Liquid crystal displays (LCDs) and photonic devices play a pivotal role to augmented reality (AR) and virtual reality (VR). The recently emerging high-dynamic-range (HDR) mini-LED backlit LCDs significantly boost the image quality and brightness and reduce the power consumption for VR displays. Such a light engine is particularly attractive for compensating the optical loss of pancake structure to achieve compact and lightweight VR headsets. On the other hand, high-resolution-density, and high-brightness liquid-crystal-on-silicon (LCoS) is a promising image source for the see-through AR displays, especially under high ambient lighting conditions. Meanwhile, the high-speed LCoS spatial light modulators open a new door for holographic displays and focal surface displays. Finally, the ultrathin planar diffractive LC optical elements, such as geometric phase LC grating and lens, have found useful applications in AR and VR for enhancing resolution, widening field-of-view, suppressing chromatic aberrations, creating multiplanes to overcome the vergence-accommodation conflict, and dynamic pupil steering to achieve gaze-matched Maxwellian displays, just to name a few. The operation principles, potential applications, and future challenges of these advanced LC devices will be discussed.

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The structure and hydrogen gas sensing properties of a trench Pd-thin oxide-Si Schottky diode are studied and compared with a planar one. The trench diode possesses additional vertical surface area and a large number of interface traps induced by injected hydrogen ions. The additional vertical surface area enlarges the entrance of H2 molecules, and the generated middle traps enhance the carrier tunneling. Also, the generated shallow traps can catch the carrier to form a thin surface charge layer and lower the barrier. The sensitivity of the trench diode is thus higher than that of the planar diode under room-temperature operation.

Augmented reality (AR) and virtual reality (VR) have the potential to revolutionize the interface between our physical and digital worlds. Recent advances in digital processing, data transmission, optics, and display technologies offer new opportunities for ubiquitous AR/VR applications. The foundation of this revolution is based on AR/VR display systems with high image fidelity, compact formfactor, and high optical efficiency. In this review paper, we start by analyzing the human vision system and the architectures of AR/VR display systems and then manifest the main requirements for the light engines. Next, the working principles of six display light engines, namely transmissive liquid crystal display, reflective liquid-crystal-on-silicon microdisplay, digital light processing microdisplay, micro light-emitting-diode microdisplay, organic light-emitting-diode microdisplay, and laser beam scanning displays, are introduced. According to the characteristics of these light engines, the perspectives and challenges of each display technology are analyzed through five performance metrics, namely resolution density, response time, efficiency/brightness/lifetime, dynamic range, and compactness. Finally, potential solutions to overcoming these challenges are discussed.

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In this paper, we present our effort in developing an opensource GPU (graphics processing units) code library for the MATLAB Image Processing Toolbox (IPT). We ported a dozen of representative functions from IPT and based on their inherent characteristics, we grouped these functions into four categories: data independent, data sharing, algorithm dependent and data dependent. For each category, we present a detailed case study, which reveals interesting insights on how to efficiently optimize the code for GPUs and highlight performance-critical hardware features, some of which have not been well explored in existing literature. Our results show drastic speedups for the functions in the data-independent or data-sharing category by leveraging hardware support judiciously; and moderate speedups for those in the algorithm-dependent category by careful algorithm selection and parallelization. For the functions in the last category, finegrain synchronization and data-dependency requirements are the main obstacles to an efficient implementation on GPUs.

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