Optoelectronic Oscillator-Enabled Fiber Optic Fabry-Pérot Ultrasonic Sensor

Fiber-optic ultrasound sensors hold considerable promise for diverse applications, benefiting from their high sensitivity and advantageous physical characteristics. However, their practical adoption is often hindered by the operational instability of conventional high-speed demodulation techniques, which rely on sideband filtering and require active quadrature-point locking. To address this fundamental constraint, this work introduced a high-sensitivity Fabry-Pérot (FP) fiber-optic ultrasound sensing system incorporating an optoelectronic oscillator. The system integrated a submicron-precision Fabry-Pérot microcavity, fabricated on the fiber tip via two-photon polymerization (TPP), with a low-phase-noise optoelectronic oscillator (OEO) of excellent frequency stability. Experimental characterization demonstrated ultrasonic sensitivity of 3.089 mV/kPa at 1 MHz and low noise-equivalent pressure of 168 Pa, achieved without high-reflectivity coatings. By merging fiber-optic sensing with microwave photonics, the proposed architecture eliminated the need for active sideband locking, thereby substantially improving operational stability in complex and dynamic environments. This advancement establishes a reliable technical pathway for precision applications including structural defect mapping, intravascular photoacoustic imaging, and underwater acoustic holography.