Patent ID: 7085055

Claim:
A diffractive optical system, comprising a transparent substrate that is divided at a surface in alignment with orthogonal two directions into minuscule square cell groups of the same shape in a checked pattern, wherein square cells that give a phase 2pπ and a phase {(2q+1)π±δπ}where 0≦δ≦0.25 and p and q are each an integer with respect to reference-wavelength light striking vertically on the surface of the transparent substrate are alternately arranged in each direction, and the phase 2pπ-giving square cells and the phase {(2q+1)π±δπ}-giving square cells are located in such a way as to be in alignment with 45° diagonal directions of said two directions, wherein the phase 2pπ-giving square cells are formed as portions of the transparent substrate having either a first height or a second height relative to a surface of the substrate and the phase {(2q+1)π±δπ}-giving square cells are formed as portions of the transparent substrate having a third height relative to the surface of the substrate, the first, second and third heights being different from one another.