eugene@wilbur.nas.nasa.gov (Eugene N. Miya) (08/16/90)
Dr. David Kahaner is a numerical analyst visiting Japan for two-years
under the aspice of the Office of Naval Research-Far East (ONRFE).
The following is the professional opinion of David Kahaner
and in no way has the blessing of the US Government or any agency of it.
[DKK]
Back issue of most reports will shortly be available via anonymous FTP.
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To: Distribution
From: David Kahaner ONRFE [kahaner@xroads.cc.u-tokyo.ac.jp]
Re: Optical Computing in Japan
7 August 1990
ABSTRACT. Optical computing activities in Japan are surveyed.
INTRODUCTION.
In recent years the field of optical computing has been rapidly broadened
into various areas, such as investigations of optical analog and/or
digital data processing, and optical and optoelectronic phenomena and
devices for optical computation. An optical computer is a computer in
which light is used somewhere. This can mean fiber optical connections
between electronic components, free space connections, or one in which
light functions as a mechanism for storage of data, logic or arithmetic.
The main motivation of many recent studies of optical computing is the
increasing interest in developing a new parallel computing system capable
of processing large amounts of data at high speed, and my own interests
in the subject are centered on this potential application.
My aim was to discover how close optical computing is to being of use to
the constituency of numerical computing that I represent, and to gain
some understanding of the ways digital optical computing and neural
computing overlap. In my opinion most scientists engaged in mainstream
scientific computation have little knowledge of neural computing and even
less of optical computing. Nevertheless, these are well established
scientific fields with thousands of researchers, professional societies,
journals, and international meetings. For example, Optical Computing '90,
held in Kobe Japan 8-12 April 1990 was a major conference on this topic
with almost 500 attendees. (See below for a summary and evaluation.)
Optical computing is seen by a number of Japanese as an essential
direction for computing research. Here are some examples of their
comments.
MITI: "electronics is the science of the twentieth century, and optics is
the science of the twenty-first."
Dr. Izuo Hayashi, Director of the Optoelectronics Technology Research
Laboratory (OTL) in Tsukuba: "The combination of photons and electrons
will create new kinds of system which we cannot imagine just using an
extension of today's technology. For instance, imagine real 3D
integration, by which I mean wafer-to-wafer communication, vertically, by
light, so that we can make stacks of hundreds of wafers by integration.
Once we master optoelectronic integration technology we can begin to
imagine new architectures."
Concerning the research activities in Japan and the U.S:
Prof. Takeshi Kamiya, Department of Electronic Engineering, University
of Tokyo: "Compared to the U.S. we have a wider variety of research
groups in Japan that are developing devices dedicated to optical
computing", while "In the U.S., I think there is a wider variety of
groups looking for new architectures for optical computing."
Dr. Ken-ichi Kitayama, supervisor at NTT Transmission Systems
Laboratories: "[ATT Bell Labs] are looking at the short term target
rather than the longer term target, and it seems that all their efforts
are now concentrated on 1995." "But NTT's long term goal is to establish
optical processing technology and to fully exploit massive parallelism by
optical means. This will produce new types of optical devices and an
optical architecture. We expect that in long run, research in a broad
range of areas will be fruitful. So for now, we consider this to be a
basic research phase, not the practical development phase." "The
photoelectronic or optoelectronic computer is the direction of the
future".
WHAT IS OPTICAL COMPUTING?
The concept of passing light through lenses to perform computations is
not new. I took a course on this in the 1960's. The fundamental idea
can be illustrated by noting that a simple lens essentially performs a
two dimensional Fourier transform of its input in real time for
arbitrarily complicated image, whereas using digital computation the
effort increases rapidly with the number of data points or pixels. Using
a lens in this way is an entirely analog process, and most of the early
research considered computation in analog terms very much like it was
described in the days of analog computing.
In recent years developments have centered on digital calculations, by
using optical devices for logic, memory or arithmetic. A stumbling block
in this research is that it is necessary to find optical materials that
react nonlinearly to input, and thus far sufficiently nonlinear materials
have not been available, or their nonlinearities are too weak for
practical application.
Work is also continuing on using optics to connect traditional circuits.
Optical communication has already made a significant impact in computer
communication via optical fibers. It is well known that optical fibers
have much lower attenuation during transmission than electrical wires in
coaxial cables. In addition they are more resistant to electromagnetic
radiation along their length. Optical cables are already being used as
I/O channels in Japan (Hitachi in 1987, Fujitsu in 1988, and NEC in
1989). Such channels have data transmission rates up to 9MB/second and
may be improved to more than double that. In addition they can be used
over much longer distances, up to about 1 kilometer for disk channels,
about 8 times as far as electrical channels. Prof. J. Goodman (Stanford
University), for example, believes that "optical interconnects" in
general are promising areas for real products. Further, if these
interconnects can be utilized to connect one chip to another (optical
output pads) it is speculated that performance in the 10 gigabit range
will be possible.
Laser beams can cross in arbitrarily complicated ways without losing
their individuality, or experiencing crosstalk, at least on larger
dimensional scales. Again the Fourier transform provides an excellent
example. Each point value of the transform is obtained by integrating
over all points in the source plane; that a lens can do this easily is in
one sense, the ultimate in parallelism. It is estimated that optics can
achieve at least 50 times the parallelism or connectivity of electronic
devices. The Japanese expertise in device technology may enable them to
capitalize on it better than others. This was aptly summarized by
Kitayama in describing research at NTT in optical computing: ``although
the applications in the future may be diversified, special purpose
hardware may first come in processing images at data rates which are
unabtainable using all electronics...One of the promising schemes would
be a combination of optical devices and VLSI. Optical neuro-chips may be
a longer-term goal...Practical application of optical hardware still
seems to stand at the far end of the time line.''
There seem to be four categories of optical computers.
(1) Optical analog. These include 2-D Fourier transform or optical
correlators, and optical matrix-vector processors.
(2) Optoelectronic. These do not yet exist, but would be constructed
using optical logic gate devices or 2-D photo diode arrays. The main
interest in this type of computing device would be to shorten the pulse
delay in chips and other logic elements by using optical
interconnections.
(3) Optical parallel digital computers. These would use the inherent
parallelism of optical devices along with digital electronics for
flexibility.
(4) Optical neural computer. Specifically designed to implement the
massive interconnection requirements of neural networks optically.
GENERAL REMARKS.
Optical computing is still a branch of experimental optics, with the
usual trappings of physical science, i.e., careful attention to fine
detail of setup and analysis. The research is not localized in any single
country. Early work by scientists at Bell Labs and other US laboratories
is now complemented by comparable work in many other countries. As long
as optical devices utilize free space the research results are clearly
dependent on the planning, creativity, and care of the individual
research group rather than on access to technology that is not widely
available. To the extent that scientists are beginning to think of
optical computing ``chips'' the Japanese researchers have the advantage
of access to the substantial resources and basic technological device
infrastructure of large Japanese industrial laboratories. The same may
apply to work at a very few US labs such as Bell Labs. Thus far, concrete
applications are several years away from being useful to the numerical
computing community. There seems to be a healthy competition between
major researchers. For example Huang at Bell Labs is working on optical
logic gates based on a principle he calls SEED, but Kamiya thinks that
the NEC approach might have certain advantages such as ability to amplify
optical signals.
RELATION TO NEURAL COMPUTING.
A neural computer, or neural network, is a special kind of highly
parallel computer with many computing elements, or nodes performing
simple operations (usually just matrix vector product) in a very
repetitive manner. In some models of neural computer (which have never
been implemented) there are postulated to be tens of thousands of nodes
each one of which is connected to all the others. Neural computers
compute in the sense that they have streams of input and output bits.
They do not require anything resembling ordinary programming; if
programming is done at all it is by dynamically changing the degree to
which the individual nodes are connected.
An important aspect of a neural network is the high degree of parallelism
associated with it. Thus it is natural that new parallel computers should
seek to implement neural networks as an application (but not the only
application). Optical computing researchers believe this parallelism can
often be implemented best using optical devices rather than traditional
wired circuits. Thus optical computing and neural computing are fields
that have developed independently and now sometimes come together for
their mutual benefit.
Today, most applications of neural computing, and in particular those in
which optics play a role are related to image processing, character,
target, or voice recognition and similar situations. However several
researchers have demonstrated optical devices that can multiply matrices
and solve small systems of linear equations, and papers are appearing
that attempt to apply neural models to more general reasoning situations.
At this time neural networks have not been applied to numerical modeling
problems and I have seen nothing on any of my visits to suggest that this
is likely. Perhaps these models are fundamentally different from what we
usually think of as algorithms.
As mentioned above the fundamental operation of a neural computer is
multiplication of an input vector (array) into a matrix with elements
called the network "weights." Both input array and weight matrix are
assumed to have non-negative elements. Let the matrix elements W(i,j) be
associated with a two dimensional light mask and the input with a light
emitting device array. Let the vector information of the input, v, be
radiated as optical intensity from laser diodes or light emitting diodes
in such a way that v(j) is radiated uniformly to the j-th column of the
matrix W in such a way that W(i,j)v(j) is the light intensity on the
back, or output side of the mask at point i,j. This is usually described
as "fan out". Then let the light intensity of the i-th row of W be
converged onto the i-th component of a light receiving device array, also
in a uniform way. By superposition, the i-th component of the output
array is then the inner product of the i-th row of W into v, and in this
way the matrix vector product is formed. The technical issues to be
dealt with include developing appropriate fan out light emitting beams
and a mechanism to permit variation of the values of the components of
W(i,j). The matrix vector multiplier above is usually part of a
"neuron", which takes each output component and returns 1 if it is large
enough, 0 otherwise. To do this optically requires optical
"thresholding."
OPTICAL COMPUTING '90.
The 1990 International Topical Meeting on Optical Computing was held 8-12
April, 1990 in Kobe, Japan. Almost 500 scientists attended this meeting.
A related meeting on Photonic Switching was held immediately after.
Participants came from Japan, USA, USSR, France, UK, FRG, China,
Switzerland, Finland, Australia, Bulgaria, Korea, Phillippines, Sweden,
Canada, Belgium, and Italy. The meeting was held in the International
Conference Center at Kobe, on an island in the Port of Kobe. There were
no parallel sessions and the first day was exclusively devoted to three
tutorials, by J. Goodman (Stanford), D. Miller (ATT Bell Labs), H. Szu
(NRL). A Proceedings, in English, is available from the International
Society for Optical Computing by referencing ISBN 4-980813-37-9. I also
have a copy of the proceedings. Many of the papers presented at OC90 are
variants or extensions of papers that are published in journals such as
Optoelectronics or Applied Optics. I am not a physicist and cannot
evaluate such aspects of this work.
An extensive collection of reprints (in English) was sent to me by
Professor Yoshiki Ichioka, Department of Applied Physics, Osaka
University, 2-1 Yamadaoka, Suita, Osaka 565, Japan, for which I am very
grateful. Ichioka and colleagues have been concentrating on building
optical devices that will perform fundamental logical functions, AND, OR,
NOR, etc. The group has created several new ways to implement some logic
devices. Their computer design using these techniques is called OPALS.
Work on this has been going on since at least 1983 and is well known
outside of Japan. However, implementation requires development of
several new kinds of devices, so this research is several years away from
practical application.
Goodman and colleagues from Stanford presented a paper on a simulated 64-
node shared memory multiprocessing system, the IBM RP3, with optical
interconnects. Similarly, a paper by staff (Matsumoto, Sakano, Noguchi,
Swabe) at NTT Transmission Systems Lab, 1-2356 Take, Yokosuka-Shi,
Kahagawa-Ken, 238-03 Japan, described a system composed of 36 T800
Transputers running a parallel processing system with optical connections
in "free space", i.e., in a box rather than in a chip. The technique
looks promising but is also at a very early stage.
A different view of optical devices was given by Dr. Peter Davis, who
works at the ATR lab. See my report "The Advanced Telecommunication
Research Institute (ATR) 14 June 1990."
OPTICAL NEURAL COMPUTING
One of the most interesting papers was on Mitsubishi's Optical Neural
Neurocomputer. A paper was presented at this meeting and several other
related papers have also been given at various neural network meetings
during the summer months. The pricipal researchers are Kazuo Kyuma and
J. Ohta at Mitsubishi Electric, Central Research Lab, 1-1 Tsukaguchi-
honmachi 8-chome, Amagasaki, Hyogo 661 Japan. While there are many
research activities, both in academia and industry, on the development of
optical chips, Mitsubishi's looks very impressive to me because they have
actually been able to fabricate a device that they claim can be mass
produced. A important aspect of this chip is that there are only two
layers rather than the three in other designs, by use of what they call a
sensitivity-variable photodiode. Further the chip allows for a dynamic
alteration in the interconnection weights between input and output. This
last feature is essential for "learning", in neural networks, i.e.,
adjustment of interconnection weights in order to obtain specified output
for given input. Ability to vary the weights is lacking in many other
projects. The Mitsubishi group estimates that they can build this chip
to contain about 1000 neurons in a one centimeter square with acceptable
power requirements (less than one watt), large dynamic range (20db) for
the weights, and low optical crosstalk. Although light beams do not
singificantly interact at large scales, at chip level scales they do and
this issue must be addressed. They estimate that such a chip can perform
more than one tera connection per second, 10**(13).
CONCLUSION.
Optical computing appears to be a research area that has already provided
a few practical applications. Its real potential for general computation
lies several years away. There are many steps from discussion of AND
gates to Fortran compilers. Nevertheless, this seems like a research
topic with high payoff potential and only modest risk (cost). The
Japanese government has set up an optoelectronics laboratory at Tsukuba
and it would be natural for them to enlarge the scope of its research
into optical computing, perhaps in conjunction with the activities that
are present at the industrial labs.
APPENDIX--EXPERT SUMMARY OF OC'90.
Professor H.J. Caulfield
Director, Center for Applied Optics
University of Alabama in Huntsville
Huntsville, Alabama 35899
Tel: (205) 895-603, Fax: (205) 895-6618
also attended this meeting and I asked him to provide me with a brief
critical overview, which is given below.
OVERVIEW OF THE KOBE MEETING, "OPTICAL COMPUTING '90"
The Kobe, Japan meeting on Optical Computing was part of an annual series
which is outlined below.
1985 USA
1986 Israel
1987 USAA
1988 France
1989 USA
1990 Japan
1991 USA
1992 Soviet Union
1993 USA
1994 Germany
It is the one major international meeting in the field. The Kobe meeting
was the largest so far - almost 600 attendees.
This reviewer feels safe in saying there were no "breakthrough" papers.
Accordingly, I offer this impressionistic assessment of work by regions.
The European work is dominated by Germany, Israel, France, and the United
Kingdom. In my judgement, the least dynamic of the groupings I have made.
The Japanese work was short on innovation but long on practice. There
were numerous papers on components they have manufactured especially
Spatial Light Modulators (SLMs). The Seiko SLM was the most discussed.
Most of the other Japanese work was on systems they had implemented. In
general, they seem to be working on parts and system manufacturing
methods, leaving the innovation primarily to the U.S. and the Soviet
Union. I regard this as very clever on their part. Money and jobs stem
from building things not inventing things.
The Soviet Union was well represented - nearly all Russians. I was
particularly impressed by their innovation. Papers V. Morozov's work on
waveguide holograms coupled to diode lasers is symbolic of important work
so far done only in Russia.
American was well represented in number and breadth. Like the Soviet
ork, the U.S. effort has no unified theme and even no agreements as to
what is important. Alan Huang and many of his AT&T coworkers presented
their well publicized but controversial (as to its current or potential
value) work on digital optical computers. Optical neural networks,
quantum mechanical effects, and hybrid analog-digital processors were
other major themes. Overall, the field is growing in numbers and
support, but no certain inner as a technology has emerged. The U.S. and
the Soviet Union are the innovators. Europe is the monitor. These are
caricatures, but they are not misleading.
--------------------------END OF REPORT--------------ishihara@etl.go.jp (Satoshi Ishihara) (09/22/90)
In article <7846@amelia.nas.nasa.gov> on 08/16/90 eugene@wilbur.nas.nasa.gov (Eugene N. Miya) wrote: |OPTICAL COMPUTING '90. I found and read Dr.Kahaner's report "optical computing in Japan" posted by eugene@wilbur.nas.nasa.gov to comp.arch and soc.culture. japan. I would like to thank them very much for their efforts to introduce our activity to the world. Just few remarks on the facts on our OC'90, now. (Sorry, but I have no time for detailed comments.) |A Proceedings, in English, is available from I don't know the definition of "Proceedings", but we call it "Conference Record", which collects 2-page summaries submitted for refereeing for the conference. |the International Society for Optical Computing xxxxxxxxx -----> Engineering Certainly, somebody wish to establish "the International Society for Optical Computing", but not yet:-) ^^^^^^^^^ They call the society SPIE. SPIE publishes it as Volume 1359 in their Proceeding Series. By the way, this "Conference Record" is also available at BCASJ (telephone: 03-817-5831) in Japan. ^^^^^^^^ Let me introduce a book with a similar title which was recently published in USA. ************************************************************** OPTICAL COMPUTING IN JAPAN Collection of about 50 papers. 525 pages, 1990. $85 (US/Canada) $98 (Other Countries-Includes Air Delivery). ISBN 0-941743-85-3. Contact: Nova Science Publishers, Inc. 283 Commack Road, Suite 300 Commack, New York 11725-3401, USA (516) 499-3103/3106 Telex #510 101 2161 Fax (1) 516-499-3146 *************************************************************** If there is anybody who is interested in the list of the titles of the papers with author's name, I will post it. ++ Satoshi ISHIHARA (Chairperson, OC'90 Steering Committee) Electrotechnical Laboratory(ETL), Japan e-mail: ishihara@etl.go.jp or ishihara%etl.go.jp@relay.cs.net