COMMISSION D : Electronics and Photonics (Nov. '01- Oct. '04)
Edited by Masayuki Izutsu and Masahiro Tsuchiya
The fields of Electronics and Photonics are huge and include many active sub-fields therein. Therefore,
it is not a good idea to deal with the whole subjects of the fields in such a limited space as in the present
report.

On the other hand, it should be a truth that Japanese research institutions have played importantroles in the past decades for the progresses of Electronics and Photonics.

It should be pointed out that thistrend is still continuing in the last several years, which includes the time period of the interest in this report,
years from 2002 to 2005. Based upon those consideration, we, the editors of this chapter, decided toinvite Japanese leading researchers to overview recent conspicuous progresses of their respective
sub-fields and to contribute to the present report. In addition, we have a special review article in the
beginning of the chapter on the invention and development of vertical cavity surface emitting laser, which
is one of the most prominent Japanese landmarks in Electronics and Photonics.

It is given by Prof. K. Igaof Japan Society for the Promotion of Science (JSPS).
The following is a list of the sub-fields that the chapter editors have taken up.
D1

Vertical Cavity Surface Emitting Lasers (Special Review)
Kenichi Iga, Japan Society for the Promotion of Science

D2

Network Devices
Yoshio Itaya, NTT Corporation

D3

Femtosecond Technology
Osamu Wada, Kobe University

D4

THz Technology
Hiromasa Ito, Tohoku University

D5

Sensor Photonics
Kazuo Hotate, University of Tokyo

D6

Photonic Signal Processing
Takashi Kurokawa, Tokyo University of Agriculture and Technology

D7

Microwave Photonics
Tadao Nagatsuma, NTT Corporation

D8

Nano-technology
1Katsuyuki Utaka, Waseda University
D9

Polymeric Photonics
Toshikuni Kaino, Tohoku University

D10

Photonic Crystals
Susumu Noda, Kyoto University

D11

Silicon Photonics
Tadamasa Kimura, Electro-Communications University

D1. Vertical Cavity Surface Emitting Lasers (Special Review)
Kenichi Iga
Japan Society for the Promotion of Science
Abstract: In this chapter, we present device physics and technology based upon vertical cavity surface
emitting laser (VCSEL). We will survey its progress along with the history of semiconductor lasers since
the late 1960’s. The VCSEL photonics is opening up a new field of applications by taking the merits ofcompactness, small power consumption, high speed capability, arrayed configuration, and so on.

1. Introduction
The vertical cavity surface emitting laser (VCSEL) [1]-[6] is a semiconductor laser which can bemonolithically fabricated on the surface of semiconductor wafer. The light output can, therefore, be taken
vertically from the surface. Its name came from these reasons suggested by K. Iga and Y. Suematsu .
The initial VCSEL as shown in Fig. 1 was invented by K. Iga in 1977 at Tokyo Institute of Technology
and the first device was demonstrated in 1979, where we used 1300nm wavelength GaInAsP/InP material
for active layer. The motivation of VCSEL invention is to make a very short cavity laser as one of dynamic
single mode (DSM) lasers. The DSM laser concept was suggested by Y. Suematsu in around 1975 [7] forrealizing single mode fiber optical communication. Another issue is to make a semiconductor laser in termsof monolithic fabrication process.
The first room temperature continuous wave (CW) device using GaAs/AlGaAs was achieved in 1988 by
F. Koyama and the present author. Since 1992, VCSELs based on GaAs have been extensively studied and980, 850 and 780nm devices were commercialized into various photonics systems. Also, CW operation in
a 1300nm GaInAsP buried-structure VCSEL was achieved in 1993. After these circumstances,
1,300-1,550nm band devices, red color GaInAlP, and blue-ultraviolet GaN-based devices have beenstudied.
Extensive studies and realization trials have been made on high performance devices for Gigabit
2

Ethernet, high speed LANs, computer links, optical interconnects, arrayed sensors, and so on. The
technical progress of devices range from infrared to ultraviolet wavelengths has been achieved by world
wide laboratories including expansion of operating spectra by developing advanced materials andfabrication technologies. The vertical cavity surface emitting laser (VCSEL) is emerging into market as animportant device for high speed LANs and optical interconnects enabling parallelism in high speed
information transmission.
In conjunction with those VCSEL related technical progresses, new areas in photonics have been
proposed. For instance, inside of VCSEL devices, a lot of nano- and quantum- structures are utilized andthe concept of VCSEL has been expanded into nano-and quantum photonics including photonic crystals.
2. Physics and Scaling Law
The VCSEL structure may provide a number of advantages including ultra-low threshold operation due
to its small cavity volume Va, dynamic single mode operation, high speed modulation, wide range
frequency tuning, and so on. These are based upon a scaling law that is described in terms of cavity volume
Va . One of the important scaling law is to express threshold current I th to achieve laser oscillation can be
written as;

I th ∝ Va(1)

Therefore, the actual threshold current of VCSELs can be made vary small obeying this equation being
1/100 – 1/1000 of conventional stripe lasers. Together with the improved optical cavity formation
technology and the scheme for injecting electrons and holes effectively into small volume of active region,
this relation has proven the scaling law.
3. Actual Devices in Various Spectral Bands
We show a typical structure of GaAs/AlGaAs VCSEL device in Fig. 2. An AlAs oxidation is considered
to be the effective process current confinement in VCSEL’s. In commercially available 850 nm devices,sub-mA thresholds and >10 mW outputs have been achieved. The power conversion efficiency of >50%
has been demonstrated. The Gigabit Ethernet has already been in markets by the use ofmultimode-fiber-based optical links. This system is being extended to 10 Gigabits/s Ether and even fastersystems. As for the reliability of VCSELs, 107 hours of room temperature operation is estimated. Life testof oxide-defined devices exhibited higher reliability.
The long wavelength device (1,300 nm) is developed for metropolitan area networks (MAN). A 1,550
nm VCSEL with a MEMS tunable function was considered to be introduced in a high end MAN system.
3

One of viable materials for long wavelength emitters is a GaInNAs system which can be formed on a GaAs
substrate. A tunnel-junction is utilized in current-injection and confinement especially in long wavelength
devices. The polarization control technology in VCSELs have been established by using (311)B substrate
as shown in Fig. 3 [8]. The orthogonal polarization suppression ratio (OPSR) of >30dB was obtained evenin high speed modulation condition.
4. VCSEL-Related Sub-Systems
A wide variety of functions, such as frequency tuning, amplification, and filtering should be integrated.
Another possible way of moduling is to use the micro-optical bench (MOB) concept to ease the assemblingof components without precise alignment. Moreover, a 2-D parallel optical logic system can deal with alarge amount of image information with high speed. To this demand, the VCSEL will be a key device. Highpower capabilities from VCSEL’s is very interesting by featuring largely extending 2-D arrays. For the
purpose of realizing coherent arrays, coherent coupling of these arrayed lasers has been tried by using a
Talbot cavity and phase compensation is considered. It is pointed out that 2-D arrays are more suitable to
make a coherent array than a linear configuration, since we can take the advantage of 2-D symmetry. The
research activity is now forwarded to monolithic integration of VCSEL’s taking the advantage of small
cavity dimensions. A densely packed array has also been demonstrated for the purpose of making highpower lasers and coherent arrays. Into VCSEL’s, surface operating photonic elements using quantum wells
such as an optical switch, frequency tuner, optical filter, and super-lattice functional devices are now tried
to be integrated.
To establish an appropriate module technology utilizing VCSELs, a micro optical bench (MOB) has been
investigated together with planar microlens array. Micro Electro Mechanical Systems (MEMS) will be very
helpful.
5. Applications
The application areas of VCSELs are summarized in Table I. The possible materials are displayed in Fig.
4. In low power consumption and high speed modulation is inevitable low power interconnect applications
enabling >10Gbits/s transmission or 1Gbits/s zero-bias operation [6]. Actually, transmission experiments
over 10Gbits/s and zero-bias transmission have been reported. A 10 Gbits/s transmission experimentthrough a 100m multimode fiber was performed [6]. VCSEL’s in long wavelength may find the market in
10 Gigabit metropolitan networks together with high-speed detectors and silica fibers. Actually, GaInAs
and GaInNAs VCSEL’s show preferable performances.
A 780 nm VCSEL array has been introduced into a high speed laser printer. A laser printer has beendeveloped by using 4x8 VCSEL array enabling 2,400 DPI high speed printer.
The red color VCSEL emitting 650-680 nm can match to the low loss band of plastic fibers. Short
distance data links are considered by using 1 mm diameter plastic fibers having graded-index have been4

developed. This system provides us of very easy optical coupling. VCSEL’s can very nicely match to thisapplication.
Green to UV VCSEL’s will be useful in the optoelectronics field as in ultra-high density opticalmemories. A VCSEL pick-up may be good for high density optical memories and variety of sensors. Fullcolor flat displays and large area projectors, illuminations and light-signals, light decorations,
UV-lithography, laser processes, medical treatment, and so on.
By taking the advantages such as wide-band and small-volume, the optical interconnect is considered to
be inevitable in the digital technology. Some parallel interconnect scheme is wanted and new concepts isbeing researched. Vertical optical interconnect of LSI chips and circuit boards may be another interesting
issue. A recent application includes high speed optical wireless data transfer to digital display.
Lightwave sensing is one of the important applications of VCSELs. An optical mouse for computer is aninteresting application. Several schemes for optical computing have been considered by utilizing 2-D arraysof VCSEL’s and surface operating switches. The application for image recognition has been considered.
Very low threshold VCSEL’s have been developed, and stack integration together with 2-D photonic
devices are now actually considered.
6. Toward Nano-Photonics and Beyond
The scaling law of semiconductor lasers is still considered toward a nano-scale laser. A dust laser is oneofthe interesting examples. A single photon emitter is an extreme case. A photonics crystal is theextension of VCSELS structure to 3-D. The strain control has been applied to highly strained
GaInAs/GaAs quantum well to elongate wavelength. A quantum dot active region is effective to prevent
lateral diffusion of carriers to make a laser very small. A nano-scale super lattice is applied for a tunneling
junction in sophisticated carrier injection scheme. A near field VCSEL may be applicable to nano-scalesensing. In summary, the ultra-parallel and ultra-high speed photonics based upon sophisticated VCSEL’s
will open up a new era of millennium [9].
References[1] K. Iga, Laboratory Notebook, March 22 (1977) .
[2] K. Iga, T. Kambayashi, and C. Kitahara: The 26th Spring Meeting of Applied Physics Societies
27p-C-1 1 (1978).
[3] H. Soda, K. Iga, C. Kitahara and Y. Suematsu: Jpn. J. Appl. Phys. 18 (1979) 2329.
[4] K. Iga, F. Koyama, and S. Kinoshita: IEEE J. Quant. Electron. QE-24 (1988) 1845.
[5] K. Iga and F. Koyama: "Fundamentals and Application of Surface Emitting Laser" Kyouritsu Pub. Co.
Ltd. Tokyo (1999).
[6] K. Iga: IEEE J. STQE 6 (2000) 1201.
[7] Y. Suematsu, M. Yamada, and K. Hayashi：Proc. IEEE, 63 (1975) 208.
5

[8] N. Nishiyama, A. Mizutani, N. Hatori, M. Arai, F. Koyama, and K. Iga: IEEE JSTQE, 5 (1999) 530.
[9] K. Iga: IEICE Trans. Electron. E85, (2002) 10.

Light Output
Reflector

Electrodepnp

AlGaAs

p

n

p

GaAs

n

AlGaAsn

Reflector

Fig. 1

GaAs
Substrate

An initial idea of surface emitting laser invented by K. Iga in 1977 [1].

Fig. 2A realistic model of VDSEL device.

6

Fig. 3A structure of 1,200nm wavelength GaInAs/GaAs VCSEL frown on (311)B GaAs. [8]Fig. 4 Semiconductor materials for VCSELs

Table I Application of vertical cavity surface emitting lasers and related photonics
Technical Fields:

Systems

1. Communications:
2. Computer Optics:

LANs, MANs, Optical links, Mobile links, VSR, etc.
Computer links, Optical interconnects, High speed/Parallel data transfer,etc.
3. Optical Memory:
CD, DVD, Near-field disks, Multi-beam, Initializer, etc.
4. Opto-Equipments:
Laser printer, Laser pointer, Mobile tools, Home appliances, etc.
5. Information Processing: Optical processors, Parallel processing, etc.
6. Optical Sensing:
Optical fiber sensing, Bar code readers, Encoders, VCSEL mouse, etc.
7. Displays:
Array light sources, High efficiency light-sources, etc.
8. Illuminations:
Multi-beam search-lights, Micro illuminators, White light VCSELs,
Adjustable illuminations, etc.

D2. Network Devices
Yoshio Itaya
NTT Corporation
The establishment of a high-speed Internet environment through ADSL, FTTH and other schemes
continues to progress. The technology supporting the networks of this broadband/ubiquitous era is optical7

communication. This technology has been advancing steadily in parallel with the development of opticaldevices. These include optical fiber for carrying light long distances, semiconductor lasers for high-speed
generation of many optical signals, optical receivers for high-speed reception of optical signals and opticalcircuit components for adding/dropping optical signals. The laying of optical fiber started with the trunk
network and is now reaching even individual homes enabling the exchange of large volumes of data amongusers. The maturing of optical technology accelerates price competition in optical device and promote thecreation of new value-added optical-component technologies. The main results of optical devices are listed
below.
1. Uncooled and directly modulated DFB laser module in the high speed operation of 10Gb/s
2. DFB-lasers integrated with electronabsorption modulator operating at 10 Gb/s
3. Wavelength tunable lasers with a wide tuning range
4. Low driving voltage InP-based n-i-n Mach-Zehnder modulator
5. 100Gb/s operations of Uni-Travelling-Carrier photodiode6. Planar Lightwave Circuit (PLC) type optical switch for Reconfigurable Optical Add/Drop Multiplexer(ROADM)
7. Variable power level equalizing array waveguide (AWG) multiplexer
8. Wideband AWG multiplexer and demultiplexer for coarse WDM systems
References
K. Kasaya, K. Tsuzuki, H. Shibata and Y. Tohmori [2003], “SOA direct modulation inwavelength-selectable laser array light sources,” OECC, pp. 431-432, July
S. Shirai, Y. Tatsuoka, C. Watatani, T. Ota, K. Takagi, T. Aoyagi, E. Omura, and N. Tomita [2004], “120
uncooled operation of direct modulated 1.3 µm AlGaInAs-MQW DFB laser diodes for 10Gb/s telecom
applications,” Proc. OFC2004, ThD2
J. Klamkin, J. T. Getty, J. M. Hutchinson, L. A. Johannson, E. J. Skogen, and L. A. Coldren [2004],“Widely-Tunable Single-Mode Bipolar Cascade SGDBR Lasers,” Proc. 19th IEEE International
Semiconductor Laser Conference, WC2, Takamatsu
Y. Muramoto, K. Yoshino, S. Kodama, Y. Hirota, H. Ito, and T. Ishibashi [2004], “100- and 160-Gbit/s
operations of uni-traveling-carrier photodiode module,” Electron. Lett., Vol. 40, No. 6, pp. 378-380
K. Tsuzuki, T. Ishibashi, T. Ito, S. Oku, Y. Shibata, R. Iga, Y. Kondo, and Y. Tohmori [2003], “40-Gbit/s
n-i-n InP Mach-Zehnder modulator with a π-voltage of 2.2 V,” Electron. Lett., Vol.39, No. 20, pp.
8

1464-1466, Oct.
Y. Hashizume, H. Takahashi, T. Watanabe, S. Sohma, T. Shibata, and M. Okuno [2003], “Compact
32-channel 2×2 optical switch array based on PLC technology for OADM systems,” ECOC 2003, Mo3-5-4,
Sep.
K. Suzuki, T. Mizuno, M. Oguma, T. Shibata, H. Takahashi, and A. Himeno [2004], “Fully-reconfigurable
wavelength-selective optical 1×N switch based transversal filter configuration, “Proc. OFC2004,
WC2,Feb.
Y. Hashizume, Y. Inoue, T. Kominato, T. Shibata, and M. Okuno [2004], “Low-PDL 16-channel Variable
Optical Attenuator Array using Silica-based PLC, “ Proc. OFC2004, WC4, Feb.
H. Takahashi [2003], “Recent progress on silica-based AWG waveguide multi/demultiplexers,” trans of
IEICE, Vol. J86-C, No. 5, pp. 491-499, May

D3. Femtosecond Technology
Osamu Wada
Kobe University
Research and development project organization named Femtosecond Technology Research Association(FESTA) was established under the support of NEDO in 1995, and extensive research activities have been
pursued at Tsukuba Lab. in Tsukuba as well as at different satellite laboratories organized by member
companies. One of the most important aims of FESTA is to develop novel solid state photonic devices
suitable for optical time-division multiplexing (OTDM) systems working in the femtosecond time domain.
Conventional semiconductor-based optoelectronic devices and electronic ICs cannot function in the
femtosecond time domain due to the limit of electronic lifetime in semiconductors. To overcome this limit,
new device physics based on novel ultrafast phenomena should be investigated. Eleven research groups
have devoted their efforts for developing new ultrafast devices including monolithic mode-locked
semiconductor lasers, waveguide-type dispersion control devices for pulse compression, and a variety of
all-optical switches such as symmetric Mach-Zehnder (SMZ) switches, intersubband transition switches,
optical semiconductor amplifier (SOA)-based switches and wavelength converters, and also novel verticalstructure optical switch based on organic film.
9All the developed devices have shown basic capabilities of ultrafast operation and 1 Tbps class operation
has been demonstrated in some of them. For example, monolithic mode-locked lasers with short cavity
length have demonstrated 500 GHz and 1 THz repetition rate operation with extremely low jitter. Also 160
Gbps clock extraction function has been demonstrated for practical applications in real systems.
SOA-based SMZ switch has been shown 160 and 320 Gbps-to-10 Gbps DEMUX operation and many
more useful functions including 3R and wavelength conversion. It has been achieved to fabricate
intersubband transition (ISBT) switches by developing new heterostructure materials based on
AlAsSb/InGaAs/InP as well as AlGaN/GaN, both having large enough conduction band discontinuity in
optical communication wavelength band. Waveguide-structure Sb-based ISBT switches have shown 1 THz
DEMUX operation. Further efforts to lower the switching energy will make these devices practical in realsystems. An interesting approach of all-optical switch has been demonstrated by a surface-normal switch
based on J-aggregate dye film. Time-to-space conversion has been achieved; a series of 1-ps pulses has
been extracted as light spots which are developed spatially on a 1-mm square switching plane. Such newswitch function could be useful for packet header recognition for packet routing in OTDM systems. Novelphysics and materials such as qunatum dots and photonic crystal have been extensively developed at
FESTA. Quntum dot SOAs have been demonstrated to function as very fast response gate switch over 100
Gbps and also wavelength conversion switch through four-wave mixing in femtosecond speed. We havedemonstrated that the polarization-insensitive operation can be achieved by controlling the dot shape,
which would be extremely important for making these devices used in practical systems.
Details of FESTA works and related references have been summarized in a publication by Wada, O. in
2004.

Fig. 1

Basic diagram of OTDM system.

10

Saturable absorber(17 µm)HR coating

HR coating

Cavity length=174 µm
Gain sections

GRIN-SCH-MQW
active layer

Fig.2

Structure of monolithic colliding pulse mode-locked laser for high repetition rate operation.

(a)

(b)
10

1

Intensity (dBm)

SHG intensity (au)

1.2
0.8
0.6
0.4
0.2
0

-20

-10
0
10
Delay time(ps)Fig. 3

0
-10
-20
-30
-40
-50
1535

20

1545
1555
1565
Wavelength(nm)1575Operation characteristics of mode-locked laser.

Switch-on
control pulseT
Signal pulses

T

Switch-off
control pulse

Fig. 4

Nonlinearwaveguide 1

Nonlinearwaveguide 2
φNL in arm 1

T

Canceling

φNL in arm 2

Structure and operation principle of symmetric Mach-Zehnder interferometer all-optical switch

using SOA nonlinear waveguides.

115Intensity (a.u.)

(a)

4
3
2

-4

1
20

40 60 80 100 120
Time delay (ps)

-6
-7
(c)
-8 10.5 Gbps
-9 baseline
231-1
-10
27-1
-11
-12
-40
-35
-30
-25
Received Power (dBm)

Intensity (a.u.)

3

(b)

2
1
0
0

Fig. 5168 Gbps
DEMUX
PRBS: 231-1
PRBS: 27-1

-5
Log (BER)002040 60 80 100 120
Time delay (ps)Input and output signals and bit error rate data for 168 Gbps-to-10 Gbps DEMUX operation

using SMZ all-optical switch.

Amplitude

(b)

(a)

Input signal (1 THz)
Ch. 1 Ch. 2

Output signal

Coupled QW

×80 periods

Output signal
Amplitude

Ch. 1

AlAsSb 8 nm
InGaAs 8 ML
AlAs 3 ML
InGaAs 8 ML
AlAsSb 8 nm

Ch. 3 Ch. 4

InAlAsInAlAsInput
signalCh. 2

Control InP sub.
signal

Ch. 3

Ch. 4

-1

0

1

2

3

4

Time [ps]Fig. 6

Waveguide device structure of intersubband all-optical switch and demonstarated DEMUX

operation for 1 THz signal.

12

THz pulse train
8 ・・・1

SQ-film

CCD camera

Delay optics

87

4

(a)

８連パルス
a
Re

p
ut
do

e
uls

6

3 2

5

1

(b)

8 7 6 54 3 2 1

Fig. 7

Time-to-space conversion applied to DEMUX function for ultrafast pulses using organic (SQ)

film-based surface normal all-optical switch.
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Kubota(NICT) [2004], “Ultrafast time-serial space-parallel converter using organic dye films,” IEICE
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14

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Ishikawa[2003]: “Similar role of waveguide bend in photonic crystal circuit and disordered defects incoupled cavity waveguides: An intrinsic problem in realizing photonic crystal circuits”, Phys. Rev.,
vol.B67, pp.115208-115215
Nakamura, S., Y. Ueno, and K. Tajima [2001], "168-Gb/s all-optical wavelength conversion with aSymmetric-Mach-Zehnder-type switch", IEEE Photon. Technol. Lett., Vol. 13, No. 10, pp. 1091-1093.
Neogi, A., H. Yoshida, T. Mozume, N. Georgiev and O. Wada [2001a]: "Temperature-insensitive
intersubband-transitions in InGaAs/AlAsSb multiple quantum well designed for optical communication
wavelength" Jpn. J. Appl. Phys. Lett., vol. 40, p. L558
Neogi, A., H. Yoshida, and O. Wada [2001b]: "Effect of thermally induced charge-carrier transfer onnear-infrared intersubband transitions in InxGa1-xAs/AlAs/AlAs1-ySby/InP coupled quantum-well structure",
Phys. Rev. B. Vol.63, p.235320
Neogi, A., H. Yoshida, T. Mozume, N. Georgiev, T. Akiyama, O. Wada, A. Tackeuchi [2001c]: "Ultrafast
all-optical modulation by near-infrared intersubband transition in n-doped InGaAs/AlAsSb quantum wells",
Opt. & Quantum Electron., Vol.33, (2001).
Neogi, A, H. Yoshida, T. Mozume, N. Georgiev, T. Akiyama and O. Wada [2001d]: "Intersubband
Transition in InGaAs/AlAsSb/InP coupled double quantum well structures optimized for communication
wavelength operation", Electron. Lett. vol. 36, 1972 (2000); Eratta - vol. 37, p.203
Neogi, A., H. Yoshida, T. Mozume, N. Georgiev, and O. Wada [2001e]: "Intersubband transition andUltrafast all-optical switching in coupled InGaAs/AlAsSb quantum well" Select. Top. J. of Quant. Electron,
p. 710
Nishikawa, S., S. Lan, N. Ikeda, Y. Sugimoto, H. Ishikawa, K. Asakawa[2002a], “Opticalcharacterization of photonic delay lines based on one-dimensional coupled defects”, Optics Lett., vol.27,
no.23, pp.2079-2081
16

Nishikawa, S., S. Lan, N. Ikeda, Y. Sugimoto, H. Ishikawa, K. Asakawa [2002b], “Design and fabricationof impurity band-based photonic crystal waveguide for optical delay lines”, Appl. Phys. Lett.,vol.81, no.11,
pp.1946-1948
Nishikawa, S., S. Kohmoto, H. Nakamura, Y. Sugimoto, N. Ikeda, T. Ishikawa,T. Akiyama, H. Ishikawa, O.
Wada [2002c]: "Dephasing time characterization of InAs quantum dots by degenerate four-wave mixing
measurement", Physica E, Vol.13, p.273
Nishikawa, S., S. Lan, O. Wada, T. Nishimura, K. Akahane and M. Kawabe[2002d]:"Lateral-Coupling-Induced Modification of Density of States and Exciton Dynamics in High-Density
Ordered In0.4Ga0.6As/GaAs(311)B Quantum Dot Arrays", Jpn. J. Appl. Phys., Vol.41, p.3766
Tajima, K., S. Nakamura, A. Furukawa, and T. Sasaki[2004], “Hybrid-integrated Symmetric

Mach-Zehnder all-optical switches and ultrafast signal processing”, IEICE Trans. Electron. Vol. E87-C, No.
7, pp. 1119-1125
Tatsuura, S.,

Osamu Wada, Makoto Furuki, Minquan Tian, Yasuhiro Sato, Izumi Iwasa, Lyong Sun Pu[2001a]:” Femtosecond two-dimensional serial to parallel pulse converter using a squarylium Dye
J-aggregate film”, Opt.Quantum Electron. Vol.33, p.1089
Tatsuura, S., Osamu Wada, Makoto Furuki, Minquan Tian, Yasuhiro Sato, Izumi Iwasa, Lyong Sun Pu[2001b]: “All-optical two-dimensional serial to parallel Pulse converter using an organic film withfemtosecond optical response”, Jpn.J.Appl.Phys. Vol.40, p.2731
Tatsuura, S., O.Wada, M.Tian, M.Furuki, Y.Sato, I.Iwasa, L.S.Pu, and H.Kawashima [2001c]: “Largekai(3) of squarylium dye J-aggregates measured using the Z-scan technique” Appl.Phys.Lett. Vol.79,
p.2517 (2001)
Tatsuura, S., M. Tian, M. Furuki, Y. Sato, I. Izawa, L. S. Pu, H. Kawashima, H. Ishikawa [2002]:“Microstructure of squarylium dye J aggregate films examined on the basis of optical behavior at low
temperature”, Appl. Phys. Lett., vol.81, p.2704-2706
Yoshida, H., T. Simoyama, A. V. Gopal, J. Kasai, T. Mozume, and H. Ishikawa [2004]: "Ultrafast
All-Optical Switching and Modulation Using Intersubband Transitions in Coupled Quantum Well
Structures", IEICE Trans. Electron., Vol.E-87C, p.1134 (Invited paper)
17

Wada, O. [2004]: “Femtosecond all-optical devices for ultrafast communication and signal processing,”
New J. Phys., Vol. 6, p.183, http://stacks.iop.org/1367-2630/6/183

D4.THz Technology
Hiromasa Ito
Tohoku University

The THz-wave region has attracted significant interest in these years. The generation of THz radiation by
optical rectification or photo-conductive switching has been extensively studied by using femto-second
laser pulses. Applied research, such as time domain spectroscopy (TDS), makes use of the high time
resolution of THz-waves and ultra broad bandwidth up to the THz region.
In contrast, monochromatic THz-wave source developments have been extensively performed.
Widely tunable monochromatic THz source based on the polariton mode scattering of LiNbO3 or MgO:
LiNbO3 crystals showed great advancement. Those are THz parametric oscillator (TPO) and THz
parametric generator (TPG). The TPO/TPG has proved to be a useful coherent THz-wave source which
operates at room temperature. It is wide tunable and also random fast frequency access in 100- to 300

m(1- to 3 THz) range and can emit peak powers of up to several tenths of a milli-Watt or more.
The difference between a TPO and a TPG is that the former has an idler cavity while the latter has not.
TPO requires only one pump source, and its linewidth is several tens of GHz. Recently developed ringcavity TPO with galvano scanner makes the TPO’s frequency response possible up to 1ms (1 kHz), andvariety of new spectroscopic imaging and analyzing applications are expected.
The linewidth of TPG is in nature wider than that of TPO. However, by introducing an injection seeding
technique to the idler, TPG spectrum is narrowed to the Fourier transform limit of the pulsewidth(~100MHz or less). The purity of the THz-wave frequency was dramatically improved to/ < 10-4.

Simultaneously, oscillation with higher output power, wider tenability and good stability, wasdemonstrated.
Surface-emitted THz-wave generation using bulk slanted-PPLN and slab optical waveguided PPLN was
successfully demonstrated. The QPM condition of the slanted-PPLN works well in both pulsed and cw
operation. Dual wavelength sources foe excitation of DFG were constructed from all telecom components
worked at 1.55

m. The waveguided structure is key for increasing conversion efficiency especially under

the CW operation.
Remarkable advancements were reported for quantum cascaded laser (QCL) research. Lower than 318

THz operation is one of the big target right now especially for homeland security purpose.
materials of InAs/GaSb has been investigated extensively.

QCL with new

Though relatively limited tuning range of one

single tip QCL, there are no doubts that it will efficiently work if the THz application targets are clearly
fixed.
References
Imai, K., K. Kawase, J. Shikata, H. Minamide, and H. Ito [2001], “An injection-seeded terahertz-wave
parametric oscillator”, Applied Physics Letters, vol. 78, pp. 1026-1028
Kawase, K., J. Shikata, K. Imai, and H. Ito [2001], “A Transform-limited, Narrow-Linewidth, THz-wave
Parametric Generator”, Applied Physics Letters, vol. 78 no. 19, pp. 2819-2821
Imai, K., K. Kawase, and H. Ito [2001], “A frequency-agile terahertz-wave parametric oscillator”, Opt.
Express 8, pp. 699-704
Ito, H., T. Hatanaka, S. Haidar, K. Nakamura, K. Kawase, and T. Taniuchi [2001], “Periodically poled
LiNbO3 OPO for generating Mid IR to terahertz waves”, Ferroelectrics, vol.253, pp.95-104
Sato, A., K. Kawase, H. Minamide, S. Wada, and H. Ito [2001], “A Tabletop Terahertz-Wave Parametric
Generator Using a Diode-Pumped Solid-State Laser”, Trends in Optics and Photonics Series (TOPS), vol.
50, pp. 456-460
Sato, A., K. Kawase, H. Minamide, S. Wada, and H. Ito [2001], “Tabletop terahertz-wave parametric
generator using a compact, diode-pumped Nd:YAG laser”, Review of Scientific Instruments, vol. 72, No. 9,
pp. 3501-3504
Kawase, K., J. Shikata, H. Minamide, K. Imai, and H. Ito [2001], “Arrayed silicon prism coupler for a
THz-wave parametric oscillator”, Applied Optics, vol.40, No.9, pp.1423-1426
Avetisyan, Y., Y. Sasaki, and H. Ito [2001], “Analysis of THz-wave surface-emitted difference-frequency
generation in periodically poled lithium niobate waveguide”, Applied Physics B, vol.73, pp.511-514
Kawase, K., H. Minamide, K. Imai, J. Shikata, and H. Ito [2002], “Injection-seeded terahertz-wave
parametric generator with wide tunability”, Applied Physics Letters, vol.80, no.2, pp.195-197
Kawase, K., J. Shikata, and H. Ito [2002], “Terahertz wave parametric source (Topical Review)”, Journal
19

of Physics D: Applied Physics, vol.35, no.3, pp.R1-R14
Karino, K., J. Shikata, K. Kawase, H. Ito, and I. Sahashi [2002], “Terahertz-wave parametric generation
characteristics of MgO: LiNbO3”, Electronics and Communications in Japan, Part 2, vol.85, no.4, pp.22-29
Kawase, K., S. Ariyoshi, C. Otani, H. Minamide, K. Imai, J. Shikata, and H. Ito [2002], “Widely tunableTHz-wave parametric generator for imaging system”, RIKEN Review, no.47, pp.48-51
Sato, A., K. Imai, K. Kawase, H. Minamide, S. Wada, and H. Ito [2002], “Narrow-linewidth operation of acompact THz-wave parametric generator system”, Optics Communications, vol.207, no.1-6, pp.53-359
Ito, H., and K. Kawase [2002], “Tunable compact THz sources and their application”, Trends in Optics andPhotonics (TOPS), vol.79, pp.75-77
Imai, K., K. Kawase, H. Minamide, and H. Ito [2002], “Achromatically injection-seeded terahertz-wave
parametric generator”, Trends in Optics and Photonics (TOPS), vol.79, pp.233-235
Sasaki, Y., Y. Avetisyan, K. Kawase, and H. Ito [2002], “Tunable THz-wave difference frequency
generation from slant-stripe-type PPLN based on surface-emitting geometry”, Trends in Optics andPhotonics (TOPS), vol. 79, pp. 20-22
Imai, K., K. Kawase, M. H., and H. Ito [2002], “Achromatically injection-seeded terahertz-wave
parametric generator”, Optics Letters, vol.27, no.24, pp.2173-2175
Sasaki, Y., A. Yuri, K. Kawase, and H. Ito [2002], “Terahertz-wave surface-emitted difference frequency
generation in slant-stripe-type periodically poled LiNbO3 crystal”, Applied Physics Letters, vol.81, issue
18, pp.3323-3325
Shikata, J., K. Kawase, T. Taniuchi, and H. Ito [2002], “Fourier-Transform Spectrometer with aTerahertz-Wave Parametric Generator”, Japanese Journal of Applied Physics, part 1, vol.41, no.1,
pp.134-138
Imai, K., S. Sugawara, J. Shikata, K. Kawase, H. Minamide, and H. Ito [2003], “The effect of injection
seeding on terahertz parametric oscillation”, Electronics and Communications in Japan, Part 2, vol.86, no.1,
pp.26-35

20

Imai, K., K. Kawase, H. Minamide, and H. Ito [2003], “A rapidly tunable terahertz-wave parametricoscillator”, Electronics and Communications in Japan, Part 2, vol.86, no.4, pp.18-26
Watanabe, Y., K. Kawase, T. Ikari, H. Ito, Y. Ishikawa, and H. Minamide [2003], “Spatial patternseparation of chemicals and frequency-independent components by Terahertz spectroscopic imaging”,
Applied Optics, vol.42, issue 28, pp.5744-5748
Kawase, K., J. Shikata, and H. Ito [2003], “Widely tunable THz-wave generation using nonlinear optics”,
Solid-state mid infrared laser sources, Edited by I. T. Sorokina and K. L. Vodopyanov, pp.433-461
Watanabe, Y., K. Kawase, T. Ikari, H. Ito, Y. Ishikawa and H. Minamide [2003], “Component spatial
pattern analysis of chemicals using terahertz spectroscopic imaging”, Applied Physics Letters, vol.83, no.4,
pp.800-802
Imai, K., K. Kawase, H. Minamide, and H. Ito [2003], “A rapidly tunable terahertz-wave parametricoscillator”, Electronics and Communications in Japan, part 2, vol.86, no.4, pp.18-26
Watanabe, Y., K. Kawase, T. Ikari, H. Ito, Y. Ishikawa, and H. Minamide [2003], “Spatial Pattern
Separation of Chemicals and Frequency-Independent Components by Terahertz Spectroscopic Imaging”,
Applied Optics, vol.42, issue 28, pp.5744-5748
Sasaki, Y., H. Yokoyama, and H. Ito [2004], “Dual-wavelength optical-pulse source based on diode lasers
for high-repetition-rate, narrow-bandwidth terahertz-wave generation”, Optics Express, vol. 12, no. 14,
pp.3066-3071
Watanabe, Y., K. Kawase, T. Ikari, H. Ito, Y. Ishikawa, and H. Minamide [2004], “Component analysis ofchemical mixtures using terahertz spectroscopic imaging”, Optics Communications, vol.234, pp.125-129
Ohtani, K., K. Fujita and H. Ohno [2004], “A low threshold current density InAs/AlGaSb superlatticequantum cascade laser operating at 14µm”, Jpn. J. Appl. Phys., vol.43, pp.L879-881.
Takahashi, M., Y. Ishikawa, J. Nishizawa, and H. Ito [2005], “Low-frequency vibrational modes ofriboflavin and related compounds”, Chemical Physics Letters 401, pp.475-482

21

D5. Sensing Photonics
Kazuo Hotate
Univesity of Tokyo
Among various types of optical fiber sensors, fiber optic distributed and multiplexed sensing
technologies have been intensively studied, which have provided schemes to measure, for example,
distribution of longitudinal strain or lateral force along an optical fiber.

In these systems, the fiber can act

as nerve networks to sense damage of materials or structures, in which the fiber is embedded.

These

techniques are the key to realize “smart materials” and “smart structures” for improving reliability, safety
and security of the society (see Fig.1).

The 16th International Conference on Optical Fiber Sensors(OFS-16) was held in Nara, Japan, in October, 2003. In the conference, almost half of the papers wererelated to these technologies.

Some representatives are described bellow.

A down-shifted frequency of Brillouin scattering caused in a fiber is changed in proportion tolongitudinal strain applied to it. By this phenomenon, a scheme for fiber-optic distributed strain sensing
was proposed and developed in Japan, in which optical time domain reflectomerty technique was used forthe distribution measurement.

However, in this scheme based on pulsed-lightwave, spatial resolution was

limited around 1m, and long measurement time is required for obtaining enough signal to noise ratio.

Onthe contrary, another technique based on continuous lightwave has recently been proposed also by Japanese
researchers.

In this technique, pump and prove lightwaves, propagating in the fiber in opposite directions,

are modulated in frequency, which realizes localized excitation of stimulated Brillouin scattering.

By this“Brillouin Optical Correlation Domain Analysis: BOCDA,” a spatial resolution of 1.0cm wasdemonstrated.
The BOCDA technique has recently been applied to find clacks caused in a concrete block, in which thesensing fiber is embedded.

Clacks with sub millimeter width have successfully been recognized, for the

first time, through strain distribution caused by the crack along the fiber.

Another feature of thistechnique is fast measurement speed. About 60Hz sampling rate has been demonstrated, which is 104
times faster than the pulsed lightwave technique. Dynamic strain measurement at multiple arbitrary points
along a fiber, which is pasted on a building model, has also been demonstrated under vibration excited byan earthquake waveform, as shown in Fig.2.

Additionally, a simplified and low cost configuration for

the BOCDA has also been developed. The BOCDA is only one technique that can realize both the highspatial resolution and the fast measurement speed.

This technique was selected as the Hasunuma Prize in2002 from the Society of Instrument and Control Engineers, SICE.
Basic principle of the BOCDA technique is “synthesis of optical coherence function: SOCF,” in which
arbitrary shapes of optical coherence function can be synthesized by modulating optical frequency of a lightsource.

This is invented also in Japan as a technique for distribution measurement.

With the SOCF

technique, a novel multiplexing way of fiber Bragg grating (FBG) strain sensors has been proposed and22

experimented.

In traditional techniques, FBGs with different Bragg wavelength were required forwavelength division multiplexing.

In these systems, number of the FBGs is limited and the system

becomes expensive.

On the contrary, FBGs with the same Bragg wavelength can be multiplexed by using

the SOCF technique.

Multiplexed and dynamic strain sensing has been successfully demonstrated by thetechnique.
By also applying the SOCF technique, a fiber optic distributed force sensing has been proposed andstudied.

Sensing mechanism is polarization mode coupling induced by lateral force in a polarization

maintaining fiber.

Propagation speed difference between the two polarization modes is used to resolve theforce-applied position.

Introducing a special laser diode, a SSG-DBR LD invented by NTT, Japan, whichhas quite a wide frequency tuning range, the spatial resolution has been improved to be 20cm.
Techniques for diagnosing fiber optic subscriber networks have also been studied using SOCF technique.
We must measure the reflectivity distribution around the optical elements, which locate at the end of the
network beyond, for example, a 5km length optical fiber, with cm order spatial resolution. Recently, it
has been found that the SOCF technique can also measure reflectivity distribution at a region beyond thecoherence length of a laser source.

By this scheme, 10cm spatial resolution with 5km measurement range

has been demonstrated.

Ex.4

Nerve System for Smart Materials

Ex.2~ 100m range
Sub cm resol.

Nerve System for Smart Structures
and Materials
Bridge, Tunnel, Dam,
Highway, Levee,……

Earthquake !!
Optical Fiber

Ex.3

Security and Safety System
Buildings

Km range
Sub m resol.

Damage !!

Optical Fiber

Burglar !

Fig. 1 Fiber optic nerve systems for smart structures and smart materials.

23

3000

(a

3000

(b)

2000

1000

Strain [µε]Strain [µε]

1000

0

-1000

dynamic
sensing pts

(c)

2000

0

-1000

Strain gauge [200Hz] @ pos. 3
Optical fiber [19Hz] @ pos. 3
Residual strain (gauge)
Residual strain (fiber)

-2000

-3000

-2000

Strain gauge [200Hz] @ pos. 4
Optical fiber [19Hz] @ pos. 4
residual strain

-3000
5

10

15

20

Time [s]

5

10

15

20

25

Time [s]Fig. 2 Dynamic and multiple-points strain measurement of a building model by BOCDA system.
(a) Building model with a fiber, and (b) and (c) dynamic strain measurement.

References
Hotate, K., and M. Tanaka [2001], “Correlation-based continuous-wave techniques provide high spatial
resolution for distributed fiber optic sensing”, SPIE OE Magazine, 11, pp.36-40 <Invited>
Hotate, K., and M. Tanaka [2001], “Correlation-based continuous-wave technique for fiber optic
distributed strain measurement using Brillouin scattering with cm-order spatial resolution −Applications
to smart materials−”, IEICE Trans. on Electron., vol.E84-C, no.12, pp.1823-1828 <Invited>
Hotate, K., and M. Tanaka [2002], “Distributed fiber Brillouin strain sensing with 1cm spatial resolution bycorrelation-based continuous-wave Technique”, IEEE Photon. Tech. Lett., vol.14, no.2, pp.179-181
Hotate, K., and M. Tanaka [2002], “Application of correlation-based continuous-wave technique for fiber
Brillouin sensing to measurement of strain distribution on a Small Size Material”, IEEE Photonic
Technology Letters, vol.14, no.5, pp.675-677
Hotate, K. [2002], “Application of synthesized coherence function to distributed optical sensing,” IOP
Measurement Sci. and Tech., vol.13, no.11, pp.1746-1755
Hotate, K. [2002], “Recent progress in Brillouin based fiber sensor technology”, 15th Intern. Conf. on
Optical Fiber Sensors (OFS-15), Portland, WC1, pp.297-300 <Invited>
Hotate, K. and S. S. L. Ong [2002], “Distributed fiber Brillouin strain sensing by correlation-based
continuous-wave technique –cm-order spatial resolution and dynamic strain measurement–”, SPIE
24

Photonics Asia, Shanghai, 4920-51, pp.299-310 <Invited>
Hotate, K. and M. Kashiwagi [2003], “High spatial resolution reflectometry for optical subscriber networks
by synthesis of optical coherence function with measurement range enhancement”, IEICE Trans. on
Electron., volE86-C, no.2, pp.213-217
Hotate, K. and S. S. L. Ong [2003], “Distributed dynamic strain measurement using a correlation-based
Brillouin sensing system”, IEEE Photon. Technol. Lett., vol.15, no.2, pp.272-274
Hotate, K. [2003], “Optical Fiber Sensors for Smart Materials/Structures and Optical Communicaitons”,
International Meeting on New Frontiers for Ubiquitous IT Services, Atsugi <Invited>
Hotate, K. [2003], “Fiber Optic Distributed Sensing for Smart Materials and Structures by Optical
Correlation Domain Technique with Continuous Lightwave”, 16th Intern. Conf. on Optical Fiber Sensors(OFS-16), Nara, SS-6, pp.510-513 <Invited>
Hotate, K., M. Enyama, S. Yamashita and Y. Nasu [2004], “A multiplexing technique of fiber Bragg
grating sensors with the same reflection wavelength by the synthesis of optical coherence function”,
Measurement Sci. and Technol., vol. 15, no.1, pp. 148-153
Hotate, K., A. Kuramoto and Z.-Y. He [2004], “Optical fiber stress-location measurement by synthesis ofbinary optical coherence function,” IEEE Photon. Technol. Lett., vol. 16, no.2, pp. 578-580
Hotate, K. [2004], “Trends and prospects for optical distributed sensing −Fiber-optic nerve systems for
smart materials and smart-structures−”, SPIE Vol.5502, Second European Workshop on Optical Fiber
Sensors, Santander, pp.51-58 <Invited>
Hotate, K. [2004], “Potential applications of optical fiber sensing technology for future society”,
International Symposium on Network and Center-Based Research for Smart Structures Technologies andEarthquake Engineering, Osaka <Invited>
Hotate, K. [2004], “Fiber optic nerve systems for smart materials and smart structures”, SPIE Optics East
2004, Philadelphia, 5604-1, pp.1-10 <Invited>
Hotate, K. [2004], “Optical Fiber Sensors for Smart Materials/Structures and Optical Communicaitons”,
Chapter 9 in “New Photonics Technologies for the Information Age”, ed., by S. Sudo and K. Okamoto,25Artech House, pp.159-179
He, Z. and K. Hotate [2002], “Distributed Fiber-optic stress-location measurement by arbitrary shaping of
optical coherence function”, Jour. of Lightwave Tech., vol.20, no.9, pp.1715-1723
Zhu, B., T. Saida and K. Hotate [2003], “Variable optical filter using dynamic grating in Er doped fiber
controlled by synthesis of optical coherence function: Proposal and experimental verification”, IEICE
Trans. on Electron., IEICE Trans., vol.E86-C, no.1, pp.97-99
Kashiwagi, M. and K. Hotate [2004], “Elongation of Measurement Range by Successively Shifting
Measurement Window in a High Spatial Resolution Reflectometry for Optical Subscriber Networks bySynthesis of Optical Coherence Function”, Measurement Sci. and Technol., vo.15, no.8, pp. 1512-1518
Enyama, M. and K. Hotate [2004], “Dynamic and random-access strain measurement by fiber Bragg
gratings with synthesis of optical coherence function”, SPIE Optics East 2004, Philadelphia, 5589-20,
pp.144-153 <Invited>

D6. Photonic signal processing
Takashi Kurokawa
Tokyo University of Agriculture and Technology
The use of ultra-short optical pulses has been highly expected in various fields of technology such as
high-speed fiber optic communication system, high-precision optical measurement, and laser processing.
These applications have increased the demands for synthesizing the optical short pulses with arbitrary
waveforms and evaluating the quality of ultra-short optical pulses. So we are constructing optical shortpulse synthesizers and analyzers.
Frequency decomposed parallel photonic signal processing using arrayed-waveguide grating is very
suitable for Tbit/s signals because the most high-speed electronics can be operated at 100 Gbit/s or less.
Figure 1 shows the operation principle. The input optical pulse or the light from the optical frequency
comb is decomposed by the first AWG, the phase and the amplitude of each frequency component ismodulated, and synthesized by the second AWG. Various kinds of photonic signal processing, including
waveform shaping, arbitrary waveform generation, optical code division multiplexing, can be achieved.
For such an application, we have developed analogue and digital type optical pulse synthesizers using
26

AWGs. The analogue type optical synthesizer has advantages that it can be operated for an optical pulse
train with any repetition frequency and has almost flat transmission profile. On the other hand, the digital
type optical synthesizer is usually applied to arbitrary waveform pulse generation in combination with
optical frequency comb and the frequency domain optical code division multiplexing (OCDM).
We also have demonstrated a novel waveform measurement system of ultra-short optical pulses basedon the two-photon absorption process in a Si-image sensor. Using an interferometer with a tilt mirror in thereference path, the relative time difference between the signal and reference pulses is spatially distributedon the Si-image sensor, so the intensity auto-correlation is monitored as an image at a time without using
moving parts.

Space(frequency)

Phase/amplitude
modulation
Parallelsignalst

AWG
Input pulse or
frequency comb (time-to-space)

Fig. 1AWG(space-to-time)tSynthesized
pulsesPrinciple of frequency decomposed parallel photonic signal processing .

References
Kurokawa, T.[2001], "Optical Signal Processing for Communication and Information Systems", Proc.
CLEO/Pacific Rim, Makuhari, Vol. , pp.532-534 <Tutorial, Invited>.
Sakai, F., Y. Tanaka, and T. Kurokawa [2001], "Two-photon absorption in a Si-photodiode array and its
application to ultrafast optical pulse waveform measurement", OSA Annual Meeting and Exhibit, WE2,Long Beach,.
Tanaka, Y., P. G. Chua, T. Kurokawa, H. Tsuda, M. Naganuma, and M. Takeda [2002], “Reflectometry
based on two-photon absorption of a silicon avalanche photodiode”, Proc. 15th Optical Fiber Sensors
Conference, Portland, pp.577-580.
Tanaka, Y., T. Kurokawa [2002], “Profilometry using two-photon absorption of silicon avalanche
photodiode”, Proceedings of SPIE, Vol. 4919, pp.102-109 <Invited>.
27

Itoh, Y., K. Aizawa, Y. Tanaka, H. Tsuda [2003], “Measurement of short optical pulse spectra using arrayedwaveguide grating”, Proc. 6th International Symposium on Contemporary Photonicsn Technology,
Post-Deadline papers, p.7.
Tanaka, Y., N. Sako, T. Kurokawa, H. Tsuda and M. Takeda [2003], “Profilometry based on two-photon
absorption in a silicon avalanche photodiode”, Optics Letters, vol.28, no.6, pp402-404.
Yamanaka, A., M. Yamamoto, Y. Tanaka, T. Kurokawa, T. Kawanishi and M. Izutsu [2003], “AMulti-wavelength light source using an optical single-side band modulator an arrayed waveguide grating”,
Proc. 5th Pacific Rim Conference on Lasers and Electro-Optics, Taipei, p.714.
Sako, N., S. Imoto, Y. Tanaka and T. Kurokawa [2003], “Measurement accuracy of profilometry based on
two-photon absorption”, Proc. 5th Pacific Rim Conference on Lasers and Electro-Optics, Taipei, p.299.
Itoh, Y., K. Aizawa, Y. Tanaka, H. Tsuda and T. Kurokawa [2003], “Optical Spectrum analyzer for opticalshort pulses”, Proc. 5th Pacific Rim Conference on Lasers and Electro-Optics, Taipei, p.41.
Imoto, S., N. Sako, Y. Tanaka and T. Kurokawa [2003], “Accuracy improvement of two-photon absorption
based measurement by temperature controlled Si-photodetecter”, Proc. 5th Pacific Rim Conference on
Lasers and Electro-Optics, Taipei, p.516.
Nezu, T., Y. Tanaka and T. Kurokawa [2003], “Delayed self-heterodyne linewidth measurement of fiber
Bragg grating laser”, Proc. 5th Pacific Rim Conference on Lasers and Electro-Optics, Taipei, p.388.
Suzuki, T., Y. Shibata and H. Tsuda [2003], “Design and the fabrication of the small v-bend opticalwaveguide using an elliptic mirror”, Proc. 11th European Conference on Integrated Optics, Prague, Czech.
Suzuki, T., Y. Shibata and H. Tsuda [2003], “Small v-bend optical silica-waveguide using an elliptic mirror
for planar lightwave circuits”, Proc. 9th Microoptics Conference, Tokyo, H-20.
Tate, A., T. Suzuki, Y. Shibata and H. Tsuda [2004], “Proposal of WDM multi/demultiplexer with deep
grooves and parabolic mirrors”, Proc. 7th International Symposium on Contemporary Photonics
Technology, Tokyo, PDP-1.
Hakamata, M., and H. Tsuda [2004], “Diffractive optical elements using the sub-wavelength scale pillar
28array structure,” SPIE Photonics West, San Jose, pp.5360-5363.
Aizawa, K., H. Aoki, Y. Ito, Y. Tanaka and T. Kurokawa [2004], “Waveform measurement of ultra-short
optical pulses based on two photon absorption in Si-image sensor”, ICO International Conference on
Optics & Photonics in Technology Frontier, Tokyo, pp.331-332.
Suzuki, T., K. Mandai, H. Tsuda, T. Kurokawa and T. Kawanishi [2004], “Optical pulse generation bycontrolling the sidebands of the phase modulated light”, OECC/COIN2004 (9th Optoelectronics andCommunications Conference/ 3rd International conference on Optical Internet, Yokohama, pp.738-739.
Ishida, M., T. Suzuki and H. Tsuda [2004], “180 degree-bend structures using a double elliptic mirror in aslab waveguide”, OECC/COIN2004 (9th Optoelectronics and Communications Conference/ 3rdInternational conference on Optical Internet, Yokohama, 13F1-4.
Suzuki, T., Y. Shibata, K. Masuda and H. Tsuda [2004], “Compact arrowhead arrayed waveguide grating
using v-bend optical waveguides,” Topical Meeting on Integrated Photonics Research, San Francisco,
IFH2.
Mandai, K., T. Suzuki, H. Tsuda, T. Kurokawa and T. Kawanishi [2004], “Arbitrary optical short pulse
generator using a high-resolution arrayed-waveguide grating”, International Topical Meeting on
Microwave Photonics, Ogunquit, pp.107-110.

D7. Microwave Photonics
Tadao Nagatsuma
NTT Corporation
Microwave photonics, which merges radio-wave (microwave) and photonics technologies, has made a
steady progress since 1990’s. The first use of the term microwave photonics was at International
Microwave Photonics (MWP) Conference held at Kyoto in 1996. The International MWP Conference has
subsequently been held yearly in the U.S., Europe and Asia-Pacific region, and came back to Japan (Awaji
Island) in 2002. Moreover, between Japan and Korea, a joint workshop on MWP has been held yearly
since 2000.

29

Research goals for MWP technology up to now can be very roughly categorized as(1)

achieving higher performance and higher functionality for telecommunications system applications
by introducing photonics technology to conventional radio-wave technology, and(2)

exploring new applications in telecommunications and other fields as well through the use ofphotonics technology by breaking through the frequency limit from microwave to millimeter waves
and further on to the submillimeter-wave region in radio-wave technologies.

(3)
The primary motivation of the former is to make positive use of special merits in optical fibers astransmission media, such as low loss, high capacity (broad bandwidth), light weight, flexible, andnon-inductive properties. The latter involves making use of not only optical fibers, but all of opticalcommunication technology and its peripheral technology (high-speed devices, measurement technologies,etc.), which have made terabit-class data signal processing possible, in the radio-wave technologies.
On the basis of the above categorization, we have seen a number of examples of research anddevelopment accomplished recently. Radio-on-fiber, optical remote-antenna and optically-controlledantenna are typical examples of the first category, while microwave and millimeter-wave measurement aswell as millimeter-wave and submillimeter-wave signal generation are in the second category.
Radio-on-fiber (RoF) technology continues to steadily advance in a form that supports the need forhigh-speed and ubiquity in telecommunications. At present, the cellular phone frequencies (around 1-2
GHz) are the focus of commercial attention, and RoF in wireless LAN (2-5 GHz) is expected to appear in
the next market place. The implementation of millimeter-wave RoF, which is currently at the hottest
research stage, will be linked to the development of millimeter-wave wireless (60-GHz band, for example),because public application of that technology has become active in recent years. As for higher
millimeter-wave frequency RoF, NTT has developed a 10-Gbit/s wireless link system using 120-GHz-band
millimeter waves, and the license was given to it as the first experimental radio station in Japan by the
Ministry of Public Management, Home Affairs, Posts and Telecommunications in 2004. In that system,
photonics technologies are effectively used for generation, modulation and emission of millimeter-wave
signals.
In addition, technology for the optical generation and detection of radio-wave signals has become
essential for various fields of measurement, as it facilitates the handling of ultrahigh-frequency
radio-waves, which has been difficult with previous technologies. One example is a project that is
attempting to introduce a millimeter and submillimeter-wave oscillator that employs photonics technology
to a receiver for use in radio-astronomy. Low-noise photonic local oscillators have been successfully
applied in the observation of millimeter-wave signals from the universe. Generation of over 1-THz
radio-wave signal is now possible by using an ultrafast photodiode called Uni-Traveling-Carrier
Photodiode (UTC-PD), although the emitted average power is still low, on the order of microwatts at thatfrequency.
30

As for the optical measurement of microwave and millimeter-wave signals, an electric-field sensor
based on electro-optic (EO) effect has become the most common, mainly because of its broad bandwidth(from MHz to THz) and small invasiveness. It has been widely applied to, for example, LSI testing,antenna characterization, EMC measurement, detectors in the imaging and spectroscopy. A magnetic-fieldsensor based on magneto-optic (MO) effect has also been studied to measure a current in place of anelectric field or a voltage.
References
Hirata, A., T. Nagatsuma, R. Yano, H. Ito, T. Furuta, Y. Hirota, T. Ishibashi, H. Matsuo, A. Ueda, T.
Noguchi, Y. Sekimoto, and S. Matsuura[2002], “Output power measurement of photonic millimeter-wave
and sub-millimeter-wave emitter at 100-800 GHz”, Electron. Lett., vol. 38, no. 15, pp. 798-800
Hirata, A., M. Harada, and T. Nagatsuma[2003a], “120-GHz wireless link using photonic techniques forgeneration, modulation, and emission of millimeter-wave signals”, IEEE J. Lightwave Technol., vol. 21,
no.10, pp. 2145-2153
Hirata, A., M. Harada, K. Sato, and T. Nagatsuma[2003b], “Low-cost millimeter-wave photonic techniques
for gigabit/s wireless link”, IEICE Trans. on Electronics, E86-C, no. 7, pp. 1123-1128
Hirata, A., H. Ishii, and T. Nagatsuma[2004a], “Design and characterization of ultra-broadband photonic
emitters for microwave and millimeter-wave applications”, Japan-Korea workshop on microwave andmillimeter-wave photonics 2004 Dig, pp. 63-66
Hirata, A., H. Togo, N. Shimizu, H. Takahashi, K. Okamoto, and T. Nagatsuma[2004b], “Low-phase noise
photonic millimeter-wave generator using an AWG integrated with a 3-dB combiner”, MWP 2004 Dig.,TD-3, pp. 209-212
Ikeda, K., T. Kuri, Y. Takahashi, and K. Kitayama[2003], “Full-duplex transmission using 2-RF-port
electroabsorption transceiver with photonic up-and downconversions for millimeter-wave radio-on-fiber
system”, IEICE Trans. on Electronics, E86-C, no. 7, pp. 1138-1145
Ito, H., T. Furuta, A. Hirata, T. Kosugi, Y. Muramoto, M. Tokumitsu, T. Nagatsuma, T. Ishibashi[2004],“Pre-amplifier-integrated uni-traveling-carrier photodiode module with a rectangular waveguide-output
port for operation in the 120-GHz band”, LEOS2004 Dig., MN2, pp. 128-129
Iwanami, M., E. Yamazaki, K. Nakano, T. Sudo, S. Hoshino, S. Wakana, M. Kishi, and M. Tsuchiya[2003],
31

“Magnetic near-field measurements over LSI package pins by fiber-edge magnetooptic probe”, IEEE J.
Lightwave Technol., vol. 21, no. 12, pp. 3273-3281
Izutsu, M.[2004], “Electrooptic light modulation technology for microwave photonics”, MWP2004 Dig.,
MA-2, pp. 12-15
Kitayama, K.[2003], “Dense wavelength division multiplexing radio-on-fiber system”, MWP2003 Dig., pp.
129-134
Kosugi, T., M. Tokumitsu, T. Enoki, M. Muraguchi, A. Hirata, and T. Nagatsuma[2004], “120-GHz Tx/Rx
chipset for 10-Gbit/s wireless applications using 0.1- m-gate InP HEMTs”, IEEE CSIC Dig., pp. 171-174
Mizuno, M., A. Hirata, K. Kawase, C. Otani, and T. Nagatsuma[2004], “Analysis of Pheochromocytoma(PC12) membrane potential under the exposure to millimeter-wave radiation”, AIP Conference Proc., no.
716, pp. 164-166
Nagatsuma, T.[2002], “Photonic measurement technologies for high-speed electronics”, Meas. Sci.
Technol. vol. 13, no.11, pp. 1655-1663
Nagatsuma, T., H. Ito[2003], “Ultrafast applications of uni-traveling-carrier photodiodes frommeasurement to signal processing”, Proc. SPIE, vol. 4992, pp. 90-104
Nagatusma, T., H. Togo, K. Narahara, N. Shimizu, and A. Sasaki[2004], “Recent progress in opticalmeasurement of radio-wave signals from gigahertz to terahertz”, MWP2004 Dig., MB-1, pp. 20-23
Nakajima, F., T. Furuta, and H. Ito[2004],”High-power terahertz-wave generation from aresonant-antenna-integrated uni-traveling-carrier photodiode”, MWP2004 Dig., WD-4, pp. 313-316
Niiho, H., M. Nakaso, K. Masuda, H. Sasai, K. Utsumi, and M. Fuse[2004], “Multi-channel wireless LAN
distributed antenna system based on radio-over-fiber techniques”, LEOS2004 Dig., MF2, pp. 57-58
Sasaki, A., and T. Nagatsuma[2002], “Reflection-type CW- millimeter-wave imaging with a highsensitivity waveguide-mounted electro-optic sensor”, Jpn. J. Appl. Phys., vol. 41,part 2, no. 1A/B, pp.
L83-L86
Sato, T., M. Tsuchiya, M. Iwanami, S. Hoshino, and M. Kishi[2003], “Current profiling for
32

m-class

planar circuit patterns by fiber-edge magneto-optic probe”, MWP 2003 Dig., pp. 341-344
Shoji, Y., and H. Ogawa[2003],”Experimental demonstration of 622 Mbps millimeter-wave over fiber link
for broadband fixed wireless access system”, IEICE Trans. on Electronics, E86-C, no. 7, pp. 1129-1137
Suzuki, H., M. Fujiwara, K. Iwatsuki, A. Hirata, and T. Nagatsuma[2005], “Photonic millimetre-wave
generator using intensity and phase modulators for 10 Gbit/s wireless link”, Electron. Lett., vol. 41, no. 6,
pp. 89-90
Takano, S., A. Ueda, T. Yamamoto, S. Asayama, Y. Sekimoto, T. Noguchi, M. Ishiguro, H. Takara, S.
Kawanishi, H. Ito, A. Hirata, and T. Nagatsuma[2003], “The first radioastronomical observation withphotonic local oscillator”, Publ. Astron. Soc. Japan, vol. 55, pp. L53-L56
Togo, H., A. Sasaki, A. Hirata, and T. Nagatsuma[2004], “Characterization of millimeter-wave antennausing photonic measurement techniques”, Int. J. RF and Microwave Computer-aided Engineering., vol. 14,
no. 5, pp. 290-297
Tsuchiya, M., E. Yamazaki, M. Iwanami, S. Mitani, T. Sato, S. Wakana, S. Hoshino, and M. Kishi[2003],“High-speed and high-spatial resolution fiber-optic measurement technique for RF magnetic field
distribution”, LEOS2003 Dig., ThS1, pp. 929-930
Tsukamoto, K., T. Higashino, T. Nakanishi, and S. Komaki[2003], “Direct optical switching code-divisionmultiple-access system for fiber-optic radio highway networks”, IEEE J. Lightwave Technol., vol. 21, no.
12, pp. 3209-3220
Usami, M., R. Fukasawa, M. Tani, M. Watanabe, and K. Sakai[2003], “Calibration free terahertz imaging
based on 2D electro-optic sampling technique”, Electron. Lett., vol. 39, no. 24, pp. 1746-1747
Yamamoto, T., and S. Kawanishi[2004], “Generation of low-noise optical frequency comb and optical beatsignal using phase modulator”, Japan-Korea workshop on microwave and millimeter-wave photonics 2004
Dig., pp. 15-19

D8. Nanotechnology

33

Katsuyuki Utaka
Waseda University
Nanotechnology covers very vast fields, such as materials, chemistry, physics, electronics, photonics,
mechanics, biotechnology, atom manipulation, fabrication technology and so on.

The research anddevelopment in these fields seem to have been carried out in their individual academic society andindustrial groups, and nanotechnology in these fields shall still continue to grow. In order to create andincubate new fields and novel devices for future prosperous society, however, cross-communication and, insome cases, fusion between various fields of nanotechnology should be required.

For this purpose, the

new technical group, named as “Next-Generation Nanotechnology (NNN) Group”, has been established in
April, 2004, to discuss next-generation nanotechnology under the Electronics Society (ES) of Institute ofElectronics, Information Communication Engineers (IEICE).

The activity of various nanotechnology isover-viewed through the topics in the meetings of the NNN Group, which are a very limited examples.
1. Photonics:

Photonic crystal (PhC) devices have been gathering increasing attention, and by the

improvement of fabrication technology using electron beam lithography well-controlled PhC functional
devices have been fabricated and reported such as very high-Q cavity and group-velocity controlled
devices for the application to narrow-band integrated WDM filter and quasi-optical memory, respectively.
A compact photonic integrated circuits combined with well-controlled quantum dots exhibited ahigh-speed wavelength converter.

As for quantum dots (QD), its size and density have begun to becontrolled by the development of crystal growth of molecular beam epitaxy (MBE) and metal-organic
vapor phase epitaxy (MO-VPE).

Generation of single photon emission and its application to quantum

communication is intensively investigated.
2. Electronics:

Due to the approaching limit of the size reduction in Si ULSI, further improvement of

fabrication process and material aspects are required.

From a viewpoint of fabrication technology ofnano-strucutures, the bottom-up methods such as self-organization and atom-manipulation have been
spotlighted, as well as increasing development of the conventional top-down methods such as electron
beam lithography and etching.

QD mentioned above is one of the promising examples.

From thematerial aspects, carbon nano-tube (CNT) is gathering increasing attention as a post-Si material due to its
larger electron mobility and larger maximum current density.
through-hole vias were reported.

CNT-gated transistors and application to

Fabrication control of CNTs from viewpoints of wall number, diameter,

density, position and so on for designed performances have been highly investigated.
3. Biotechnology:

Application of nanotechnology to biotechnology is highly spotlighted, since bio-celland bio-molecular themselves are in the range of nanometer size. Some of the promising applications are
sensing and marking of cells or proteins such as cancer, delivering of medicine to target cells or killingthem, and so on.

These technologies lead to the remedy of incurable diseases with reduced pains throughthe nanotechnology.

As such nanotechnologies, the followings have been reported; micelling of34

self-organized nano-capsules, nano-pillars to detect proteins with high sensitivity by CNT or polymer andtheir fabrication by nano-inprinting, nano-particles for marking killing of cancer cells.

Hereafter,

collaboration between nanotechnology and medical engineering has been further required with taking theadvantages of each nanotechnology.
4. Mechanics:

Micro electro-mechanical systems (MEMS) machines have been further down-sized toreach the level to handle nano-size materials such as cells through the improvement of fabrication
technology. This opens the way to the application of the nano electro-mechanical systems (NEMS) torealization of novel artificial materials and structures by controlled bottom-up technology in the fields ofelectronics and bio-science such as molecular motors and DNA capturing, which have been partly
demonstrated.

Improving of flexibility and motion-freedom dimensions and further utilization of NEMS

machines are highly required.

D9. Polymeric Photonics
Toshikuni Kaino
Tohoku University
Polymeric optical materials are of great interest for applications in optical telecommunication and data
communication devices because of their ease in processing, excellent flexibility, low cost, and high volume
production in comparison with silica-based materials. One of the important polymer photonic devices is
optical waveguides that can be fabricated using very simple and cost effective methods. The use ofsoft-lithography instead of standard photolithography and dry etching technologies is attractive because
inexpensive optical device can be realized.

Polymerization or decomposition using multi-photon

absorption of materials is also a good method for optical waveguide fabrication. Direct waveguide
patterning can be done using this method.
also very simple and attractive.

Laser induced self-writing technology of optical waveguide is

Using these processes, it is possible to fabricate and interconnect multiple

optical devices at once.
Polymers are also easy to functionalize where high speed optical switching and signal modulation can beattained. Ultra fast and highly efficient optical processing requires nonlinear optical (NLO) materials where
high-speed signals will be operated.

For that, EO polymers have been paid a lot of attention because of

their high potential for next generation EO modulators and/or switches.

It is reported that higher

bandwidth, lower drive voltage EO modulators than that of typical inorganic EO crystal, LiNbO3. were
fabricated using a chromophore-shape-controlled EO polymer.

However, in general, EO polymer has alarge optical loss (more than a few dB/cm), and it is necessary to reduce the total insertion loss for a35

practical EO device. So an EO polymer device serially grafted with a passive waveguide composed of ahigh transparent polymer was fabricated using soft-lithography, photolithography and spin-coating
techniques. Monolithically integration of passive waveguide with active devices such as EO-modulator on asingle substrate is possible.

If the entire structure is on one circuits, the manufacturing, packaging, andassembly costs are reduced dramatically.
Azo-dye, stilbene-dye, or polyene-dye functionalized polymers have been investigated as 2nd-order NLO
materials, showing efficient NLO characteristics with low absorption loss.

In this case, dye in the polymer

should be aligned in a specific direction to possess 2nd-order optical nonlinearity.

So, poling process toalign dyes in the polymer is inevitable i.e., electric field poling is used to obtain 2-nd order NLO polymers.
The polymer films on glass substrates were poled by parallel electrode poling or corona poling. The
nonlinear electronic polarization of the dye-functionalized polymers originates from mesomeric effects thatusually depend on the size of the-conjugated systems of the dye. The

the 2nd-order NLO hyperpolarizability-conjugation length dependence ofhas been investigated.

UV Exposure

Hot Embossing

Photoresist

Core

Glass

Undercladding

UV-Cured Resin

Original Master

Silicone Rubber Mold

Overcladding

PMMA
Replica

Stamper

Waveguide

Figure 1. Fabrication process of polymer optical waveguide using hot embossing technology

Passive
Stamper

Soft-Lithography

Photolithograph
EO Polymer

Spin-Coating36

EO Polymer
Passive
Polymer

100µm

Figure 2. Process flow for serially grafted EO polymer waveguide(Serially grafted structure)

Waveguide grating, that is an important device in optical communication and signal processing systems,
has such functions as input-output coupler, wavelength filter, and wavelength division multiplexer.

An

azo-dye functionalized polymer is one of the candidates for fabricating grating through the photochemical
reaction of the azo-dye through two laser beam interference.
two mechanisms.

This reaction can be explained by following

The first mechanism is reversible trans-cis-trans isomerization of the dye where strong

interference beam was irradiated. A surface relief grating can be fabricated through the movement of the
azo-dye attached matrix polymer due to the conformational change of the dye through its isomerization.
These surface relief gratings based on the isomerization mechanism were optically or thermally erasable.
The second mechanism is irreversible photobleaching of the dye that occurs under higher energy
irradiation.

In this case,-conjugated system in azo dye is broken and as a result, permanent refractive

index change of the polymer occurs,Compact polymer optical amplifier devices also have of special attention that can be incorporated into
integrated optical circuits. Incorporation of laser dyes into polymers as active gain region is effective forthe amplification.

These doped polymers provide a convenient method of creating high gain with wide

range of visible wavelength. Rare-earth doped polymers are also used for longer wavelength amplification.
Waveguide amplifier devices have the potential to be used in compact optical system such asmonolithically integrated photonic circuits.
References
A. Yeniary, R.Y. Gao, K. Takayama, R.F. Gao, A.F. Garito, (2004) Ultra-Low Loss Polymer Waveguides, J.
Lightwave Technol., 22, 154-158
H. Ma, A.K-Y. Jen, L.R. Dalton, Polymer-Based Optical Waveguides; Materials, Processing and Devices,
Advanced Mater., 14, 1339-1365,
H. Mizuno, S. Jordan, O. Sugihara, T. Kaino, N. Okamoto, M.Ohama, (2004)

Polymeric Optical

Waveguides with Plastic Optical Guides for Passive Alignment Fabricated by Hot Embossing, Jpn. J. Appl.
Phys., 43, L1496-L1498
37

H. Mizuno, O. Sugihara, T. Kaino, Y. Ohe, N. Okamoto, M.Hoshino, (2004)

Thick Photoresist Original

Master: A New Tool for Fabrication of Polymeric Optical Waveguides with Large Core by Hot Embossing,
J. Nonlinear Optical Phys. Mater., 13, 513-517
H. Mizuno, O. Sugihara, T. Kaino, N. Okamoto, M. Tomiki, M. Hoshino, (2004) Fabrication method oflarge core polymeric optical waveguide through replication process using anisotropically etched silicon,
Optics Letters, 28, 2378-2380
H. Mizuno, O. Sdugihara, T. Kaino, N. Okamoto, M. Hoshino, (2003) Low-loss polymeric opticalwaveguides with latge cores fabricated by hot embossing, Proc. SPIE Organic Photonics Materials andDevices VI, San Jose, 5351, 268-275
T.Shioda, (2002) Fluorinated Polyimide Waveguide Fabricated Using Replication Process with
Antistacking, Appl. Phys. Lett., 41, 1379-1381
O. Sugihara, H. Tsuchie, H. Endo, N. Okamoto, T. Yamashita, M. Kagami, T. Kaino, (2004) Light-Induced
Self-Written Polymeric Optical Waveguides for Single-Mode Propagation and for Optical Interconnection,
IEEE Photon. Tech. Lett., 16, 804-806
B. Cai, O. Radmer, C. Zawadski, H. H. Yao, N. Keil, T. Kaino, (2004) DAST Crystal Waveguide
Fabrication by Photobleaching Method, Nonlinear Optical Phys. Mat., 13, 195-208
B.

Cai,

T.

Ushiwata,

K.

Komatsu,

T.

Kaino,(2004)

FabricationofSerially

Grafted

4-(4-dimethyl-aminostyryl)-1-methylpyridinium Tosylate Crystal Waveguide by Photobleaching, Jpn. J.
Appl. Phys., 41, L390-L392
T. Kaino, B. Cai, K. Takayama, (2002) Fabrication of DAST Channel Optical Waveguides, Adv, Funct.
Mater, 12, 599-603
T. Kaino, K. Takayama, B. Cai, K. Komatsu, (2001) Fabrication of Nonlinear Optical Waveguide,
Ferroelectrics, 257, 13-26
K. Takayama, K. Komatsu, T. Kaino, (2001) Serially Grafted Waveguide Fabrication of Organic Crystal
and Transparent Polymer, Jpn. J. Appl. Phys., 40, 5149-5150

38

Y. Suzuki, K. Komatsu, T. Kaino, and Y. Honda, (2003). “Serially grafted optical waveguide fabrication of
NLO polyimide and transparent polymers”, Opt. Mater., 21, 521-524
T. Ushiwata, E. Okamoto, T. Kaino, (2002) Development of Thermally Stable Novel EO-polymers, Mol.
Cryst. Liq. Cryst., 374, 303-314
T. Ushiwata, E. Okamoto, K. Komatsu, T. Kaino, (2001) Synthesis and optical properties of azo dye
attached novel second order NLO polymers with high thermal stability, Proc. SPIE Organic Photonics
Materials and Devices III, San Jose, 4279, 17-24
A. Kaneko, E. Okamoto, T. Kaino, (2002) Synthesis and Characterization of Novel Side-Chain Nonlinear
Optical Polymers with Furan Derivative as an Acceptor, Jpn. J. Appl. Phys., 41, L559-L561
T. Taima, K. Komatsu, T. Kaino, C.P. Franceschina, L. Tartara, G.P. Banfi, V. Degiorgio, (2003)
Third-order nonlinear optical properties of 2-adamanthyl amino-5-nitropyridine caused by cascaded
second-order nonlinearity, Optical Materials, 21, 83-86
T. Hattori, T. Shibata, S. Onodera, T. Kaino, (2004) Thermo-optically Tunable Wavelength Filter with
Permanent Refractive Index Grating into Azo-Polymer Waveguide, Jpn. Jpn. App. Phys., 43, 1492-1495
B. Cai, T. Hattorit, H-H. Deng, K. Komatsu, C. Zawadski, N. Keil, T. Kaino, (2001) Refractive Index
Control and Grating Fabrication of 4-(4-dimethyl-aminostyryl)-1-methylpyridinium Tosylate Crystal, Jpn.
J. Appl. Phys., 40, L964-L966
F.L. Labarther, T. Buffeteau, C. Sourisseau, (2001) Time dependent analysis of the formation of ahalf-period surface relief grating on amorphous azopolymer films, J. Appl. Phys., 90. 3149-3158
J.Y. Kim, T.H. Kim, T. Kiura, T. Fukuda, H. Matsuda, (2002) Surface relief grating and liquid crystalalignment on azobenzene functionalized polymers, Opt. Mater, 21, 627-631
T. Kobayashi, J-B. Savaitier, G. Jordan, W.J. Blau, Y. Suzuki, T. Kaino, (2004) Near-infrared laser emission
from luminescent plastic waveguides, Appl. Phys. Lett., 85, 185-187
M.A. Reilly, C. Marinelli, C.N. Morgan, R.V.P ently, I.H. White, R. Roman, M. Ariu, R. Xia, D.D.C.
Bradley,(2004) Rib waveguide dye-doped polymer amplifier with up to 26 dB optical gain at 625 nm,

Appl. Phys. Lett., 85, 5137-5139
39

T, Hirose, T, Omatsu, R, Kato, K. Hoshino, K. Harada, T. Watanabe, M. Fujii, (2003) Azo-benzene
polymer thin film laser amplifier with grating couplers based on light-induced relief hologram, Opt.
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W.H. Wong, E.Y.B. Pun, K.S. Chgan, (2004) Er3+-Tb3+ co-doped polymer optical waveguide amplifier,Appl. Phys. Lett., 82, 176-178
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M. Karimi, N. Granpayeh, M.K.M. Farshi, (2004) Analysis and design of a dye-doped polymer opticalfibre amplifier, Appl. Phys. B., 78, 387-396

D10. Photonic Crystals
Susumu Noda
Kyoto University
Photonic crystals, in which the refractive index changes periodically, provide an exciting new tool forthe manipulation of photons and have received a keen interest from a variety of fields.
In these five years, manipulation of photons by using 2D photonic crystals has been extensively studied,and remarkable progresses have been made in waveguides, bends, cavities, and their combination, as wellas the connection to the outer space.

For example, although the waveguide loss was very high(70dB/mm) five years ago, it is now reduced down to 0.7dB/mm. On another hand, in waveguide bends,
topology optimization methods enable us to achieve even a 120 degree bend, which is beyond the initial
prediction. The nanocavity Q factor has been drastically increased owing to the invention of a generaldesign rule: a Gaussian-like confinement suppresses the out-of-slab leakage of light significantly.
Ultrahigh-Q nanocavities with Q factor of the order of 105〜106 has been recently achieved. Encouragedby the success of ultrahigh Q nanocavities, tuning or nonlinear switching operation of photonic-nanodevices has started. The new concept of “In-Plane Hetero” structure has been applied to the defectengineering, and photonic-nanostructure devices with high functionality has been realized.
Progresses in 3D photonic crystals have been also remarkable. The demonstration of spontaneous40

emission control by 3D photonic crystals has been long-waited after the photonic crystal concept appeared.
The recent success in the introduction of light-emitters and artificial point defects into 3D photonic crystals
with full bandgap has enabled to demonstrate it. It has been successfully shown that the spontaneousemission is suppressed by 100 times at the complete bandgap while a strong emission is observed at theartificial defect.
Progresses in band edge and/or band engineering have been also made. When the operation wavelength
approaches the band edge and/or the mode edge of a waveguide, the group velocity of light can be slowed
down. Such kind of velocity control of light is very important and it has been recently demonstrated. On
another hand, when the band edge itself is utilized, a large area laser cavity can be constructed. Novel 2D
lasers based on 2D band edge effect have been developed.
In conclusion, the recent progresses of photonic crystals are really remarkable, and the initially promisedfeatures have been well demonstrated. In the following 10 years, higher quality and more reliable devices
will be developed with the aid of the progress of nanotechnology. In the case of the 2D photonic crystalslab, the combination with Si LSI technology will proceed with an all-optical main part, but with thecontrol driven by the electronics. Sensing applications, memory, single photon emitters, in summary all
new application areas will be also developed since extremely high Q nanocavities has already beenachieved. In the case of 3D photonic crystals, the fabrication technology will develop continuously and an
ultimate control of photons will be demonstrated. Materials will be expanded from semiconductors, toorganic, magnetic, etc.
References:
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Applied Physics Letters, vol.85, no.23, pp.5769-5771.

Y. Tanaka, T. Asano, R. Hatsuta, and S. Noda [2004], “Analysis of a line-defect waveguide on asilicon-on-insulator two-dimensional photonic-crystal slab,” IEEE/OSA Journal of Lightwave Technology,
vol.22, no.12, pp.2787-2792.

B. S. Song, T. Asano, Y. Akahane, Y. Tanaka, and S. Noda [2004], “Transmission and reflection
characteristics of in-plane hetero-photonic crystals,” Applied Physics Letters, vol.85, no.20, pp.4591-4593.

M. Fujita, A. Sugitatsu, T. Uesugi, and S. Noda [2004], “Fabrication of Indium Phosphide compound
photonic crystal by Hydrogen Iodide/Xenon inductively coupled plasma etching,” Japanese Journal ofApplied Physics, vol.43, no.11, pp.L1400-L1402.

41

M. Okano and S. Noda [2004], “Analysis of multimode point-defect cavities in three-dimensional photonic
crystals using group theory in frequency and time domains,” Physical Review B, vol.70, no.12,
pp.125105-1-125105-15.

A. Sugitatsu, T. Asano, and S. Noda, “Characterization of line-defect-waveguide lasers in two-dimensional
photonic-crystal slabs,” Applied Physics Letters, vol.84, no.26, pp.5395-5397 (2004).

T. Asano, K. Kiyota, D. Kumamoto, B. S. Song, and S. Noda [2004], “Time-domain measurement ofpicosecond light-pulse propagation in a two-dimensional photonic crystal-slab waveguide,” Applied
Physics Letters, vol.84, no.23, pp.4690-4692.

S. Ogawa, M. Imada, S. Yoshimoto, M. Okano, and S. Noda [2004], “Control of light emission by 3D
photonic crystals,” Science, vol.305, no.5681, pp.227-229. (published online 3 June 2004
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T. Asano and S. Noda [2004], “Tuning holes in photonic-crystal nanocavities,” Nature, vol.429,
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D. Ohnishi, T. Okano, M. Imada, and S. Noda [2004], “Room temperature continuous wave operation of asurface-emitting two-dimensional photonic crystal diode laser,” Optics Express, vol.12, no.8,
pp.1562-1568.

H. Takano, Y. Akahane, T. Asano, and S. Noda [2004], “In-plane-type channel drop filter in a
two-dimensional photonic crystal slab,” Applied Physics Letters, vol.84, no.13, pp.2226-2228.

M. Yokoyama and S. Noda [2004], “Finite-difference time-domain simulation of two-dimensional photonic
crystal surface-emitting laser having a square-lattice slab structure,” IEICE Transactions, Special Issue on
Photonic Crystals and Their Device Applications, vol.E87C, no.3, pp.386-392.

S. Noda and T. Baba [2004], “Special issue on photonic crystals and their device applications,” IEICE
Transactions on Electronics, vol.E87C, no.3, pp.257.

E. Miyai and S. Noda [2004], “Structural dependence of coupling between a two-dimensional photonic
crystal waveguide and a wire waveguide,” Journal of the Optical Society of America B, vol.21, no.1,
pp.67-72.

M. Okano, S. Kako, and S. Noda [2003], “Coupling between a point-defect cavity and a line-defect42

waveguideinthree-dimensional

photonic

crystal,”PhysicalReview

B,

vol.68,

no.23,

pp.235110-1-235110-10.

M. Fujita, T. Ueno, T. Asano, S. Noda, H. Ohhata, T. Tsuji, H. Nakada, and N. Shimoji [2003], “Organic
light-emitting diode with ITO/organic photonic crystal,” Electronics Letters, vol.39, no.24, pp.1750-1752.

Y. Akahane, T. Asano, B. S. Song, and S. Noda [2003], “High-Q photonic nanocavity in a two-dimensional
photonic crystal,” Nature, vol.425, no.6961, pp.944-947.

M. Yokoyama and S. Noda [2003], “Polarization mode control of two-dimensional photonic crystal laser
having a square lattice structure,” IEEE Journal of Quantum Electronics, vol.39, no.9, pp.1074-1080.

Y. Akahane, T. Asano, B. S. Song, and S. Noda [2003], “Investigation of high- Q channel drop filters using
donor-type defects in two-dimensional photonic crystal slabs,” Applied Physics Letters, vol.83, no.8,
pp.1512-1514.

T. Asano, B. S. Song, Y. Tanaka, and S. Noda [2003], “Investigation of a channel-add/drop-filtering device
using acceptor type point defects in a two-dimensional photonic crystal slab,” Applied Physics Letters,
vol.83, no.3, pp.407-409.

B. S. Song, S. Noda, and T. Asano [2003], “Photonic devices based on in-plane hetero photonic crystals,”
Science, vol.300, no.5625, pp.1537.

S. Ogawa, M. Imada, and S. Noda [2003], “Analysis of thermal stress on wafer bonding of dissimilarmaterials for the introduction of InP-based light-emitter into GaAs-based three dimensional photonic
crystals,” Applied Physics Letters, vol.82, no.20, pp.3406-3408.

T. Asano, M. Mochizuki, S. Noda, M. Okano, and M. Imada (2003), “A channel drop-filter using a single
defect in a 2D photonic crystal slab - Defect engineering with respect to polarization mode and ratio ofemissions from upper and lower sides -,” IEEE/OSA Journal of Lightwave Technology, vol.21, no.5,
pp.1370-1376.

D. Ohnishi, K. Sakai, M. Imada, and S. Noda (2003), “Continuous wave operation of surface emitting
two-dimensional photonic crystal laser,” Electronics Letters, vol.39, no.7, pp.612-614.

Y. Tanaka, T. Asano, Y. Akahane, B. S. Song, and S. Noda (2003), “Theoretical investigation of propagation
loss of a line defect waveguide in a two-dimensional photonic crystal slab with tapered air holes,” Applied
43

Physics Letters, vol.82, no.11, pp.1661-1663.

Y. Akahane, M. Mochizuki, T. Asano, Y. Tanaka, and S. Noda (2003), “Design of a channel drop filter byusing a donor-type cavity with high-quality factor in a two-dimensional photonic crystal slab,” Applied
Physics Letters, vol.82, no.9, pp.1341-1343.

A. Sugitatsu and S. Noda (2003), “Room temperature operation of a two dimensional photonic crystal slab
defect-waveguide-laser with optical pump,” Electronics Letters, vol.39, pp.123-125.

E. Miyai, M. Okano, M. Mochizuki, and S. Noda (2002), “Analysis on coupling between 2D photonic
crystal slab and external waveguide,” Applied Physics Letters, vol.81, no.20, pp.3729-3731.

M. Okano, A. Chutinan, and S. Noda (2002), “Analysis and design of single-defect cavities in athree-dimensional photonic crystal,” Virtual Journal of Nanoscale Science & Technology, vol.6, no.18.

M. Okano, A. Chutinan, and S. Noda (2002), “Analysis and design of single-defect cavities in athree-dimensional photonic crystal,” Physical Review B, vol.66, no.16, pp.165211-1-6.

N. Yamamoto and S. Noda (2002), “Accurate identification of the band gap of photonic crystals fromtransmission spectra,” Journal of Applied Physics, vol.92, no.5, pp.2256-2259.

S. Noda, M. Imada, A. Chutinan, and N. Yamamoto (2002), “III-V based-semiconductor photonic crystals,”
Optical and Quantum Electronics, vol.34, no.8, pp.723-736.

S. Noda, M. Imada, M. Okano, S. Ogawa, M. Mochizuki, and A. Chutinan (2002), “Semiconductor
three-dimensional and two-dimensional photonic crystals and devices,” IEEE Journal of Quantum
Electronics, vol.38, no.7, pp.726-735.

T. Asano, S. Noda, K. Kiyota, Y. Tanaka, Y. Akahane, B. S. Song, M. Mochizuki, and M. Imada (2002),“Channel-add operation of a device using defects in a two-dimensional photonic crystal slab,” Materials
Research Society Symposium Proceedings “Materials and devices for optoelectronics and microphotonics”,
vol.722, pp.363-367.

M. Imada, A. Chutinan, S. Noda, and M. Mochizuki (2002), “Multidirectionally distributed feedback
photonic crystal lasers,” Virtual Journal of Nanoscale Science & Technology, vol.5, no.18.

44

M. Imada, S. Noda, A. Chutinan, M. Mochizuki, and T. Tanaka (2002), “Channel drop filter using a single
defect in a 2-D photonic crystal slab waveguide,” IEEE/OSA Journal of Lightwave Technology, vol.20,
no.5, pp.845-850.

M. Imada, A. Chutinan, S. Noda, and M. Mochizuki (2002), “Multidirectionally distributed feedback
photonic crystal lasers,” Physical Review B, vol.65, no.19, pp.195306-1-195306-8.

A. Chutinan, M. Okano, and S. Noda (2002), “Wider bandwidth with high transmission through waveguide
bends in two-dimensional photonic crystal slabs,” Applied Physics Letters, vol.80, no.10, pp.1698-1700.

S. Noda and M. Imada (2002), “2D photonic crystal surface-emitting laser using triangular-lattice
structure,” IEICE Transactions on Electronics, vol.E85C, no.1, pp.45-51.

S. Ogawa, K. Tomoda, and S. Noda (2002), “Effects of structural fluctuations on three-dimensional
photonic crystals operating at near-infrared wavelengths,” Journal of Applied Physics, vol.91, no.1,
pp.513-515.

T. Tanaka, S. Noda, A. Chutinan, T. Asano, and N. Yamamoto (2002), “Ultra-short pulse propagation in 3D
GaAs photonic crystals,” Optical and Quantum Electronics, vol.34, no.1-3, pp.37-43.

T. Asano, S. Yoshizawa, and S. Noda (2001), “Carrier relaxation dynamics in an ultrafast all-opticalmodulator using an intersubband transition,” Applied Physics Letters, vol.79, no.27, pp.4509-4511.

A. Chutinan, M. Mochizuki, M. Imada, and S. Noda (2001), “Surface-emitting channel drop filters using
single defects in two-dimensional photonic crystal slabs,” Applied Physics Letters, vol.79, no.17,
pp.2690-2692.

S. Noda (2001), “Teaching light new tricks,” SPIE OE Magazine, vol.1, no.10, pp.28-31.

M. Yokoyama, K. Akimoto, M. Imada, and S. Noda (2001), “Wafer fusion condition for GaAs/AlGaAs
system and its application to laser diode,” Japanese Journal of Applied Physics, vol.40, no.8A,
pp.L847-L849.

S. Noda, M. Yokoyama, M. Imada, A. Chutinan, and M. Mochizuki (2001), “Polarization mode control of
two-dimensional photonic crystal laser by unit cell structure design,” Science, vol.293, no.5532,
pp.1123-1125.

45

S. Noda (2001), “Two- and three-dimensional photonic crystals in III-V semiconductors,” MRS Bulletin,vol.26, no.8, pp.618-621.

K. Sakoda, N. Kawai, T. Ito, A. Chutinan, S. Noda, T. Mitsuyu, and K. Hirao (2001), “Photonic bands ofmetallic systems. I. Principle of calculation and accuracy,” Physical Review B, vol.64, no.4,
pp.45116-1-45116-8.

D11 Silicon Photonics
Tadamasa Kimura
Electro-Communication Technology
1. Introduction
The recent demonstration of a Raman optical amplifier and a Raman laser in silicon by UCLA
researchers in 2004 [1] and by Intel [2,3] aroused people who were engaged not only in the silicon
photonics but also in the silicon electronics to become aware of the possibility of silicon photonics. Thoughvarious types of silicon photonic devices have been studied and some passive devices have been developedin the progress of silicon optoelectronics and photonics, the lack of an efficient light emitter (silicon laser
and light emitting diode) and an optical amplifier has been a major roadblock. Ozdal Boyraz and Bahram
Jalali of UCLA have described pulsed Raman laser emission at 1675 nm with a 25-MHz repetition rate,using a silicon waveguide as the gain medium. The laser has a clear threshold at 9 W of peak pump pulse
power and a slope efficiency of 8.5 percent in 2004[1], and the Intel group achieved a continuous-wave
Raman silicon laser in 2005[3].
Many researchers have attempted to create an efficient silicon LED or a silicon laser. A relatively strong
visible light emission from porous silicon reported by Canham in 1990 was one of the major breakthroughs
to the silicon photonics. This led to the development of the luminescence of nanocrystalline silicon
embedded in silicon dioxide. Another approach was to incorporate exotic impurities such as erbium or
thulium in silicon. The first Er-doped silicon LED was reported by H. Ennen et al. in 1985 [5] and an
efficient LED (external efficiency of 10% at 300K) was reported by SI microelectronics in 2003[6].
Er-doped fiber amplifier (EDFA) contributed greatly to the development of the long distance optical fiber
communication system However, in the development of WDM (wavelength division multiplexing) system,its 15-30nm bandwidth cannot cover the broadening of the wavelength, and the Raman fiber amplifier andlaser have been developed for light amplification and generation [7]. Semiconductor Raman lasers andamplifiers were studied in some semiconducting materials such as GaP [8, 9].

46

The silicon Raman laser has some favourable features compared with other efforts such as defect or
impurity incorporation in Si. . Firstly, it uses a pure crystalline silicon and is compatible with standard
silicon manufacturing technology. Secondly, the lasing and amplification is not in principle restricted to
fixed wavelength ranges. However, the Raman laser requires a strong light for excitation and this should be
solved in use for optoelectronic systems.
The luminescence of nc-Si in SiO2 at visible wavelengths has also attracted a great attention from thepoint of view of both physics and practical application. The materials are, however, high resistive and it
needs optical excitation.
In contrast, Er-doped silicon has a possibility of realising electrically excitable LEDs or LDs. Though ahigh external efficiency (10%) was reported for a Si LED at 1.54 µm Si by ST microelectronics[6], theLED was composed of a thin Er-doped SiO2 sandwiched with p- and n-silicon and it was high resistive andwas still far from a laser diode due to current injection. Strong enhancement in the 1.54µm luminescencefrom Er and nc-Si codoped SiO2 reported by M. Fujii et al. had also attracted a great attention [10] andhave been followed by lots of studies for the energy transfer mechanisms, efficiency, excitation crosssection, optical gains etc. The excitation cross section of Er (2 x 10-17 cm2 was increased by 4-5 orders
compared with that of Er doped SiO2 (8 x 10-21cm2 where the Er ions are excited by direct absorption ofphotons [11]. However, this material is also high resistive and needs optical excitation. One of the
problems of Er-doped silicon to be solved is the limitation of the Er concentration at around 1019 - 1020/cm3.
Too high Er concentration resulted in concentration quenching due to strong interaction among Er ions athigh Er concentrations. Recently, an Er-Si-O new crystal which shows a superlattice structure has beenreported by H.Isshiki et al. [12]. This material contains Er not as an impurity element but as a constituent
atom at around 20at%. It shows a semiconducting property and at the same time, a strong
photoluminescence with a fine-structured luminescence at 1.54µm at room temperature. Efforts are now
made to make optical waveguide amplifiers, LEDs or LDs using this material. In the following, activities
of Japanese researchers in the field of silicon photonics in these five years are reviewed.
2. Optical waveguides
PLC (planar lightwave circuit) technology which is now deployed in fiber-optic telecommunications
systems has been practiced since the late 1980’s and is based on silica waveguide technology.
Light-guiding channels are defined on a silicon platform. The core layer with an elevated refractive index
is patterned using photolithography and dry etching. This technology is well suited to the fabrication ofpassive devices. PLC established its fame due to compactness, commercial productivity, reliability etc. andis widely used in the photonic technology combined with the fiber optics technology. Various passive
photonic devices have been developed such as AWG (arrayed waveguide grating), optical switch,
dispersion compensation devices, and filter. Japan is one of the leading countries in the PLC technology
and lots of efforts have been and still are made to develop this technology both in the research as well as in47

the production fields. Though PLCs is one of the vicious technologies in the silicon photonics, the reviewof the PLC technology will appear somewhere from the general photonic technology point of view.
(1) Silicon-wire waveguides:
In the PLC waveguides, the difference in the refractive index between the core- and clad-layers is from
0.3 % to 2 %, which leads to the bending radius from 25 mm to 2 mm and limits the size reduction.
Reduction in the bending radius requires a lager refractive index difference. Recently, silicon wire
waveguide has been attracted lots of attention. Submicron size silicon wires are used as cores and the air or
SiO2 are used as clad. The high refractive index of silicon (nr∼3.5) compared to the air (nr=1) or SiO2
(nr=1.4) can reduce the bending radius down to several microns. Moreover, a use of the silicon
semiconductor as a clad may open the way to the development of active waveguide devices. The key
problems are the propagation loss due to scattering at the core/clad boundary and the coupling loss to
optical fibers Even a tiny roughness at the core/clad boundary may cause a large scattering of light at theboundary due to the large refractive index difference between core and clad causes
S. Itabashi and co-workers with NTT Microsystem Integration laboratories fabricated a Si channel
waveguide on an SOI substrate; that is, Si core of a size of e.g. 0.3 x 0.3 µm2 with SiO2 clad [13]. With
improved fabrication methods, the propagation loss down to less than 3dB/cm and the bending radius of <5 µm with almost negligible bending loss were attained. Coupling loss to optical fiber was reduced using a
spot-size converter and the loss of <3dB/point was obtained for a normal single mode fiber. They alsofabricated various passive functional devices; multimode interference branch, directional coupler, starcoupler, microspectrometer, lattice filter, ring resonator, 1D photonic crystal filter etc. They also fabricatedsome active functional devices; wavelength converter and all-optical modulator, where the semiconducting
properties of Si, two photon absorption and four wave mixing, were used. Their work was well reviewed
by themselves in [14].
T. Baba and his coworkers attempted to fabricate a silicon wire waveguide on SOI [15]. They reported a
propagation loss coefficient of 10 cm-1 which was caused by the light scattering at the rough interfaces.
They also showed a bend loss of less than 1 dB at a 0.5 µm radius. They also reported an AWG
demultiplexer using Si photonic wire waveguides [16]. An AWG of 110 × 93 µm2 size on SOI was
fabricated on SOI. The demultiplexing function was observed in the wavelength range of 1.50-1.57 µm
with a channel spacing of < 6 nm and a free spectral range of > 90 nm.
They studied on the suppression of the polarization crosstalk [17]. The crosstalk from TE-like to
TM-like polarization was evaluated experimentally to be -13 dB to -10 dB at a wavelength of 1.55 µm,
which was compared with -25 dB obtained by 3-D finite-difference time-domain (FDTD) simulation for a
90º bend with a radius of 0.35-1.75 µm is less than. The large experimental value was explained by a small
tilt of waveguide side-walls, which seriously increased the crosstalk. They proposed that a U-shape bend
could be the most effective for the suppression of the crosstalk. They also achieved the insertion loss of48

less than 0.1dB for the elliptical intersection [18]. H. Yamada et al. reported an optical add-drop
multiplexers based on Si-wire waveguides [19].
(2) Porous silicon waveguides:
Waveguides using porous silicon have been also studied extensively. Koshida et al. reported
three-dimensionally buried porous silicon optical waveguides with an extremely high refractive index
contrast in 1999 [20]. They achieved a buried bent PS waveguide with a curvature of 250µm. One of thefeatures of the porous silicon waveguide is that the refractive index of PS is easily controlled both by thepore size and the incorporation of impurity atoms into pores. PS optical microcavities are fabricated using
porosity-multilayer PS [21]. Nagata et al. [22] formed silica waveguides by oxidation of selectively
anodized porous silicon. They incorporated titanium into core to obtain a desired large refractive index
difference and obtained the optical loss of 0.3dB/cm at 632.8nm in the slab-waveguides.
(3) Photonic crystal waveguides:
Photonic crystal (PC) structures which show well-defined photonic bandgap have been extensively
studied. Especially, Si photonics crystals fabricated on SOI substrates have been developed due to its
matured fabrication processes. Various photonic devices have been demonstrated using 1D, 2D or 3D
photonic crystals by Japanese researchers; filters [23, 24], waveguides [25-31], resonators [32, 33] etc. Si
nanopillars fabricated on SiO2 using SOI are extensively studied [34-36]. Optical waveguides of a
submicron bent radius with almost complete optical confinement has been reported using e.g. a simple
pillar missing line defect structure of 2D Si pillars [26, 29]. Optical delay lines are also designed andfabricated using impurity band-based photonic crystal waveguides which are composed of
one-dimensional cylindrical air holes formed in Si on SiO2 ridge waveguides [38], suppression of off-plane
diffractive leakage has been a serious problem in SOI-PC line-defect waveguides, but it is overcome byadopting a narrow line-defect and phase-shifted-hole line-defect waveguide structures [25].
Two-dimensional ordered arrays of submicron-size dielectric microspheres such as silica [39] or Si3N4 [40]are found to show the photonic band structure and promising photonic crystals. 3D photonic crystals whichshow full bandgaps have also fabricated and propagation of light beams along line defects formed ina-Si/SiO2 3D photonic crystals were observed [41-43]. Reduction of a coupling loss between photonic
crystal-based optical devices and optical fibers may be one of the key technologies for the industrialization.
Heterostructured photonic crystals fabricated by the autocloning technology solved this problem andachieved the coupling loss 0.43dB with a net propagation loss of 0.1dB/mm [44]. There are lots of studies
and reports on the developments of photonic crystal optical devices other than waveguides, but they are notdescribed in this report.
(4) Surface Plasmon Waveguides:
49Surface plasmon propagation along metal nanoparticle chains can be used to form subwavelength-scale
optical waveguides. By converting the optical mode into nonradiative surface plasmons, electromagnetic
energy can be guided in structures with lateral dimensions of less than 10% of the free-space wavelength[45]. Several studies have also been reported by Japanese researchers. Nanodot couples were fabricatedusing a linear array of closely spaced metallic nanoparticles [46].
Other surface plasmon waveguide structures were also studied; a nanometer-sized oxide core with a metal
clad [47] or two parallel metallic plates (surface plasmon polariton gap waveguide) [48]. In the former, thepropagation length of the surface plasma polariton extended from 2µm to 6µm corresponding to thewavelength of 532nm to 830nm, respectively.
3. Silicon-based luminescence materials and devices(1) Nanocrystalline Si (n-Si) and porous Si:
The difficulties of making Si LDs, LEDs or optical amplifier for practical use have been the main
obstacle for the development of the Si photonic technology. Due to the indirect gap band structure of Si,
the radiative recombination rate is too low to surpass other nonradiative recombinations at defects or at
surfaces. Observation of strong luminescence from porous silicon by Canham was an indication of theenhanced radiative recombination in nanosize semiconductor particles.
Photoluminescence and electroluminescence of nc-Si have been studied worldwide. Various processes forthe formation of nanocrystalline Si (quantum wells, wires and dots) were devised. Efficientphotoluminescence at controlled wavelengths .in the visible region was obtained by changing the size ofnanocrystalline Si spheres embedded in SiO2. Electroluminescence of nc-Si in SiO2 was also achieved byapplying direct current in the visible region from red to blue. Excitation was carried out by impact
excitation and the external quantum efficiency is lower than 1% [49-51] which is compared with a recent
report of 2% from nc-Si embedded in Si3N4 [52]. Visible electroluminescence of nc-Si from CaF2/nc-Si
embedded in CaF2 multilayers formed on a p-Si substrate was also reported, where the luminescence wasobtained by recombination of electrons and holes injected by tunneling into nc-Si from ITO and p-Si,
respectively [53, 54].
(2) Er-doped Si:
Luminescence of rare-earth doped semiconductors, especially electroluminescence of Er-doped Si has
been attracted much attention since H. Ennen reported the electroluminescence from Er-implanted Si at
1.54 µm [5]. This emission was due to the 4f-4f transition of Er3+ and the wavelength coincides with thatof optical communication. Lots of efforts have been done to find the way to realizing laser diodes andamplifier, but there are still problems which should be overcome. To realize a sufficient gain for lasing in
the device size of mm or less, the Er concentration of the order of 1021-1022/cm3 is necessary, but the50solution limit of Er in crystalline Si is around 1019/cm3. Temperature quenching: due to energy backtransfer from excited Er3+ to host Si at room temperature and concentration quenching due to energy
exchange among Er3+ ions at high Er concentrations (above ∼1020/cm3) should also be suppressed.
Oxygen co-incorporation or use of silicon-rich SiO2, amorphous Si, porous Si [55] as hosts could increase
the solution limit of Er at 1020/cm3 and suppress the temperature quenching extensively and the increased
photoluminescence or electroluminescence were obtained. .However, the Er concentration is stillinsufficient for LD or amplifier.
(3) Er and nc-Si codoped SiO2:
Another attractive approach to the efficient Er luminescence is the co-doping of nc-Si and Er into SiO2
which were demonstrated for the first time by Japanese researchers [10] and lots of studies on the energy
transfer mechanisms, efficiency, luminescence characteristics etc have been carried out world-wide. . The
main features of the materials are increased photoluminescence excitation cross section (10-16cm2) byabout 4-5 orders compared with that of Er doped SiO2, (10-21cm2) [11]. In Er-doped SiO2, excitation of Er3+
ions is due to direct absorption of photons by 4f-electrons of Er3+ ions. However, in Er and nc-Si codoped
SiO2, nc-Si is first excited by irradiation of the above band

gap light of nc-Si and then the e-h

3+

recombination energy is effectively resonant-transferred to Er ions [56]. The advantage of these materials
in comparison with Er-doped SiO2 is that a simple lamp is used for the excitation. However, the materials
are in principle high resistive and EL may be possible only by impact excitation.
(4) ErSiO superlattice crystals:
Recently, superlattice structured ErSiO was synthesized by H. Isshiki et al, a group of Japan and theNetherlands [12]. This ErSiO is a crystal which contain Er at ∼1022/cm3 as a constituent atom, and shows afine structure in the Er-related 1.54µm photoluminescence at room temperature. It also shows asemiconducting nature and is excited by the recombination of e-h pairs. Even at such a high Er
concentration, defects are not caused in contrary to the case of Er doping and therefore the concentrationquenching does not occur. . The superlattice structure is composed of Er2O3 and Si layers with a period of
0.9nm, and it is speculated that the energy back transfer is suppressed due to the separation of Er3+ and host
Si from its superlattice structure. Due to its semiconducting nature, studies on ErSiO LDs, LEDs andelectrically excited waveguides with gain at 1.54µm are now in progress [57, 58].
(5) β-FeSi2 on Si:
Heteroepitaxial growth of SiFe2 by molecular epitaxy and its photoluminescence properties were studied[59, 61]. Room temperature electroluminescence from β-FeSi2 on Si [62], p-Si/β-FeSi2 particles/n-Si [63]and from a Si-based p-i-n diodes with β-FeSi2 particles embedded in the intrinsic Si at 1.55 µm [64] havebeen reported.
51

(6) III-V compounds on Si:
Heteroepitaxial growth of luminescent III-V compound semiconductors on Si substrates has also been
also studied extensively to utilize high their luminescence efficiency. .Following the success of epitaxial
growth of GaP on Si/Si [65], lattice matched GaP1-xNx (x = 2.9 %) -was successfully grown epitaxially on
Si with no threading and misfit dislocations [66,-68], GaAsP LED diode was fabricated and showed
infrared and visible luminescence at room temperature [69]. Polycrystalline GaN films were obtained byreactive rf-magnetron sputter-deposition on Si (110) and photoluminescence was observed at 100K [70, 71]
and a possibility of epitaxial growth of crystalline GaN films was expected. LEDs using strained GaSb
quantum dots (QDs) embedded in Si within the active region was fabricated and showed an external
quantum efficiency of 0.3% was obtained for near band edge luminescence at 11 K [72].
4 Switches and modulators
Various types of optical switches or modulators using Si have been proposed and studied. MEMS
switch/modulator has been developed extensively but it is beyond the scope of this review. Free-carrier
absorption of infrared signal light due to the optically excited carriers in Si was studied for optical switch[73]. The response was limited by the slow free carrier lifetime. Nondegenerate two photon absorption
processes inside silicon wire waveguides was also successfully applied for ultra fast switch, modulation
and wavelength conversion [74]. Optical pulses of 1.6 ps at 1 GHz repetition rate have been successfully
converted from 1552 nm to 1536 nm. TPA process is expected for high speed photonic signal processing in
the Si photonic device system.
5. Concluding Remarks
Si laser has been our long-cherished dream and its realization using Raman amplification by UCLA andIntel attracted lots of attention and the research of Si photonic systems including both active and passive
devices will be accelerated. There are still lots of important studies concerning Si photonics; which are notmentioned in this review; Si/Ge and Ge dots for infrared detectors, microcavity, and optical MEMs devices
and so on. Research on silicon photonics in Japan has been mainly carried out at university laboratories
and institutes and is material or physics-oriented rather than device fabrication. For example, study on the
Raman amplification gain of Si was already measured by Japan and Semiconductor Research Institute. It
is expected that Japanese government and companies become aware of the importance of Si photonics andpromote cooperative developments of Si photonics technology with universities and institutes.
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