Research On FBG Distributed Strain Reconstruction Method And Demodulation Application

One of the most important sensing components of modern optical sensing field,Fiber Bragg grating(FBG),is widely used in various fields of military and civilian,which can be applied to measure many physical quantities.FBG can be used to measure strain directly.When detecting uniform strain,the shift of center wavelength(Bragg wavelength)of FBG reflection spectrum is proportional with the measured strain,so the strain can be demodulated by detecting the variation of Bragg wavelength.When the FBG is used to detect non-uniform strain,the reflection spectrum will be chirped and no longer present a shape of single peak,even if the corresponding relationship still exists between non-uniform strain and reflection spectrum,and the demodulation of FBG's non-uniform strain is far more complex compared with the uniform strain.Due to special demands of detecting the inhomogeneous strain,FBG distributed strain detection has become an important research direction of FBG sensing technology.In this paper,the reconstruction methods and demodulation applications for FBG axial distributed strain are studied.The main contents are as follows.Firstly,with in-depth understanding of fiber Bragg grating refractive index modulation model and basic optical transmission theory,the principle of FBG sensor is discussed.And the basic reconstruction and demodulation technique of FBG compared and analyzed.Secondly,the FBG axial distributed strain reconstruction method based on the layer peeling(LP)algorithm is analyzed.The constant amplitude of complex coupling coefficient method is proposed to improve the peeling algorithm,that is QAC-LP.Simulation is carried out,and the results show that the accuracy of QAC-LP reconstruction is much better than that of LP;At the same time,the idea of polynomial function initialization(PFI)is used to optimize genetic algorithm and particle swarm optimization algorithm.The results show that the PFI method can improve the efficiency of the optimization algorithm.By analysis and comparison of different reconstruction methods on speed,accuracy and scope of application,we draw the conclusion that the genetic algorithm based on PFI is the better method than the other FBG distributed strain reconstruction methods discussed in this paper.In addition,the FBG reflection spectrum detection is realized by using the modified optical low coherence reflection(OLCR)system,and the PFI-based genetic algorithm is applied to the FBG-OLCR dynamic scanning detection system.The LabVIEW reconstruction program mixed with the MATLAB is developed.And also,we design the axial distributed strain tuning device of FBG,which is used in experiments.Finally,FBG distributed strain detection experiments are conducted and analysed.The accuracy and repeatability of the system performance are the basis of the experiment.As while the FBG spectra of uniform and non-uniform strain are detected,and the distributed strain results by PFI-based genetic algorithm are obtained.Comparing the experimental results with the simulation analysis results of ANSYS,we can know that the system can basically realize the distributed strain detection.