OPTICAL WAVEGUIDE TYPE DIFFRACTION GRATING AND METHOD FOR MANUFACTURING THE SAME

摘要

A method for manufacturing an optical waveguide type diffraction grating, characterized in that an optical waveguide having an optical waveguide region added with an additive for varying the refractive index through irradiation with a light of a specified wavelength for inducing variation of refractive index and a phase grating having a specified pattern of irregularities are provided, the optical waveguide and the phase grating are spaced apart from each other by such a distance that generates a specified optical path difference between zero-order transmission light and second-order diffraction light so that the modulation intensity of interference light between the zero-order transmission light and the second-order diffraction light of the refractive index variation inducing light is equal to or lower than 85% of the modulation intensity when optical path difference is assumed to be not present between the zero order transmission light and the second order diffraction light, and the refractive index variation inducing light is allowed to impinge on the phase grating to form the interference fringe of first-order diffraction light in the optical waveguide region of the optical waveguide, thus forming a diffraction grating in the optical waveguide region. The method can manufacture easily an optical waveguide type diffraction grating having a sufficiently low cutoff quantity in normally transmitting wavelength band of 0.9 lambda >B<-0.95 lambda >B< ( lambda >B< is peak cutoff frequency).