Quarter-wave plate, and optical pickup device

摘要

A quarter-wave plate includes a base member including a ridge and trough periodic structure with a structural period of λmin/2<P<λmin arranged on one side of the base member, where λmin is the minimum wavelength among the wavelengths of a plurality of light fluxes which pass the quarter-wave plate. In the quarter-wave plate, refractive index of a ridge portion of the ridge and trough periodic structure for the wavelength λmin and a light transmittance have predetermined values. The ridge and trough periodic structure satisfies the predetermined condition relating to the structural height and the structural width of the ridge portion.