Abstract: An object of this invention is to improve wavelength selectivity. Two optical waveguides (10 and 12) are disposed side by side on surfaces at different heights from each other, and a diffraction grating (14) is disposed between them. The two optical waveguides (10 and 12) cross at an angel &thgr; in an area (16) where they mutually approach. Here, &thgr; is not zero, and preferably should be approximately 0.5°.

Abstract: A diffraction grating is disposed adjacent to a ridge waveguide formed on a substrate (cladding). Assumed that a light propagation direction at the waveguide is z, a direction of width of the waveguide is x, and ends of the diffraction grating of this embodiment is x=gmin when z=0 and x=gmax when z=L/2, the ends of the diffraction grating can be expressed as the following functions f(z). Namely, f(Z)=gmin+(gmax−gmin)×(2z/L)n when 0≦z≦L/2, and f(Z)=gmin+(gmax−gmin)×(2-2z/L)n when L/2≦z≦L, where n>1.

Abstract: The coupled waveguide structure comprises first and second rectangular waveguides, disposed closely. The aspect ratio of the first waveguide is substantially inverse in number to that of the second waveguide.

Abstract: An optical add/drop multiplexer device which is capable of extracting or inserting optical signals of arbitrary wavelength and having a wavelength selection characteristic with a narrow bandwidth, and which is compact in size and highly reliable. The device is formed by a substrate member; a plurality of optical waveguides, formed over the substrate member in layers with a prescribed interval along a direction perpendicular to a plane of the substrate member, each optical waveguide having a portion arranged in parallel and in proximity to an adjacent optical waveguide to form a coupling section; and a diffraction grating member, provided at the coupling section and having a prescribed period along a light propagation direction, for reflecting light signals with a specific wavelength among light signals entered from one of adjacent optical waveguides to another one of the adjacent optical waveguides.

Abstract: A wavelength-tunable semiconductor laser of distributed feedback (DFB) type wherein a diffraction grating having periodic corrugations along the direction of travel of light is formed on an active layer of at least one of layers adjacent thereto. An electrode on one side is separated into four or more electrodes in the direction of the cavity of the laser. Nonadjoining ones of them are electrically connected to form two electrode groups. The total length of first regions corresponding to a first one of the two electrode groups is larger than the total length of second regions corresponding to the second electrode group. The refractive indexes of the first regions are changed through current injection change to the first electrode group to vary the lasing wavelength and the gain of the second regions is controlled through current injection to the second electrode group, thereby generating output light of a constant output power and a variable single wavelength.

Abstract: A method for manufacturing a semiconductor apparatus, providing steps of (i) laminating a first polysilicon layer on the whole surface of a semiconductor substrate through a first oxide layer, (ii) removing the first polysilicon layer and first oxide layer in an element separation region so as to form a trench therein and to treat the residual first polysilicon layer and first oxide layer as a bottom gate electrode and an insulating film respectively, (iii) forming a monocrystalline silicon layer by epitaxial growth on the whole surface of the semiconductor substrate including the trenches, (iv) removing the monocrystalline silicon layer in the element separation region, laminating a second oxide layer on the whole surface of the semiconductor substrate including the removing portion, and making the second oxide layer remain as an element separation film in only the element separation region, and (v) forming a gate oxide film and a top gate electrode on the residual monocrystalline silicon film, and forming a