Research On The BOTDR Sensing System Based On Psendo-random Sequences Modulation

The fully distributed fiber sensing technology based on BOTDR (Brillouin OpticalTime Domain Reflectometry, BOTDR) is a one-dimensional application on fibergeometry measurement technique, which use parameters as a function of the length of thefiber position and its external physical parameters, can conduct on the path of the fiberalong the fiber length distribution for continuous measurement, providing means ofsimultaneous access to the measured physical quantity with time and spatial distribution ofthe state change. Compared with the traditional measuring instrument, it has theadvantages of full-scale continuity, long-distance, high-capacity, non-destructive testingand network intelligence and so on. However, because the spontaneous Brillouinscattering is extremely weak, BOTDR system spatial resolution and dynamic rangeperformance mutually restrict each other. Therefore, based on in-depth analysis BOTDRsensing mechanism, the paper proposes a pseudo-random sequence used in the sensingsystem to improve the signal to noise ratio measurement system to obtain a bettermeasurement results.Firstly, the paper focuses on the classification of distributed optical fiber sensingtechnology and the domestic and international development of that based on Brillouinscattering, introduces three fiber scattering effects, derived Brillouin frequency shift,scattering spectral intensity and temperature, strain the quantitative relationship betweenthe signal detection theory, BOTDR system, and focuses on the coherent detectionprinciple, given the system’s performance parametric analysis.Secondly, the paper proposes the use of pseudo-random sequence coding techniquesto improve the performance of Brillouin distributed optical fiber sensing system,introduces the concept and the mechanism of pseudo-random sequence, andpseudo-random sequence generated by the nature of the verification. At last, we used them sequence in BODTR system, and simulation results showed that using m-sequences toimprove the signal to noise ratio of the system had a significant effect.Moreover, the paper used the m sequence in fiber optic sensing system BOTDRdesigning and coding light pulses scattering signal acquisition module and associating demodulation processing module. Through theoretical analysis and experimental research,the paper prove that compared with the single-pulse detection scheme, this method caneffectively reduce test system noise without reducing the spatial resolution of the premise.The paper also verified the feasibility of the use of m-sequences to improve systemperformance.Finally, we designed the BOTDR distributed optical fiber sensing system based oncoded light pulses and coherent demodulation, expounded its various subsystems, andcompared distributed temperature measurements proved by single pulse detection scheme,which can effectively reduce test system noise without reducing the spatial resolution ofthe premise.