Research On Brillouin Optical Time Domain Analysis Based On Optical Comb Amplification

Optical fibers were developed in the early 1970's,as means to support long-reach,high-rate optical communication.Since then,optical fibers also established their added value as an exceptional sensing platform.Alongside many other types of sensors,fibers support the distributed measurements of temperature and mechanical strain.Distributed fiber sensors are widely employed in structural health monitoring and perimeter defense.One of the physical mechanisms that are underlying distributed fiber sensors is that of stimulated Brillouin scattering(SBS).The most widely employed measurement configuration is Brillouin optical time domain analysis(BOTDA).Firstly,the theory of stimulated Brillouin scattering and the sensing mechanism of BOTDA technique is introduced.The SNR of the sensing system is also discussed.Due to the pump depletion,the SNR of the end fiber in the sensing system is very low.To address this issue,A method of optical comb amplification is proposed to compensate pump depletion and enhance SNR of the sensing system.In order to verify the effectiveness of this optical comb amplification method,a contrast experiment is employed.The performance of the sensing system is estimated thorough five aspects including 3D Brillouin gain spectrum(BGS),Brillouin spectrum,Brillouin time-domain curve,Brillouin frequency shift(BFS)and temperature measurement curve.The experimental results indicate that the SNR of the end fiber in new sensing system is enhanced 5dB.The accuracy of BFS and linearity of temperature measurement curve are also improved.In addtion,to improve measurement efficiency and realize commercialization of the BOTDA system,the related theoretical and technical problems of automatic control based on the BOTDA system are researched.Furthermore,a host computer software is programmed in the LabVIEW environment to achieve the above functions.Not only integrated control of each module of BOTDA system but also processing of the collected data are realized by this software.In addition,we added the function of displaying measurement results and alarms.