Augmented reality (AR) is quickly becoming an integral part of daily life, from education and healthcare to gaming and entertainment. However, the bulk and weight of AR glasses have made them uncomfortable for extended wear, hampering their widespread adoption. A recent breakthrough from POSTECH promises to address this issue. One of the primary challenges in designing AR glasses is the waveguide, which serves as the optical pathway for projecting virtual images directly to the user's eye. Traditional waveguides suffer from chromatic dispersion, necessitating separate layers for red, green, and blue light—typically requiring three to six stacked glass sheets. This increases both the weight and the thickness of the devices, making them less user-friendly. Professor Junsuk Rho and his team at POSTECH have developed an innovative solution: an achromatic metagrating that can handle all colors in a single glass layer. This design features an array of nanoscale silicon-nitride (SiN) pillars, whose geometry was meticulously optimized using a stochastic topology-optimization algorithm to guide light with maximum efficiency. In experimental tests, the researchers successfully generated vivid full-color images using a waveguide just 500 micrometers thick—about one-hundredth the diameter of a human hair. They also achieved a comfortable 9-millimeter eyebox, ensuring that the images remain sharp even if the user's eyes shift slightly. The new waveguide not only eliminates color blur but also surpasses multilayer optics in terms of brightness and color uniformity. If commercialized, this technology could revolutionize AR glasses, making them as thin and lightweight as regular eyewear. This would significantly reduce user fatigue and lower manufacturing costs due to a simplified production process, bringing us closer to an era of truly everyday AR devices. "This work represents a crucial milestone for the development of next-generation AR displays," Professor Rho noted. "With scalable, large-area fabrication techniques, the commercialization of this technology is now within reach." The study, led by Professor Junsuk Rho and co-authored by Seokwoo Kim, Joohoon Kim, and Seokil Moon, involved interdisciplinary collaboration between POSTECH's departments of Mechanical, Chemical, and Electrical Engineering, as well as the Graduate School of Interdisciplinary Bioscience & Bioengineering. It was also supported by the Visual Team at Samsung Research. The findings were published online in Nature Nanotechnology on April 30, 2025. This research was backed by various funding sources, including POSCO Holdings N.EX.T Impact, Samsung Research, the Ministry of Trade, Industry and Energy's Alchemist Project, the Ministry of Science and ICT's Global Convergence Research Support Program, and the Mid-Career Researcher Program.