Liquid crystal light valve image projection system with color selective

Abstract

An optical system is disclosed which incorporates a color selective prepolarizer to improve contrast and reduce stress induced birefringence while allowing a blue mirror to be used to enhance the projected image. The invention includes a source lamp for providing a first beam of unpolarized white light energy; a prepolarizing beam splitter which extracts from the first beam, second and third beams. The second beam contains undesirable color components of a first polarization state, which are removed from the system by reflection to an optical dump. The third beam includes prepolarized light of one color and the first polarization and white light of the second polarization. A main polarizing prism is provided for splitting the third beam into fourth and fifth beams having the first and second polarizing states respectively. The main prism effectively directs the white light to the light valve where it is modulated and returned to the main prism for projection in the conventional manner. The fifth beam being monochromatic and of the first polarization state is directed to the blue mirror where it is filtered to remove residual red and green components, altered in polarization state from the first state to the second state and altered in intensity by a preselected gradient operator before being returned to the main prism for superimposition on the light valve image. The invention includes projection optics for displaying the composite image.