Moritake Yuto, Ono Masaaki, Notomi Masaya
Department of Physics, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan.
PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan.
Nanophotonics. 2022 Feb 2;11(9):2183-2189. doi: 10.1515/nanoph-2021-0648. eCollection 2022 Apr.
Topological photonics mimicking topological insulators has recently attracted considerable attention. The Su-Schrieffer-Heeger (SSH) model, which is a fundamental topological system, has been experimentally demonstrated in many photonic systems owing to its simplicity. In particular, a zigzag chain, which is described by the SSH model, shows intriguing functionality such as polarization-dependent switching of topological edge states. To date, the far-field imaging of topological edge states in plasmonic chains has not been reported because of the constraint imposed by the diffraction limit. In this study, we experimentally observed the photonic topological edge states of zigzag plasmonic chains composed of metal nanodiscs in the optical region through far-field imaging. Using a chain longer than the diffraction limit, light scattering from the two edges of the zigzag chains was resolved. In the case of such a long chain, it was revealed that tiny gaps of several nanometers between the discs, which are difficult to fabricate, are necessary. Therefore, we propose connected chains and investigate the effect of the shape of the connected part, which reveals that similar topological edge states can be obtained even in the connected chains. The polarization dependence of edge-state imaging showed switching of the systems in trivial and topological phases in the same zigzag chain. Far-field observations serve as an easy and effective tool for the investigation and application of photonic topological edge states.
模仿拓扑绝缘体的拓扑光子学最近引起了广泛关注。作为一种基本的拓扑系统，苏-施里弗-黑格（SSH）模型因其简单性已在许多光子系统中得到实验验证。特别是，由SSH模型描述的锯齿形链展现出诸如拓扑边缘态的偏振依赖开关等有趣功能。迄今为止，由于衍射极限的限制，尚未有关于等离子体链中拓扑边缘态的远场成像报道。在本研究中，我们通过远场成像实验观察了光学区域中由金属纳米盘组成的锯齿形等离子体链的光子拓扑边缘态。使用一条长于衍射极限的链，分辨出了锯齿形链两端的光散射。在这种长链的情况下，发现圆盘之间需要有几纳米的微小间隙，而这很难制造。因此，我们提出了连接链，并研究了连接部分形状的影响，结果表明即使在连接链中也能获得类似的拓扑边缘态。边缘态成像的偏振依赖性显示了同一锯齿形链在平凡相和拓扑相中的系统开关特性。远场观测是研究和应用光子拓扑边缘态的一种简便有效的工具。
