Research On The Key Technologies To Improve The Spatial Resolution Of OFDR

Among distributed optical fiber sensing technology,optical frequency domain reflectometry(OFDR)has attracted the attention of researchers due to its large dynamic range,high spatial resolution and high sensitivity.However,the current OFDR distributed sensing system has certain shortcomings in the spatial resolution under long-distance testing,which limits its wide application and commercial product development.Firstly,this article introduced the working principle of OFDR and its polarization fading effect,and discussed the relevant parameters of the OFDR system;then analyzed the main reason that affects the spatial resolution of the OFDR system,that is the nonlinear tuning effect of the light source.Secondly,the methods of compensating the nonlinear effect of the light source were studied from the aspects of hardware and software,and a new compensation algorithm and an improved optical path structure were proposed;Finally,an OFDR system was built for experimental verification.The main research works of this paper are as follows:1.Analyzed the basic working principle of OFDR based on the structure of Michelson interferometer;analyzed the generation and influence of polarization fading effect,and adopted the polarization diversity receiving method to elimate this effect;analyzed the influence of the parameters of laser and acquisition card on the performance of OFDR system;the nonlinear tuning effect of the light source and its influence on the OFDR were studied;the methods of compensating the nonlinear effect of the light source were studied.2.An algorithm for compensating the nonlinear tuning effect of the light source based on matching Fourier transform was proposed.The working principle of this algorithm was analyzed,and the compensation process was described in detail.It was found that this algorithm can effectively improve the spatial resolution of OFDR system through simulation experiments.3.Analyzed the shortcomings of the traditional system optical path structure,and improved the optical path structure,that is,the delay fiber in the auxiliary interferometer was replaced with the tested fiber in the main interferometer.The improved system optical path structure simplified the optical path structure because the main interferometer and the auxiliary interferometer shared the same optical fiber,and eliminated the influence of external disturbances and different phase noises generated by the light source on the optical fibers of different lengths on the spatial resolution of the OFDR system.4.An OFDR distributed sensing system was build for experimental research.The results showed that under the test lengths of 215 m and 1160 m,the spatial resolutions of the OFDR system after compensation for the nonlinearity of the light source by onedimensional interpolation method,deskew filtering method,and matching Fourier transform method were 2.1cm,3.5cm,6.5cm;90cm,30 cm,cannot be accurately identified.After using the improved optical path structure,under the test length of1160 m,for one-dimensional interpolation method,the spatial resolution was increased from 90 cm to 25cm;for the deskew filtering method,the spatial resolution was increased from 30 cm to 6cm.