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

Abstract

Whispering gallery mode (WGM) crystalline resonator is an excellent platform for acoustic sensing because the quality ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> ) factor of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sup> 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- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> mode. Based on the multi-mode calcium fluoride (CaF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) resonator supports different <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> (10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> ∼10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> ), fast switching with ultrahigh sensitivity and wide dynamic response range can be achieved by locking modes with different <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> . The mode with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> of 5.13 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> 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- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> of 6.24 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> , the dynamic response range is improved by 38.3 dB.