Display market has undergone dramatic changes as the near eye displays (NED) are gaining increasing attention because they offer a deeper level of human-computer interaction with the advancement of electronic devices and computer sciences. The NEDs can be presented in two ways: virtual reality (VR) and augmented reality (AR). The former is completely immersive while the latter combines the digital information with the surrounding scenes. Although several VR headsets have been commercialized for consumers and AR products for prosumers because of their high cost, but there is still a long way to go to satisfy the strict requirements of human vision system. For example, the headset design should be ergonomic so that the users are comfortable when wearing it for a long time. It is critically important to maintain a thin form factor and lightweight while improving the viewing performance, including image quality, resolution, field of view, fatigue free, etc. In this dissertation, we focus on improving the viewing performance of AR/VR displays by developing new cholesteric liquid crystal (CLC) based reflective flat optical elements. Firstly, we introduce the basic CLC properties that are relevant to the reflective patterned optical elements. Secondly, we investigate the flat optical elements with patterned CLC structures from several aspects, including the photoalignment mechanism, polarization field generation, and device fabrication. Then we theoretically analyze the optical properties of the patterned CLC devices, providing the spectral and angular responses of the liquid crystal (LC) grating with different birefringence and device thickness. Finally, we explore new applications of these novel patterned CLC devices to address some major challenges in AR and VR displays. More specifically, a chromatic aberration correction method is applied to the pancake VR system based on our fabricated broadband CLC lens. Such a diffractive optical element exhibits an opposite dispersion behavior to the refractive lens. Thus, by combining our diffractive CLC optical element with a Fresnel lens, the chromatic aberration of the VR system is reduced significantly. In addition, a dual-depth AR system using two custom-designed CLC lenses with different optical powers is presented to mitigate the vergence-accommodation conflict (VAC) issue by generating multiple image depths. To address some existing challenges in waveguide-based AR eyeglasses, we propose and develop a switchable polarization volume grating (PVG) enabled by the patterned CLC layer. Some potential applications are demonstrated, including a significantly suppressed rainbow effect, enhanced light efficiency, and expanded field of view. The unique properties and benefits of switchable PVGs is expected to open a new door for AR and VR displays, especially the novel optical systems for waveguide-based AR displays.
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Doctor of Philosophy (Ph.D.)
College of Optics and Photonics
Optics and Photonics
Optics and Photonics
Length of Campus-only Access
Doctoral Dissertation (Open Access)
Li, Yannanqi, "Reflective Planar Optics with Cholesteric Liquid Crystal for Near-Eye Displays" (2023). Electronic Theses and Dissertations, 2020-. 1606.