High-Sensitivity Fiber-Optic Low-Frequency Acoustic Detector Based on Cross-Correlation Demodulation

Fiber-optic acoustic sensors based on Fabry-Perot (F-P) interference structure have advantages of compact structure, high sensitivity, convenience to manufacture and immunity to electromagnetic interference. To simplify the demodulation system of the fiber-optic F-P sensor and reduce the demodulation cost, a low-frequency acoustic detector based on the principle of optical cross-correlation (OCC) demodulation is proposed. A fiber-optic F-P interference sensor based on the phenylene sulfide (PPS) diaphragm is used as a low-frequency acoustic detection unit. The OCC demodulation system of the F-P acoustic sensors mainly includes a superluminescent diode (SLED), a flat glass wafer and single-mode fibers. The flat glass wafer is used as the static correlation reference cavity of the PPS diaphragm-based F-P acoustic sensor. The experimental results show that the detector is responsive to low-frequency acoustic waves from below 20 Hz to 250 Hz. For the acoustic waves with a frequency of 20 Hz, the minimum detection limit (MDL) of sound pressure is 0.65 mPa. The detector has the potential for low-cost and high-sensitivity acoustic detection for applications such as infrasonic detection and photoacoustic gas detection.