Arbitrary order exceptional point induced by photonic spin-orbit interaction in coupled resonators

TL;DR

This paper demonstrates how to realize arbitrary order exceptional points in coupled resonators using photonic spin-orbit interaction, leading to enhanced sensitivity to perturbations in optical systems.

Contribution

It introduces a simple system of identical resonators near a waveguide to achieve arbitrary order exceptional points via spin-momentum locking, independent of resonator positions.

Findings

Achieved arbitrary order exceptional points in coupled resonators.

Experimental demonstration of response functions at exceptional points.

Numerical and analytical evidence of enhanced sensitivity to perturbations.

Abstract

Many novel properties of non-Hermitian systems are found at or near the exceptional points-branch points of complex energy surfaces at which eigenvalues and eigenvectors coalesce. In particular, higher-order exceptional points can result in optical structures that are ultrasensitive to external perturbations. Here we show that an arbitrary order exceptional point can be achieved in a simple system consisting of identical resonators placed near a waveguide. Unidirectional coupling between any two chiral dipolar states of the resonators mediated by the waveguide mode leads to the exceptional point, which is protected by the transverse spin-momentum locking of the guided wave and is independent of the positions of the resonators. Various analytic response functions of the resonators at the exceptional points are experimentally manifested in the microwave regime. The enhancement of sensitivity to external perturbations near the exceptional point is also numerically and analytically demonstrated.