针对工作在一定入射角度范围内的衍射光学元件, 提出了复合带宽积分平均衍射效率的计算公式。为了满足军用仪器上瞄准镜的光学性能需求, 设计了两个结构参数相同的 50 mm长出瞳距的目镜。目镜系统的焦距为 25 mm, 视场角为 30°, 出瞳直径为 8 mm。基于 Erfle目镜结构形式, 首先设计了一个传统折射式长出瞳距目镜。在此基础上, 引入单层衍射光学元件, 设计了一个折衍射混合式长出瞳距目镜。该混合目镜的畸变小于 7.77%, 在 40 lp/mm处, 中心视场的 MTF(调制传递函数)高于0.85, 最大视场的 MTF高于 0.2。系统中采用的单层衍射光学元件衍射面上的入射角度为 0°～30°, 对应的复合带宽积分平均衍射效率为 95.23%。对比折射式目镜, 折衍射混合目镜不仅成像质量得到改善, 而且总长减小了 22.87%, 重量减轻了 38.79%, 具有结构紧凑、重量轻等特点。

For diffractive optical elements (DOEs) working within a range of incident angles, we propose a formula for comprehensive polychromatic integral diffraction efficiency (PIDE). To satisfy the optical performance requirements of military instruments, two eyepieces with the same structural parameters and 50 mm long exit pupil distance were designed. The focal length of the eyepiece system is 25 mm, field of view is 30°, and the exit pupil diameter is 7 mm. Based on the structure of the Erfle eyepiece, a conventional refractive eyepiece with long exit pupil distance was designed. On the same basis, a refractive-diffractive hybrid eyepiece with long exit pupil distance was designed with a single-layer DOE. The distortion of the hybrid eyepiece was less than 7.77%; at 40 lp/mm, the MTF of the center field of view (FOV) was above 0.85, and MTF of the maximum FOV was above 0.2. The comprehensive PIDE of the single-layer DOE used in the hybrid eyepiece was 95.23%, with the range of incident angle upon the microstructure surface of 0.-30.. Compared with the conventional refractive eyepiece, the refractive-diffractive hybrid eyepiece not only improved the imaging quality, but also reduced the total length by 22.87% and weight by 38.79%, and had the characteristics of compact structure, light weight, and so on.