Shimomura Kazuhiko

A new type optically-controlled field-effect transistor was demonstrated. This device was composed of GaAs material system for the FET region and GaInAs/InP material system for the absorption region, and these regions were electrically isolated by polyimide and SiO2. When 1.55 mum wavelength light entered the absorption region, about 120 muA of source-to-drain current was modulated due to the field-screening effect.

In this article we report theoretical as well as experimental studies of the electric-field-induced refractive index change in InGaAs/InP quantum-well structures, viz., quantum-film, quantum-wire, and quantum-box structures. The refractive index change, easily measured using a Mach-Zehnder interferometer setup, was around 1%, 4%, and 7% in quantum film, quantum wire, and quantum box, respectively, in the longer-wavelength region corresponding to the positive refractive index change peak. Moreover, we will discuss that the refractive index change dependency on the polarization of incident light in a quantum film can be controlled by introducing suitable tensile strain in it. It was found that for a well width of II nm, 0.3% tensile strain should be induced to obtain polarization-independent refractive index change. (C) 1994 John Wiley and Sons, Inc.

Current modulation of an optically-controlled field-effect transistor using the field-screening effect of photogenerated carriers is numerically calculated. When the optical input power is 1 mW, more than 6 mA of current modulation can be obtained in this device.

Semiconductor waveguide optical switches and modulators are reviewed from the view point of material and structure. As material for switches and modulators, effects of both variations of refractive index and absorption are considered. As for the structure of switches and modulators, basic characteristics of devices, including length, speed, and consumption power; are investigated and recent experimental performances are shown. For further improvement of switches and modulators, the importance of low-dimensional quantum-well structures and strained quantum-well structures are pointed out.

A field-effect-type photodetector is proposed. The proposed device is an field-effect-transistor (FET) structure whose output current is controlled by the potential applied to the FET resulting from the field-screening effect of the photogenerated carriers in a diode overlaid on the FET.

A low switching voltage of less than 2V was achieved in a GaInAs/InP MQW intersectional waveguide optical switch operating at 1.55-mu-m. This switch was fabricated by only one-step epitaxial growth followed by a pattern etching process using electron beam lithography for electrical isolation and photolithography for waveguide formation.

We propose a novel integrated-twin-guide (ITG) optical switch with a built-in TIR region to enlarge the spatial separation of output lights, which is suitable for a compact optical switching matrix array. A switching operation was observed in a GaInAsP/InP MQW ITG optical switch utilizing electric-field induced refractive index variation.

We demonstrate a low-drive voltage intersectional waveguide optical switch using 1.6-mu-m GaInAs/InP MQW structure, which was fabricated by only one-step epitaxial growth of MQW structure followed by one-step pattern etching of the waveguide. Extinction ratio at the straight port of 9.9 dB and that at the reflection port of 4.4 dB were obtained at an applied voltage of -4 V.

Operational wavelength range for low insertion loss and high extinction ratio of GaInAs(P)-InP intersectional optical switches consisting of low-dimensional quantum-well structures, such as quantum-box, quantum-wire, and quantum-film structures, is theoretically analyzed. As a result, it is found that superior operation characteristics can be attained with the lower dimensional quantum-well structure, for instance, operational wavelength range of around 10 nm for insertion loss less than 1 dB and extinction ratio higher than 50 dB can be obtained with the device using a quantum-box structure.

An electric-field induced refractive index variation in GaInAs/InP five-layered quantum box structure was observed for the first time. The wavelength dependence of the refractive index variation was also measured to confirm the quantum box effect. The size of the GaInAs/InP quantum box was estimated to be (22-30 nm)2 with the thickness of 7.5 nm, from the spectral property of the field-induced refractive index variation. The maximum value of the refractive index variation in the quantum box was evaluated to be 7% around 1.52-mu-m wavelength at an applied electric field of 8 x 10(4)V/cm.

We propose and analyze a new type of intersectional optical switch using positive refractive index variation in quantum well structure. The switch structure has a built-in refractive index difference in the waveguide, due to which the incident light is reflected to cross port at the OFF state. When the electric field applied to the electrode (ON state), the built-in refractive index difference vanishes by the positive refractive index variation in the quantum well, and the light transmits to straight port. Low insertion loss of lesser than 1 dB and high extinction ratio of more than 20 dB can be obtained at both cross and straight port.

An electric-field induced refractive index variation in GalnAs/InP five-layered quantum box structure was observed for the first time. The wavelength dependence of the refractive index variation was also measured to confirm the quantum box effect. The size of the GalnAs/InP quantum box was estimated to be (22–30 nm)&lt sup&gt 2&lt /sup&gt with the thickness of 7.5 nm, from the spectral property of the field-induced refractive index variation. The maximum value of the refractive index variation in the quantum box was evaluated to be 7% around 1.52 pm wavelength at an applied electric field of 8 x 10&lt sup&gt 4&lt /sup&gt V/cm. © 1991 IEEE

An intersectional optical switch structure with an intersecting angle of 6° was fabricated on OMVPE grown GalnAs/InP MQW wafer (λg = 1.S56/µm), and switching operation using field-induced refractive index variation was successfully demonstrated at the reverse bias voltage of 8 V at 1.6 µm wavelength region. Based on this switching, the field-induced refractive index variation in QW was estimated as around 1 percent. © 1989 IEEE