Research On The Signal Processing Technology Of The BOTDR Sensing System

The sensing system of BOTDR has become the mainstream of the fiber optic sensingtechnology because of its high detect accuracy, long sensing distance, wide dynamic rangeand the simultaneous detection for temperature and strain. In this paper, we study on therelated technology of distributed optical sensing system based on brillouin optical timedomain reflectometry. Complementary correlated prometheus orthonormal sequence isused for producing pulse sequence, we also analyse the new model of brillouin scatteringspectrum and put forward new algorithm of parameters demodulation.Firstly, we explain the generation mechanism of brillouin scattering and research onthe relationship between brillouin frequency shift and the light intensity and sensingperformance parameters like temperature and strain. We also discuss two detectionmethods of brillouin optical time domain reflectometer. At the same time, we analyse themain performance objective of the system.Secondly, the spontaneous brillouin scattering signal is quite weak, so it is verydifficulty to detect the signal. Moreover, increasing the pulse width of the incident light toimprove the signal power will reduces the spatial resolution of the system. In order tosolve this problem, we propose complementary correlated prometheus orthonormalsequence for optical pulse coding. In this paper, we elaborate the generation mechanism ofthe ccpons and principle of using in the sensing system. Meanwhile, we analyse the effectof the optical pulse coding techniques for the improvement of the system, signal-to-noiseratio. Through the simulation analysis, we have proved that the technology can keep thesystem spatial resolution under the premise of improving the SNR of the system,increasing the sensing distance and improving the resolution of the system.Finally, in order to improve parameter extraction accuracy of the brillouin scatteringspectrum, we use the linear weight combination of a lorentzian and a gaussian. Concurre-ntly, we apply hybrid optimization algorithm which is made of the particle swarmoptimization and the levenberg-marquardt as parameters demodulation algorithm. Thenumerical results show that the new modeland the hybrid optimization algorithm give a guarantee to suit the accurate measurement with brillouin scattering spectrum. Besides, wedesign the sensing system based on electro-optic shift frequency of BOTDR. Throughsimulations verification and experiments, it indicates that the new model and the hybridoptimization algorithm are feasible and effective for using in the parameter extraction ofbrillouin scattering spectrum.