Eigenfrequency splitting with EPs order tunability in a coupled triple cavity system

TL;DR

This paper introduces a coupled triple ring resonator system demonstrating tunable eigenfrequency splitting at higher-order exceptional points, significantly enhancing refractive index sensing sensitivity by up to 10^8 times.

Contribution

It proposes a novel three-cavity system showing real eigenfrequency splitting at higher-order EPs with tunable order via cladding perturbation, advancing non-Hermitian optical device applications.

Findings

Real eigenfrequency splitting achieved in PT and anti-PT domains.

Sensitivity enhancement of approximately 10^8 in RI sensing.

Order of EP tunable through cladding perturbation.

Abstract

Degeneracies of non-Hermitian Hamiltonian i.e., exceptional points (EPs) of parity-time (PT)-symmetric systems have received considerable research attention due to their various possible applications in optical devices. At EPs, at least two eigenvalues as well as their eigenvector coalesce. Recently, the effect of the eigenfrequency splitting on transfer function near EP was studied for an optical system consisting of two micro ring resonators, which led to complex splitting in PT-symmetric and anti-PT-symmetric sensors. In present work, we propose a simple system of three coupled ring resonators to show real splitting in both PT-symmetric and anti-PT-symmetric parameter domains by exploiting higher-order EPs. We indirectly couple two rings with equal amount of gain and loss via an intermediate neutral ring. This system is then tested for refractive index (RI) sensing by modulating the cladding index and we numerically show a huge enhancement in sensitivity as compared to those reported in previous studies of micro ring resonators. Importantly, the enhancement is found to be of the order of 10^8. Further, we have found that the order of EP can be tuned by perturbating the cladding. The outcomes of this study may set up a wide range of applications in non-Hermitian triplet cavity systems.