Patent ID: 8604410

Claim:
A phase plate comprising: a transparent substrate; and a periodic structure that is formed on a substrate surface of the transparent substrate and that has a period of at most a visible light wavelength, wherein the phase plate is configured so as to provide light having a predetermined design wavelength of the visible light wavelength that vertically enters the substrate surface with a phase difference from ¼ wavelength to ¾ wavelength, wherein the periodic structure is configured so as to reduce a volume occupation rate with increasing distance from the transparent substrate in a plane parallel to the substrate surface of the transparent substrate, the periodic structure having a height of at least 200 nm from the substrate surface, and wherein, in a cross section that is parallel to both a period direction of the periodic structure and a normal direction of the substrate surface, an angle between a first direction in which a center of a width of a unit periodic structure at a position closest to the substrate surface is connected with a center of a width of a unit periodic structure at a position farthest from the substrate surface and a normal direction of the substrate surface is from 5 degrees to 30 degrees.