The Effect Of Polarization Random Noise And Its Suppression In Golay-coded Brillouin Optical Time Domain Analysis Fiber Sensor

Distributed optical fiber sensing technology is widely used in traffic,geological and construction safety and health monitoring for its advantages of anti electromagnetic radiation,chemical corrosion resistance and long-distance distribution measurement.As one of the distributed optical fiber sensing technologies,Brillouin optical time domain analysis(BOTDA)has outstanding technical advantages in long-distance,high spatial resolution and other sensing measurement,so it has been widely concerned.In recent years,in order to break the mutual restriction between sensing distance,sensing spatial resolution and measurement accuracy,many signal-to-noise ratio enhancement technologies have been proposed one after another.Among them,pulse coding technology can improve the signal-to-noise ratio while maintaining the spatial resolution of the sensor,so it has become one of the research hotspots at home and abroad.The main work and research contents of this paper are as follows:1)This paper analyzes the sensing mechanism and framework of the BOTDA,and discusses the influencing factors of four performance indexes of spatial resolution,measurement accuracy,sensing distance and measurement time,as well as the relationship between them: When the pulse width is reduced,the spatial resolution will be improved,but the measurement accuracy and effective sensing distance will be reduced.This contradiction can be effectively overcome by pulse coding technology,so as to improve the sensing performance.2)This paper analyzes the coding process of BOTDA,and focuses on the improvement of signal-to-noise ratio and sensor performance by Golay-coding technology.It is concluded that the Return to Zero format is a necessary condition for Golay-coding technology to be used in the BOTDA system,and the increase of the pulse width and the number of coding bits has a limited effect on the improvement of the sensor signal-to-noise ratio due to the pump consumption.Then,the measurement control and signal processing process of Golay-coded BOTDA system are introduced.3)The polarization dependence of stimulated Brillouin scattering(SBS)and its influence on BOTDA sensing are analyzed.By studying the polarization random noise in Golay-coded BOTDA,it is found that it damage the sensing accuracy seriously.A scheme based on Brillouin phase-shift spectrum to suppress polarization random noise is proposed,and the improvement of sensing accuracy is verified by simulation and experiment.4)The influence of wavelet image threshold denoising technology on the sensing performance of Golay-coded BOTDA system is analyzed.The results show that although its effect of suppressing polarization random noise is weak,it can reduce the influence of white noise on the sensor and further improve the sensor accuracy.