Experimental Platform Construction And Key Technology Research Of Heterodyne Detection Brillouin Optical Time-Domain Reflection

As is known to all,optical fiber,as the most important transmission and sensing medium in the world,has an irreplaceable status.As a sensing medium,optical fiber has the advantages of being easily received by various optical detectors,high sensitivity and stable performance.As a transmission medium of optical fiber,with the convenience of photoelectric or electro-optical conversion,in the transmission process without electromagnetic interference,non-invasive and small signal loss advantages.Optical Fiber Sensing Technology can be rapidly developed by using Optical Fiber as the transmission and Sensing medium at the same time.According to different detection methods,it can be divided into the following three categories:point-based,quasi-distributed and Distributed Optical Fiber Sensing Technology(DOFS),where DOFS is one of the most popular research topics in the world.OFS can be divided into the following three types according to different scattering light types:Brillouin scattering DOFS,Raman scattering DOFS and Rayleigh scattering DOFS.Although based on Brillouin scattering DOFS compared with two other DOFS is late some,but the sensor on the temperature and stress can be achieved when the sensing distance and accuracy of the experimental parameters are better than the other two DOFS,moreover by detecting frequency shift of Brillouin scattering signal and strength parameters,such as sensor can simultaneously realize the double parameter sensing of temperature and stress.Therefore,DOFS based on Brillouin scattering has attracted many researchers and achieved fruitful research results.Based on based on Brillouin scattering in the DOFS of a large number of investigation and research,this paper design a Domain based on light Frequency Shift(ODFS)Optical Domain Frequency Shift,the heterodyne detection of Brillouin Optical time-domain reflectometer(ODFS-BOTDR)system design scheme,design scheme based on the experimental platform ODFS-BOTDR set,and built the experiment platform on the related theory and experimental research.The main research contents are as follows:Firstly,this paper briefly introduces five DOFS based on Brillouin scattering and their research status at home and abroad,and classifies and compares these five technologies according to their principles.The Brillouin scattering in optical fiber is analyzed from the principle and the characteristics of the scattering signal.By detecting the frequency shift and intensity of the Brillouin scattering signal,the dual-parameter sensing of temperature and stress can be realized simultaneously.A solution was proposed to solve the problem that the sensing parameters of Brillouin scattering signal were sensitive to the cross of stress and temperature,and the detection method of Brillouin scattering signal was briefly summarized,which laid a theoretical foundation for the subsequent establishment of the ODFS-BOTDR experimental platform.Secondly,an ODFS-BOTDR experimental platform construction scheme based on ODFS is designed.The platform consists of five modules,namely,light source module,light pulse modulation module,incident light power adj ustable module,heterodyne detection module and optical domain frequency shifting module.The technical indicators of each module were analyzed,and the key device selection scheme and detailed parameters of each module were introduced in detail,which provided a theoretical basis and reference standard for the subsequent construction of ODFS-BOTDR.Then,the ODFS-BOTDR experimental platform was built according to the construction scheme of the experimental platform,and the relationship between scattered light and incident light power in the optical fiber was explored and verified through experiments.To the optical fiber and modulation method used in this experiment platform,a Stimulated Brillouin Scattering threshold measurement scheme is proposed,and the factors influencing the threshold of Stimulated Brillouin Scattering(are explored through experiments.An ODFS-based approach is proposed,and its correctness is verified by experiments.Theoretical analysis of optical pulse modulation parameters,design of optical pulse modulation scheme and modulation of ODFS-BOTDR experimental platform required by the pulse signal;The introduction of a polarizer in the local signal path can generate randomly varying polarization states to eliminate the adverse effects caused by polarization states.The introduction of a polarizer can not only solve the problem of polarization sensitivity,but also make the system structure simple and reduce the cost.Finally,debugging ODFS-BOTDR experimental platform for each device,to the best working state,through the oscilloscope gathering since the deep scattering signal in the release,and carries on the digital signal processing of the collected signal,verify the feasibility of the experiment platform,for the subsequent treatment of optical fiber measurement temperature and strain of double sensor research laid a solid foundation.