Patent ID: 6896373

Claim:
An optical system for a projection display, comprising: a light source for producing light; a light path switching device having a plurality of modes of operation for receiving and reflecting the light, the plurality of modes comprising at least a first mode for directing the light towards a projection lens of the projection display and a second mode for directing the light away from the projection lens; and a total internal reflection (TIR) prism set disposed between the light path switching device and the projection lens and comprising a first prism, a second prism and a third prism, a first gap being formed between the first prism and the second prism and a second gap being formed between the first prism and the third prism; wherein the light enters the light path switching device by total internal reflection; under the first mode, the light reflected by the light path switching device passes through the first and the second gaps and enters the projection lens; and under the second mode, the light reflected by the light path switching device is totally reflected at the boundary of the second prism near the first gap so that the light reflected by the light path switching device is prevented from reentering the first gap.