Frolov Aleksandr Yu, Van de Vondel Joris, Panov Vladimir I, Van Dorpe Pol, Fedyanin Andrey A, Moshchalkov Victor V, Verellen Niels
Faculty of Physics, Lomonosov Moscow State University, Moscow, Russian Federation.
Department of Physics and Astronomy, Quantum Solid-State Physics, KU Leuven, Leuven, Belgium.
Nanophotonics. 2021 Dec 22;11(3):543-557. doi: 10.1515/nanoph-2021-0612. eCollection 2022 Jan.
All-dielectric nanoantennas, consisting of high refractive index semiconductor material, are drawing a great deal of attention in nanophotonics. Owing to their ability to manipulate efficiently the flow of light within sub-wavelength volumes, they have become the building blocks of a wide range of new photonic metamaterials and devices. The interaction of the antenna with light is largely governed by its size, geometry, and the symmetry of the multitude of optical cavity modes it supports. Already for simple antenna shapes, unraveling the full modal spectrum using conventional far-field techniques is nearly impossible due to the spatial and spectral overlap of the modes and their symmetry mismatch with incident radiation fields. This limitation can be circumvented by using localized excitation of the antenna. Here, we report on the experimental near-field probing of optical higher order cavity modes (CMs) and whispering gallery modes (WGMs) in amorphous silicon nanoantennas with simple, but fundamental, geometrical shapes of decreasing rotational symmetry: a disk, square, and triangle. Tapping into the near-field using an aperture type scanning near-field optical microscope (SNOM) opens a window on a rich variety of optical patterns resulting from the local excitation of antenna modes of different order with even and odd parity. Numerical analysis of the antenna and SNOM probe interaction shows how the near-field patterns reveal the node positions of - and allows us to distinguish between - cavity and whispering gallery modes. As such, this study contributes to a richer and deeper characterization of the structure of light in confined nanosystems, and their impact on the structuring of the light fields they generate.
全介质纳米天线由高折射率半导体材料构成，在纳米光子学领域备受关注。由于其能够在亚波长体积内高效操控光流，已成为众多新型光子超材料和器件的基础组成部分。天线与光的相互作用很大程度上取决于其尺寸、几何形状以及它所支持的众多光学腔模的对称性。对于简单的天线形状，由于模式的空间和光谱重叠以及它们与入射辐射场的对称性不匹配，使用传统远场技术解析完整的模式光谱几乎是不可能的。通过使用天线的局部激发可以规避这一限制。在此，我们报告了对具有简单但基本的、旋转对称性递减的几何形状（圆盘、正方形和三角形）的非晶硅纳米天线中的光学高阶腔模（CMs）和回音壁模（WGMs）进行的实验近场探测。使用孔径型扫描近场光学显微镜（SNOM）接入近场，为因不同奇偶性的不同阶天线模的局部激发而产生的丰富多样的光学图案打开了一扇窗口。天线与SNOM探针相互作用的数值分析表明近场图案如何揭示 - 并使我们能够区分 - 腔模和回音壁模的节点位置。因此，这项研究有助于更丰富、更深入地表征受限纳米系统中光的结构，以及它们对所产生光场结构的影响。
