We present a double-layer dielectric metasurface obtained by stacking a silicon nanodisk array and a silicon photonic crystal slab with equal periodicity on top of each other. We focus on the investigation of electric near-field enhancement effects occurring at resonant excitation of the metasurface and study its optical properties numerically and experimentally. We find that the major difference in multi-layer metasurfaces when compared to conventional single-layer structures appears to be in Rayleigh–Wood anomalies: they are split into multiple different modes, which are themselves spectrally broadened. As a proof of concept, we cover a double-layer metasurface with a lanthanide-doped up-conversion particle layer and study its interaction with a 1550 nm photoexcitation. We observe a 2.7-fold enhanced up-conversion photoluminescence by using the stacked metasurface instead of a planar substrate, although only around 1% of the up-conversion material is exposed to enhanced near fields. Two mechanisms are identified explaining this behavior: First, enhanced near fields when exciting the metasurface resonantly, and second, light trapping by total internal reflection in the particle layer when the metasurface redirects light into high angle diffraction orders. These results pave the way for low-threshold and, in particular, broadband photon up-conversion in future solar energy and biosensing applications.

中文翻译：

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双层超表面可增强光子上转换

我们提出了一个双层电介质超表面，该表面是通过以相等的周期性堆叠一个硅纳米盘阵列和一个硅光子晶体平板而获得的。我们专注于研究超表面共振激发时发生的电近场增强效应，并通过数值和实验研究其光学性质。我们发现，与常规单层结构相比，多层超表面的主要差异似乎在于瑞利—伍德异常：它们被分为多种不同的模式，它们自身在光谱上得到了拓宽。作为概念的证明，我们用镧系元素掺杂的上转换粒子层覆盖了双层超表面，并研究了其与1550 nm光激发的相互作用。我们观察到2。尽管只有大约1％的上转换材料暴露在增强的近场中，但通过使用堆叠的超表面而不是平面基板，可实现7倍的增强上转换光致发光。确定了两种机制来解释这种行为：第一，共振激发超颖表面时增强了近场，第二，超颖表面将光重定向到高角度衍射级时，粒子层中的全内反射捕获了光。这些结果为在未来的太阳能和生物传感应用中实现低阈值，尤其是宽带光子上变频铺平了道路。当共振激发超颖表面时，增强了近场；其次，超颖表面将光重定向到高角度衍射级时，粒子层中的全内反射捕获了光。这些结果为在未来的太阳能和生物传感应用中实现低阈值，尤其是宽带光子上变频铺平了道路。当共振激发超颖表面时，增强了近场；其次，超颖表面将光重定向到高角度衍射级时，粒子层中的全内反射捕获了光。这些结果为在未来的太阳能和生物传感应用中实现低阈值，尤其是宽带光子上变频铺平了道路。