Patent ID: 7764354

Claim:
A multi-layer diffraction type polarizer comprising: a lamination of at least two polarizing diffraction gratings each comprising a birefringent material, wherein the polarizing diffraction gratings each straightly transmits incident light having a first polarization direction without functioning as a diffraction grating, and diffracts incident light having a second polarization direction perpendicular to the first polarization direction by functioning as a diffraction grating, and each of the polarizing diffraction gratings comprises a birefringent material layer formed on a transparent substrate and having an ordinary refractive index of n 0 and an extraordinary refractive index of n e , (n 0 ≠n e ), the birefringent material layer being processed to have a periodical concavo-convex shape having a step height of d in cross section, a homogeneous refractive index transparent material having a refractive index equal to n 0 or n e is filled in at least the concave portions, and the retardation value |n e −n 0 |×d is (m+0.45 to 0.55) times (m is zero or a positive integer) the wavelength λ of the incident light.