Design And Implementation Of Phase Demodulation System In Heterodyne BOTDA

In this thesis the principles of spontaneous Brillouin scattering(SPBS)and stimulated Brillouin scattering(SBS)have been discussed based on the summary of the research status of Brillouin optical time domain analysis(BOTDA)technique.According to the mechanism of SBS,the temperature and strain characteristics of Brillouin frequency shift have been analyzed and the corresponding relations between Brillouin frequency shift and temperature/strain are studied.The principle of the traditional direct detection BOTDA system and the heterodyne detection BOTDA system which can detect Brillouin amplitude and phase shift simultaneously are introduced.The comparison bewteen direction and heterodyne detection BOTDA system is conducted.The expressions of stimulated Brillouin scattering transfer function and signal-to-noise ratio(SNR)improvement of two kinds are derived.Based on the analysis of heterodyne BOTDA system,on the basis of in-depth study of the brillouin phase demodulation method,designs the simulation phase demodulation system and digital phase demodulation system.Phase demodulation system is set up in Simulink system simulation model,simulation of the radio frequency signal and the phase difference of vibration signal extraction.For simulation of phase demodulation system with orthogonal demodulation module AD0105 B of AOM in hardware structure,system frequency instability caused by the error of proposed the corresponding solution.Using Labview software to build the digital phase demodulation simulation platform,the platform using the zero test,correlation test and the I/Q ort hogonal test to extract the phase information is achieved,and under the condition of different noise analysis of the performance of three methods: under the condition of small noise,the zero test are greatly influenced by noise,the relevant test,I/Q quadrature test basic is not affected,keep better demodulation accuracy;Big noise under the condition of the zero test is highly affected by the noise,loss of demodulation ability,relevant test edge drift phenomenon occurs,demodulation accuracy is lower,the I/Q quadrature test affected small,still keep demodulation accuracy.Late for three kinds of digital demodulation algorithm is put forward the corresponding optimization scheme: in the zero test,to join the superposition average process,reduces the sensitivity of algorithm for noise;In the relevant test,the iteration is presented in the relevant detection scheme,greatly improve the anti-noise ability of the algorithm,is suitable for low noise accurately extract the phase information.In I/Q orthogonal test,the all phase of data pretreatment process,solves the I/Q orthogonal test to detect the spectrum leakage problems of the whole cycle sequences.