Optical system for projection displays using spatial light modulators

Abstract

An optical system for a projection display employing three reflective spatial light modulations (SLM's) is described. Two or the three SLM imaging paths employ typical image combining and projection optical techniques. However, the third SLM imaging path employs a relay lens to produce an intermediate image of the SLM which is subsequently combined with the other two images. Each color component is directed onto one of three SLM's, each through its own polarizing beamsplitter (PBS) cube. In two of the three SLM's, image forming light is reflected from each SLM and passes through its respective PBS, and the two colors are then recombined using a dichroic coating. A lens then images the two-color image, and projects it onto a screens. The third SLM traverses a completely separate path. In this case, the image forming light reflected by the SLM and passing through the PBS is first imaged by a relay lens of approximately unity magnification to produce an intermediate image plane. This intermediate image (of the third colors SLM) is then recombined with the first two color images using PBS or a dichroic coating. The recombination is accomplished in a manner that ensures that the three color images are located at the back focal distance of the projection lens.