提出了一种新型无遮拦红外折反射光学系统的设计方法以解决原系统存在的中心遮拦问题。分析了传统离轴两反望远系统由于存在线性像散而无法实现无遮拦设计的原因，给出了消线性像散的条件。基于上述条件提出了通过对接共轴透镜组实现无遮拦折反射系统设计的基本思想。最终，通过联接不同的中继镜组完成了无遮拦中波、长波红外系统的设计。设计的应用于制冷型3~5 μm中波和8~12 μm长波红外的两套无遮拦折反光学系统的焦距为200 mm，F数为2，全视场为2.75°×2.2°。各视场光学传递函数显示设计的光学系统的成像质量接近衍射极限。得到的结果表明，利用消线性像散的共焦离轴两反系统与同轴透镜组联合设计，可以得到高性能无遮拦的折反射红外光学系统。

A new design method for unobsured catadioptric infrared optical systems was presented to avoid the obstruction of traditional catadioptric systems. The linear aberration reasons of conventional off-axis two-mirror telescopes were analyzed. As the unobscured optical system is difficult to be designed because of the linear astigmatism in the off-axis two-mirror telescope, the conditions to eliminate the linear astigmatism were discussed. On the conditions, an design idea of unobsured catadioptric optical systems was proposed through associating with coaxal lenses. By combining different relay lenses, two unobsured catadioptric infrared optical systems were implemented for 3-5 μm MW IR and 8-12 μm LW IR applications. The optical design parameters of the two systems are effective focal length of 200 mm, F=2, and the full field of view of 2.75°×2.2°. The performance of the two systems approaches to diffractive limit from Modulation Transfer Function(MTF) curves of all field of view. The design results show that the high performance unobscured catadioptric infrared optical systems will be obtained by combination of zero linear astigmatism confocal off-axis two-mirror telescopes with coaxal lenses.