Patent ID: 6947214

Claim:
A diffractive optical element comprising: a plurality of diffraction gratings including two diffraction gratings made of different materials from each other, wherein at least one of said plurality of diffraction gratings includes a region in which grating side surfaces are inclined, and inclinations thereof are different according to positions thereof and in accordance with an incident angle or emergent angle of a specified ray of light, and wherein at least one of said diffraction grating is a diffraction grating disposed in an i-th layer counting from an incident side of said plurality of diffraction gratings, and includes a region in which an inclination angle φ i (j) of said grating side surface is changed so as to satisfy at least one of the following expressions: φ i ( j )= C i ·θ i ( j ) φ i ( j )= C i ·θ i ( j )′ where the incident angle of the specified ray incident into a j-th grating portion counting from a center portion of the i-th layer diffraction granting is θ i (j), the emergent angle thereof is θ i (j), and C1 is an optional real number which is 0. 2 or more and 2.0 or less.