A field lens design of illumination and projection optics for dynamic infrared scene generator based on DMD

Abstract

Dynamic infrared scene generator is an essential means for testing the performance of infrared imaging systems. DMD(Digital Micromirror Device) is widely adopted as spatial light modulator for the dynamic infrared scene generator. We present a new optical architecture for illumination and projection, in which a relatively large aperture lens both contributing focal power in illumination and projection. At present, the rotation of each micromirror array of DMD is limited to ±12 deg. The narrow tilt angle of micromirror of DMD makes it difficult to separate the incident and the reflected light beams when telecentric architecture is applied. A TIR (total internal reflection) prism is commonly introduced to avoid this interference of illumination system and projection system. In this article, a field lens is introduced to replace the TIR prism to do the separation, in respect that the TIR prism for infrared is not available normally and has a great energy loss during the beams travelling through the prism. The matching of exit pupil of illumination and entrance pupil of projection is a basic requirement for DMD illumination and projection system design. This lens reused structure makes exit pupil of illumination and entrance pupil of projection at infinity from the device surface, since we locate the position of stops of illumination and projection system at the focal plane of the field lens. This architecture with fold mirror added could offer a relatively compact optical mechanic structure.