Patent ID: 7230762

Claim:
A polarization phase difference plate, comprising: a diffraction grating with a constant period having a plurality of convex parts being arranged, which is formed at least on one of surfaces of a substrate in a thickness direction, said polarization phase difference plate being formed to be capable of utilizing structural birefringence of said diffraction grating, wherein: cross-sectional shape of said convex part is formed in a taper shape from a bottom part thereof towards a top part; a flat part is formed at least between said convex parts being adjacent to each other; said period of said diffraction grating is formed in a size that is equal to or smaller than a wavelength of light to be used; said substrate and said diffraction grating are formed by a same substance; and said bottom part of said convex part in a period direction of said diffraction grating is formed to have a dimension that is 0.7–0.8 times said period of said diffraction grating.