中文摘要：

利用双层衍射元件设计了一款折衍混合投影式头盔光学系统。系统的衍射效率在可见光波段〉90％，提高了像面图像的对比度，增加了色彩真实性。在出瞳距离为25mm，出瞳直径为10mm条件下，系统的视场角为50°，有效焦距为32mm，直径为19．2mm，重量为7．8g，继承了投影式头盔光学系统的轻小性特征；调制传递函数（MTF）在38lp／mm时，边缘视场达到0．3以上，中心视场达到0．6，充分满足2．8cm（1．1in）彩色LCD微显示器的SXGA显示模式；系统垂轴色差为8．2μm，场曲为0．4m^-1，畸变为5％，成像质量满足虚拟环境和可视化训练要求。文中给出了双层衍射元件的二元面特征曲线，每周期刻蚀八个台阶时，最小特征尺寸为6．3μm，且易于加工实现。

英文摘要：

A head-mounted projective optical system with double-layer Diffractive Optical Element （DOE） was designed and the detailed design procedure was given. The diffraction efficiency of the system at each wavelength in designed band is larger than 90%, which improves the image contrast and color reliability significantly. The Field of View （FOV） is 50° while the eye relief and exit pupil size are 25 mm and 10 mm. The features of 19.2 mm system size and 7.8 g overall weight guarantee the lightness and compactness of the optical system. The Modulation Transfer Function （MTF） value at 0° FOV is 0.6 for 38 lp/mm spatial frequency,and more than 0.3 for all FOV, which satisfies the requirement of the color micro-display sized 2.8 cm（1.1 in） diagonal with a SXGA resolution. The lateral color of 8.2μm, field curvature of 0.4 m^-1 and the distortion less than 5% are obtained, which means the designed optical system has good performance in the field of virtual reality and collaborative environments. The phase and line frequency versus aperture of the two binary surfaces are given.When the number of etching levels is eight, the minimum feature sizes of both the diffractive surfaces are 6.3 μm, which is not a very high demand for technique.