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 important roles in the past decades for the progresses of Electronics and Photonics.  It should be pointed out that this trend 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 to invite 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. Iga of 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

                            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 1960fs. The VCSEL photonics is opening up a new field of applications by taking the merits of compactness, 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 be monolithically 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] for realizing single mode fiber optical communication. Another issue is to make a semiconductor laser in terms of 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 and 980, 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 been studied.

Extensive studies and realization trials have been made on high performance devices for Gigabit 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 and fabrication technologies. The vertical cavity surface emitting laser (VCSEL) is emerging into market as an important 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 and the 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  to achieve laser oscillation can be written as;




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 VCSELfs. 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 of multimode-fiber-based optical links. This system is being extended to 10 Gigabits/s Ether and even faster systems. As for the reliability of VCSELs, 107 hours of room temperature operation is estimated. Life test of 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. 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 even in 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 assembling of components without precise alignment. Moreover, a 2-D parallel optical logic system can deal with a large amount of image information with high speed. To this demand, the VCSEL will be a key device. High power capabilities from VCSELfs 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 VCSELfs taking the advantage of small cavity dimensions. A densely packed array has also been demonstrated for the purpose of making high power lasers and coherent arrays. Into VCSELfs, 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 experiment through a 100m multimode fiber was performed [6]. VCSELfs in long wavelength may find the market in 10 Gigabit metropolitan networks together with high-speed detectors and silica fibers. Actually, GaInAs and GaInNAs VCSELfs show preferable performances.

A 780 nm VCSEL array has been introduced into a high speed laser printer. A laser printer has been developed 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 been developed. This system provides us of very easy optical coupling. VCSELfs can very nicely match to this application.

Green to UV VCSELfs will be useful in the optoelectronics field as in ultra-high density optical memories. A VCSEL pick-up may be good for high density optical memories and variety of sensors. Full color 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 is being 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 an interesting application. Several schemes for optical computing have been considered by utilizing 2-D arrays of VCSELfs and surface operating switches. The application for image recognition has been considered. Very low threshold VCSELfs 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 one of  the interesting examples. A single photon emitter is an extreme case. A photonics crystal is the extension 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-scale sensing. In summary, the ultra-parallel and ultra-high speed photonics based upon sophisticated VCSELfs will open up a new era of millennium [9].



[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. HayashiFProc. IEEE, 63 (1975) 208.

[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.



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



Fig. 2  A realistic model of VDSEL device.


Fig. 3  A 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:           LANs, MANs, Optical links, Mobile links, VSR, etc.

2. Computer Optics:           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 optical communication. This technology has been advancing steadily in parallel with the development of optical devices. 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 optical circuit 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 among users. The maturing of optical technology accelerates price competition in optical device and promote the creation 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 photodiode

6.       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



K. Kasaya, K. Tsuzuki, H. Shibata and Y. Tohmori [2003], gSOA direct modulation in wavelength-selectable laser array light sources,h OECC, pp. 431-432, July


S. Shirai, Y. Tatsuoka, C. Watatani, T. Ota, K. Takagi, T. Aoyagi, E. Omura, and N. Tomita [2004], g120 uncooled operation of direct modulated 1.3 m AlGaInAs-MQW DFB laser diodes for 10Gb/s telecom applications,h Proc. OFC2004, ThD2


J. Klamkin, J. T. Getty, J. M. Hutchinson, L. A. Johannson, E. J. Skogen, and L. A. Coldren [2004], gWidely-Tunable Single-Mode Bipolar Cascade SGDBR Lasers,h Proc. 19th IEEE International Semiconductor Laser Conference, WC2, Takamatsu


Y. Muramoto, K. Yoshino, S. Kodama, Y. Hirota, H. Ito, and T. Ishibashi [2004], g100- and 160-Gbit/s operations of uni-traveling-carrier photodiode module,h 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], g40-Gbit/s n-i-n InP Mach-Zehnder modulator with a -voltage of 2.2 V,h Electron. Lett., Vol.39, No. 20, pp. 1464-1466, Oct.


Y. Hashizume, H. Takahashi, T. Watanabe, S. Sohma, T. Shibata, and M. Okuno [2003], gCompact 32-channel 2~2 optical switch array based on PLC technology for OADM systems,h ECOC 2003, Mo3-5-4, Sep.


K. Suzuki, T. Mizuno, M. Oguma, T. Shibata, H. Takahashi, and A. Himeno [2004], gFully-reconfigurable wavelength-selective optical 1~N switch based transversal filter configuration, gProc. OFC2004, WC2,Feb.


Y. Hashizume, Y. Inoue, T. Kominato, T. Shibata, and M. Okuno [2004], gLow-PDL 16-channel Variable Optical Attenuator Array using Silica-based PLC, g Proc. OFC2004, WC4, Feb.


H. Takahashi [2003], gRecent progress on silica-based AWG waveguide multi/demultiplexers,h 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 vertical structure optical switch based on organic film.

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 real systems. 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 new switch function could be useful for packet header recognition for packet routing in OTDM systems. Novel physics 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 have demonstrated 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.


Fig.2       Structure of monolithic colliding pulse mode-locked laser for high repetition rate operation.



Fig. 3      Operation characteristics of mode-locked laser.



Fig. 4      Structure and operation principle of symmetric Mach-Zehnder interferometer all-optical switch using SOA nonlinear waveguides.




Fig. 5      Input and output signals and bit error rate data for 168 Gbps-to-10 Gbps DEMUX operation using SMZ all-optical switch.



Fig. 6      Waveguide device structure of intersubband all-optical switch and demonstarated DEMUX operation for 1 THz signal.



Fig. 7      Time-to-space conversion applied to DEMUX function for ultrafast pulses using organic (SQ) film-based surface normal all-optical switch.



Akiyama, T., Nikolai Georgiev, Teruo Mozume, Haruhiko Yoshida, Achanta Venu Gopal, and Osamu Wada [2001a]: "Nonlinearity and recovery time of 1.55 m intersubband absorption in InGaAs/AlAs/AlAsSb coupled quantum wells", Electron. Lett. Vol.37, p.129


Akiyama, T., N. Georgiev, T. Mozume, H. Yoshida, A. V. Gopal, and O. Wada [2001b]: "Nonlinearity and recovery time of 1.55 m intersubband absorption in InGaAs/AlAs/AlAsSb coupled quantum wells", Electron. Letts. Vlol.37, 129


Akiyama, T., N. Georgiev, T. Mozume, H. Yoshida, A. V. Gopal, and O. Wada [2002]: "1.55 um picosecond all-optical switching by using absorption in InGaAs-AlAs-AlAsSb coupled quantum wells", IEEE Photon. Tech. Letts. Vol.14, 495


Arahira, S., and Y. Ogawa [2002], e480-GHz subharmonic synchronous mode locking in a short-cavity colliding-pulse mode-locking laser diodef, IEEE Photon. Technol. Lett., vol.14, no.4, p.537


Arahira, S., S. Sasaki, K. Tachibana, and Y. Ogawa [2004], eAll-optical 160-Gb/s clock extraction with a mode-locked laser diode modulef, IEEE Photon. Technol. Lett., vol.16, no.6, p.15658.


Dorren, , X. Yang, D. Lenstra, H. de Waardt, G. D. Khoe, T. Simoyama, H. Ishikawa, H. Kawashima, and T. Hasama[2003], gUltrafast refractive-index dynamics in a multiquantum-well semiconductor optical amplifier h, JIEEE Photon. Technol. Lett., vol.15, pp.792-794


Fiuruki, M., I. Iwasa, S. Tatsuura, Y. Sato, M. Tian, T. Matsubara, H. Mitsu, M. Naruse(NICT), F. Kubota(NICT) [2004], gUltrafast time-serial space-parallel converter using organic dye films,h IEICE Trans. Electron.., Vol. E87-C, No. 7, p. 1161-1165


Gopal, A. V., H. Yoshida, T. Akiyama, A. Neogi, T. Mozume, N. Georgiev, and O. Wada [2001a]: gAbsorption saturation of intersubband transition in InGaAs/AlAsSb quantum well characterized by absorption spectral analysish Jpn. J. Appl. Phys. Lett. Vol.40, L1015


Gopal, A. V., H. Yoshida, A. Neogi, T. Mozume, N. Georgiev, T. Simoyama, O. Wada, and H. Ishikawa [2001b]: "Large improvement in intersubband saturation intensity in InGaAs/AlAsSb quantum well", Electron. Letts. Vol.37, 1265


Gopal, A. V., H. Yoshida, A. Neogi, T. Mozume, N. Georgiev, T. Simoyama, O. Wada, and H. Ishikawa [2002a]: "Intersubband absorption saturation in InGaAs/AlAsSb quantum wells", IEEE J. Quant. Electron vol.38, no.11, pp.1515-1520


Gopal, A. V., H. Yoshida, T. Simoyama, T. Mozume, and H. Ishikawa [2002b]: "Well width and doping density dependence of the 1.35 um intersubband transition in InGaAs/AlAsSb quantum wells", Appl. Phys. Letts. Vol.80, 4696


Gopal, A. V., H. Yoshida, T. Simoyama, T. Mozume, and H. Ishikawa [2002c]: "1.35 um intersubband transition in InGaAs/AlAsSb single quantum wells", Electron. Letts. Vol.38, p.600


Gopal, A. V., H. Yoshida, T. Simoyama. N. Georgiev, T. Mozume, H. Ishikawa[2003], gUnderstanding the ultra-low intersubband saturation intensity in InGaAs-AlAsSb quantum wellsh, IEEE J. Quantum Electron., vol.39, pp.299-305


IWASA, I., Makoto FURUKI, Minquan TIAN, Yasuhiro SATO, Lyong Sun PU, Satoshi TATSUURA, Osamu WADA[2002] gUltrafast optical demultiplexer using a spincoated squarylium-dye filmh, IEICE Transaction of Electronics, Volume E85-C, No. 1, p. 167


Kanamoto, K., S. Lan, N. Ikeda, Y. Tanaka, Y. Sugimoto, K. Asakawa, and H. Ishikawa[2004], gSingle photonic-crystal defect switch for all-optical ultrafast operation using two photon absorptionh, IEICE Trans. Electron.,, Vol. E87-C, No. 7, p.1142


Lan, S., Satoshi Nishikawa, and Osamu Wada [2001a]: gLeveraging deep photonic bandgaps in photonic crystal impurity bandsh, Applied Physics Letters, Vol. 78, p.2101


Lan, S., Satoshi Nishikawa, Osamu Wada[2001b], Kouichi Akahane, Yoshitaka Okada, and Mitsuo Kawabe: gDifferent responses of localized and extended excitons to exciton-exciton scattering manifested in excitation density-dependent photoluminescence excitation spectrah, Journal of Applied Physics, Vol. 89, p.6171


Lan, S., Satoshi Nishikawa, Hiroshi Ishikawa, and Osamu Wada[2001c]: gDesign of impurity band-based photonic crystal waveguides and delay lines for ultrashort optical pulsesh, Journal of Applied Physics, Vol. 90, p.4321


Lan, S., Satoshi Nishikawa, Hiroshi Ishikawa, and Osamu Wada[2002a]:gEngineering photonic crystal impurity bands for waveguides, all-optical switches and optical delay linesh, IEICE Transactions on Electronics, Vol. E85-C, p.181


Lan, S., and Hiroshi Ishikawa[2002b]: gCoupling of defect pairs and generation of dynamical band gaps in the impurity bands of nonlinear photonic crystals for all-optical switchingh, Journal of Applied Physics, Vol. 91, p.2573


Lan, S., Satoshi Nishikawa, Yoshimasa Sugimoto, Naoki Ikeda, Kiyoshi Asakawa, and Hiroshi Ishikawa [2002c]: gAnalysis of defect coupling in one- and two-dimensional photonic crystalsh, Physical Review B, Vol. 65, p.165208


Lan, S., Satoshi Nishikawa, Hiroshi Ishikawa, Osamu Wada, Kouichi Akahane, Hai-Zhi Song, Yoshitaka Okada, and Mitsuo Kawabe [2002d]: gComparison of the optical properties of InGaAs/GaAs(311)B two-dimensional quantum dot superlattices and quantum wellsh, Japanese Journal of Applied Physics, Vol. 41, p.2807


Lan, S., and Hiroshi Ishikawa [2002e]: gReflection type all-optical switch for ultrashort pulses by modulating the absorption of a single asymmetrically confined photonic crystal defecth, Optics Letters, Vol. 27, p.1259


Lan, S., and Hiroshi Ishikawa [2002f]: gBroadband waveguide intersections with low cross-talk in photonic crystal circuitsh, Optics Letters vol.27,no.17, pp.1567


Lan, S., K. Kanamoto, T. Yang, S. Nishikawa, Y. Sigimoto, N. Ikeda, H. Nakamura, K. Asakawa, and H. Ishikawa[2003]: gSimilar role of waveguide bend in photonic crystal circuit and disordered defects in coupled cavity waveguides: An intrinsic problem in realizing photonic crystal circuitsh, Phys. Rev., vol.B67, pp.115208-115215


Nakamura, S., Y. Ueno, and K. Tajima@[2001], "168-Gb/s all-optical wavelength conversion with a Symmetric-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 on near-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 and Ultrafast 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], gOptical characterization of photonic delay lines based on one-dimensional coupled defectsh, Optics Lett., vol.27, no.23, pp.2079-2081


Nishikawa, S., S. Lan, N. Ikeda, Y. Sugimoto, H. Ishikawa, K. Asakawa@[2002b], gDesign and fabrication of impurity band-based photonic crystal waveguide for optical delay linesh, 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], gHybrid-integrated Symmetric Mach-Zehnder all-optical switches and ultrafast signal processingh, 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]:h Femtosecond two-dimensional serial]to]parallel pulse converter using a squarylium Dye J-aggregate filmh, Opt.Quantum Electron. Vol.33, p.1089


Tatsuura, S., Osamu Wada, Makoto Furuki, Minquan Tian, Yasuhiro Sato, Izumi Iwasa, Lyong Sun Pu@[2001b]: gAll-optical two-dimensional serial]to]parallel Pulse converter using an organic film with femtosecond optical responseh, 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]: gLarge kai(3) of squarylium dye J-aggregates measured using the Z-scan techniqueh 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]: gMicrostructure of squarylium dye J aggregate films examined on the basis of optical behavior at low temperatureh, 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)


Wada, O. [2004]:  gFemtosecond all-optical devices for ultrafast communication and signal processing,h New J. Phys., Vol. 6, p.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 ring cavity TPO with galvano scanner makes the TPOfs frequency response possible up to 1ms (1 kHz), and variety 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, was demonstrated.

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



Imai, K., K. Kawase, J. Shikata, H. Minamide, and H. Ito [2001], gAn injection-seeded terahertz-wave parametric oscillatorh, Applied Physics Letters, vol. 78, pp. 1026-1028


Kawase, K., J. Shikata, K. Imai, and H. Ito [2001], gA Transform-limited, Narrow-Linewidth, THz-wave Parametric Generatorh, Applied Physics Letters, vol. 78 no. 19, pp. 2819-2821


Imai, K., K. Kawase, and H. Ito [2001], gA frequency-agile terahertz-wave parametric oscillatorh, Opt. Express 8, pp. 699-704


Ito, H., T. Hatanaka, S. Haidar, K. Nakamura, K. Kawase, and T. Taniuchi [2001], gPeriodically poled LiNbO3 OPO for generating Mid IR to terahertz wavesh, Ferroelectrics, vol.253, pp.95-104


Sato, A., K. Kawase, H. Minamide, S. Wada, and H. Ito [2001], gA Tabletop Terahertz-Wave Parametric Generator Using a Diode-Pumped Solid-State Laserh, Trends in Optics and Photonics Series (TOPS), vol. 50, pp. 456-460


Sato, A., K. Kawase, H. Minamide, S. Wada, and H. Ito [2001], gTabletop terahertz-wave parametric generator using a compact, diode-pumped Nd:YAG laserh, Review of Scientific Instruments, vol. 72, No. 9, pp. 3501-3504


Kawase, K., J. Shikata, H. Minamide, K. Imai, and H. Ito [2001], gArrayed silicon prism coupler for a THz-wave parametric oscillatorh, Applied Optics, vol.40, No.9, pp.1423-1426


Avetisyan, Y., Y. Sasaki, and H. Ito [2001], gAnalysis of THz-wave surface-emitted difference-frequency generation in periodically poled lithium niobate waveguideh, Applied Physics B, vol.73, pp.511-514


Kawase, K., H. Minamide, K. Imai, J. Shikata, and H. Ito [2002], gInjection-seeded terahertz-wave parametric generator with wide tunabilityh, Applied Physics Letters, vol.80, no.2, pp.195-197


Kawase, K., J. Shikata, and H. Ito [2002], gTerahertz wave parametric source (Topical Review)h, Journal of Physics D: Applied Physics, vol.35, no.3, pp.R1-R14


Karino, K., J. Shikata, K. Kawase, H. Ito, and I. Sahashi [2002], gTerahertz-wave parametric generation characteristics of MgO: LiNbO3h, 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], gWidely tunable THz-wave parametric generator for imaging systemh, RIKEN Review, no.47,  pp.48-51


Sato, A., K. Imai, K. Kawase, H. Minamide, S. Wada, and H. Ito [2002], gNarrow-linewidth operation of a compact THz-wave parametric generator systemh, Optics Communications, vol.207, no.1-6, pp.53-359


Ito, H., and K. Kawase [2002], gTunable compact THz sources and their applicationh, Trends in Optics and Photonics (TOPS), vol.79, pp.75-77


Imai, K., K. Kawase, H. Minamide, and H. Ito [2002], gAchromatically injection-seeded terahertz-wave parametric generatorh, Trends in Optics and Photonics (TOPS), vol.79, pp.233-235


Sasaki, Y., Y. Avetisyan, K. Kawase, and H. Ito [2002], gTunable THz-wave difference frequency generation from slant-stripe-type PPLN based on surface-emitting geometryh, Trends in Optics and Photonics (TOPS), vol. 79, pp. 20-22


Imai, K., K. Kawase, M. H., and H. Ito [2002], gAchromatically injection-seeded terahertz-wave parametric generatorh, Optics Letters, vol.27, no.24, pp.2173-2175


Sasaki, Y., A. Yuri, K. Kawase, and H. Ito [2002], gTerahertz-wave surface-emitted difference frequency generation in slant-stripe-type periodically poled LiNbO3 crystalh, Applied Physics Letters, vol.81, issue 18, pp.3323-3325


Shikata, J., K. Kawase, T. Taniuchi, and H. Ito [2002], gFourier-Transform Spectrometer with a Terahertz-Wave Parametric Generatorh, 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], gThe effect of injection seeding on terahertz parametric oscillationh, Electronics and Communications in Japan, Part 2, vol.86, no.1, pp.26-35


Imai, K., K. Kawase, H. Minamide, and H. Ito [2003], gA rapidly tunable terahertz-wave parametric oscillatorh, 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], gSpatial pattern separation of chemicals and frequency-independent components by Terahertz spectroscopic imagingh, Applied Optics, vol.42, issue 28, pp.5744-5748


Kawase, K., J. Shikata, and H. Ito [2003], gWidely tunable THz-wave generation using nonlinear opticsh, 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], gComponent spatial pattern analysis of chemicals using terahertz spectroscopic imagingh, Applied Physics Letters, vol.83, no.4, pp.800-802


Imai, K., K. Kawase, H. Minamide, and H. Ito [2003], gA rapidly tunable terahertz-wave parametric oscillatorh, 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], gSpatial Pattern Separation of Chemicals and Frequency-Independent Components by Terahertz Spectroscopic Imagingh, Applied Optics, vol.42, issue 28, pp.5744-5748


Sasaki, Y., H. Yokoyama, and H. Ito [2004], gDual-wavelength optical-pulse source based on diode lasers for high-repetition-rate, narrow-bandwidth terahertz-wave generationh, Optics Express, vol. 12, no. 14, pp.3066-3071


Watanabe, Y., K. Kawase, T. Ikari, H. Ito, Y. Ishikawa, and H. Minamide [2004], gComponent analysis of chemical mixtures using terahertz spectroscopic imagingh, Optics Communications, vol.234, pp.125-129


Ohtani, K., K. Fujita and H. Ohno [2004], gA low threshold current density InAs/AlGaSb superlattice quantum cascade laser operating at 14mh, Jpn. J. Appl. Phys., vol.43, pp.L879-881.


Takahashi, M., Y. Ishikawa, J. Nishizawa, and H. Ito [2005], gLow-frequency vibrational modes of riboflavin and related compoundsh, Chemical Physics Letters 401, pp.475-482


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 gsmart materialsh and gsmart structuresh 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 were related to these technologies.  Some representatives are described bellow.

A down-shifted frequency of Brillouin scattering caused in a fiber is changed in proportion to longitudinal 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 for the 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.  On the 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 gBrillouin Optical Correlation Domain Analysis: BOCDA,h a spatial resolution of 1.0cm was demonstrated.

The BOCDA technique has recently been applied to find clacks caused in a concrete block, in which the sensing 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 this technique 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 by an 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 high spatial resolution and the fast measurement speed.  This technique was selected as the Hasunuma Prize in 2002 from the Society of Instrument and Control Engineers, SICE.

Basic principle of the BOCDA technique is gsynthesis of optical coherence function: SOCF,h in which arbitrary shapes of optical coherence function can be synthesized by modulating optical frequency of a light source.  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 and experimented.  In traditional techniques, FBGs with different Bragg wavelength were required for wavelength 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 the technique.

By also applying the SOCF technique, a fiber optic distributed force sensing has been proposed and studied.  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 the force-applied position.  Introducing a special laser diode, a SSG-DBR LD invented by NTT, Japan, which has 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 the coherence length of a laser source.  By this scheme, 10cm spatial resolution with 5km measurement range has been demonstrated.



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


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.




Hotate, K., and M. Tanaka [2001], gCorrelation-based continuous-wave techniques provide high spatial resolution for distributed fiber optic sensingh, SPIE OE Magazine, 11, pp.36-40 <Invited>


Hotate, K., and M. Tanaka [2001], gCorrelation-based continuous-wave technique for fiber optic distributed strain measurement using Brillouin scattering with cm-order spatial resolution |Applications to smart materials|h, IEICE Trans. on Electron., vol.E84-C, no.12, pp.1823-1828 <Invited>


Hotate, K., and M. Tanaka [2002], gDistributed fiber Brillouin strain sensing with 1cm spatial resolution by correlation-based continuous-wave Techniqueh, IEEE Photon. Tech. Lett., vol.14, no.2, pp.179-181


Hotate, K., and M. Tanaka [2002], gApplication of correlation-based continuous-wave technique for fiber Brillouin sensing to measurement of strain distribution on a Small Size Materialh, IEEE Photonic Technology Letters, vol.14, no.5, pp.675-677


Hotate, K. [2002], gApplication of synthesized coherence function to distributed optical sensing,h IOP Measurement Sci. and Tech., vol.13, no.11, pp.1746-1755


Hotate, K. [2002], gRecent progress in Brillouin based fiber sensor technologyh, 15th Intern. Conf. on Optical Fiber Sensors (OFS-15), Portland, WC1, pp.297-300 <Invited>


Hotate, K. and S. S. L. Ong [2002], gDistributed fiber Brillouin strain sensing by correlation-based continuous-wave technique –cm-order spatial resolution and dynamic strain measurement–h, SPIE Photonics Asia, Shanghai, 4920-51, pp.299-310 <Invited>


Hotate, K. and M. Kashiwagi [2003], gHigh spatial resolution reflectometry for optical subscriber networks by synthesis of optical coherence function with measurement range enhancementh, IEICE Trans. on Electron., volE86-C, no.2, pp.213-217


Hotate, K. and S. S. L. Ong [2003], gDistributed dynamic strain measurement using a correlation-based Brillouin sensing systemh, IEEE Photon. Technol. Lett., vol.15, no.2, pp.272-274


Hotate, K. [2003], gOptical Fiber Sensors for Smart Materials/Structures and Optical Communicaitonsh, International Meeting on New Frontiers for Ubiquitous IT Services, Atsugi <Invited>


Hotate, K. [2003], gFiber Optic Distributed Sensing for Smart Materials and Structures by Optical Correlation Domain Technique with Continuous Lightwaveh, 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], gA multiplexing technique of fiber Bragg grating sensors with the same reflection wavelength by the synthesis of optical coherence functionh, Measurement Sci. and Technol., vol. 15, no.1, pp. 148-153

Hotate, K., A. Kuramoto and Z.-Y. He [2004], gOptical fiber stress-location measurement by synthesis of binary optical coherence function,h IEEE Photon. Technol. Lett., vol. 16, no.2, pp. 578-580


Hotate, K. [2004], gTrends and prospects for optical distributed sensing |Fiber-optic nerve systems for smart materials and smart-structures|h, SPIE Vol.5502, Second European Workshop on Optical Fiber Sensors, Santander, pp.51-58 <Invited>


Hotate, K. [2004], gPotential applications of optical fiber sensing technology for future societyh, International Symposium on Network and Center-Based Research for Smart Structures Technologies and Earthquake Engineering, Osaka <Invited>


Hotate, K. [2004], gFiber optic nerve systems for smart materials and smart structuresh, SPIE Optics East 2004, Philadelphia, 5604-1, pp.1-10 <Invited>


Hotate, K. [2004], gOptical Fiber Sensors for Smart Materials/Structures and Optical Communicaitonsh, Chapter 9 in gNew Photonics Technologies for the Information Ageh, ed., by S. Sudo and K. Okamoto, Artech House, pp.159-179


He, Z. and K. Hotate [2002], gDistributed Fiber-optic stress-location measurement by arbitrary shaping of optical coherence functionh, Jour. of Lightwave Tech., vol.20, no.9, pp.1715-1723


Zhu, B., T. Saida and K. Hotate [2003], gVariable optical filter using dynamic grating in Er doped fiber controlled by synthesis of optical coherence function: Proposal and experimental verificationh, IEICE Trans. on Electron., IEICE Trans., vol.E86-C, no.1, pp.97-99


Kashiwagi, M. and K. Hotate [2004], gElongation of Measurement Range by Successively Shifting Measurement Window in a High Spatial Resolution Reflectometry for Optical Subscriber Networks by Synthesis of Optical Coherence Functionh, Measurement Sci. and Technol., vo.15, no.8, pp. 1512-1518


Enyama, M. and K. Hotate [2004], gDynamic and random-access strain measurement by fiber Bragg gratings with synthesis of optical coherence functionh, 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 short pulse 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 is modulated, 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 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 based on the two-photon absorption process in a Si-image sensor. Using an interferometer with a tilt mirror in the reference path, the relative time difference between the signal and reference pulses is spatially distributed on the Si-image sensor, so the intensity auto-correlation is monitored as an image at a time without using moving parts.



Fig. 1   Principle of frequency decomposed parallel photonic signal processing .



Kurokawa, T.[2001], "Optical Signal Processing for Communication and Information Systems", Proc. CLEO/Pacific Rim, Makuhari, Vol.U, 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], gReflectometry based on two-photon absorption of a silicon avalanche photodiodeh, Proc. 15th Optical Fiber Sensors Conference, Portland, pp.577-580.


Tanaka, Y., T. Kurokawa [2002], gProfilometry using two-photon absorption of silicon avalanche photodiodeh, Proceedings of SPIE, Vol. 4919, pp.102-109 <Invited>.


Itoh, Y., K. Aizawa, Y. Tanaka, H. Tsuda [2003], gMeasurement of short optical pulse spectra using arrayed waveguide gratingh, 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], gProfilometry based on two-photon absorption in a silicon avalanche photodiodeh, Optics Letters, vol.28, no.6, pp402-404.


Yamanaka, A., M. Yamamoto, Y. Tanaka, T. Kurokawa, T. Kawanishi and M. Izutsu [2003], gA Multi-wavelength light source using an optical single-side band modulator an arrayed waveguide gratingh, Proc. 5th Pacific Rim Conference on Lasers and Electro-Optics, Taipei, p.714.


Sako, N., S. Imoto, Y. Tanaka and T. Kurokawa [2003], gMeasurement accuracy of profilometry based on two-photon absorptionh, 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], gOptical Spectrum analyzer for optical short pulsesh, Proc. 5th Pacific Rim Conference on Lasers and Electro-Optics, Taipei, p.41.


Imoto, S., N. Sako, Y. Tanaka and T. Kurokawa [2003], gAccuracy improvement of two-photon absorption based measurement by temperature controlled Si-photodetecterh, Proc. 5th Pacific Rim Conference on Lasers and Electro-Optics, Taipei, p.516.


Nezu, T., Y. Tanaka and T. Kurokawa [2003], gDelayed self-heterodyne linewidth measurement of fiber Bragg grating laserh, Proc. 5th Pacific Rim Conference on Lasers and Electro-Optics, Taipei, p.388.


Suzuki, T., Y. Shibata and H. Tsuda [2003], gDesign and the fabrication of the small v-bend optical waveguide using an elliptic mirrorh, Proc. 11th European Conference on Integrated Optics, Prague, Czech.


Suzuki, T., Y. Shibata and H. Tsuda [2003], gSmall v-bend optical silica-waveguide using an elliptic mirror for planar lightwave circuitsh, Proc. 9th Microoptics Conference, Tokyo, H-20.


Tate, A., T. Suzuki, Y. Shibata and H. Tsuda [2004], gProposal of WDM multi/demultiplexer with deep grooves and parabolic mirrorsh, Proc. 7th International Symposium on Contemporary Photonics Technology, Tokyo, PDP-1.


Hakamata, M., and H. Tsuda [2004], gDiffractive optical elements using the sub-wavelength scale pillar array structure,h SPIE Photonics West, San Jose, pp.5360-5363.


Aizawa, K., H. Aoki, Y. Ito, Y. Tanaka and T. Kurokawa [2004], gWaveform measurement of ultra-short optical pulses based on two photon absorption in Si-image sensorh, 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], gOptical pulse generation by controlling the sidebands of the phase modulated lighth, OECC/COIN2004 (9th Optoelectronics and Communications Conference/ 3rd International conference on Optical Internet, Yokohama, pp.738-739.


Ishida, M., T. Suzuki and H. Tsuda [2004], g180 degree-bend structures using a double elliptic mirror in a slab waveguideh, OECC/COIN2004 (9th Optoelectronics and Communications Conference/ 3rd International conference on Optical Internet, Yokohama, 13F1-4.


Suzuki, T., Y. Shibata, K. Masuda and H. Tsuda [2004], gCompact arrowhead arrayed waveguide grating using v-bend optical waveguides,h Topical Meeting on Integrated Photonics Research, San Francisco, IFH2.


Mandai, K., T. Suzuki, H. Tsuda, T. Kurokawa and T. Kawanishi [2004], gArbitrary optical short pulse generator using a high-resolution arrayed-waveguide gratingh, 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 1990fs. 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.


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 of photonics technology by breaking through the frequency limit from microwave to millimeter waves and further on to the submillimeter-wave region in radio-wave technologies.


The primary motivation of the former is to make positive use of special merits in optical fibers as transmission media, such as low loss, high capacity (broad bandwidth), light weight, flexible, and non-inductive properties. The latter involves making use of not only optical fibers, but all of optical communication 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 and development accomplished recently. Radio-on-fiber, optical remote-antenna and optically-controlled antenna are typical examples of the first category, while microwave and millimeter-wave measurement as well 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 for high-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 that frequency.

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-field sensor based on magneto-optic (MO) effect has also been studied to measure a current in place of an electric field or a voltage.



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], gOutput power measurement of photonic millimeter-wave and sub-millimeter-wave emitter at 100-800 GHzh,  Electron. Lett., vol. 38, no. 15, pp. 798-800


Hirata, A., M. Harada, and T. Nagatsuma[2003a], g120-GHz wireless link using photonic techniques for generation, modulation, and emission of millimeter-wave signalsh, IEEE J. Lightwave Technol., vol. 21, no.10, pp. 2145-2153


Hirata, A., M. Harada, K. Sato, and T. Nagatsuma[2003b], gLow-cost millimeter-wave photonic techniques for gigabit/s wireless linkh, IEICE Trans. on Electronics, E86-C, no. 7, pp. 1123-1128


Hirata, A., H. Ishii, and T. Nagatsuma[2004a], gDesign and characterization of ultra-broadband photonic emitters for microwave and millimeter-wave applicationsh, Japan-Korea workshop on microwave and millimeter-wave photonics 2004 Dig, pp. 63-66


Hirata, A., H. Togo, N. Shimizu, H. Takahashi, K. Okamoto, and T. Nagatsuma[2004b], gLow-phase noise photonic millimeter-wave generator using an AWG integrated with a 3-dB combinerh, MWP 2004 Dig., TD-3, pp. 209-212


Ikeda, K., T. Kuri, Y. Takahashi, and K. Kitayama[2003], gFull-duplex transmission using 2-RF-port electroabsorption transceiver with photonic up-and downconversions for millimeter-wave radio-on-fiber systemh, 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], gPre-amplifier-integrated uni-traveling-carrier photodiode module with a rectangular waveguide-output port for operation in the 120-GHz bandh, LEOS2004 Dig., MN2, pp. 128-129


Iwanami, M., E. Yamazaki, K. Nakano, T. Sudo, S. Hoshino, S. Wakana, M. Kishi, and M. Tsuchiya[2003], gMagnetic near-field measurements over LSI package pins by fiber-edge magnetooptic probeh, IEEE J. Lightwave Technol., vol. 21, no. 12, pp. 3273-3281


Izutsu, M.[2004], gElectrooptic light modulation technology for microwave photonicsh, MWP2004 Dig., MA-2, pp. 12-15


Kitayama, K.[2003], gDense wavelength division multiplexing radio-on-fiber systemh, MWP2003 Dig., pp. 129-134


Kosugi, T., M. Tokumitsu, T. Enoki, M. Muraguchi, A. Hirata, and T. Nagatsuma[2004], g120-GHz Tx/Rx chipset for 10-Gbit/s wireless applications using 0.1-m-gate InP HEMTsh, IEEE CSIC Dig., pp. 171-174


Mizuno, M., A. Hirata, K. Kawase, C. Otani, and T. Nagatsuma[2004], gAnalysis of Pheochromocytoma (PC12) membrane potential under the exposure to millimeter-wave radiationh, AIP Conference Proc., no. 716, pp. 164-166


Nagatsuma, T.[2002], gPhotonic measurement technologies for high-speed electronicsh, Meas. Sci. Technol. vol. 13, no.11, pp. 1655-1663


Nagatsuma, T., H. Ito[2003], gUltrafast applications of uni-traveling-carrier photodiodes from measurement to signal processingh, Proc. SPIE, vol. 4992, pp. 90-104


Nagatusma, T., H. Togo, K. Narahara, N. Shimizu, and A. Sasaki[2004], gRecent progress in optical measurement of radio-wave signals from gigahertz to terahertzh,  MWP2004 Dig., MB-1, pp. 20-23


Nakajima, F., T. Furuta, and H. Ito[2004],hHigh-power terahertz-wave generation from a resonant-antenna-integrated uni-traveling-carrier photodiodeh, MWP2004 Dig., WD-4, pp. 313-316


Niiho, H., M. Nakaso, K. Masuda, H. Sasai, K. Utsumi, and M. Fuse[2004], gMulti-channel wireless LAN distributed antenna system based on radio-over-fiber techniquesh, LEOS2004 Dig., MF2, pp. 57-58


Sasaki, A., and T. Nagatsuma[2002], gReflection-type CW- millimeter-wave imaging with a high- sensitivity waveguide-mounted electro-optic sensorh, 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], gCurrent profiling for m-class planar circuit patterns by fiber-edge magneto-optic probeh, MWP 2003 Dig., pp. 341-344


Shoji, Y., and H. Ogawa[2003],hExperimental demonstration of 622 Mbps millimeter-wave over fiber link for broadband fixed wireless access systemh, IEICE Trans. on Electronics, E86-C, no. 7, pp. 1129-1137 


Suzuki, H., M. Fujiwara, K. Iwatsuki, A. Hirata, and T. Nagatsuma[2005], gPhotonic millimetre-wave generator using intensity and phase modulators for 10 Gbit/s wireless linkh, 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], gThe first radioastronomical observation with photonic local oscillatorh, Publ. Astron. Soc. Japan, vol. 55, pp. L53-L56


Togo, H., A. Sasaki, A. Hirata, and T. Nagatsuma[2004], gCharacterization of millimeter-wave antenna using photonic measurement techniquesh, 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], gHigh-speed and high-spatial resolution fiber-optic measurement technique for RF magnetic field distributionh, LEOS2003 Dig., ThS1, pp. 929-930


Tsukamoto, K., T. Higashino, T. Nakanishi, and S. Komaki[2003], gDirect optical switching code-division multiple-access system for fiber-optic radio highway networksh, IEEE J. Lightwave Technol., vol. 21, no. 12, pp. 3209-3220


Usami, M., R. Fukasawa, M. Tani, M. Watanabe, and K. Sakai[2003], gCalibration free terahertz imaging based on 2D electro-optic sampling techniqueh, Electron. Lett., vol. 39, no. 24, pp. 1746-1747


Yamamoto, T., and S. Kawanishi[2004], gGeneration of low-noise optical frequency comb and optical beat signal using phase modulatorh, Japan-Korea workshop on microwave and millimeter-wave photonics 2004 Dig., pp. 15-19


D8. Nanotechnology

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 and development in these fields seem to have been carried out in their individual academic society and industrial groups, and nanotechnology in these fields shall still continue to grow.  In order to create and incubate new fields and novel devices for future prosperous society, however, cross-communication and, in some cases, fusion between various fields of nanotechnology should be required.  For this purpose, the new technical group, named as gNext-Generation Nanotechnology (NNN) Grouph, has been established in April, 2004, to discuss next-generation nanotechnology under the Electronics Society (ES) of Institute of Electronics, Information Communication Engineers (IEICE).  The activity of various nanotechnology is over-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 a high-speed wavelength converter.  As for quantum dots (QD), its size and density have begun to be controlled 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 of nano-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 the material 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.   CNT-gated transistors and application to through-hole vias were reported.  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-cell and 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 killing them, and so on.  These technologies lead to the remedy of incurable diseases with reduced pains through the nanotechnology.  As such nanotechnologies, the followings have been reported; micelling of self-organized nano-capsules, nano-pillars to detect proteins with high sensitivity by CNT or polymer and their 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 the advantages of each nanotechnology.

4. Mechanics:  Micro electro-mechanical systems (MEMS) machines have been further down-sized to reach 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) to realization of novel artificial materials and structures by controlled bottom-up technology in the fields of electronics 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 of soft-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.  Laser induced self-writing technology of optical waveguide is also very simple and attractive.  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 be attained. 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 a large optical loss (more than a few dB/cm), and it is necessary to reduce the total insertion loss for a practical EO device. So an EO polymer device serially grafted with a passive waveguide composed of a high 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 a single substrate is possible.  If the entire structure is on one circuits, the manufacturing, packaging, and assembly 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 to align 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 that usually depend on the size of the -conjugated systems of the dye. The -conjugation length dependence of the 2nd-order NLO hyperpolarizability  has been investigated. 




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





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.  This reaction can be explained by following two mechanisms.  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 for the 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 as monolithically integrated photonic circuits. 



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


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 of large 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 optical waveguides with latge cores fabricated by hot embossing, Proc. SPIE Organic Photonics Materials and Devices 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) Fabrication of Serially 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


Y. Suzuki, K. Komatsu, T. Kaino, and Y. Honda, (2003). gSerially grafted optical waveguide fabrication of NLO polyimide and transparent polymersh, 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 a half-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 crystal alignment 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


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. Commun., 228, 279-283


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


J. Thompson, M. Anni, S. Lattante, D. Pisignano, R.I. Blyth, G. Gigli, R. Cingolani, (2004) Amplified spontaneous emission in the near infrared from a dye-doped polymer thin film, Synth. Metals, 143, 305-307


M. Karimi, N. Granpayeh, M.K.M. Farshi, (2004) Analysis and design of a dye-doped polymer optical fibre 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 for the 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 well as 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 general design 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. Encouraged by the success of ultrahigh Q nanocavities, tuning or nonlinear switching operation of photonic-nano devices has started. The new concept of gIn-Plane Heteroh structure has been applied to the defect engineering, and photonic-nanostructure devices with high functionality has been realized.

  Progresses in 3D photonic crystals have been also remarkable.  The demonstration of spontaneous 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 spontaneous emission is suppressed by 100 times at the complete bandgap while a strong emission is observed at the artificial 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 promised features 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 crystal slab, the combination with Si LSI technology will proceed with an all-optical main part, but with the control 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 been achieved. 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, to organic, magnetic, etc. 



M. Fujita, T. Ueno, K Ishihara, T. Asano, S. Noda, H. Ohata, T. Tsuji, H. Nakada, and N. Shimoji [2004], gReduction of operating voltage in organic light-emitting diode by corrugated photonic crystal structure,h Applied Physics Letters, vol.85, no.23, pp.5769-5771.


Y. Tanaka, T. Asano, R. Hatsuta, and S. Noda [2004], gAnalysis of a line-defect waveguide on a silicon-on-insulator two-dimensional photonic-crystal slab,h 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], gTransmission and reflection characteristics of in-plane hetero-photonic crystals,h Applied Physics Letters, vol.85, no.20, pp.4591-4593.


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


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


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


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


S. Ogawa, M. Imada, S. Yoshimoto, M. Okano, and S. Noda [2004], gControl of light emission by 3D photonic crystals,h Science, vol.305, no.5681, pp.227-229. (published online 3 June 2004 (10.1126/science.1097968))


T. Asano and S. Noda [2004], gTuning holes in photonic-crystal nanocavities,h Nature, vol.429, doi:10.1038, no.6988.


D. Ohnishi, T. Okano, M. Imada, and S. Noda [2004], gRoom temperature continuous wave operation of a surface-emitting two-dimensional photonic crystal diode laser,h Optics Express, vol.12, no.8, pp.1562-1568.


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


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


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


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


M. Okano, S. Kako, and S. Noda [2003], gCoupling between a point-defect cavity and a line-defect waveguide in three-dimensional photonic crystal,h Physical Review 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], gOrganic light-emitting diode with ITO/organic photonic crystal,h Electronics Letters, vol.39, no.24, pp.1750-1752.


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


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


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


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


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


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


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


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


Y. Tanaka, T. Asano, Y. Akahane, B. S. Song, and S. Noda (2003), gTheoretical investigation of propagation loss of a line defect waveguide in a two-dimensional photonic crystal slab with tapered air holes,h Applied Physics Letters, vol.82, no.11, pp.1661-1663.


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


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


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


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


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


N. Yamamoto and S. Noda (2002), gAccurate identification of the band gap of photonic crystals from transmission spectra,h Journal of Applied Physics, vol.92, no.5, pp.2256-2259.


S. Noda, M. Imada, A. Chutinan, and N. Yamamoto (2002), gIII-V based-semiconductor photonic crystals,h 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), gSemiconductor three-dimensional and two-dimensional photonic crystals and devices,h 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), gChannel-add operation of a device using defects in a two-dimensional photonic crystal slab,h Materials Research Society Symposium Proceedings gMaterials and devices for optoelectronics and microphotonicsh, vol.722, pp.363-367.


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


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


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


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


S. Noda and M. Imada (2002), g2D photonic crystal surface-emitting laser using triangular-lattice structure,h IEICE Transactions on Electronics, vol.E85C, no.1, pp.45-51.


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


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


T. Asano, S. Yoshizawa, and S. Noda (2001), gCarrier relaxation dynamics in an ultrafast all-optical modulator using an intersubband transition,h Applied Physics Letters, vol.79, no.27, pp.4509-4511.


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


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


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


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


S. Noda (2001), gTwo- and three-dimensional photonic crystals in III-V semiconductors,h 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), gPhotonic bands of metallic systems. I. Principle of calculation and accuracy,h 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. Though various types of silicon photonic devices have been studied and some passive devices have been developed in 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 and laser have been developed for light amplification and generation [7]. Semiconductor Raman lasers and amplifiers were studied in some semiconducting materials such as GaP [8, 9].

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 the point 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 a high external efficiency (10%) was reported for a Si LED at 1.54 mm Si by ST microelectronics[6], the LED was composed of a thin Er-doped SiO2 sandwiched with p- and n-silicon and it was high resistive and was still far from a laser diode due to current injection. Strong enhancement in the 1.54mm luminescence from Er and nc-Si codoped SiO2 reported by M. Fujii et al. had also attracted a great attention [10] and have been followed by lots of studies for the energy transfer mechanisms, efficiency, excitation cross section, 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 of photons [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 at high Er concentrations. Recently, an Er-Si-O new crystal which shows a superlattice structure has been reported 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 1.54mm 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 1980fs 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 of passive devices. PLC established its fame due to compactness, commercial productivity, reliability etc. and is 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 in the production fields. Though PLCs is one of the vicious technologies in the silicon photonics, the review of 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 the boundary 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 mm2 with SiO2 clad [13]. With improved fabrication methods, the propagation loss down to less than 3dB/cm and the bending radius of < 5 mm 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 also fabricated various passive functional devices; multimode interference branch, directional coupler, star coupler, microspectrometer, lattice filter, ring resonator, 1D photonic crystal filter etc. They also fabricated some 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 of 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 250mm. One of the features of the porous silicon waveguide is that the refractive index of PS is easily controlled both by the pore 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 and fabricated 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 by adopting 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 which show full bandgaps have also fabricated and propagation of light beams along line defects formed in a-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 and achieved 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 not described in this report.


(4) Surface Plasmon Waveguides:

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 fabricated using 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, the propagation length of the surface plasma polariton extended from 2µm to 6µm corresponding to the wavelength 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 the enhanced radiative recombination in nanosize semiconductor particles.

Photoluminescence and electroluminescence of nc-Si have been studied worldwide. Various processes for the formation of nanocrystalline Si (quantum wells, wires and dots) were devised. Efficient photoluminescence at controlled wavelengths .in the visible region was obtained by changing the size of nanocrystalline Si spheres embedded in SiO2. Electroluminescence of nc-Si in SiO2 was also achieved by applying 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 was obtained 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 mm [5]. This emission was due to the 4f-4f transition of Er3+ and the wavelength coincides with that of optical communication. Lots of efforts have been done to find the way to realizing laser diodes and amplifier, 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 the solution limit of Er in crystalline Si is around 1019/cm3. Temperature quenching: due to energy back@transfer 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 still insufficient 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) by about 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 recombination energy is effectively resonant-transferred to Er3+ 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 the Netherlands [12]. This ErSiO is a crystal which contain Er at ~1022/cm3 as a constituent atom, and shows a fine structure in the Er-related 1.54mm photoluminescence at room temperature. It also shows a semiconducting 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 concentration quenching 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 and electrically excited waveguides with gain at 1.54mm are now in progress [57, 58].


(5) -FeSi2 on Si:

Heteroepitaxial growth of SiFe2 by molecular epitaxy and its photoluminescence properties were studied [59, 61]. Room temperature electroluminescence from -FeSi2 on Si [62], p-Si/-FeSi2 particles/n-Si [63] and from a Si-based p-i-n diodes with -FeSi2 particles embedded in the intrinsic Si at 1.55 mm [64] have been reported.


(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 by reactive 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 and Intel 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 not mentioned 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 and promote cooperative developments of Si photonics technology with universities and institutes.



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