Liquid-crystal polarization volume gratings for near-eye displays

Abstract

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.