Holographic Optical Elements for Augmented Reality: Principles, Present Status, and Future Perspectives
Holographic Optical Elements for Augmented Reality: Principles, Present Status, and Future Perspectives
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DOI：
10.1002/adpr.202000049
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发表时间：
2020-10
期刊：
影响因子：
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通讯作者：
J. Xiong;Kun Yin;Kun Li;Shin‐Tson Wu
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文献类型：
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作者：
J. Xiong;Kun Yin;Kun Li;Shin‐Tson Wu
全息术是指将干涉相干光束的完整波场记录到介质（全息图）中的过程，可以用来再现原始波场。自 Dennis Gabor 于 1948 年发明以来，由于材料和记录方法的进步，记录全息图的质量得到了显着提高。由于波前操纵的独特特性，全息光学元件 (HOE) 在数据存储、太阳聚光、成像和显示领域得到了广泛的应用。最近，增强现实（AR）在学术界和工业界获得了前所未有的研究兴趣，因为它有可能成为下一代显示器，从根本上改变我们的日常生活。 AR的基本概念是将虚拟数字内容与真实周围环境无缝融合。然而，AR 的透视功能以及向观看者的眼睛提供高保真图像的要求，在视场 (FOV)、眼区尺寸、图像对比度和正确聚焦线索的生成等方面对光学设计提出了巨大的挑战。一般来说，具有传统几何光学的AR系统基于部分镜面组合。自由曲面可以用于像差校正并获得更高的图像质量，但系统外形尺寸与FOV和眼箱的乘积之间的权衡仍然是商业化的巨大障碍。最近，由于 HOE 的多样化功能以及设计和材料选择的较大自由度，基于 HOE 的 AR 系统获得了越来越大的发展势头。已经提出了各种系统来解决与焦点提示生成、系统形状因数、FOV 和眼箱尺寸相关的问题。在这篇综述中，我们将首先介绍全息方法和 HOE 形成的基础物理原理。接下来，我们将描述 HOE 的一些独特的光学特性及其功能。之后，我们将简要回顾HOE在几种AR显示系统中的应用，并讨论它们的优缺点。最后，我们将对 AR 显示器 HOE 的未来发展提出一些看法。
Holography refers to the process of recording a complete wave field of interfered coherent beams into a medium (hologram), which can be used to reproduce the original wave field. Since its invention by Dennis Gabor in 1948, the quality of recorded holograms has been dramatically improved due to advancements in materials and recording methodology. As a result of the unique property of wavefront manipulation, holographic optical elements (HOEs) have since found pervasive applications in the fields of data storage, solar concentration, imaging, and display. Lately, augmented reality (AR) has gained unprecedented research interest in both academia and industry because of its potential to become the next-generation display, which could fundamentally transform our daily lives. The basic concept of AR is to seamlessly blend virtual digital contents with real surrounding environments. However, the see-though capability of AR, along with the requirement of delivering high-fidelity images to the viewer’s eyes, poses great challenges to optical designs in terms of field of view (FOV), eye box size, image contrast ratio, and generation of correct focus cues, just to name a few. Generally, AR systems with traditional geometric optics are based on a partialmirror combination. Freeform surfaces can be adopted for aberration correction and achieving higher image quality, but the tradeoff between system form factor and the product of FOV and eye box remains a huge obstacle toward commercialization. Recently, HOE-based AR systems have gained increasing momentum because of the diverse functions of HOEs and large degrees of freedom in design and choice of materials. Various systems have been proposed to resolve the issues related to focus cue generation, system form factor, FOV, and eye box size. In this review, we will first introduce holography methods and the underlying physics of HOE formation. Next, we will describe some unique optical properties of HOEs and their functionalities. After that, we will briefly review the applications of HOEs in several AR display systems and discuss their pros and cons. Finally, we will cast some perspectives on future developments of HOEs for AR displays.