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. Here, we present a topology-optimized metasurface resonant waveguide grating (MRWG) composed of titanium dioxide on a glass substrate, capable of operating simultaneously at red, yellow, green, and blue wavelengths. Through adjoint-based topology optimization, while considering nonlocal effects, we significantly enhance its diffraction efficiency, achieving numerical efficiencies up to 78% and Q-factors as high as 1362. Experimentally, we demonstrated efficiencies up to 59% with a Q-factor of 93. Additionally, we applied our topology-optimized metasurface to color selectivity, producing vivid colors at 4 narrow-band wavelengths. Our investigation represents a significant advancement in metasurface technology, with potential applications in see-through optical combiners and augmented reality platforms.
It is published in Nano Letters.
非局域超穎介面，以共振波導光柵（RWGs）為例，通過窄帶共振模式在空間和角度上調控光學波前，不同於局域超穎介面的寬頻和廣角響應。然而，RWGs 的正向設計技術在效率上仍受到限制。在此，我們展示了一種由二氧化鈦組成、置於玻璃基板上的拓撲優化超穎介面共振波導光柵（MRWG），該光柵能夠同時在紅、黃、綠和藍波長下運行。通過基於伴隨法的拓撲優化，考慮到非局域效應，我們顯著提升了其繞射效率，數值高達 78%，品質因子（Q 值）高達 1362。實驗結果顯示，我們達到了 59% 的效率和 93 的 Q 值。此外，我們將拓撲優化的超穎介面應用於顏色選擇，在四個窄帶波長下產生了鮮豔的顏色。我們的研究在超穎介面技術上代表了一個重要的進步，具有應用於透視光學混和器和擴增實境平台的潛力。
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