Patent ID: 7221509

Claim:
A polarization splitting device comprising: an optically isotropic substrate; an optically anisotropic film formed on said optically isotropic substrate; and a diffraction grating comprising: a first cyclically structural portion formed on a first surface of said optically anisotropic film such that depressions are cyclically arranged with a predetermined pitch along a direction of the first surface of said optically anisotropic film; and a second cyclically structural portion comprising an optically transparent material filling in the depressions and having a refractive index approximately equivalent to a refractive index of said optically anisotropic film in a direction of ordinary light rays and extraordinary light rays and configured to cover said first cyclically structural portion such that an edge surface of said second cyclically structural portion forms a plane approximately equal to a plane formed by the front surface of said optically anisotropic film, wherein diffraction light having a diffraction angle greater than a predetermined angle among diffraction light diffracted by said diffraction grating is inhibited from being discharged outside of said optical isotropic substrate; and wherein said predetermined pitch satisfies a relationship λ( ns/na )< d <2λ( ns/na ), wherein λ represents an incident light wave length, ns represents a refractive index of an optically isotropic substrate of a polarization split device, and na represents a refractive index of an ambient atmosphere around the polarization split device.