Quantitative robustness analysis of topological edge modes in C6 and valley-Hall metamaterial waveguides
Quantitative robustness analysis of topological edge modes in C6 and valley-Hall metamaterial waveguides
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DOI：
10.1515/nanoph-2019-0137
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发表时间：
2019-07
期刊：
影响因子：
7.5
通讯作者：
B. Orazbayev;R. Fleury
中科院分区：
文献类型：
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作者：
B. Orazbayev;R. Fleury
摘要通过采用由亚波长共振散射体的密集周期性排列组成的合成光子物质，设计时间反演不变的光子拓扑绝缘体的最新进展已经扩展到深亚波长尺度。有趣的是，这种拓扑超材料晶体支持在拓扑边界处的亚波长体积中局部化的边缘状态，提供了一种基于工程化大块超材料绝缘体的拓扑来设计亚波长波导的独特方式。虽然拓扑结构保证了这些边缘模式的存在，但它们对反向散射的鲁棒性通常是不完整的，因为时间反演的光子模式总是可以通过互易性相互耦合。与受Kramers定理保护的电子自旋不同，光子自旋主要受较弱的对称性（如晶体对称性或谷守恒）保护。在本文中，我们定量研究了两种常用的拓扑设计，即超材料自旋霍尔（SP）效应的基础上C6对称性，和超材料谷霍尔（VH）绝缘体的基础上谷保存的亚波长边缘模式的鲁棒性。对于第一次，鲁棒性进行评估的位置和频率的障碍，并为所有可能的接口类型，通过执行合奏平均的边缘模式传输通过许多随机实现的障碍。与我们在手性超材料波导上的先前研究中的结果相反，这里提出的统计研究表明了特定界面对这些边缘模式的鲁棒性的重要性，以及在位置和频率无序中所述的VH边缘的上级鲁棒性，提供了一个Z字形界面。
Abstract Recent advances in designing time-reversal-invariant photonic topological insulators have been extended down to the deep subwavelength scale, by employing synthetic photonic matter made of dense periodic arrangements of subwavelength resonant scatterers. Interestingly, such topological metamaterial crystals support edge states that are localized in subwavelength volumes at topological boundaries, providing a unique way to design subwavelength waveguides based on engineering the topology of bulk metamaterial insulators. While the existence of these edge modes is guaranteed by topology, their robustness to backscattering is often incomplete, as time-reversed photonic modes can always be coupled to each other by virtue of reciprocity. Unlike electronic spins which are protected by Kramers theorem, photonic spins are mostly protected by weaker symmetries like crystal symmetries or valley conservation. In this paper, we quantitatively studied the robustness of subwavelength edge modes originating from two frequently used topological designs, namely metamaterial spin-Hall (SP) effect based on C6 symmetry, and metamaterial valley-Hall (VH) insulators based on valley preservation. For the first time, robustness is evaluated for position and frequency disorder and for all possible interface types, by performing ensemble average of the edge mode transmission through many random realizations of disorder. In contrast to our results in the previous study on the chiral metamaterial waveguide, the statistical study presented here demonstrates the importance of the specific interface on the robustness of these edge modes and the superior robustness of the VH edge stated in both position and frequency disorder, provided one works with a zigzag interface.