A Calibration-Free Self-Quadrature Locked Extrinsic Fiber Acoustic Sensor With Ultrahigh Sensitivity

Acoustic sensors with high sensitivity, broadband response, and low noise are indispensable for auditory detection and environmental monitoring. Extrinsic fiber acoustic sensors are currently a research hotspot for their all-portable components and immunity to polarization fading but are limited by their sensitivity and minimum detectable pressure (MDP) due to interferometric drifts, which demand sophisticated control and calibration. Here, we propose a self-quadrature locked (SQL) extrinsic fiber acoustic sensor that eliminates the calibration procedure of searching for the quadrature point (Q-point). With a compact and convenient SQL control with proper optics designs, our sensor achieves a wideband detection ranging from 20 Hz to 10 kHz with an outstanding sensitivity of 95.21 V/Pa (−80.4 dB re 1 V/<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>Pa) and an MDP of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$21.1~\mu $ </tex-math></inline-formula>Pa/<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sqrt {\text {Hz}} $ </tex-math></inline-formula> at its resonance frequency of 5400 Hz. We demonstrate the weak sound detection capability of our sensor and its superb performance in audio clones and real-time speech recognition, indicating its promising prospects for high-fidelity acoustic sensing.