Yan Wenchao, Liu Weijie, Cheng Weizhao, Chen Feng
Opt Lett. 2023 Sep 1;48(17):4532-4535. doi: 10.1364/OL.499860.
Bound states in the continuum (BICs) are intriguing localized states that possess eigenvalues embedded within the continuum of extended states. Recently, a combination of topological band theory and BIC physics has given rise to a novel form of topological matter known as topological BICs. In this work, we experimentally demonstrate the photonic topological subspace-induced BICs. By using femtosecond-laser writing, we experimentally establish a photonic nontrivial three-leg ladder lattice, thereby directly observe the localized propagation of two kinds of topological edge states which exist at different boundaries. Interestingly, such edge states appear in the continuum of the bulk modes, and the topological properties are inherited from its independent subspace Hamiltonian which contains a celebrated Su-Schrieffer-Heeger lattice. This work not only presents a novel, to the best of our knowledge, platform for investigating topological physics in optics, but also unveils exciting prospects for future exploration of other remarkable BICs.
连续域束缚态（BICs）是一类引人入胜的局域态，其本征值嵌入在扩展态的连续谱中。最近，拓扑能带理论与BIC物理的结合催生了一种新型拓扑物质，即拓扑BICs。在这项工作中，我们通过实验证明了光子拓扑子空间诱导的BICs。利用飞秒激光直写技术，我们通过实验构建了一个光子非平凡三腿梯子晶格，从而直接观测到存在于不同边界的两种拓扑边缘态的局域传播。有趣的是，这些边缘态出现在体模的连续谱中，其拓扑性质继承自其独立子空间哈密顿量，该哈密顿量包含著名的Su-Schrieffer-Heeger晶格。这项工作不仅为研究光学中的拓扑物理提供了一个新颖的（据我们所知）平台，也为未来探索其他显著的BICs揭示了令人兴奋的前景。
