Shuichi Nagai

Multimode interference photonic switches (MIPS)

The switching characteristics of multimode interference photonic switches (MIPS) are analyzed by wide-angle finite difference beam propagation method (FD-BPM). As a result, it is found that the MIPS with a multimode interference (MMI) length of 599 /spl mu/m can switch the output light polarization insensitively with a crosstalk of less than -20 dB for a wavelength range of 70 nm. These analyses show that the MIPS can also have a 3-dB coupler function. Experimentally, an InGaAsP/InP 1/spl times/2 MIPS with a thicker InP cladding layer was fabricated and exhibited switching operation with crosstalks of -8 dB and -10 dB at 0 and 20 mA current injections, respectively. For a 2/spl times/2 MIPS with a thinner InP cladding layer, better switching characteristics with a crosstalk of -13 dB and an extinction ratio of 17 dB were realized.

INGAASP/INP MULTI-MODE INTERFERENCE PHOTONIC SWITCHES FOR MONOLITHIC PHOTONIC INTEGRATED CIRCUITS

InGaAsP/InP semiconductor photonic switches using multi-mode interference (MIPS) are proposed for monolithic photonic integrated circuits. Changing the refractive indices of index-modulated regions located in the center of a multi-mode waveguide, controls its switching functions. It is predicted from calculations by an FD-TD (finite difference time domain) method that these devices can operate in various kinds of output schemes with typical device dimensions of about 8 µm width and 540 µm length. 1×2 InGaAsP/InP MIPSs with a high-mesa structure have been fabricated, and fundamental switching characteristics were measured. At the preliminary stage, switching was observed at 20 mA current injection with about 37% extinction ratio. Switching efficiency and cross talk of the MIPS can be improved by optimizing the device dimensions and structure. The flexibility of setting the index-modulated regions suggests versatile operation of the MIPS, such as a photonic space division switch, a variable power splitter, or as an optical modulator.

Low-Pressure Direct-Liquid-Cooling Technology for GaN Power Transistors

Power concentration due to tremendous chip size reduction requires superior thermal conductivity. We first demonstrate the reduction in junction temperatures in low-pressure direct liquid cooling (LP-DLC) of GaN power devices for high-power and high-voltage switching applications. In the LP-DLC structure, junction temperature reductions of up to 55 K or 100% higher power levels were demonstrated by introducing a working fluid to a package. The thermal resistance has decreased to 28% in the LP-DLC structure with a radiator.

Via hole machining in sapphire using an ultrafast laser

GaN is expected to replace GaAs and Si materials in the next generation high power density Microwave Monolithic Integrated Circuits (MMIC), thanks to its excellent material characteristics. Sapphire is one of the most promising substrate materials for GaN-based MMIC for its excellent physical characteristics and cost effectiveness. Interconnects across MMIC devices are made possible by via holes through sapphire layer, which is typically > 100 um in depth. Since sapphire is chemically stable and physically strong, it is very difficult to make such deep via holes in sapphire using conventional techniques, such as wet or dry etching. Our picosecond laser provides a viable, and probably unique, solution to this problem. It was demonstrated that > 300 um holes can be machined in sapphire with our 526 nm picosecond laser.GaN is expected to replace GaAs and Si materials in the next generation high power density Microwave Monolithic Integrated Circuits (MMIC), thanks to its excellent material characteristics. Sapphire is one of the most promising substrate materials for GaN-based MMIC for its excellent physical characteristics and cost effectiveness. Interconnects across MMIC devices are made possible by via holes through sapphire layer, which is typically > 100 um in depth. Since sapphire is chemically stable and physically strong, it is very difficult to make such deep via holes in sapphire using conventional techniques, such as wet or dry etching. Our picosecond laser provides a viable, and probably unique, solution to this problem. It was demonstrated that > 300 um holes can be machined in sapphire with our 526 nm picosecond laser.

New structure of multi-mode interference photonic switch with partial index-modulation regions (MIPS-P)

We propose a new structure of multi-mode interference photonic switches with partial index-modulation regions to realize flexible power switching among multi-ports. The switching characteristics for a 3/spl times/3 configuration are analysed to show potential for versatile functions.