Max Planck Institute for Intelligent Systems , Heisenbergstrasse 3 , 70569 Stuttgart , Germany.
School of Physics and Astronomy , University of Birmingham , Birmingham B15 2TT , United Kingdom.
Nano Lett. 2018 Jul 11;18(7):4584-4589. doi: 10.1021/acs.nanolett.8b01848. Epub 2018 Jun 27.
Janus monolayers have long been captivated as a popular notion for breaking in-plane and out-of-plane structural symmetry. Originated from chemistry and materials science, the concept of Janus functions have been recently extended to ultrathin metasurfaces by arranging meta-atoms asymmetrically with respect to the propagation or polarization direction of the incident light. However, such metasurfaces are intrinsically static and the information they carry can be straightforwardly decrypted by scanning the incident light directions and polarization states once the devices are fabricated. In this Letter, we present a dynamic Janus metasurface scheme in the visible spectral region. In each super unit cell, three plasmonic pixels are categorized into two sets. One set contains a magnesium nanorod and a gold nanorod that are orthogonally oriented with respect to each other, working as counter pixels. The other set only contains a magnesium nanorod. The effective pixels on the Janus metasurface can be reversibly regulated by hydrogenation/dehydrogenation of the magnesium nanorods. Such dynamic controllability at visible frequencies allows for flat optical elements with novel functionalities including beam steering, bifocal lensing, holographic encryption, and dual optical function switching.
Janus 单层膜一直以来都被认为是打破面内和面外结构对称的一种流行概念。源于化学和材料科学，Janus 函数的概念最近通过相对于入射光的传播或偏振方向不对称地排列元原子而被扩展到超薄超表面。然而，这种超表面本质上是静态的，一旦器件被制造出来，它们所携带的信息可以通过扫描入射光的方向和偏振状态来直接解密。在这封信件中，我们提出了一种在可见光谱区域中的动态 Janus 超表面方案。在每个超单元中，三个等离子体像素被分为两组。一组包含一个镁纳米棒和一个彼此正交的金纳米棒，作为互补像素。另一组只包含一个镁纳米棒。Janus 超表面上的有效像素可以通过镁纳米棒的加氢/脱氢反应来可逆地调节。这种在可见光频率下的动态可控性允许具有新颖功能的平板光学元件，包括光束转向、双焦点透镜、全息加密和双光学功能切换。
