| Raman Optical Time Domain Reflectometry(ROTDR)is an effective means to obtain distributed temperature information.It has important application value in many major fields such as national strategic facilities,deep sea and deep ground,polar scientific research,largescale water conservancy projects,smart grids,etc.It has provided efficient measurement and monitoring tools for scientific research in these fields and played a huge role,effectively promoting the progress of related scientific research.The spatial resolution of the existing longdistance ROTDR(sensing distance greater than 10.0 km)is often difficult to exceed 1.0 m,due to the principle of OTDR is limited by the pulse width of the probe light.This does not meet the needs of national infrastructure temperature security monitoring.To solve this scientific problem,this dissertation proposes the chaos ROTDR system to improve the spatial resolution for monitoring temperature.In this scheme,pulsed laser is replaced by broadband chaotic laser as the sensing light source.The main research contents are as follows:(1)The optical fiber Raman scattering signal propagation equation based on chaotic pulsed laser is proposed,and the effect of chaotic pulse width on the spatial resolution of the ROTDR system is investigated.Firstly,the random fluctuation of intensity and broad-spectrum characteristics of chaotic laser are analyzed,and the generation method of chaotic pulsed laser is studied.Then,the superposition characteristics of fiber Raman scattering signals based on the OTDR principle are studied,and the relationship model between the pulse width and the system spatial resolution is established.Finally,the Raman scattering characteristics of chaotic pulsed laser in the sensing fiber and the regulation of the environmental temperature field on the chaotic Raman scattering signal are analyzed.(2)A chaos ROTDR scheme based on time-domain differential reconstruction method and short-scale time-domain correlation compression method is proposed.Based on the chaotic random amplitude characteristics carried by the chaotic Raman backscattered signal,this dissertation proposes a Time-Domain Differential Reconstruction(TDDR)method and a ShortScale Time-Domain Correlation Compression(SSTDCC),and the ROTDR model based on chaotic pulsed laser is simulated.Among them,the TDDR method performs time-domain differential reconstruction of the chaotic Raman backscattered signal to strip the chaotic Raman scattered signal at a unit position along the fiber.In addition,based on the SSTDCC mechanism,a demodulation equation of the relationship between the temperature in the FUT region and the correlation peak-to-peak value is proposed to realize the distributed temperature demodulation along the fiber.Simulation results show that a spatial resolution of 5 mm and a temperature resolution of 0.1 K are achieved over a sensing distance of 10.0 km.(3)The scheme of ROTDR based on chaotic p laser is experimentally investigated,which overcomes the limitation of the pulse width on the spatial resolution of the system.Firstly,the influence of system devices on the performance of chaotic pulsed laser is analyzed.Then,the characteristics of the chaotic Raman backscattered signal were explored experimentally,and the modulation mechanism of the ambient temperature field on the chaotic Raman backscattered signal was analyzed.Finally,a Raman distributed optical fiber sensing system based on the chaotic pulsed laser was built.The experimental results show that the spatial resolution of 10 m is achieved at a sensing distance of 1.25 km based on a 500 ns chaotic pulsed laser(the corresponding spatial resolution of the traditional ROTDR system is 50.0 m). |
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