OPTICAL WAVEGUIDE, SPOT SIZE CONVERTER, POLARIZATION FILTER, OPTICAL COUPLER, OPTICAL DETECTOR, OPTICAL SPLITTER, AND LASER ELEMENT

摘要

PROBLEM TO BE SOLVED: To provide an optical waveguide that can be manufactured by a simplified process, is high in accuracy and has a function equal to a vertical taper waveguide, and to provide a spot size converter, polarization filter, optical coupler, optical detector, optical splitter, and laser element that use the optical waveguide.SOLUTION: An optical waveguide comprises: a core area 1 in which incident light is confined to waveguide the incident light and whose thickness is substantially even; and a clad area 2 that sandwiches the core area 1 from both surfaces in a thickness direction. The core area 1 is an optical waveguide 10 of which an effective refractive index consecutively varies along a waveguide direction of the core area 1 and in which the effective refractive index of the core area 1 is at least higher than a refractive index of the clad area 2. The core area 1 comprises: a first area 1a; and a second area 1b that is lower in the refractive index than the first area 1a, and the first area 1a and second area 1b are arranged so as to have a cycle almost equivalent to a wavelength of the incident light or a small cycle.