Invited Talk, at the 4th Asia-Pacific Microwave Photonics Conference(APMP 2009) , co-sponsered by IEEE/LEOS, April 22-24, 2009,
Beijing, P.R. China.

Ultrafast, low-energy-consumption,
semiconductor-based, all-optical devices
Yoshiyasu Ueno, Jun Sakaguchi,*1 Ryoichi Nakamoto,*2 and Takehiro Nishida
Graduate School of Electronic Engineering
University of Electro-Communications (UEC), Chofu city, Tokyo, Japan
website: http://www.ultrafast.ee.uec.ac.jp/, email: ueno@ee.uec.ac.jp*1, present affiliation: Nara Institute of Science and Technoloy, Nara, *2: Sumitomo Electric Industries, Ltd., Yokohama.
One of the two most important origins of these up-to-datebroadband optical-communication technology is thetransparency bandwidth throughout 125-μm-diamieter silica
fiber cables developed well in the last 40 years. Thistransparency bandwidth approaches 100 THz (1014 Hz) in the
optical frequency domain (Fig. 1(b), even though that of themost conventional C-band is limited to only 4 THz by the Erion-doped fiber amp’s gain bandwidth). The other importantorigin is electronic signal processors developed in these 40
years since Intel Corporation had released the mankind-firstsignal processor, Intel 4004 in 1971, whose signal’s bit-rate
was 500 kb/s (Fig. 2(a)). Recently, in contrast, the 10-Gb/selectric signal’s waveforms such as the one we are generatingin our lab. (Fig. 2(b)) is not special at all.

Abstract— The relatively-low electric-energy-consumption level(3 pJ/bit) of the most fundamental all-optical semiconductor
gate device (i.e., signal-wavlength converter), with respect to its
ultrafast response speed in the 200-Gb/s range, are briefly
reviewed.

I.

INTRODUCTION

It was December 1901 when Mr. Guglielmo Marconi andhis colleagues finally succeeded in their transmit-andreceiving the mankind-first, wireless signals across the
Atlantic Ocean. After our research activities in the materials,
devices, and system schemes in the last 100 years since then,
the world-wide demands in network systems’ capacities arecontinuously rising up. For instance, the number of opticalfiber-link subscribers in Japan has exceeded that of DSL in2007 (Fig. 1(a) [1]). In both Korea and Japan, the numbers of
optical-fiber-link subscribers per 100 inhabitants have reachednearly ten [2]. The network capacities between wireless basestations have been strengthened by optical-fiber links on an
every week basis.

(a)

(b)

?

100 Million
108

Subscriber numbers

Subscriber numbers

91 Billion
10

10 Million
107

?

?

1 Million
106

FTTH (100M)
DSL (10M)

100 thousand
105

Consumer market
in Japan

CATV (8M)
MOBILE (200k)

10 thousand
104
2002/03

03/2002

03/2005

2008/03

03/2008

Month/Year

Fig. 2: the first, 500-kb/s processor, Intel 4004 in 1971 (a),in contrast to the recent microwave signal’s waveform (b).

(a)

As the electronic signal-processing speed has been
accelerated from classical 10 Mb/s to beyond 1 Gb/s, however,
the energy-consumption rate per one-bit gate operation has
more rapidly been increased as a matter of fact. This is
recognized as one of the simplest reasons why the nearly-40year-long continuous growth in the popular CPU clock
frequency has recently been stalled near 3 GHz [3], and now
dual-core and even quad-core processors have been developed.
In other words, silicon materials inside such CPU chips oftoday could otherwise become chemically unreliable due to its
own huge heat-energy dissipation, since the speed acceleration
deteriorates the energy consumption rate per one-bit gate(b)
Fig. 1: Broadband subscriber numbers in Japan (a),in contrast to the bandwidth of our ‘optical wires’ (b).
1

operation. In a similar manner, the electric energy consumed
24 hours a day by millions of IP router processors has started
to appear as a bigger and bigger issue, simply because optoelectronic devices’ bit-rates are regularly much faster thanthose of standard signal processors or CPU’s. One of thesymbolic examples would be Cisco’s high-end router released
in 2006 [4], which consumes 1-MW electricity (and another 1
MW for air-conditioning its machine room), for taking care of
total 92-Tb/s through-put signals in its 40-Gb/s baseline bitrate. These numbers indicate that this router’s signal
processors consume total 10 nJ per one-bit IP-routing process.

physically due to signal processors’ heat dissipation (60 pJ/bit
in Ref. 5), microwave signal’s connection losses, andmoreover their propagation losses in these ultrahigh-frequency
ranges. This microwave devices’ bottleneck in speed andenergy consumption has been believed to be broken-through inthe future, by our technological “transition” from electronic to
all-optical signal processors with III-V semiconductormaterials (instead of silicon). Even though the global R&D
activities for all-optical signal processors such as the one in
Fig. 3 are staying in pre-competitive stages up to now,varieties of all-optical gate operations have experimentally
been proposed and studied in some details by world-wide
research institutes in the last decade (Table I). The bit rate of
optical signals in these pioneering experiments has ranged innearly three orders of magnitudes, i.e., from 1 Gb/s up to 640
Gb/s. Furthermore, as long as the energy of optical one-bit
signal that all-optically controls (i.e., drives) these gates in bitwise manners is concerned, its (optical) energy consumption
has been staying in a very low range, that is, in the order of
100 fJ per one-bit signal pulse, throughout the experiments inTable 1. (In some of them, some of the present authors had
directly been involved in.)

Optical Logic Gate

Digital Optical Signal, A

Control'AND' output,'XOR' output,
etc.

Digital Optical Signal, B

Fig. 3: Fundamental scheme of an all-optical gate.

In Table II in this work, the present authors have proposeda set of possible specifications of “optical signal processors”
in the near future, with paying attention to more fundamental
all-optical gates in the recent research level in Table I. Highdensity integrated optical signal processors in bit rates
between 300 and 600 Gb/s in years 2010-2025 will be realistic
in front of us researchers, in the following manners.

Table I: Diversity in the types of all-optical gate operation[6-19], since early 1990’s through present
Bit rate
640 Gb/s
640 Gb/s

Logic function
Demultiplexing
Clock extraction

Year
2007
2007

Reference[6][7]

320 Gb/s
200 Gb/s
160 Gb/s
160 Gb/s
100 Gb/s
80 Gb/sWavelength conversion
Wavelength conversion
Wavelength conversion
Wavelength conversion
AND gate
3R regeneration

2006
2009
2005
2000
1998
1999-2001

10-40 Gb/s

Add-Drop, 3R, λ-conv, etc. 1990's[16]

1 Gb/s
1 Gb/s
1 Gb/s

Shift register
1996
Random number generation 1999
Regenerative-loop memory 1998

[17]
[18]
[19]

Regarding the density of optical integration, assuming thefoot-print size will be reduced to 200×200 μm2 by combining
independently on-going nano-photonics research near us suchas the monolithically integrated photonic-bandgap-circuit
technology [20-21] together with the growing planarlightwave-circuit (PLC) technology in industrial institutes [22],one optical processor chip will start containing as many gates(about 3,000) as that in the first electronic signal processor,
Intel 4004 (2,300). One of the other challenging parts
indicated in Table II is the electric energy consumption, whichmust be in the order of 0.1 per one-bit gate operation so thatthe total energy consumption per one chip does not exceed
100 Watt, even with such ultrafast gate-operation times per
second. This degree of reduction in energy consumption
seems to be realistic in the near future.

[8]
[9]
[10]
[11, 12][13][14, 15]

Table II: One of future directions, optical signal processor
Electronic

Optical signal processors

Specification

Intel 4004

Present research level

Near-Future level

Year

Year 1971

Year 2000-2010

Year 2010-2025

Speed

500 kb/s

200-300 Gb/s

300-600 Gb/s

3-10 pJ /bit/gate

0.1 pJ /bit/gate

Foot-print size

70×70 μm2

1,000×3,000 μm2

200×200 μm2

Number of gates

2,300 transisters

few per chip

3,000 gates per chip

Energy consumption per bit

Energy dissipation

II.

Taking into account such optical signal processor vision
for our future, we in this work will outline some of our recent
results, where we’ve independently paid attention to thedependence of the electric energy consumption of our alloptical gate on its speed in the following Sections. III and IV.
III. OUR ALL-OPTICAL SEMICONDUCTOR GATEEXPERIMENTS IN THE 200-GB/S BIT-RATE RANGE

100 Watt per chip

Figure 4 shows few quick views from our all-optical gateoperation experiments in 2006-2008 [9, 23]. Fig. 4(a) shows
one of the simplest structures of our all-optical semiconductor
gates (i.e., delayed-interference signal-wavelength converter(DISC) [8-12]), (b)-(c) show microscope photos ofsemiconductor-optical-amp (SOA) chips whose lengths are

ALL-OPTICAL SIGNAL PROCESSORS IN THE NEAR FUTURE

After the long-running R&D activities for developing
faster electronic processors in the last 10-20 years, theirhighest speed seems to be limited to 40-100 Gb/s [5],2our lensed-optical-fiber cables (Namiki Precision Jewel Co.,
Ltd., Japan, partially seen at the respective semiconductorwaveguide facets in Fig. 4(c)) [23]. Several types of MachZehnder interferometer parts for use inside the DISC gate
were built with using AR-coated bi-refringent calcite crystals
as fixed short-time delays in the order of a few picoseconds,
and several polarized optics combined in the commerciallyavailable low-loss cassettes-in-cartridge manners (Optoquest
Co., Ltd., Saitama, Japan).

ranging from 500 to 1,100 μm, and (d) shows a schematic
view of the most important, ultrafast photon-electroninteraction mechanism that physically drives the gate.
λ= λ1
λ= λ2

SOA
λ= λ2

MZI, Δt

(a)

(a)

(c)

(b)
Holes
Optical pulses

Amplified pulses

(b)

(d)

Electrons

Fig. 4: All-optical gate-operation experiments in our lab.
(a) device structure, (b) SOA chips, (c) material physics.

1.5

Input data, 1560 nm
100100010111…

1.0
0.5

(c)

1.5

Intensity (a. u.)

Intensity (a. u.)t

Gated waveform, 1540 nm(d)100100010111…

1.0

0.5

0

Relative intensity (dB)0-75 -50 -25
0+25 +50 +75
Fig. 5(a) and 5(c) show typical waveforms of our 200-Gb/s,-75 -50 -25
0+25 +50 +75
Time (ps)4,992-bit-long optical input data signal, measured with an allTime (ps)optical cross-correlator with using a conventional inorganic
Fig. 5: Our 200-Gb/s experiments in May 2008 [9].
nonlinear-optics crystal (FR-103XL, Femtochrome Research,
Inc., USA). Our experimental set up is shown in Fig. 5(b). The
Wavelength (nm)
uniform input data signal was generated with a 12.5-GHz
1580
1560
1540
1520
synchronously-and-harmonically mode-locked fiber-ring laser+10(Ultrafast Optical Clock, Pritel, Inc., USA), dispersionInput
Outputdecreasing adiabatic-soliton-compression fibers (Pritel, Inc.),0
commercial LiNbO3 e-o modulators, research-level electroabsorption modulators, a 12.5-Gb/s electronic pulse-pattern-10
generator (Anritsu Corp.), four stages (two commercial andtwo home-made) of low-dispersion low-loss 1:2 optical-20
multiplexers, a home-made high-precision sub-harmonically190
192
194
196
synchronized optically sampled monitoring system, andOptical frequency (THz)several of low-dispersion Er-doped fiber amps. The patternlength of the microwave 12.5-Gb/s baseline data signal wasFig. 6: Spectra before and after the wavelength
set to 312, so that the waveform-monitoring system
conversion in a wavelength range, 1520-1580 nm
synchronizes to the data pattern in the 312:1 sub-harmonic(i.e, in an optical-frequency range, 190-198 THz) [9].
frequency (40 MHz). In the meantime, the pattern length of
the 200-Gb/s data signal reached 4,992 after being separated
Fig. 5(d) shows one of the typical 200-Gb/s optical output
with intentionally-long de-correlation time-delay cables and data signals carrying the same binary-code patternthen all-optically multiplexed by a factor of 16 from the 12.5- ‘10010010111’, taken from the output port of the wavelengthGb/s signal, with the four stages of multiplexers.
converter gate in Fig. 4(a). According to its principles ofIn the following experiments, several types of semi- operation [12], each of the output data signal pulses wascustomized nonlinear SOA chips from EU, USA, and Japan generated after each of the 200-Gb/s λ1 (1558 nm) input data
were carefully diagnosed-and-selected, and then precisely signal pulses in Fig. 5(a) all-optically gated the co-propagating
coupled to the in-coming and out-going optical signals with λ2 (1540 nm) cw light. The ultra-short width of the output

3

data-signal pulses approximately matched to that of the input
data-signal pulses. (In fact, the width of our output pulses wasmore identical to that of the input pulses, than those previously
reported in Ref. 8.)

unexpectedly simple, bi-linear dependence of the power
consumption on the gate speed, in the range from 20 through100 Gb/s. Consequently, they indicated linear dependence ofthe energy consumption per one-bit operation on the gate
speed. The measured numbers were only 5 pJ/bit in 50-Gb/s,
10 pJ/bit in 100-Gb/s, and 20 pJ/bit (extrapolated) in the 200Gb/s bit-rate. Throughout the experiments in Fig. 7, we
accelerated the gate speed with the conventional opticalacceleration scheme (i.e., holding-beam scheme [24]).

Figure 6 shows of optical data signals’ spectra before andafter the wavelength conversion in the optical frequency scale,as well as in the conventional wavelength scale. As is shownin the figure, the center wavelength (center optical frequency)of the optical data signal was converted from λ1= 1558 nm(f1= 192.4 THz) to λ2= 1540 nm (f2= 194.7 THz). The
frequency components of the respective spectra werebroadened to both sides of the center component, due to thedigital modulation. Consequently, the width of our frequency
spectra was in the order of the bit-rate (200 GHz) in a manner
similar to Return-to-Zero (RZ)-format experiments done inmuch lower bit-rates. [It should be noted that the reason why the

Table III: Electric energy consumption per one-bit operation
Bit rate

Electric dc power consumption, POP(mW, @ΔΦNL=0.3 π)

10measuredB#4 1100 μm
B#3 500 μm

103

100

1000

Bandwidth, B (GHz)

Fig. 7: Measured dependence of electric power consumption
on the wavelength-converter’s bit-rate [23].
IV.

[9, 23]

100 Gb/s

10 pJ/bit/gate[23]

50 Gb/s

5 pJ/bit/gate[23]

3 pJ/bit/gate

Item

Value (typical)

Injected electron's energy consumption per one-bit operation

3 pJ/bit

Reference

Volume density of heat-energy dissipation

50 MW/cm

Injected electron's number consumption per one-bit operation

2×10 electrons/bit[9]

Surface density of injected electron's current

40 kA/cm

2[9]Surface density of propagating optical signal's average power

2 MW/cm

[9]
3

[9]

7

2

[9]

16

-3

Volume density of (unintentionally doped) impurity atoms< 1 × 10 cm

Volume densities of excited electrons and holes

0.3 to 3.0 × 10 cm

Volume densities of group-III and group-V atoms

22

2.0 × 10 cm

Three-dimensional device size (width, thickness, and length)

300×100×1,100 μm

17

-3

-3
3

[9]

We are expecting that the energy consumption in the orderof 20 pJ/bit in the recent research level will be dramaticallyreduced in step-wise manners in the near future (Tables II and
III). More recently, in fact, energy consumption of about 5
pJ/bit was sufficient in the experiments in Refs. 8 and 10,
where they effectively accelerated the gate with a blue-shiftedband-pass-filtering scheme [25]. In our 200-Gb/s experiments,
3 pJ/bit was sufficient where we accelerated the gate with anonlinear-polarization-rotation scheme [9].

1021020 pJ/bit/gate (extrapolated)

Table IV: The active density numbers in the ultra-hight-purity
crystalline semiconductor materials in our experiments

envelope of our measured λ1 spectrum looks smoother was because
this spectrum was averaged in time over inherently instable opticalfrequency position of our 12.5-GHz mode-locked pulses. The λ2spectrum looks less smooth in contrast, because the stability of
optical-frequency position of the converted signal was dramatically
improved after ‘re-generated’ from a highly stable DFB-laser light.]

4

after conventional acceleation after effective acceleration Reference

200 Gb/s

DC-ELECTRIC ENERGY CONSUMPTION RATE WHICHSCALES LINEARLY WITH BIT-RATE

The ultrafast (in speed), very energy-efficient (in energy
consumption), and compact-size nature of the all-optical gatesare originated from their high-purity high-density nature of thecrystalline semiconductor materials inside the SOA’s. In Table
IV, we summarized the densities of optical, electronic, andthermal properties in those semiconductor materials under
their carefully designed working conditions.

Almost all of the authors in previous experiments since
early 1990’s [6-19] had diagnosed the optical energy
consumption, that is, the energy of optical input data pulse
which were all-optically driving their all-optical gates. As was
mentioned in Sec. II, this amount of energy has been verysmall, in the order of 100 fJ per one-bit gate operation. Itshould be noted here these all-optical gates continuously
consume-and-dissipate several times larger electric energy,
for electronically biasing the SOA with a direct current (in theorder of 100-500 mA) across the electric potential between its
anode and cathode (about 1.0 Volt). Typical amounts of the
dc-bias currents had been described in almost all of the abovementioned mile-stone reports. Any scientific behaviors of theamount of dc-electric energy consumption had, however,
never been systematically studied until very recently, to theauthors’ knowledge.

V.

OTHER NEW APPLICATIONS OF ALL-OPTICAL GATESWe must be able to extend our fundamental gate tovarieties of new devices including flip-flop buffer memories[6-21]. Figure 8 shows another example, i.e., a mode-lockedpulse laser that consists of the gate in Fig. 4, a positive
feedback loop, and an external cw laser. The width of its
coherent, controllable, optical-frequency-comb spectrum has
extended to 550 GHz at present [26-27]. In the future, thisscheme will reduce the sizes of optical-frequency-comb-based
optical-metrology equipments, from NIM-rack sizes topersonally portable sizes, for use in our biological, continental,
under-ground, submarine, and even cosmic research fields.

Figure 7 shows two series of dependences of the dcelectric power consumption in our all-optical SOA-DISC gate
on its effective gate speed [23]. These results have indicated4[9]J. Sakaguchi, T. Nishida, and Y. Ueno, “200-Gb/s wavelength
conversion using a delayed-interference all-optical semiconductor gateassisted by nonlinear polarization rotation,” in press, Optics Comm.,
Elsevier, Netherlands, http://dx.doi.org/10.1016/j.optcom.2009.01.028.
[10] Y. Liu, E. Tangdiongga, Z. Li, S. Zhang, H. de Waardt, G.D. Khoe, and
H.J.S. Dorren, “Error-free all-optical wavelength conversion at 160
Gb/s using a semiconductor optical amplifier and an optical bandpass
filter,” J. Lightwave Technol. 24 (2006) 230.
[11] S. Nakamura, Y. Ueno, and K. Tajima, “168-Gb/s all-optical
wavelength conversion with a symmetric-Mach-Zehnder-type switch,”
IEEE Photonics Technol. Lett. 13 (2001) 1091.
[12] Y. Ueno, S. Nakamura, and K. Tajima, “Nonlinear phase shifts induced
by semiconductor optical amplifiers with control pulses at repetition
frequencies in the 40-160-GHz range for use in ultrahigh-speed alloptical signal processing,” J. Opt. Soc. Am. B19 (2002) 2573.
[13] K.L. Hall and K.A. Rauschenbach, “100-Gbit/s bitwise logic,” Optics
Lett. 23 (1998) 1271.
[14] D. Cotter, R.J. Manning, K.J. Blow, A.D. Ellis, A.E. Kelly, D. Nesset,
I.D. Phillips, A.J. Poustie, and D.C. Rogers, “Nonlinear optics for highspeed digital information processing,” Science vol. 286, pp. 1523-1528,
Nov. 1999.
[15] Y. Ueno, S. Nakamura, and K. Tajima, “Penalty-free error-free alloptical data pulse regeneration at 84 Gb/s by using a symmetric-MachZehnder-type semiconductor regenerator,” IEEE Photonics Technol.
Lett. 13 (2001) 469.
[16] e.g.: Kristian E. Stubkjaer, “Semiconductor optical amplifier-based alloptical gates for high-speed optical processing,” IEEE J. Selected
Topics in Quantum Electron. vol. 6, no. 6, Millenium Issue (Editor in
Chief: Alan Eli Willner), Nov./Dec. 2000, pp. 1428-1435.
[17] A.J. Poustie, R.J. Manning, and K.J. Blow, “All-optical circulating shift
register using a semiconductor optical amplifier in a fiber loop mirror,”
Electron. Lett. 32 (1996) 1215.
[18] A.J. Poustie, K.J. Blow, R.J. Manning, and A.E. Kelly, “All-opticalpseudorandom number generator,” Optics Comm. 159 (1999) 208.
[19] A.J. Poustie, A.E. Kelly, R.J. Manning, and K.J. Blow, “All-opticalregenerative memory with full write/read capacity,” Optics Comm. 154(1998) 277.
[20] H. Nakamura, Y. Sugimoto, K. Kanamoto, N. Ikeda, Y. Tanaka, Y.
Nakamura, S. Ohkouchi, Y. Watanabe, K. Inoue, H. Ishikawa, and K.
Asakawa, “Ultra-fast photonic crystal/quantum dot all-optical switch
for future photonic network,” Optics Express 12 (2004) 6606.
[21] K. Asakawa, Y. Sugimoto, et al., “Photonic crystal and quantum dot
technologies for all-optical switch and logic device,” New J. Phys. 8(2006) 208.
[22] e.g.: J.L. Pleumeekers, P.W. Evans, W. Chen, R.P. Schneider Jr., R.
Nagarajan, “A new era in optical integration,” Optics and Photonics
News vol. 20, no. 3, Optical Society of America, March 2009.
[23] J. Sakaguchi, F. Salleras, K. Nishimura, and Y. Ueno, “Frequencydependent electric dc power consumption model including quantumconversion efficiencies in ultrafast all-optical semiconductor gatesaround 160 Gb/s,” Optics Express 15 (2007) 14887.
[24] R.J. Manning and D.A.O. Davies, “Three-wavelength device for alloptical signal processing,” Opt. Lett. 19 (1994) 889.
[25] M.L. Nielsen, J. Mørk, R. Suzuki, J. Sakaguchi, and Y. Ueno,“Experimental and theoretical investigation of the impact of ultra-fastcarrier dynamics on high-speed SOA-based all-optical switches,”
Optics Express 14 (2006) 331.
[26] R. Suzuki, T. Ohira, J. Sakaguchi, and Y. Ueno, '40-GHz mode-locked
pulse generation with a new scheme of SOA-based pulse generators,'
CLEO/QELS 2006, May 21-26, 2006, Long beach, USA, paper no.
CMG5.
[27] R. Nakamoto, H. Takeuchi, J. Sakaguchi, and Y. Ueno, "1.55-μm,
mode-locked, single-longitudinal-mode, 10-GHz, 2-ps, ultra-short
optical pulse train from our original semiconductor-based pulse-source
scheme," Topical Conference on Nanophotonics (NANO), OpticalSociety of America, May 26-29, 2008, Southeast Univ., Nanjing, P.R.
China, paper no. Nano-08-191.

DISC-type polarization converter

SOA

MZI Δt

BPF

P
Q

(a)

DFB-LDf0

Etalon Δf

Delay

Outputmode-locked pulses
Wavelength (nm)Distance in air, z (mm)
-20

0

+20

(b)
1.0

2 ps
0.5

0
-100

-50

0

Time (ps)

+50

1552

0

Intensity (dBm/nm)

Intensity (a. u.)

1.5

+100

1550

1548

1546

(c)
-20

550 GHz
-40
-60
193.0

193.5

194.0

Optical frequency (THz)

Fig. 8: Mode-locked pulse generation [26, 27].
VI.

CONCLUSION

With referring to one of our future vision (Table II) andthe recent 200-Gb/s gate research results (Sec. III), theelectric-energy-consumption level of all-optical gates has been
decreased to 3 pJ/bit (Sec. IV). This level seems to be one-totwo orders of magnitude smaller than those of electronic
devices in the respective speed ranges ([5] in Sec. I).
ACKNOWLEDGMENTS
The authors acknowledge Kohsuke Nishimura, Kiyoshi
Asakawa, Nobuhiko Ozaki, Naoya Wada, Satoshi Shinada,
Kaoru Minoshima, Ferran Salleras Vila, Rei Suzuki, Takashi
Ohira, and Takeru Yamaji, respectively, for their productive
discussion, strong supports, and continuous encouragement.
REFERENCES
[1]

[2]
[3]

[4]
[5]

[6]

[7]

[8]

Statistics of the numbers of broadband subscribers investigated by the
Telecommunications Bureau, the Ministry of Internal Affiers andCommunications, Japan.
Statistics summarized by the Organization for Economic Co-operation
and Development (OECD).
Philip E. Ross, “Why CPU frequency stalled,” IEEE Spectrum, April
2008; Sally Adee, and, “37 years of Moore’s law,” IEEE Spectrum,
May 2008.
Product brochure of the carrier routing system (CRS-1), October 2006,
CISCO Systems, Inc., San Jose, California, USA.
e.g.: C. Schubert, R.H. Derksen, M. Möller, R. Ludwig, C-J. Weiske, J.
Lutz, S. Ferber, A. Kirstädter, G. Lehmann, and C. Schmidt-Langhorst,“Integrated 100-Gb/s ETDM receiver,” J. Lightwave Technol. 25(2007) 122.
E. Tangdiongga, Y. Liu, H. de Waardt, G.D. Khoe, A.M.J. Koonen, and
H.J.S. Dorren, “All-optical demultiplexing of 640 to 40 Gb/s using
filtered chirp of a semiconductor optical amplifier,” Optics Lett. 32(2007) 835.
E. Tangdiongga, H.C.H. Mulvad, H. de Waardt, G.D. Khoe, A.M.J.
Koonen, and H.J.S. Dorren, “SOA-based clock recovery anddemultiplexing in a lab trial of 640-Gb/s OTDM transmission over 50km fiber link,” ECOC 2007, Sept. 2007, Berlin, Germany.
Y. Liu, E. Tangdiongga, Z. Li, H. de Waardt, A.M.J. Koonen, G.D.
Khoe, X. Shu, I. Bennion, and H.J.S. Dorren, “Error-free 320-Gb/s alloptical wavelength conversion using a single semiconductor opticalamplifier,” J. Lightwave Technol. 25 (2007) 103.

5