Polarization conversion device, polarized illumination optical device, and liquid crystal projector

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:

• two polarization conversion elements each of which includes
• 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 which is formed of a dielectric multilayer which gives a phase difference of a ¼ 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 polarization conversion elements are arranged so that the edge lines are parallel to each other and are inclined by about 45° with respect to the polarization direction of the one linearly polarized light beam.

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:

• two polarization conversion elements each of which includes
• 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 polarization conversion elements each of which formed of a dielectric multilayer which gives a phase difference of a ¼ 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
• one of the polarization conversion elements is arranged so that the edge lines of the one of the polarization conversion elements are inclined by an angle θ1 with respect to the polarization direction of the one linearly polarized light beam,
• the other polarization conversion element is arranged so that the edge lines of the other polarization conversion element are inclined by an angle θ2 with respect to the polarization direction of the one linearly polarized light beam, and
• 2×(θ1−θ2) is substantially equal to 90°.