The University of Tokyo · Engineering
Professor Mitsuru Takenaka's research lab specializes in advanced photonic devices and integrated optics, focusing on novel semiconductor materials and nanostructured waveguide platforms for next-generation optical communication and signal processing. Key research directions include all-optical logic devices such as bistable laser diodes and optical flip-flops, high-performance germanium photodetectors with low dark current, and ultra-compact photonic integrated circuits using high-index-contrast waveguides and III-V/Si hybrid integration. The lab emphasizes innovative fabrication techniques—such as gas-phase doping and atomic layer deposition—to achieve low-loss, high-efficiency, and scalable photonic components.
Figures are computed from collected data and may differ slightly.
All-optical flip-flop operation of multimode interference bistable laser diodes (MMI-BLDs) was experimentally demonstrated for the first time. The MMI-BLD was prepared with a conventional ridge waveguide laser diode fabrication procedure, suitable for photonic integrated circuits. Bistable switching via two-mode bistability was obtained with approximately 0-dBm input powers due to cross-gain saturation and the saturable absorbers. Bit-length conversion was successfully obtained with noninverted
We have investigated the dark current of a germanium (Ge) photodetector (PD) with a GeO₂ surface passivation layer and a gas-phase-doped n+/p junction. The gas-phase-doped PN diodes exhibited a dark current of approximately two orders of magnitude lower than that of the diodes formed by a conventional ion implantation process, indicating that gas-phase doping is suitable for low-damage PN junction formation. The bulk leakage (Jbulk) and surface leakage (Jsurf) components of the dark current were
We proposed a novel InP based photonic wire waveguide with an InAlAs oxide cladding. The InGaAsP/InAlAs-oxide structure in the vertical direction provides an ultrahigh index contrast waveguide, and it allows a bend radius of a few mum with no vertical leakage loss. The InP photonic wire waveguide with a 500x300-nm rectangular channel core (refractive index n ~ 3.36) and an InAlAs oxide cladding (n ~ 2.4) was numerically analyzed using the three-dimensional time-domain beam propagation method (3D
We propose a novel bistable laser diode (BLD) with active multimode interference (MMI) cavity. Bistable switching can be realized between two cross-coupled modes by means of gain saturation. Static characteristics of the multimode interference (MMI)-BLD are analyzed using a finite-difference beam propagation method. The photon-carrier interactions are calculated using the carrier-rate equation. This model gives accurate distributions of photon and carrier densities, optical gain, and refractive
We present a novel optical phase modulation scheme on a Si photonic platform that uses a III-V/Si hybrid metal-oxide-semiconductor (MOS) capacitor formed by bonding an n-type InGaAsP membrane on a p-type Si waveguide. We numerically revealed that the phase modulation efficiency was improved by a factor of 7-8 owing to electron accumulation at the InGaAsP MOS interface when the n-type Si layer in a Si MOS optical phase shifter was replaced by an n-type InGaAsP layer. To realize the III-V/Si hybri
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