RETARDATION ELEMENT AND OPTICAL HEAD DEVICE

摘要

A retardation element having three retardation layers that are stacked parallel to each other and have a refractive index anisotropy, in which the retardation and optical axis azimuth of each retardation layer are adjusted to obtain characteristics that the ellipticities at three desired design wavelengths are increased to the peaks near one. The retardation element can be efficiently adapted, for example, to an optical head device for changing linear polarized light of a light source with three different wavelengths to circular polarized light.