Patent ID: 8226250

Claim:
An optical element comprising: a base member configured to have an optical surface; a concave-convex structure configured to have an average pitch smaller than a shortest wavelength of a use wavelength range; and an intermediate layer formed between the optical surface and the concave-convex structure, made of a material different from that of the concave-convex structure, and having a refractive index between a refractive index of the base member and a refractive index of the material of the concave-convex structure, wherein the optical surface is formed into a shape having a rotational symmetry axis, wherein a thickness of the intermediate layer or each of thicknesses of the intermediate layer and the concave-convex structure varies so as to increase as a distance from the rotational symmetry axis increases, and wherein the optical element satisfies the following condition for θ(h) that satisfies a condition of 0.3≦n×sin(θ(h))<1: Dc<D ( h )< Dc /cos(θ( h )) where Dc represents the thickness of the intermediate layer at a position of the rotational symmetry axis, n represents the refractive index of the intermediate layer, D(h) represents the thickness of the intermediate layer at a h-position away from the rotational symmetry axis by a distance h, and θ(h) represents an angle that a light ray reaching the intermediate layer at the h-position in parallel with the rotational symmetry axis forms in the intermediate layer with a normal to a concave-convex structure-side most superficial surface of the intermediate layer at the h-position.