Polarizing prism for panel type liquid crystal display front projector and optical system using the polarizing prism

Claim 1

A polarizing prism for a panel type LCD front projector, comprising: a polarized beam separating prism, beam converting means, and a triangular prism, which in combination provide a first surface for receiving a non-polarized light beam emitted from a light source and collimated into a parallel beam by a reflecting mirror, a second surface being an incidence surface coated with a polarized beam separating coating for separating the incident light into longitudinal and transverse beams in such a manner that the transverse beam with a polarization direction parallel to the second surface reflects from the second surface while the longitudinal beam with a polarization direction perpendicular to the second surface transmits through the second surface, a third surface for reflecting the beam reflected from the second surface, a fourth surface for reflecting the beam reflected from the third surface, the beam converting means for rotating the polarized direction of the beam reflected from the second surface through an angle of 90° prior to being incident on a fifth surface, thereby converting it into a longitudinal beam, the fifth surface for receiving the longitudinal beam transmitted through the second surface and the longitudinal beam transmitted through the beam converting means, the fifth surface being coated with a coating for splitting each incident, longitudinal beam into beams at a ratio of 50:50, a sixth surface for reflecting 50% of the longitudinal beam transmitted through the second surface and then reflected by the fifth surface and 50% of the longitudinal beam transmitted through the beam converting means and then transmitted through the fifth surface, a seventh surface for radiating the remaining 50% of the longitudinal beam transmitted through the second surface and then transmitted through the fifth surface and the remaining 50% of the longitudinal beam transmitted through the beam converting mean and then reflected by the fifth surface onto a color filter, and an eighth surface for radiating the light beam reflected from the sixth surface onto the color filter, whereby light beams respectively passing through the seventh and eighth surfaces have equal intensities; and wherein the triangular prism is for receiving the light beam transmitted through the second surface and transmitting it to the fifth surface.