Patent ID: 8120848

Claim:
A waveplate comprising: a dielectric substrate; and a periodic structure formed on said dielectric substrate, said periodic structure having a period which is equal to or smaller than a wavelength of an incident light, wherein said periodic structure is constructed of a deposited film, wherein a refractive index of said deposited film gradually changes in a thickness-wise direction of said deposited film, such that the refractive index (1) gradually increases in a first part, extending from a surface of said deposited film to a first intermediate portion of said deposited film, (2) is a constant value equal to a value at the first intermediate portion in a second part, extending between the first intermediate portion and a second intermediate portion of said deposited film, and (3) gradually decreases from the constant value in a third part, extending from the second intermediate portion to an interface of said deposited film with said dielectric substrate, and wherein said deposited film is composed of a composition of SiO 2 and TiO 2 in the first and third parts, said deposited film is composed of TiO 2 in the second part, and the second part is the thickest of the first to third parts.