Methods of Enhancing Optical Performance in AR & VR: Dynamic Range and Image Quality

Abstract

With rapid development and commercialization of consumer head mounted displays (HMDs), developing compact, light-weighted HMDs while maintaining high image performances and visual comforts becomes a critical task. In HMDs, the display engine, optical combiner and viewing optics are the imaging and optical backbones of HMDs, and are the most important elements affecting the image quality and performance. The display engine renders the virtual image contents seen by the eye. Its parameters directly affect the rendered image performance and fidelity, such as resolution, frame rate, and dynamic range. The optical combiner is to couple the displayed virtual image with the real world scene. A well-designed optical combiner can provide high efficiency, high uniformity images with correct depths for both virtual image and see-through scenes. The viewing optics is a bridge between the display engine and the optical combiner, which magnifies the image from the display engine and couples the image into the optical combiner. Its image quality is also important to the image contrast, resolution and brightness. In this dissertation, we presented our methods of improving the optical performance for each of the mentioned optical elements. For the display engine, we aim to improve its dynamic range by adopting a dual-layer modulation method. A systematic approach regarding to the design, calibration, and rendering algorithm is presented. To solve the vergence-accommodation conflict (VAC) in a lightguide-based system, we studied the image performance and artifacts when the image focal depth is deviated from its preferred infinitely-collimated depth. For the optical combiner, a method of designing a micro-structural mirror array geometrical lightguide with optimal optical efficiency, uniformity and minimal stray light is demonstrated. For the viewing optics, a method of designing a monolithic freeform prism as an image collimator is presented. It is much more compact compared with the traditional viewing optics, while maintaining high image quality.