Publications by authors named "Hidetaka Nishi"

Ultrashort-distance optical interconnects are becoming increasingly important due to continuous improvements in servers and high-performance computers. As light sources in such interconnects, directly modulated semiconductor lasers with an ultrasmall active region are promising. In addition, using Si waveguides is important to provide low loss optical links with functions such as wavelength filtering and switching.

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We evaluate the nonlinear coefficient of graphene-on-silicon waveguides through the coincidence measurement of photon-pairs generated via spontaneous four-wave mixing. We observed the temporal correlation of the photon-pairs from the waveguides over various transfer layouts of graphene sheets. A simple analysis of the experimental results using coupled-wave equations revealed that the atomically-thin graphene sheets enhanced the nonlinearity of silicon waveguides up to ten-fold.

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Toward the realization of low-cost, long-, and extended-reach 400GbE data-center applications, the performance of pulse amplitude modulated (PAM) signals is studied using a state-of-the-art, high-performance 1.3-μm distributed feedback directly modulated laser, without any optical amplification or complex digital processing. Amplifierless PAM-4 transmissions of up to 64-Gb/s are achieved over 40 km of standard single-mode fiber (SSMF) for standard KP4-FEC, while 84-Gb/s PAM-8 signals are evaluated over 10 km SSMF.

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We demonstrate 20-μm-long twin-mirror membrane distributed-reflector (DR) lasers for chip-to-chip optical interconnects. The lasers employ distributed Bragg reflectors (DBRs) at both ends of a 20-μm-long λ/4-phase shifted distributed feedback (DFB) section. We achieve single-mode lasing in a λ/4-phase shifted DFB mode at room temperature with a threshold current of 0.

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Environmental sustainability information in the manufacturing industry is not easily shared between stages in the product lifecycle. In particular, reliable manufacturing-related information for assessing the sustainability of a product is often unavailable at the design stage. Instead, designers rely on aggregated, often outdated information or make decisions by analogy (e.

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We demonstrate monolithic integration of a 50-μm-long-cavity membrane distributed-reflector laser with a spot-size converter, consisting of a tapered InP wire waveguide and an SiOx waveguide, on SiO/Si substrate. The device exhibits 9.4-GHz/mA modulation efficiency with a 2.

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We demonstrate the generation and demultiplexing of quantum correlated photons on a monolithic photonic chip composed of silicon and silica-based waveguides. Photon pairs generated in a nonlinear silicon waveguide are successfully separated into two optical channels of an arrayed-waveguide grating fabricated on a silica-based waveguide platform.

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By way of a brief review of Si photonics technology, we show that significant improvements in device performance are necessary for practical telecommunications applications. In order to improve device performance in Si photonics, we have developed a Si-Ge-silica monolithic integration platform, on which compact Si-Ge-based modulators/detectors and silica-based high-performance wavelength filters are monolithically integrated. The platform features low-temperature silica film deposition, which cannot damage Si-Ge-based active devices.

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We present a compact and stable terahertz (THz) vector spectroscopy system using silicon photonics technology. A silicon-based integrated phase control circuit greatly reduces the physical size of the continuous-wave THz spectroscopy system and enhances environmental phase stability. Differential lightwave phase control using two carrier-injection electro-optic modulators enables fast and linear phase sweeps of THz-waves.

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We experimentally demonstrate a high-quality phase shift keying demodulator based on a silicon photonic wire waveguide. Since the birefringence of the waveguide generates extremely huge differential group delay, an ultra-compact and high-extinction-ratio delay line interferometer is devised in TE and TM modes. We firstly calculated and simulated the requirements for propagation length and waveguide's dimensions.

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On the silicon (Si) photonic platform, we monolithically integrated a silica-based arrayed-waveguide grating (AWG) and germanium (Ge) photodiodes (PDs) using low-temperature fabrication technology. We confirmed demultiplexing by the AWG, optical-electrical signal conversion by Ge PDs, and high-speed signal detection at all channels. In addition, we mounted a multichannel transimpedance amplifier/limiting amplifier (TIA/LA) circuit on the fabricated AWG-PD device using flip-chip bonding technology.

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We demonstrate a monolithic integration of variable optical attenuators (VOAs) and photodetectors (PDs) based on submicrometer silicon (Si) rib waveguide with p-i-n diode structure for near infrared (NIR) light. To make the Si PD absorptive for NIR, we introduced lattice defects at the rib core by means of argon ion implantation. At reverse bias of 5 V, the PD exhibits dark current of approximately 1 nA, responsivity of approximately 65 mA/W at 1560-nm wavelength, and a 3-dB cut-off frequency of approximately 350 MHz, while the VOA shows approximately 100 MHz.

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We investigated influence of carrier lifetime on performance of silicon (Si) p-i-n variable optical attenuators (VOAs) on submicrometer Si rib waveguides. VOAs were fabricated with and without intentional implantation of lattice defects into their intrinsic region. Carrier lifetime was measured by pulse responses for normal incidence of picosecond laser pulse of 775 nm to the VOA, as approximately 1 ns and approximately 7 ns for the VOAs with and without defects, respectively.

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We demonstrate the monolithic integration of germanium (Ge) p-i-n photodetector (PDs) with silicon (Si) variable optical attenuator (VOAs) based on submicrometer Si rib waveguide. A PD is connected to a VOA along the waveguide via a tap coupler. The PDs exhibit low dark current of ~60 nA and large responsivity of ~0.

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