US Patent 7532261 Projection system with polarization direction rotating member

An exemplary projection system includes a light source unit, a polarization direction rotating member, a polarization direction restoration polarizer, an LCD panel, and a projection lens. The light source unit is configured for emitting polarized light with a first polarization direction along an axis. The polarization direction rotating member includes a solid body and a through hole defined in the solid body. The polarized light has a first portion incident on the solid body and a second portion passing through the through hole. The polarization direction rotating member is configured for rotating the first polarization direction of the first portion to a second polarization direction and allowing the second portion to pass the through hole with the first polarization direction kept unchanged. The polarization direction restoration polarizer is configured for changing the second polarization direction of the first portion to the first polarization direction.