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)
D2 Network
Devices
Yoshio
Itaya, NTT Corporation
D3 Femtosecond
Technology
Osamu
Wada,
D4 THz
Technology
Hiromasa
Ito,
D5 Sensor
Photonics
Kazuo
Hotate,
D6 Photonic
Signal Processing
Takashi
Kurokawa,
D7 Microwave
Photonics
Tadao
Nagatsuma, NTT Corporation
D8 Nano-technology
Katsuyuki
Utaka,
D9 Polymeric
Photonics
Toshikuni
Kaino,
D10 Photonic
Susumu
Noda,
D11 Silicon
Photonics
Tadamasa
Kimura,
D1.
Vertical Cavity Surface Emitting Lasers (Special Review)
Kenichi Iga
Abstract:
In this chapter, we present device physics and technology based upon vertical
cavity surface emitting laser (VCSEL). We will survey its progress along with
the history of semiconductor lasers since the late 1960’s. The VCSEL photonics
is opening up a new field of applications by taking the merits 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;
(1)
Therefore, the actual threshold current of VCSELs can be made vary
small obeying this equation being 1/100 – 1/1000 of conventional stripe lasers.
Together with the improved optical cavity formation technology and the scheme
for injecting electrons and holes effectively into small volume of active
region, this relation has proven the scaling law.
3.
Actual Devices in Various Spectral Bands
We show a typical structure of GaAs/AlGaAs VCSEL device in Fig.
2. An AlAs oxidation is considered to be the effective process current
confinement in VCSEL’s. In commercially available 850 nm devices, sub-mA
thresholds and >10 mW outputs have been achieved. The power conversion
efficiency of >50% has been demonstrated. The Gigabit Ethernet has already
been in markets by the use 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 VCSEL’s is very
interesting by featuring largely extending 2-D arrays. For the purpose of
realizing coherent arrays, coherent coupling of these arrayed lasers has been
tried by using a Talbot cavity and phase compensation is considered. It is
pointed out that 2-D arrays are more suitable to make a coherent array than a
linear configuration, since we can take the advantage of 2-D symmetry. The
research activity is now forwarded to monolithic integration of VCSEL’s taking the advantage of small cavity dimensions. A densely
packed array has also been demonstrated for the purpose of making high power
lasers and coherent arrays. Into VCSEL’s, surface operating photonic elements
using quantum wells such as an optical switch, frequency tuner, optical filter,
and super-lattice functional devices are now tried to be integrated.
To establish an
appropriate module technology utilizing VCSELs, a micro optical bench (MOB) has
been investigated together with planar microlens array. Micro Electro
Mechanical Systems (MEMS) will be very helpful.
5. Applications
The application areas of VCSELs are summarized in Table I. The possible materials are displayed
in Fig.
4. In
low power consumption and high speed modulation is inevitable low power
interconnect applications enabling >10Gbits/s transmission or 1Gbits/s
zero-bias operation [6]. Actually, transmission experiments over 10Gbits/s and
zero-bias transmission have been reported. A 10 Gbits/s transmission experiment
through a 100m multimode fiber was performed [6]. VCSEL’s in long wavelength
may find the market in 10 Gigabit metropolitan networks together with
high-speed detectors and silica fibers. Actually, GaInAs and GaInNAs VCSEL’s
show preferable performances.
A 780 nm VCSEL
array has been introduced into a high speed laser printer. A laser printer has
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. VCSEL’s can very nicely match to this application.
Green to UV
VCSEL’s 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 VCSEL’s and surface operating
switches. The application for image recognition has been considered. Very low
threshold VCSEL’s have been developed, and stack integration together with 2-D
photonic devices are now actually considered.
6.
Toward Nano-Photonics and Beyond
The scaling law of semiconductor lasers is still considered toward
a nano-scale laser. A dust laser is 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 VCSEL’s will open up a new era of millennium [9].
References
[1] K.
Iga, Laboratory Notebook, March 22 (1977) .
[2] K.
Iga, T. Kambayashi, and C. Kitahara: The 26th Spring Meeting of Applied Physics
Societies 27p-C-1 1 (1978).
[3] H.
Soda, K. Iga, C. Kitahara and Y. Suematsu: Jpn. J. Appl. Phys. 18 (1979) 2329.
[4] K.
Iga, F. Koyama, and S. Kinoshita: IEEE J. Quant. Electron. QE-24 (1988) 1845.
[5] K.
Iga and F. Koyama: "Fundamentals and Application of Surface Emitting
Laser" Kyouritsu Pub. Co. Ltd.
[6] K.
Iga: IEEE J. STQE 6 (2000) 1201.
[7] Y. Suematsu, M. Yamada, and
K. Hayashi：Proc.
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,
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,
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
References
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D3. Femtosecond Technology
Osamu Wada
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.
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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], “Optical characterization of
photonic delay lines based on one-dimensional coupled defects”, Optics Lett.,
vol.27, no.23, pp.2079-2081
Nishikawa,
S., S. Lan, N. Ikeda, Y. Sugimoto, H. Ishikawa, K. Asakawa [2002b], “Design and fabrication of
impurity band-based photonic crystal waveguide for optical delay lines”, Appl.
Phys. Lett.,vol.81, no.11, pp.1946-1948
Nishikawa,
S., S. Kohmoto, H. Nakamura, Y. Sugimoto, N. Ikeda, T. Ishikawa,T. Akiyama, H.
Ishikawa, O. Wada [2002c]:
"Dephasing time characterization of InAs quantum dots by degenerate
four-wave mixing measurement", Physica E, Vol.13, p.273
Nishikawa,
S., S. Lan, O. Wada, T. Nishimura, K. Akahane and M. Kawabe [2002d]: "Lateral-Coupling-Induced
Modification of Density of States and Exciton Dynamics in High-Density Ordered
In0.4Ga0.6As/GaAs(311)B Quantum Dot Arrays", Jpn. J. Appl. Phys., Vol.41,
p.3766
Tajima,
K., S. Nakamura, A. Furukawa, and T. Sasaki [2004], “Hybrid-integrated Symmetric Mach-Zehnder all-optical
switches and ultrafast signal processing”, IEICE Trans. Electron. Vol. E87-C,
No. 7, pp. 1119-1125
Tatsuura,
S., Osamu Wada, Makoto Furuki,
Minquan Tian, Yasuhiro Sato, Izumi Iwasa, Lyong Sun Pu [2001a]:” Femtosecond two-dimensional
serial‐to‐parallel pulse converter using a squarylium Dye J-aggregate film”,
Opt.Quantum Electron. Vol.33, p.1089
Tatsuura,
S., Osamu Wada, Makoto Furuki, Minquan Tian, Yasuhiro Sato, Izumi Iwasa, Lyong
Sun Pu [2001b]: “All-optical two-dimensional
serial‐to‐parallel Pulse converter using an organic film with femtosecond
optical response”, Jpn.J.Appl.Phys. Vol.40, p.2731
Tatsuura,
S., O.Wada, M.Tian, M.Furuki, Y.Sato, I.Iwasa, L.S.Pu, and H.Kawashima [2001c]: “Large kai(3) of squarylium
dye J-aggregates measured using the Z-scan technique” Appl.Phys.Lett. Vol.79,
p.2517 (2001)
Tatsuura,
S., M. Tian, M. Furuki, Y. Sato, I. Izawa, L. S. Pu, H. Kawashima, H. Ishikawa [2002]: “Microstructure of squarylium
dye J aggregate films examined on the basis of optical behavior at low
temperature”, Appl. Phys. Lett., vol.81, p.2704-2706
Yoshida,
H., T. Simoyama, A. V. Gopal, J. Kasai, T. Mozume, and H. Ishikawa [2004]:
"Ultrafast All-Optical Switching and Modulation Using Intersubband
Transitions in Coupled Quantum Well Structures", IEICE Trans. Electron.,
Vol.E-87C, p.1134 (Invited paper)
Wada, O. [2004]: “Femtosecond all-optical devices for
ultrafast communication and signal processing,” New J. Phys., Vol. 6, p.183, http://stacks.iop.org/1367-2630/6/183
D4.THz Technology
Hiromasa Ito
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 TPO’s 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.
References
Imai, K., K.
Kawase, J. Shikata, H. Minamide, and H. Ito [2001], “An injection-seeded
terahertz-wave parametric oscillator”, Applied Physics Letters, vol. 78, pp.
1026-1028
Kawase, K., J.
Shikata, K. Imai, and H. Ito [2001], “A Transform-limited, Narrow-Linewidth,
THz-wave Parametric Generator”, Applied Physics Letters, vol. 78 no. 19, pp.
2819-2821
Imai, K., K.
Kawase, and H. Ito [2001], “A frequency-agile terahertz-wave parametric
oscillator”, Opt. Express 8, pp. 699-704
Ito, H., T.
Hatanaka,
Sato, A., K.
Kawase, H. Minamide,
Sato, A., K.
Kawase, H. Minamide,
Kawase, K., J.
Shikata, H. Minamide, K. Imai, and H. Ito [2001], “Arrayed silicon prism
coupler for a THz-wave parametric oscillator”, Applied Optics, vol.40, No.9,
pp.1423-1426
Avetisyan, Y.,
Y. Sasaki, and H. Ito [2001], “Analysis of THz-wave surface-emitted
difference-frequency generation in periodically poled lithium niobate
waveguide”, Applied Physics B, vol.73, pp.511-514
Kawase, K., H.
Minamide, K. Imai, J. Shikata, and H. Ito [2002], “Injection-seeded terahertz-wave
parametric generator with wide tunability”, Applied Physics Letters, vol.80,
no.2, pp.195-197
Kawase, K., J.
Shikata, and H. Ito [2002], “Terahertz wave parametric source (Topical
Review)”, Journal of Physics D: Applied Physics, vol.35, no.3, pp.R1-R14
Karino, K., J.
Shikata, K. Kawase, H. Ito, and I. Sahashi [2002], “Terahertz-wave parametric generation
characteristics of MgO: LiNbO3”, Electronics and Communications in
Kawase, K., S. Ariyoshi, C. Otani, H. Minamide,
K. Imai, J. Shikata, and H. Ito [2002],
“Widely tunable THz-wave parametric generator for imaging system”, RIKEN
Review, no.47, pp.48-51
Sato, A., K. Imai, K. Kawase, H. Minamide, S.
Wada, and H. Ito [2002],
“Narrow-linewidth operation of a compact THz-wave parametric generator system”,
Optics Communications, vol.207, no.1-6, pp.53-359
Ito, H., and K. Kawase [2002], “Tunable compact THz sources and their
application”, Trends in Optics and Photonics (TOPS), vol.79, pp.75-77
Imai, K., K. Kawase, H. Minamide, and H. Ito [2002],
“Achromatically injection-seeded terahertz-wave parametric generator”, Trends
in Optics and Photonics (TOPS), vol.79, pp.233-235
Sasaki, Y., Y. Avetisyan, K. Kawase, and H. Ito [2002], “Tunable
THz-wave difference frequency generation from slant-stripe-type PPLN based on
surface-emitting geometry”, Trends in Optics and Photonics (TOPS), vol. 79, pp.
20-22
Imai, K., K. Kawase, M. H., and H. Ito [2002],
“Achromatically injection-seeded terahertz-wave parametric generator”, Optics
Letters, vol.27, no.24, pp.2173-2175
Sasaki, Y., A. Yuri, K. Kawase, and H. Ito [2002],
“Terahertz-wave surface-emitted difference frequency generation in
slant-stripe-type periodically poled LiNbO3 crystal”, Applied
Physics Letters, vol.81, issue 18, pp.3323-3325
Shikata, J.,
K. Kawase, T. Taniuchi, and H. Ito [2002], “Fourier-Transform Spectrometer with
a Terahertz-Wave Parametric Generator”, Japanese Journal of Applied Physics,
part 1, vol.41, no.1, pp.134-138
Imai, K., S. Sugawara, J. Shikata, K. Kawase, H.
Minamide, and H. Ito [2003],
“The effect of injection seeding on terahertz parametric oscillation”,
Electronics and Communications in Japan, Part 2, vol.86, no.1, pp.26-35
Imai, K., K. Kawase, H. Minamide, and H. Ito [2003], “A rapidly
tunable terahertz-wave parametric oscillator”, Electronics and Communications
in
Watanabe, Y., K. Kawase, T. Ikari, H. Ito, Y.
Ishikawa, and H. Minamide [2003],
“Spatial pattern separation of chemicals and frequency-independent components
by Terahertz spectroscopic imaging”, Applied Optics, vol.42, issue 28,
pp.5744-5748
Kawase, K., J. Shikata, and H. Ito [2003], “Widely
tunable THz-wave generation using nonlinear optics”, Solid-state mid infrared
laser sources, Edited by I. T. Sorokina and K. L. Vodopyanov, pp.433-461
Watanabe, Y., K. Kawase, T. Ikari, H. Ito, Y.
Ishikawa and H. Minamide [2003],
“Component spatial pattern analysis of chemicals using terahertz spectroscopic
imaging”, Applied Physics Letters, vol.83, no.4, pp.800-802
Imai, K., K.
Kawase, H. Minamide, and H. Ito [2003], “A rapidly tunable terahertz-wave
parametric oscillator”, Electronics and Communications in
Watanabe, Y.,
K. Kawase, T. Ikari, H. Ito, Y. Ishikawa, and H. Minamide [2003], “Spatial
Pattern Separation of Chemicals and Frequency-Independent Components by
Terahertz Spectroscopic Imaging”, Applied Optics, vol.42, issue 28,
pp.5744-5748
Sasaki, Y., H. Yokoyama, and H. Ito [2004],
“Dual-wavelength optical-pulse source based on diode lasers for
high-repetition-rate, narrow-bandwidth terahertz-wave generation”, Optics
Express, vol. 12, no. 14, pp.3066-3071
Watanabe, Y.,
K. Kawase, T. Ikari, H. Ito, Y. Ishikawa, and H. Minamide [2004], “Component
analysis of chemical mixtures using terahertz spectroscopic imaging”, Optics
Communications, vol.234, pp.125-129
Ohtani, K., K. Fujita and H. Ohno [2004], “A low
threshold current density InAs/AlGaSb superlattice quantum cascade laser operating
at 14μm”, Jpn. J. Appl. Phys., vol.43, pp.L879-881.
Takahashi, M., Y. Ishikawa, J. Nishizawa, and H.
Ito [2005],
“Low-frequency vibrational modes of riboflavin and related compounds”, Chemical
Physics Letters 401, pp.475-482
D5. Sensing Photonics
Kazuo Hotate
Univesity of
Among various types of optical fiber sensors, fiber optic distributed
and multiplexed sensing technologies have been intensively studied, which have
provided schemes to measure, for example, distribution of longitudinal strain
or lateral force along an optical fiber.
In these systems, the fiber can act as nerve networks to sense damage of
materials or structures, in which the fiber is embedded. These techniques are the key to realize
“smart materials” and “smart structures” for improving reliability, safety and
security of the society (see Fig.1).
The 16th International Conference on Optical Fiber Sensors (OFS-16) was
held in
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
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 “synthesis of optical coherence
function: SOCF,” in which arbitrary shapes of optical coherence function can be
synthesized by modulating optical frequency of a light source. This is invented also in
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,
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.
References
Hotate, K., and M. Tanaka [2001], “Correlation-based continuous-wave
techniques provide high spatial resolution for distributed fiber optic
sensing”, SPIE OE Magazine, 11, pp.36-40 <Invited>
Hotate, K., and M. Tanaka [2001], “Correlation-based continuous-wave
technique for fiber optic distributed strain measurement using Brillouin
scattering with cm-order spatial resolution －Applications to smart
materials－”, IEICE Trans. on Electron., vol.E84-C, no.12, pp.1823-1828
<Invited>
Hotate, K., and M. Tanaka [2002], “Distributed fiber Brillouin strain
sensing with 1cm spatial resolution by correlation-based continuous-wave
Technique”, IEEE Photon. Tech. Lett., vol.14, no.2, pp.179-181
Hotate, K., and M. Tanaka [2002], “Application of correlation-based
continuous-wave technique for fiber Brillouin sensing to measurement of strain
distribution on a Small Size Material”, IEEE Photonic Technology Letters,
vol.14, no.5, pp.675-677
Hotate, K. [2002], “Application of synthesized coherence function to
distributed optical sensing,” IOP Measurement Sci. and Tech., vol.13, no.11,
pp.1746-1755
Hotate, K. [2002], “Recent progress in Brillouin based fiber sensor
technology”, 15th Intern. Conf. on Optical Fiber Sensors (OFS-15),
Hotate, K. and S. S. L. Ong [2002], “Distributed fiber Brillouin
strain sensing by correlation-based continuous-wave technique –cm-order spatial
resolution and dynamic strain measurement–”, SPIE Photonics Asia, Shanghai,
4920-51, pp.299-310 <Invited>
Hotate, K. and M. Kashiwagi [2003], “High spatial resolution
reflectometry for optical subscriber networks by synthesis of optical coherence
function with measurement range enhancement”, IEICE Trans. on Electron.,
volE86-C, no.2, pp.213-217
Hotate, K. and S. S. L. Ong [2003], “Distributed dynamic strain
measurement using a correlation-based Brillouin sensing system”, IEEE Photon.
Technol. Lett., vol.15, no.2, pp.272-274
Hotate, K. [2003], “Optical Fiber Sensors for Smart
Materials/Structures and Optical Communicaitons”, International Meeting on New
Frontiers for Ubiquitous IT Services, Atsugi <Invited>
Hotate, K. [2003], “Fiber Optic Distributed Sensing for Smart
Materials and Structures by Optical Correlation Domain Technique with
Continuous Lightwave”, 16th Intern. Conf. on Optical Fiber Sensors (OFS-16),
Hotate, K., M. Enyama, S. Yamashita and Y. Nasu [2004], “A
multiplexing technique of fiber Bragg grating sensors with the same reflection
wavelength by the synthesis of optical coherence function”, Measurement Sci.
and Technol., vol. 15, no.1, pp. 148-153
Hotate, K., A. Kuramoto and Z.-Y. He [2004], “Optical fiber
stress-location measurement by synthesis of binary optical coherence function,”
IEEE Photon. Technol. Lett., vol. 16, no.2, pp. 578-580
Hotate, K. [2004], “Trends and prospects for optical distributed
sensing －Fiber-optic nerve systems for smart materials and smart-structures－”, SPIE Vol.5502, Second European Workshop on Optical Fiber Sensors,
Santander, pp.51-58 <Invited>
Hotate, K. [2004], “Potential applications of optical fiber sensing
technology for future society”, International Symposium on Network and
Center-Based Research for Smart Structures Technologies and Earthquake
Engineering,
Hotate, K. [2004], “Fiber optic nerve systems for smart materials and
smart structures”, SPIE Optics East 2004,
Hotate, K. [2004], “Optical Fiber Sensors for Smart
Materials/Structures and Optical Communicaitons”, Chapter 9 in “New Photonics
Technologies for the Information Age”, ed., by S. Sudo and K. Okamoto, Artech
House, pp.159-179
He, Z. and K. Hotate [2002], “Distributed Fiber-optic stress-location
measurement by arbitrary shaping of optical coherence function”, Jour. of
Lightwave Tech., vol.20, no.9, pp.1715-1723
Zhu, B., T. Saida and K. Hotate [2003], “Variable optical filter using
dynamic grating in Er doped fiber controlled by synthesis of optical coherence
function: Proposal and experimental verification”, IEICE Trans. on Electron.,
IEICE Trans., vol.E86-C, no.1, pp.97-99
Kashiwagi, M. and K. Hotate [2004], “Elongation of Measurement Range
by Successively Shifting Measurement Window in a High Spatial Resolution
Reflectometry for Optical Subscriber Networks by Synthesis of Optical Coherence
Function”, Measurement Sci. and Technol., vo.15, no.8, pp. 1512-1518
Enyama, M. and K. Hotate [2004], “Dynamic and random-access strain
measurement by fiber Bragg gratings with synthesis of optical coherence
function”, SPIE Optics East 2004,
D6. Photonic signal processing
Takashi Kurokawa
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 .
References
Kurokawa, T.[2001], "Optical Signal
Processing for Communication and Information Systems", Proc. CLEO/Pacific
Rim, Makuhari, Vol.Ⅱ,
pp.532-534 <Tutorial, Invited>.
Tanaka, Y., P.
G. Chua, T. Kurokawa, H. Tsuda, M. Naganuma, and M. Takeda [2002], “Reflectometry based on two-photon
absorption of a silicon avalanche photodiode”, Proc. 15th Optical
Fiber Sensors Conference,
Tanaka, Y., T.
Kurokawa [2002],
“Profilometry using two-photon absorption of silicon avalanche photodiode”,
Proceedings of SPIE, Vol. 4919, pp.102-109 <Invited>.
Itoh, Y., K.
Aizawa, Y. Tanaka, H. Tsuda [2003], “Measurement of short optical pulse spectra
using arrayed waveguide grating”, Proc. 6th International Symposium on
Contemporary Photonicsn Technology, Post-Deadline papers, p.7.
Tanaka, Y.,
Yamanaka, A., M. Yamamoto, Y. Tanaka, T. Kurokawa, T. Kawanishi and M. Izutsu [2003], “A
Multi-wavelength light source using an optical single-side band modulator an
arrayed waveguide grating”, Proc. 5th Pacific Rim Conference on Lasers and
Electro-Optics, Taipei, p.714.
Sako, N., S. Imoto, Y. Tanaka and T. Kurokawa [2003],
“Measurement accuracy of profilometry based on two-photon absorption”, Proc.
5th Pacific Rim Conference on Lasers and Electro-Optics,
Itoh, Y., K. Aizawa, Y. Tanaka, H. Tsuda and T.
Kurokawa [2003], “Optical Spectrum analyzer for optical short pulses”, Proc.
5th Pacific Rim Conference on Lasers and Electro-Optics,
Imoto, S., N. Sako, Y. Tanaka and T. Kurokawa [2003],
“Accuracy improvement of two-photon absorption based measurement by temperature
controlled Si-photodetecter”, Proc. 5th Pacific Rim Conference on Lasers and
Electro-Optics,
Nezu, T., Y. Tanaka and T. Kurokawa [2003],
“Delayed self-heterodyne linewidth measurement of fiber Bragg grating laser”,
Proc. 5th Pacific Rim Conference on Lasers and Electro-Optics,
Suzuki, T., Y. Shibata and H. Tsuda [2003],
“Design and the fabrication of the small v-bend optical waveguide using an
elliptic mirror”, Proc. 11th European Conference on Integrated Optics,
Suzuki, T., Y. Shibata and H. Tsuda [2003],
“Small v-bend optical silica-waveguide using an
elliptic mirror for planar lightwave circuits”, Proc. 9th
Microoptics Conference,
Tate, A., T. Suzuki, Y. Shibata and
H. Tsuda [2004], “Proposal of WDM multi/demultiplexer with deep grooves and
parabolic mirrors”, Proc. 7th International Symposium on Contemporary Photonics
Technology,
Hakamata,
M., and H. Tsuda [2004], “Diffractive optical elements using the sub-wavelength
scale pillar array structure,” SPIE Photonics West,
Aizawa, K., H. Aoki, Y. Ito, Y. Tanaka and T. Kurokawa [2004], “Waveform measurement of
ultra-short optical pulses based on two photon absorption in Si-image sensor”,
ICO International Conference on Optics & Photonics in Technology Frontier,
Tokyo, pp.331-332.
Suzuki, T., K. Mandai, H. Tsuda, T. Kurokawa and
T. Kawanishi [2004], “Optical
pulse generation by controlling the sidebands of the phase modulated light”, OECC/COIN2004 (9th Optoelectronics and
Communications Conference/ 3rd International conference on Optical Internet,
Ishida, M., T. Suzuki and H. Tsuda [2004], “180 degree-bend structures using a double
elliptic mirror in a slab waveguide”, OECC/COIN2004 (9th Optoelectronics and
Communications Conference/ 3rd International conference on Optical Internet,
Suzuki, T., Y. Shibata, K. Masuda and H. Tsuda [2004],
“Compact arrowhead arrayed waveguide
grating using v-bend optical waveguides,” Topical Meeting on Integrated Photonics Research,
Mandai, K., T. Suzuki, H.
Tsuda, T. Kurokawa and T. Kawanishi [2004], “Arbitrary optical short pulse generator using a
high-resolution arrayed-waveguide grating”, International Topical Meeting on
Microwave Photonics, Ogunquit, pp.107-110.
D7. Microwave Photonics
Tadao Nagatsuma
NTT Corporation
Microwave
photonics, which merges radio-wave (microwave) and photonics technologies, has
made a steady progress since 1990’s. The first use of the term microwave
photonics was at International Microwave Photonics (MWP) Conference held at
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.
(3)
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.
References
Hirata, A., T. Nagatsuma, R. Yano, H. Ito, T.
Furuta, Y. Hirota, T. Ishibashi, H. Matsuo, A. Ueda, T. Noguchi, Y. Sekimoto,
and S. Matsuura[2002], “Output power measurement of photonic millimeter-wave
and sub-millimeter-wave emitter at 100-800 GHz”, Electron. Lett., vol. 38, no. 15, pp.
798-800
Hirata, A., M. Harada, and T. Nagatsuma[2003a],
“120-GHz wireless link using photonic techniques for generation, modulation,
and emission of millimeter-wave signals”, IEEE J. Lightwave Technol., vol. 21,
no.10, pp. 2145-2153
Hirata, A., M. Harada, K. Sato, and T.
Nagatsuma[2003b], “Low-cost millimeter-wave photonic techniques for gigabit/s
wireless link”, IEICE Trans. on Electronics, E86-C, no. 7, pp. 1123-1128
Hirata, A., H. Ishii, and T. Nagatsuma[2004a],
“Design and characterization of ultra-broadband photonic emitters for microwave
and millimeter-wave applications”, Japan-Korea workshop on microwave and
millimeter-wave photonics 2004 Dig, pp. 63-66
Hirata, A., H. Togo, N. Shimizu, H. Takahashi,
K. Okamoto, and T. Nagatsuma[2004b], “Low-phase noise photonic millimeter-wave
generator using an AWG integrated with a 3-dB combiner”, MWP 2004 Dig., TD-3,
pp. 209-212
Ikeda, K., T. Kuri, Y. Takahashi, and K.
Kitayama[2003], “Full-duplex transmission using 2-RF-port electroabsorption
transceiver with photonic up-and downconversions for millimeter-wave
radio-on-fiber system”, IEICE Trans. on Electronics, E86-C, no. 7, pp.
1138-1145
Ito, H., T. Furuta, A. Hirata, T. Kosugi, Y.
Muramoto, M. Tokumitsu, T. Nagatsuma, T. Ishibashi[2004],
“Pre-amplifier-integrated uni-traveling-carrier photodiode module with a
rectangular waveguide-output port for operation in the 120-GHz band”, LEOS2004
Dig., MN2, pp. 128-129
Iwanami, M., E. Yamazaki, K. Nakano, T. Sudo, S.
Hoshino, S. Wakana, M. Kishi, and M. Tsuchiya[2003], “Magnetic near-field
measurements over LSI package pins by fiber-edge magnetooptic probe”, IEEE J.
Lightwave Technol., vol. 21, no. 12, pp. 3273-3281
Izutsu, M.[2004], “Electrooptic light modulation
technology for microwave photonics”, MWP2004 Dig., MA-2, pp. 12-15
Kitayama, K.[2003], “Dense wavelength division
multiplexing radio-on-fiber system”, MWP2003 Dig., pp. 129-134
Kosugi, T., M. Tokumitsu, T. Enoki, M.
Muraguchi, A. Hirata, and T. Nagatsuma[2004], “120-GHz Tx/Rx chipset for
10-Gbit/s wireless applications using 0.1-m-gate InP HEMTs”, IEEE CSIC Dig.,
pp. 171-174
Mizuno, M., A. Hirata, K. Kawase, C. Otani, and
T. Nagatsuma[2004], “Analysis of Pheochromocytoma (PC12) membrane potential
under the exposure to millimeter-wave radiation”, AIP Conference Proc., no.
716, pp. 164-166
Nagatsuma, T.[2002], “Photonic measurement
technologies for high-speed electronics”, Meas. Sci. Technol. vol. 13, no.11,
pp. 1655-1663
Nagatsuma, T., H. Ito[2003], “Ultrafast
applications of uni-traveling-carrier photodiodes from measurement to signal
processing”, Proc. SPIE, vol. 4992, pp. 90-104
Nagatusma, T., H. Togo, K. Narahara,
N. Shimizu, and A. Sasaki[2004], “Recent progress in optical measurement of
radio-wave signals from gigahertz to terahertz”, MWP2004 Dig., MB-1, pp. 20-23
Nakajima, F., T. Furuta, and H.
Ito[2004],”High-power terahertz-wave generation from a
resonant-antenna-integrated uni-traveling-carrier photodiode”, MWP2004 Dig.,
WD-4, pp. 313-316
Niiho, H., M. Nakaso, K. Masuda, H. Sasai, K.
Utsumi, and M. Fuse[2004], “Multi-channel wireless LAN distributed antenna
system based on radio-over-fiber techniques”, LEOS2004 Dig., MF2, pp. 57-58
Sasaki, A., and T. Nagatsuma[2002], “Reflection-type
CW- millimeter-wave imaging with a high- sensitivity waveguide-mounted
electro-optic sensor”, Jpn. J. Appl. Phys., vol. 41,part 2, no. 1A/B, pp.
L83-L86
Sato, T., M. Tsuchiya, M. Iwanami, S. Hoshino,
and M. Kishi[2003], “Current profiling for m-class planar circuit patterns by
fiber-edge magneto-optic probe”, MWP 2003 Dig., pp. 341-344
Shoji, Y., and H. Ogawa[2003],”Experimental
demonstration of 622 Mbps millimeter-wave over fiber link for broadband fixed
wireless access system”, IEICE Trans. on Electronics, E86-C, no. 7, pp.
1129-1137
Suzuki, H., M. Fujiwara, K. Iwatsuki, A. Hirata,
and T. Nagatsuma[2005], “Photonic millimetre-wave generator using intensity and
phase modulators for 10 Gbit/s wireless link”, Electron. Lett., vol. 41, no. 6,
pp. 89-90
Takano, S., A. Ueda, T. Yamamoto, S. Asayama, Y.
Sekimoto, T. Noguchi, M. Ishiguro, H. Takara, S. Kawanishi, H. Ito, A. Hirata,
and T. Nagatsuma[2003], “The first radioastronomical observation with photonic
local oscillator”, Publ. Astron. Soc. Japan, vol. 55, pp. L53-L56
Tsuchiya, M., E. Yamazaki, M. Iwanami, S.
Mitani, T. Sato, S. Wakana, S. Hoshino, and M. Kishi[2003], “High-speed and
high-spatial resolution fiber-optic measurement technique for RF magnetic field
distribution”, LEOS2003 Dig., ThS1, pp. 929-930
Tsukamoto, K., T. Higashino, T. Nakanishi, and
S. Komaki[2003], “Direct optical switching code-division multiple-access system
for fiber-optic radio highway networks”, IEEE J. Lightwave Technol., vol. 21,
no. 12, pp. 3209-3220
Usami, M., R. Fukasawa, M. Tani, M.
Watanabe, and K. Sakai[2003], “Calibration free terahertz imaging based on 2D
electro-optic sampling technique”, Electron. Lett., vol. 39, no. 24, pp.
1746-1747
Yamamoto, T., and S. Kawanishi[2004],
“Generation of low-noise optical frequency comb and optical beat signal using
phase modulator”, Japan-Korea workshop on microwave and millimeter-wave
photonics 2004 Dig., pp. 15-19
D8. Nanotechnology
Katsuyuki Utaka
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 “Next-Generation Nanotechnology (NNN) Group”, has been
established in April, 2004, to discuss next-generation nanotechnology under the
Electronics Society (ES) of
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
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.
References
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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,
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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
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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). “Serially grafted optical waveguide fabrication
of NLO polyimide and transparent polymers”, Opt. Mater., 21, 521-524
T. Ushiwata, E. Okamoto, T. Kaino,
(2002) Development of Thermally Stable Novel EO-polymers, Mol. Cryst. Liq.
Cryst., 374, 303-314
T. Ushiwata, E. Okamoto, K. Komatsu,
T. Kaino, (2001) Synthesis and optical properties of azo dye attached novel
second order NLO polymers with high thermal stability, Proc. SPIE Organic
Photonics Materials and Devices III, San Jose, 4279, 17-24
A. Kaneko, E. Okamoto, T. Kaino,
(2002) Synthesis and Characterization of Novel Side-Chain Nonlinear Optical
Polymers with Furan Derivative as an Acceptor, Jpn. J. Appl. Phys., 41, L559-L561
T. Taima, K. Komatsu, T. Kaino, C.P.
Franceschina, L. Tartara, G.P. Banfi, V. Degiorgio, (2003) Third-order
nonlinear optical properties of 2-adamanthyl amino-5-nitropyridine caused by
cascaded second-order nonlinearity, Optical Materials, 21, 83-86
T. Hattori, T. Shibata, S. Onodera,
T. Kaino, (2004) Thermo-optically Tunable Wavelength Filter with Permanent
Refractive Index Grating into Azo-Polymer Waveguide, Jpn. Jpn. App. Phys., 43, 1492-1495
B. Cai, T. Hattorit, H-H. Deng, K.
Komatsu, C. Zawadski, N. Keil, T. Kaino, (2001) Refractive Index Control and
Grating Fabrication of 4-(4-dimethyl-aminostyryl)-1-methylpyridinium Tosylate
Crystal, Jpn. J. Appl. Phys., 40,
L964-L966
F.L. Labarther,
T. Buffeteau, C. Sourisseau, (2001) Time dependent analysis of the formation of
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
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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.
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W.H. Wong, E.Y.B. Pun, K.S. Chgan, (2004) Er3+-Tb3+
co-doped polymer optical waveguide amplifier, Appl. Phys. Lett., 82, 176-178
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Pisignano, R.I. Blyth, G. Gigli, R. Cingolani, (2004) Amplified spontaneous
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M. Karimi, N. Granpayeh, M.K.M. Farshi, (2004)
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D10. Photonic
Susumu Noda
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
“In-Plane Hetero” 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.
References:
M. Fujita, T.
Ueno, K Ishihara, T. Asano, S. Noda, H. Ohata, T. Tsuji, H. Nakada, and N.
Shimoji [2004], “Reduction of operating voltage in organic light-emitting diode
by corrugated photonic crystal structure,” Applied Physics Letters, vol.85,
no.23, pp.5769-5771.
Y. Tanaka, T.
Asano, R. Hatsuta, and S. Noda [2004], “Analysis of a line-defect waveguide on
a silicon-on-insulator two-dimensional photonic-crystal slab,” IEEE/OSA Journal
of Lightwave Technology, vol.22, no.12, pp.2787-2792.
B. S. Song, T.
Asano, Y. Akahane, Y. Tanaka, and S. Noda [2004], “Transmission and reflection
characteristics of in-plane hetero-photonic crystals,” Applied Physics Letters,
vol.85, no.20, pp.4591-4593.
M. Fujita, A.
Sugitatsu, T. Uesugi, and S. Noda [2004], “Fabrication of Indium Phosphide
compound photonic crystal by Hydrogen Iodide/Xenon inductively coupled plasma
etching,” Japanese Journal of Applied Physics, vol.43, no.11, pp.L1400-L1402.
M. Okano and
A. Sugitatsu,
T. Asano, and S. Noda, “Characterization of line-defect-waveguide lasers in
two-dimensional photonic-crystal slabs,” Applied Physics Letters, vol.84,
no.26, pp.5395-5397 (2004).
T. Asano, K.
Kiyota, D. Kumamoto, B. S. Song, and S. Noda [2004], “Time-domain measurement
of picosecond light-pulse propagation in a two-dimensional photonic
crystal-slab waveguide,” Applied Physics Letters, vol.84, no.23, pp.4690-4692.
S. Ogawa, M. Imada,
T. Asano and
D. Ohnishi, T.
Okano, M. Imada, and
H. Takano, Y.
Akahane, T. Asano, and S. Noda [2004], “In-plane-type channel drop filter in a
two-dimensional photonic crystal slab,” Applied Physics Letters, vol.84, no.13,
pp.2226-2228.
M. Yokoyama and
S. Noda and T.
Baba [2004], “Special issue on photonic crystals and their device
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E. Miyai and
M. Okano,
M. Fujita, T.
Ueno, T. Asano, S. Noda, H. Ohhata, T. Tsuji, H. Nakada, and N. Shimoji [2003],
“Organic light-emitting diode with ITO/organic photonic crystal,” Electronics
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Asano, B. S. Song, and S. Noda [2003], “High-Q photonic nanocavity in a
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M. Yokoyama and
Y. Akahane, T.
Asano, B. S. Song, and S. Noda [2003], “Investigation of high- Q channel drop
filters using donor-type defects in two-dimensional photonic crystal slabs,”
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T. Asano, B. S.
Song, Y. Tanaka, and S. Noda [2003], “Investigation of a
channel-add/drop-filtering device using acceptor type point defects in a
two-dimensional photonic crystal slab,” Applied Physics Letters, vol.83, no.3,
pp.407-409.
B. S. Song,
S. Ogawa, M.
Imada, and S. Noda [2003], “Analysis of thermal stress on wafer bonding of
dissimilar materials for the introduction of InP-based light-emitter into
GaAs-based three dimensional photonic crystals,” Applied Physics Letters,
vol.82, no.20, pp.3406-3408.
T. Asano, M.
Mochizuki, S. Noda, M. Okano, and M. Imada (2003), “A channel drop-filter using
a single defect in a 2D photonic crystal slab - Defect engineering with respect
to polarization mode and ratio of emissions from upper and lower sides -,”
IEEE/OSA Journal of Lightwave Technology, vol.21, no.5, pp.1370-1376.
D. Ohnishi, K.
Sakai, M. Imada, and S. Noda (2003), “Continuous wave operation of surface
emitting two-dimensional photonic crystal laser,” Electronics Letters, vol.39,
no.7, pp.612-614.
Y. Tanaka, T.
Asano, Y. Akahane, B. S. Song, and S. Noda (2003), “Theoretical investigation
of propagation loss of a line defect waveguide in a two-dimensional photonic
crystal slab with tapered air holes,” Applied Physics Letters, vol.82, no.11,
pp.1661-1663.
Y. Akahane, M.
Mochizuki, T. Asano, Y. Tanaka, and S. Noda (2003), “Design of a channel drop
filter by using a donor-type cavity with high-quality factor in a
two-dimensional photonic crystal slab,” Applied Physics Letters, vol.82, no.9,
pp.1341-1343.
A. Sugitatsu
and
E. Miyai, M.
Okano, M. Mochizuki, and S. Noda (2002), “Analysis on coupling between 2D
photonic crystal slab and external waveguide,” Applied Physics Letters, vol.81,
no.20, pp.3729-3731.
M. Okano, A.
Chutinan, and S. Noda (2002), “Analysis and design of single-defect cavities in
a three-dimensional photonic crystal,” Virtual Journal of Nanoscale Science
& Technology, vol.6, no.18.
M. Okano, A.
Chutinan, and S. Noda (2002), “Analysis and design of single-defect cavities in
a three-dimensional photonic crystal,” Physical Review B, vol.66, no.16,
pp.165211-1-6.
N. Yamamoto and
S. Noda, M.
Imada, A. Chutinan, and N. Yamamoto (2002), “III-V based-semiconductor photonic
crystals,” Optical and Quantum Electronics, vol.34, no.8, pp.723-736.
S. Noda, M.
Imada, M. Okano,
T. Asano, S.
Noda, K. Kiyota, Y. Tanaka, Y. Akahane, B. S. Song, M. Mochizuki, and M. Imada
(2002), “Channel-add operation of a device using defects in a two-dimensional
photonic crystal slab,” Materials Research Society Symposium Proceedings
“Materials and devices for optoelectronics and microphotonics”, vol.722,
pp.363-367.
M. Imada, A.
Chutinan, S. Noda, and M. Mochizuki (2002), “Multidirectionally distributed
feedback photonic crystal lasers,” Virtual Journal of Nanoscale Science & Technology,
vol.5, no.18.
M. Imada,
M. Imada, A.
Chutinan, S. Noda, and M. Mochizuki (2002), “Multidirectionally distributed
feedback photonic crystal lasers,” Physical Review B, vol.65, no.19,
pp.195306-1-195306-8.
A. Chutinan, M.
Okano, and S. Noda (2002), “Wider bandwidth with high transmission through
waveguide bends in two-dimensional photonic crystal slabs,” Applied Physics
Letters, vol.80, no.10, pp.1698-1700.
S. Noda and M.
Imada (2002), “2D photonic crystal surface-emitting laser using
triangular-lattice structure,” IEICE Transactions on Electronics, vol.E85C,
no.1, pp.45-51.
S. Ogawa, K.
Tomoda, and
T. Tanaka,
T. Asano,
A. Chutinan, M.
Mochizuki, M. Imada, and S. Noda (2001), “Surface-emitting channel drop filters
using single defects in two-dimensional photonic crystal slabs,” Applied
Physics Letters, vol.79, no.17, pp.2690-2692.
M. Yokoyama, K.
Akimoto, M. Imada, and
S. Noda, M.
Yokoyama, M. Imada, A. Chutinan, and M. Mochizuki (2001), “Polarization mode
control of two-dimensional photonic crystal laser by unit cell structure
design,” Science, vol.293, no.5532, pp.1123-1125.
K. Sakoda, N.
Kawai, T. Ito, A. Chutinan, S. Noda, T. Mitsuyu, and K. Hirao (2001), “Photonic
bands of metallic systems.
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 1980’s and is based on silica waveguide technology. Light-guiding
channels are defined on a silicon platform. The core layer with an elevated
refractive index is patterned using photolithography and dry etching. This
technology is well suited to the fabrication 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.
(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
(5) β-FeSi2 on Si:
Heteroepitaxial
growth of SiFe2 by molecular epitaxy and its photoluminescence
properties were studied [59, 61]. Room temperature electroluminescence from β-FeSi2
on Si [62], p-Si/β-FeSi2 particles/n-Si [63] and
from a Si-based p-i-n diodes with β-FeSi2 particles embedded in the
intrinsic Si at 1.55 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
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