针对大屏幕投影显示对成像物镜提出的超短焦、大视场角、超薄化、大相对孔径以及高清晰度等要求，设计了一种新型折反射式超薄投影成像系统。采用TI公司的0.65″数字微反射镜片(DMD)作为空间光调制器，利用非球面反射镜校正畸变并缩短投影距离，然后通过一个折叠反射镜对光路进一步转折来实现超薄化投影显示。系统由5片透射镜片和1片非球面反射镜组成，焦距为2.8 mm，F/#为3.5，最小视场角为55°，最大视场角为78.5°，在投影距离为120 mm时画面尺寸显示为65.2″。设计结果表明：在像面的Nyquist频率处，95%以上视场的MTF＞0.6，最大畸变量为0.8TV%，一个像元尺寸内能量集中度在90%以上。为了进一步验证折反射式超薄投影镜头的性能，加工并组装了原理样机。实验结果表明其图像显示效果良好，能够满足超薄化、低成本、小型批量化生产等设计要求。

A novel ultra-thin refract-reflect projection display system was designed to meet the severe requirements of imaging lens in large screen projection display for ultra-short focal length, larger field of view, ultra-thin, larger relative aperture and higher resolution. A 0.65 inch (16.51 cm) Digital Micromirror Device (DMD) produced by TI Inc. was employed as the spatial light modulator and an aspheric mirror was used to correct distortion and shorten projection distance. Furthermore, a fold mirror was also taken to turn back the optical path to achieve ultra-thin projection display. The system is consisted of five lenses and an aspheric mirror, of which the focal length is 2.8 mm , the F-number is 3.5 and the minimum and the maximum field angles are 55° and 78.5°, respectively. When the projection distance is set to be 120 mm, the screen size can be 65.2 inch (165.6 cm). With the design, it shows that the Modulation Transfer Function(MTF) of over 95% field of view of the system is higher than 0.6 at the Nyquist frequency of the image plane. The maximum distortion is 0.8TV%, and 90% geometric encircled energy in the point target is focused in one pixel. To verify the performance of the ultra-thin refract-reflect projecting lens, a principle prototype was fabricated and assembled. The experimental results show that the system has excellent display performance, and meets the design requirements of ultra-thin, low cost and small-scale mass production.