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A dual Fabry-Perot (FP) interferometric fiber-optic acoustic sensor based on sandwich-structure composite diaphragm is proposed, where fixed phase difference is generated by two FP interferometers (FPIs) with different cavity length. An ellipse fitting differential cross multiplication (EF-DCM) interrogation process is applied for phase demodulation to overcome drawbacks of quadrature point based intensity demodulation, such as temperature drifting, optical power jitter and limited dynamic range. Besides, benefiting from the large area sandwich-structure composite diaphragm, high sensitivity and wide flat frequency response are obtained. Experimental results show that phase sensitivity is -121.11 dB re 1 rad/&#x03BC;Pa@250 Hz and sensitivity fluctuation is below 0.8 dB between 2-250Hz. To prove the high stability of the demodulation system, acoustic signal test is performed at different wavelength and different optical power and a fluctuation below 3% is observed. Moreover, profiting from the dual FP sensor structure, the acoustic sensor is get rid of influence of temperature drifting which usually leads to variation of cavity length of fiber optic acoustic sensor. The proposed sensor structure also overcomes drawbacks of traditional dual wavelength demodulation such as extra noise introduced by erbium doped fiber amplifier (EDFA) and high cost.

High Sensitivity and High Stability Dual Fabry-Perot Interferometric Fiber-Optic Acoustic Sensor Based on Sandwich-Structure Composite Diaphragm