Experimental realization of exceptional surfaces enhanced displacement sensing with robustness

The application of exceptional points in non-Hermitian photonic systems has attracted attention in the field of ultra-high-sensitivity sensing. However, the realization of an exceptional point (EP) in experiments requires precise control of the multiple parameters of the sensor, which limits the practical applicability of EP-enhanced sensors. In this work, the exceptional surface (ES)-enhanced displacement sensing is experimentally demonstrated in a fiber ring resonator to break through this restriction. Expanding EPs to an ES makes the system immune to fabrication errors and environmental uncertainties, thereby improving the system's robustness and maintaining a high sensing sensitivity by working exactly at EPs. Compared with a diabolic point-based structure, a significant sensitivity enhancement of the displacement sensing is observed by monitoring the frequency splitting in the spectrum. Our proposed structure has strong robustness against changes in the resonator dissipation and frequency fluctuations and could, therefore, pave the way for practical non-Hermitian photonic sensing applications.