Research On Key Technologies Of Optical Frequency Domain Reflection With High Spatial Resolution

Fiber optic sensing is widely used in engineering.Optical frequency domain reflection technology(OFDR)has attracted more and more attention because of its high spatial resolution and high sensitivity.Firstly,in this paper the basic composition and working principle of the optical frequency domain reflector system are introduced,its main parameters are discussed,and the influence of laser and receiver on the system is analyzed.Then we discuss the non-linear output of the laser and how to deal with the problem.In the next place,the methods of polarization fading and suppression of optical fibers are analyzed.At last,the method of eliminating system noise is tested.Finally,based on the above analysis,a distributed optical frequency domain reflection sensing experimental system integrated in the chassis is built and relevant experiments are carried out.The main contents of this paper are as follows:1.Based on the Mach-Zehnder interferometer,the basic principle of optical frequency domain reflection technology is analyzed,the scattering and bending losses of optical fibers are studied,and the low noise receiver technology is analyzed.Through the analysis,it can be found that the position of the fiber to be measured is related to the frequency of the beat signal reflected in the optical frequency domain,and the variation of external physical quantities is related to the drift of Rayleigh scattering.2.The output phase nonlinearity effect and its influence of the laser are analyzed,and the compensation method of the non-linearity phase is explored.According to the mathematical form of phase noise,the possible adverse effects of this problem are analyzed and simulated.By means of spline interpolation and deskew filtering,the negative effects of nonlinear effects are suppressed,and simulation and experimental studies are carried out.Finally,it is determined that the deskew filtering is more suitable for the system in this thesis.3.The method of combining wavelet decomposition threshold reconstruction and adaptive filtering is proposed to pretreat the signal in order to reduce the impact of system noise.The simulation and actual system tests show that the method can significantly reduce the impact of reflection peak sidelobes.Secondly,the influence of polarization fading is analyzed,and the polarization diversity method is used to suppress the polarization fading.4.Based on the above research and analysis of optical frequency domain reflection technology,an experimental system is built to conduct sensing experiments.The results show that the system can achieve 5 cm spatial resolution at 216.8 m,618.6 m and 1325.1 m distances,and the system can still maintain good resolution at 3979.9 m distances.