Abstract: An integrated semiconductor laser apparatus is constructed in such an arrangement that a core layer is located in the proximity of an active layer so as to be in an evanescent-field area of light propagating in the active layer and that a carrier concentration of a second cladding layer is higher than that of a first cladding layer. Thus, most evanescent waves of light propagating in the core layer propagate in the first cladding layer of the low carrier concentration. Since the rate of evanescent waves absorbed by carriers is very low, the integrated semiconductor laser apparatus can propagate the light with small losses.

Abstract: This invention relates to a distributed feedback semiconductor laser which achieves distributed feedback by gain coupling by providing periodical changes in the thickness of the active layer (5) or the absorptive layer, and aims to achieve light distributed feedback mainly of periodical perturbation of the gain factor by diminishing the periodical perturbation of refractive index caused by the changes in the thickness of the active layer (5) or the absorptive layer. This invention is characterized by a refractive index canceling structure comprising a combination of layers (6) and (7) of different refractive indices to cancel periodical changes in refractive index caused by the periodical structure of the active layer (5) or the absorptive layer.

Abstract: An optical switch comprises a substrate, a lower cladding layer, a waveguide layer, and an upper cladding layer each formed of a semiconductor, and in which at least one of the three layers except the substrate has a quantum well structure at a quantum confined potential. The well plane of the quantum well structure is symmetrical with respect to the center position thereof, and varies in proportion to the square of the distance from the center position. If an electric field is applied perpendicular to the well plane, the respective changes in the absorption coefficient and refractive index in the vicinity of the absorption edge are influenced by absorption peak shifts attributable to both 1e-1hh and 1e-11h transitions. Thus, the optical switch operates in response to both TE and TM mode light without depending on polarization.

Abstract: An optical directional coupler switch is fabricated from a semiconductor substrate having a (111) plane. Thus, refractive indexes are changed for TE and TM modes by electrooptic effect, although the change amount is different between TE and TM modes. Therefore, a switching operation is realized for an incident light having any polarization. A device length L is preferrably set to meet an equation of "L.sub.TE .ltoreq.L.ltoreq.L.sub.TM " (L.sub.TE and L.sub.TM are coupling lengths for TE and TM modes) to decrease a cross-talk, even if the coupling lengths are different between TE and TM modes, considering that the difference is small.

Abstract: A distributed feedback semiconductor laser having a diffractive grating on an active layer in order to generate stimulated emission by recombing electrons with positive holes thereon by the light distributed feedback. This laser can achieve precisely single wavelength longitudinal mode lasing as a thin buffer layer is grown on the surface of the semiconductor layer which has been etched with irregular pattern corresponding to the diffractive grating while the corrugated pattern is being maintained intact and an active layer is grown on the surface thereof in a manner to fill in the valleys of the corrugated pattern as much as possible so that a diffractive grating is formed on the active layer and light distributed feedback is caused mainly by the periodic perturbation of gain coefficients stimulated by the diffractive grating.

Abstract: Electrodes are provided in the vicinity of the switching region of a carrier injection type optical switch, and carriers are removed rapidly through these electrodes when the switch is turned OFF. As the result, a switching speed is increased.

Abstract: A light modulation device according to the present invention comprises a substrate, a substrate layer, an optical waveguide layer, and buffer layers, in the order from the bottom upward, all formed of either n-type or p-type compound semiconductor crystal. In this light modulation device, in order to capture the light in the optical waveguide layer, the composition ratio of the compound semiconductor is so determined that refractive index is at least approximately 0.1% higher in the optical waveguide layer than in the substrate layer and in the buffer layers. Further, the carrier density is low in the optical waveguide layer and in the buffer layers so that the applied voltage is applied mainly to the optical waveguide layer. Because of such construction, the light modulation device according to the present invention is free from strict conditions required in an etching process, is small in absorption loss of light, and can be used as a component of monolithic optical integrated circuit.