We studied three types of lasers emitting narrow beam divergence of output light: 1) a spot-size converter integrated laser diodes (SS-LDs) with a vertically tapered waveguide, 2) one with a laterally tapered waveguide, and 3) one consisting of a small cross section of active region. We compared them with regard to their performance in coupling efficiency to a cleaved single mode fiber, threshold current, output power, and reliability. Both the spot-size converted integrated lasers with vertically and laterally tapered waveguide repeatedly provided low threshold currents of as low as 6 mA and low coupling loss to the fiber of 1.2 to 2.5 dB in two inch wafer processes. As a result of the aging test, the SS-lasers were predicted to have the same degradation rate as a conventional buried heterostructure laser. The laser having a small cross section of active layer also has low coupling loss and high efficiency up to 85.

This paper presents 160-Gbit/s full channel time-division demultiplexing using a semiconductor optical amplifier hybrid integrated demultiplexer on a planer lightwave circuit. Error-free demultiplexing from a 160-Gbit/s signal to 8 channel 20 Gbit/s signals is successfully demonstrated. Results of a 160-Gbit/s optical time-division-multiplexed full channel OTDM signal transmission experiment using the circuit and successful 80-km transmission are presented.

This paper describes a new, low power 16-bit Digital Signal Processor (DSP). The DSP has a double-speed MAC mechanism, an accelerator for Viterbi decoding, and a block floating section which contribute to lower power consumption. The double-speed MAC can perform two multiply and accumulate operations in one instruction cycle. Since MAC operations are so common in digital signal processing, this mechanism can reduce the average clock frequency of the DSP resulting in lower power consumption. The Viterbi accelerator and block floating circuitry also reduce the clock frequency by minimizing the number of required cycles needed to be executed. The DSP was fabricated using a 0.8 µm CMOS 2-aluminum layer process technology to integrate 644 K transistors on a 9.30 mm9.09 mm die. It can realize an 11.2 kbps VSELP speech CODEC while consuming only 70 mW at 3.5 V Vdd.

This paper describes a 16-b fixed point digital signal processor(DSP), especially its multiply-accumulate(MAC) unit, memories, and instruction set.By adopting a redundant binary multiplier and a variable pipeline structure, this DSP's MAC unit, compared to a conventional MAC unit, consumes about 15% less power and operates 24% faster. Furthermore, its doublespeed MAC mechanism can realize twice the performance of a single MAC operation while consuming only 69% more power. By being able to more finely control which portions of memory are activated, the data ROM and data RAM's precharge current was reduced to about 1/8 of the conventional ROM and RAM's. We redesigned the instruction set and reduced its width from 32 b to 24 b based on the analysis of data generated by simulating an application program on our previous DSP. The reduction in instruction width made our on-chip instruction memory size 33% smaller than the previous one. This chip is fabricated with a 0.5- µm double-metal-layer CMOS process and achieves 80-MOPS-peak double speed multiply-accumulate performance.