Three-dimensional varifocal meta-device for augmented reality display

Augmented reality (AR) displays have revolutionized how we experience virtual content in real-world environments. However, they face significant challenges, particularly the vergence-accommodation conflict (VAC) and limited eyebox size. VAC occurs because traditional AR displays at a fixed focal depth, causing visual discomfort and eye strain. Meanwhile, a small eyebox restricts the viewing area where users can see the full display, requiring precise positioning of the headset.

A team of researchers from Tsinghua University, University of Southern California, Harbin Institute of Technology, and City University of Hong Kong have made a breakthrough in addressing these issues. As reported in PhotoniX, they developed a three-dimensional varifocal meta-device composed of three cascaded metasurfaces with Moiré and off-center Fresnel lens phase profiles. The innovation uses TiO₂ nanopillars with varying diameters arranged on a SiO₂ substrate to create polarization-insensitive metasurfaces. By tuning mutual angles of the metasurfaces, the focal length and lateral position of the focal point can be dynamically adjusted. This enables virtual content to be displayed at different depths and positions without the need for bulky mechanical components. Professor Zihan Geng, corresponding author of the study, said: "Our meta-device provides a lightweight, integrated solution for AR displays that simultaneously addresses the vergence-accommodation conflict and expands the eyebox. This meta-device can form images at arbitrary position in three-dimensional space." The researchers demonstrated their technology by integrating it into an AR display system, successfully projecting virtual objects at different depths and positions. Unlike conventional pupil steering technologies that require bulky mechanical components or complex liquid crystal-based systems, this approach maintains image intensity without significantly increasing system thickness. This advancement brings us closer to more comfortable and immersive AR experiences, with potential applications extending beyond consumer electronics to fields like medical visualization, industrial design, and education. For details, see the original Gold Open Access article by Y. Song et al., "Three-dimensional varifocal meta-device for augmented reality display," PhotoniX 6, 6 (2025), doi: 10.1186/s43074-025-00164-9.