Patent ID: 7859768

Claim:
An optical element comprising in order from a light-entering side: a first layer; a second layer; and a base member, wherein the first layer includes a concavo-convex structure with convex portions and concave portions alternately formed at a pitch smaller than a wavelength λ of entering light, and wherein the second layer satisfies the following conditions: nb · n ⁢ ⁢ s - 0.15 ≤ n ⁢ ⁢ A ≤ nb · n ⁢ ⁢ s + 0.10 λ 8 · n ⁢ ⁢ A ≤ dA ≤ λ n ⁢ ⁢ A where ns represents an effective refractive index of the first layer, nb represents a refractive index of the base member, and nA and dA respectively represent a refractive index and a thickness of the second layer.