Non-Hermitian physical systems (e.g. systems with loss) can have a special type of degeneracy called “exceptional points” which are branch points of complex energy surfaces at which eigenvalues and eigenvectors coalesce. These points of degeneracy can result in optical structures that are ultrasensitive to external perturbations, and therefore can enhance the performance of optical sensors. The sensitivity enhancement is proportional to the order of exceptional points. High order exceptional points have been hotly sought in recent years. This, however, is rather difficult to achieve since it usually involves tuning of multiple system parameters. In this paper, we theoretically and experimentally demonstrate a novel mechanism that can give rise to arbitrary order exceptional points without tuning any parameters. This is achieved by employing a chain of spherical resonators unidirectionally coupled with each other via photonic spin-orbit interaction. Our results lay the foundation for future exploration of topological and non-Hermitian properties of high order exceptional points.
Read more at Nature Communications: https://www.nature.com/articles/s41467-019-08826-6
19 Feb 2019