Research On Distributed Strain Sensing System Based On Optical Frequency Domain Reflectometry

Optical frequency domain reflectometry(OFDR)has the advantages of high spatial resolution,high sensing accuracy and high sensitivity.It has a wide range of applications in optical fiber link detection,strain and shape sensing,temperature sensing,vibration sensing and other fields.However,when OFDR is applied to strain sensing,it is restricted by the nonlinear sweep effect of light source and the displacement of distance domain under large strain,which limits the more common application of OFDR technology.Starting from the principle of OFDR strain sensing,this paper proposes a method to compensate the frequency sweep nonlinearity of light source and improve the performance of strain sensing,builds a strain sensing system,conducts theoretical analysis and experimental verification,and studies the application of the system in the fields of shape inversion and automatic data processing.The main contents of this paper are as follows: The nonlinear sweep effect of OFDR light source and its compensation method are studied.The influence of the nonlinear sweep frequency of the light source on the spatial resolution of the system is analyzed.The experiment was performed to verify the hardware compensation method based on synchronous sampling of external clock.After compensation,it reaches the spatial resolution of 0.107 mm at the measuring length of 10 m.A software compensation method based on zero crossing correction is proposed,which achieves a spatial resolution of 0.13 mm at a measuring length of 155 m after compensation.The displacement of signal range domain caused by strain and its compensation method are discussed.In this paper,the influence of distance domain misalignment of local optical fiber segment caused by strain on cross-correlation strain demodulation performance is analyzed,and a misalignment compensation method based on the starting point correction of sliding window is proposed to accurately demodulate the strain when the strain value at the distal end of the optical fiber is greater than.Strain sensing experiments were carried out.The strain sensing system was built to realize one-dimensional distributed strain sensing.The spatial resolution and strain resolution of the strain sensing reached 4.4mm and 20με at a measuring length of10 m,and the spectral drift and strain change showed an obvious linear relationship under small strain conditions.The linear goodness of fit R was 0.99898.The shape inversion model is constructed,the surface deformation and the fiber axial strain transfer model are established,and the design algorithm is used to reconstruct the two-dimensional shape of the surface.In addition,write the automatic data processing program,integrated data collection and processing functions,debug the program and optimize,achieve automatic data processing.