Tomohiro Kita 교수

We demonstrated wavelength tunable laser diodes with Si-wire waveguide ring resonators as an external optical cavity. The footprint of the optical cavity including the semiconductor optical amplifier is as small as 0.8 mm × 0.6 mm which is less 1/10 of those made of silicon oxinitride material. Wavelength tuning range of approximately 55 nm was demonstrated, which covers entire L-band of the optical communication wavelength system. Furthermore, a spectral linewidth narrower than 100 kHz was obta

The compact, high-speed, low-power consumption Mach-Zehnder interferometer (MZI)-type optical switch using thermo-optical effect is a key device in future optical integrated circuits. In this study, we achieved ultra-high-speed switching operation of 0.4 μs and low electrical power operation of 23 mW with a small device footprint by loading an asymmetric doped MZI structure and an integrated heat sink. This optical switch can be fabricated in the standard manufacturing process of silicon photoni

We fabricated wavelength-tunable laser diodes using a Si photonic wavelength filter that consists of ring resonators and an asymmetric Mach-Zehnder interferometer. The footprint of the optical cavity including the semiconductor optical amplifier is small, 2.6 mm × 0.5 mm, which is about 1/9 of those for tunable laser diodes made of silicon oxynitride. The wavelength could be tuned over approximately 62 nm, which covers the entire L-band of the optical communication wavelength range. The maximum

We present a wavelength-tunable laser diode with a 99-nm-wide wavelength tuning range. It has a compact wavelength-tunable filter with high wavelength selectivity fabricated using silicon photonics technology. The silicon photonic wavelength-tunable filter with wide wavelength tuning range was realized using two ring resonators and an asymmetric Mach-Zehnder interferometer. The wavelength-tunable laser diode fabricated by butt-joining a silicon photonic filter and semiconductor optical amplifier

Compact, wavelength-tunable light sources are desired for the enhancement of information communication technology and bio-imaging applications. We propose a compact, wavelength-tunable laser diode with a wide wavelength-tunable range around 1230 nm consisting of a quantum-dot optical amplifier and a silicon photonic tunable filter. High-quality InAs quantum dots grown with the sandwiched sub-nano separator technique were used as the optical gain medium. The wavelength-tunable filter was construc

We propose a tunable dual-wavelength heterogeneous quantum dot laser diode. The tunable dual-wavelength laser consists of a quantum dot semiconductor optical amplifier as the optical gain medium and an external cavity fabricated from silicon photonics technology as the wavelength tunable filter. We successfully demonstrated dual-wavelength lasing oscillation by tuning the difference frequency from approximately 34 to 400 GHz.

Abstract A heterogeneous wavelength-tunable laser diode combining quantum dot and silicon photonics technologies is proposed. A compact wavelength-tunable filter with two ring resonators was carefully designed and fabricated using silicon photonics technology. The tunable laser combining the wavelength-tunable filter and an optical amplifier, which includes InAs quantum dots, achieved a 44.0 nm wavelength-tuning range at around 1250 nm. The broadband optical gain of the quantum dot optical ampli

We fabricated wavelength-tunable laser diodes with external cavity consist of Si photonic wire waveguide ring resonators. About 51.5 nm wavelength tuning operation, which covers the entire L-band of the optical communication wavelength range, was obtained. The cavity length dependence of the spectral line width was verified to obtain narrower spectral linewidth. The observed spectral linewidth of 3.78 mm long cavity and 8.19 mm long cavity are 131.0 and 64.8 kHz, respectively. The advantage of l

Abstract Optical phased arrays (OPAs) have received considerable attention as solid-state beam scanners. However, conventional OPAs that actively control the phase difference between arrays are characterized by excessive power consumption for high-precision beam emission. In this study, we fabricated an OPA comprising Bragg grating and arrayed waveguide grating (AWG). Multi-mode waveguide is used in AWG to reduce the effect of manufacturing error. This device realizes wide and high-resolution tw

Abstract To realize fast switching of a few μ s and low-power consumption, we apply a differential control method to a thermo-optic Mach–Zehnder interferometer optical switch loaded with a direct-current injection-type phase shifter using multimode interference. We achieve ultrafast switching of several tens of ns, which is considerably higher than the conventional switching speed. With differential control, we demonstrate extremely fast optical switching with <mml:math xmlns:mml="http://www.w3.

We fabricated wavelength tunable laser diodes with Si photonic wire waveguide ring resonators as an external optical cavity. Less than 100 kHz narrow spectral linewidth was obtained with small footprint. Our wavelength tunable laser diode shows sufficient good performance for practical use in digital coherent optical transmission systems.

Abstract We propose a thermo-optic phase shifter utilizing multimode interference in a silicon waveguide. The electrodes were attached to the section where the multimode interference had the minimum optical electric field around the sidewalls. We designed the multimode waveguide width to reduce optical propagation loss in the C–L wavelength band (1.53–1.625 μ m). We succeeded in developing a low optical loss thermo-optic phase shifter with less than 0.1 dB in the wavelength range of 1.5 to 1.6 μ

The authors fabricated a gated-vertical (In,Ga)As quantum dot with an Al2O3 gate insulator deposited using atomic layer deposition and investigated its electrical transport properties at low temperatures. The gate voltage dependence of the dI∕dV−V characteristics shows clear Coulomb diamonds at 1.1K. The metal-insulator gate structure allowed the authors to control the number of electrons in the quantum dot from 0 to a large number estimated to be about 130.

We demonstrated a Si-photonics-based heterogeneous tunable laser in the 1.55- µm- band with quantum dot reflective semiconductor optical amplifier. Relatively low threshold current could be achieved owing to high gain characteristic.