温度对红外光学系统的影响分析及消热差设计

Influence of temperature on infrared optical system and athermal design

分析了温度对红外光学系统结构参数的影响,计算了温度变化引起系统的离焦量和调制传递函数,给出了红外光学系统消热差设计的基本原理;利用ZEMAX光学设计分析软件,结合实际的长波红外光学系统,分析其在20℃,-40℃和60℃时的成像质量。分析结果表明,该系统在常温时成像质量接近衍射极限,系统全视场调制传递函数在特征频率20 lp/mm处达0.6,87.6%的能量集中在探测器的一个像元内,成像质量优良;但是当温度在-40~60℃变化时,系统成像质量急剧恶化,不再满足使用要求,在分析的基础上采用折衍射混合光学被动式消热差技术中对其进行进一步设计,经消热差设计后该红外光学系统的成像质量得到了极大的改善,全视场调制传递函数在特征频率20 lp/mm处达0.55以上,且能量分布集中,满足红外探测系统的使用要求。

The influence of temperature changes on infrared optical system structure parameters was analyzed. The defocusing distance and modulation transfer function（ MTF） caused by temperature shift were calculated. The theoretical basis of athermal design for infrared optical system was given. Based on a factual long-wave infrared optical system,the imaging qualities at the working temperature of 20 ℃,-40 ℃ and 60 ℃ were analyzed by ZEMAX. The analytic results show that the image quality of the system approaches the diffraction limit at the working temperature of 20 ℃. The MTF is greater than 0. 6 in the whole field of view when the Nyquist frequency of detector is 20 lp / mm,and 87. 6% of the diffraction energy is focused in a single pixel,and the imaging quality of the system is good. However,the imaging quality decreases seriously at the working temperature of-40 ℃ to 60 ℃,so the system can＇t satisfy the design requirement.Based on the above analysis,the infrared optical system was redesigned by optical passive athermal with hybrid refractive / diffractive. The imaging quality of this infrared optical system is greatly improved after athermal design. The MTF is greater than 0. 55 in the whole field of view when the Nyquist frequency of detector is 20 lp / mm,and the energy distribution is very concentrated,which can meet the requirements of infrared detection system.