Invited Talk at 42nd International Conference on Solid State Devices
and Materials (ssdm2010), Sept. 22-24, 2010, Univ. of Tokyo, Tokyo, Japan.

Roadmap of ultrafast energy-saving
optical semiconductor devices to Year 2025
Yoshiyasu Ueno 11

National University of Electro-Communications (UEC)
Chofu city, Tokyo 182-8585, Japan, e-mail: ueno@ee.uec.ac.jp

Abstract: Evolution in energy efficiency of many-core parallel
processors through year 2025 looks unclear, because the serial
speed of new electronic cores has stopped to evolve. With reviewing application-research activities in opto-electronics, instead, the author estimates what possibilities the still-crude
100-times-faster serial processors (e.g. 200-Gb/s) will contribute
through year 2025.

1. Introduction
In the last 40 years (since this ssdm conference started
in 1969), our world has changed dramatically. Until 10years ago, semiconductor devices, systems, and their heatdissipations used to be not consuming nor influencing visible portions of the total primary energy supply (TPES, fromcrude oil, coal, natural gas, nuclear powers, and others) ofus, the mankind. Now in USA, data centers are consuming
1.5% of its nation-wide electric-energy supply [1], whichcorresponds to all outputs from 10 nuclear power reactors.
In USA, the amount of primary energy supply (40 EJ/year=40×1018 J/year) for generating the nation-wide electricenergy occupies almost 40% of USA’s TPES (100 EJ/year)[2]. Figure 1(a) shows the unexpectedly steady increases
over the last 40 years, in primary energy supplies for generating electricity in the world and selected countries including the above number (40 EJ/year) from USA, according to the statistics in [2].
Zetta

Tr・Clk Product

1.E+21
1.E+201.E+19

Primary Energy Supply for generating
the annual total electricity supply in the country (EJ)

Exa

Moore’s magic?

1.E+181.E+171000.01.E+16Peta

1.E+15
1.E+14100.0

1.E+13

系列1Japan
P.R. China

系列2Japan

10.0

Tera

India

系列3EU (15)
UK

系列5

USA

系列6

1.0World

Pen 4(2002)

1.E+11系列4UK

Core 2 Quad(2007)

1.E+12

1.E+10Giga

Pentium Pro(1996)

1.E+0980386(1985)

1.E+08系列78086(1978)

1.E+07(b)1.E+060.11970

1980

1990

Year

2000

2010

(a)1.E+05

Y. Ueno, February 2010
1.E+04

1960

1970

1980

1990

2000

2010

2020

Fig. 1. 40-year-long increases in international-level energy supplies (a) and indexes of micro-processor performance (b).

The primary energy supply for generating world-wide
electricity reached 170 EJ/year. Silicon and other semiconductor materials are playing (or about to play) roles in almost all electricity-consuming systems such as computers,
communication systems, back-lights of displays, and now
room lights. Many of the biggest impacts to our world in
the last 40 and coming 40 years will be strongly influenced

by semiconductor materials industry and particularly by theperformance of micro-processors.
Instead of the number of transistors which appears tofollow the Gordon Moore’s law [3], Fig. 1(b) in this workshows the product of clock frequency and transistor number(Tr⋅Clk), measured floating-point operations per second(FLOPS), and measured instructions per second ((M)IPS)
of micro-processors in the last 40 years since its birth in1971. This figure suggests that the big growth of the orderof 1010 in FLOPS is proportional not to Tr but to the product Tr⋅Clk. It suggests next that a factor of 104 (among thefactor 1010) came from growth in Clk, while another, muchlarger factor of 106 came from the Moore’s law (growth inTr).
The larger growth factor (106) from Tr than that (104)from Clk is symbolic; nearly 40 years we had already reliedon and will rely with coming many-core processors on evenfurthermore-folded parallel-processing architectures which
consist of command-level, intra-core-level, intra-processorlevel, intra-sever level, and intra-network level, ratherthan the transistor speed. Many network applications willtolerate with more-folded parallel architectures, such asvideo streaming where time delays between packet arrivals
and machine loads in packet reconstruction procedures are
accepted somehow. Other applications may not tolerate,
however [4]. For such intolerant applications, it could be
difficult for skilled programmers to keep the time-to-output
efficiency in all tasks, and/or to enhance the system performance per unit energy in the coming 40 years.
In the above majority R&D direction with developing
much more cores, the time-domain speed of transistors
seem to completely stop to grow beyond 3 GHz. The coming big challenges are located still in the new few generations of ultra-fine lithography, and newly in the increasing
microwave losses along the intra-processor microwave-guided connections, instead of new challenges intransistors. The microwave-connection-loss issue is inherent and will be enhanced more by the still expanding parallel architectures.
An ultimately alternative direction has been widely
recognized to be the extremely-quantum signal-processing
system (called as quantum computer) since nearly 20 years
ago. It is believed, however, to take care of an extremely
limited range of existing signal-processing applications.
2. 300-GHz optical gates and memories for network
systems
It seems safer for us in coming 40 years to have an op-tion other than the above two directions (furthermore parallel architecture with the fixed speed and quantum computer). We probably have one option, in fact; Scientificallynear the middle point of the above two directions, a groupof international research institutes have been studying thethird direction, that is, optical-signal-processing devices
and materials [5-12].

Optical data

Optical data

Optical data

Drive energy (electric dc-bias)

Fig. 2. Fundamental elements of optical processors are optical
logic gates and optical buffer memories [5-12].
Distance in air, z (mm)Intensity (a. u.)+10+20Gated waveform, 1540 nm-10(a)

100100010111…

1.0

0.5

00

Intensity (dBm/nm)

-20

1.5

Wavelength (nm)-201552

1550

1548

1546(b)550 GHz-40

tronic processors. Nontheless, because of theabove-mentioned present status of electronic processors, we have very recently started estimating
the potential performance of optical processors inyear 2025, taking into account potential progresses
in bias-energy consumption and size, from material
physics viewpoints (i.e., semi-classically-quantum
opto-electronics with III-V semiconductors). Depending upon the pros and cons of optical-porocessor’s potential performance, the group ofparallel-intolerent signal-processing applications
will be specified better, hopefully in collaboration
with computer specialists. This type of activities
will support R&D of all-optical devices for use inultrafast network-node systems, as well.
In this invited talk, we will present an outline of
the above-mentioned estimations towards opticalprocessors. Any sudden ideas, weird ideas, or fundamental questions are always welcome during andafter the talk.
Acknoledgments
We thank Drs. Naoya Wada and Satoshi Shinada and their co-workers in NICT, Koganei city
for their long good collaboration with us in UEC
since early 2008.
References[1] e.g.: D.A.B. Miller, Annual Mtg. of IEEE Photonics Society,Turkey, Oct. 2009, paper TuY1, ; M. Pickavet and R. Tucker,
0193.0193.5
194.0-75 -50 -25
0+25 +50 +75
ECOC 2008, Brussels.
Optical frequency (THz)Time (ps)[2] International Energy Agency (IEA), Paris, “Energy balancesof OECD countries and non-OECD countries.” Separately,
Fig. 3. 200-Gb/s data waveform generated by our III-V semiconthe author has assumed the typical heat-to-electricity enerductor optical gate (a)[10] and the 550-GHz bandwidth of clock
gy-conversion ratio (0.41), near its thermo-dynamical limit.
generated with a similar optical-gate scheme [7].
[3] P.E. Ross, "Why CPU frequency stalled," IEEE Spectrum,April 2008; S. Adee, "37 years of Moore's law," IEEE SpecThis group of institutes including us (UEC) has beentrum, May 2008.
trying to develop optical de-multiplexers, optical wave[4] D. Patterson, “The trouble with multi-core,” IEEE Spectrum
length converters, optical 3R repeaters, synchronized opti47 (2010) 24.
cal clock sources, optical buffers, etc. so that they work in[5] R. Manning and D.A.O. Davies, Opt. Lett. 19 (1994) 889.
the near-future optical communication systems. The typical[6] Y. Ueno, S. Nakamura, and K. Tajima, J. Opt. Soc. Am. B19
optical data speed has reached 200-to-300 Gb/s [6, 8, 10].
(2002) 2573.
The electric-dc-bias energy consumption has been im[7] R. Suzuki, T. Ohira, J. Sakaguchi, and Y. Ueno, CLEO/QELS
proved dramatically to less than 10 pJ/bit [9], from those
2006, Long beach, USA, paper no. CMG5.
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Lightwave Technol. 25 (2007) 103.
are about 500×500 μm.
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Express 15 (2007) 14887.
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(2009) 1728.
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