二维大视场离轴反射式光学系统设计

Optical design of the off-axis reflective system with wide fov

宽视场光学成像系统可以增大光学遥感器观测范围、提高探测效率。近年来,基于自由曲面的光学系统设计和制造取得了重大进展,为设计大视场、大相对孔径、高分辨率、高成像质量、无遮挡离轴反射系统提供了可能性。首先,分析了大视场离轴反射系统的像差特性,指出当不断增加系统视场角,尤其是子午方向视场角时,与视场相关的非对称高级像差量将剧烈增加;像场连续性要求更加凸显。接着,提出了一种二维大视场长焦距离轴光学系统设计方法:在常规光学系统初始结构基础上,采用多重结构形式,使子午方向视场角离散化,光学系统特定曲面分解为两个子曲面;并构建系统约束条件,通过约束系统外形尺寸、优化系统结构形式进而完成系统优化设计。最后,基于提出的方法,设计了一款焦距为1000 mm,像方F数为10,视场角为40°×16°的自由曲面离轴四反光学系统。设计结果表明:该系统全视场范围内成像质量较好,50 lp/mm的特征频率下,400~750 nm可见光波段内光学调制传递函数优于0.26,证明该方法切实有效。

Generally,the observation ranges and detection efficiencies of optical remote sensors can be en⁃hanced using wide-field optical imaging systems.Accordingly,the design and manufacturing of freeformsurface-based optical systems have achieved significant progress recently,making the construction of widefield,rapid,higher-quality-resolution and-imaging,and obstacle-free off-axis reflection systems feasible.The first part of this paper presents a detailed analysis of the aberration characteristics of an off-axis reflec⁃tion system.This asymmetric higher level aberration increases dramatically as the field of view(FOV),specifically the meridional FOV,of the system increases.These characteristics place a prominent require⁃ment on image field continuity.The second part of this paper presents a new design approach for two-di⁃mensional(2-D)large FOV optical systems with long focal lengths.First,we built multiple structural forms based on conventional optical systems,leading to a discretized meridional field angle,and with certain specific surfaces of the optical system decomposed into two sub-surfaces.Following this,system optimi⁃zation was achieved by constraining the system size and improving its structural form.Finally,we designed the off-axis reflective freeform surface optical system.The imaging quality was good within the entire FOV,realizing 2-D large-field imaging of 40°×16°,a focal length of 1 m,and an F-number of 10.The test results prove that the proposed design is good,yielding an optical modulation transfer function of better than 0.26,particularly in the visible spectrum of 400-750 nm with a characteristic frequency of 50 lp/mm.