Two-Dimensional Topology Optimized Nonlocal Metasurfaces for Augmented Reality

Metasurfaces have been widely explored in augmented reality (AR) platforms to replace bulky optical components. However, metasurface-based free-space combiners lack spectral multifunctionality capability, limiting the separation between ambient light and display light. While nonlocal metasurfaces offer a potential solution, existing designs typically rely on vertical stacking or spatial multiplexing yet often suffer from reduced efficiency. Here, we demonstrate a topology-optimized nonlocal metasurface that achieves high-<i>Q</i> resonances at RGB wavelengths via first-order reflective diffraction, enabling compact, multifunctional free-space combiners for AR. By introducing two-dimensional design freedom into resonant waveguide gratings, we realize freeform structures with high diffraction efficiencies, narrow spectral bandwidths, and precise wavelength selectivity. Experimental results validate close agreement with simulations, showing vivid color reproduction and a strong suppression of spectral leakage. Integrated into a free-space AR platform, our metasurface achieves high color purity with reduced display power, offering a promising path toward advanced optical displays and spectrally selective photonic systems.