An official website of the United States government
Recently, augmented reality (AR) displays have attracted considerable attention due to the highly immersive and realistic viewer experience they can provide. One key challenge of AR displays is the fundamental trade-off between the extent of the field-of-view (FOV) and the size of the eyebox, set by the conservation of etendue sets this trade-off. Exit-pupil expansion (EPE) is one possible solution to this problem. However, it comes at the cost of distributing light over a larger area, decreasing the overall system's brightness. In this work, we show that the geometry of the waveguide and the in-coupler sets a fundamental limit on how efficient the combiner can be for a given FOV. This limit can be used as a tool for waveguide designers to benchmark the in-coupling efficiency of their in-coupler gratings. We design a metasurface-based grating (metagrating) and a commonly used SRG as in-couplers using the derived limit to guide optimization. We then compare the diffractive efficiencies of the two types of in-couplers to the theoretical efficiency limit. For our chosen waveguide geometry, the metagrating's 28% efficiency surpasses the SRG's 20% efficiency and nearly matches the geometry-based limit of 29% due to the superior angular response control of metasurfaces compared to SRGs. This work provides new insight into the efficiency limit of waveguide-based combiners and paves a novel path toward implementing metasurfaces in efficient waveguide AR displays.
more »
« less
This content will become publicly available on December 1, 2026
Design and experimental validation of a high-efficiency multi-zone metasurface waveguide in-coupler
Augmented reality waveguide displays often suffer from low efficiency, inherently caused by losses from multiple interactions of incoming light with the in-coupler. These losses impose a fundamental limitation on system brightness and lead to field-dependent losses (i.e., losses that depend on the angle of incidence on the in-coupler). While previous theoretical work established the field-dependent in-coupling efficiency limit and introduced a multi-zone in-coupler architecture, that analysis was based on idealized assumptions. We present the first experimental realization, design optimization, and rigorous validation of a three-zone metasurface in-coupler that approaches the theoretical efficiency limit for a given waveguide geometry under realistic operating conditions. Each metasurface zone is individually optimized using rigorous coupled-wave analysis, guided by a custom feedback loop that incorporates realistic diffraction efficiency targets based on simulated metasurface performance. This optimization process was adapted to include real-world factors like material loss and non-ideal coupling efficiency sums. The metasurfaces are fabricated using atomic layer deposition and are experimentally characterized via diffraction and reflection measurements. The simulated field-dependent in-coupling efficiency across the horizontal field agrees well with the measured efficiency, confirming the validity of our multi-zone optimization strategy for practical device engineering. This study exemplifies the practical feasibility of metasurface-based in-couplers for waveguide displays and establishes a critical, experimentally proven pathway toward high-efficiency augmented reality displays, directly addressing the input coupling efficiency bottleneck.
more »
« less
- PAR ID:
- 10698471
- Publisher / Repository:
- Optical Materials Express
- Date Published:
- Journal Name:
- Optical Materials Express
- Volume:
- 15
- Issue:
- 12
- ISSN:
- 2159-3930
- Page Range / eLocation ID:
- 3129
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Augmented reality (AR) devices, as smart glasses, enable users to see both the real world and virtual images simultaneously, contributing to an immersive experience in interactions and visualization. Recently, to reduce the size and weight of smart glasses, waveguides incorporating holographic optical elements in the form of advanced grating structures have been utilized to provide light-weight solutions instead of bulky helmet-type headsets. However current waveguide displays often have limited display resolution, efficiency and field-of-view, with complex multi-step fabrication processes of lower yield. In addition, current AR displays often have vergence-accommodation conflict in the augmented and virtual images, resulting in focusing-visual fatigue and eye strain. Here we report metasurface optical elements designed and experimentally implemented as a platform solution to overcome these limitations. Through careful dispersion control in the excited propagation and diffraction modes, we design and implement our high-resolution full-color prototype, via the combination of analytical–numerical simulations, nanofabrication and device measurements. With the metasurface control of the light propagation, our prototype device achieves a 1080-pixel resolution, a field-of-view more than 40°, an overall input–output efficiency more than 1%, and addresses the vergence-accommodation conflict through our focal-free implementation. Furthermore, our AR waveguide is achieved in a single metasurface-waveguide layer, aiding the scalability and process yield control.more » « less
-
Three-dimensional (3D) vision in augmented reality (AR) displays can enable highly immersive and realistic viewer experience, hence, attracts much attention. Most current approaches create 3D vision by projecting stereoscopic images to different eyes using two separate projection systems, which are inevitably bulky for wearable devices. Here, we propose a compact stereo waveguide AR display system using a single piece of thin flat glass integrated with a polarization-multiplexed metagrating in-coupler and two diffractive grating out-couplers. Incident light of opposite circular polarization states carrying stereoscopic images are first steered by the metagrating in-coupler to opposite propagation directions in the flat glass waveguide, subsequently extracted by the diffractive grating out-couplers, and finally received by different eyes, forming 3D stereo vision. Experimentally, we fabricated a display prototype and demonstrated independent projection of two polarization-multiplexed stereoscopic images.more » « less
-
Kress, Bernard C; Peroz, Christophe (Ed.)The creation of new see-through near-eye displays (NEDs) architectures is a topic of intense research focus. A fundamental problem that each design must address is the field of view (FOV) and eyebox of NEDs are limited by etendue conservation for a fixed display optics size. Waveguide architecture provides the solution to increasing the eyebox in NEDs without increasing the optics size through exit pupil expansion. Brightness and uniformity are two key features of waveguide architecture. In this work, we focus on the brightness of the waveguide since the image uniformity can be compensated by the display engine. We show that the geometry of the waveguide sets a fundamental limit on the in-coupling efficiency for a given FOV. This limit can be used as a tool for waveguide designers to benchmark the in-coupling efficiency of their incoupler gratings. With this derived limit, we designed and optimized a metasurface-based grating (metagrating) and a surface relief grating (SRG) as in-couplers. The diffractive efficiencies of the two types of in-couplers were then compared to the theoretical efficiency limit. The metagrating's 28% efficiency surpasses the SRG's 20% efficiency and nearly matches the geometry-based limit of 29% due to the superior angular response control of metasurfaces compared to SRGs. This work provides a new understanding of the brightness efficiency limit of waveguide-based combiners and paves a novel path toward implementing metasurfaces in efficient waveguide AR displays.more » « less
-
Waveguide combiners for augmented reality are a popular architecture because they can remain compact while delivering a large etendue to the user. Waveguides propagate light via total internal reflection, passing light from the display engine to the user through the substrate itself. While the operating principles are straightforward, the design is much more complex, with thousands of possible paths for light inside the glass. We introduce a method for simulating light propagation through the waveguide based on beam interactions with surfaces rather than non-sequential ray tracing. This method calculates spatial efficiency one hundred times faster than non-sequential ray tracing. It can also calculate how the waveguide affects image quality at any eyebox position using clipped beams to obtain the modulation transfer function. We also introduce a targeted optimization approach, making optimization faster and more effective. This approach localizes the optimization for each field to only those parts of the waveguide that contribute to the eyebox, mitigating losses of light that are unnecessarily out-coupled elsewhere. Using this method, we optimize an L-shaped waveguide and a crossed-grating waveguide using target diffraction efficiency values as variables and efficiency, uniformity, and image quality as optimization goals. In this ideal case, we quadruple the L-shaped waveguide's efficiency and double the crossed-grating waveguide's efficiency compared to similar designs in other work.more » « less
