Abstract: An optical device includes an optical input waveguide, a branch/cross waveguide, an optical output waveguide and connection waveguides that connect the optical input and optical output waveguides to the cross/branch waveguide. The spot size of light propagating through the cross/branch waveguide is larger than the spot size of light propagating through optical input waveguides, the optical output waveguides, or the connection waveguides.

Abstract: An optical device consisting of a core layer, a first clad layer in contact with the core layer, a second clad layer, third clad layer and at least one electrode for applying a certain voltage or supplying a certain current. The second clad layer is deposited on the third clad layer and the core layer is provided between the first clad layer and the second clad layer. The core layer, first clad layer, second clad layer and third clad layer consist of a material with a negative refractive index variation coefficient, and the third clad layer has a refractive index smaller than that of the second clad layer.

Abstract: An optical device comprises a core layer; a first clad layer, with the core layer being deposited on a part of surface of the first clad layer; a second clad layer, with the core layer being provided between the first clad layer and the second clad layer; a third clad layer deposited on the second clad, an electrode for heating, and a substrate having a heat-sink function. At least one of the core layer and the clad layers comprises a material having a positive refractive index variation coefficient. The third clad layer has a refractive index smaller than that of the second clad layer.

Abstract: The spot size of light propagating through a cross waveguide 22 is larger than the spot size of light propagating through optical input waveguides 21a and 21b, optical output waveguides 23a and 23b, or connection waveguides 24a, 24b, 25a and 25b.

Abstract: A surface acoustic wave filter device includes a piezoelectric substrate having mirror-polished surfaces on both sides, so that it is essentially free from warping. One surface of the substrate is provided with two filter stages which are cascade connected with each other thereby to sufficiently attenuate bulk wave spurious noise below a practically negligible extent. The filter device can be manufactured with an improved yield.

Abstract: A surface acoustic wave filter device includes a substrate which comprises quartz or the like piezoelectric having a small temperature coefficient and which is formed with unidirectional transducers of asymmetrical construction. A floating electrode is spaced from intermediate position between adjacent positive and negative electrodes which are arranged in interdigital manner, to effectively utilize a mechanical reflection caused by the floating electrode. In consideration of the sign and magnitude of the reflection factor of the floating electrodes, short-circuited electrodes only are used for the floating electrodes. The surface acoustic wave filter device has improved temperature characteristic, insertion loss characteristic and phase characteristic.

Abstract: A composite member includes a structural member having a surface in a mirror-finished condition and a film layer of an amorphous material provided on the surface. The amorphous material is preferably at least one selected from amorphous SiC, amorphous SiN, amorphous SiGe and amorphous GeN. In producing the composite member, a surface of a structural member is polished into a mirror-finished condition which is a finish condition by the usual mirror-finishing. The film layer of the amorphous material is then provided on the surface in the mirror-finished condition by plasma CVD process.