Research On BOTDR Distributed Optical Fiber Sensor Monitoring System

With the development of economic and urbanization construction,China has rapidly become the world’s largest infrastructure market in the past 30 years,and the number of large-scale structural projects such as bridges,tunnels and gas pipelines has reached an unprecedented scale.These structural projects will also bring many security issues.Therefore,how to carry out effective health monitoring of large-scale infrastructure is of great significance.Health monitoring for facilities such as bridges,tunnels,oil and gas pipelines,and transmission lines is mainly based on strain or temperature monitoring.The traditional strain monitoring and temperature monitoring mainly rely on resistive sensors for point measurement.Due to their own electrical characteristics,such sensors are extremely susceptible to electromagnetic interference,are also easily corroded by the environment,and cannot achieve long-term monitoring,and the information at each position of the monitored structure cannot be continuously obtained,which not suitable for use in engineering.Compared with traditional electrical sensors,distributed optical fiber sensing technology has the advantages of continuous measurement,strong resistance to electromagnetic interference,corrosion resistance,light weight and small size.In distributed optical fiber sensing technology,Brillouin optical time domain Reflective(BOTDR)distributed optical fiber sensing technology has the advantages of simple single-ended measurement structure,long transmission distance,and the ability to measure temperature and strain simultaneously,which can realize real-time monitoring of the health status of engineering infrastructure.In this paper,after a lot of research and in-depth research on the BOTDR distributed optical fiber sensing technology,a BOTDR distributed optical fiber sensing monitoring system solution suitable for engineering is designed,and the experimental construction is carried out to verify its feasibility.In the selection of system components,the pulse generator is designed to be multi-parameter adjustable,which is convenient for different scenarios.The modular design of the device is proposed to facilitate integration,which lays the foundation for the later prototype development.The specific research contents are as follows:First,the domestic and international research status of distributed optical fiber sensing technology is introduced,including academic research dynamics and product research dynamics.This paper analyzes the generation mechanism of self-published Brillouin scattering and stimulated Brillouin scattering,and focuses on the stimulated Brillouin scattering threshold,Brillouin spectrum characteristics,the relationship between Brillouin frequency shift and temperature strain,the relationship between Brillouin light intensity and temperature strain,and the detection technology of Brillouin scattering signal.Secondly,design the BOTDR distributed optical fiber sensor monitoring system scheme,and build the system in the laboratory,introduce the selection principles of the devices used in the system and analyze its performance indicators.At the same time,in the process of platform construction,the design scheme is continuously optimized through experimental phenomena to obtain better sensing effects.Finally,the Brillouin signal was observed on the spectrum analyzer through experiments to verify the feasibility of the scheme.Finally,the characteristics of the self-published Brillouin frequency shift signal collected by the experimental platform and the signal detection and processing methods are introduced.Using MATLAB,the time-domain signals acquired by the experiment were subjected to Hilbert envelope detection,wavelet threshold denoising and L-M algorithm Lorentz fitting,and the Brillouin spectrum distribution information at different distances along the fiber was obtained.