近日，南开大学的陈志刚&Hrvoje Buljan及其研究团队取得一项新进展。经过不懈努力，他们实现了拓扑轨道角动量提取与涡旋输运的双重保护。相关研究成果已于2024年11月20日在国际知名学术期刊《自然—光子学》上发表。
该研究团队利用拓扑缺陷展示了一种限制和引导任意高阶电荷涡旋的方案。该方案依赖于双重拓扑保护：一是由于手性对称导致的动量空间中的非平凡缠绕，二是由于轨道角动量（OAM）模式在缺陷结构中复杂耦合导致的实空间中的非平凡缠绕。研究人员揭示了一种涡旋协调的旋转对称性，它建立了涡旋拓扑电荷与系统旋转对称阶数之间的普遍关系。
作为示例，研究人员构建了具有单一核心但具有不同Cn对称性的光子缺陷晶格，并实现了仅对应于中间间隙处一个选定零能量涡旋模式的光学涡旋的稳健传输，同时保持了其OAM。
此外，研究人员还表明，这种拓扑结构可用于涡旋滤波，以从混合激发中提取出选定的OAM模式。这项研究结果阐明了涡旋性、缺陷和更高阶拓扑之间的基本相互作用，这可能为开发基于OAM的光子器件（如涡旋导波管、光纤和激光器）开辟一条新途径。
据悉，涡旋现象在自然界中无处不在。在光学领域，尽管已经存在许多用于涡旋生成和检测的技术，但如何以期望的轨道角动量（OAM）实现涡旋输运的拓扑保护仍然是一个挑战。
附：英文原文
Title: Topological orbital angular momentum extraction and twofold protection of vortex transport
Author: Hu, Zhichan, Bongiovanni, Domenico, Wang, Ziteng, Wang, Xiangdong, Song, Daohong, Xu, Jingjun, Morandotti, Roberto, Buljan, Hrvoje, Chen, Zhigang
Issue&Volume: 2024-11-20
Abstract: Vortex phenomena are ubiquitous in nature. In optics, despite the availability of numerous techniques for vortex generation and detection, topological protection of vortex transport with desired orbital angular momentum (OAM) remains a challenge. Here, by use of topological disclination, we demonstrate a scheme to confine and guide vortices featuring arbitrary high-order charges. Such a scheme relies on twofold topological protection: a non-trivial winding in momentum space due to chiral symmetry, and a non-trivial winding in real space due to the complex coupling of OAM modes across the disclination structure. We unveil a vorticity-coordinated rotational symmetry, which sets up a universal relation between the vortex topological charge and the rotational symmetry order of the system. As an example, we construct photonic disclination lattices with a single core but different Cn symmetries and achieve robust transport of an optical vortex with preserved OAM solely corresponding to one selected zero-energy vortex mode at the mid-gap. Furthermore, we show that such topological structures can be used for vortex filtering to extract a chosen OAM mode from mixed excitations. Our results illustrate the fundamental interplay of vorticity, disclination and higher-order topology, which may open a new pathway for the development of OAM-based photonic devices such as vortex guides, fibres and lasers.
DOI: 10.1038/s41566-024-01564-2
Source: https://www.nature.com/articles/s41566-024-01564-2