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Acoustic sensors with ultrahigh sensitivity, broadband response, and high resolution are essential for high-precision nondestructive weak signal detection technology. In this paper, based on the size effect of an ultrahigh-quality (Q) calcium fluoride (CaF2) resonator, a weak acoustic signal is detected by the dispersive response regime in which an acoustic, elastic wave modulates the geometry and is converted to a resonance frequency shift. Through the structural design of the resonator, the sensitivity reaches 11.54 V/Pa at 10 kHz in the experiment. To our knowledge, the result is higher than that of other optical resonator acoustic sensors. We further detected a weak signal as low as 9.4 µPa/Hz1/2, which greatly improved the detection resolution. With a good directionality of 36.4 dB and a broadband frequency response range of 20 Hz–20 kHz, the CaF2 resonator acoustic sensing system can not only acquire and reconstruct speech signals over a long distance but also accurately identify and separate multiple voices in noisy environments. This system shows high performance in weak sound detection, sound source localization, sleep monitoring, and many other voice interaction applications. [ABSTRACT FROM AUTHOR]

Whispering gallery mode (WGM) crystalline resonator is an excellent platform for acoustic sensing because the quality (Q) factor of 1011 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 (CaF2) resonator supports different Q (106∼109), 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 × 108 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 × 106, the dynamic response range is improved by 38.3 dB. [ABSTRACT FROM AUTHOR]

The whispering gallery mode resonator based on a fluoride crystalline material offers the advantage of an ultrahigh quality factor, however, its fast tuning remains a challenge. We propose a tuning method for a CaF2 crystalline resonator using external pressure loading. Through our theoretical calculations and simulations, we discovered that the frequency shift induced by deformation during the pressure tuning of the crystalline resonator is greater than that induced by changes in refractive index. Both shifts were of the same order of magnitude, indicating that both factors must be considered. The experimental results show tuning rates of 1114.6 and 888.2 MHz/MPa in the transverse electric and transverse magnetic modes, respectively. The tuning system can respond to a signal frequency of up to 1.2 MHz. [ABSTRACT FROM AUTHOR]