PURPOSE: To improve a response speed and reliability by providing a grating which varies in refractive index at an approach part which is part of optical waveguides and varying the refractive index of the optical waveguide part or its periphery.

CONSTITUTION: For example, the equivalent refractive indexes of the optical waveguide parts 1 and 2 are denoted as n1 and n2 and light is incident on a port 1-1. Light with wavelength which satisfies λ=n1+n2 is projected from a port 2-1, and light with wavelength which satisfies λ=1-n2 is projected from a port 2-2; and light with wavelength λ=2n1 is projected from a port 1-1 and light with other wavelength is projected from a port 1-2. For the purpose, the cores or clads of the optical waveguides nearby a grating are varied in refractive index to vary the equivalent refractive indexes n1 and n2, thereby varying the wavelength λ of demultiplexing. Therefore, when this optical circuit is used for a wavelength filter, optical switch, etc., the response speed and reliability are improved because of no mechanical part.