Metalens Breakthrough Clears Two Hurdles for Full-Color AR and VR Glasses

Augmented reality (AR) and virtual reality (VR) glasses now stacked with bulky lenses could soon shrink to a single eyeglass-like optical element, after a team at Pohang University of Science and Technology (POSTECH) developed technologies for producing sharp full-color images using metalenses. The findings, published in the journal Nature Communications, address two major hurdles to commercializing metalenses: high optical performance and scalable manufacturing.

A metalens is an ultrathin lens made of densely arranged nanoscale structures that control the path of light, letting it perform in a single flat optical element what conventional optics need multiple stacked glass lenses to do. The central challenge has been achromatic performance — focusing red, green and blue light at the same point without color blur — using low-refractive-index materials that are cheap and suitable for mass production. The POSTECH team solved this by controlling the height of nanoscale pillars called meta-atoms, in addition to their lateral width, letting them precisely focus red, green and blue light at the desired point, much as varying a building's number of floors changes a cityscape even when its footprint stays the same.

In one study, the team directly fabricated complex three-dimensional nanopillars using two-photon lithography, a high-precision 3D printing technique, and used an inverse-design approach to automatically select the best structure for each position on the metalens. The result was a full-color achromatic metalens made from relatively low-cost, low-refractive-index materials, which the team confirmed produced sharp color images when integrated with an OLED display.

A second study focused on mass production: the team fabricated a height-encoded nano-template using grayscale electron-beam lithography and applied it to nanoimprint lithography, a stamping-like replication process, enabling structures of different heights to be replicated at once rather than the uniform-height patterns conventional nanoimprint methods produce. "These studies are significant because they demonstrate manufacturing technologies that could help bring full-color achromatic metalenses for AR and VR displays into practical industrial use through advanced nanofabrication," said Junsuk Rho, who led the research, adding that the technologies could also apply to imaging systems and optical sensors.