Ultrahigh-Resolution High-Order WGM Microsphere Temperature Sensor

Enhancing temperature measurement resolution is an essential pursuit within the domain of high-precision temperature control systems. This article proposes an ultrahigh-resolution high-order whispering-gallery modes (WGMs) temperature sensor using Pound–Drever–Hall (PDH) tracking technique. The high-order WGM with an average quality factor ( $Q$ factor) above $10^{7}$ is excited in silica-microsphere resonators through a sufficiently thin tapered fiber coupling. The WGM resonators with high $Q$ factor enable narrow-bandwidth resonance, enhancing the resolution of subtle changes and improving the detection limit. By employing the PDH tracking technique to characterize the resonant frequency of microsphere resonators, the sensing system can monitor the environmental temperature in real time and achieve an ultrahigh resolution of $1.78\times 10^{-6}~^{\circ }$ C and an accuracy of $2.32\times 10^{-5}~^{\circ }$ C. With the packaged WGM microsphere temperature sensor, the temperature control system achieves an accuracy of 0.1 m°C. This ultrahigh-resolution WGM temperature sensor exhibits immense potential for applications in temperature monitoring and control systems.