Light-tuned exceptional point multi-parameter sensor based on azo-functionalized whispering gallery mode capillary micro-resonator

The nonlinear topological response exhibited near exceptional points (EPs) significantly enhances the mode-splitting sensitivity of non-Hermitian systems to external perturbations. This paper proposes an innovative approach to achieve flexible manipulation of the exceptional-point states in a whispering-gallery-mode (WGM) microcavity through the integration of photo-sensitive azobenzene coatings. This method provides a simple, efficient, and stable approach for the preparation and adjustment of the EP state with no need to precisely adjust the positions of nanoscatterers to make the microcavity reach the EP state. Its performance in nanoparticle detection has been studied as the system operates near the EP. In comparison with the WGM microcavity systems operating near the diabolic points, our proposed system operating in the vicinity of the EP shows a significant increase in nanoparticle sensitivity by approximately 2.5 times. In addition, by infiltrating the sample liquids into the hollow channel of the silica capillary, precise detection of small refractive index (RI) change of the liquid analytes can be achieved within the RI range of 1.33951–1.34028. The light-controlled WGM sensor with EP-enhanced sensitivity shows great potential in the field of high-resolution optical sensing. At the same time, it lays the foundation and paves a new way for the development of tunable photonic devices based on exceptional points.