Patent ID: 8094246

Claim:
A polarization conversion device, wherein when either one of a first linearly polarized light beam and a second linearly polarized light beam whose polarization directions are perpendicular to each other is incident, the polarization conversion device converts the one into the other linearly polarized light beam, the polarization conversion device comprising: a prism sheet including a plurality of long-and-narrow rectangular prism elements which are arranged so that edge lines, each of which is formed of a pair of inclined surfaces of the corresponding long-and-narrow rectangular prism element, are parallel to each other and lie in a same plane; and a retardation film that is formed on each inclined surface so that an optical axis of the retardation film matches a normal line of each inclined surface of the rectangular prism element, the retardation film that is formed of a dielectric multilayer which gives a phase difference of a ½ wavelength to light being incident on the prism sheet substantially vertically from a bottom-surface side of the rectangular prism elements and being transmitted through the prism sheet, wherein the rectangular prism elements are arranged so that the edge lines are inclined by about 45° with respect to the polarization direction of the one linearly polarized light beam.