Research On Key Technologies And Applications Of Multi Parameter Optical Fiber Sensing

Optical fiber sensing is divided into point sensor based on fiber grating structure and distributed fiber sensing technology using the principle of detecting laser pulse scattering.In the optical fiber sensing system,sensors are based on optical fiber production or optical fiber itself,with strong anti-electromagnetic interference ability,passive,adapt to the harsh environment,distributed,easy to network and many other advantages.They have been widely studied in recent years and have been applied in many fields such as civil engineering,perimeter security,energy and transportation.At present,the optical fiber sensing application system based on FBG is limited in the number of FBG sensors and the monitoring distance of the system due to fiber loss,Rayleigh scattering,and the limited bandwidth of the light source of the FBG sensing system based on ASE light source.It has always been a difficult point in the research of the FBG sensing system to realize long-distance,multi parameter sensing.Distributed optical fiber sensing,such as Phase OTDR and BOTDR,does not require peripheral sensors.The sensing optical fiber is both a communication medium and a sensor.The distributed optical fiber sensing system shows its unique advantages for application scenarios such as long-distance sensing links,complex geographical environments,and difficult energy supply.However,the current distributed optical fiber sensor still has defects and deficiencies in monitoring distance,monitoring capacity and index performance.It is urgent to improve the performance index of distributed optical fiber sensing,establish correlation between monitoring parameters and physical quantities that are of great concern or influence in practical application,and expand the application scope.In view of the above problems and development needs,this paper has carried out research on key technologies and applications of multi parameter optical fiber sensing.The specific contents are as follows:(1)This paper studies,designs,monitors and identifies the discrete optical fiber sensor(FBG)and distributed optical fiber sensor(DOFS).First,based on the principle of discrete optical fiber sensor,the cantilever based FBG sensor is analyzed.Based on the sensing characteristics of FBG sensor,an ultra long distance demodulation scheme based on broad spectrum light source and swept frequency light source is designed.A ultra long distance FBG demodulation scheme based on swept frequency light source is proposed,The scheme can accurately measure the wavelength of FBG in the range of 100km through Raman fiber amplifier,and the system error is about 20pm,which effectively solves the problems such as limited sensing capacity of traditional FBG sensing system and difficulty in realizing long-distance sensing.(2)For the distributed optical fiber sensing technology,the distributed acoustic wave/vibration sensing technology based on optical fiber Rayleigh scattering and the distributed temperature/vibration sensing technology based on Brilllouin scattering are mainly studied.First,the sensing principle and demodulation technology of Phase OTDR are analyzed.A distributed acoustic wave/vibration sensing technology scheme based on heterodyne interference is designed,and the technical indicators of the scheme are analyzed through experiments,The distributed optical fiber vibration sensing system designed in this scheme can realize vibration detection and phase recovery with a sensing distance of 40km.At the same time,in view of the increasing application of power optical cable,the complexity of optical cable erection and the difficulty of power optical cable identification,a multi-channel optical cable rapid identification system based on Phase OTDR is designed,and the experiment verifies that φ-OTDR’s 4-channel power optical cable identification system has a signal-to-noise ratio better than 15 dB.(3)Through the analysis of Brillouin scattering frequency shift caused by the interaction of optical field and optical fiber sound field when narrow linewidth pulse light is transmitted in single-mode fiber and the characteristics of Brillouin scattering signal,a Brillouin scattering demodulation scheme based on heterodyne interference and microwave frequency scanning is proposed,and the frequency shift change characteristics of factors such as fiber temperature and strain are analyzed through the BOTDR based on this scheme,The experimental results show that the system can realize 100km optical fiber temperature/strain monitoring,the spatial resolution is lm when the monitoring distance is 10km,and the temperature monitoring accuracy is ±1℃;The monitoring distance is 60km,and the temperature monitoring accuracy can be ±1℃ when the spatial resolution is 100m.The above technical indicators provide important technical support for establishing correlation between monitoring parameters and physical quantities that are focused on in practical application,and for carrying out associated physical quantity monitoring.(4)Based on the temperature/strain sensing characteristics of BOTDR,combined with the distributed sensing needs of power pipelines,and supported by BOTDR strain and temperature data,the temperature characteristics of overhead transmission lines during icing are analyzed.Combined with the temperature change characteristics of transmission lines during icing simulated by finite element method,a monitoring scheme for initial icing of overhead transmission lines based on BOTDR is proposed;Carry out lightning simulation experiments on overhead transmission lines,and propose a distributed monitoring technology scheme for overhead transmission lines based on BOTDR in combination with the temperature change characteristics of lightning strike points.The experimental results show that when the discharge capacity is 125C,the BFS rises at least 8MHz instantaneously,and the spatial BFS distribution conforms to the Gaussian distribution,which provides effective data and feature analysis for realizing the distributed monitoring of lightning strikes on long-distance overhead transmission lines.