Research On Diaphragm Design And Quadrature Phase Demodulation Method Of Optical Fiber Acoustic Sensor

Acoustic vibration signal is a micro-pressure signal with rapidly changing.It has great application prospects for the detection and analysis of acoustic signals by optical fiber acoustic vibration sensing system.Research on high quality optical fiber acoustic vibration sensor and high stability demodulating system has great significance.In terms of sensors,a polyphenylene sulfide gold plated diaphragm with high-reflectivity is proposed for solve the disadvantages of optical fiber sensor diaphragm with low light reflectivity,low interference intensity and poor signal contrast.The polyphenylene sulfide gold plated diaphragm improves the interference signal strength and contrast.In terms of demodulation,a quadrature phase demodulation method based on polarization birefringent crystal is proposed to improve the stability of the phase demodulating system.The excellent characteristics of the proposed gold plated diaphragm and the high stability of the quadrature phase demodulating system based on polarization birefringent crystal are verified by experiments.The main research work includes:1.The polyphenylene sulfide gold plated diaphragm is designed.In the simulation analysis,the influence of diaphragm reflectivity and sensor F-P cavity length on the interference fringe contrast is obtained.The surrounding fixed diaphragm vibration model is constructed,and the acoustic characteristics and resonant modes of the composite diaphragm are analyzed by ANSYS finite element simulation.The interference signal intensity of the optical fiber acoustic vibration sensor based on the composite diaphragm and the polyphenylene sulfide diaphragm is tested separately,and the sensitivity is tested.The results show that the composite diaphragm interference signal strength is 3.1 times higher than that of the ordinary diaphragm.The detection sensitivity is 11.1 nm/Pa at the frequency of 25 kHz.2.A quadrature phase demodulation method based on polarized birefringent crystal is proposed.The quadrature phase optical path difference is obtained by birefringent crystals with different thicknesses.For the low-coherence interferometry principle,two low-coherence interference signals are generated with quadrature phases,and the phase information is extracted by differential cross multiplication.In the theoretical simulation,the demodulation error is 0.62‰ under the condition that the center wavelength drift in ±20 nm.The system cavity length variation range is ±?,the demodulation error is 2‰,which proves that the system has high stability.3.The orthogonal phase demodulating system based on polarized birefringent crystal is built and the experiment is carried out.The results show that the signal noise ratio of the demodulating system is 70 dB,and the minimum detection phase of the demodulating system is 0.014 rad/Hz^1/2,which is superior to the similar acoustic vibration demodulating system.The experimental results show that the demodulating system has a large dynamic range measurement capability when the displacement range is [-1?m,+1?m].Under the condition that the center wavelength of the light source drifts by 20 nm,the demodulation phase diversification is 0.8%,which verifies that the demodulating system has high stability.