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Whispering-gallery-mode optical microcavities have been extensively used for realizing low-threshold and narrow-linewidth lasers due to their ultrahigh quality factor and small mode volume. These microlasers are of great interest as ultrasensitive sensors due to narrower linewidth and stronger light–matter interaction compared with passive optical microcavities. Here, we demonstrate a microwave synthesizer that is based on the beat note of a dual-mode laser from an ultrahigh-quality-factor erbium-doped silica microbottle cavity. The stable kilohertz-bandwidth beating note can be continuously tuned within a 2-GHz frequency range by adjusting the lasing wavelength difference of the dual-mode laser. Furthermore, this microwave signal is used for high-resolution temperature sensing by leveraging the thermal gradient distribution of the microbottle cavity. The temperature sensing sensitivity obtained from the frequency shift of the beat note is 19.54 MHz/°C, and the corresponding temperature resolution is 8.2 × 10−3 °C, demonstrating excellent temperature sensing performance. Our scheme demonstrated here can also be used for the sensing of different physical quantities, such as strain and optical power.
Xu et al. (Mon,) studied this question.