Ultra-thin full-colour waveguide for lightweight AR glasses

AR continues to gain traction across sectors including healthcare, education, gaming, and entertainment. Yet, widespread adoption has remained hindered by the physical limitations of current devices – particularly the bulky optics required to display full-colour virtual imagery.

At the heart of the challenge is the waveguide: a critical component that acts as a conduit for light, delivering digital images to the user’s eye. Conventional AR waveguides rely on stacking multiple layers of glass – each handling a different colour (red, green, or blue) – to compensate for chromatic dispersion. This approach significantly increases the thickness and weight of AR headsets, limiting comfort and wearability.

Led by Professor Junsuk Rho, researchers at POSTECH have devised a novel solution: an achromatic metagrating that operates across the full visible spectrum within a single, ultra-thin waveguide layer. Their innovation replaces the traditional multi-layer structure with a precisely engineered array of silicon-nitride (Si₃N₄) nanopillars. These structures were optimised using a stochastic topology algorithm to redirect light with high precision and minimal loss.

The team demonstrated their design in a 500µm-thick waveguide – roughly one-hundredth the diameter of a human hair – producing sharp, vivid full-colour imagery. Crucially, the prototype also maintained a 9mm eyebox, meaning users could move their eyes slightly without losing image clarity.

According to the researchers, the design not only eliminates colour distortion but also surpasses traditional optics in terms of brightness and colour consistency. The simplified structure is expected to ease manufacturing and lower production costs, while reducing device weight to a level comparable with ordinary spectacles.

Professor Rho commented: “This work marks a key milestone for next-generation AR displays. Coupled with scalable, large-area fabrication, it brings commercialisation within reach.”

The study was published in Nature Nanotechnology on 30th April 2025. Co-authored by Seokwoo Kim, Joohoon Kim, and Seokil Moon, the research was carried out across POSTECH’s Departments of Mechanical, Chemical, and Electrical Engineering, along with the Graduate School of Interdisciplinary Bioscience & Bioengineering. The work was conducted in collaboration with Samsung Research’s Visual Team and received support from 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 Programme, and the Mid-Career Researcher Programme.