Research On Dual Wavelength Demodulation Technology Of Fabry Perot Cavity Optical Fiber Sensor

Optical fiber Fabry-Perot(FP)sensors are used to detect temperature,pressure,stress and other physical quantities in various fields due to their advantages of anti-interference,corrosion-resistance and good-stability.However,the application of optical fiber FP sensors in the field of vibration measurement is limited by the existing demodulation technology,because it is difficult for the existing demodulation technology to simultaneously achieve a large-dynamic-range,high-precision and high-speed.In the existing demodulation technologies,dual wavelength demodulation has the advantages of high speed and high precision,which is most likely to meet the requirements of vibration monitoring.In this thesis,the realization of large dynamic range demodulation of FP cavity fiber sensors based on dual wavelength demodulation technology is studied.Main contents are as follows:1.The basic principle of fiber Fabry Perot sensor and the principle of existing dual wavelength demodulation technology are studied.The reason of restricting the existing dual wavelength demodulation technology to realize large dynamic range demodulation is found out.The idea of combining two different wavelength optical signals into one optical signal for demodulation is proposed.2.According to the conjecture,a novel dual wavelength differential cross multiplying cavity length demodulation algorithm is proposed.The relationship between the value of dual wavelength and the demodulation range is studied by theoretical derivation and simulation,and the influence of optical signal bandwidth,initial cavity length error and noise on the new algorithm is discussed.3.According to the characteristics of the new algorithm,a dual wavelength demodulation system is constructed,and the optical path,circuit and upper computer parts of the system are designed and completed.4.The new algorithm is tested by simulation and experiment,and the demodulation performance of the new algorithm is analyzed based on the test results.The simulation and experimental results show that the dual wavelength differential cross multiply cavity length demodulation algorithm can be applied to the large range dynamic cavity length demodulate.The experimental results show that the algorithm can achieve high-precision demodulation with repeatability less than 0.0042%,resolution less than 15nm and root mean square error less than 30nm.The theoretical analysis of the algorithm shows that the demodulation range of the algorithm depends on the values of the two wavelengths used in the algo rithm.The smaller the distance between the two wavelengths,the larger the dynamic demodulation range.When the two wavelengths are 1553nm and 1547nm,the effective demodulation range of the dynamic cavity length of 100?m can be achieved.Based on the above research,the dual wavelength differential cross multiplying cavity length demodulation method is much suitable for the dynamic fiber FP sensor cavity length demodulation,and has advantages of high precision,high speed and large dynamic range,which has high application value in the field of noise detection and underwater acoustic monitoring.