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Dive into the research topics where Seiichi Itabashi is active.

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Featured researches published by Seiichi Itabashi.


Optics Express | 2005

Four-wave mixing in silicon wire waveguides.

Hiroshi Fukuda; Koji Yamada; Tetsufumi Shoji; Mitsutoshi Takahashi; Tai Tsuchizawa; Toshifumi Watanabe; Junichi Takahashi; Seiichi Itabashi

We report the observation of four-wave mixing phenomenon in a simple silicon wire waveguide at the optical powers normally employed in communications systems. The maximum conversion efficiency is about -35 dB in the case of a 1.58-cm-long silicon wire waveguide. The nonlinear refractive index coefficient is found to be 9x10-18 m2/W. This value is not negligible for dense wavelength division multiplexing components, because it predicts the possibility of large crosstalk. On the other hand, with longer waveguide lengths with smaller propagation loss, it would be possible to utilize just a simple silicon wire for practical wavelength conversion. We demonstrate the wavelength conversion for data rate of 10-Gbps using a 5.8-cm-long silicon wire. These characteristics are attributed to the extremely small core of silicon wire waveguides.


Optics Express | 2008

Silicon photonic circuit with polarization diversity

Hiroshi Fukuda; Koji Yamada; Tai Tsuchizawa; Toshifumi Watanabe; Hiroyuki Shinojima; Seiichi Itabashi

We devised a silicon photonic circuit with polarization diversity that consists of polarization splitters and polarization rotators. The splitter is based on a simple directional coupler and the rotator has an off-axis double-core structure. Both devices can be made by using planar fabrication technology and require no complex proceses for the fabrication of three-dimensional structures. We fabricated a polarization-independent wavelength filter based on Si wire waveguides as an application of the polarization diversity. The filter consists of the polarization splitters, the rotators, and a ring resonator. The polarization-dependent loss of the filter is about 1 dB. A 10-Gbps data transmission with scrambled polarization is demonstrated.


Optics Express | 2006

Ultrasmall polarization splitter based on silicon wire waveguides

Hiroshi Fukuda; Koji Yamada; Tai Tsuchizawa; Toshifumi Watanabe; Hiroyuki Shinojima; Seiichi Itabashi

We describe an ultrasmall polarization splitter based on a simple directional coupler consisting of silicon wire waveguides. The size is only 7 x 16 microm(2), and the polarization extinction ratio is about 15 dB for a single coupler. A double-coupler structure improves the extinction ratio to over 20 dB. The excess loss is smaller than 0.5 dB for both types of device. In the device, the shape of the high-speed waveform is retained at any angle of polarization. Our polarization splitter represents a first step towards accomplishing an ultrasmall optical circuit with polarization diversity based on silicon wire waveguides.


Applied Physics Letters | 2007

Fast all-optical switching using ion-implanted silicon photonic crystal nanocavities

Takasumi Tanabe; Katsuhiko Nishiguchi; Akihiko Shinya; Eiichi Kuramochi; Hiroshi Inokawa; Masaya Notomi; Koji Yamada; Tai Tsuchizawa; Toshifumi Watanabe; Hiroshi Fukuda; Hiroyuki Shinojima; Seiichi Itabashi

On-chip all-optical switching based on the carrier plasma dispersion in an argon ion (Ar+) implanted photonic crystal (PhC) nanocavity that is connected to input/output waveguides is described. A high dose of Ar+ is introduced, and annealing is used to recrystallize the silicon and thus create dislocation loops at the center of the PhC slab. Dislocation loops enable the fast recombination of the carriers, which allows a fast switching recovery time for PhC switches. The switching window (∼70ps) is three times smaller than that without ion implantation, while the required operating energy remains almost the same (<100fJ).


Optics Express | 2008

Polarization rotator based on silicon wire waveguides.

Hiroshi Fukuda; Koji Yamada; Tai Tsuchizawa; Toshifumi Watanabe; Hiroyuki Shinojima; Seiichi Itabashi

We describe a polarization rotator based on an off-axis double-core structure consisting of a silicon wire waveguide and a silicon-oxinitride waveguide. The rotator can be made by planar fabrication technology and do not require complex processes, such as three-dimensional structure formation. A rotator with 35-microm long provides the polarization rotation angle of 72 degrees and the polarization extinction ratio of 11 dB with the excess loss of about 1 dB. Our polarization rotator represents a significant step towards accomplishing an optical circuit with polarization diversity based on silicon wire waveguides.


Proceedings of the IEEE | 2009

On-Chip Optical Interconnect

Keishi Ohashi; Kenichi Nishi; Takanori Shimizu; Masafumi Nakada; Junichi Fujikata; Jun Ushida; Sunao Torii; Koichi Nose; Masayuki Mizuno; Hiroaki Yukawa; Masao Kinoshita; Nobuo Suzuki; Akiko Gomyo; Tsutomu Ishi; Daisuke Okamoto; Katsuya Furue; Toshihide Ueno; Tai Tsuchizawa; Toshifumi Watanabe; Koji Yamada; Seiichi Itabashi; Jun Akedo

We describe a cost-effective and low-power-consumption approach for on-chip optical interconnection. This approach includes an investigation into architectures, devices, and materials. We have proposed and fabricated a bonded structure of an Si-based optical layer on a large-scale integration (LSI) chip. The fabricated optical layer contains Si nanophotodiodes for optical detectors, which are coupled with SiON waveguides using surface-plasmon antennas. Optical signals were introduced to the optical layer and distributed to the Si nanophotodiodes. The output signals from the photodiodes were sent electrically to the transimpedance-amplifier circuitries in the LSI. The signals from the photodiodes triggered of the circuitries at 5 GHz. Since electrooptical modulators consume the most power in on-chip optical interconnect systems and require a large footprint, they are critical to establish on-chip optical interconnection. Two approaches are investigated: 1) an architecture using a fewer number of modulators and 2) high electrooptical coefficient materials.


Optics Express | 2011

First demonstration of high density optical interconnects integrated with lasers, optical modulators, and photodetectors on single silicon substrate

Yutaka Urino; Takanori Shimizu; Makoto Okano; Nobuaki Hatori; Masashige Ishizaka; Tsuyoshi Yamamoto; Takeshi Baba; Takeshi Akagawa; Suguru Akiyama; Tatsuya Usuki; Daisuke Okamoto; Makoto Miura; Masataka Noguchi; Junichi Fujikata; Daisuke Shimura; Hideaki Okayama; Tai Tsuchizawa; Toshifumi Watanabe; Koji Yamada; Seiichi Itabashi; Emiko Saito; Takahiro Nakamura; Yasuhiko Arakawa

Optical interconnects integrated with lasers, silicon optical modulators and germanium photodetectors on a single silicon substrate were demonstrated for the first time. A 5 Gbps line bit rate and 3.5 Tbps/cm2 transmission density were achieved.


Optics Letters | 2003

Silicon-wire-based ultrasmall lattice filters with wide free spectral ranges.

Koji Yamada; Tetsufumi Shoji; Tai Tsuchizawa; Toshifumi Watanabe; Junichi Takahashi; Seiichi Itabashi

Using silicon-on-insulator-based silicon-wire waveguides with submicrometer cross sections, we constructed ultrasmall channel-dropping lattice filters for 1.5-microm infrared systems. The waveguides low-loss bends with 2.5-microm radius reduce the total length of the filter to less than 100 microm and enlarge the free spectral range to more than 80 nm. The measured spectra show fine channel-dropping characteristics, and the results agree well with numerical predictions. Moreover, we have succeeded in tuning the dropping wavelength by adjusting the lengths of the delay lines.


Optics Express | 2008

Generation of high-purity entangled photon pairs using silicon wire waveguide

Kenichi Harada; Hiroki Takesue; Hiroshi Fukuda; Tai Tsuchizawa; Toshifumi Watanabe; Koji Yamada; Yasuhiro Tokura; Seiichi Itabashi

We observed high-purity correlated and entangled photon pairs generated through spontaneous four-wave mixing (SFWM) in a silicon wire waveguide (SWW). Employing a nano-scale silicon waveguide with a low loss mode size converter, we obtained a high coincidence to accidental coincidence ratio (CAR) of around 200 that was larger than that of cooled dispersion shifted fiber (DSF) by a factor 3.2, and observed the two-photon interference fringe of time-bin entangled photons with > 95% visibility without subtracting the accidental coincidences.


IEEE Journal of Selected Topics in Quantum Electronics | 2010

Frequency and Polarization Characteristics of Correlated Photon-Pair Generation Using a Silicon Wire Waveguide

Kenichi Harada; Hiroki Takesue; Hiroshi Fukuda; Tai Tsuchizawa; Toshifumi Watanabe; Koji Yamada; Yasuhiro Tokura; Seiichi Itabashi

We report the frequency and polarization characteristics of correlated photon pairs generated in a Si wire waveguide (SWW). We confirmed that the bandwidth for correlated photon-pair generation was at least >2.8 THz. Moreover, we carried out a classical four-wave mixing experiment using strong pump and idler lights to estimate the bandwidth for correlated photon-pair generation. The results indicated that it is possible to generate photon pairs over a bandwidth as large as ~12 THz. We also showed that the generation efficiencies of the signal and idler photons for the horizontal polarization mode were much higher than those for the vertical polarization mode. This is probably caused by the large efficiencies in the group indexes and the effective cross-sectional areas for the two polarization modes. Furthermore, the bandwidth for the correlated photon-pair generation in the vertical polarization mode was ~±1 THz, and this was much narrower than that for the horizontal polarization mode. The difference between the bandwidths of the two polarization modes indicates that the SWW dispersion for the vertical polarization mode is significantly larger than that for the horizontal polarization mode. We then confirmed that the noise photons generated by spontaneous Raman scattering in an SWW were suppressed to below the detection limit of our setup.

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Koji Yamada

Nippon Telegraph and Telephone

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Toshifumi Watanabe

Nippon Telegraph and Telephone

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Tai Tsuchizawa

Nippon Telegraph and Telephone

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Hiroshi Fukuda

Nippon Telegraph and Telephone

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Hiroshi Fukuda

Nippon Telegraph and Telephone

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