-to-use tech-Rui Kubo

Research Engineer, Distributed Computing
Technology Project, NTT Software Innovation
Center.
He received the M.S. degree in information
systems from the University of Electro-Communications, Tokyo, in 2003. Since joining NTT in
2003, he has been engaged in R&D of sensor
networks and distributed computing. As a resultof organizational changes in July 2012, he is now
in NTT Software Innovation Center. He is amember of the Japanese Society for Artificial
Intelligence.

niques, to help create value-added services that use
big data.
References
[1]

[2]
[3]
[4]

J. Dean and S. Ghemawat, “MapReduce: Simplified Data Processingon Large Clusters,” OSDI ’04.
http://static.usenix.org/events/osdi04/tech/full_papers/dean/dean_
html/index.html
Apache Hadoop. http://hadoop.apache.org/
Hadoop Wiki. http://wiki.apache.org/hadoop/PoweredBy
J. Lin and C. Dyer, “Data-Intensive Text Processing with MapReduce,” Morgan and Claypool Publishers, 2010.

Makoto Onizuka

Distinguished Technical Member, Distributed
Computing Technology Project, NTT Software
Innovation Center and Visiting Associate Professor at the Graduate School of Information Systems, University of Electro-Communications.
He received the Ph.D. degree in computer science from Tokyo Institute of Technology in 2007.
His primary research interests include systems
and algorithms for data-intensive cloud computing.

Yoshifumi FukumotoResearch Engineer, Distributed Computing
Technology Project, NTT Software Innovation
Center.
He received the B.E. degree from the Facultyof Environment and Information Studies from
Keio University, Kanagawa, in 2009. Since joining NTT in 2009, he has been engaged in R&D
of distributed computing and distributed storage.
As a result of organizational changes in July
2012, he is now in NTT Software Innovation
Center. He is a member of the Database Societyof Japan.

Vol. 10 No. 12 Dec. 2012Feature Articles: Platform Technologies forOpen Source Cloud Big Data

Jubatus in Action: Report on
Realtime Big Data Analysis byJubatus
Keitaro Horikawa, Yuzuru Kitayama, Satoshi Oda,
Hiroki Kumazaki, Jungyu Han, Hiroyuki Makino,
Masakuni Ishii, Koji Aoya, Min Luo, andShohei Uchikawa
Abstract

This article revisits Jubatus, a scalable distributed framework for profound realtime analysis of big
data that improves availability and reduces communication overheads among servers by using parallel
data processing and by loosely sharing intermediate results. After briefly reviewing Jubatus, it describes
the technical challenges and goals that should be resolved and introduces our design concept, open
source community activities, achievements to date, and future plans for expanding Jubatus.

1. Introduction
There is little doubt that data is of great value andimportance in databases, data mining, and other datacentered applications. With the recent spread of networks, attention is being focused on the large quantities of a wide variety of data being generated andtransmitted as big data. This trend is accelerating [1]as a result of advances in information and communications technology (ICT), which simplifies the collection and analysis of big data.
Even now, there is a strong need to make new discoveries and find patterns that were not noticed
before, by taking huge amounts of data in a certain
area that has been stockpiled, such as a dozen or so
years of clinical data, and analyzing it from all angles,
as one scenario in which big data is put to good use inbusiness. This trend is not limited to operations confined to a specific area; it includes the possibility ofswiftly finding new business possibilities or synergistic effects by focusing on relationships in big dataspanning different fields or specialist areas. We thinkthat this trend will expand into cross-domain big data
analysis in the future*1.
There are two major types of big data and techniques for analyzing it.
(1)	Stockpile type: Lumped high-speed analysis of
accumulated big data (batch processing)(2)	Stream type: Sequential high-speed analysis ofdata stream being continuously generated without accumulation (realtime processing)With case (2) in particular, the ambiguity inherent
in the environment is creating a growing need tomake judgments and decisions on the basis of insufficient information.
In this article, we revisit Jubatus, a framework
intended for realtime stream-type big data analysis
that provides profound analysis ability by online
machine learning as added value. Jubatus was introduced in the June 2012 issue of NTT Technical
Review [1]. That article focused on a key mechanism
called mix. In this article, after briefly reviewing
Jubatus, we describe the technical challenges andgoals that should be resolved and introduce ourdesign concept, open source community activities,*1	 Cross domain: Access to data spanning different domains.
http://en.wikipedia.org/wiki/Cross-domain_solution

NTT Technical Review

Feature Articles

achievements to date, and future plans for expanding
Jubatus.
2. Jubatus
2.1 Overview
Jubatus is a scalable distributed computing framework for online machine learning. The origin of thename is the Latin term for that agile animal the cheetah. It is pronounced “yu-ba-tus”. Developed jointly
by Preferred Infrastructure Corporation and NTT
Software Innovation Center, it is currently publishedon websites as a Japan-originated big data open
source project [2]–[4].
The goal of Jubatus is to enable swift and profoundanalysis of stream-type big data. One example of its
use is as a social media application for automaticallyclassifying the huge number of tweets*2 (over 8000
per second) generated all over the world. This processing includes the three requirements: large volume, fast, and profound. In other words, it supports
natural language processing and automatic multicategory classification, at high speed without lag, of adata stream of 16 Mbit/s.
However, these three requirements basically have a
trade-off relationship and it is intrinsically difficult tosatisfy all of them simultaneously. Jubatus satisfies
both profound analysis and scalability. Here, profound analysis is the automatic categorization of
unstructured information intended for human beings,
such as natural language. It can also replace humanlabor for unclearly formulated processing work, suchas recommendation, prediction, and relationship discovery. From the technical perspective, it involves
challenges in the areas of machine learning, artificial
intelligence, and pattern recognition.
On the other hand, scalability encompasses theissues of (1) increases in processing requests and (2)increases in data size. Issue (1) can be further divided
into throughput (volume of requests to be handled perunit time) and response (response for each instance,
without lag). In general, batch processing focuses on
throughput while realtime processing focuses on
response. Approaches to issue (2) are either processing the data without waiting or dividing and storingit.
Jubatus answers the need for making prompt judgments in situations exhibiting uncertainty and ambiguity. After our comprehensive investigation of the*2 Tweets: short messages sent using the popular social networking
service and microblogging service Twitter.

Vol. 10 No. 12 Dec. 2012

design concept, under which information for judgment is being collected continuously and decisions
are being made without lag, we separate the profoundanalysis (functionality) from the scalability (nonfunctionality). More specifically, a profound analysis
design likens the logic of online machine learning toan engine or central processing unit (CPU), which
can be continuously upgraded as removable analysis
modules. A scalable design is seen as a common
infrastructure chassis or motherboard, which can bescaled by installing analysis modules into the common framework. The ultimate goal of Jubatus is toprovide everyone with scalable machine learning.
Our policy is to provide a broadly easy-to-understandonline machine learning framework for big data thatis easy to use, with hardware that scales out over
inexpensive commodity servers to enable massively
parallel distributed processing and software that is
not restricted to a few data scientists, programmers,
and specialists.
2.2 Applicable areas
Google’s PageRank is well known as a techniquefor calculating the importance of web pages from allover the world [5]. Since website link structures are
updated comparatively slowly, batch analysis is suitable in this case. Social media such as Twitter tweets,on the other hand, are characterized by having finer
granularity than the web, by having light content, by
having small chunks of data that are transmitted inlarge numbers from a wider demographic than that of
web users, and by the immediacy of information
being vital. Through social media, we can analyze
how a broad user population reacts to changes andevents in the external environment and make effective
practical use of realtime analysis of stream-type big
data, with cases applied to business enterprises.
We have provided primary classifications of Twitter
information as an application of Jubatus. Since theinformation representation is in natural language andis presented with a limited number of characters,
expressions having distinctive omissions, abbreviations, coined words, jargon, and mannerisms were
included in the analysis subject matter. From the over2000 tweets per second in the Japanese language
alone, it is difficult for humans themselves to extract
and organize useful information instantly by sight.
Therefore, general-purpose primary filters that provide major classifications and refining functions areuseful. Using the approximately 1600 companies
listed on the first section of the Tokyo Stock Exchange
as the classification categories, Jubatus speedilyFeature Articles

Development ofhigh-speed framework

Machine learning engine
Data

Data

Data

Classification

Regression

Recommendation

High-performance engine +high-speed framework
Stream-type big data
Classification

Regression

Recommendation+
Analysis
results

Analysis
results

Analysis
results
Online execution of profound analysis

Fig. 1. Outline of the design concept.

classifies the 2000 tweets per second into their corresponding business categories and supplies information to an analysis application. This implementation
uses an online machine learning technique called
Jubatus classifiers (multi-valued classification). We
used highly trustworthy published information, suchas Wikipedia, as training data and automatically constructed a learning model for classification. Unlike
item classification by keyword matching or related
words, we use online learning to update the vector
equations of separate planes that divide an n-dimensional feature vector space*3 into a number of categories.
We can also expect the system to become smarteron its own by continuing to incorporate big data fromoutside, with the effect that even unknown words will
be classified appropriately. The categories for the
primary classification are not limited to businesses: it
is possible to broaden the application to countries,
local governments, municipalities, celebrities, products, and etc.
2.3 Architecture and functions
The design concept of Jubatus is outlined in Fig. 1.
As stated above, Jubatus is composed of a cluster ofmachine learning engines and a high-speed framework that supports them.
In contrast to previous machine learning engine
units, which usually handled small- to medium-scaledata and required batch processing and individual
development, Jubatus has a huge variety of engines
installed in a high-speed framework and a development mechanism with common specifications forhigh-speed big data processing with errors within a*3	 n-dimensional feature vector space: n is the number of words thatcharacterize the Japanese language. In this case, it is approximately 2000.



permitted range tolerated [6]. June 2012 saw therelease of version 0.3 of Jubatus and we are planning
to augment the lineup of machine learning functions
and strengthen the support framework. The types ofmachine learning that we currently support so far are
outlined in Table 1.
Jubatus will be useful for applications that require
speedy judgment. It is expected to be able to discoverand analyze original relationships among the data
volume from different domains.
2.4 Distributed processing architecture
The distributed processing architecture is shown indetail in Fig. 2. The stream of big data flows from left
to right. Clients are configured of a number of user
processes and proxy processes.
The proxy processes relay clients’ requests to theserver processes, enabling the servers be transparent
to the user processes. User processes are implemented by using the Jubatus client application programming interface (API); they are written in a scripting
language or in a general programming language.
We appreciate the outside contributions from theopen source community, so we enabled the use of alarge variety of language bindings [7], such as
Python, Ruby, and Java. Communications between
proxy processes and server processes are based on
MessagePack [8] remote procedure calls (RPCs).
Non-block input/output enables more efficient communications and synchronization control. The server
processes perform the training, prediction processing, and learning model synchronization, which has
linearly increasing performance with the number ofservers. In addition, Zookeeper [9] processes manage
the cooperation between proxy and server processes,
the balancing between distributed servers, the monitoring of server state (alive/dead), and the selection of
new leaders.
NTT Technical Review

Feature Articles

Table 1. Examples of functionalities for machine learning.
Supported machine learning engines

Functionalities for machine learning

Classification

Learning request
Classification request

Regression

Learning request
Analogy request

Recommendation

Update or deletion of row data (user ID/items)
Search for similar data
Figure out recommendation items

Statistics

UpdateCalculation of: sum, deviation, maximum & minimum, entropy, moment

Graph mining

Node creation, deletion, update, reference
Edge creation, deletion, update, referenceCentrality measures
Shortest path calculations between two nodesServer processes
Big data
streamUser processes

Proxy processes
API

API

API

mix
(learning modelsynchronization)

ZooKeeper

Fig. 2. Distributed processing architecture.

Table 2. Characteristics of Jubatus distributed processing.
Batch processing

Jubatus

Processing capability

Stream type: on-demand processing without data
Stockpile type: Lumped process with data accumulation
accumulation

Running time

Scheduled type: Start and end timing are defined.

The characteristics of Jubatus distributed processing are compared with those of batch processing in
Table 2. For example, when there are 1000 distrib-

Vol. 10 No. 12 Dec. 201224 hours per day, 7 days per week, i.e., non-stop

uted parallel processing servers, batch processing(e.g., using Map-Reduce) means that the 1000 servers
all execute Map simultaneously, and then all of themFeature Articles.GIGPF

Automatic generation and guarantee of interface
consistency by the modifications of three files

Source file

Commands forautomatic generation
Automaticallygenerated file

Classification

Regression

Statistics

Recommendations

mpidl
Jubatus client

Jubakeeper
Common type declarations

IDL
jenerator
RPC
definition

Jubatus server

HeaderBody(implementation)

jenerator

HeaderHeadermpidl

Body(implementation)

Body(implementation)
jenerator
mpidl: MessagePack IDL

Fig. 3. Automatic creation of template interface by IDL.

together execute Reduce to summarize the results. By
contrast, with Jubatus, each server repeats the learning and analysis autonomously.
In parallel processing among distributed servers,
one technique for satisfying both profound analysis
and scalability is mix processing [1], [6], [10]. This
processing can be regarded as resembling a groupstudy meeting for self-teaching and checking answers(or called synchronization) with others. If all the1000 servers synchronize their answers after every
single learning or analysis task, then overall there will
be a huge drop in processing speed due to the waiting
time, but a moderate frequency of synchronization
may enable the data learning and analysis without
any decrease in overall performance.
Let us introduce mix processing and the unified
update-mix-analyze (UMA) interface.
-	Update: Asynchronous execution of updaterelated queries and additions or changes to big
data-	Mix: Loose sharing of intermediate analysis
results within the component servers-	Analyze: Abstraction interface that suggests theexecution of reference queries and analysis
requests from clients.
The aim is to implement a common interface that is
independent of the analysis logic. In the future, wewill continue upgrading the machine learning engine,
but designing and maintaining an easy-to-understandframework with consistent interfaces are also important tasks.
3. Improvements in development efficiency
To improve the agility of development and ease theburden on developers, a full range of designs andtools is being provided in Jubatus.
(1) Feature vector conversion
Whatever the data, it is necessary to capture its feature vectors as the input format for machine learning.
Conversely, if feature vectorization is successful, themachine learning algorithms only need to be processed appropriately. We have provided a tool thatdefines this important feature vectorization by meansof an outgoing settings file, without hard-coding it asprogram logic.
(2) IDL and jenerator
In Jubatus version 0.01, any addition to the analysis
logic led to the need for manual editing and verification of seven files every time. Therefore, we devised
a mechanism for automatically maintaining interface
consistency and localizing the interface alteration
work. We define the interface by using an interface
description language (IDL) file, and template skeletons of six files are generated automatically by a tool
called a jenerator (Fig. 3). As a result, approximately
3000 lines of code can be generated automatically byusing a 100-line definition file, and unification of thesource code maintenance work is also improved by
IDL. The meaning and usage of the API can be simply
NTT Technical Review

Feature Articles- Service innovation- Remarkable analysis results

Effective utilization
Value discovery
Techniqueimprovements
Actual data

Developers
Data scientists- Implementation- Actual analysis

Jubatus ecosystem
Service innovation
Infrastructure for big data
Business Incubator- Idea- New angles- Expansion of worldwide
analysis market- Leading-edge techniques

Implementation of idea

NTT R&D cloud
Brush-up

R&D: research and development

Fig. 4. Jubatus ecosystem.

understood just by reading the IDL file, which greatly
improves the development efficiency.
4. Performance evaluation
We verified the performance beforehand while
expanding the analysis logic. This evaluated the scalability of Jubatus.
(1)	Classification: We classified Twitter tweets on a
global scale (8000 per second) with two or threecommodity servers. An accuracy rate of 90% inbatch processing was achieved with dataobtained within 10 s. The quantity of training
data was not necessarily that large.
(2)	Recommendations: The update frequency of
online shopping transactions can be over
100,000 times per second per server and it ispossible to produce recommendations for 30
million users within a response time of 0.1 s(approximately ten times as fast as Mahout). We
also verified that the throughput (number ofregistered data items per second) scales up linearly with increasing number of servers.
(3) Graph mining-	Addition of 100 million edges: by ten commodity servers in parallel for 5 minutes-	Scalability in edge addition through an increasein the number of servers: (1, 2, 4, 8) servers ==>Vol. 10 No. 12 Dec. 2012

(3, 6, 13, 25) at 10,000 edges per second(throughput).
-	Analysis latency: {update, mix, centrality}: 0.1
to 0.3 μs per node; {shortest-path}: from 0.1 µs
to several tens of microseconds per node (pathsof approximately 1000 hops). This is up to athousand times as fast as one well-known graphdatabase product.
-	Data size: Retention of over 16 million edges
per server (8 GB of memory) ==> Retention of
100 million edges with 50 GB.
5. Open source status and future schedule
As of July 2012, Jubatus is in its third version andan OSS release is available. It provides an integrated,easy-to-use infrastructure aimed at specialists, programmers, and developers. It also provides an infrastructure designed to let data scientists slot in analysis
algorithms that they want to try out and rapidly scale
up. The open source community will continue towork actively on this.
A Jubatus analysis idea contest (Jubatus Challenge
Japan 2012) was held from July to September, 2012[11]. The aim of this contest was to seek ideas andbusiness scenarios that reveal the potential of Jubatus
to the maximum by active application of open innovation. An important point is the design of a Jubatus
Feature Articles

ecosystem. Our main challenge is to act like a catalyst
in a chemical reaction amidst organic links formed bymain components without any deficiencies in the
Jubatus infrastructure technology, machine learningalgorithms, big data, or data scientists, in other words,
to design a realtime machine learning and analysis
ecosystem such as that shown in Fig. 4.
6. Future expansion
To date, the big data analysis business has centeredon making industrial use of the discovery of previously unnoticed relationships by data mining, andbatch processing analysis has centered on taking alarge volume of data that had been stockpiled andanalyzing it from many angles by trial and error to
obtain original discoveries. Henceforth, it will be
important to perform research and development fromthe following viewpoints.
(1)	Cross domain relationship analysis: Instead ofanalyzing big data confined to a specific area,
discover original business possibilities and synergistic effects from relationships within big
data spanning different fields or specialist
areas.
(2)	Realtime analysis: Support speedy operations
and create competitive advantages by making
rapid decisions based on stream-type data analysis.
(3)	Profound, realtime, big data analysis: Develop
highly value-added techniques that meet the

Keitaro Horikawa

Senior Research Engineer, Supervisor, Distributed Computing Technology Project, NTT Software Innovation Center.
He received the B.S. and M.S. degrees in information engineering from Niigata University in1988 and 1990, respectively. Since joining NTT
in 1990, he has been engaged in R&D of software
design and architecture, concurrent distributed
object computing, metaprogramming and computational reflection, single-sign-on for web services, lightweight programming languages,
mobile cloud computing and big data computing,
CSCW, CSCL, and game theoretical modelingfor decision making and human factors in R&D.
He received the Best Paper Award for Young
Researchers from the Information Processing
Society of Japan (IPSJ) National Convention in
1995. As a result of organizational changes in
April 2012, he is now in NTT Software Innovation Center. He is currently managing distributed
computing projects including Jubatus. He has
PMP certification by PMI and TOGAF 9 certification by the Open Group.



need for automatic judgment (based on machinelearning) where decision logic has not been previously defined, but can reflect any change instatus rapidly on the fly for automatic judgmenton the microsecond time-scale to provide rigorous analysis results that cannot wait until tomorrow or the day after and where actions taken
through human judgment (decision-making
route) would be too slow.
In the future, we will continue to promote open
source development and open innovation and the
expansion of real-life cases.
References[1]

S. Oda, K. Uenishi, and S. Kinoshita, “Jubatus: Scalable Distributed
Processing Framework for Realtime Analysis of Big Data,” NTT
Technical Review, Vol. 10, No. 6, 2012.
https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr2012
06ra2.html[2] Jubatus website. http://jubat.us/[3] Jubatus on Twitter. https://twitter.com/jubatusofficial[4] Jubatus on github. https://github.com/jubatus/jubatus[5] “The PageRank Citation Ranking: Bringing Order to the Web,”http://infolab.stanford.edu/~backrub/pageranksub.ps[6] NTT Press release, “Leading Development of Scalable Distributed
Computing Framework for Real-Time Analysis of Big Data,”
http://www.ntt.co.jp/news2011/1110e/111026a.html[7] Language binding. http://en.wikipedia.org/wiki/Language_binding[8] MessagePack. https://github.com/msgpack/msgpack-rpc[9] Zookeeper. http://zookeeper.apache.org/[10] S. Oda, S. Nakayama, K. Uenishi, and S. Kinoshita, “Jubatus: Distributed Processing Technique Enabling Realtime Processing of Big
Data,” IEICE Tech. Rep., Vol. 111, No. 409, IN2011-126, pp. 35–40,
Jan. 2012.
[11] Jubatus Challenge. http://www.facebook.com/JubatusChallenge2012

Yuzuru Kitayama

Senior Research Engineer, Distributed Computing Technology Project, NTT Software Innovation Center.
He received the B.E. and M.S. degrees in engineering from Kobe University, Hyogo, in 1996
and 1998, respectively. Since joining NTT in
1998, he has been engaged in the development
and management of large-scale web search systems and R&D of distributed processing systems.
As a result of organizational changes in April
2012, he is now in NTT Software Innovation
Center.

NTT Technical Review

Feature Articles

Satoshi Oda

Researcher, Distributed Computing Technology Project, NTT Software Innovation Center.
He received the B.E. and M.E. degrees in engineering from Keio University, Kanagawa, in2003 and 2005, respectively. Since joining NTT
Information Sharing Platform Laboratories in
2005, he has been engaged in R&D of information security, fast implementation of cryptography, and security protocols. As a result of organizational changes in April 2012, he is now in NTT
Software Innovation Center. He received the2007 Outstanding Presentation Award from theJapan Society for Industrial and Applied Mathematics (JSIAM) and the 2009 Life Intelligenceand Office Information System (LOIS) ResearchAward. He is a member of JSIAM.

Hiroki Kumazaki

Researcher, Distributed Computing Technology Project, NTT Software Innovation Center.
He received the B.E. and M.E. degrees in engineering from Nagoya Institute of Technology,
Aichi, in 2010 and 2012, respectively. Since joining NTT Software Innovation Center in 2012, hehas been researching distributed computing systems.

Jungkyu Han

Researcher, Distributed Computing Technology Project, NTT Software Innovation Center.
He received the B.S. and M.S degrees in computer science and engineering from Seoul
National University, Korea, in 2005 and 2007,
respectively. Since joining NTT in 2007, he has
been engaged in R&D of stream data accumulation and distributed processing systems. As aresult of organizational changes in April 2012, heis now in NTT Software Innovation Center. His
current interests include big data analysis.

Masakuni Ishii

Researcher, Distributed Computing Technology Project, NTT Software Innovation Center.
He received the B.S. degree in mathematics
and computer science from the University of
Arizona, USA, in 2007 and the M.S. degree incomputer engineering from Keio University,
Kanagawa, in 2009. Since joining NTT in 2010,
he has been engaged in R&D of stream data
accumulation and distributed processing systems. As a result of organizational changes in
April 2012, he is now in NTT Software Innovation Center. He is a member of IPSJ.

Koji Aoya

Senior Research Engineer, Distributed Computing Technology Project, NTT Software Innovation Center.
He received the M.S. degree in mathematics
from Osaka University in 2001. After joining
NTT Information Sharing Platform Laboratories
in 2001, he was engaged in R&D of information
security, fast implementation of cryptography(especially ECDSA), and some applied protocols
such as electronic money. In 2007, he was transferred to NTT DATA Corporation, where he wasengaged in marketing and developed some solutions for retail and airline industries in the related
departments. Since moving to NTT Software
Innovation Center in 2012, he has been incubating and developing the market for Jubatus.

Min Luo

Scientist, Distributed Computing Technology
Project, NTT Software Innovation Center.
He received the B.S. and M.S. degrees from
Wuhan University, China, in 2004 and 2007,
respectively, and the Ph.D. degree in computerscience from Tokyo Institute of Technology in2011. After that, he was a full-time Associate
Researcher at Tokyo Institute of Technology.
Since joining NTT Software Innovation Centerin 2012, he has been engaged in research on
realtime big data analysis. He received the Best
Paper Award from the International Conferenceon Web-Age Information Management (WAIM)
in 2010.

Hiroyuki Makino

Researcher, Distributed Computing Technology Project, NTT Software Innovation Center.
He received the B.E. and M.S. degrees in engineering from Doshisha University, Kyoto, in2007 and 2009, respectively. Since joining NTT
Information Sharing Platform Laboratories in2009, he has been engaged in R&D of identity
federation systems and distributed processing
systems. As a result of organizational changes in
April 2012, he is now in NTT Software Innovation Center. He is a member of the Institute ofElectronics, Information and Communication
Engineers (IEICE).

Vol. 10 No. 12 Dec. 2012

Shohei Uchikawa

Senior Research Engineer, Supervisor, Group
Leader, Distributed Computing Technology Project, NTT Software Innovation Center.
He received the B.E. degree in informationengineering from Tokyo Institute of Technology
in 1988. After joining NTT Information Processing Systems Laboratories in 1988, he wasengaged in developing operating system software
for the Denden Information Processing System(DIPS) and designing a high-availability information system that uses DIPS. Following thegradual termination of the DIPS project in the
1990s, he took on the job of integrating several
high-availability client/server type information
systems as a systems engineer. In 2008, hemoved to NTT Communications as a generalmanager in the Platform Service Department andhe contributed to the company’s application service provider business. He returned to NTT in
2011. As a result of organizational changes in
April 2012, he is now in NTT Software Innovation Center.

Feature Articles: Optical Semiconductor Technologies
for Photonic Networks

High-speed Tunable Distributed
Amplification Distributed Feedback(TDA-DFB) Lasers
Nobuhiro Nunoya, Hiroyuki Ishii, and Ryuzo Iga
Abstract

In this article, we describe experimental results and an accurate wavelength control method for tunabledistributed amplification distributed feedback (TDA-DFB) lasers, which can offer fast wavelengthswitching and high controllability because wavelengths can be changed continuously. They should provide light sources for future photonic networks such as wavelength routing systems.

1. Introduction
The capacity of optical fiber communication networks has increased greatly through the use of wavelength division multiplexing (WDM) systems, where
signals with multiple wavelengths are transported ina single fiber. Since signals with different wavelengths do not interfere with each other, they can beseparated easily by using an arrayed waveguide grating or other interferometer device.
A wavelength routing system has been studied for
future photonics network systems, where transmission paths are selected dynamically by using the
wavelength of the signal lightwave as destination
information. High-speed wavelength switching
reduces the amount of data that must be transmitted
and makes possible optical switching systems without electrical bandwidth and delay limitations. Thereis a real need for light sources that can change wavelength quickly and accurately for use in systems thatuse dynamic wavelength switching.
The various tunable wavelength lasers, which canbe roughly divided into hybrid and monolithic types,
are shown in Fig. 1. The hybrid types consist of botha semiconductor part for gain and other material parts
for tuning, so they are also called external cavity
lasers. Their wavelengths can be controlled by changing the center wavelength of the external filter orreflector. The tuning speed depends on the responseof the external filter or reflector. On the other hand,the monolithic types have gratings or other structures
for selecting the wavelength in the semiconductor,
and the lasing wavelength is changed by changing therefractive index.
The refractive index of the semiconductor can bechanged by changing its temperature, which can beeasily and stably controlled with a Peltier device. As
a result, a tunable distributed feedback (DFB) laser
array with temperature control [1], [2] which is anextremely stable tunable wavelength laser, has beendeveloped. However, since the temperature-induced
refractive index change is relatively slow, high-speed
wavelength changing is very difficult to achieve.
Carrier effects, such as the plasma effect and theband filling effect, induced by current injection, also
cause a refractive index change. Since these phenomena happen quickly, they are used in tunable distributed Bragg reflector (DBR) lasers [3] as well as
sampled grating (SG) DBR lasers [4] and superstructure grating (SSG) DBR lasers [5]. However, a change
in the reflection peak wavelength is incompatible
with a longitudinal mode (phase) change because thegain region and the wavelength tuning region are
separated. Therefore, a phase tuning section is needed
so that multiple sections can be controlled for stable
operation. In addition, a feedback function that corrects the operating condition is difficult to achieve
because there is a possibility of mode hopping during
wavelength switching and long-term operation.
Tunable wavelength lasers with high-speed and
NTT Technical Review

Feature Articles

DFB type

SOA

Filter
DFB type

PLC

SOA(a) Hybrid (external cavity) type(b) Monolithic type
PLC: planar lightwave circuit
SOA: semiconductor optical amplifierFig. 1. Kinds of tunable wavelength lasers.

Gain electrode

Tuning electrode
ActiveTuning

L1

L2
Section 1

L: length

Section 2
λ/4 phase shift- Repetition of active and tuning layers- Constant ratio of active and tuning layer lengths- Asymmetric period structure

Fig. 2. Cross sectional schematic view of TDA-DFB laser.

accurate wavelength switching, require mode-hopfree operation with a single tuning electrode that utilizes carrier effects induced by current injection. The
tunable distributed amplification distributed feedback(TDA-DFB) laser was invented in our laboratory forhigh-speed and mode-hop-free operation [6]–[8].
2. TDA-DFB laser with asymmetric structure
A schematic view of a TDA-DFB laser is shown in
Fig. 2. Active gain and tuning layers for wavelength
control are arranged alternately along the cavity,
which is similar to a structure that combines a DFB
laser and a DBR laser. While the repetition periods ofthe active and tuning layers differ on the left handside (section 1) and right hand side (section 2) by al/4 phase shift, their ratio is constant throughout theVol. 10 No. 12 Dec. 2012

entire cavity. Since the electrodes for the same layers
are connected to each other in the device, the wavelength of the TDA-DFB laser can be controlled by asingle tuning electrode.
The tuning principle of the TDA-DFB laser is
explained in Fig. 3. Before tuning, the wavelengths of
the reflection peaks of sections 1 and 2 are the same
because the refractive indices of the tuning and active
layers are the same. Moreover, since the phase condition is satisfied at the Bragg wavelength owing to thel/4 phase shift, lasing occurs at the reflection peakwavelength. When the tuning current is increased, therefractive index of the tuning layer is reduced andboth the reflection peak and longitudinal modes movesynchronously to the shorter wavelength side. Since
the ratio of the active layer length to tuning layer
length is constant, as previously mentioned, theFeature Articles

Reflection spectra
Sections 1 & 2

Tuning current
Lasing modeLongitudinal modes (phase)λReflection spectra
Section 2
Section 1

Mode-hop-free operation

λAsymmetric structure∝1/L2

Expanded tuning range

∝1/L1

λ
Sub-mode suppression

Fig. 3. Principle of mode-hop-free tuning.

Absorption
LD 1

600 µm

LD 2
LD 3
LD 4
LD 5
LD 6

TDA-DFB-LD
705 µm

MMI

SOA2500 µm

Fig. 4. Photograph of top view of TDA-DFB laser array.

average Bragg wavelength change is proportional to
the longitudinal mode (phase) change related to cavity length. As shown by these results, mode-hop-freetuning can be achieved.
When the refractive index of the tuning layer isfurther reduced by increasing the tuning current, satellite reflection peaks are generated beside the mainreflection peak with a period that is inversely proportional to the repetition period of the active and tuning
layers. However, since the asymmetric structure withdifferent repetition periods prevents overlaps between
the satellite peaks of sections 1 and 2, no sub-modes
are generated. Consequently, the continuous tuningwavelength range for TDA-DFB lasers with an asymmetric structure can be expanded.
A top view of a monolithically integrated TDADFB laser array is shown in Fig. 4. One TDA-DFB
laser can change wavelength by 7 nm to 8 nm. To
cover the C band (wavelength range from 35 nm to
40 nm) used for optical fiber communication, six
TDA-DFB lasers with an asymmetric structure, amultimode interference (MMI) coupler, and a semiconductor optical amplifier (SOA) are integrated
monolithically. The relationship between the lasing
wavelength and the tuning voltage for each laser
diode (LD) is shown in Fig. 5. A tuning wavelength
NTT Technical Review

Feature Articles

1580
LD 1

Wavelength (nm)

1570

LD 2

1560

LD 3
LD 4

1550

LD 5

1540
LD 6

1530
0.8

1

1.2
1.4
Tuning voltage (V)

1.6

Fig. 5. Relationship between wavelength and tuning voltage.

Frequency

Carrier effect (ns order)

Tuning current

Thermal drift(µs-ms order)

Ch. 2
Allowable range

Ch. 1tChannel switching time

CarrierTemperature

Refractive index

Refractive index

Wavelength(Frequency )Wavelength(Frequency )

Fast

Slow

Fig. 6. Diagram of channel switching (left) and explanation of phenomena (right).

range of more than 40 nm can be obtained by covering the different wavelength ranges of the lasers withdifferent grating periods. The results in Fig. 5 show awavelength slightly shorter than the C band, but optimized grating periods will provide operation over theentire C band.
3. Channel switching
The frequency variations that occur during channel
switching operation are explained in Fig. 6. Carrier
effects occur within a few nanoseconds in carrierinjection-type tunable wavelength lasers. However, atemperature change is simultaneously produced by
the heat generated by the current injection. Therefore,
relatively slow wavelength variations also appear
Vol. 10 No. 12 Dec. 2012

(thermal drift). Since the refractive index changes
caused by carrier effects and the thermal effect are
opposite, frequency variations are observed, as shownin Fig. 6. Since the TDA-DFB laser can operate without mode hopping during thermal drift, it is easy tocontrol the wavelength, and the wavelength variations can be calculated.
The channel switching time is defined as the time
taken for a wavelength to enter the allowable wavelength range. For high-speed switching, it is important to reduce the thermal drift by suppressing thetemperature change [8]–[10]. With the TDA-DFB
laser array, variations in generated heat can be
reduced by utilizing the array’s tuning layers as heatcompensators. Controlling the tuning current of oneof the other lasers so that it is opposite to the tuningFeature Articles

Clock

Tuning current
Active current
100-ms period

Digitizing
oscilloscope

TunablefilterTuning

TDA-DFB-LD

ActiveTime & intensity data

Photodetector

PersonalcomputerWavelength (frequency) data

Fig. 7. Measurement setup for monitoring wavelength trajectory during channel switching.

5
w/o compensation

4

Frequency deviation (GHz)

Frequency deviation (GHz)5with compensation

3
2

Target frequency range

1
0
–1

0

2

4
Time (ms)

6

8

10

(a) Channels of same LD

4

w/o compensation
with compensation

3

with compensation& local heating

2
Target frequency range

1
0
–1

0

2

4
Time (ms)

6

8

10

(b) Channels of different LDs

Fig. 8. Peak wavelength traces during channel switching.

current of the operating laser enables the generated
heat to be kept constant.
The measurement setup for monitoring the change
in wavelength during channel switching is shown in
Fig. 7. For channel switching between channels of
the same laser, the active current is constant and thetuning current changes within 100 ms. While thetransparent wavelength of the tunable filter is beingchanged, time domain intensity profiles are measured
repeatedly. They are combined, and the peak wavelength can then be traced. Details of the experiment,such as the injection current for each region, are given
elsewhere [8].
The results of channel switching in the same laser

are shown in Fig. 8(a). With thermally compensatedoperation, when the tuning current increases, the tuning current of the next laser decreases. Without thermal compensation, the switching time, which isdefined as an allowable frequency range of 1 GHz,
was 3 ms. With thermal compensation, the switchingtime was reduced to less than 0.2 ms.
Results obtained for switching between channels in
different lasers are shown in Fig. 8(b). For thermallycompensated operation, the tuning current was injected continuously to keep the heat constant while theactive current was switched between the two lasers.
As a result, the channel switching time was reduced
to around 0.3 ms. However, even if the total current
NTT Technical Review

Feature Articles

injected into the entire chip is constant, the large
active current will be changed, which will induce alarge local temperature change. To suppress this, we
attempted to use local heating by applying a relatively large tuning current before switching. We succeeded in suppressing the local temperature variation
and, as a result, the thermal drift fell to less than 1
GHz with a time resolution of 40 µs.
4. Conclusion
A TDA-DFB laser with an asymmetric structure,
which is a kind of high-speed tunable wavelength
laser without mode hopping, has been developed for
future WDM network systems. The mode-hop-freetuning range was expanded to about 8 nm by using an
asymmetric period structure. Consequently, a tuning
range of over 40 nm was obtained for a monolithically integrated TDA-DFB laser array, consisting of
six asymmetric TDA-DFB lasers, an MMI coupler,
and an SOA.
We also demonstrated thermal drift reduction during channel switching by using a thermal compensation technique. The channel switching time with afrequency deviation of less than 1 GHz was reduced
from 3 ms to 0.2 ms when both channels were in thesame laser. For channel switching between different
lasers, a channel switching time of less than 40 µs wasachieved by using thermal compensation with thelocal heating.
The asymmetric TDA-DFB laser array will be useful for advanced photonic networks based on WDM
systems because of its high-speed and accurate wavelength tuning. In the future, we will research bothVol. 10 No. 12 Dec. 2012device structures and operating methods to makeeven faster and more accurate channel switching.
References[1]

H. Ishii, K. Kasaya, and H. Oohashi, “Spectral Linewidth Reduction
in Widely Wavelength Tunable DFB Laser Array,” IEEE J. Sel. Top.
Quantum. Electron., Vol. 15, No. 3, pp. 514–520, 2009.
[2] H. Ishii, K. Kasaya, and H. Oohashi, “Wavelength-tunable Lasers for
Next-generation Optical Networks,” NTT Technical Review, Vol. 9,
No. 3, 2011.
https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr2011
03fa7.html[3] M. Yamaguchi, M. Kitamura, S. Murata, I. Mito, and K. Kobayashi,“Wide range wavelength tuning in 1.3 µm DBR-DC-PBH-LDs by
current injection into the DBR region,” Electron. Lett., Vol. 21, No. 2,
pp. 63–65, 1985.
[4] V. Jayaraman, Z. -M. Chuang, and L. A. Coldren, “Theory, design,and performance of extended tuning range semiconductor lasers withsampled gratings,” IEEE Journal of Quantum Electron., Vol. 29, No.
6, pp. 1824–1834, 1993.
[5] Y. Tohmori, Y. Yoshikuni, T. Tamamura, H. Ishii, Y. Kondo, and M.
Yamamoto, “Broad-Range Wavelength Tuning in DBR Lasers with
Super Structure Grating (SSG),” IEEE Photon. Technol. Lett., Vol. 5,
No. 2, pp. 126–129, 1993.
[6] H. Ishii, Y. Kondo, F. Kano, and Y. Yoshikuni, “A tunable distributed
amplification DFB laser diode (TDA-DFB-LD),” IEEE Photon. Technol. Lett., Vol. 10, No. 1, pp. 30–32, 1998.
[7] N. Nunoya, H. Ishii, Y. Kawaguchi, Y. Kondo, and H. Oohashi, “Wideband tuning of tunable distributed amplification distributed feedback
laser array,” Electron. Lett., Vol. 44, No. 3, pp. 205–207, 2008.
[8] N. Nunoya, H. Ishii, Y. Kawaguchi, R. Iga, T. Sato, N. Fujiwara, andH. Oohashi, “Tunable Distributed Amplification (TDA-) DFB Laserwith Asymmetric Structure,” IEEE J. Sel. Top. Quantum Electron.,Vol. 17, No. 6, pp. 1505–1512, 2011.
[9] H. Okamoto, H. Yasaka, K. Sato, Y. Yoshikuni, K. Oe, K. Kishi, Y.
Kondo, and M. Yamamoto, “A wavelength-tunable duplex integrated
light source for fast wavelength switching,” J. Lightwave. Technol.,Vol. 14, No. 6, pp. 1033–1041, 1996.
[10] N. Fujiwara, H. Ishii, H. Okamoto, Y. Kawaguchi, Y. Kondo, and H.
Oohashi, “Suppression of Thermal Wavelength Drift in Super-Structure Grating Distributed Bragg Reflector (SSG-DBR) Laser with
Thermal Drift Compensator,” IEEE J. Sel. Top. Quantum. Electron.,Vol. 13, No. 5, pp. 1164–1169, 2007.

Feature Articles

Nobuhiro Nunoya

Senior Research Engineer, Photonics Device
Laboratory, NTT Photonics Laboratories.
He received the B.E., M.E., and Ph.D. degrees
in physical electronics from Tokyo Institute ofTechnology in 1997, 1999, and 2001, respectively. He joined NTT Photonics Laboratories in
2002. From 2008 to 2009, he was a visiting
researcher at the University of California, Santa
Barbara, CA, USA. His research interests include
semiconductor lasers and integrated devices for
optical communications. He is a member of theJapan Society of Applied Physics (JSAP), theInstitute of Electronics, Information and Communication Engineers (IEICE), and the IEEE/
Photonics Society.

Ryuzo Iga

Senior Research Engineer, Photonics Device
Laboratory, NTT Photonics Laboratories.
He received the B.E. and M.E. degrees inapplied fine chemistry and the D.E. degree inelectromagnetic energy engineering from Osaka
University in 1985, 1987, and 1995, respectively.
Since joining NTT Opto-electronics Laboratories in 1987, he has been engaged in research on
the crystal growth of III-V semiconductor compounds. His doctoral dissertation was on selective growth by laser-assisted MOMBE. In 1999,
he joined NTT Photonics Laboratories. His current research interests include MOVPE growthtechnologies for the fabrication of optical integrated devices. He is a member of JSAP.

Hiroyuki Ishii

Research Group Leader, Senior ResearchEngineer, Supervisor, Photonics Device Laboratory, NTT Photonics Laboratories.
He received the B.E., M.E., and Ph.D. degrees
in electronics and communication engineeringfrom Waseda University, Tokyo, in 1988, 1990,
and 1999, respectively. Since joining NTT Optoelectronics Laboratories (now NTT Photonics
Laboratories) in 1990, he has been engaged indevelopmental research on semiconductor lasers
and integrated devices for optical communications systems. He is a member of JSAP, IEICE,
and the IEEE/Photonics Society.



NTT Technical Review

Feature Articles: Optical Semiconductor Technologies
for Photonic Networks

Electroabsorption Modulator
Integrated Light Sources for
Future High-speed Ethernet
Takeshi Fujisawa, Shigeru Kanazawa, Kiyoto Takahata,
and Hiroyuki Ishii
Abstract

Recent progress in electroabsorption modulator integrated distributed feedback (EADFB) lasers forhigh-speed data communications is described. For 100 Gigabit Ethernet (100GbE) applications, anultrasmall optical semiconductor chip, in which four 1.3-µm 25-Gbit/s EADFB lasers and an opticalmultiplexer are monolithically integrated, has been developed for future 100GbE transceivers. This small
chip enables the overall transmitter size and the number of optical components to be significantly
reduced compared with conventional 100GbE transmitters. Furthermore, for future beyond-100-Gbit/s
applications, we have developed 50-Gbit/s EADFB lasers and obtained very clear eye openings evenafter 40-km transmission.

1. Introduction
To cope with the demand for huge data capacities inlocal area networks (LANs), 100 Gigabit Ethernet(100GbE) has recently been standardized [1]. In
100GbE, the optical transmitter consists of four 1.3µm, 25-Gbit/s light sources with a lane spacing of 800
GHz and an optical multiplexer (MUX). So far, work
has focused mainly on the development of discrete
25-Gbit/s light sources [2]–[6] for the first-generationtransceiver, which is called a centum form-factor
pluggable (CFP) transceiver. Since optical components in this transceiver are placed discretely, the size,
power consumption, and number of optical components are large. Moreover, since there is a limitationon the transceiver size, reductions in size and power
consumption are essential, and these require largescale-integration of the discrete components.
Future high-speed LANs beyond 100 Gbit/s will
use a multilane system. Therefore, it is essential toincrease the serial data rate of the discrete light sourcein order to reduce the required number of wavelength
lanes, which will lead to smaller transmitters, lower
power consumption, and reduced fabrication cost.
This article describes recent progress in electroabsorption modulator integrated distributed feedback(EADFB) lasers for high-speed data communications. For 100GbE applications, an ultrasmall opticalsemiconductor chip [7]–[9], in which four 1.3-µm 25Gbit/s EADFB lasers and an optical MUX are monolithically integrated, has been developed for future
100GbE transceivers. This small chip enables theoverall transmitter size and the number of opticalcomponents to be significantly reduced comparedwith those of conventional 100GbE transmitter. Furthermore, for future beyond-100-Gbit/s applications,
we have developed 50-Gbit/s EADFB lasers [10] andobtained very clear eye openings even after 40-km
transmission.
2. Monolithically integrated
light source for 100GbE
A micrograph of the fabricated device is shown in
Fig. 1. It consists of four 1.3-µm EADFB lasers and amultimode interferometer (MMI) coupler for the
MUX. InGaAlAs-based compressive-strained quantum wells (QWs) are used for the DFB lasers and
NTT Technical Review

Vol. 10 No. 12 Dec. 2012

MUX
PD LD EAM

2.4 mmFig. 1. Micrograph of the fabricated chip.

3
Lane 02.5
Module output power (mW)monitor photodiodes (PDs) and the lasing mode is thetransverse electric (TE) mode. To increase the output
power of the DFB lasers while retaining single mode
lasing, we introduced a novel rear-grating structure[9]. This structure is composed of two sections: one isa conventional l/4 wavelength-shifted grating placedat the rear facet side and the other is just an active
region without a grating placed at the front facet side.
Both facets are coated with antireflection films. With
the active region placed in front of the conventional
phase-shifted DFB laser, the lasing mode is amplified
in the active region and the longitudinal optical distribution becomes asymmetric, resulting in high output
power from the front facet. The design is described in
more detail in Ref. [9].
For an electroabsorption modulator (EAM), an
effective way to reduce the power consumption of theelectrical driver is to reduce the EAM’s driving voltage. To do this, we used InGaAlAs-based, tensilestrained QWs to obtain a large extinction ratio andsteep extinction curves [11]. We also made the total
thickness of the insulator region small to effectively
bias the QW region with low voltage.
A shallow-ridge waveguide is buried with benzocyclobutene (BCB) for the EADFB laser section toensure a large modulation bandwidth. The low dielectric constant of BCB makes the parasitic capacitancelower, and hence the electric/optical (E/O) bandwidth
larger. An MMI coupler is used for the MUX becauseof its small length and low wavelength sensitivity.
Deep-ridge waveguides with the InGaAsP-core buried with BCB were used for the MUX region. Since
deep-ridge waveguides have stronger optical confinement owing to the large refractive index contrast in
the lateral direction, they have low bending and radiation losses compared with shallow-ridge waveguides,
leading to a smaller chip size.
Metal-organic vapor-phase epitaxy (MOVPE) wasused for crystal growth and a butt-joint technique wasused to optimize the structures of the DFB laser,
EAM, PD, and MUX, separately. The lengths of the
DFB lasers, monitor PDs, EAMs, and MMI are 400µm, 150 µm, 150 µm, and 250 µm, respectively. The
width of the MMI is 20 µm. The distance between
adjacent EADFB lasers is 600 µm. The fabricatedchip is as small as 2.0 mm × 2.4 mm and it is packaged in a specially designed module [8].
The module output power as a function of the injection current to the DFB lasers is shown in Fig. 2. All
measurements for the module were done at 40°C.
From the shorter wavelength side, we label the wavelength lanes 0 to 3. The output power at the injection

2 mmFeature Articles

Lane 1
Lane 2

2

Lane 3
1.5
1
0.5
0

0

50

100

150

Injection current (mA)

Fig. 2. M odule output power as a function of injection
current.

current of 150 mA was over 2 mW for all the lanes.
The lasing spectra at the injection current of 100 mA
are shown in Fig. 3. Single-mode lasing with a sidemode suppression ratio of over 50 dB was obtained
for all lanes, showing the usefulness of the rear-grating structure for DFB lasers used in monolithicallyintegrated devices. The static extinction curves areshown in Fig. 4. The injection current to the DFB
lasers was 100 mA. Static extinction ratios larger than
20 dB as well as steep extinction curves suitable forlow-voltage operation were obtained for all lanes.
The dynamic extinction ratios of the EAMs as a function of driving voltage (Vpp) are shown in Fig. 5. The
bias voltage to the modulator was set at a level where
the cross point of the optical eye diagram was 50%.
For all lanes, the dynamic extinction ratios wereFeature Articles

Lane 0Lane 1

Lane 2

12

Lane 3

Dynamic extinction ratio (dB)Intensity (10 dB/div)

10

1290

1295

1300

1305

1310

8

6

4

2

Lane 0Lane 2

Lane 1

Lane 3

Wavelength (nm)Fig. 3. Lasing spectra of the monolithically integrated lightsource.

0

0

0.5

1

1.5

2

2.5

Modulator driving voltage (V)Fig. 5. D ynamic extinction ratio as a function of driving
voltage for 25-Gbit/s operation.

Static extinction ratio (dB)0–10

dynamic extinction ratios to the modulator are summarized in Tables 1 and 2. Clear eye openings wereobtained for all driving voltages even after 10-km
transmission.

Lane 0Lane 1

3. EADFB lasers forbeyond-100-Gbit/s applications

Lane 2–20

Lane 3

–30

0

–1

–2

–3

Modulator bias voltage (V)Fig. 4. Static extinction curves.

larger than 4 dB, which is the minimum value for 10km 100GbE (100GBASE-LR4) even with a driving
voltage of 0.5 V.
With the module, we performed a 10-km transmission experiment on single-mode optical fiber using a
25-Gbit/s, non-return-to-zero, 231-1 pseudorandom
bit stream signal. The eye-diagrams after 10-km
transmission with Vpp = 0.5 V, 1 V, and 2 V for all thelanes are shown in Fig. 6. The bias voltages andFor future high-speed LANs beyond 100 Gbit/s, theserial data rate should be increased to reduce therequired number of lanes. Fewer lanes enables reductions in the size, power consumption, and fabrication
cost of the whole transmitter. For this purpose, wedeveloped 50-Gbit/s discrete EADFB lasers [10]. The
basic structure of the device is described in Refs. [5],[6]. The lasing spectra of the EADFB lasers areshown in Fig. 7. The measurement was done at 45°C.
From the shorter wavelength side, we label the lanes
0 to 7. The wavelength spacing is 400 GHz (half ofthat for 100GbE). The layer structure was the samefor all the EADFB lasers. The 50-Gbit/s eye diagrams
after 40-km transmission are shown in Fig. 8. The
driving voltages were 2 V and the dynamic extinction
ratios were larger than 8 dB for all lanes. Very clear
eye openings were obtained. Since all the EADFB
lasers had the same layer structure, we could integratethem monolithically, as in the case of the 100GbE
light source.

NTT Technical Review

Feature Articles

Lane 0Lane 1

Lane 2

Lane 3

0.5 V

1V

2V

Fig. 6. 25-Gbit/s eye diagrams for all the lanes after 10-km transmission for different values of Vpp.

Table 1. Bias voltages to EAMs.
Lane 0 (V)Lane 1 (V)Lane 2 (V)Lane 3 (V)

0.5

–1.08

–1.28

–1.51

–1.74

1

–0.95

–1.14

–1.43

–1.64

2

–0.93

–1.06

–1.26

–1.53

Intensity (10 dB/div.)

Lane 0 1 2 3 4 5 6 7Vpp (V)

Table 2. Dynamic extinction ratios of EAMs.
Vpp (V)
0.5

Lane 0 (dB) Lane 1 (dB) Lane 2 (dB) Lane 3 (dB)
4.99

5.05

4.32

4.4

1

8.11

9.31

6.97

6.92

2

10.78

10.63

9.79

9.88

45ºC
1290 1295 1300 1305 1310 1315 1320
Wavelength (nm)Fig. 7. Lasing spectra of 50-Gbit/s EADFB lasers.

Lane 0Lane 1

Lane 2

Lane 3

Lane 4Lane 5

Lane 6

Lane 7

Fig. 8. 50-Gbit/s eye diagrams after 40-km transmission.

Vol. 10 No. 12 Dec. 2012Feature Articles

4. Conclusion
Recent progress in 1.3-µm InGaAlAs-based
EADFB lasers for high-speed data communications
was described. For 100GbE, an ultrasmall integrated
light source was developed. Monolithic integration of
the optical components on one chip let us reduce thesize of the 100-Gbit/s transmitter chip. This small
chip enables us to make small-form-factor 100GbE
transceivers. For beyond-100-Gbit/s applications, 50Gbit/s EADFB lasers were also developed. These
devices are promising for future high-capacity data
links.
References[1]	100GbE Task Force. http://www.ieee802.org/3/ba/[2] H. Oomori, H. Ooe, M. Seki, Y. Fujimura, K. Matsumoto, and Y.
Murakami, “An extremely compact electro-absorption modulator
integrated DFB laser module for 100Gbps Ethernet over 75km SMF
reach,” Proc. of the 34th European Conference and Exhibition on
Optical Communication (ECOC 2008), P.2.0.7, Brussels, Belgium,
2008.
[3] H. Takahashi, T. Shimamura, T. Sugiyama, M. Kubota, and K. Nakamura, “High-power 25-Gb/s Electroabsorption Modulator Integrated
with a Laser Diode,” IEEE Photon. Technol. Lett., Vol. 21, No. 10, pp.
633–635, 2009.
[4] T. Saito, T. Yamatoya, Y. Morita, E. Ishimura, C. Watatani, T. Aoyagi,
and T. Ishikawa, “Clear eye opening 1.3µm-25/43 Gbps EML withnovel tensile-strained asymmetric QW absorption layer,” Proc. of theTakeshi Fujisawa

Researcher, Photonic Device Laboratory, Optical Integrated Device Research Group, NTT
Photonics Laboratories.
He received the B.E., M.E., and Ph.D. degrees
in electronic engineering from Hokkaido University in 2001, 2003, and 2005, respectively. His
current research interests include theoreticalmodeling of optoelectronic devices and development of semiconductor lasers. He is a member ofIEEE and the Institute of Electronics, Information and Communication Engineers (IEICE).
From 2003 to 2006, he was a Research Fellow of
the Japan Society for the Promotion of Science.

Shigeru Kanazawa

Researcher, Photonic Device Laboratory, Optical Integrated Device Research Group, NTT
Photonics Laboratories.
He received the B.S. and M.S. degrees in electronics and communication engineering from
Tokyo Institute of Technology in 2005 and 2007,
respectively. He joined NTT Photonics Laboratories in 2007. He has been engaged in R&D of
optical semiconductor devices and integrated
devices for optical communications systems. He
is a member of Japan Society of Applied Physics(JSAP) and IEICE.



35th European Conference and Exhibition on Optical Communication(ECOC 2009), P.8.1.3, Vienna, Austria, 2009.
[5] T. Fujisawa, M. Arai, N. Fujiwara, W. Kobayashi, T. Tadokoro, K.
Tsuzuki, Y. Akage, R. Iga, T. Yamanaka, and F. Kano, “25-Gbit/s 1.3μm InGaAlAs-based electroabsorption modulator integrated with a
DFB laser for metro-area (40 km) 100-Gbit/s Ethernet system,” IEE
Electronics Lett., Vol. 45, No. 17, pp. 900–901, 2009.
[6] T. Fujisawa, K. Takahata, T. Tadokoro, W. Kobayashi, A. Ohki, N.
Fujiwara, S. Kanazawa, T. Yamanaka, and F. Kano, “Long-reach
100Gbit Ethernet light source based on 4×25-Gbit/s 1.3-μm InGaAlAs EADFB lasers,” IEICE Trans. on Electronics, Vol. E94-C, No. 7,
pp. 1167–1172, 2011.
[7] T. Fujisawa, S. Kanazawa, H. Ishii, N. Nunoya, Y. Kawaguchi, A.
Ohki, N. Fujiwara, K. Takahata, R. Iga, F. Kano, and H. Oohashi,“1.3-μm, 4×25-Gbit/s, monolithically integrated light source formetro area 100-Gbit/s Ethernet,” IEEE Photonics Technology Lett.,Vol. 23, No. 6, pp. 356–358, 2011.
[8] S. Kanazawa, T. Fujisawa, A. Ohki, H. Ishii, N. Nunoya, Y. Kawaguchi, N. Fujiwara, K. Takahata, R. Iga, F. Kano, and H. Oohashi, “A
compact EADFB laser array module for a future 100-Gbit/s Ethernet
transceiver,” IEEE Journal of Selected Topics in Quantum Electronics, Vol. 17, No. 5, pp. 1191–1197, 2011.
[9] T. Fujisawa, S. Kanazawa, K. Takahata, W. Kobayashi, T. Tadokoro,
H. Ishii, and F. Kano, “1.3-μm, 4×25G, EADFB laser array modulewith large-output-power and low-driving-voltage for energy-efficient
100GbE transmitter,” Optics Express, Vol. 20, No. 1, pp. 614–620,
2012.
[10] T. Fujisawa, K. Takahata, W. Kobayashi, T. Tadokoro, N. Fujiwara, S.
Kanazawa, and F. Kano, “1.3-μm, 50-Gbit/s electroabsorption modulators integrated with a DFB laser for beyond 100G parallel LAN
applications,” IET Electronics Lett., Vol. 47, No. 12, pp. 709–710,
2011.
[11] H. Fukano, T. Yamanaka, M. Tamura, and T. Kondo, “Very-low-driving voltage electroabsorption modulators operating at 40Gb/s,” J.
Lightwave Technol., Vol. 24, pp. 2219–2224, 2006.

Kiyoto Takahata

Senior Research Engineer, Photonic Device
Laboratory, Optical Integrated Device ResearchGroup, NTT Photonics Laboratories.
He received the B.E. and M.E. degrees inphysical engineering from Kyoto University in1988 and 1990, respectively, and the Ph.D.
degree in electronics and communication engineering from Tokyo Institute of Technology in2010. In 1990, he joined NTT Opto-electronics
Laboratories (now NTT Photonics Laboratories),
where he was initially engaged in research on a
wavelength conversion device based on a semiconductor laser. Since 1993, he has been engaged
in research on high-speed monolithically integrated photoreceivers, ultrafast optical packet
processing based on optoelectronic circuits, andsemiconductor lasers. He is a member of JSAP
and IEICE.

Hiroyuki Ishii

Senior Research Engineer, Supervisor, Photonic Device Laboratory, Optical Integrated
Device Research Group, NTT Photonics Laboratories.
He received the B.E., M.E., and Ph.D. degrees
in electronics and communication engineeringfrom Waseda University, Tokyo, in 1988, 1990,
and 1999, respectively. Since joining NTT Optoelectronics Laboratories (now NTT Photonics
Laboratories) in 1990, he has been engaged indevelopmental research on semiconductor lasers
and integrated devices for optical communications systems. He is a member of JSAP, IEICE,
and the IEEE/Photonics Society.

NTT Technical Review

Feature Articles: Optical Semiconductor Technologies
for Photonic Networks

High-speed Photodetector
Technologies
Yoshifumi Muramoto, Toshihide Yoshimatsu,
Masahiro Nada, and Tadao Ishibashi
Abstract

We have developed several kinds of high-speed photodetector technologies for broadband photonic
networks. This article reviews three of NTT’s high-speed photodiodes: ultrahigh-speed photodiodes,
specially designed photodiodes with high responsivity and low operating voltage, and avalanche photodiodes.

1. Introduction
Because of the popularity of the Internet and videoon-demand services, the capacity of photonic network systems must be continuously increased. A
semiconductor photodetector, which converts an
optical signal into an electrical signal, is a key device
in receivers in photonic network systems. The general demands for photodetectors are faster operating
speeds for higher bit-rates, higher efficiency for better sensitivity, and lower operating voltage for lower
power consumption by the receiver.
In the 1990s, we developed the uni-traveling-carrier
photodiode (UTC-PD) structure that makes the bestuse of electron transport and has the advantages ofsimultaneous high-speed and high-output operation[1]. Since UTC-PDs can maintain their photodetection function for input signals with frequencies above
1 THz, they have been used as terahertz microwave
generators [2].
In the receivers of photonic network systems, highresponsivity is also very important to improve receiver sensitivity. To meet this requirement, we havedeveloped the maximized-induced-current photodiode (MIC-PD) by modifying the UTC-PD [3]. The
MIC design can maximize the responsivity at arequired bandwidth by means of a hybrid (combined
p-type and depleted (p: positive semiconductor))
absorption layer. This technology has been successfully applied to photodiodes for 100-Gbit/s receiversof digital coherent transmission systems.
Moreover, avalanche photodiodes (APDs), which
provide amplification as well as photodetection, areused in access and metro networks and Ethernet. We
had already developed APDs for 10-Gbit/s operation
but there have recently been requests for high-speed
APDs, e.g., for 25-Gbit/s receivers for 100-Gbit/sbased Ethernet.
2. Ultrahigh-speed photodiodes (UTC-PDs)
One widely used photodetector is the p-i-n photodiode (pin-PD), which has a depleted absorption layerof intrinsic semiconductor (i-layer) between positively and negatively doped electrode layers (p- andn-type semiconductor layers). In a pin-PD, two typesof charge carriers—both negative electrons and positive holes—are photogenerated and contribute to theexternal induced current. Because holes have a much
lower velocity than electrons (1/10 the speed), thedevice’s response speed is dominated by hole transport. Therefore, we developed the UTC-PD, which
can achieve ultrahigh-speed operation, by removing
this limiting factor for the pin-PD. As illustrated inFig. 1, carriers are generated in the p-type absorption
layers and only electrons are injected into the depleted carrier collection layer, whose thickness isdesigned independently of the absorption layer. Since
the holes are majority carriers in the p-type absorption layer, their transport is the collective motion witha high response time determined by the dielectricrelaxation time. Eventually, only electrons behave as
NTT Technical Review

Feature Articles

p-contact layer
ElectronspOvershoot effectpn-contact layer

Holesi
Absorption layer (InGaAs)n

Collection layer (InP)

Fig.1. Schematic band diagram of UTC-PD.

active carriers in the UTC-PD; thus, UTC-PDs canachieve ultrahigh-speed and high-current operation
without the space-charge-effect induced by holeaccumulation.
A 3-dB bandwidth (f3dB) of over 300 GHz has
been obtained for a UTC-PD. We have developed a
UTC-PD-based terahertz photomixer module for frequencies beyond 1 THz [2].
3. Specially designed PD with high responsivity
and low operating voltage: MIC-PD
A drawback of the UTC-PD is low responsivity
when the absorber has been designed to be relatively
thin in order to achieve high-speed operation. To optimize both the response speed and responsivity, we
have developed the MIC-PD. In the MIC-PD design,
the absorption layer consists of p-type and depleted
layers, as shown in Fig. 2. Although there is holetransport contributing to the output current, the thickness of the depleted absorption layer does not have to
be as large as in a pin-PD, and it is adjusted to retain
the advantage of the high-speed potential of the UTCPD. This combined p-type and depleted absorption
layer allows us to maximize responsivity and operating speed simultaneously. Namely, the responsivity
can be higher than that of a UTC-PD with the same
bandwidth and the operating speed can be higher thanthat of a pin-PD with the same responsivity.
We have developed various MIC-PD structures foradvanced photonic network systems. One is a dualVol. 10 No. 12 Dec. 2012

polarization quadrature phase shift keying (DPQPSK) (or digital coherent) system [4], which is now
being intensively investigated toward future highspeed, high-capacity optical transmission systems. In
this system, the PD is required to operate in a wide
bandwidth with a high average photocurrent induced
by a high-power local oscillator input. Because a highphotocurrent induces a space charge effect in thedepletion layer of a PD, bandwidth reduction occurs.
To overcome this problem, we have developed a composite-field MIC-PD which can optimize the bandwidth by suppressing the space charge effect even at
low bias voltages [5]. The band diagrams and electricfield distributions of a conventional MIC-PD and the
new composite-field MIC-PD are shown in Figs. 2(a)and (b), respectively. An f3dB of more than 30 GHz
is required for a PD in a 100-Gbit/s digital coherent
system. To meet these system needs, the thickness ofthe photoabsorption layer is reduced in order toshorten the carrier-transit time. A thinner absorption
layer generally results in higher device capacitance,
which reduces the operating speed. However, byincorporating an undoped carrier collection layer of awide-bandgap material, we were able to widen thedepletion width and maintain low junction capacitance. Moreover, an n-type field control layer tailors
the step-like field profile, leading to sufficient field
for hole transport in the depleted absorber even at a
low bias voltage. In the collection layer, only electrons are traveling carriers; here, a low field (10 kV/cm) is sufficient to keep the electron transit timeFeature Articles

Field-control layer
Electrons

Electrons
p

p
i

i
Holes

i

Holes

n

n

Absorption layer
Collection layer
Field intensity E

Field intensity E

n-contact layer

Eh
Ee
Depth

Eh
Ee
Depth

Ee: field required for electrons
Eh: field required for holes(a) MIC-PD(b) Composite field MIC-PD

Fig. 2. Schematic band diagram and field intensities of conventional MIC-PD and new composite-field MIC-PD.

Photocurrent

3

0.3 mA
0.8 mA
2.0 mA
4.0 mAO/E response (dB)

VPD=–2 V
0

–3

–6

0

10

20
30
Frequency (GHz)40

50

Fig. 3. Frequency response curves of fabricated composite-field MIC-PD.

short. An important point is that the field control layer
generates a much higher electrical field in the depleted absorption layer and the partial absorber layer
suppresses the space charge effect. Consequently, thecomposite-field MIC-PD allows a lower operating
voltage and higher output current with higher responsivity than a conventional PD.
The frequency responses of a fabricated compositefield MIC-PD for optical-to-electrical (O/E) conversion with average photocurrents of 0.3 mA, 0.8 mA,
2.0 mA, and 4.0 mA are shown in Fig. 3. The reverse
bias voltage supplied to the PD was as low as 2.0 V,which suits the common power supply voltage with atransimpedance amplifier of +3.3 V. The f3dB
reached more than 35 GHz for average photocurrent
from 0.3 mA to 4.0 mA. We confirmed that there wasno degradation in the frequency response caused by
the space charge effect up to 4 mA. These goodresults show that composite-field MIC-PDs are suitable devices for receivers front-end of 100-Gbit/s
digital coherent systems.

NTT Technical Review

Feature Articles

n-contact layer
Electric field
confinement

Field buffer layer

MIC structurei-absorption layer

Field control layer (n)Avalanche layer: InAlAs
Field control layer (p)p-absorption layerp-contact layer
Semi-insulating InP substrate

Fig. 4. Schematic cross section of the high-speed APD.

4. High-speed APDs
APDs offer improved responsivity because of theinternal gain due to the multiplication of carriers in ahigh electric field. This function of APDs is very
important and they have been used in the 10-Gbit/s
metro and access systems. The technology trend is
now toward systems with higher bit rates such as the
100-Gbit/s Ethernet system in which the speed ofeach lane is 25 Gbit/s (25 Gbit/s × 4 channels). For
use in such novel high-speed systems, we have developed a new APD with the MIC design [6].
The schematic cross section of our high-speed APD
is shown in Fig. 4. The general figure of merit of an
APD is expressed by the product of the multiplication
factor (M) and f3dB. This product depends on thematerial and thickness of the avalanche layer. We
chose InAlAs as the material to obtain a higher Mf3dB product.
Another feature of our device is that field confinement is achieved by the inverted p-down structurewith a top n-contact. Field confinement is very
important for device reliability in order to avoid degradation caused by suppression of the leakage current
on the surface. Zn diffusion [7] and/or Si-ion implantation [8] are conventionally used for APD fabrication, but we decided not to use them in order to simplify the fabrication process. This simplicity also
allows better reproducibility and lower fabrication
cost. However, the field confinement becomes thesource of edge breakdown at the periphery of the ncontact mesa, which limits operation at a large multiplication factor in active area. To solve this problem,
we added a field buffer layer underneath the n-contact
layer and n-type field control layer.
Vol. 10 No. 12 Dec. 2012

The variation in f3dB with multiplication factor M
is shown in Fig. 5. The maximum value of f3dB was
23 GHz, and it decreased with increasing M. For M
higher than 15, f3dB values fell on a straight line,
indicating an M-f3dB product of 235 GHz. Owing to
the high responsivity achieved the MIC design, highmultiplied responsivity of 9.1 A/W was obtained at
f3dB of 18.5 GHz.
High multiplied responsivity with sufficient bandwidth is important in practical network systems. The
present result is compared with previously reported
values in Fig. 6. As seen in this figure, the obtained
value of 168 GHz A/W for our APD is superior to allother reported ones. Consequently, our APD is apromising candidate for high-speed network systems,e.g., 100-Gbit/s Ethernet systems with 25-Gbit/s
operation.
5. Conclusion
The MIC design, which is a modification of the
UTC-PD structure, can optimize responsivity andoperating speed. MIC-PDs for 100-Gbit/s digital
coherent system possess high current capability while
maintaining a high f3dB, even at a low bias voltage.
Our APD structure is fabricated with an inverted pdown layout to utilize the MIC design and field confinement by a top n-contact mesa. To avoid local
breakdown associated with field confinement, a fieldbuffer layer is applied. The best measured multiplied
responsivity of 9.1 A/W was obtained at f3dB of 18.5
GHz, which is sufficient performance for 25-Gbit/s
operation in 100-Gbit/s Ethernet systems.

Feature Articles

100

Multiplied
responsivity: 9.1 A/W

23 GHzM×f3db= 235 GHz

10

3
0

O/E response (dB)

f3db (GHz)18.5 GHz

M=10

–3
–6
–9

–12
–15
–18
–21

0

10

20

30

40

50

Frequency (GHz)
1
1

10

100

Multiplication factor

Fig. 5. Gain-bandwidth characteristics of fabricated APD.

Acknowledgment
This work was partly supported by the Ministry ofInternal Affairs and Communications of Japanthrough the R&D project “High-speed Optical Transport System Technologies”.

10This work

Multiplied responsivity (A/W)

8
MR ×f3db=150 A/W·GHz

6

References

MR×f3db=100 A/W·GHz

[1]

4
[2]

2
[3]
0

5

10

15

20

25

30

35

40

[4]

f3db (GHz)

Fig. 6. Summary of published multiplied responsivity(MR) against f3db in operating conditions.

[5]T. Ishibashi and H. Ito, “Uni-traveling-carrier photodiodes,” Tech.
Dig. Ultrafast Electronics and Optoelectronics, Lake Tahoe, CA,
USA, pp. 83–87, 1997.
A. Wakatsuki, Y. Muramoto, and T. Ishibashi, “Development of Terahertz-wave Photomixer Module Using a Uni-traveling-carrier Photodiode,” NTT Technical Review, Vol. 10, No. 2, 2012.
https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr2012
02fa5.html
Y. Muramoto and T. Ishibashi, “InP/InGaAs pin photodiode structure
maximising bandwidth and efficiency,” Electron. Lett., Vol. 39, No.
24, pp. 1749–1750, 2003.
Y. Miyamoto, A. Sano, E. Yoshida, and T. Sakano, “Ultrahigh-capacity Digital Coherent Optical Transmission Technology,” NTT Technical Review, Vol. 9, No. 8, 2011.
https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr2011
08fa2.html
T. Yoshimatsu, Y. Muramoto, S. Kodama, T. Furuta, N. Shigekawa, H.
Yokoyama, and T. Ishibashi, “Suppression of space charge effect in
MIC-PD using composite field structure,” Electron. Lett., Vol. 46, No.

NTT Technical Review

Feature Articles

[6]

[7]

13, 2010.
M. Nada, Y. Muramoto, H. Yokoyama, T. Ishibashi, and S. Kodama,“InAlAs APD with high multiplied responsivity-bandwidth product(MR-bandwidth product) of 168 A/W·GHz for 25 Gbit/s high-speed
operations,” Electron. Lett., Vol. 46, pp. 397–399, 2012.
E. Yagyu, E. Ishimura, M. Nakaji, S. Ihara, Y. Mikami, H. Itamoto, T.
Aoyagi, K. Yoshiara, and Y. Tokuda, “Design and Characteristics of[8]

Guardring-Free Planar AlInAs Avalanche Photodiodes,” Journal ofLightwave Technology, Vol. 27, No. 8, pp. 1011–1017, 2009.
Y. Hirota, Y. Muramoto, T. Takeshita, T. Ito, H. Ito, A. Ando, and T.
Ishibashi, “Reliable non-Zn-diffused InP/InGaAs avalanche photodiode with buried n-InP layer operated by electron injection mode,”
Electron. Lett., Vol. 40, No. 21, pp. 1378–1379, 2004.

Yoshifumi Muramoto

Masahiro Nada

Toshihide Yoshimatsu

Tadao Ishibashi

Senior Research Engineer, High-Speed Devices and Technology Laboratory, NTT Photonics Laboratories.
He received the B.E. and M.E. degrees from
Osaka Prefecture University in 1990 and 1992,
respectively. He joined NTT Opto-Electronics
Laboratories in 1992 and has been engaged inresearch on monolithically integrated photoreceivers and high-speed photodetectors. He is amember of the Institute of Electronics, Information and Communication Engineers (IEICE) andthe Japan Society of Applied Physics (JSAP).

Senior Research Engineer, High-Speed Devices and Technology Laboratory, NTT Photonics Laboratories.
He received the B.E. and M.E. degrees inapplied physics from Tohoku University, Miyagi,
in 1998 and 2000, respectively. He joined NTT
Photonics Laboratories in 2000. He has been
engaged in research on ultrafast optoelectronic
devices. He received the SSDM Paper Award
from SSDM in 2004. He is a member of IEICE
and JSAP.

Vol. 10 No. 12 Dec. 2012

Researcher, High-Speed Devices and Technology Laboratory, NTT Photonics Laboratories.
He received the B.E. and M.E. degrees fromthe University of Electro-Communications,Tokyo, in 2007 and 2009, respectively. Sincejoining NTT in 2009, he has been involved inresearch on high-speed, high-sensitivity avalanche photodiodes. He is a member of IEICE,
JSAP, and IEEE.

Research Professor at NTT Photonics Laboratories and Engineering Manager at NTT Electronics Corporation.
He received the B.E., M.E., and Ph.D. degrees
in applied physics from Hokkaido University in
1971, 1973, and 1986, respectively. Since joining
Nippon Telegraph and Telephone Public Corporation (now NTT) in 1973, he has been involved
in research on high-speed and optoelectronic
semiconductor devices, including IMPATT
diodes, field-effect transistors, heterostructure
bipolar transistors, high-speed photodiodes, avalanche photodiodes, THz photomixers, andMach-Zehnder modulators. He received the
Ichimura Award in 1992 and IEICE Electronics
Society Award in 2001. He is a fellow of IEICE,
JSAP, and IEEE.

Feature Articles: Optical Semiconductor Technologies
for Photonic Networks

InGaAs Metamorphic Laser for
Low-power-consumption Operation
Masakazu Arai, Wataru Kobayashi, and Masaki Kohtoku
Abstract

In this article, we review our efforts to reduce the power consumption of optical transmitter modules
for Ethernet and telecommunications use. To reduce the power consumption, we aim to eliminate thelight source’s temperature controller and improve the stability of the output power and modulation characteristics under ambient temperature conditions. We describe a 1.3-µm-range metamorphic laser on a
GaAs substrate that exhibits improved temperature characteristics. It has a characteristic temperature of
220 K and is capable of lasing up to 200°C. In addition, the bias current for 10-Gbit/s modulation at hightemperature has been reduced. This laser is promising for uncooled light sources operating with low
power consumption.

1. Introduction
Network traffic is rapidly increasing and so is theenergy consumed by communication systems. Therefore, it is important to find a way to reduce the power
consumption of transmitter modules. In an opticaltransmission module, a temperature controller suchas a Peltier device consumes more power than othercomponents. The temperature controller suppresses
deviations in laser characteristics such as output
power and modulation characteristics, which are sensitive to the ambient temperature. If we can improve
the laser’s temperature characteristics, we may beable to eliminate the need for a temperature controller, which will allow a significant reduction in power
consumption.
In this article, we describe our efforts towards
achieving a 1.3-μm-range laser with low power consumption. The 1.3-μm range has zero dispersion andis used for metro, access, and Ethernet systems.
For 1.3- and 1.55-μm-range optical fiber communication light sources, an InGaAsP-based laser has
already been used. It is fabricated on an InP substrate
and an InGaAsP quantum well is used as the active
region. This type of laser performs well at aroundroom temperature; however, an increase in the ambient temperature degrades the output power and theinjection current (operating current) increases, asshown in Fig. 1(a). Therefore, a temperature controller has been indispensable and power consumption
has been difficult to reduce. There is strong demand
for a laser with good temperature characteristics, as
shown in Fig. 1(b).
The temperature dependence of a laser can be
explained as follows. The laser light is amplified bycurrent injection in a quantum well acting as an active
region. As the ambient temperature is increased, theinjected electrons tend to overflow from the quantum
well into other regions such as the barrier layer, theseparately confined heterostructure (SCH), and the
cladding layer, as shown in Fig. 2. The electrons that
overflow from the quantum well recombine withholes without light emission, which leads to anincrease in threshold current at high temperature.
Therefore, to stabilize the laser performance against
temperature fluctuations, it is necessary to make a
deep quantum well that has a large potential gap fromthe barrier layer.
Several materials used for 1.3-μm-range lasers andtheir performances are listed in Table 1. With a conventional active region made from InGaAsP-basedmaterial on an InP substrate, it is difficult to makedeep potential quantum wells and have an operating
current at high temperature of over 40 mA at 10
Gbit/s. InGaAlAs-based materials on an InP substrate
have been studied with a view to improving the
NTT Technical Review

Feature Articles

Output power(a) Poor temperature
characteristics

Required
power
level

× Degradation of output power at hightemperature
× Increase in threshold current at hightemperature

25˚C
85˚C

Temperature controller is indispensable(power consumption: high).

Injection
current
increase

Injection current(b) Good temperature
characteristics

Temperature dependence of output
power is small.
Threshold current increase is small.

85˚C

Output power

25˚C

Temperature controller can be eliminated(power consumption: low).

Injection current

Fig. 1. Temperature characteristics of lasers.

Room temperature

High temperature

Energy of electrons

Energy of electrons

Overflowing electrons

Electrondensity

Non-radiative
recombination

Barrier Well BarrierzzFig. 2. Degradation mechanism at high temperature (carrier overflow from quantum well).

Table 1. Materials for 1.3-μm-range lasers and their performances.
Substrate
InP

GaAs

Active region material

Operating current for
10 Gbit/s at 85°C for L=200 µm

Features

InGaAsP

42 mA

Poor temperature characteristics
Temperature controller requiredHigh reliability

InGaAlAs

33 mA

Better temperature characteristics than InGaAsPInGaAs metamorphic

15 mA

Better temperature characteristics than InGaAlAs
L: cavity length

Vol. 10 No. 12 Dec. 2012Feature Articles

Plan view
TEM image

Laser structurep-electrodep-electrodep-cladding

Cross-sectional
TEM

Active region (MQW)
1 µm
n-cladding
Metamorphic buffer
n-InGaAs: 1.6 µm
n-GaAs substraten-electrode0.3 µm

MQW: multiple quantum welln: negative
p: positive

0.2 µmPlan view
TEM image
Dislocation network is formed at buffer interface.

Fig. 3. Transmission electron microscope (TEM) images of metamorphic buffer.

temperature, and they are gradually being used for
uncooled light sources. On the other hand, strained
InGaAs lasers on a GaAs substrate have superiortemperature characteristics to those on an InP substrate because a larger band offset between the cladding and SCH can be selected. However, the critical
thickness of a strained quantum well limits the emission wavelength to below 1.2 μm. To overcome thisobstacle, InGaAsN quantum wells and InAs quantum
dot lasers that provide 1.3-μm emission on a GaAs
substrate have been developed. However, their reliability and modulation speed still need to be
improved. Another approach is to use a metamorphic
buffer on GaAs [1]–[3]. This technique enables us to
use materials with a lattice constant between that of
InP and GaAs and to make a 1.3-μm-range laser on a
GaAs substrate with good temperature characteristics.
2.

Metamorphic growth technique

The metamorphic growth technique allows us togrow a material whose lattice constant is different
from that of the substrate. Therefore, we can design
the device materials without being constrained bysubstrate lattice-constant limitations. In this study, weused an InGaAs layer grown on a GaAs substrateunder special conditions by metal-organic vapor
phase epitaxy (MOVPE). Conventionally, strain
relaxation occurs if the strained layer thicknessexceeds the critical thickness and threading dislocations appear in the upper layer and the surface tends
to become rough. With metamorphic growth, a stabledislocation network is formed in the thin layer
between GaAs and the InGaAs buffer layer, whichleads to a low threading dislocation density in theupper layer. We can regard this layer as a virtual
InGaAs substrate because the strain is fully relaxed
and there is little surface roughness. Transmission
electron microscope images of a fabricated metamorphic laser are shown in Fig. 3. We confirmed that thedislocations are concentrated at the buffer boundary
and the dislocation density is low enough to make ahigh-performance laser.
3. Fabrication and characteristics
A schematic of the fabricated metamorphic laser isshown in Fig. 4. The metamorphic buffer consists of
n-doped In0.12Ga0.88As 1.6 μm thick (n: negative).
The In0.1Ga0.9As layer with reduced indium content
on this metamorphic buffer is fully relaxed and acts
as a virtual InGaAs substrate. The n-InGaAlAs lower
cladding layer is lattice matched to the virtual
In0.1Ga0.9As substrate. The active layer consists ofthree compressive-strained InGaAs quantum wells
sandwiched between In0.1Ga0.9As barrier layers. The
p-InGaP upper cladding has the same refractive index
and lattice constant as the lower n-InGaAlAs cladding (p: positive). We chose InGaAlAs for the lower
NTT Technical Review

Feature Articles

cladding because it has better surface roughness than
InGaP cladding. On the other hand, we chose InGaP
for the upper cladding because it has the advantage ofletting us make a ridge structure by wet chemical
etching. This technique enables a narrow ridge structure and single lateral mode operation. We made andevaluated a Fabry-Pérot-type laser structure.
The temperature dependence of the output power isshown in Fig. 5. This device had a 200-μm-long cavity. One facet had a highly reflective coating and theother was in the as-cleaved condition. Insets show thelasing spectra at various currents at room temperature. We confirmed high output power and lasing at
up to 140°C. Eye diagrams obtained with 10-Gbit/s
non-return-to-zero direct modulations are shown in
Fig. 6. We confirmed clear eye openings from 25°C
to 100°C and the potential for making an uncooled
light source.

p-electrodep-InGaAs: 200 nm
p-InGaP cladding:1500 nm

i-InGaAs SCH: 120 nm
InGaAs/GaAs,
6 QWs

i-InGaAs SCH: 120 nm
n-InAlGaAs cladding: 1500 nm
In0.1Ga0.9As: 100 nm
Metamorphic buffer
n-In0.12Ga0.88As: 1600 nm

4. Improvements in temperature characteristics

n-GaAs (100) substraten-electrodeAs mentioned above, a metamorphic laser consistsof materials whose lattice constants are between
those of InP and GaAs, so the design is very flexible.

i: intrinsic

Fig. 4 . Schematic of fabricated metamorphic laser.

Cavity length: 200 µm
One facet: as-cleaved
Other facet: highly reflective coating
Continuous wave operation
(c)

15

25˚C

40˚C

Intensity (dBm)

SiO2,
polyimide–30(c)Ibias=70 mA

–50
–70
1250

55˚C

1275
1300
Wavelength (nm)

1325

70˚C
10

Intensity (dBm)

Output power (mW)

–10

(b)
85˚C

100˚C

–10

(b)
Ibias=40 mA

–30
–50
–70
1250

5

1275
1300
Wavelength (nm)

(a)

130˚C
142˚C

0
0

20

40

60

80

Current (mA)

100

120

140

Intensity (dBm)

115˚C
–10
–30

1325

(a)
Ibias=10 mA

–50
–70
1250

1275
1300
Wavelength (nm)1325

Fig. 5. Temperature dependence of output power and lasing spectra.

Vol. 10 No. 12 Dec. 2012Feature Articles(a) 25°C(b) 85°C(c) 100°C

Fig. 6. 10-Gbit/s eye diagrams of metamorphic laser.

InGaAlAs electron
stopper layer

Electrons

n-InGaAlAs
cladding

SCH andbarrierp-InGaP
cladding
1.3-µm emission

MQWs

Holes

Fig. 7. Band diagrams of improved device using an InGaAlAs electron stopper.

25°C

10

135°C

9

145°C

8
Output power (mW)

35°C
45°C
55°C
65°C
75°C
85°C
95°C
105°C
115°C
125°C

155°C

7

165°C

6
5

175°C

4

185°C

3
195°C

2

200°C

1
0
0

50

100

150

200

250

300

Current (mA)

Fig. 8. I-L characteristics of improved devices.

For the cladding materials, we used n-InGaAlAs
and p-InGaP for the reasons mentioned above. We
newly introduced a p-InGaAlAs layer as an electron
stopper into the p-InGaP cladding and obtained
improved temperature characteristics.
The temperature dependence of the I-L (injection
current versus output light power) characteristics of
1200-μm-long devices is shown in Fig. 8. The temperature dependence of the threshold current was
lower than in the case without an electron stopper
layer. The maximum operating temperature is as highas 200°C, compared with 175°C for the laser without
an electron stopper layer. The characteristic temperature T0, which indicates the threshold increase as afunction of temperature, was improved from 80 K to220 K. T0 at temperatures between T1 and T2 (in °C)
is expressed as
Ith(T2) =Ith(T1)·exp ((T2-T1)/T0).

We are optimizing the device structure by performing
simulations and experiments. Here, we report someof our results. Band diagrams of a metamorphic laser
before and after improvement are shown in Fig. 7.


By contrast, a conventional laser on an InP substrate has a characteristic temperature between 50 K
and 80 K. With its high characteristic temperature,
the metamorphic laser exhibits only a small increasein threshold current at high temperature. Therefore,
NTT Technical Review

Feature Articles

environments where the temperature exceeds 100°C
in an integrated circuit.
5. Concluding remarks

Fig. 9. Eye diagram for improved device for 10-Gbit/s lowbias operation.

We are conducting trials of low-power-consumption light sources using a metamorphic laser. Thislaser offers high-speed operation and good temperature characteristics, which enable it to operate withlow power consumption. In the future, we will apply
this technique to a distributed feedback laser and integration with other types of substrates.
References

the operating current for uncooled operation can be
reduced, which makes this laser a good candidate fora low-power-consumption light source.
The eye diagram of a 200-μm-long device for directmodulation below 85°C is shown in Fig. 9. The bias
current for 10-Gbit/s modulation below 85°C is as
low as 15 mA, which is about half the value for aconventional laser on an InP substrate and lowpower-consumption operation was confirmed. We
believe that this laser can be used as a light source in

Masakazu Arai

Senior Research Engineer, Crystal Growth andFabrication Process Research Group, NTT Photonics Laboratories.
He received the B.E., M.E., and Ph.D. degrees
from Tokyo Institute of Technology in 1999,
2001, and 2003, respectively. During his Ph.D.
work, he was engaged in the design and fabrication of vertical cavity surface-emitting lasers.
From April 2003 to March 2004, he was at the
P&I Lab, Tokyo Institute of Technology as a
post-doctoral scientist. He joined NTT Photonics
Laboratories in 2004. He has been engaged inresearch on the MOVPE growth of III-V semiconductors and the development of semiconductor lasers. He is a member of the IEEE Photonics
Society and the Japan Society of Applied Physics(JSAP).

[1]
[2]

[3]

T. Uchida, H. Kurakake, H. Soda, and S. Yamazaki, “1.3 µm InGaAs/
GaAs strained quantum well lasers with InGaP cladding layer,” Electron. Lett., Vol. 30, No. 7, pp. 563–565, 1994.
I. Tångring, S. M. Wang, M. Sadeghi, A. Larsson, and X. D. Wang,“Metamorphic growth of 1.25–1.29 µm InGaAs quantum well lasers
on GaAs by molecular beam epitaxy,” Journal of Crystal Growth, Vol.
301–302, pp. 971–974, 2007.
M. Arai, T. Fujisawa, W. Kobayashi, K. Nakashima, M. Yuda, and Y.
Kondo, “High-temperature operation of 1.26 µm Fabry-Perot laser
with InGaAs metamorphic buffer on GaAs substrate,” Electron Lett.,Vol. 44, No. 23, pp. 1359–1360, 2008.

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.

Wataru Kobayashi

Researcher, Crystal Growth and Fabrication
Process Research Group, NTT Photonics Laboratories.
He received the B.S. and M.S. degrees inapplied physics and the Ph.D. degree in nanoscience and nanoengineering from Waseda University, Tokyo, in 2003, 2005, and 2011, respectively. He joined NTT Photonics Laboratories in2005. He has been engaged in R&D of opticalsemiconductor devices. He is a member of theInstitute of Electronics, Information and Communication Engineers (IEICE).

Vol. 10 No. 12 Dec. 2012Feature Articles: Optical Semiconductor Technologies
for Photonic Networks

Current-injection
Photonic-crystal Laser
Takaaki Kakitsuka and Shinji Matsuo
Abstract

This article introduces current-injection photonic-crystal lasers featuring ultralow power consumption, which were achieved by using photonic-crystal nanocavities and small buried active regions fabricated through a crystal regrowth process. They should provide light sources suitable for future lowerpower-consumption information and communications technology (ICT) devices.

1. Introduction
1.1 Development of photonic networks
Photonic networks have been developed for longreach optical-fiber communications (telecom).
Recently, optical communication technologies havebegun to be applied to short-reach data transmission
in datacenters (datacom) as optical interconnections
between routers and datacenters and between racks
and between electronic circuit boards, as shown in
Fig. 1. The next challenge is photonic networks forinter-chip and intra-chip transmission (computercom)
in microprocessors.
The development has been driven by the explosive
growth in information volume on networks including
the Internet with the spread of FTTH (fiber to thehome), which has increased the need for high-speed
information processing at datacenters. Informationand communications technology (ICT) devices withlarge information capacities, high functionality, andhigh-speed operation have been developed. TheseICT devices use electrical data transmission, but thetransmission capacity per pin in a microprocessor islimited and an increase in the transmission capacity
necessitates greater power consumption. Photonic
networks based on wavelength division multiplexing(WDM) are suitable for high-capacity transmission.
In addition, the energy consumption per bit is expected to be lower for optical transmission than for electrical transmission for high-speed operation. Therefore, the application of optical interconnection and
WDM-based photonic networks to short-reach datatransmission has begun to be discussed.
1.2 Optical sources for photonic networks
Photonic networks consist of various kinds of optical devices: the most essential one is a semiconductor
laser as a light-emitting device. The relationships
between the active region areas of semiconductor
lasers and their energy costs are shown in Fig. 2. In
general, semiconductor lasers with larger active
regions can generate higher output power, but require
higher injection current for high-speed modulationand thus have a higher energy cost. For long-reachtelecom applications, semiconductor lasers with large
active regions are essential because high output
power is required. For short-reach applications, on
the other hand, semiconductor lasers with small
active regions are essential because of the greaterneed to reduce their energy costs. Vertical cavity surface emitting lasers (VCSELs), which can haveshorter cavity lengths and smaller active regions,have recently begun to be applied to datacom applications. However, even VCSELs have limits on how
much the active region can be reduced in size. For
computercom use, the energy cost of a semiconductor
laser should be less than 10 fJ/bit, which requires asemiconductor laser with an active region smaller
than 1 µm2, as shown in Fig. 2. Such lasers have notbeen achieved yet. NTT has focused on photonic
crystal, which has the potential to enable the fabrication of semiconductor lasers with tiny cavities andsmall active regions.

NTT Technical Review

Feature Articles

Telecom

Datacom

Computercom

Datacenter

BackboneLD

Switch and filter

PD

Metro area
CMOS chip
AccessUser
Long-haul

WAN

LAN

Rack/board

Chip

Trend of optical transport
LAN: local area network
LD: laser diodePD: photodiode
WAN: wide area network

Fig. 1. Trend of short-reach photonic network.

104
Telecom

Energy cost (fJ/bit)

103
Edge-emitting
laser

Datacom

InP

102
Computercom

1.00 µm

Fig. 3. SEM image of photonic crystal.

Nanocavity laser

101

100
10–1

100

101

102

103

Active region area (µm2)

Fig. 2. Energy cost of semiconductor lasers.

2. Photonic crystal
A photonic crystal is an artificial structure whoserefractive index is periodically modulated with submicrometer periodicity [1]. A scanning electron
microscope (SEM) image of a two-dimensional photonic crystal with periodically placed air holes in theVol. 10 No. 12 Dec. 2012

InGaAsP quantum well

VCSEL

semiconductor slab is shown in Fig. 3. The semiconductor and air have significantly different refractive
indices, and their periodic placement in the photonic
crystal prevents light of a particular wavelength fromexisting in the semiconductor. This behavior, which islike a photonic insulator, is a feature of a photonic
crystal. If some air holes are removed in a linear fashion (creating a line defect structure) from a twodimensional photonic crystal with a slab structure, as
shown in Fig. 3, then the lightwave can exist in theline defect region. In other words, the line defect acts
as a waveguide. In this way, photonic crystals cancontrol lightwaves by the alignment and size of the
air holes.

Feature Articles

Conventional photonic-crystal laser(horizontally uniform layer structure)(a) Carrier and optical confinement

LEAP laser(buried heterostructure)
Cavity mode
(optically confined)

InGaAsP slab(c) Carrier and optical confinement

InP buried slab
Active region(b) Heat diffusion

Carrier diffusion

Small heat diffusion
InGaAsP slab

InGaAsConfined carrier Active region(d) Heat diffusion
Large heat diffusion
Inp
InGaAs

InP substrate

InP substrate

Fig. 4. Comparison of the conventional photonic-crystal laser and LEAP laser.

3. Lambda-scale embedded active region
photonic-crystal (LEAP) laser
Various photonic-crystal lasers have been reported;
however, most of them are fabricated using a horizontally uniform layer slab structure, like InGaAsP
MQW (multiple quantum well) with high thermal
resistance, as illustrated in Figs. 4(a) and (b). The
semiconductor laser needs to confine both light andelectrical charge carriers in the active region for lasing. Therefore, ordinary semiconductor lasers have adouble-heterostructure, in which the active region issandwiched by wide-bandgap semiconductors. However, photonic-crystal lasers with a horizontally uniform layer structure can confine only light not carriers because they cannot have a double-heterostructure
horizontally against the substrate. Therefore, the lasing characteristics of photonic-crystal lasers with thehorizontally uniform layer structure are significantly
limited because their performance is adversely affected by carrier diffusion and a temperature rise. To
solve these problems, we have utilized a structurewith the active region limited to within a line defectin the photonic crystal slab (buried heterostructure)(Figs. 4(c) and (d)). We call this laser the lambdascale embedded active-region photonic-crystal laser,or LEAP laser for short. Since the refractive index ofthe active region (InGaAsP- or InGaAlAs-based
MQW) is higher than that of the region burying it(InP), the lightwave is strongly confined in the active
region. The active region can also confine carriers
because its bandgap is smaller than that of the burying region. In addition, the thermal conductivity of
InP (68 W/m∙K) is higher than that of InGaAsP (4W/m∙K) and this enables effective heat diffusion (Fig.
4(d)).
The advantages of the buried heterostructure areshown in Fig. 5. The optical input-output characteristics of optically pumped photonic-crystal lasers using
an optical pump wavelength of 0.98 µm and pumping
diameter of 4 µm were numerically simulated. In theconventional photonic-crystal laser with the horizontally uniform layer structure, generated carriers
spread outside the cavity and the low thermal conductivity causes a significant rise in temperature. Sincehigh temperature degrades the optical properties of
the active region, the laser’s resulting output power islow. On the other hand, in a buried-heterostructure
laser with an active region of 4 × 0.3 µm2, carriers arestrongly confined in the active region and the temperature rise is negligible. Therefore, high output
power can be obtained at room temperature. The useof the buried heterostructure is expected to greatly
improve the lasing characteristics of photonic-crystal
NTT Technical Review

Feature Articles(b) Buried heterostructure(a)Temperature distribution
420(K)
400
380
360
340
320
300

∆T = 2.5°C

76Output power (µW)

5
CavityBuriedheterostructure

4

Carrier distribution(c) Horizontally uniform layer structure

3

Temperature distribution∆T = 120°C

2
Horizontally uniform
layer structure

1
0
0

50

100

150

200

Carrier distribution
420(K)
400
380
360
340
320
300

Input power (µW)

Fig. 5. Simulated lasing characteristics: (a) light-in light-out (L-L) curve, (b) temperature distribution and carrier distributionof the buried heterostructure and (c) horizontally uniform layer structure at input power of 200 μW.

lasers.
Taking advantage of NTT’s expertise in laser fabrication, especially crystal regrowth techniques forsemiconductors, we successfully fabricated the buried-heterostructure active region in the line-defectwaveguide in the photonic crystal slab. The size of theactive region is 5 × 0.3 × 0.15 µm3. Input and output
interfaces are easily fabricated using line-defectwaveguides. We have successfully demonstrated
optically pumped photonic-crystal lasers operatingwith power consumption of less than 10 fJ/bit [3].
4. Current-injection LEAP laser
We made an optically pumped LEAP laser using
the buried heterostructure for the first time. However,for practical use in a photonic network, current-injection operation is essential. Current-injection operation of a semiconductor laser requires a pin-junction(p: positive-type semiconductor, i: intrinsic semiconductor, n: negative-type semiconductor). In ordinary
lasers, the pin-junction is fabricated in the direction
perpendicular to the substrate. Since the LEAP laser
Vol. 10 No. 12 Dec. 2012

needs a slab structure, a pin-junction in the perpendicular direction is difficult to fabricate. We fabricated a pin-junction in the plane of the photonic-crystal
slab by using Zn diffusion and Si ion implantation
into the non-doped InP burying region. The fabricatedcurrent-injection LEAP laser is shown in Fig. 6(a).
This is the world’s first current-injection photoniccrystal laser operating with continuous-wave light atroom temperature [4]. We achieved a threshold current of 0.39 mA. High-speed modulation at 10 Gbit/s
and energy cost of 170 fJ/s were also demonstrated.
However, initial devices suffered from a large leakage
current, which limited the resulting reductions inthreshold current and energy cost despite the active
region being small. The origin of the leakage current
was the InGaAs etching layer sustaining the air
bridge. The small bandgap of InGaAs causes the current leakage. We successfully reduced the leakage
current by using InAlAs, which has a larger bandgap
than InP, instead of InGaAs for the etching layer. The
measured current-light-output curve is shown in
Fig. 6(b). Lasing with a very low threshold current of
14 µA was successfully demonstrated at roomFeature Articles

(b)

(a)

1.6
1.4
Output power (µW)

e

p-e

lect

trod
le c

rod

n-e

e

Active region

p-InP(Zn diffusion)n-InP(Si ion implantation)

1.2

25.0°C

1.0
40.0°C0.8

80.1°C0.6
0.4

90.2°C0.2
0.0

60.0°C

95.0°C
0

50

100
150
Current (µA)

200

Fig. 6. (a) Structure and (b) lasing characteristics of current-injection LEAP laser.

temperature (25°C). The use of an InGaAlAs-MQW
active region enabled high-temperature operation up
to 95°C. These figures for low threshold current andhigh operating temperature are records for photonic-crystal lasers [5].

References
[1]

[2]

5. Conclusion
The LEAP laser is a key device for future photonic
networks with large capacity and low power consumption. We believe that current-injection LEAP
lasers operating with power consumption of less than
10 fJ/bit will be achieved in the near future. We willcontinue our research and development toward integration of the LEAP laser with silicon photonics andCMOS (complementary metal oxide semiconductor)
and ultimately aim at devices integrating microprocessors and photonic networks.



[3]

[4]

[5]

M. Notomi, “Manipulating Light by Photonic Crystals,” NTT Technical Review, Vol. 7, No. 9, 2009.
https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr2009
09rp1.html
S. Matsuo, A. Shinya, T. Kakitsuka, K. Nozaki, T. Segawa, T. Sato, Y.
Kawaguchi, and M. Notomi, “High-speed ultracompact buried heterostructure photonic-crystal laser with 13 fJ of energy consumed per
bit transmitted,” Nat. Photon., Vol. 4, No. 9, pp. 648–654, 2010.
S. Matsuo, A. Shinya, C.-H. Chen, K. Nozaki, T. Sato, Y. Kawaguchi,
H. Taniyama, and M. Notomi, “20-Gbit/s directly modulated photonic crystal nanocavity laser with ultra-low power consumption,”Opt. Express, Vol. 19, No. 3, pp. 2242–2250, 2011.
S. Matsuo, K. Takeda, T. Sato, M. Notomi, A. Shinya, K. Nozaki, H.
Taniyama, K. Hasebe, and T. Kakitsuka, “Room-temperature continuous-wave operation of lateral current injection wavelength-scale
embedded active-region photonic-crystal laser,” Opt. Express, Vol. 20,
No. 4, pp. 3773–3780, 2012.
T. Sato, K. Takeda, A. Shinya, K. Nozaki, H. Taniyama, W. Kobaya­
shi, K. Hasebe, T. Kakitsuka, M. Notomi, and S. Matsuo, “95°C cw
Operation of InGaAlAs Multiple-quantum-well Photonic-crystal
Nanocavity Laser with Ultra-low Threshold Current,” Proc. of theIEEE Photonics Conference, WF-2, Burlingame, California, USA,2012.

NTT Technical Review

Feature Articles

Takaaki Kakitsuka

Senior Research Engineer, Nano-structure
Photonic Device Research Group, Advanced
Opto-electronics Laboratory, NTT Photonics
Laboratories and NTT Nanophotonics Center.
He received the B.S. and M.S. degrees in physics and the Dr.Eng. degree from Kyushu University, Fukuoka, in 1994, 1996, and 2012, respectively. He joined NTT Opto-electronics Laboratories in 1996. He has been engaged in researchon semiconductor lasers and optical functional
devices. From 2009 to 2011, he was in NTT
Research and Development Planning Department. He is a member of the IEEE Photonics
Society, the Institute of Electronics, Information
and Communication Engineers (IEICE), theJapan Society of Applied Physics (JSAP), and
the Physical Society of Japan.

Vol. 10 No. 12 Dec. 2012

Shinji Matsuo

Senior Research Engineer, Supervisor, Group
Leader, Nano-structure Photonic Device
Research Group, Advanced Opto-electronics
Laboratory, NTT Photonics Laboratories and
NTT Nanophotonics Center.
He received the B.E. and M.E. degrees in electrical engineering from Hiroshima University in1986 and 1988, respectively and the Ph.D. degree
in electronics and applied physics from Tokyo
Institute of Technology in 2008. In 1988, hejoined NTT Opto-electronics Laboratories,
Atsugi, where he was engaged in research on
photonic functional devices using MQW-pin
modulators and VCSELs. In 1997, he researched
optical networks using WDM technologies at
NTT Network Innovation Laboratories, Yokosuka. Since 2000, he has been researching highspeed tunable optical filters and lasers for photonic packet switching and photonic-crystal
lasers for computercom applications at NTT
Photonics Laboratories, Atsugi. He is a memberof the IEEE Photonics Society, IEICE, and
JSAP.



Regular Articles

Advertising EffectivenessMeasurement Using Crowd
Measurement and Facial Image
Processing Techniques
Hiroyuki Arai, Naoki Ito, Kaori Kataoka,
and Yukinobu Taniguchi
Abstract

As digital signage becomes more common, there is increasing need for camera-based techniques thatcan measure the effectiveness of advertising. NTT is researching and developing 1) a crowd measurement
technique to measure the number of people at a location; 2) a transient-audience measurement technique
to measure the number of people passing through that location; and 3) a face detection, orientation
estimation, and attribute classification technique to detect faces in an image and estimate the age and sexof each person. Version 3 of our advertising effectiveness measurement system combines these threetechniques.

1. Introduction
Digital signage is rapidly becoming common atplaces where people gather, such as stations and commercial facilities, as a tool for providing services suchas information guides and advertising. Its usage formats have recently diversified to include studies on its
application as a means of providing information during disasters, and digital signage is expected to permeate all aspects of our lives in the future [1].
Concerning the spread of digital signage, we areseeing the start of advertising distribution in a format
in which the media companies that own the signage
sell advertising spots (locations and times for displaying ads) and advertisers purchase those spots to display their ads. This is raising questions about how
much effectiveness can be expected for a given
expenditure and whether the resultant effectivenessmatches expectations, so it has become necessary tomeasure and comprehend the advertising effectiveness of digital signage.
In simple terms, advertising effectiveness has many
facets, such as the exposure effectiveness (how manypeople does the advertising reach), perception effectiveness (what impressions and information are given
to the audience), and action effectiveness (by how
much does the number of customers or sales volume
increase), which are similar to television programviewing rate and website page views. Of these, exposure effectiveness is thought to be a basic and also
common index as a foundation for comprehending
advertising effectiveness. For digital signage, exposure effectiveness is assumed to be information suchas the number of people at that location—the total
number of people at a given instant (total audience)and the number of people passing through (transient
audience)—and, of those, the number of people actually looking at the screen and their attributes (sex andage) (Fig. 1).
NTT has developed three techniques that use images captured by cameras with the aim of applying themto the measurement of digital signage advertising
effectiveness: 1) a crowd measurement technique [2]that measures the total number of people at a location,2) a transient audience measurement technique thatmeasures the total number of people passing throughNTT Technical Review

Regular Articles

Signage(display screen)

Area from which
signage can be seen

Number and attributes (ageand sex) of people actuallylooking at the screen

Number of people at that location- Total number of people at that instant- Number of people passing throughFig. 1. Assumed advertising effectiveness index of digital signage.

that location, and 3) a face detection, orientation estimation, and attribute classification technique [2] that
detects faces in an image and estimates the orientations of those faces and the age and sex of thosepeople. The latest version V3 (version 3) of ouradvertising effectiveness measurement system integrates these techniques. Below, we overview theseimage processing techniques and our advertising
effectiveness measurement system V3.
2. Image processing techniques
2.1 Crowd measurement technique
The crowd measurement technique developed at
NTT can measure the total number of people within
an image at the instant it was acquired. Previous techniques for measuring the total number of people in animage generally involve detecting specific shapes
such as the whole body or upper half of each person
in an image, or following individual moving objects
within a series of images (using a tracking technique),or a combination of those. However, those previous
techniques can suffer from occlusion, whereby one
person is superimposed on another in the image, as
shown in the upper part of Fig. 2, which makes correct detection difficult. For that reason, previous
techniques have the problem that they can be applied
only to comparatively limited numbers of people(such as about 5–10).
NTT’s crowd measurement technique [2] estimates
Vol. 10 No. 12 Dec. 2012

the total number of people within an image in a manner that avoids the effects of occlusion by utilizing thearea of an image. It works by modeling the geometrical relationships between the camera, floor, and people and the geometrical relationships between themin the image, as shown in the lower part of Fig. 2. Thisapproach is completely different from those of previous techniques in that it does not detect each person
individually, but makes it possible to estimate
approximately how many people are there overall.
The features of this technique are that it can estimate
the number of people in a crowded situation and it
enables the use of general-purpose cameras that arepointing obliquely downward. A more detailed
description is given in Ref. [3].
2.2 Transient audience measurement techniqueTransient audience measurement is a techniqueused in a location that people pass through, such as apassageway, in order to measure how many people
pass through it. This has already been partially implemented as a technique for measuring the transient
audience from an image. In a typical setup of the current method, the camera is attached to a high pointsuch as the ceiling; it captures images taken in the
downward direction, and the technique determines
the transient audience number by image analysis.
Although one of the features of the conventional
method is that it enables accurate measurement, it is
only applicable to a limited area because measurementRegular Articles

Conventional method

Detection is difficult when crowded.

Scaning from edge of image

Target pattern

4 people?

2 people

Crowd measurement technique (NTT)
Estimation of number of people
from surface area

Estimation of number of people
including occlusions

Pixel
Image

CameraSurface area
Image and geometrical model

About 2 people

About 7 people

Can be used even with large crowds (on theorder of 50 to 100 people)

Fig. 2. Overview of crowd measurement techniques.

is possible only under the camera or nearby, whichmakes it difficult to measure the transient audience inan entire passageway or station concourse, for example.
To measure within a wider range, it is necessary to
install a camera that points obliquely downward anduse images captured within a wide range. A previous
technique that can be applied in such a case is called
tracking. This detects each person individually froman image and traces that person’s movement path.
Various improvements have already been made to thetracking technique, but the occlusion problem (people
overlapping or being hidden in the images) inevitably
makes it difficult to perform stable measurements inplaces such as station passageways, and the processing results can drop greatly for a crowd.
To exceed the limitations of the existing techniques,
NTT has developed a transient audience measurement technique that uses an approach that is completely different from previous ones. It calculates the
final transient audience by combining two tech

niques: a fluid analysis technique that is applied forcrowded conditions and a one-dimensional tracking
technique aimed at greater measurement accuracy inuncrowded condition.
2.2.1 Fluid analysis technique (measurement
algorithm applied to crowds)
The fluid analysis technique can estimate the transient audience by treating the overall flow of people
as if it were the flow of a fluid. The basic concept isshown in Fig. 3, where to simplify the explanation,
we show the view directly downward whereas inpractice the processing is done on images captured bya camera pointing obliquely downward. In general,
the flow rate of a liquid or gas in a pipe can be calculated as the product of the pipe’s cross-sectional area,
the fluid’s speed, and the fluid’s density; however,this concept can also be applied to a flow of people.
In other words, when the processing area is set on animage or on the floor, we can calculate the transient
audience (flow rate) at a later stage if we have (1) thedensity (number of people within the area) and (2) the
NTT Technical Review

Regular Articles* To simplify the explanation, this shows a view from directly above.
After
fixed time

Measurement area

(1) Density (number of people
within the area)

×(2) Speed (average speed of all
people)Transientaudience

Fig. 3. Overview of fluid analysis for transient audience measurement.

movement speed of people. We can calculate thenumber of people within the area (1) by using thecrowd measurement technique described above andwe can calculate their speed (2) by taking several
consecutive images in a time series and detecting corresponding pairs of feature points and considering thesimilarity of their feature vectors. Note that since
perfect correspondence is rare, we chose to use analgorithm that determines speed through a voting
mechanism, which can avoid the influence of featurepoint miscorrespondence. Note also that the description relates to one-way flow, for simplicity, but inpractice it is also applicable to flows in both directions in passageways. This technique enables us tocalculate the transient audience in a stable manner,even in locations such as a crowded station concourse, specifically in a state where there are several
dozen people, e.g., 50 or 100, in front of the screen.
2.2.2 O ne-dimensional tracking technique(measurement algorithm during quiet
times)
The fluid analysis technique described above has
the great advantage that it enables stable measurement even when the area is crowded, but it does havethe disadvantage that the accuracy is insufficient during quiet times when the number of people is between
one and five. To overcome that disadvantage, we havedeveloped a one-dimensional tracking technique thatcan measure highly accurately during quiet times andalso enables rapid processing (Fig. 4). It detects theimage area to which a moving object belongs, forms
an input image series, and projects that area in a oneVol. 10 No. 12 Dec. 2012

dimensional version in accordance with a conversion
coefficient called a weighting value. The theoreticalbackground of the weighting value is given in Ref.
[3]. The results of this processing are such that a peakin the projected values corresponds to the position ofa person, and the sum of projected values in the vicinity of that peak corresponds to the number of people
in that vicinity (the number of people contributing tothat peak). We can measure the transient audience foreach direction of movement by estimating the personnumber at each peak in the projected values andsimultaneously following their positions.
Note that the final transient audience is computedby creating a weighted average of the numbers
obtained by fluid analysis and one-dimensional tracking. The weight is adjusted to suit the congestion
level, which is estimated by the crowd measurement
technique described in section 2.1.
2.3 F
 ace detection, orientation estimation, andattribute classification technique
The face detection, orientation estimation, andattribute classification technique developed at NTT
picks out faces within images, estimates the orientation of each detected face, and estimates the attributes(sex and age) of that person. These three processes
share the same fundamentals in common: each process pre-analyzes a large quantity of image data gathered beforehand and utilizes that analysis in making
its decisions (Fig. 5).
Examples of attribute classification are given
below. First of all, a large volume of image data of theRegular Articles

Input image

Weighting value
Foreground pixels

Foreground image

The sum of the projected value
at each peak corresponds tothe number of people.

Projection ofweighting value*

Tracking while
specifying thenumber of people
at each peak

Number of people
being tracked

2

1 0* Weighting value: conversion coefficient from surface
area to audience number

Fig. 4. Overview of one-dimensional tracking technique.

While scanning the retrieval window, the system
calculates feature vectors and compares them withones in dictionaries.

Recognition
dictionaries

Results
Face
detection

Calculation andstatistical analysisof feature vectors

Faceorientation
estimation• Position of face
• Orientation of face
• Attributes(age and sex)Comparison

Attribute
identification

Image being
processed

Large quantityof facial images

Advance processing

Detection and classification processing

Fig. 5. Overview of face detection, orientation estimation, and attribute classification technique.

faces of people of both sexes and various different
ages, captured from various different angles, isgathered beforehand. A feature vector, which is thedigitization of the features of the entire face, is calculated for each facial image. Then, for each age andsex group, the technique analyzes what kind of distri

bution the feature vectors have. The analysis results
are called a recognition dictionary. During the actual
processing, the system decides which age and sex
group the face belongs to by calculating the feature
vectors for the entire face in a manner similar to therecognition dictionary creation process, for the face
NTT Technical Review

Regular Articles

Audience graph
20
15

Personal computer

Total no.
of people
No. paying
attention

10

Camera5–5Images–4–3–2Time (minutes)
before image
0 was captured–1

Attribute ratio graph

Signage(display)

Sex
Male

Female

35–49

50+

Age
(years)19

20–34

Image recognition
Transient audience graph
20

Forwarddirection
Backward
direction

10

–15

–10

–5

0

Fig. 6. Overview of advertising effectiveness measurement system V3.

area within the image detected by the face detection
processing, and by comparing them with those in therecognition dictionary.

keting segments which denote females between theages of 20 and 34 as F1 and males between the agesof 35 and 49 as M2.

3. Advertising effectivenessmeasurement system V3

4. Conclusion

Our advertising effectiveness measurement system
V3 combines the above-described crowd measurement technique; transient audience measurement
technique; and face detection, orientation estimation,
and attribute classification technique. It can measure
the advertising effectiveness index of digital signage.
An overview is shown in Fig. 6. The abovementioned
image processing is done while camera images arebeing imported to a personal computer, and theresults are output as log data in real time. The system
can use either one or two cameras and perform processing in one of the following two formats: (1) all of
the image processing is done by one camera or (2)face detection, orientation estimation, and attributeclassification are done by the camera close to thesignage while the crowd measurement and transient
audience measurement are done by the second camera, which captures a wider range. The attribute classification results are output in accordance with marVol. 10 No. 12 Dec. 2012

This article introduced image processing techniques for measuring the advertising effectiveness ofdigital signage and the measurement system V3. We
will proceed with implementing these techniques asmethods of measuring digital signage advertising
effectiveness. In addition, since these techniques
could be applied to fields other than digital signage,
such as marketing information acquisition and safety
management support in locations where large numbers of people gather, such as stations and various
event facilities, we would like to proceed with not
only the advertising effectiveness of digital signage
but also validation of its applicability to fields such as
safety management support in various locations.
References[1]

K. Muramoto, “Digital Signage Standardization,” NTT Technical
Review, Vol. 10, No. 10, 2012.
https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr2012
10gls.html

Regular Articles[2]

T. Kinebuchi, H. Arai, I. Miyagawa, S. Ando, K. Kataoka, and H.
Koike, “Image Processing Techniques for Measuring Advertising
Effectiveness of Digital Signage,” NTT Technical Review, Vol. 7, No.
12, 2009.
https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr2009
12sf2.html

Hiroyuki Arai

Senior Research Engineer, Image Media Processing Group, Visual Media Project, NTT
Media Intelligence Laboratories.
He received the M.S. degree in physics andPh.D. degree in information science from Hokkaido University in 1991 and 2009, respectively.
Since joining NTT in 1991, he has been engaged
in research on map recognition systems, image
processing, and pattern recognition. He was a
fellowship researcher of the Natural Vision Project of the National Institute of Information andCommunications Technology of Japan (NICT)
from 2000 to 2005. He is a member of the Institute of Electronics, Information and Communication Engineers (IEICE), and the Institute of
Image Information and Television Engineers ofJapan.

Naoki Ito

Research Engineer, Image Media Processing
Group, Visual Media Project, NTT Media Intelligence Laboratories.
He received the M.E. degree from Toyohashi
University of Technology, Aichi, in 2001. He
joined NTT in 2001 and engaged in research on
character recognition. He moved to NTT EASTin 2004 and engaged in the development of security systems. He moved to NTT Cyber Space
Laboratories in 2008. As a result of organizational changes in July 2012, he is now in NTT
Media Intelligence Laboratories. He is a memberof IEICE.



[3]

H. Arai, I. Miyagawa, H. Koike, and M. Haseyama, “Estimating Number of People Using Calibrated Monocular Camera Based on Geometrical Analysis of Surface Area,” IEICE Trans. on Fundamentals ofElectronics, Communications and Computer Sciences, Vol. E92-A,
No. 8, pp. 1932–1938, 2009.

Kaori Kataoka

Research Engineer, Image Media Processing
Group, Visual Media Project, NTT Media Intelligence Laboratories.
She received the B.S. and M.S. degrees inphysics from Waseda University, Tokyo, in 1998
and 2000, respectively. Since joining NTT CyberSpace Laboratories in 2000, she has been
engaged in research on image processing andpattern matching. As a result of organizationalchanges in July 2012, she is now in NTT MediaIntelligence Laboratories. She is a member of
IEICE.

Yukinobu Taniguchi

Senior Research Engineer, Supervisor, ImageMedia Processing Group, Visual Media Project,
NTT Media Intelligence Laboratories.
He received the B.E., M.E., and Dr.Eng.
degrees in mathematical engineering from the
University of Tokyo in 1990, 1992, and 2002,
respectively. He joined NTT Human Interface
Laboratories in 1992. As a result of organizational changes in July 2012, he is now in NTT
Media Intelligence Laboratories. He received theBest Paper Award from IEICE in 2000. He is amember of IEICE, the Information Processing
Society of Japan, and the Association for Computing Machinery.

NTT Technical Review

Global Standardization Activities

Report on ITU Radiocommunication
Assembly 2012 andITU World Radiocommunication
Conference 2012
Masashi Nakatsugawa
Abstract

This report summarizes the activities and outcomes of the Radiocommunication Assembly 2012 (RA12) and World Radiocommunication Conference 2012 (WRC-12), which were held from January to
February 2012 in Geneva, Switzerland. RA and WRC are the major conferences of ITU-R (International Telecommunication Union, Radiocommunication Sector).

1. Radiocommunication Assembly 2012
The Radiocommunication Assembly (RA) convenes before the World Radiocommunication Conference (WRC) to approve draft Recommendations
prepared by Study Groups (SGs) of ITU-R (International Telecommunication Union, Radiocommunication Sector), to review and approve draft ITU-R
Resolutions which describe the working methods andprocesses of the SGs, to evaluate the activities of theSGs, and to approve the Questions and structure of
the SGs including the appointment of SG Chairmen
and Vice-Chairmen for the next study period. RA-12[1], [2] was held on January 16–20, 2012, at the Centre International de Conférences Genève (CICG) in
Switzerland. 526 participants attended the conference
from 102 Member States. There were 28 Japanesedelegates, of which eight were from NTT and NTT
DOCOMO.
The structure of RA-12 is shown in Fig. 1. Under
the Plenary, which manages the coordination over theentire conference activities, five committees, COM1
to COM5, were established. Among these committees, COM4 and COM5 handled the items related tothe procedures and processes of the SG activities.



1.1 Approval of draft Recommendations
RA-12 considered the draft Recommendations prepared by the SGs. Four (three new and one revised)draft Recommendations were approved, while one
was referred back to the SG for reconsideration. Oneof the new Recommendations was ITU-R M.2012,
which defines detailed specifications for IMTAdvanced radio interfaces (IMT: International
Mobile Telecommunications). Two radio interfaces,
LTE-Advanced based on 3GPP and WirelessMANAdvanced based on IEEE, were included in the Recommendation (LTE: Long Term Evolution, 3GPP:
3rd Generation Partnership Project, MAN: metropolitan area network). The objective of the draft
revised Recommendation that was not approved wasto cease adjustment of UTC (coordinated universaltime) with a leap second. Three main opinions wereexpressed: to support the revision (USA, Japan, andsome others), to oppose the revision (UK, China, andsome others), and to require more information before
forming an opinion (Arab and African countries). It
was difficult to reach a consensus. RA-12 decided torequest further study by SG7 and to propose that theissue be discussed at WRC-12 as an agenda item fora future WRC.

NTT Technical Review

Global Standardization Activities

COM1 Steering
Chairman: Dr. A. R. Jamieson (New Zealand)

COM2 Budget control
Chairman: Mr. N. A. Bin Hammad (UAE)Plenary
Chairman:
Dr. A. R. Jamieson(New Zealand)

COM3 Editorial
Chairman: Mr. C. Rissone (France)

COM4 Structure and work programmeof the SGs
Chairman:Dr. B. Arbesser-Rastburg (ESA)WG4A Work programme
WG4B Resolutions relating to SG activities
WG4C New technologies
WG5A Working methods

COM5 Working methods of the
RA and SGs
Chairman: Dr. R. Haines (USA)WG5B Liaisons and term of office
WG5C SC and other mattersFig. 1. Structure of RA-12.

1.2 Approval of ITU-R Resolutions
RA-12 reviewed ITU-R Resolutions defining various matters concerning ITU-R activities. It approved
32 (6 new and 26 revised) ITU-R Resolutions andsuppressed one. New Resolutions include a study on
the technical requirements for utilizing cognitive
radios, a study on reducing the energy consumptionof wireless communication systems to reduce greenhouse gas emissions, a study on the spectrum usageof electronic news gathering (ENG) systems for
global/regional harmonization, and agreement for
academic organizations to participate in ITU-R
activities. Revised Resolutions describe working procedures and methods applied for SG activities; clarifying the provisions for approval of ITU-R Recommendations that are not based on Questions; facilitation of the procedure for simultaneous adoption andapproval (PSAA) without the two-stage correspondence process and reduction of the voting period
from 3 months to 2 months; and guidelines for electing SG Vice-Chairman to balance the distribution
between region, gender, and expertise, for facilitating
participation by developing countries, and for determining the total number of Vice-Chairmen taking
account of the SG workload.

Vol. 10 No. 12 Dec. 2012

1.3 Approval of Questions
RA-12 approved 223 Questions including a study
on technologies and performance of radio communication systems for the smart grid system and assessment of the impact on the existing systems, future
trends in millimeter-wave fixed radio systems, andinvestigation of super-high-vision systems.
1.4 Appointment of the Chairman and ViceChairmen of each SG
The structure of the SGs in the previous study
period was maintained (Fig. 2). The Chairman andVice-Chairmen of each SG were elected. Dr. Akira
Hashimoto (NTT DOCOMO), Noriyuki Kawai(KDDI), and Yukihiro Nishida (NHK) were elected
as Chairman of SG5, Vice-Chairman of SG4, andVice-Chairman of SG6, respectively.
2. World Radiocommunication Conference 2012
WRC is the largest ITU-R international conference.
It is normally held every three or four years to update
the Radio Regulations (RR). The RR provide international rules and regulations for spectrum allocation toradio services, use of satellite orbits, and administrative and operational procedures for radio stations, allGlobal Standardization Activities

SG1 Spectrum management
Chairman: Dr. S. Y. Pastukh (Russian Federation)
Vice-Chairmen: 11
SG3 Radiowave propagation
Chairman: Mr. B. Arbesser-Rastburg (ESA)
Vice-Chairmen: 8
SG4 Satellite services
Chairman: Mr. C. Hofer (USA)Vice-Chairmen: Mr. N. Kawai (KDDI) and 9 others
SG5 Terrestrial services
Chairman: Dr. A. Hashimoto (NTT DOCOMO)
Vice-Chairmen: 11
SG6 Broadcasting service
Chairman: Mr. C. Dosch (Germany)
Vice-Chairmen: Mr. Y. Nishida (NHK) and 11 others
SG7 Science services
Chairman: Mr. V. Meens (France)
Vice-Chairmen: 5

Fig. 2. SG structure, and the Chairmen and Vice-Chairmen.

Japan's seats were located far back on the ground floor because they were assigned
according to French alphabetical order.

Fig. 3. View of the main conference room.

of which are needed for the use of radio waves. WRC12, which was preceded by RA-12, was held for aperiod of four weeks from 23 January to 17 February
2012 at the same venue as RA-12 [3], [4]. Approximately 3000 participants from 160 Member States

attended (Fig. 3); there were 71 delegates from Japanin WRC-12, among which eight were from the NTT
Group (NTT and NTT DOCOMO).
The structure of WRC-12 is shown in Fig. 4. Under
the Plenary, there were seven Committees: theNTT Technical Review

Global Standardization Activities

COM1 Steering
Composed of the Chairman and Vice-Chairmen of the Conference plus the
Chairmen and Vice-Chairmen of the Committees.

COM2 Credentials
Chairman: Mr. Y. K. Selek (Turkey)

COM3 Budget Control
Chairman: Mr. B. Gracie (Canada)

WG4A Radiolocation
Plenary

COM4 Aeronautical, Maritime, etc.
Chairman: Mr. J. Mettrop (UK)

Chairman:Mr. T. Al Awadhi(UAE)

WG4B Aeronautical
WG4C Maritime and amateur
WG5A Science

COM5 Satellite etc.
Chairman: Mr. M. Abe (Japan)

WG5B Satellite
WG5C Fixed, Mobile and Broadcasting
WG6A General issues

COM6 WRC-15 agenda item etc.
WG6B Regulations update
Chairman: Mr. A. Zourmba (Cameroon)
WG6C Agenda items for future WRC

COM7 Editorial
Chairman: Ms. M. T. Alajouanine (France)

Fig. 4. Structure of WRC-12.

Steering Committee, Credentials Committee, Budget
Control Committee, Editorial Committee, and three
Committees for specific agenda items. The WRC-12
agenda items are shown in Fig. 5 and some of them
are discussed below.
2.1 W orldwide/regional harmonization of spectrum for electronic news gathering (ENG)(A.I. 1.5)
This agenda item was intended to identify a common frequency for electronic news gathering (ENG).
The conclusion, reached after enthusiastic discussionthat resulted in no frequency being identified for
ENG, was that it is possible to avoid the impact on
existing broadcasting and telecommunications services in Japan. Since ITU-R Resolution 59 was
adopted to promote the development of the databasesummarizing the frequencies available for ENG ineach country, a WRC Resolution on the frequency
Vol. 10 No. 12 Dec. 2012

database of existing services was not adopted.
2.2 L ong-term spectrum availability for the aeronautical mobile-satellite (R) service in the
bands 1525–1559 MHz and 1626.5–1660.5
MHz (A.I. 1.7)
Procedures such as frequency coordination meetings were considered because of increasing demand
for aircraft communications. Japan sought flexibility
in frequency coordination for Multi-functional Transport Satellite (MTSAT).
As a result, methods for objectively determining
spectrum requirements were adopted, and it was
specified that there would be a call for a meeting of
the notifying administrations to review the issues if
unsatisfactory points were found in the coordination
result. Thus, a new frequency coordination procedure
was implemented toward the new spectrum that Japanrequired.
Global Standardization Activities

A.I. 1.1
A.I. 1.2
A.I. 1.3
A.I. 1.4

To delete country footnotes or to have country name deleted from footnotes, if no longer required
Enhancing the international regulatory framework
To consider spectrum requirements and possible regulatory actions in order to support the safe operation of UAS
Introduction of new aeronautical mobile (R) service (AM(R)S) systems in the bands 112−117.975 MHz, 960−1164 MHz and5000−5030 MHz
A.I. 1.5
Worldwide/regional harmonization of spectrum for electronic news gathering (ENG)
A.I. 1.6
Spectrum use by the passive services between 275 GHz and 3000 GHz, and possible procedures for free-space optical-links
A.I. 1.7
Long-term spectrum availability for the aeronautical mobile-satellite (R) service in the bands 1525−1559 MHz and 1626.5−
1660.5 MHz
A.I. 1.8
Technical and regulatory issues relative to the fixed service in the bands between 71 GHz and 238 GHz
A.I. 1.9
New digital technologies for the maritime mobile service
A.I. 1.10 Frequency allocation requirements with regard to operation of safety systems for ships and ports and associated regulatory
provisions
A.I. 1.11 A primary allocation to the space research service (Earth-to-space) within the band 22.55−23.15 GHz
A.I. 1.12 To protect the primary services in the band 37−38 GHz from interference resulting from aeronautical mobile service operations
A.I. 1.13 Spectrum usage of the 21.4−22 GHz band for the broadcasting-satellite service and the associated feeder-link bands in Regions
1 and 3
A.I. 1.14 Implementation of the radiolocation service in the range 30−300 MHz
A.I. 1.15 Possible allocations in the range 3−50 MHz to the radiolocation service for oceanographic radar applications
A.I. 1.16 Passive systems for lightning detection in the meteorological aids service in the frequency range below 20 kHz
A.I. 1.17 To ensure the adequate protection of mobile service and other services in the band 790−862 MHz in Regions 1 and 3
A.I. 1.18 Radiodetermination-satellite service (space-to-Earth) allocations in the band 2483.5−2500 MHz
A.I. 1.19 Regulatory measures and their relevance, in order to enable the introduction of software-defined radio and cognitive radio
systems
A.I. 1.20 Spectrum identification for gateway links for high altitude platform stations (HAPS) in the range 5850−7075 MHz
A.I. 1.21 Primary allocation to the radiolocation service in the band 15.4−15.7 GHz
A.I. 1.22 Effect of emissions from short-range devices on radiocommunication services
A.I. 1.23 Allocation of about 15 kHz in parts of the band 415−526.5 kHz to the amateur service on a secondary basis
A.I. 1.24 Extending existing allocation to the meteorological-satellite service in the band 7750−7850 MHz to the band 7850−7900 MHz
A.I. 1.25 Possible additional allocations to the mobile-satellite service
A.I. 2To examine the revised ITU-R Recommendations incorporated by reference in the Radio Regulations
A.I. 4
To review the resolutions and recommendations of previous conferences
A.I. 7
Possible changes of procedures for frequency assignments pertaining to satellite networks
A.I. 8.1
Report of the Director of the Radiocommunication Bureau
A.I. 8.1.1 Activities of the Radiocommunication Sector;
Issue A: Protection of radiocommunication services against interference from ISM equipment
Issue B: Updating of the “Remarks” columns in the Tables of Article 9A of Appendix 30A and Article 11 of Appendix 30 to theRadio Regulations
Issue C: Earth observation applications
A.I. 8.1.2 Difficulties or inconsistencies encountered in the application of the Radio Regulations
A.I. 8.1.3 Action in response to Resolution 80 (Rev.WRC-07)
A.I. 8.2
Items for inclusion in the agenda for the next WRC

Fig. 5. WRC-12 agenda items.

2.3 T echnical and regulatory issues related to the
fixed service in the bands between 71 GHz
and 238 GHz (A.I. 1.8)
Sharing conditions between fixed service (FS) andpassive services such as radio astronomy and theEarth Exploration-Satellite Service (EESS) in the
bands between 71 GHz and 238 GHz were considered. There were two conflicting positions—nochange to the current RR to promote studies on fixedwireless system (FWS) or the introduction of a mandatory spectrum emission mask to protect passive
service—and a compromise was sought. The final
agreement was to introduce recommended values forthe spectrum mask with revision of Resolution 750.
As the footnote concerning mask implementation


allows administrations to continue to use their existing spectrum mask, no modifications to Japan’s regulation are needed. Moreover, study activities at ITUR have been reinforced because Resolutions 731 and732, which were the basis of the sharing study, wereretained with some revisions.
2.4 A primary allocation to the space researchservice (Earth-to-space) within the band
22.55–23.15 GHz (A.I. 1.11)
New frequency allocation to the space researchservice (SRS) (Earth-to-space), e.g., SELENE2, wasconsidered under this agenda item. Japan has someexisting systems offering FS in the band being considered, such as entrance links to mobile base stations
NTT Technical Review

Global Standardization Activities

and subscriber radio.
Spectrum at 22.55–23.15 GHz was newly allocatedto SRS (Earth-to-space), which is in line with theJapanese proposal. The operation and development of
FS in the band 22.55–23.15 GHz is not constrained
because of the very limited number of SRS earth stations in the world and because their locations should
be sufficiently far from international borders inaccordance with the restriction specified in the relevant footnote.

MHz and 6560–6640 MHz, were identified for the
HAPS gateway links in Australia and four Africancountries for national use. Requisites are to satisfy
sharing conditions described in the ITU-R Report toprotect existing services and to gain explicit consent
from administrations possibly affected by the HAPS
gateway links before operation commences. Although
Japan has its FWS in the band being considered, there
will be no problem if sharing conditions are satisfied.

2.5 P
 ossible allocations in the range 3–50 MHz tothe radiolocation service for oceanographic
radar applications (A.I. 1.15)
This item treats a proposal to allocate spectrum tooceanographic radars performing sea surface monitoring for wave heights, ocean currents, and large
objects’ tracks. The need for data to mitigate theeffects of disasters, including tsunamis, to observe
climate change, and to ensure safe maritime travel led
to consideration of a new spectrum allocation for
operational use by oceanographic radar networks.
Eight frequency bands were newly allocated to theradiolocation service, including the band (24,450–
24,600 kHz) proposed by Japan.

2.8 P ossible additional allocations to the mobilesatellite service (A.I. 1.25)
New spectrum allocation to the mobile-satellite
service (MSS) from several candidate bands was considered. Japan tried to avoid allocation to MSS of thenationally allocated bands used for broadcasting andtelecommunication services. There was no allocation
to MSS under this agenda item, but a new agenda
item for WRC-15, to consider a new allocation to
MSS in the range 22–26 GHz, was approved.

2.6 R egulatory measures and their relevance, inorder to enable the introduction of softwaredefined radio and cognitive radio systems(A.I. 1.19)
It was considered whether RR revisions wereneeded to enable the introduction of software-definedradio (SDR) and cognitive radio (CR) systems, andthe conclusion was that no changes were needed.
Regarding CR, the RCC (Regional Commonwealthin the Field of Communications) insisted that new
WRC Resolutions be produced, while APT (Asia
Pacific Telecommunity), CITEL (Inter-American
Telecommunication Commission), CEPT (European
Conference of Postal and Telecommunications
Administrations) were of the view that no such Resolution was needed. Finally, Resolution 956 was suppressed, and a new WRC Recommendation wasapproved.
2.7 S
 pectrum identification for gateway links forhigh altitude platform stations (HAPS) (A.I.
1.20)
Spectrum identification for gateway links for highaltitude platform stations (HAPS) in the range 5850–
7075 MHz was considered. Two bands, 6440–6520
Vol. 10 No. 12 Dec. 2012

2.9 I tems for inclusion in the agenda for the nextWRC (A.I. 8.2)
The agenda items for the next WRC in 2015 (WRC15) are shown in Fig. 6. Among them, the following
items were proposed by Japan.
-	to consider additional spectrum allocations to themobile service on a primary basis and identification of additional frequency bands for IMT(International Mobile Telecommunications) andrelated regulatory provisions, to facilitate thedevelopment of terrestrial mobile broadband
applications-	to consider possible additional primary allocations to the fixed-satellite service (FSS) (Earthto-space) of 250 MHz in Region 2 and 300 MHz
in Region 3 within the range 13–17 GHz-	to consider a primary allocation to the radiolocation service for automotive applications in the
77.5–78.0 GHz frequency band
In addition, the following agenda items were proposed by other regional organizations or produced
from the discussions at RA-12 or WRC-12.
-	to examine the results of ITU-R studies on theuse of the frequency band 694–790 MHz by themobile (except aeronautical mobile) service inRegion 1 and take the appropriate measures-	to consider the use of frequency bands allocatedto the FSS not subject to Appendices 30, 30A andGlobal Standardization Activities

A.I. 1.1
Additional frequency bands for International Mobile Telecommunications (IMT)
A.I. 1.2
Use of the frequency band 694−790 MHz by the mobile service in Region 1
A.I. 1.3
Broadband public protection and disaster relief (PPDR)
A.I. 1.4
Amateur service on a secondary basis within the band 5250−5450 kHz
A.I. 1.5
Use of frequency bands allocated to the FSS for unmanned aircraft systems (UAS)
A.I. 1.6
To consider possible additional primary allocation:
A.I. 1.6.1 Fixed-satellite service of 250 MHz in the range between 10 GHz and 17 GHz in Region 1
A.I. 1.6.2 Fixed-satellite service of 250 MHz in Region 2 and 300 MHz in Region 3 within the range 13−17 GHz
A.I. 1.7
Use of the band 5091−5150 MHz by the FSS (Earth-to-space)
A.I. 1.8
Earth stations located on board vessels (ESVs)
A.I. 1.9
To consider:
A.I. 1.9.1 Fixed-satellite service in the frequency bands 7150−7250 MHz and 8400−8500 MHz
A.I. 1.9.2 Possibility of allocating the bands 7375−7750 MHz and 8025−8400 MHz to the maritime-MSS
A.I. 1.10 Mobile-satellite service within the frequency range from 22 GHz to 26 GHz
A.I. 1.11 Primary allocation for the Earth exploration-satellite service (Earth-to-space) in the 7−8 GHz range
A.I. 1.12 Extension of the allocation to the EESS (active) in the frequency band 9300−9900 MHz by up to 600 MHz
A.I. 1.13 Possibility of increasing the 5 km distance limitation for the space research service (space-to-space) allocation
A.I. 1.14 Continuous reference time-scale, whether by the modification of UTC or some other method
A.I. 1.15 On-board communication stations in the maritime mobile service
A.I. 1.16 New Automatic Identification System (AIS) to improve maritime radiocommunication
A.I. 1.17 Possible spectrum requirements and regulatory actions to support wireless avionics intra-communications (WAIC)
A.I. 1.18 Primary allocation to the radiolocation service for automotive applications in the 77.5−78.0 GHz frequency band
A.I. 2To examine the revised ITU-R Recommendations incorporated by reference in the Radio Regulations
A.I. 4
To review the resolutions and recommendations of previous conferences
A.I. 7
Possible changes, and other options of procedures for frequency assignments pertaining to satellite networks
A.I. 8
To delete country footnotes or to have country name deleted from footnotes, if no longer required
A.I. 9
Report of the Director of the Radiocommunication Bureau
A.I. 10
Items for inclusion in the agenda for the next WRC

Fig. 6. WRC-15 agenda items.

3. Future activities
Most of the revised RR signed by administrations at
WRC-12 (Fig. 7) will take effect internationally fromJanuary 2013. In line with this, Japanese laws andregulations will also be updated and revised in 2012.
As the agenda items for WRC-15 include spectrum
allocations to specific systems such as IMT and FSS,
it should draw worldwide attention to these matters.
The NTT Group will continue to make contributions
to the ITU-R and APG (APT Conference Preparatory
Group) meetings toward WRC-15.
References
Fig. 7. Indication of signed Administrations.

[1]
[2]

30B for the control and non-payload communications of unmanned aircraft systems in non-segregated airspaces-	to consider the feasibility of achieving a continuous reference time-scale, whether by the modification of UTC or some other method



[3]
[4]

ITU-R RA-12.
http://www.itu.int/ITU-R/index.asp?category=conferences&rlink=ra-12&lang=en
Ministry of Internal Affairs and Communications, “Results of ITU
RA-12,” Jan. 2012 (in Japanese).
ITU-R WRC-12.
http://www.itu.int/ITU-R/index.asp?category=conferences&rlink=wr
c-12&lang=en
Ministry of Internal Affairs and Communications, “Results of ITU
WRC-12,” Feb. 2012 (in Japanese).

NTT Technical Review

Global Standardization Activities

Masashi Nakatsugawa

Executive Manager, Wireless Access Systems
Project, NTT Access Network Service Systems
Laboratories.
He received the B.E. degree in electronics andcommunication engineering and the M.E. degree
in electrical engineering from Waseda University,
Tokyo, in 1987 and 1989, respectively, and the
M.S. degree in electrical engineering from the
California Institute of Technology, USA, in
1999. He joined NTT Radio Communication
Systems Laboratories in 1989. His researchexperience includes MMIC circuit design, packaging technology, software-defined radio, andwide-area wireless access systems. From 2010 to2012, he was a senior manager at the Radio Division, Technical Planning Department, NTT,
where he was involved in regulatory and standardization activities for wireless systems. He iscurrently responsible for the development offundamental technologies for wireless accesssystems. He received the 1996 Young Engineer
Award from the Institute of Electronics, Information and Communication Engineers (IEICE), andthe YRP Award from the YRP (Yokosuka
Research Park) R&D Promotion Committee in
2002. He is a member of IEEE, IEICE, and theJapan Society of Applied Physics.

Vol. 10 No. 12 Dec. 2012

Practical Field Information about
Telecommunication Technologies

Weather-resistance Tests for
Recycled Polyethylene
Abstract

This article reports on weather-resistance tests performed on recycled plastic materials by the Technical Assistance and Support Center to evaluate the effectiveness of resource-saving technologies. Since
the formulation of the NTT Global Environmental Charter in 1991, the NTT Group has been increasingly committed to deploying resource-saving technologies in its telecommunication facilities toward a
recycling-oriented society. In 2002, both NTT EAST and NTT WEST began to deploy communication
cables using recycled plastic materials collected during facility upgrading and to design facilities so thatthe communication infrastructure makes a positive contribution to global environment protection
efforts.
This is the fourteenth in a bimonthly series on the theme of practical field information about 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.

1. Introduction
Communication cables extend for a total of two
million kilometers throughout Japan and new cable
deployment in conjunction with facility upgrading
continues on a daily basis. Plastic materials in communication cables are used for the cable jacket andfor the dielectric layer between the signal line andground line in metallic cable. In particular, polyethylene (PE) is widely used in communication cables
because of its high shock resistance, superior electrical insulation properties, and low-loss characteristics
as an insulator.
PE is the leading type of plastic produced in Japan(Table 1). There has been much interest in ways ofrecycling some of the base material from spent PE inorder to save resources, and many manufacturers are
pursuing the development of PE recycling technologies. The NTT Group has to deal with a huge amountof communication cables, and the use of recycled PE
in communication cables could make a big contribution to the creation of a recycling-oriented society
from the viewpoint of resource saving. With this inmind, the NTT Group has been promoting the deployment of cables using recycled PE.


2. Weather-resistance test forrecycled plastic materials
2.1 Test conditions
Many types of communication facilities requirelong-term reliability of 10 years or more. These
include communication cables, which are used forlong periods of time after initial installation, so longterm reliability is a requirement. In addition, communication cables must be deployable in a variety ofenvironments including communication buildings,
underground tunnels, and outdoor settings. It is generally known that PE deteriorates under ultraviolet
light and heat. Thus, when PE is intended to be used
for the communication cable jackets, its long-term
reliability in an outdoor environment is an important
issue.
Before recycled communication cables using recycled PE for their outer jackets are deployed, they arechecked to determine whether they pass standard
performance tests with respect to weather resistance.
However, their weather-resistance characteristics
should be checked in real environments when facilities are being studied to ensure that they will exhibit
high reliability and when maintenance plans are
NTT Technical Review

Practical Field Information about Telecommunication Technologies

Table 1. Plastic production by type.
Unit: 1000 tons
2000

2005

2010

Polyethylene (PE)

3342

3240

2684

Polypropylene

2721

3063

2467

Vinyl chloride resin

2410

2151

1602

Styrene resin

2024

1734

1265

Polyethylene terephthalate (PET)

699

684

572

Other thermoplastic resins

1561

1787

1463

Thermohardening resins

1457

1286

920

Other resins

233

199

211

14,44614,145

11,185

Ratio of PE production to total plastic production 23.13%

22.91%

24.00%

Total

Source: The Japan Plastics Industry Federation

Fig. 1. R ecycled PE samples set up at an outdoor exposure site. The magnified view on theright shows sheen remaining.

being formulated. Weather-resistance testing data isalso extremely valuable for facility optimization
design work, which is an ongoing endeavor. Consequently, the Technical Assistance and Support Centerhas been planning outdoor exposure experiments targeting recycled PE in actual environments and is currently conducting a verification experiment on thelong-term reliability of cable outer jackets using
recycled material. The plan for this verification
experiment is outlined below. (In this article, wereport on deterioration characteristics for exposure
periods up to 7 years.)
1)	Exposure periods/location: Samples shall be
exposed in an outdoor environment at a locationin Okinawa for fiscal years 2004–2014 andshall be collected and evaluated 1, 3, 5, 7, and10 years after installation. The experimental
setup for outdoor sample exposure is shown in
Fig. 1.
2)	Evaluation standards and items: A tensile test
conforming to in-house standards shall be perVol. 10 No. 12 Dec. 2012

formed to evaluate tensile strength and elongation.
3)	Samples: Samples having 0%, 50%, and 100%
recycled material shall be prepared for comparison purposes. A sample shall be in the formof a sheet 1.0 mm thick.
4)	Tensile test: From a sample sheet that has been
subjected to the exposure test for a scheduled
number of years, No. 3 test specimens conforming to JIS K 6251 shall be punched out andsubjected to a tensile test at a speed of 200 mm/
min using a high-precision, universal testingmachine (Shimadzu Scientific Instruments
Autograph AG-X (Fig. 2)). The number ofsamples per test shall be 5.
2.2 Test results (for 7-year test)
This section presents the results of weather-resistance tests obtained to date for samples exposed forseveral periods up to 7 years. Using the pre-exposuretest characteristics of the samples for reference, wePractical Field Information about Telecommunication Technologies

 A tensile test is performed after
both ends of the sample havebeen fixed to the equipment.
 Elongation and tensile strength
are measured until the sample
breaks.
Sample shape: JIS K 6251 No. 3

Sample shape diagram

Fig. 3. S urface of recycled PE sample after 7 years of
outdoor exposure.

Fig. 2. Tensile test machine and sample shape.

Relative tensile strength (%)

130
120

Tensile strength gradually increased.

110
100
90
80

Percentage of recycled PE

70

0%

50%

100%

60
50
Initial

1

3

5

7

Fig. 4. Change in tensile strength.

examined the changes in these characteristics after
the test. Specifically, we took a sample that had been
subjected to the exposure test for the specified time
period and first made a visual inspection of its surface. We then evaluated the sample’s rate of elongation and tensile strength by means of a tensile test.
1)	Visual surface inspection: We found that samples collected from the exposure-test site had
become distorted from their original shape. We
also noticed that they retained their sheen(Fig. 1 (right)) and that no significant traces ofultraviolet-light deterioration were evident. A
scanning electron microscopy image of the surface of a sample exposed in an actual outdoor
environment for 7 years is shown in Fig. 3. The
magnification is ×3000. While some unevenness could be seen in the sample’s surface, nocracks or similar defects could be observed on
the surface despite the long exposure.
2)	Tensile test: We collected samples exposed foreach of the scheduled test periods and subjected
them to a tensile test. Results are shown in
Figs. 4 and 5.
Figure 4 plots the average value and variation (indicated by an error bar) for five samples of the relative
fracture strength (as a percentage of the initial value)
after each scheduled exposure period. These results
show that the tensile strength of the sample PE gradually increased as the sample deteriorated throughexposure. This indicates that a sample of this material
hardens as a result of deterioration, which is how
ordinary PE behaves when left to deteriorate.
Figure 5 plots the change in the magnitude of elongation at sample fracture (as a percentage of the initial value) for each exposure period. The vertical axis
shows the relative elongation. The change over the
7-year period shows that the amount of elongation
tended to decrease as deterioration progressed. We
NTT Technical Review

Practical Field Information about Telecommunication Technologies

Relative elongation (%)

130

Elongation gradually decreased.

120
110
100
90
80
70

Percentage of recycled PE

60
50

0%
Initial

1

50%
3

100%
5

7

Fig. 5. Change in elongation.

conclude that the material’s hardening with deterioration made elongation increasingly difficult, which isthe same behavior as shown by ordinary PE. A comparison of sample characteristics for different mixing
ratios of recycled materials (0%, 50%, and 100%)
showed no substantial observable differences in tensile strength or elongation retention.
Moreover, for all mixing ratios, the elongation rateof freshly produced recycled material (data notshown) sufficiently exceeded the valued specified in
the domestic standard for using such material for acommunication cable outer jacket (NTT-required
elongation rate: 400% or greater).
The above results show that using recycled PE forcommunication cable outer jackets in an outdoor
environment presents no problems in long-term useof at least 7 years.
3. Summary
It has been 10 years since NTT EAST and NTT
WEST began to use recycled PE in the outer jacketsof metal cable used for communication purposes.
Fortunately, there have been no field reports of problems with recycled PE, which suggests that theweather-resistance standards applied at the time ofVol. 10 No. 12 Dec. 2012

deployment were valid. We think that the data presented in this report reinforces the validity of thosestandards. Specifically, the results of our study showthat recycled PE used in outdoor communication
facilities has stable characteristics for at least 7 years
in actual environments.
The NTT Group in involved in a variety of activities
for reducing environmental load. We think that thestraightforward material evaluation described in thisreport is an important means of judging the validity ofsuch activities and of providing valuable data for
improving facility technologies in the future.
4. Concluding remarks
We presented the results of weather-resistance tests
for recycled PE used in communication cable outer
jackets. We hope that the information provided here
contributes to the reader’s understanding of communication-facility materials. In addition to tests related
to the materials introduced here, the Technical Assistance and Support Center is also investigating problems in facilities and equipment with undeterminedcauses. If you have a problem that cannot be
explained, please consult with us at the Technical
Assistance and Support Center.

External Awards
GFP2012 Best Innovation Design Paper Award (3rd place)
Winners: Rai Takahashi (Rai Kou), Hiroshi Fukuda, Tai Tsuchizawa,
Hidetaka Nishi, Tatsuro Hiraki, and Koji Yamada, NTT Microsystem
Integration Laboratories
Date: August 31, 2012
Organization: IEEE 9th International Conference on Group IV Photonics (GFP2012)
For “Silicon/silica-hybrid delay line interferometer for DPSK
demodulation”.
A 1-bit delay line interferometer based on silicon/silica-hybrid
waveguides is demonstrated for a differential phase-shift keying(DPSK) demodulator. A 10-Gb/s non-return-to-zero DPSK signal isdemodulated with error-free operation in telecommunications
bands.
Published as: R. Kou, H. Fukuda, T. Tsuchizawa, H. Nishi, T. Hiraki,
and K. Yamada, “Silicon/silica-hybrid delay line interferometer for
DPSK demodulation,” Proc. of 2012 IEEE 9th International Conference on Group IV Photonics (GFP), pp. 174–176, San Diego, CA,
USA.
Best Paper Award
Winners: Takuya Otsuka, Takashi Aoki, Eiichi Hosoya, and Akira
Onozawa, NTT Microsystem Integration Laboratories
Date: September 20, 2012
Organization: IEEE Computer Society, MCSoC201
For “An Image Recognition System for Multiple Video Inputs overa Multi-FPGA System”.
A multi-user shared FPGA-based cloud computing platform ispresented for an image recognition application with multiple video
inputs (FPGA: field programmable gate array). The platform is madeof a sea of FPGA devices connected as a hierarchical ring network.
The users place IP (Internet protocol) cores called tiles on the platform and connect them together to form a sequence. An architecturefeaturing a parallel pipeline of tiles and an intra-tile selector network
was chosen to let users work their own tile sequences in parallel
without causing any interference with other users.
A set of application programming interfaces (APIs) for writingtiles, deleting tiles, and configuring the intra-tile selector network is
implemented. With the APIs, the system manipulates the tiles on

FPGAs in response to users’ demands. The platform is suitable forrunning applications requiring low-latency and high-throughput
data-processing capability. A HOG (histograms of oriented gradients) feature extractor and a Real AdaBoost classifier are implemented to perform image recognition.
Published as: T. Otsuka, T. Aoki, E. Hosoya, and A. Onozawa, “AnImage Recognition System for Multiple Video Inputs over a MultiFPGA System,” Proc. of 2012 IEEE 6th International Symposium on
Embedded Multicore SoCs (MCSoC 2012), Aizu-Wakamatsu, Fukushima, Japan.
Outstanding Paper Award
Winners: Dinesh Babu Jayagopi†1, Dairazalia Sanchez-Cortes†1,
Kazuhiro Otsuka†2, Junji Yamato†2, and Daniel Gatica-Perez†1†1	 Idiap Research Institute†2 NTT Communication Science Laboratories
Date: October 25, 2012
Organization: ACM ICMI2012 (14th ACM International Conference on Multimodal Interaction)
For “Linking Speaking and Looking Behavior Patterns with Group
Composition, Perception, and Performance”.
This paper addresses the task of mining typical behavioral patterns
from small-group face-to-face interactions and linking them tosocial-psychological group variables. Towards this goal, we definegroup speaking and looking cues by aggregating automaticallyextracted cues at the individual and dyadic levels. Then, we define abag of nonverbal patterns (bag-of-NVPs) to discretize the group cues.
The topics learnt using the Latent Dirichlet Allocation (LDA) topic
model are then interpreted by studying the correlations with groupvariables such as group composition, group interpersonal perception,and group performance. Our results show that both group behavior
cues and topics have significant correlations with (and predictive
information for) all the above variables. For our study, we use interactions with unacquainted members i.e., newly formed groups.
Published as: D. B. Jayagopi, D. Sanchez-Cortes, K. Otsuka, J.
Yamato, and D. Gatica-Perez, “Linking Speaking and Looking
Behavior Patterns with Group Composition, Perception, and Performance,” Proc. of the International Conference on Multimodal Interaction (ICMI), Santa Monica, USA, 2012.

NTT Technical Review