Shu Xiaoqian, Li Aodong, Hu Guangwei, Wang Jian, Alù Andrea, Chen Lin
Wuhan National Laboratory for Optoelectronics and School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, 430074, China.
Department of Electrical and Computer Engineering, National University of Singapore, Singapore, Singapore.
Nat Commun. 2022 Apr 19;13(1):2123. doi: 10.1038/s41467-022-29777-5.
Exceptional points (EPs) are degeneracies at which two or more eigenvalues and eigenstates of a physical system coalesce. Dynamically encircling EPs by varying the parameters of a non-Hermitian system enables chiral mode switching, that is, the final state of the system upon a closed loop in parameter space depends on the encircling handedness. In conventional schemes, the parametric evolution during the encircling process has to be sufficiently slow to ensure adiabaticity. Here, we show that fast parametric evolution along the parameter space boundary of the system Hamiltonian can relax this constraint. The proposed scheme enables highly efficient transmission and more compact footprint for asymmetric mode converters. We experimentally demonstrate these principles in a 57 μm-long double-coupled silicon waveguide system, enabling chiral mode switching with near-unity transmission efficiency at 1550 nm. This demonstration paves the way towards high-efficiency and highly integrated chiral mode switching for a wide range of practical applications.
例外点（EPs）是物理系统中两个或更多个本征值和本征态合并的简并点。通过改变非厄米系统的参数动态环绕例外点可实现手性模式切换，即系统在参数空间中闭环后的最终状态取决于环绕的手性。在传统方案中，环绕过程中的参数演化必须足够缓慢以确保绝热性。在此，我们表明沿着系统哈密顿量的参数空间边界进行快速参数演化可以放宽这一限制。所提出的方案可为非对称模式转换器实现高效传输和更小的占用空间。我们在一个57μm长的双耦合硅波导系统中通过实验证明了这些原理，能够在1550nm处实现接近单位传输效率的手性模式切换。这一演示为广泛的实际应用中实现高效和高度集成的手性模式切换铺平了道路。
