Department of Materials Science and Engineering, Stanford University, Stanford, CA, USA.
Department of Mechanical Engineering, Stanford University, Stanford, CA, USA.
Nat Nanotechnol. 2020 Nov;15(11):956-961. doi: 10.1038/s41565-020-0754-x. Epub 2020 Aug 17.
Dielectric microcavities with quality factors (Q-factors) in the thousands to billions markedly enhance light-matter interactions, with applications spanning high-efficiency on-chip lasing, frequency comb generation and modulation and sensitive molecular detection. However, as the dimensions of dielectric cavities are reduced to subwavelength scales, their resonant modes begin to scatter light into many spatial channels. Such enhanced scattering is a powerful tool for light manipulation, but also leads to high radiative loss rates and commensurately low Q-factors, generally of order ten. Here, we describe and experimentally demonstrate a strategy for the generation of high Q-factor resonances in subwavelength-thick phase gradient metasurfaces. By including subtle structural perturbations in individual metasurface elements, resonances are created that weakly couple free-space light into otherwise bound and spatially localized modes. Our metasurface can achieve Q-factors >2,500 while beam steering light to particular directions. High-Q beam splitters are also demonstrated. With high-Q metasurfaces, the optical transfer function, near-field intensity and resonant line shape can all be rationally designed, providing a foundation for efficient, free-space-reconfigurable and nonlinear nanophotonics.
具有数千到数十亿品质因数 (Q 因子) 的介电微腔显著增强了光物质相互作用，其应用范围涵盖高效片上激光、频率梳产生和调制以及灵敏的分子检测。然而，随着介电腔的尺寸减小到亚波长尺度，其共振模式开始将光散射到许多空间通道中。这种增强的散射是一种强大的光操纵工具，但也会导致高辐射损耗率和相应的低 Q 因子，通常为十几个。在这里，我们描述并实验演示了在亚波长厚的相位梯度超表面中产生高 Q 因子共振的策略。通过在单个超表面元件中包含细微的结构扰动，创建了将自由空间光弱耦合到其他束缚和空间局域模式的共振。我们的超表面可以实现>2500 的 Q 因子，同时将光引导到特定方向。还演示了高 Q 分束器。通过高 Q 超表面，可以合理设计光学传递函数、近场强度和共振线形状，为高效、自由空间可重构和非线性纳米光子学提供基础。
