Abstract: A substrate type optical waveguide element includes a bent waveguide that guides a basic mode, that converts an unneeded mode other than the basic mode to a slab mode, and that is a rib type. Furthermore, the substrate type optical waveguide element includes a removing portion that is arranged at an outer circumferential portion of the bent waveguide, and that removes, from the bent waveguide, the slab mode converted in the bent waveguide.

Abstract: An optical device includes an input waveguide and an output waveguide. The optical device includes an interference region that includes an input unit optically coupled with the input waveguide, that includes an output unit optically coupled with the output waveguide, and that has a larger waveguide width than a waveguide width of the input waveguide and a waveguide width of the output waveguide. Further, the optical device includes an unnecessary light waveguide that is included in the output unit in the interference region and that is arranged parallel to the output waveguide. The unnecessary light waveguide is a single-mode waveguide that includes a rib portion and a slab portion with a smaller thickness than a thickness of the rib portion, and that guides only a fundamental mode of light.

Abstract: An optical waveguide device has a function of removing or suppressing a higher-order mode component of propagating light. The optical waveguide device includes a curved waveguide having a curved shape where a curvature continuously changes. A first waveguide is coupled to one end of the curved waveguide and a second waveguide is coupled to the other end of the curved waveguide. A curvature of the first waveguide and the curvature of the curved. waveguide are equal to each other in a coupling point in which the first waveguide is coupled to the curved waveguide, and a curvature of the second waveguide and the curvature of the curved waveguide are equal to each other in a coupling point in which the second waveguide is coupled to the curved waveguide.

Abstract: An optical module has an optical amplifier that amplifies an optical signal in which multiple wavelengths are multiplexed, an optical demultiplexer that separates the multiple wavelengths from the optical signal having been amplified by the optical amplifier, a first photodetector that monitors the optical signal at an input side of the optical amplifier, a second photodetector that monitors each of the multiple wavelengths at an output side of the optical demultiplexer, and a control circuit that controls a center wavelength of a filter of the optical demultiplexer based upon a first output from the first photodetector and a second output from the second photodetector.

Abstract: An optical module has an optical amplifier that amplifies an optical signal in which multiple wavelengths are multiplexed, an optical demultiplexer that separates the multiple wavelengths from the optical signal having been amplified by the optical amplifier, a first photodetector that monitors the optical signal at an input side of the optical amplifier, a second photodetector that monitors each of the multiple wavelengths at an output side of the optical demultiplexer, and a control circuit that controls a center wavelength of a filter of the optical demultiplexer based upon a first output from the first photodetector and a second output from the second photodetector.