A see-through Maxwellian display with aberration-free pupil steering is proposed and experimentally demonstrated. The system uses a polarization-dependent off-axis lens coupler set fabricated with cholesteric liquid crystal. Electrically addressable polarization converters are used to switch among pupils.
A glasses-like augmented reality (AR) display with an extended field-of-view (FOV) using a liquid crystal polarization-dependent combiner (PDC) is proposed. The novel PDC consists of two polarization-selective volume lenses (PVLs) that can control the beam path depending on the polarization states. The viewing angle limited by the system etendue can be extended twice. Besides, the PVL is based on patterned liquid crystal which can be thin and flat. The proposed configuration provides a promising solution for the limited FOV issue in glasses-like AR displays.
Virtual reality (VR) systems bring fantastic immersive experiences to users in multiple fields. However, the performance of VR displays is still troubled by several factors, including inadequate resolution, noticeable chromatic aberration, and low optical efficiency. Pancharatnam-Berry phase optical element (PBOE) exhibits several advantages, such as high efficiency, simple fabrication process, compact, and lightweight, which is an excellent candidate for VR systems. We have demonstrated that by using three kinds of PBOEs, the above-mentioned problems can be solved satisfactorily. The first PBOE is PB grating/deflector (PBD), which can deflect the left-handed and the right-handed circularly polarized beams to two opposite directions. Therefore, if we insert a PBD to the VR system and carefully design the deflection angle, it can optically separate each display pixel into two virtual pixels and superimpose them to obtain a higher pixel density. In this way, the pixel per inch (PPI) of the original display can be doubled. The second PBOE is PB lens (PBL). As one kind of diffractive optical lenses, it has an opposite chromatic dispersion to that of a refractive lens. When a PBL with an appropriate focal length is hybridized with a refractive Fresnel lens, the system’s chromatic aberration can be significantly reduced. The third PBOE is multi-domain PB lens. The effective focal length of each domain can be customized independently. This multi-domain PBL can function as a diffractive deflection film in the VR system. If such a diffractive deflection film is cooperated with a directional backlight, the etendue wasting can be reduced prominently, and more than doubled optical efficiency can be achieved in both Fresnel and “Pancake” VR systems. These ultrathin PBOEs will find promising applications in future VR systems
Liquid crystal-based reflective polarization volume gratings (PVGs), also known as a linear Bragg–Berry phase optical element or a member of volume Bragg gratings (VBGs), is a functional planar structure with a patterned orientation of optical axis. Due to the strong polarization selectivity, nearly 100% diffraction efficiency, large diffraction angle, and simple fabrication process, PVGs have found potential applications in novel photonic devices and emerging near-eye displays. In this work, we start from the operation principles and liquid crystal configurations to discuss the optical properties, including diffraction efficiency, angular and spectral response, and polarization state of the diffracted light. Specifically, we emphasize promising applications of PVGs for near-eye displays and novel photonic devices. Through analyzing the functionalities of PVGs with simulations, PVG-based novel devices are proposed. We further develop polarization volume lenses (PVLs) with high diffraction efficiency, low f/#, and large diffraction angles. Previously reported planar lenses are of thin form factor but with on-axis imaging and large f/#. By patterning PVGs with parabolic phase, the obtained PVLs exhibit a small f/#, high diffraction efficiency, and large off-axis diffraction angle. The PVLs offer a new design for near-eye systems, especially for augmented reality (AR) displays. Based on PVLs, we propose a new multi-focal-plane AR system with a polarization multiplexing method to eliminate the vergence-accommodation conflict.
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