Ding Yuqiang, Gu Yuchen, Yang Qian, Yang Zhiyong, Huang Yuge, Weng Yishi, Zhang Yuning, Wu Shin-Tson
College of Optics and Photonics, University of Central Florida, Orlando, FL, 32816, USA.
Joint International Research Laboratory of Information Display and Visualization, Southeast University, Nanjing, 210096, China.
Light Sci Appl. 2024 Aug 12;13(1):185. doi: 10.1038/s41377-024-01537-8.
Augmented reality (AR) displays, heralded as the next-generation platform for spatial computing, metaverse, and digital twins, empower users to perceive digital images overlaid with real-world environment, fostering a deeper level of human-digital interactions. With the rapid evolution of couplers, waveguide-based AR displays have streamlined the entire system, boasting a slim form factor and high optical performance. However, challenges persist in the waveguide combiner, including low optical efficiency and poor image uniformity, significantly hindering the long-term usage and user experience. In this paper, we first analyze the root causes of the low optical efficiency and poor uniformity in waveguide-based AR displays. We then discover and elucidate an anomalous polarization conversion phenomenon inherent to polarization volume gratings (PVGs) when the incident light direction does not satisfy the Bragg condition. This new property is effectively leveraged to circumvent the tradeoff between in-coupling efficiency and eyebox uniformity. Through feasibility demonstration experiments, we measure the light leakage in multiple PVGs with varying thicknesses using a laser source and a liquid-crystal-on-silicon light engine. The experiment corroborates the polarization conversion phenomenon, and the results align with simulation well. To explore the potential of such a polarization conversion phenomenon further, we design and simulate a waveguide display with a 50° field of view. Through achieving first-order polarization conversion in a PVG, the in-coupling efficiency and uniformity are improved by 2 times and 2.3 times, respectively, compared to conventional couplers. This groundbreaking discovery holds immense potential for revolutionizing next-generation waveguide-based AR displays, promising a higher efficiency and superior image uniformity.
增强现实（AR）显示器被誉为空间计算、元宇宙和数字孪生的下一代平台，它使用户能够感知叠加在现实世界环境上的数字图像，促进了更深层次的人机数字交互。随着耦合器的快速发展，基于波导的AR显示器简化了整个系统，具有纤薄的外形和高光学性能。然而，波导组合器仍存在挑战，包括低光学效率和图像均匀性差，这严重阻碍了其长期使用和用户体验。在本文中，我们首先分析了基于波导的AR显示器中光学效率低和均匀性差的根本原因。然后，我们发现并阐明了偏振体光栅（PVG）在入射光方向不满足布拉格条件时固有的异常偏振转换现象。这一新特性被有效地利用来规避耦合效率和视场均匀性之间的权衡。通过可行性演示实验，我们使用激光源和硅基液晶光引擎测量了不同厚度的多个PVG中的光泄漏。实验证实了偏振转换现象，结果与模拟结果吻合良好。为了进一步探索这种偏振转换现象的潜力，我们设计并模拟了一个视野为50°的波导显示器。通过在PVG中实现一阶偏振转换，与传统耦合器相比，耦合效率和均匀性分别提高了2倍和2.3倍。这一开创性的发现对于革新下一代基于波导的AR显示器具有巨大潜力，有望实现更高的效率和卓越的图像均匀性。
