基于大视场超短焦离轴光学系统连续自由曲面设计方法的研究

Ultrashort throw projectors allow large screens in very limited space and without concerns about shadows that obstruct the image, which is the development trend of projector industry. However, the technical problems of graph distortion, non-uniform illumination and high cost restrict its industrialization development. The freeform mirror is the core component of ultrashort throw projection systems, and the high performance design method and the corresponding manufacturing technology are the key factors of ultrashort throw projectors to achieve rapid development. Project proposes a kind of continuous freeform design method for off-axis system, which combines non-imaging optics and imaging optics to solve the problems of the distortion of the image edge and the non-uniform illumination in the wide field of view and ultrashort throw imaging system, and reduces the dependence on the initial shape of the freeform surface design. Gridding continuous description method of freeform surface is proposed to avoid the surface shape error caused by the fitting of freeform surface by discretization design, which maximizes the performance of freeform surface. The influence of the surface shape error and assembling error to optical properties of freeform surface is investigated, which improves the freeform surface design theory. The validity of the proposed method is verified by the design and test of a universal ultrashort throw freeform module. The purpose of this project is to establish the design theory of continuous optical freeform surface, which can provide theoretical and technical support for the construction of freeform surface and off-axis complex optical system design.

具有紧凑空间并能避免光线遮挡的超短焦技术是投影光学发展的重要方向，但图形畸变、照度不均匀、成本高的技术难题限制其产业化发展。自由曲面反射面是超短焦成像系统的核心元件，其高性能设计及相应的制造技术是这类超短焦系统得到快速发展的关键。本项目提出一种离轴连续自由曲面设计方法，可实现成像与非成像光学的结合，解决大视场、超短焦成像系统边缘畸变和照度不均匀的设计难题，降低自由曲面设计对初始面型的依赖；研究网格化连续自由曲面空间解构，避免离散化计算拟合自由曲面造成的面形误差，真正发挥自由曲面卓越的光学性能；研究自由曲面面形和装配误差对光学性能的影响规律，完善自由曲面光学系统设计理论；通过具有通用性的超短焦自由曲面模组的设计和测试验证所提方法的正确性。本项目旨在建立连续光学自由曲面设计理论，为满足产业急需的离轴复杂自由曲面构造及系统设计提供理论和技术支撑。

超短焦投影系统可满足小空间的需求，是投影技术发展的趋势。但是，超小的投射比必然造成图像畸变、照度不均匀等问题，采用自由曲面是目前唯一可行的途径。自由曲面的引入，从设计和制造上都增加了难度，其高性能设计及相应的制造技术是这类超短焦系统得到快速发展的关键。.项目提出一种三维离轴网格化自由曲面设计方法，利用主光线作为网格节点，通过控制节点法矢量实现网格单元的光滑连接，保证自由曲面的可加工性，可实现成像与非成像光学的结合，解决大视场、超短焦成像系统边缘畸变和照度不均匀的设计难题，其研究成果对其他离轴三维自由曲面光学系统的设计也具有一定的指导意义。建立了大视场超短焦光学系统的光学模型，以极限投射比为目标，明确超短焦光学系统技术指标的要求；利用自由曲面设计方法实现大视场、超短焦自由曲面反射面的设计；研究自由曲面面形误差和装配误差对光学性能的影响，基于数值计算和光学仿真，建立反射镜参数和短焦性能参数的映射模型，优化自由曲面模组的结构参数；研究光学自由曲面超精密加工方法，实现超短焦投影系统的自由曲面反射镜的超精密制造；完成了超短焦自由曲面投影仪的光学性能测试，包括照度均匀性、畸变、图像分辨率等，验证了自由曲面设计理论的正确性及超短焦方案的可行性。所搭建的超短焦投影系统样机，满足以下参数：视场角＞135°，F数＜2，投射比<0.21，畸变<1%，分辨率MTF＜0.3@92.59lp/mm；照度均匀性>97%。