Waveguide-based augmented reality displays: perspectives and challenges

Abstract

Augmented reality (AR) displays, as the next generation platform for spatial computing and digital twins, enable users to view digital images superimposed on real-world environment, fostering a deeper level of human-digital interactions. However, as a critical element in an AR system, optical combiners face unprecedented challenges to match the exceptional performance requirements of human vision system while keeping the headset ultracompact and lightweight. After decades of extensive device and material research efforts, and heavy investment in manufacturing technologies, several promising waveguide combiners have been developed. In this review paper, we focus on the perspectives and challenges of optical waveguide combiners for AR displays. We will begin by introducing the basic device structures and operation principles of different AR architectures, and then delve into different waveguide combiners, including geometric and diffractive waveguide combiners. Some commonly used in-couplers and out-couplers, such as prisms, mirrors, surface relief gratings, volume holographic gratings, polarization volume gratings, and metasurface-based couplers, will be discussed, and their properties analyzed in detail. Additionally, we will explore recent advances in waveguide combiner design and modeling, such as exit pupil expansion, wide field of view, geometric architectures of waveguide couplers, full-color propagation, and brightness and color uniformity optimization. Finally, we will discuss the bottlenecks and future development trends in waveguide combiner technologies. The objective of this review is to provide a comprehensive overview of the current state of waveguide combiner technologies, analyze their pros and cons, and then present the future challenges of AR displays.

On-Chip Meticulous Grayscale High-Resolution Meta-Display

“…In the recent decade, the invention of metasurfaces has exhibited the unprecedented capability of free-space light-field manipulation, − leading to various meta-display functionalities and applications. − More recently, the incorporation of metasurfaces onto optical waveguides has emerged as a compact platform for the manipulation of guided waves, garnering substantial attention and unveiling a progressive avenue of research . Through point-by-point modulating the guided waves along the on-chip scheme, various functionalities and application scenarios based on on-chip integrated metasurfaces have been enabled, including on-chip beam-steering, on-chip metalens, − vortex beam generator, , multiplexed meta-holography, − virtual/augmented reality, − screen display, etc. Thus, this also provides a new avenue to fulfill the increasing requirements of on-chip miniaturization and integration for advanced optical meta-display devices.…”

FOV expansion by polychromatic light source for holographic near-to-eye display

“…Therefore, waveguide combiners become popular due to its advantage of supporting a large pupil by pupil replication to achieve large eye-box while not sacrificing FOV 1 . Surface-relief grating (SRG) 2 , partially reflective mirror array (PRMA) 3 , and holographic optical element (HOE) 4 are the commonly used solutions for the in-and out-coupler for AR waveguide combiners which couple and decouple the projected image into and out of the waveguide. Among these couplers, PRMA usually has relatively low yield rate due to the complicated multi-layer coating process onto each mirror.…”

Recent Applications of Optical Elements in Augmented and Virtual Reality Displays: A Review

“…In this paper, a "waveguide" refers to a thin glass slab, usually 1 mm or less thick, optimized for the exit pupil expansion (EPE) techniques. 34 In the waveguide configuration with the EPE, the light from individual pixels of the display panel is collimated to different angles and delivered to the eye through the waveguide. The spatial information on the display panel is fully transformed into the angular information on the collimated beams.…”