US Patent 7350928 Projection display system

A projection display system comprises an illumination device, a prism assembly, a projection lens and a reflective light valve. The prism assembly has a first light incident surface, a first light emitting surface and a second light emitting surface. The first light emitting surface is an optical curved surface. An illumination beam is incident on the light valve after it enters the prism assembly from the first light incident surface. A modulated beam is generated after it is processed through the light valve. Finally, the modulated beam is projected into the projection lens through the prism assembly. Because a surface of the prism assembly is set to be an optical curved surface to replace a lens in the projection lens or the illumination device, a back focal length of the system is shortened and the projection lens or the illumination device is simplified.