# Enhanced Nanoparticle Sensing by Sagnac–Fizeau Shift in a Microcavity Based on Exceptional Surfaces

## TL;DR

This paper introduces a new sensing method using a microcavity to detect nanoparticles with higher precision.

## Contribution

A novel nanoparticle sensing mechanism using Sagnac–Fizeau shift in an ES-based microcavity is proposed.

## Key findings

- The Sagnac–Fizeau shift enhances frequency splitting in the sensing structure.
- The detection limit for weak perturbations is significantly reduced compared to traditional methods.

## Abstract

The exceptional surface (ES) in non-Hermitian physics has attracted much attention due to its strong robustness and enhanced frequency splitting in the sensing field. However, the detection limit of the ES-based sensing structure is still limited by the mode linewidth in the optical microcavity. In this paper, we demonstrate that Sagnac–Fizeau shift in a microcavity based on an ES separates the dark mode from the bright mode, further enhancing the frequency splitting in the transmission spectrum. Moreover, a strategy for manipulating spectral line shape is realized by the phase in the reflection loop. Compared with the traditional ES-based sensing structure, the proposed nanoparticle sensing mechanism significantly reduces the detection limit for weak perturbations. This work will contribute to the development of high-precision nanoparticle sensors.