Optical design of MWIR/LWIR scene projector with hamonic diffraction element

For the requirements of performance testing and evaluation of IR guidence system which works in dual-bands of MW/LW, a DMD based dual-bands infrared scene simulation system was designed, including a projection lens and illumination optical system. The aberration characteristics and design methods of the IR dual-bands projection system with long exit pupil relief and back focal length were discussed. An inverted-telephoto structure with a harmony diffraction surface was used to solve the aberrations such as coma, astigmatism, distortion and chromatic aberration which were difficult to balance. In the design of the illumination system, directly irradiation combined with the Khler illumination principle was adopted to achieve a uniform illumination in the case of oblique incidence, also the improvement of light energy utilization and suppression of the stray light as well. The designed IR MW/LW scene simulator has a full field of view of 5, F# of 2.4, and exit pupil relief of 190 mm. The distortion of the lens is less than 0.1%. At the Nyquist frequency of 36 lp/mm, the modulation transfer function(MTF) is higher than 0.4 in the band of MWIR; at the intermediate frequency of 20 lp/mm, the MTF is higher than 0.38 in the band of LWIR, at every field of view. The relative illumination is higher than 98.5%, which meets the requirement of the scene simulation.