Reflective Planar Optics with Cholesteric Liquid Crystal for Near-Eye Displays

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

High-Precision Beam Angle Expander Based on Polymeric Liquid Crystal Polarization Lenses for LiDAR Applications

A novel beam steering angle expander is demonstrated by cascading two polymeric liquid crystal polarization lenses with different diopters. The lens module performs as a planar telescope, which has features such as a light weight, low cost, and high precision. The magnifier offers wide-angle, continuous steering when integrated with an active fine-angle beam steering device. The potential application for LiDAR is emphasized

High-Precision Beam Angle Expander Based on Polymeric Liquid Crystal Polarization Lenses for LiDAR Applications

A novel beam steering angle expander is demonstrated by cascading two polymeric liquid crystal polarization lenses with different diopters. The lens module performs as a planar telescope, which has features such as a light weight, low cost, and high precision. The magnifier offers wide-angle, continuous steering when integrated with an active fine-angle beam steering device. The potential application for LiDAR is emphasized

Fast-Response Liquid Crystal Phase Modulators with an Excellent Photostability

We report a new mixture, which is modified from Merck TL-216, for liquid-crystal-on-silicon spatial light modulators (SLMs). To achieve 2π phase change at λ = 633 nm with 5 V operation voltage, the measured response time is about 3 ms at 50 °C. Meanwhile, our mixture exhibits no sign of photodegradation and even the total dosage has exceeded 400 MJ/cm2 at a blue laser wavelength λ = 465 nm. In comparison, E7 died at about 30 MJ/cm2. Widespread applications of this material for high brightness SLMs, near-eye displays, and head-up displays are foreseeable

Achromatic diffractive liquid-crystal optics for virtual reality displays

Abstract Diffractive liquid-crystal optics is a promising optical element for virtual reality (VR) and mixed reality as it provides an ultrathin formfactor and lightweight for human factors and ergonomics. However, its severe chromatic aberrations impose a big challenge for full-color display applications. In this study, we demonstrate an achromatic diffractive liquid-crystal device to overcome this longstanding chromatic aberration issue. The proposed device consists of three stacked diffractive liquid crystal optical elements with specifically designed spectral response and polarization selectivity. The concept is validated by both simulations and experiments. Our experimental results show a significant improvement in imaging performance with two types of light engines: a laser projector and an organic light-emitting diode display panel. In addition, our simulation results indicate that the lateral color shift is reduced by ~100 times in comparison with conventional broadband diffractive liquid-crystal lens. Potential applications for VR-enabled metaverse, spatial computing, and digital twins that have found widespread applications in smart tourism, smart education, smart healthcare, smart manufacturing, and smart construction are foreseeable

Submillisecond-Response Polymer Network Liquid Crystal Phase Modulators

A submillisecond-response and light scattering-free polymer-network liquid crystal (PNLC) for infrared spatial light modulators is demonstrated. Our new liquid crystal host exhibits a higher birefringence, comparable dielectric anisotropy, and slightly lower visco-elastic constant than a commonly employed commercial material, HTG-135200. Moreover, the electro-optical performance of our PNLCs with different monomer concentrations, cell gaps, and liquid crystal (LC) hosts is compared and discussed from four aspects: operating voltage, hysteresis, relaxation time, and light scattering loss. The temperature effect on hysteresis is also analyzed. Potential applications of PNLCs for laser beam steering and spatial light modulators especially in the infrared region are foreseeable