Research On Sensing Technology Based On Coded Rayleigh BOTDA System

This paper describes the development background and current research status of Brillouin distributed optical fiber sensing technology,and mainly elaborates the research status of the Brillouin optical time domain analysis(BOTDA).The characteristics of Brillouin scattering in optical fiber is maintained.And the corresponding relations between Brillouin frequency shift and the temperature/strain in optical fiber are studied.According to the sensing theory and performance analysis of Rayleigh BOTDA based on coding,the coded Rayleigh BOTDA experimental system has been studied and designed.According to the coding and decoding principle,encoding technologies of the coded Rayleigh BOTDA system,such as Golay coding and Simplex(abbreviated as S)coding,have been introduced.The implementation methods Golay coding and S coding in Rayleigh BOTDA system are studied in depth.The article analyzes signalto-noise ratio improvement quantity of the coded Rayleigh BOTDA system,and it is verified by using Matlab simulation.Simplex code Rayleigh BOTDA sensing system based on the Avalanche Photo Diode(APD)detector is presented.The system contains two kinds of noise,random shot noise and thermal noise.The Rayleigh BOTDA system applied coding technology can improve the signal to noise ratio while maintaining the same spatial resolution.In the system,the random shot noise power is related to signal power,and the thermal noise power that is irrelevant to signal power mainly depends on the performance of the APD detector.By analyzing the variance of current volatility which is relevant to two kinds of noise and S code encoding and decoding rules,the mean square error of coding system is obtained,then the signal-to-noise ratio and coding gain formula are deduced.And it is verified by using Matlab simulation.Finally the Golay coded Rayleigh BOTDA experimental system is designed,the key part of experimental system is the design of encoding and decoding subsystem.Before the design of coded system,the design and measurement of the single pulse code Rayleigh BOTDA system is carried out.The theoretical analysis of the stimulated Brillouin scattering(SBS)transient coupled wave equation of non return to zero(NRZ)code and return to zero(RZ)is presented,including the influence of acoustic field amplitude and Brillouin gain.The experiments were conducted to study the NRZ and RZ Golay coded Rayleigh BOTDA system.