结合面型和视场优化策略的自由曲面设计方法

为了增大光学系统的视场，针对含有自由曲面的离轴反射式光学系统设计，提出了一种面型优化策略和视场优化策略相结合的优化设计方法。该方法从小视场出发，以表征光学系统波像差的Zernike标准多项式各项系数为评价依据，确定像差分量优化顺序，有针对性地选取和优化XY多项式项系数；计算各视场波像差在全视场波像差的占比，据此调整各视场的优化权重。在小视场范围内优化获得满足光学系统性能指标的结构参数后，逐步拓展视场范围，交替使用面型和视场优化策略，实现全视场范围内光学系统的优化设计。应用该方法设计焦距1 200 mm、F数为12、视场303的含有自由曲面的离轴三反光学系统，仅通过优化15项XY多项式系数表征自由曲面，设计结果接近衍射极限，且有利于指导更宽视场的自由曲面光学系统设计。

Freeform surface design method combined with surface and field-of-view optimization

An optimization design method combining surface optimization strategy and field-of-view optimization strategy was presented for expanding the field-of-views, which is used for the design of off-axis reflective optical system with freeform surface. Based on the coefficients of Zernike standard polynomials representing the wavefront error of the optical system, sequence of the aberration was determined. The optimization procedure was implemented in small field-of-views to achieve satisfied results, and then the field-of-view was expanded gradually, and the optimization steps were repeated. At last, the optical system structure parameters were got for the full field-of-views. With proper XY polynomial terms as well as optimization weight of different field-of-views selected and optimized, an F-12 off-axis three-mirror system was designed with 1 200 mm focal length and 303 field-of-view, in which, only 15 XY polynomials terms were adopted for the freeform surface. The imaging quality of the system is close to the diffraction limit that meets application requirements. This method can also guide the design of optical systems with freeform surface and larger field-of-view.