Research On Key Technologies Of Distributed Optical Fiber Transverse Load Sensor

Nowadays,the development direction of optical fiber sensors tends to realize distributed sensing.As people's requirements for sensing technology are gradually improved with the development of science and technology,the existing optical fiber sensors are insufficient to meet many measurement requirements.As one of the important branches of fiber optic sensors,fiber optic pressure sensors are widely used in various industries.Based on the principle of stimulated Brillouin scattering theory,this thesis firstly calculated the frequency shift and stimulated threshold of optical fiber,and discussed the forming condition and excitation mode of the Brillouin dynamic grating based on stimulated Brillouin scattering,as well as the basic characteristics of BDG?Brillouin dynamic grating?,which lays a foundation for the subsequent experiments.Secondly,the cross section of optical fiber under the action of transverse load was analyzed in detail,and the variation of each physical quantity of optical fiber under the action of transverse load was deduced.After theoretical calculation,the refractive index,wavelength are linearly correlated with the transverse load.ANSYS software was used to analyze the stress and strain at the macro level,and the order of magnitude of stress variables obtained from the simulation results was very small,with the maximum value being 2.8473×10^-4m/m and the minimum value being 4.8607×10^-7m/m,thus ignoring the influence of the shape variables of the fiber on each characteristic under the circumstance of small stress.After that,based on the existing equipment in the laboratory,the BOTDA system was improved and built based on the polarization-preserving fiber to measure the Brillouin frequency shift of the polarization-preserving fiber selected in the experiment.Through curve fitting,the Brillouin frequency shift of Panda polarization-maintaining fiber was 10.87GHz.According to the measured Brillouin frequency shift as the frequency difference before pumping light of the two beams excited by the Brillouin dynamic grating,it was confirmed by experimental comparison of reflection spectrum that the Brillouin dynamic grating was successfully stimulated.Finally for lateral transverse load measurement based on Brillouin dynamic grating,an experiment was carried out to detect the single point measurement under different load form,to explore the characteristics of the Brillouin scattering signal and the superposition average algorithm was analyzed,to deal with the original signal measured in experiment measured the transverse load of a single point of cases,the change of the amount of frequency shift.After data fitting,the sensitivity of transverse load acting on the experimental fiber fast and slow axis was 5.18GHz/Nmm^-1 and-6.14GHz/Nmm^-1,respectively.Finally,the experimental pump light signal was changed to measure the distributed transverse load,and the spatial resolution of the 103m Panda polarization-maintaining fiber was obtained as 3m.