In this paper, we propose a novel acoustic sensing scheme that achieves ultra-high sensitivity sensing detection by cascading fiber-optic microbubble Fabry-Perot (FP) cavities with high-Q whispering gallery mode (WGM) microsphere cavities. The system demonstrates outstanding sensitivity in acoustic sensing. Specifically, the microsphere cavity serves as a gain cavity for detection. Compared with FP cavity detection, it not only enhances sensitivity by 3-4 orders of magnitude but also utilizes the inherent thermal locking effect of the microsphere cavity for mode locking, thereby increasing acoustic sensing sensitivity by 3-4 times. It has reached the current highest sensitivity index of FP cavity low-frequency acoustic sensing. This study introduces a novel approach to designing efficient sensing systems, paving the way for the future development of compact, low-cost, and ultra-high-sensitivity acoustic sensing technologies.

Whispering-gallery-mode (WGM) optical microcavity acoustic sensors have attracted extensive attention owing to their high sensitivity, broad bandwidth, miniaturization and anti-electromagnetic interference capability. This review systematically surveys medium-adapted acoustic sensing and function extension applications of WGM microcavities. Starting from perturbation theory, we distinguish between optical quality factor Q₀ and mechanical quality factor Q_m, and elucidate the intrinsic sensitivity–bandwidth trade-off dominated by mechanical dynamics. We summarize advances in air-coupled and liquid-phase acoustic detection, photoacoustic imaging, and multiparameter multifunctional sensing. Practical bottlenecks including calibration deficiency, thermal drift-induced crosstalk, packaging trade-offs, long-term stability and array scalability are analyzed. Joint hardware–process–algorithm optimization strategies are discussed, providing references for advancing WGM microcavity acoustic sensors toward real-world engineering deployment.