Modeling of a fiber Fabry-Pérot sensor in the broken PT-symmetric region

Abstract

Parity-time (PT)-symmetric optical sensors operating around exceptional points have recently gained much attraction due to their improved sensitivity for measuring small perturbations. Previously, most of the PT-symmetric sensors have been based on detecting the mode splitting that arises due to the perturbation-induced change in coupling strength between two sub-cavities of the PT-symmetric system. Here, we present a model of a fiber Fabry-Pérot linear cavities sensor tailored to operate in the broken parity-time symmetric region. We propose, what we believe to be, a new sensing metric based on the mode’s linewidth change as a function of perturbation-induced loss changes in one of the cavities. The coupling strength between the two sub-cavities remains unchanged in our proposed sensor. We derive a mathematical expression that describes a square root dependence of the full-width-half-maximum change as a function of the refractive index change-induced loss, which is introduced via a tapered fiber in one of the fiber cavities. The proposed fiber Fabry-Pérot refractive index sensor has a maximum sensitivity of 2.26 × 107 GHz/RIU and the lowest detection limit of 10−9 RIU, widely outperforming comparable cavity sensors subject to the same refractive index change, gain, and loss settings.