基于DMD的目标模拟器应用于长波红外波段(8~12 μm)时, DMD的衍射效应对系统的成像对比度造成较大影响。为使系统获得高对比度的红外图像, 需要对DMD的衍射特性进行分析。首先根据DMD的结构和工作原理, 将DMD等效为一特殊的二维闪耀光栅, 并利用光栅衍射理论和傅里叶变换, 推导出DMD二维光栅衍射模型; 然后利用MATLAB对DMD在8~12 μm波段的衍射模型进行仿真计算; 最后对仿真结果进行了实验验证。通过仿真计算和实验分析得出结论: 基于DMD的目标模拟器应用于长波红外波段时, 照明光束需要选取合适的入射角; 当入射空间方位角为0°, 入射天顶角为44~48°时, 目标模拟器生成的红外图像对比度达到最佳,系统成像质量最好。

Diffraction effects play a significant role in DMD-based scene projection in the long-wave infrared band (8-12 μm). The contrast provided by these projector systems can become noticeably worse because of the diffraction effect of the DMD. So it is necessary to analyze the diffraction characteristics of DMD when it is applied to DMD-based scene projector in this wavelength band. Firstly, DMD was treated as a special blazed grating, and a grating diffraction model of DMD was constructed by diffraction theory and Fourier transform. Then, simulation calculation was conducted in MATLAB environment. Finally, the simulation result was verified by experiment of scene projection. It is shown that there exists a suitable illuminating incident angle range to achieve high contrast image in the long-wave infrared(8-12 μm) band. When incident azimuth angle is 0°and incident zenith angle is between 44°and 48°, the scene projector will have a good imaging contrast.