制冷型中/长波红外双波段一体化全反射式光学系统设计

为避免透射式系统存在的色差问题，采用离轴反射式光学系统，在三镜后加分色片，分别成像到中波探测器及长波探测器的焦面上，实现对中波红外和长波红外两个谱段信息的同时成像。该一体化系统由3个离轴反射镜和一个分色片构成，为校正系统像差，三镜采用XY多项式曲面。采用二次成像结构形式，具有100%冷光阑效率。系统F数为2.67，视场角11.4°×1.8°，工作波段为中波3.55~3.93 μm，长波10.3~12.5 μm。中波红外系统MTF平均值大于0.5@25 lp/mm，长波红外系统MTF平均值大于0.4@12.5 lp/mm，采用光学被动式消热差法对光学系统进行温度补偿，温度适应范围为-40℃~+60℃。

Design of Cooled Medium/Long Wave Infrared Dual-band Integrated Reflective Optical System

A three-mirror anastigmatic(TMA) optical system was adopted to prevent chromatic aberration of the refractive system by adding a dichroic beam splitter behind the tertiary mirror to simultaneously implement the image to the MWIR and LWIR detectors. The integrated system included three off-axis mirrors and a dichroic beams plitter. The surface of the tertiary mirror was an XY polynomial freeform surface that could correct system aberrations. The structure of the system was re-imaged with 100% cold shield efficiency. The F-number was 2.67, the full field of view(FOV) was 11.4°×1.8°, the working band is 3.55-3.93 μm for the MWIR channel and 10.3-12.5 μm for the LWIR channel. The modulation transfer function (MTF) average values of MWIR were greater than 0.5 at 25 lp/mm, and the MTF average values of the LWIR were greater than 0.4 at 12.5 lp/mm. The temperature compensation of the optical system was optical passive athermalization. The temperature range was -40℃ to +60℃.