Fast Switching Acoustic Sensor With Ultrahigh Sensitivity and Wide Dynamic Response Range Based on Ultrahigh-Q CaF2 Resonator

Whispering gallery mode (WGM) crystalline resonator is an excellent platform for acoustic sensing because the quality ( Q ) factor of 10 ¹¹ can theoretically increase sensitivity by more than three orders of magnitude. However, ultrahigh sensitivity and wide dynamic response range cannot be achieved simultaneously, due to the extremely narrow linewidth and small linear range of ultrahigh- Q mode. Based on the multi-mode calcium fluoride (CaF ₂ ) resonator supports different Q (10 ⁶ ∼10 ⁹ ), fast switching with ultrahigh sensitivity and wide dynamic response range can be achieved by locking modes with different Q . The mode with Q of 5.13 × 10 ⁸ shows a high sensitivity of 280 mV/Pa at 1 kHz frequency, which is better than other WGM acoustic sensors currently reported. When switching to the lower- Q of 6.24 × 10 ⁶ , the dynamic response range is improved by 38.3 dB.