High-contrast ratio and high-efficiency anamorphic DLP illumination system design with a freeform surface lens

In this paper, an anamorphic digital light processing illumination system design with a freeform surface lens is described. A lens with a freeform surface lens is combined with the achromatic total internal reflection prism set for application in a relay lens system. In order to achieve a high contrast ratio without sacrificing illumination system efficiency, the novel, to the best of our knowledge, design uses an x-y polynomial surface for the freeform surface lens to reduce the overlap angle of the anamorphic angular distribution in angular space. Moreover, there is no need to use a baffle at the aperture stop in this novel design. We can reach a half-cone angle of 17.49° in the y direction of the angular distribution in angular space. The overlap angle is only 0.98°. Finally, with this novel design, we can achieve a high contrast ratio of 9128:1 and an illumination system efficiency is 66.4%. The four-corner average spot size at the active area of the digital micromirror device chip is controlled at about 240 µm, and the optical distortion is less than 1%. The corresponding lateral color aberration is 3.61 µm.