Research On Brillouin Sensing Characteristics Of Distributed Strain Fiber Optic Cables

As a transmission and sensing element,optical cable occupies an irreplaceable position in the field of optical fiber communication and optical fiber sensing with its own unique advantages.In recent years,with the widespread promotion and use of distributed optical fiber sensing technology in the engineering field,optical cable With the complexity and change of the engineering environment,there are more and more types of optical fiber,and there are large differences in its sensing performance.A suitable optical cable is the key to ensure accurate measurement of parameters such as strain and temperature.In addition to the accuracy of the measurement system itself,the reason for the measurement error caused by the distributed strain optical cable in engineering strain monitoring is mainly caused by the difference in the packaging material and structure of the optical cable.Aiming at the impact of the difference in strain monitoring of different packaged strain optical cables on the overall measurement performance,this paper uses Brillouin optical time domain analysis(BOTDA)technology to measure the Brillouin sensing characteristics of different packaged strained optical cables The research is carried out mainly from the two aspects of temperature and strain sensing characteristics to provide a reference for the application of various strained optical cables in engineering.The specific work is as follows:First,analyze the related theory of Brillouin scattering in optical fiber,and analyze the performance index of BOTDA system based on stimulated Brillouin scattering and the differential pulse pair-Brillouin optical time domain analysis(Differential Pulse Pair-Brillouin Optical Time Domain Analysis,DPP-BOTDA)technology was analyzed in detail,and a high spatial resolution DPP-BOTDA system for experimental measurement was built.Secondly,the DPP-BOTDA system is used to measure the Brillouin frequency shift and temperature coefficient of four kinds of tightly sleeved strained optical cables with different packaging structures,and the differences in temperature sensing characteristics of the optical cables in the unstrained state are experimentally studied.The thickness and structure of the outer protective layer of the optical cable,and the influence of the same kind of optical cable sheath and coating layer on the temperature characteristics are analyzed.It is found that the outer protective layer can improve the temperature sensing sensitivity within a certain temperature range,while the coating layer has almost no effect on it.Impact and other related conclusions.Finally,a comparative analysis of the strain sensing characteristics of four kinds of tight-buffered strain optical cables was conducted through distributed strain measurement.The results show that tight-buffered encapsulation can effectively increase the strain limit of the optical cable.Among the several types of optical cables studied in this paper,the strain limit is the largest.Reach over 42,000??However,the outer protective layer of the optical cable has different degrees of attenuation to the strain sensitivity.The influence of the material and structure difference of the sheath and the coating layer on the strain limit,strain sensitivity and elastic limit of the optical cable is analyzed.Finally,OFDR was used to measure the breakpoints in the point gluing mode,and it was found that the breakpoints were distributed at the edge of the gluing point,which was the maximum lateral and radial stress point.