Abstract: An optical waveguide composed of a core section, and a cladding section disposed so as to enclose the core section, wherein a cavity the inner surface of which inclines with respect to the core section of the optical waveguide is defined on one of principal planes parallel to the core section so as to traverse partly or perfectly a section of the core, and the cavity is filled with a material having a higher index of refraction than that of the core section. Whereby an optical waveguide which can be downsized and is excellent in productivity, a method for fabricating the same, and a coupling structure of the optical waveguide to a light-receiving device are provided.

Abstract: It is the object of the invention to integrally conform functions of devices of optical fiber types with those of SiO.sub.2 waveguides, miniaturize optical devices and provide optical waveguide devices with various optical functions. A SiO.sub.2 waveguide, which is composed of a SiO.sub.2 waveguide clad with low refractive index and a SiO.sub.2 waveguide core with high refractive index, is formed on a Si substrate. The core and the clad on an area, where the direction of the core coincides with the orientation of crystallization of a Si substrate, are removed. A V-groove is formed along the orientation of crystallization of the exposed Si substrate. Both the end surfaces of an optical fiber grating, which is fitted in the V-groove, face those of the remaining SiO.sub.2 waveguide. The cores of the SiO.sub.2 waveguides and the optical fiber grating are optically coupled with each other.

Abstract: There are provided a first optical waveguide having a first curved portion, a second optical waveguide having a second curved portion that extends along and is disposed inside the first curved portion, a third optical waveguide having a third curved portion, an end portion of the third curved portion being connected to both end portions of the first and second curved portions.

Abstract: A waveguide-type optical device is constituted by an optical waveguide circular rod inside which an optical waveguide device is fixed and supported, an optical fiber circular rod inside which the end of an optical fiber is fixed and supported and a circular sleeve from both ends of which these optical waveguide circular rod and optical fiber circular rod are fitted. An optical waveguide and an optical fiber can be readily aligned by forming the circular rod in a circle so that one optical waveguide in an optical waveguide device is located in the center and the circular rod in a circle so that one optical fiber is located in the center. Another optical waveguide and another optical fiber can be readily aligned by setting a position in the peripheral direction and fitting both the circular rods and to the circular sleeve. An optical fiber and an optical waveguide device can be readily connected.

Abstract: Semiconductor device can be connected to an external optical fiber, by providing a short optical fiber, optically coupled to a semiconductor, which is held in a ferrule having the same diameter as an external ferrule of the external fiber. The semiconductor device comprises an optical semiconductor laser diode, a short optical fiber optically coupling at its first end face with the optical semiconductor laser diode, a ferrule for housing the optical fiber, and a sleeve which has an inner diameter slightly larger than an outer diameter of the ferrule and into which the ferrule is inserted. The connection to an external optical fiber is given by inserting a connector of the external optical fiber into the sleeve. The present invention provides compact optical semiconductor device suitable for automatic mounting thereof.