Keiro Komatsu

An experiment on high-speed optical time-division switching

An experimental high-speed optical time-division switching system has been realized. The system is able to exchange digitally encoded color video signals at 256-Mbit/s highway speed. Bistable laser diodes and directional coupler switch matrices are adopted as optical memories and optical read/write gates, respectively, in an optical time switch. The bistable laser diode operates as an optical flip-flop circuit which can be set and reset by optical and electrical signals, respectively. 256-Mbit/s highway speed has been realized with sufficient input highway operating margin using the same wavelength as that of bistable laser diodes for an electrooptical converter. Results of this experiment will be helpful data for use in constructing future optical telecommunications networks, where a variety of broad-band services need to be realized.

Polarization-insensitive semiconductor optical amplifier array grown by selective MOVPE

Polarization-insensitive 1.3 /spl mu/m wavelength semiconductor optical amplifier (SOA) arrays are developed for the first time, by using a new fabrication process with selective MOVPE. In a four-channel array, the SOAs have uniform device characteristics of more than 20 dB signal gain and less than 1 dB polarization sensitivity.<<ETX>>

4*4 GaAs/AlGaAs optical matrix switches with uniform device characteristics using alternating Delta beta electrooptic guided-wave directional couplers

Integrated 4*4 GaAs/AlGaAs optical matrix switches constructed from 12 electrooptic directional couplers have been realized. In order to achieve uniform device characteristics, molecular beam epitaxy and reactive ion beam etching were chosen as the crystal growth technique and waveguide fabrication technique, respectively, in addition to the simplified tree structure as a matrix switch architecture. As a result, matrix switches with quite uniform device characteristics, such as small switching voltage deviation and little path dependence in +or-0.5-dB propagation loss, have been realized. >

Surface migration effect and lateral vapor-phase diffusion effect for InGaAsP/InP narrow-stripe selective metal-organic vapor-phase epitaxy

Migration from a masked region and lateral vapor-phase diffusion are the mechanisms of growth-rate enhancement and compositional change for InGaAsP/InP selective metal-organic vapor-phase epitaxy (MOVPE). A novel threshold mask width where the lateral vapor-phase diffusion starts to occur is proposed. When the mask width is less than the threshold mask width, the major mechanism of selective MOVPE is the surface migration from the dielectric mask region, and the lateral vapor-phase diffusion is very small. On the other hand, when the mask width is larger than the threshold mask width, the major mechanism of selective MOVPE switches to lateral vapor-phase diffusion. We discuss the effective migration length on a dielectric mask and the mechanism of the narrow-stripe selective MOVPE for several growth conditions by considering the concept of the threshold mask width.

Low threshold and high uniformity for novel 1.3-/spl mu/m-strained InGaAsP MQW DC-PBH LDs fabricated by the all-selective MOVPE technique

1.3-/spl mu/m-strained InGaAsP multiquantum-well (MQW) double-channel planar buried heterostructure laser diodes (DC-PBH-LDs) were fabricated by all-selective metalorganic vapor phase epitaxy (MOVPE). In the fabrication process, the strained MQW active layer and current-blocking structures were directly formed by selective MOVPE without a semiconductor etching process. A low-threshold current (I/sub th/=2.6 mA@25/spl deg/C for 200-/spl mu/m-long 70%-90% facets) and excellent high-temperature operation (T/sub 0/=84 K, 25/spl deg/C-60/spl deg/C and T/sub 0/=70 K, 25/spl deg/C-85/spl deg/C) were achieved. Furthermore, extremely uniform threshold current and slope efficiency were observed, The median time to failure for these LDs was estimated to be more than 100000 h under the 85/spl deg/C-5 mW aging condition.

All-selective MOVPE-grown 1.3-/spl mu/m strained multi-quantum-well buried-heterostructure laser diodes

Strained InGaAsP multi-quantum-well (MQW) double-channel planar-buried-hetero (DC-PBH) laser diodes (LDs) were fabricated by selective metalorganic-vapor-phase epitaxy (MOVPE). In the laser fabrication process, both the strained MQW active layer and current blocking structure were directly formed by selective MOVPE without any semiconductor etching process. The LDs are called all-selective MOVPE-grown BH LDs. The laser fabrication process can achieve both a precisely controlled gain waveguide structure and an excellent current blocking configuration, realizing the optimized DC-PBH structure. These aspects are essential to the high-performance and low-cost LD, which is strongly demanded for optical access network systems or fiber-to-the-home networks. This paper will show the excellent high-temperature characteristics for 1.3-/spl mu/m Fabry-Perot LDs which have a record threshold current of 18 mA with a low-operation current of 56 mA for 10 mW, and 74 mA for 15 mW at 100/spl deg/C with extremely high uniformity. Furthermore, reliable long-term operation at high temperature (85/spl deg/C) and high-output power of 15 mW has been demonstrated for the first time.

Angled-facet S-bend semiconductor optical amplifiers for high-gain and large-extinction ratio

The extinction ratio of an optical gate with a spot-size-converter-integrated semiconductor optical amplifier (SSC-SOA) is deteriorated following the direct coupling of unguided light between the input and output fibers. In this letter, an S-bend waveguide structure is introduced into an active waveguide to suppress such direct coupling. Angled facet structures are also introduced for obtaining low facet reflectivity. The fabricated SSC-SOA operating at 1.55-/spl mu/m wavelength achieves an extinction ratio up to 70 dB and a fiber-to-fiber gain of 20 dB.

Very low power consumption semiconductor optical amplifier array

Very low power consuming and polarization insensitive semiconductor optical amplifier arrays with submicron-wide InGaAsP active layers are realized by selective MOVPE technique. 20-dB signal gain at a low injection current of 25 mA was achieved in four-channel arrays.<<ETX>>

A transceiver PIC for bidirectional optical communication fabricated by bandgap energy controlled selective MOVPE

A transceiver PIC consisting of a DFB-LD, a receiver PD and a Y-shaped branch waveguides is realized by in-plane bandgap energy controlled selective MOVPE. Both active and passive core layers are formed in one step selective growth, and complicated fabrication procedure is no longer required. More than 1 mW fiber coupled power and 7 GHz receiver bandwidth are obtained. The modulation and detection operations at 500 Mb/s are successfully demonstrated.

Requirements for modulator-integrated DFB LD's for penalty-free 2.5-Gb/s transmission

Wavelength chirp of modulator-integrated distributed-feedback laser diodes (DFB LDs) is governed by device parameters such as the modulator facet reflectivity, isolation resistance, grating coupling factor, and differential gain. We determined values of these parameters necessary for ensuring penalty-free 2.5-Gb/s transmission over at least 80-km of standard fiber. The influences of the device parameters on wavelength chirp behavior and 2.5-Gb/s data transmission performance are investigated using a new method of characterizing wavelength chirp. By transmitting light from the LD while modulating the modulator, we can determine the light intensity fluctuation after the transmission caused by wavelength chirp. This intensity fluctuation ratio (/spl Delta/I/I) is used to monitor the wavelength chirp. We use integrated devices which satisfy all these requirements, and which are grown by selective metal-organic vapor phase epitaxy (MOVPE), to demonstrate penalty-free 2.5-Gb/s transmission, even over 120-km of standard fiber. >