Patent ID: 8576486

Claim:
An optical element having an anti-reflection function comprising: a base; and a large number of structures arranged on a surface of the base, the structures being projections or depressions, wherein the structures are arranged in a hexagonal lattice, a quasi-hexagonal lattice, a tetragonal lattice, or a quasi-tetragonal lattice at a pitch shorter than or equal to a wavelength of light in a use environment, wherein an effective refractive index in a depth direction of the structures gradually increases toward the base and has two or more inflection points, wherein at least one pair of a first changing point and a second changing point formed in that order in a direction from the top to the bottom of the structures are formed on a side surface of the structures excluding the top and the bottom, and wherein a slope in the direction from the top to the bottom of the structures becomes gentler at the first changing point and then becomes steeper at the second changing point.