[论文解读] Multifrequency and multimode topological waveguides in a Stampfli-triangle photonic crystal with large valley Chern numbers

Bei Yan, Yiwei Peng+10 more|Figshare|Apr 29, 2021

Topological Materials and Phenomena被引用 4

一句话总结

本文提出了一种基于Stampfli-三角光子晶体的多频带、多模拓扑波导，其谷陈类数较大，可实现同时传输两个低频和四个高频的拓扑边缘态。通过使用具有相反谷陈类数区域的Z形波导，作者实验上实现了频率和位置选择性激发，实现了高容量的拓扑传输，并提出了一种用于集成光子学的频率依赖型多模光束分离器。

ABSTRACT

The multifrequency quantum valley Hall effect (QVHE) with a large valley Chern number has been realized to significantly improve the transmission capacity of topological waveguides and increase the mode density of topological waveguides. However, multifrequency and multimode QVHEs have not been realized simultaneously. In this work, using tight-binding model calculations and numerical simulations, a valley photonic crystal (VPC) consisting of a Stampfli-triangle photonic crystal is constructed, and its multiple degeneracies in the low-frequency and high-frequency bands split simultaneously to realize the QVHE with multiple topological edge states (TESs). The multifrequency and multimode topological transmission with two low-frequency modes and four high-frequency modes is realized by means of simulations and experiments through a Z-shaped waveguide constructed using two VPCs with opposite valley Chern numbers to prove the realization of a large valley Chern number in the two frequency bands. The two low-frequency modes are successfully distinguished with position-dependent selective excitations, which experimentally demonstrates the occurrence of a large valley Chern number. A frequency-dependent multimode beam splitter is theoretically proposed for high-performance integrated photonic device applications. These results provide new ideas for high-efficiency and high-capacity optical transmission and communication devices and their integration; furthermore, they broaden the application range of TESs.

研究动机与目标

• 在光子晶体中实现同时支持多频带和多模拓扑边缘态，以提升传输容量。
• 利用Stampfli-三角晶格结构，在低频和高频带中均实现较大的谷陈类数。
• 通过位置和频率依赖的激发，实验上实现可区分的拓扑边缘态。
• 提出一种频率选择型多模光束分离器，用于高性能集成光子应用。

提出的方法

• 基于Stampfli-三角晶格构建谷光子晶体（VPC），并设计亚波长尺寸的介电结构。
• 采用紧束缚模型计算分析能带简并性，并预测拓扑特性。
• 通过数值模拟研究由两个谷陈类数相反的VPC连接而成的Z形波导，以实现拓扑边缘态传输。
• 实施位置依赖的选择性激发，以区分低频拓扑边缘态。
• 在制备的波导结构中，实验验证了多频带和多模拓扑传输。
• 基于观测到的拓扑模式复用，提出了一种理论上的频率依赖型多模光束分离器。

实验结果

研究问题

• RQ1 光子晶体是否能够在多个频带中支持具有大谷陈类数的拓扑边缘态？
• RQ2 如何在单一波导结构中实验实现多频带和多模拓扑传输？
• RQ3 不同频率和位置的拓扑边缘态是否可以被选择性激发并加以区分？
• RQ4 谷陈类数在实现高容量拓扑波导中起到何种作用？
• RQ5 如何利用拓扑模式复用来推动集成光子器件的设计？

主要发现

• 通过位置选择性激发，实验分辨出两个低频拓扑边缘态，证实了大谷陈类数的存在。
• 在波导中同时观测到四个高频拓扑边缘态，证明了高频带中的多模传输。
• Z形波导结构成功实现了低频和高频模式的拓扑保护传输，仿真与实验结果一致。
• 观测到的拓扑边缘态对结构无序表现出强鲁棒性，证实了其拓扑本质。
• 基于拓扑模式复用，提出了一套理论框架，用于设计频率依赖型多模光束分离器。
• 本研究通过在单一光子晶体平台上实现多频带拓扑波导，显著提升了模式密度和传输容量。