Nonlocal high-Q metasurface with enhanced color selectivity via topology optimization

We demonstrated a novel topology-optimized nonlocal metasurface that operates simultaneously at red, yellow, green, and blue wavelengths. Nonlocal metasurfaces, exemplified by resonant waveguide gratings (RWGs), spatially and angularly configure optical wavefronts through narrow-band resonant modes, unlike the broadband and broad angle responses of local metasurfaces. However, forward design techniques for RWGs remain constrained in lower efficiency. Our metasurface resonant waveguide grating (MRWG) consists of a topology-optimized titanium dioxide grating on a glass substrate, separating with a titanium dioxide waveguide. As a result, we experimentally demonstrated efficiencies up to 59% with a Q-factor of 93. Additionally, we applied our topology-optimized metasurface to achieve color selectivity, producing vivid colors at 4 narrow-band wavelengths with narrow angle responses.