Modeling Analysis And Optimization Design Of Simplex Coding BOTDA System

This paper mainly discusses the Brillouin scattering properties in fiber based on the introduction of Brillouin Optical Time Domain Analysis(BOTDA)technique.And analysis the relationship between temperature and strain with Brillouin frequency shift(BFS)according to the mechanism of stimulated Brillouin scattering.The sensing theory and performance of BOTDA system based on Simplex coding are analyzed,and also carried out the system modeling analysis and optimization design.Firstly,introduce the application principle of Simplex coding in BOTDA system,analysis the principle of coding and decoding;studied the limitation of SBS threshold of optical fiber to the performance of coding BOTDA system in depth,and analyzed the limitation of SBS threshold on system coding length quantitatively;The maximum length of the system under the fixed fiber length,and simulates the time-domain output of the system using 100 ns pulsed light and the peak power of 10mw?20mw and 30 mw respectively,illustrates the limit SBS threshold in encode BOTDA system coding length and signal to noise ratio furthermore.Secondly,considering the problem of the incident light power in the BOTDA system is limited by the optical fiber threshold of stimulated Brillouin scattering(SBS),the multi-wavelength light source is used to improve the SBS threshold;analyzed the SBS threshold of the multiwavelength BOTDA system theoretically,designed the experimental scheme to measure the SBS threshold of single-wavelength and multi-wavelength systems;analysis the improvement of SNR on system using multi-wavelength technology.The results show that when the three-wavelength light is used,the signal-to-noise ratio of the system can be increased by about 4.77 dB,the wavelength of 5 is improved by about 6.99 dB,and the wavelength of 40 is increased by about 16.01 dB,provided the theoretical basis on the experiment research of Simplex coding BOTDA system.Finally,a Rayleigh BOTDA system with single-ended incident and singleended operation is proposed based on the conventional double-ended BOTDA system.Analyzed two kinds of noise in S-coded Rayleigh BOTDA system based on avalanche photodiode(APD)detection: thermal noise and random shot noise.Considering the effect of multiplicative factor of APD on the signal-to-noise ratio of the system,the signal-to-noise ratio and coding gain of the system under the optimal multiplication factor are deduced,the optimal code length under the condition of multiplication factor is obtained and simulated it by MATLAB.