Abstract
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/μPa@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.
Highlights
Acoustic waves exist in many situations in the world
An ellipse fitting differential cross multiplication (EF-Differential cross multiply (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
Light signals reflected from FP interferometers (FPIs) are collected and converted to voltage signals by two photodetectors (New Focus, 1623) respectively
Summary
Acoustic waves exist in many situations in the world. Some of them are generated from natural processes such as volcano eruption [1], pipeline leakage [2], and partial discharge [3], [4]. Diaphragm-based fiber optic acoustic sensors have attracted much interest because of their high sensitivity [8]–[10], wide frequency band [11]–[13], and high dynamic range [14]. Compared with traditional dual wavelength demodulation, two quadrature signals are generated from two FP interferometers (FPIs) with different cavity length instead of two different wavelengths In this case, only one single frequency laser is used in the proposed demodulation method, which simplifies the demodulation system and decreases the cost greatly. Since power of the single frequency laser is high enough, extra EDFA is not necessary any more, which decreases the system noise greatly
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