Patent ID: 6561652
Filing Date: 2003-05-13
Classification: G02B,H04N

Abstract:
A projection system for full colour image display, comprising:a light source for emitting a white light beam and an illumination optical system to direct and collimate the white light beam; a polarizing beam splitter having a non-cubic shape to reflect a particular polarization of the input light; a trichroic prism assembly for separating the three primary colours from the white light beam and for directing the separated light to three valves respectively, the reflective polarization modulating light each light valve producing the corresponding colour image signal; said trichroic prism assembly being used to recombine the reflected light beams; said polarizing beam splitter being used to direct the light beam either back to the light source or to the screen depending on a polarization change imparted by the reflective light valves; a projective lens system to image the light onto a screen and to form a full colour image, wherein said polarizing beam splitter comprises a right angle prism and a trapezoidal prism having a polarizing coating between them, an acute angle of the trapezoidal prism is 74Â±5Â°, which is selected to match a surface of said right angle prism and in that the trichroic prism assembly comprises three prisms, two of them triangle prisms, and the third one being a trapezoidal prism having dichroic coatings coated on the surface between the prisms.