Light-controlled exceptional point sensor based on azo-functionalized whispering gallery mode microcavity

Nonlinear topological responses in the vicinity of exceptional points (EPs) significantly enhance mode splitting sensitivity of non-Hermitian systems to external perturbations. In this paper, a new method is proposed to flexibility control EP state of the whispering gallery mode microcavity integrated with photo-sensitive azobenzene coating, which provides a simple, efficient and stabilized scheme to prepare and tune the EP state with no need to delicately control the interaction between the nanoscatters and the microcavity. By introducing one pair of defects infiltrated with liquid samples, refractive index sensing could be realized when the system is operating around EP and the measurement range of 1.33 to 1.4 covers the RI range of most biological analytes. And moreover, performances of the proposed system in nanoparticle detection are also investigated. In comparison with its counterpart operating around diabolic points, our proposed system exhibits more than quadruple increase in sensitivity. Our proposed EP sensor based on light-controlled tuning of the system state makes it a promising candidate for applications in the field of optical sensing and paves a way toward developing tunable EP-based photonic devices.