视场大小是评价头盔显示器在虚拟现实等领域的关键性能指标, 为了克服视场增加带来各类像差急剧增大的困难, 提出了一种基于双自由曲面的大视场头盔显示光学系统。首先, 分析了双椭球结构实现大视场与低畸变的基本原理, 指出了其难以校正除畸变以外其他像差的原因。接着, 提出根据系统对称性和光路走向采用竖直方向对称、水平方向不对称的自由曲面反射镜校正离轴像差, 完成了基于双自由曲面反射镜的大视场头盔显示光学系统设计。系统视场范围为106.3°(H)×80°(V), 最大相对畸变为6.97%, 出瞳直径8 mm, 点眼距19 mm。单目系统向外倾斜8°时, 双目视场范围为122.3°(H)×80°(V), 双目重叠视场为90.3°(H)×80°(V), 瞳距在55~71 mm范围内可调节。对系统性能分析结果表明: 相比双椭球结构, 系统成像质量得到较大提高; 视场范围和相对畸变满足虚拟现实领域的应用要求。

Field-of-view(FOV) is the key performance indicator to evaluate a head-mounted display (HMD) in areas such as virtual reality. In order to overcome the difficulties of a sharp increase of optical system aberrations with the increased FOV, a wide FOV HMD optical system with double freeform surfaces was proposed. First, the principles of the double ellipsoid HMD which could achieve large FOV and low distortion were analyzed, and the reason of the aberration correction limitations of the double ellipsoid HMD was pointed out. Then wide FOV HMD optical system with double freeform mirrors was proposed. Two free-form mirrors were used by the new optical system which were symmetrical in vertical direction and asymmetrical in horizontal direction to correct off-axis aberrations brought by increasing FOV. The FOV of the new optical system was 106.3°(H)×80°(V). The maximum relative distortion is 6.97%. The exit pupil diameter was 8 mm and the eye clearance distance was 19 mm. Through tilt outside 8° the binocular FOV was 122.3°(H)×80°(V) and the binocular overlapped FOV was 90.3°(H)×80°(V). The IPD is adjustable within 55-71 mm. The analysis of optical performance indicates that image quality is greatly improved, and the relative distortion and FOV can meet the application requirements of the virtual reality.