Wu Bei, Wang Jiamin, Xiao Meng, Xu Jing, Chen Yuntian
Opt Express. 2017 Jan 23;25(2):1040-1049. doi: 10.1364/OE.25.001040.
We study mode coupling of an edge state with bulk states in a coupled waveguide chain in the presence of gain and losses. In a low non-Hermiticity regime, it is found that the edge state associated with the interface between two topologically different waveguide chains is well isolated from the bulk states, sharing the exact same features as the well-known Su-Schrieffer-Heeger Model. As the non-Hermiticity increases, the two bands of the overall waveguide chain merge together, which leads to the overlap in the band diagram between the edge state and states of lower bands. We find that before the PT-symmetry breaking, the edge state is strongly coupled to bulk states of lower bands, evident by the anti-crossing feature in the band diagram. The strong mode hybridization is verified by a non-Hermitian coupled mode theory developed from reaction conservation, and is further examined using phenomenological models. We envisage that the strong coupling between the edge state and the bulk state may be useful in expanding our understanding in topological photonics in non-Hermitian condition, as well as in applications such as mode conversion between edge and bulk states.
我们研究了在存在增益和损耗的耦合波导链中，边缘态与体态之间的模式耦合。在低非厄密性 regime 中，发现与两个拓扑不同的波导链之间的界面相关的边缘态与体态很好地隔离，具有与著名的 Su-Schrieffer-Heeger 模型完全相同的特征。随着非厄密性增加，整个波导链的两个能带合并在一起，这导致边缘态与较低能带的态在能带图中出现重叠。我们发现，在 PT 对称性破缺之前，边缘态与较低能带的体态强烈耦合，能带图中的反交叉特征证明了这一点。通过基于反应守恒发展的非厄密耦合模理论验证了强模式杂化，并使用唯象模型进行了进一步研究。我们设想，边缘态与体态之间的强耦合可能有助于扩展我们对非厄密条件下拓扑光子学的理解，以及在边缘态与体态之间的模式转换等应用中发挥作用。
