R&D Spirits
Planar Lightwave Circuit Technology: The Key toConstructing Large-capacity Optical Networks
Yasufumi Yamada
Department Director
Design Department
Planar Lightwave Circuits GroupPhotonics Business GroupNTT Electronics Corporation

As Fiber to the Home (FTTH) continues to expand, one promising approach to ensuring sufficient network transmission capacity is planar lightwave circuit (PLC) technology for fabricating optical integrated circuits. This technology is being developed by NTT Electronics Corporation (NEL), the major hardware manufacturer in the NTT Group. What features does NEL’s
PLC technology provide, and what strategy will NEL adopt to stay ahead of its competitors? We
put these and other questions to Yasufumi Yamada, manager of the Planar Lightwave Circuits
Group.

Keeping one step ahead of the competition
through next-generation multifunction
technologies

technology platform for designing and manufacturing PLC products to devising cost-reduction measures and upgrade techniques.

—Dr. Yamada, could you summarize your current
R&D activities for us?

—What is the current trend in PLC products andtechnology and what is NEL’s approach?

In the Planar Lightwave Circuits Group of NEL*, I
manage the development and design of PLC products. “PLC” refers to optical circuits formed bydepositing a film of silica glass on a silicon substrate
and processing that layer to form optical waveguides.
Today, as the move to FTTH progresses, it is becoming essential to ensure enough transmission capacity
between offices to enable the processing of hugeamounts of traffic. The key to achieving this is various types of wavelength-multiplexing products
including optical power splitters, arrayed-waveguidegrating (AWG) optical multiplexers/demultiplexers,
optical switches, variable optical attenuators, andoptical couplers. In our group, we are working onPLCs from a total perspective, from establishing aTo put it simply, there is a shift taking place fromsingle-function products to multifunction products.
At present, the current focus of the PLC business ison single-function products like optical splitters andAWGs. However, we are beginning to see the commercialization of multifunction products as next-generation products. I think that the PLC business will
become centered on these multifunction products inabout one or two years’ time (Figs. 1(a) and 1(b)). Ialso believe that this trend proves that the market for
PLC products is growing. Up to now, NEL has shownconsiderable strength in achieving exceptional performance in individual products while also providing
an extensive lineup of products. Our competitors,
however, have recently begun to flex their muscles
and competition is intensifying. We must find waysof differentiating NEL from its competitors, so we arefocusing our energy on developing innovative multi-* http://www.nel-world.com/

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R&D Spirits

1st generation

Optical power
splitter

VOA/AWG module

Multiple functions
Arrayed waveguidegrating (AWG)

2nd generation
Variableopticalattenuator

IN1
IN2VOA

IN3

AWG

OUT···

IN32Signal
monitorPhotograph of the V-AWG
Integration
3rd generation

Reconfigurable
add/drop
multiplexer

Fig. 1(a). PLC generations.

AWG
temp. Power VOA
control monitor control
Module controller

Customer
control
module

VOA: variable optical attenuator
MSA: multi-source agreement

Fig. 1(b). Example of 3rd-generation products.
(MSA compatible V-AWG (VOA+AWG))

function products.

trends in technologies that we excel in.

—What are some of the technical issues surrounding
product development?

—What lies ahead in your research?

One thing that slows up the manufacturing of PLC
products is the fiber connection process. In general,fibers can be connected by fusing, but connecting acable having ten, twenty, or even more fibers can beextremely time-consuming since those fibers must beconnected one at a time. Moreover, most of this work
is done manually, so using a less costly labor force
overseas is one obvious way for a company to differentiate itself in the PLC business. However, we feelthat such an approach is unbecoming to NEL. We’dmuch rather find a technical solution to this problem.
One possibility here is optical wiring board technology that attempts to apply the same ideas behind
an electrical wiring board to light. Another idea is toinstall a connector on the board to enable one-touchconnection. Yet another is PLC direct-connection
technology that I myself researched during my days
at NTT Laboratories. This technology achieves fiberless connection using a PLC having a fairly complicated structure. In any case, taking the best technology from our research results at NEL and turning it
into new products is a strong point of the NTT Group,
which is known for its collective strength. Making
use of this, I believe that we ourselves can create
Vol. 3 No. 1 Jan. 2005

Our main problems for the time being are how tocreate products with a stable level of quality using
existing technology and how to create them at low
cost. Then, once we have reached a certain level inthis regard, our next task is to reduce the amount ofmanual labor that goes into PLC products, as I justmentioned. And while some areas of PLCs are still at
the research stage, needs are growing, and we’d liketo get our new products out the door in one to twoyears.

Maintaining top share through technicalexpertise and brand power—What are other companies up to in regard to PLC
technology and product development?
Despite the severe competition in the PLC business,
I think it would be fair to say that NEL is strongest at
this point in time. As I mentioned earlier, the main
focus in terms of products is currently on AWGs andsplitters. If we examine how the share for these twoproducts breaks down among various manufacturers,
we see that NEL has the top share in AWGs. As forsplitters, we have yet to establish an overseas market
7

R&D Spirits

for these, but we are nevertheless shipping the mostunits at this time. Our competitors are quickly gaining on us, however, and we cannot rest on our laurels.
In particular, a number of our rivals have reached afairly high technical level in PLCs, and we are coming to compete with them head-on in terms of market
share, technology, and price.

Pursuing optical integration technology fromearly days at NTT Laboratories—Dr. Yamada, what was your major at university?
Why did you enter NTT Laboratories?

While it is true that NEL has brand power and that
we were quick to market AWGs and to expand ourshare, I am proud of the fact that we have consistently been receiving high marks from users. But to maintain our reputation here, we must strive to develop
new products and bring costs down. The front line of
the PLC business is fast paced with endless worries
and concerns, but all things considered I think I amenjoying this work more than when I was a researcher
pursuing only technology. I now deal with issues
more attuned to the real world like how to increase
profit or how to lower product price. In pure research,
it is difficult to appreciate how interesting this can be.

At university, I majored in crystal physics in thedepartment of applied physics and researched thestructure and characteristics of various types of transparent crystals by optical means. I have therefore hadsome association with optical fiber since those earlydays. But what really got me interested in this field
was a set of articles that appeared in a newspaper
while I was on my master’s course. It introduced tome trailblazing research on optical fiber and lasers inrelation to optical communications. I found this subject immensely appealing and thought that I too
would like to pursue this kind of research. I then readthat this research was being conducted at none otherthan Nippon Telegraph and Telephone Corporation,
the forerunner of NTT. Therefore, an absolute condition for me to pursue optics-related research was toenter NTT Laboratories.

—Are you collaborating with any outside companies
or research institutions?

—What research themes have you been involved withup to now?

Speaking just for myself, no, I am not collaboratingwith anyone at this time. But with regard to collaboration on PLC technology, another section in NEL isentering into multi-source agreements with a numberof American and European companies. Their aim isto establish a de facto standard for multifunction
products, but results have been slow in coming. The
reason for desiring such a standard is that most large
orders for PLC products have been for custom use.
Some standard products are included in catalogs, butit has not been easy to get customers to use them. In
the case of electronic circuit components, it has long
been the practice in design work to use inexpensive
standard products in large volumes whenever possible. But PLCs are not yet used in large volumes as
packaged products, and this might be the reason forthe lack of progress in establishing a de facto standard. On the other hand, some progress is being seenin the standardization of core-network products likesplitters. For example, NEL began mass productionof a 1 × 8 splitter ahead of its competitors, and thesplitters of those companies are now modeled on ourproduct in terms of dimensions, shape, and otherattributes.

I am happy to say that for a 22-year period beginning during my time at NTT Laboratories and running to the present, my only research theme has been
optical integration technology. Although I researched
non-PLC material in 1982, the year I entered NTT
Laboratories, I got started in research on silica-based
PLC in the following year. At first, I researched thefabrication of optical waveguides by the microprocessing of a layer of silica glass deposited on a silicon
substrate. Although there had already been about twoyears of research in this area, nobody knew whether
PLC technology would amount to anything. Ourgroup consisted of only three people, but we werenevertheless able to fabricate prototype devices that
could demonstrate the basic functions of optical splitting/coupling, wavelength adding/dropping, andswitching, for example.
We then wondered where we could go from there,
and in 1986, our group started to expand significantly with research divided into two main topics. One
was waveguides and associated performance and theother was hybrid products. At that time, I became
interested in ways of combining multiple functions,and I consequently started researching hybrid integrated platform technology. The idea here was to—How is NEL evaluated by users?

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PLC platform
OE-device
Over-cladding
CoreElectricalwire
Hybrid integrated
WDM transceiver module

Receiver part (1.55 µm)
Under-cladding

Silica layer

WDM filter

PD

PLC platform
1.55 µm
Passive alignment

1.3 µm

OE-device

Silica PLC
WDM circuit
LDAlignmentmarks

Monitor PD
Transmitter part (1.3 µm)

AuSn solder
padInput
1.55 µm
Output1.3 µmWaveguide
PLC platform

Electrode

OE: opto-electronic

Fig. 2. Hybrid PLC technique.

mount a semiconductor laser or other device directly
on top of a silica-based PLC. Unfortunately, we were
not able to form a base surface with a highly precise
height on top of a PLC while making high-quality
waveguides at the same time, and our research wassuspended before a practical product was achieved.
Later, around 1993, when NTT decided to pursue
true FTTH, the need was seen for components such as
splitters and optical transceiver modules for laying
optical fiber up to individual homes. This time, thedecision was made to actively develop fabrication
technology for hybrid PLCs and to develop businessfor them (Fig. 2). Once a practical optical transceivermodule was achieved, it was transferred from NTT
Laboratories to NEL. But even after five years ofsales, the cost performance of this product was not as
good as expected, and its manufacture was discontinued in 2002. As a result, nothing remains of myresearch results in any tangible form. Nevertheless,despite many twists and turns, I am now back toVol. 3 No. 1 Jan. 2005

researching and developing the same theme that I
have been involved with since entering NTT. Such acase is rare at NTT and I feel very fortunate to begiven this chance.
—What, in particular, have you been searching for inyour research?
For most people, the first thing that comes to mind
on hearing the words “integrated circuit” is an electrical integrated circuit as opposed to the optical integrated circuit that I have been involved with. The
main difference between the two is that the former isachieved by “monolithic integration” in which muchcan be done by simply writing a process onto silicon,
while the latter is achieved by “hybrid integration”
that combines various types of materials. In short, theresearch and development of optical integration
attempts to demonstrate the “wonders of combination” with respect to various technologies. That is the9

R&D Spirits

first thing that I have been searching for in my work.
Besides that, I have always been pursuing the problem of “how to connect light.” In the case of electricity, a signal flows whenever electricity in any state
comes in contact with a conductor. For light, however, no signal will be transmitted unless the positionand orientation of the optical connection are perfectly aligned. Ensuring good optical connections
between fibers is fundamental to optical technology.
However, while this is simple in theory, it can be quitedifficult to achieve. It is no exaggeration to say thatthe various issues surrounding optical integration allcome back to this primary problem in the end. Looking back at my R&D activities over the years, I thinkthey all come down to a quest for ways of “connecting light.” This problem is one that concerns the business of optical communications as well, andresearchers will no doubt continue to pursue solutions to it in the years to come.
—Dr. Yamada, what is your personal policy as anengineer and as a researcher and developer? And
what do you find interesting about R&D?
In my second year in NTT, the supervisor thatassigned me my research theme said something to me
that I still keep in mind in relation to my work. He
said that “Searching in the light under a lamppost fora key dropped elsewhere in the dark is unlikely tolead to you finding it—you must go to the place
where you dropped it.” In other words, to achieve
your objective you must do whatever it takes, no matter how difficult it is. He often said that ignoring thisadvice would result in failure as a researcher. I agreewith this completely. It is this that I find interesting
about research and development. Once you decide to
do what is really necessary in your work, you will
eventually get results despite the difficulty. After considering various ideas and trying different approaches in a trial-and-error manner, you should eventuallyend up on the right path. I don’t think there are thatmany endeavors that can provide such a feeling ofsatisfaction as the R&D process.

A win-win relationship with NTT
Laboratories: an essential requirement for
ongoing development

ority. It has often been said that we have not madesufficient effort in the past to lower costs. This must
be corrected, but we must also keep in mind that technical prowess has been the foundation of NEL fromthe start. Moving forward, I see us working to cut
costs extensively over the next year and then, fornext-generation multifunction products, to concentrate our expertise on achieving absolute technicalsuperiority. That’s how I see things from here.
—At this stage, can you envision the research themeof the future?
It’s a bit vague, but I’d like to bring the ultimate
concept of an opto-electronic assembly to the productlevel. This would merge hybrid integration technology for direct mounting of semiconductor opticaldevices, which I was researching at NTT Laboratories before that research was suspended, with themultifunction technology that we are working on now(Fig. 3). We have not yet worked out the details, but
I think a specific target will gradually come into view
during our present work on multifunction technology.
—What is your ultimate goal as an engineer?
My life’s work has been to bring PLC technology tothe level of an industry. I have been involved with
PLC technology since its birth, and while I haveexperienced many ups and downs and have even seen
a product that I myself developed come to naught, I

Electronic assembly
Chip

Optical assembly

LSI

OE-device

MCM
PLC
connector

OE-MCM(PLC platform)

Board—Dr. Yamada, what lies ahead for PLC R&D?
My goal is to see that NEL optical products become
distinguished in the end by absolute technical superi10

MCM: multichip module

Fig. 3. Future concept of opto-electronic assembly.

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R&D Spirits

think there are few examples of a researcher whose
career has paralleled the birth and growth of a single
technology. As this appears to have been my fate, I’dlike to see this technology grow into an industrial
field. In other words, I’d like to see it take root in theform of silicon devices for electrical integration andPLCs for optical integration. I hope to participate inthis endeavor even if not in an R&D capacity. Since I
have left NTT Laboratories, I’d be glad to participate
in a business or production-management role. Whatever the form, my ultimate dream is to participate
actively at the front line of PLC technology as a PLC
pioneer.
—What is your opinion of and hopes for NTT Laboratories?
I’d like NTT Laboratories to research those areasthat present particular difficulties for us. For this reason, we need to make it clear to NTT Laboratories
what areas might be a problem for us, and to this end,
we need to make more of an effort to communicate
our needs. In this way, NTT Laboratories canresearch the technology that we need and we can takethe results of that research and provide it in someform to the world at large. That is to say, I’d like toconstruct a win-win relationship with NTT Laboratories.

Interviewee profile■ Career highlights
Yasufumi Yamada received the B.S., M.S., andPh.D. degrees from Waseda University, Tokyo, Japan,in 1980, 1982 and 1990, respectively.
In 1982, he joined Nippon Telegraph and Telephone
Public Corporation (now NTT). Since 1983, he had
been engaged in research and development on silica
planar lightwave circuits (PLC) at Opto-electronicLaboratories. His main field had been packaging technique for PLCs, especially optical hybrid integration
technique where LDs or PDs are assembled on thePLC chip surface in order to establish highly functional optical modules. In 1998, he moved to NTT Electronics Corporation where he has been engaged in
PLC business development. He became a Department
Director of Design Department, Planar Lightwave Circuit Group in April, 2004.
■ Major awards
Inose Award, and Best Paper Award, of IEICE (TheInstitute of Electronics, Information and Communication Engineers) (1998).

—Dr. Yamada, could you leave us with a message foryoung researchers and our other readers?
Certainly. I think the most important thing for a
researcher and developer is to pursue what one
believes in with a great sense of purpose. I take great
pride in having done just that in my research work up
to now. If you think only of whether certain research
will lead to a journal paper, you will accomplish little. My advice might be difficult to take if you needsound results in a hurry, but I’d like to see a researcher
carefully and steadily pursue what he or she believes
to be truly important even if that means no journal
paper for the time being.
In addition, I mentioned earlier that NEL is a world
leader in the field of optics and a cutting-edge enterprise having state-of-the-art technologies. For thoseresearchers that would also like to spread new opticaltechnologies throughout society with us, please comeand join us. And finally, to our customers, I’d like tosay that we hope you look forward to the productsthat we provide, and for our part, we hope to provide
products that always surpass your expectations.
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