Takuo Tanemura

Optimization of Modulation-Canceling Reflective Semiconductor Optical Amplifier for Colorless WDM Transmitter Applications

Self-seeded reflective semiconductor optical amplifier (RSOA) has been drawing special attention as potentially low-cost colorless wavelength-division-multiplexed transmitter. In this paper, we present numerical and experimental analyses of RSOA to find the optimal condition to induce strong modulation canceling effect over wide temperature range. Three InGaAlAs/InP multiple-quantum-well RSOAs with different length are compared numerically and experimentally to reveal the existence of critical RSOA length to induce efficient modulation-cancelling effect. By using the optimal RSOA length of 1 mm, we experimentally demonstrate 2.5-Gb/s self-seeded transmission at 1550-nm wavelength over a 25-km standard single-mode fiber at both 25 and 50xa0°C. In addition, we demonstrate feasibility of higher-temperature (70xa0°C) as well as higher-bitrate (10 Gb/s) operation by employing the amplified self-seeded configuration with appropriately selected RSOAs.

Integrated Reconfigurable Unitary Optical Mode Converter Using MMI Couplers

Reconfigurable unitary optical mode converters that can convert multiple orthogonal spatial modes into different orthogonal modes without fundamental optical loss are important for mode-division-multiplexed (MDM) optical communication, imaging, and quantum computation. In this letter, we propose a novel integrated reconfigurable unitary optical mode converter, which consists of cascaded multimode interference couplers and phase shifter arrays. We numerically investigate its ability to realize arbitrary unitary mode conversion and demonstrate its applicability to mode unscrambling as well as mode switching in MDM transmission systems.

Comprehensive analysis on electrically pumped metallic cavity lasers

We present the design of an electrically pumped metallic cavity laser based on optical, electrical and thermal simulations. By inserting an InAlAs blocking layer, leakage current is effectively suppressed, leading to 50% reduction of threshold current together with better thermal stability. Through combined optical and electrical analyses, the insulation layer thickness is set to be 60 nm, where the device shows optimized overall performance.

Surface-normal electro-optic-polymer modulator with silicon subwavelength grating

We propose novel silicon-based surface-normal optical modulator using electro-optic (EO) polymer. The EO polymer is embedded inside a thin silicon subwavelength grating layer, which is used as both the interdigitated electrodes for effective poling of the EO polymer, and as high-Q resonant structure for the incident light to enable efficient modulation. We numerically demonstrate 10-dB intensity modulation at 1550-nm wavelength under a refractive index change of only 3.8 × 10−4, corresponding to the driving voltage below 1V. Total-reflectance phase modulator is also demonstrated by adding a backside reflector. With inherently high-speed response over several tens of GHz, scalability to dense 2-D array integrated with CMOS driver circuitry, and relatively easy and low-cost fabrication without epitaxial process, the proposed device may find versatile applications in optical interconnects, free-space optical communications, imaging and sensing.

Design and experimental investigation of monolithic polarization controller with InGaAlAs/InAlAs multiple quantum wells

We design active integrated polarization controller using half-ridge-waveguide polarization converter and InGaAlAs/InAlAs multiple-quantum-well-based phase shifters. From the numerical simulation and preliminary measurement, we demonstrate the feasibility of polarization switching to arbitrary state with less than 16.2-mW DC power consumption using a 5.6-mm-long device.

Capsule-shaped metallic-cavity semiconductor lasers for low-energy on-chip light sources

We review our recent studies on capsule-shaped InP/InGaAs metallic-cavity lasers. By introducing an optimal curvature at the metallic sidewalls of conventional rectangular metallic lasers, the electric fields of the resonant mode are pushed effectively into the center of the mesa, which allows dramatic reduction of the plasmonic loss. The validity of the scheme is verified both numerically and experimentally. From three-dimensional finite-difference time-domain simulation and rate-equation analysis, we estimate that the threshold current can be reduced to as low as 60 μA with the effective modal volume of 0.45 μm3. Up to 4-fold increase in Q value is confirmed experimentally for the cavity structure with an optimal curvature.

Silicon rib waveguide electro-absorption optical modulator using transparent conductive oxide bilayer

We propose a novel ultra compact electro-absorption optical modulator based on a silicon rib waveguide and numerically demonstrate its performance. The proposed design employs two types of transparent conductive oxide (TCO) layers with different carrier densities to achieve both high modulation efficiency and low optical insertion loss. The thin TCO layer with high carrier density enables efficient modulation through the metal–oxide–semiconductor structure. On the other hand, the upper TCO layer with low carrier density allows low-resistance electrical contact for the top electrode without large optical loss. Using an indium tin oxide bilayer with optimized carrier densities, we numerically demonstrate a 4.3 dB extinction ratio and a 2.6 dB optical insertion loss with 1 µm device length. We estimate that the modulator operates under a low driving voltage of 1.3 V, exhibiting an ultra low energy consumption of 22.5 fJ/bit and a broad RC modulation bandwidth of over 40 GHz.