Analysis and Optimization of Acoustic Sensor Based on Fiber Fabry-Pérot Etalon

Abstract

Fiber optic sensors have been extensively studied in recent years. Due to the advantages of high sensitivity, compact structure, and anti-electromagnetic interference, the sensors based on the Fabry-Pérot (FP) cavity have become a research hotspot. The Fabry-Pérot etalon (FPE) acoustic sensor consists of two Plano-Concave Lenses coated with a highly reflective film, the Graded Index Lenses (GRIN) lenses, the optical fibers and a glass tube. Acoustic detection is realized by detecting the small change in the refractive index of the cavity medium caused by sound pressure, and the phase modulation technology realizes the modulation and demodulation of the acoustic signal. Matlab is used to analyze the influence of refractive index changes on the resonance spectrum and sensitivity curve, so the cavity mirrors with the reflectivity of 99% are selected. The structure of the FPE sensor is optimized using Zemax software. The optimal length of the sensor is 29.973 mm and the diameter is 6 mm. The high quality factor values of experiment and simulation are both 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> . At the same time, the experimental results show that the sensor has a response in the range of 50 Hz-20 kHz, with a high Signal-to-Noise Ratio (SNR) of 61.97 dB when the sound pressure is 19.795 Pa, and the sensitivity response is linear, reaching 0.19013 V/Pa. The research results provide useful guidance for the optimal design of the sensor, and the correctness of the theory is verified by the performance test of the optical acoustic sensor.