Polymer microbottle with flexible tunability for ultrasensitive ultrasound sensing

Optical whispering-gallery-mode microcavities have attracted significant attention for their potential in ultrasensitive ultrasound sensing, despite always relying on expensive tunable lasers in applications. In this study, we integrated an electrothermal tuning function inside the microcavity, enabling fast scanning of modes by applying voltages, which helps provide real-time searching and tracking of the optimal mode. Our device demonstrated a quality factor exceeding 10⁶ with a broad tuning range over 33 GHz. This structure achieved high sensitivity in ultrasound detection, with a noise equivalent pressure (NEP) of 3.35 mPa/Hz^1/2 at 20 MHz. We further reported the advantages of the mode thermal broadening effect for ultrasound detection, with successfully obtaining high-contrast photoacoustic images. Our research introduces an innovative approach for cost-effective, high-stability ultrasound detection with microcavity, showing great value for application in photoacoustic imaging.