Patent ID: 8451428

Claim:
A computer generated hologram which forms a light intensity distribution on a predetermined plane, the hologram comprising: a plurality of anisotropic cells having different refractive indices with respect to linearly polarized light in a first direction and linearly polarized light in a second direction perpendicular to the linearly polarized light in the first direction, wherein said plurality of anisotropic cells are made of an identical material and includes a first anisotropic cell, a second anisotropic cell, a third anisotropic cell, and a fourth anisotropic cell which have different thicknesses, said plurality of anisotropic cells change phases of linearly polarized light in the first direction and linearly polarized light in the second direction, which are included in incident light on said plurality of anisotropic cells, thereby making a first light intensity distribution formed on the predetermined plane by the linearly polarized light in the first direction included in the incident light different from a second light intensity distribution formed on the predetermined plane by the linearly polarized light in the second direction included in the incident light, said second anisotropic cell has a thickness larger than a thickness of said first anisotropic cell by α, said fourth anisotropic cell has a thickness larger than a thickness of said third anisotropic cell by α, said third anisotropic cell has the thickness larger than the thickness of said first anisotropic cell by β, and said plurality of anisotropic cells satisfy: 0.75×(λ/ N )/{( n 1 +n 2 )/2 −n a }<α<1.25×(λ/ N )/{( n 1 +n 2 )/2 −n a }, 0.75×(λ/ N )/| n 1 −n 2 |<β<1.25×(λ/ N )/| n 1 −n 2 |, and i×N/ 2+0.25<β/α< i×N/ 2+0.75 where λ is a wavelength of the incident light on said plurality of anisotropic cells; n 1 is the refractive index of said plurality of anisotropic cells with respect to the linearly polarized light in the first direction; n 2 is the refractive index of said plurality of anisotropic cells with respect to the linearly polarized light in the second direction; n a is a refractive index of an atmosphere; N is the number of phase levels of a phase distribution according to which the phases of the linearly polarized light in the first direction and the linearly polarized light in the second direction, which are included in the incident light, are changed; and i is an integer not less than 2.