Physical problems of diffraction waveguide used in large field of view

Abstract

Diffraction gratings have been widely used in waveguides. They can transmit light beams or images from the in-coupling end to the out-coupling end at predetermined positions. However, when they are applied to augmented reality and virtual reality with large field of view and color light sources, there will arise some problems such as mismatch and missing field of view, non-uniform emission, and others. Therefore, starting from these physical problems, the upper limit of the field of view for diffractive waveguide and the complete theoretical boundary formula of the field of view are derived, and on this basis, in-depth research is conducted on monochromatic waves and multicolor waves, respectively. It is concluded that the single-layer diffractive waveguide supports the theoretical upper limit of the monochromatic wave field angle of about 48° under normal high refractive index of <i>n</i> = 1.75, and supports the theoretical upper limit of the multicolor wave field angle of 26.4° for coefficient <i>q</i> = 1.3. Clearly, a larger field of view requires a higher refractive index <i>n</i> and a smaller <i>q</i> value. The boundary conditions of field integrity indicate that reducing the maximum diffraction angle of the long wave and thinning the thickness of the waveguide layer can solve the problem of missing field of view. The practical maximum diffraction angle generally does not exceed 75°, and the thickness of the waveguide layer is about 0.5 to 1.0 mm generally based on the incident field of view. Finally, a method of expanding each total internal reflection field of view into a ray tracing diagram and a distribution function of pupils to receive light energy at various angles are obtained. In this way, the optimal position of the out-coupling grating region can be achieved, and the inverse of the distribution function is used to constrain the angular distribution of the projected light or the grating efficiency, and then receiving uniform exit image at any position becomes possible. The uniformity of the monochromatic waveguide increases from 0.27 to 0.15, and the uniformity of the long wave in the single grating multicolor waveguide rises from 0.4 to 0.28. The results of these studies will undoubtedly help to solve the problem in the diffractive waveguides used in large field of view and multicolor light.

Augmented reality system based on full-color holographic optical elements lens

“…显示是一个智能化的人机交互平台，现已进入各个产业。随着显示设备的小 型化和微型化，光学透视型增强现实(AR，Augmented reality)系统逐渐进入大 众的视野中。它将虚拟图像与真实场景的光同时成像到人眼的视网膜上，从而实 现对真实世界理解的"增强" ，其应用方向主要是近眼显示和抬头显示 [1][2][3] 。增强 现实系统同时允许来自真实场景的光和微显示器虚拟图像的光传输到人眼中，实 现更为真实的人机交互界面。由于微显示器不能遮挡人眼，系统需要在人眼之前 放一个透明的光学合束元件，该元件还要产生额外的光焦度实现图像的放大，现 多采用光波导 [4][5][6] 或者自由空间合束 [7,8] 的结构，每种技术路线都需要对系统参数 进行权衡 [9] 。目前研究较多的技术路线是基于光波导的近眼显示系统，它将光限 制在一个厚度为数毫米的平板玻璃内传输到人眼中，更容易做成眼镜的形状，其 原理如图 1 所示 [10,11] 。 图 1 光波导 AR 显示系统原理示意图 Fig. 1.…”