Application Research Of Optical Fiber Sensing And Fiber Grating Sensing Technology In Environmental Monitoring

Optical fiber sensors,which has the features of anti-electromagnetic interference,corrosion resistance,good electrical insulation,high sensitivity and wide-range monitoring,has gradually become a hot research topic in the field of sensing.Among them,the distributed optical fiber vibration sensing system based on Rayleigh scattering is capable of measuring the vibration,strain and transmission loss continuously along the sensing fiber.What's more,it can be applied in the fields of monitoring submarine optical cables,perimeter security and so on.The fiber sensing system based on fiber Bragg grating has the advantages of easily being multiplexed for distributed sensing,which is widely used in environmental monitoring,health monitoring of large military and civilian facilities,oil pipeline safety monitoring and so on.This dissertation mainly focuses on developing a long-distance distributed fiber vibration sensing system and improving the performance of time-division multiplexed fiber Bragg grating sensing systems.The main work of this thesis is as follows:Firstly,the domestic and international research status of Rayleigh scattering optical fiber sensing technology and fiber Bragg grating sensing technology is summarized.Then this thesis expounds the operating principle of optical time domain reflectometry and phase optical time domain reflectometry.Also,the temperature and strain sensing principle of fiber Bragg grating is studied.Secondly,this thesis designs the hardware circuit of the Raman amplification system,builds the distributed optical fiber vibration sensing system based on Raman amplification technology,and achieves a sensing measurement of 60 km.Thirdly,the different optical parameters on the influence of reflection spectral characteristics of fiber Bragg grating is analyzed,which mainly includes the length of the grating,grating refractive index modulation depth and apodization function.On this basis,the design and research of specific weak-reflective Bragg gratings is done by OptiGrating.Finally,in order to improve the performance of time-division multiplexed fiber Bragg grating temperature sensing systems,a G-S composite coding is used in combination with superposition average.The simulation results show that G-S composite coding technology not only guarantees the spatial resolution of the system is constant,but also expands the sensing range,enhancing the overall performance of sensing system.