High-fidelity weak time-varying signal sensing with whispering gallery mode microcavity

Whispering gallery mode microcavities provide an attractive platform for ultrasensitive detection of time-varying signals. However, practical sensing signals may simultaneously induce resonance frequency shifts, linewidth variations, and operating point deviations, degrading the fidelity of signal sensing in the transmission method. To overcome this limitation, we propose a general microcavity-based high-fidelity sensing scheme that exploits the complex field information of transmitted light to acquire richer cavity mode characteristics in real time. Different from the transmission method, the proposed scheme additionally measures the phase information to simultaneously retrieve the resonance frequency shift and linewidth variation of the cavity mode, enabling high-fidelity signal recovery under concurrent frequency shift and linewidth variation, as well as when the operating point deviates beyond the effective dynamic range. Heterodyne detection is adopted as a typical implementation to validate the feasibility of this scheme through theoretical analysis and experimental verification. The results demonstrate up to a 24-fold reduction in recovery error, accompanied by a more than 5.9-fold extension of the effective dynamic range, while heterodyne detection yields a signal-to-noise ratio improvement of 29.5 dB beyond the effective operating range of transmission detection. The scheme potentially provides a key route for advancing microcavity sensing toward practical high-fidelity applications.