Field-validated underwater microcavity acoustic sensor

Whispering-gallery-mode resonators offer a promising route to broadband, high-sensitivity underwater acoustic detection. However, their frequency-dependent sensing mechanism is not yet fully understood. In this paper, we present a comprehensive acoustic sensing model in which fiber vibration serves as the dominant transduction mechanism. This model demonstrates good agreement with water tank experiments across 100 Hz to 100 kHz. The laboratory tests reveal that the sensitivity of the sensor is 1–2 orders of magnitude higher than the reference hydrophone. The robustness of the sensor was first established through free-fall and seawater immersion tests. Subsequently, we successfully demonstrated its performance in in situ lake and sea trials, where we reconstructed underwater acoustic pressure maps that showed strong agreement with measurements from a commercial reference hydrophone. This work not only clarifies the sensing mechanism of underwater microtoroidal sensors but also demonstrates their significant potential for practical underwater acoustic applications.