Waveguide type diffraction grating and an optical wavelength filter

PROBLEM TO BE SOLVED: To provide a waveguide type optical diffraction grating that operates independently of polarization and is capable of controlling reflection spectral characteristic.SOLUTION: Provided is a waveguide type optical diffraction grating, in which there are set a left side waveguide area L, a central waveguide area C, and a right side waveguide area R in a waveguide core that constitutes this waveguide type optical diffraction grating. The cycle of this waveguide type optical diffraction grating is formed as a structure that is asymmetrical in the thickness direction in the left side waveguide area L and the right side waveguide area R. The cycle is modulated. Furthermore, a phase adjustment unit PAP (length Q) is provided that adjusts a phase difference between a forward wave proceeding through this waveguide type optical diffraction grating in an input direction and a reflected wave proceeding in a direction opposite the input direction, the phase adjustment unit PAP being set so that the sum of the phase of the forward wave and the phase of the reflected wave occurring in the phase adjustment unit PAP is constant regardless of the polarization state of an input light to the phase adjustment unit PAP.SELECTED DRAWING: Figure 2