Theoretical And Experimental Research Of Temperature Sensing Measurement Based On SBS Effect In Optical Fiber

Stimulated Brillouin scattering(SBS),as a typical nonlinear optical effect in optical fibers,has been widely used in many applications,such as fiber lasers,slow light delay,optical fiber sensing,microwave photonics,wavelength division multiplexing(WDM)system and so on.The linear dependence of Brillouin frequency shift(BFS)on temperature / strain has formed the basis of point/distributed temperature/strain sensors,which originates from the variation of sound speed and fiber refractive index.This linear relationship ensures a wide range of monitoring temperature and/or strain in industrial applications,such as communication networks,chemistry,petroleum,natural gas and civil engineering.Moreover,with the rapid development of optical fiber technology,the multi-wavelength fiber laser sensor utilizing SBS effect has drawn extensive attention in recent years.In this thesis,a series of theoretical and experimental researches on multi-wavelength fiber lasers based on SBS effect have been carried out.The main contents are as follows:1)Firstly,the background knowledge of the research subject is introduced,mainly giving an account of the classification as well as the advantages and disadvantages of traditional optical fiber sensors.Secondly,the research significance of novel multi-wavelength fiber laser sensors is analyzed.Thirdly,the potential of Brillouin scattering for sensing application is introduced,and the research status of multi-wavelength Brillouin optical fiber laser sensor is enumerated.Finally,the main content and innovation of this paper are explained.2)The multi-wavelength output and sensing mechanism of stimulated Brillouin scattering are introduced in detail and the formation process of outputing multi-wavelength by SBS is explained.Then the temperature sensing characteristics of Brillouin frequency shift in fiber are analyzed,along with the theory calculation process of Stokes wavelength width and temperature resolution.At last,other different sensing systems based on Brillouin scattering are presented.3)A multi-wavelength Brillouin-Erbium fiber laser(MW-BEFL)with switchable frequency intervals for L band is proposed and experimentally demonstrated,changing between single and double Brillouin frequency shift(BFS)through an optical switch.Up to 24 stable output channels with frequency interval of 10 GHz are observed,and 12 stable output channels with frequency interval of 20 GHz are obtained,respectively.In addition,the effects of different 980 nm pump power and seed pump power/wavelength on the number of Stokes waves are discussed by experiments.The stability of the waveform is studied,and the influence of the coupling coefficient on the output waveform is analyzed.4)A multi-wavelength fiber laser sensor combing erbium amplification with Brillouin gain has been designed and experimentally studied,and 31 output channels are generated.The basic characteristics of the sensing device as a multi-wavelength laser are analyzed.The effects of different temperature on the center frequency shift of each order Stokes wave is studied,proving the linear dependence of Brillouin frequency shift on temperature,with a temperature sensitivity coefficient of /15.27 MHz?.The error influence of humidity on the proposed temperature sensor and the one caused by frequency fluctuation are analyzed,obtaining the measurement errors of ?.08660? and ?2850.?,respectively.