Research On Brillouin Optical Fiber Sensing Technique Based On Gain Spectrum Modulation

Since the advent of the first single-mode fiber in the 1970 s,fiber-optic sensing technology has been widely used in various fields.And because distributed optical fiber sensing systems have significant advantages in ultra-long distance,corrosion resistance and electromagnetic interference resistance,it has strong demand and broad application prospects in the fields of petroleum exploration,national defense safety,and building safety monitoring.Among them,Brillouin optical fiber sensing has attracted much attention due to the significant advantages of temperature/strain distributed monitoring with ultra-long sensing distance.However,a big factor restricting the development of Brillouin optical fiber sensing is the dynamic response speed.The domestic and foreign teams have done a lot of research on the dynamic response speed of Brillouin optical fiber sensing.After fully understanding the research of each group,this paper proposes a fast Brillouin optical fiber sensing technique based on gain spectrum modulation.Compared with other Brillouin optical fiber sensing systems,it has the advantages of large dynamic range,adjustable resolution and no complicated demodulation.This paper focuses on gain spectrum modulation in fast Brillouin sensing.In this paper,the feasibility of gain spectrum modulation is analyzed in principle,and the corresponding experimental results are analyzed.Finally,the ideal Brillouin gain spectrum is obtained.The specific research contents of this paper are as follows:(1)The system of optical fiber sensing is systematically explained,including its principle and related applications,and the development process of Brillouin optical fiber sensing system and current research hotspots are introduced in general.It also outlines the progress of the fast Brillouin sensing system at home and abroad.(2)The relevant theoretical knowledge of Brillouin optical fiber sensing is introduced in detail.Firstly,the related knowledge of stimulated Brillouin scattering in optical fiber is introduced in detail,and the working principle of Brillouin sensing is introduced.Then,taking BOTDA as an example,the factors limiting traditional Brillouin sensing are introduced in detail: The length of the fiber,the average number of times,the limited switching time of the optical frequency,and the number of sweep points.Then according to these limiting factors,several methods proposed to improvethe dynamic response speed of Brillouin sensing are introduced respectively,and the advantages and disadvantages of these technologies are further analyzed.(3)Based on the traditional Brillouin optical fiber sensing,based on the inherent Brillouin gain spectrum of the fiber,a new method is proposed.The amplitude modulation linear chirp pulse modulation module is used to modulate the pump light input to the sensing fiber to be tested.Amplitude modulates linear chirped pulse light,so that the probe light obtained by the signal receiving module obtains a wide range of linear regions in frequency,so that when the temperature/strain of the outside changes,the time domain signal strength of the signal receiving module occurs.The corresponding change.The system can change the sensitivity of the system by changing the spectrum of the pulsed light according to actual needs.This paper further proposes a comparison of the proposed system scheme with several existing technologies: the gain spectrum modulation technique can greatly improve the dynamic response range compared to the optical Frequency agile technique and the slope assist technique;compared to the optical chirp technique and the optical comb technique The detection signal of the gain spectrum modulation technique has only one frequency,so subsequent complicated electrical operations such as multiple fitting demodulation are not required,and theoretically,time can be greatly saved in obtaining the disturbance signal.(4)Brillouin modulation is applied to the fast Brillouin optical fiber sensing system based on Brillouin gain spectrum modulation proposed in(3).The principle analysis of Brillouin modulation is carried out in detail,and the feasibility of gain spectrum modulation is verified by simulation..The modulator is used to generate a linear chirped gain spectrum modulation system.The selection of key devices and their causes are introduced.Finally,the satisfactory Brillouin gain spectrum is obtained,and the experimental results are discussed and analyzed.