By developing a streamlined architecture for waveguide displays for augmented reality (AR), researchers at Pohang University of Science and Technology (POSTECH) aim to take a big weight off the wearers of AR glasses. The weight and bulk of traditional near-eye optical designs for AR make the glasses too heavy and uncomfortable for prolonged wear. This has impeded the widespread adoption of AR, even though many sectors, from health care and education to entertainment and gaming, can benefit from AR technology. One of the hurdles to making AR glasses more ergonomic is the need for multiple waveguide layers to achieve full-color images. In AR optics, the lens also serves as a “highway of light,” guiding virtual images directly to the user’s eye. Due to chromatic dispersion, conventional designs require separate waveguide layers for red, green, and blue light. These layers entail three to six stacked glass sheets, which add both weight and thickness to AR glasses. Augmented reality (AR) glass prototype and experimental results based on metagrating. Courtesy of POSTECH. To eliminate the need for multiple layers, the POSTECH team developed a single-layer waveguide display using achromatic metagratings. The metagratings maintain high-quality projected images by ensuring an achromatic propagation angle within the single waveguide substrate. The achromatic metagratings comprise periodic arrays of rectangular nanostructures made from silicon-nitride (Si3N4). The researchers fine-tuned the geometry of the arrays using a stochastic topology-optimization algorithm to allow light to be steered with maximum efficiency. The arrays guide red, green, and blue light at the same angle. In experiments, the researchers demonstrated the ability of their device to produce full-color images using a 500-µm-thick, single-layer waveguide. The single-layer waveguide substrate reduced the device form factor and weight, while enhancing brightness and color uniformity. The eyebox for the device was 9 mm, a sufficient size to ensure that images remain sharp even if the viewer’s eyes shift slightly. The compact, single-layer waveguide design outperforms multilayer optics in the areas of brightness and color uniformity and erases color blur. This approach could overcome the limitations of traditional AR near-eye optical designs, which rely on multilayer grating couplers that require complex fabrication processes and are too heavy for head-mounted applications. Once commercialized, the new technology could make AR glasses as thin and light as ordinary eyewear, reducing wearer fatigue and trimming manufacturing costs thanks to a simpler process. “This work marks a key milestone for next-generation AR displays,” professor Junsuk Rho said. “Coupled with scalable, large-area fabrication, it brings commercialization within reach.” The research was published in Nature Nanotechnology (www.doi.org/10.1038/s41565-025-01887-3).