Research On Fiber Bragg Grating Demodulation System And Error Correction Algorithm

Fiber Bragg Grating(FBG)sensor is one of the best and most promising optical devices in optical fiber sensing field.With its high sensitivity,anti-electromagnetic interference capability,ease of multiplexing and distributed measurement,small size,light weight and other advantages,not only is the FBG widely used in civil engineering,structural safety monitoring,electric power,chemical engineering and other fields,but also it is attracting more and more researchers in the fields of aerospace,oil exploitation and deep sea resource development,whose environmental conditions are extremely poor.The center wavelength of the FBG sensor is very sensitive to changes of physical quantities such as temperature,strain,and pressure in the environment,and there is a linear relationship between the center wavelength of FBG and the changing physical quantity.Therefore,the use of fiber Bragg grating sensors to achieve the physical measurement of the environment is simple,effective and high accuracy.The key of FBG sensing technology is the demodulation of the central wavelength of FBG.At present,researchers have designed and designed many demodulation methods,such as unbalanced Mach-Zehnder interferometer method,edge filter method,matching grating method and so on.Although the demodulation system based on these methods can demodulate the central wavelength of fiber grating,in practical engineering applications,these demodulation systems is expensive,or the accuracy is not high,or the structure is complicated.Therefore,it is of great practical significance to design a demodulation system with high demodulation accuracy,moderate cost,and high performance / price ratio for engineering applications.Firstly,in this paper,the development and classification of fiber gratings,the characteristics of fiber grating sensors,demodulation technology and applications at home and abroad are briefly introduced.Secondly,starting with the theory of coupled-mode theory,the theoretical models of FBG and the principle of temperature sensing and stress / strain sensing are introduced.The common methods of FBG demodulation and their advantages and disadvantages are analyzed and compared.The F-P filter method based on F-P etalon and F-P filter is chosen as the demodulation scheme of the system,and its detailed description is given.Thirdly,a fiber grating demodulation system is built based on F-P filter,which includes the whole system design,the optical path,the data acquisition part and the software part.The part of the optical path is mainly related to the analysis and testing of optical components;data acquisition part includes a brief introduction of the virtual instrument and the data acquisition card used in the model;software part includes the overall flow chart,peak search algorithm chart and implementation of interpolation algorithm,and finally completed the entire demodulation system.Fourthly,the problem of demodulation deviation between the rising and falling strokes when the F-P filter is driven by triangular wave is analyzed and corrected.The effects of the hysteresis and non-linearity of the F-P ceramic internal piezoelectric ceramics on the transmission spectra of FP etalon and reflectance spectra of fiber Bragg grating are analyzed.Based on this,a relative position correction algorithm of sampling points is proposed,and the algorithm is analyzed and demonstrated in detail.Finally,the system was tested for temperature.The calibration of the relative position of the sampling point was verified by the temperature change experiments.The wavelength calibration,repeatability test and stability experiment were carried out for the demodulation system.The experimental results show that the proposed method can effectively suppress the demodulation deviation of the two triangulations and improve the demodulation accuracy.For the two FBGs,the demodulation bias is reduced by 23.5 times and 28.3 times respectively.Demodulation system reproducibility and stability is better.