Optical metasurfaces have been extensively investigated, demonstrating diverse and multiple functionalities with complete control over the transmitted and reflected fields. Most optical metasurfaces are, however, static, with only a few configurations offering (rather limited) electrical control, thereby jeopardizing their application prospects in emerging flat optics technologies. Here, we suggest an approach to realize electrically tunable optical metasurfaces, demonstrating dynamic Fresnel lens focusing. The active Fresnel lens (AFL) exploits the electro-optic Pockels effect in a 300 nm thick lithium niobate layer sandwiched between a continuous thick and a nanostructured gold film serving as electrodes. We fabricate and characterize the AFL, focusing 800–900 nm radiation at a distance of 40 μm, with the focusing efficiency of 15%, and demonstrating the modulation depth of 1.5%, with the driving voltage of ±10 V within the bandwidth of ∼6.4 MHz. We believe that the electro-optic metasurface concept introduced is useful for designing dynamic flat optics components.

中文翻译：

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反射中菲涅耳透镜的电调谐

光学超表面已被广泛研究，展示了多种功能，可以完全控制透射和反射场。然而，大多数光学超表面是静态的，只有少数配置提供（相当有限的）电控制，从而危及它们在新兴平面光学技术中的应用前景。在这里，我们提出了一种实现电可调光学超表面的方法，展示了动态菲涅耳透镜聚焦。有源菲涅尔透镜 (AFL) 在 300 nm 厚的铌酸锂层中利用电光普克尔斯效应，该层夹在连续厚的和用作电极的纳米结构金膜之间。我们制造并表征了 AFL，在 40 μm 的距离处聚焦 800-900 nm 辐射，聚焦效率为 15%，并证明了 1.5% 的调制深度，在 ~6.4 MHz 的带宽内驱动电压为 ±10 V。我们相信引入的电光超表面概念对于设计动态平面光学组件很有用。