The Study Of A FBG Demodulation System Based On The Dynamic Scanning Of DFB Laser

Fiber Bragg grating (FBG) sensor attracts much attention and widely appliedbecause of its unique characteristics of wavelength coding and ease of constitutingquasi distributed sensing network. However, the existing FBG sensor demodulationmethods mostly convert the wavelength into the intensity, phase, or other physicalquantities, which are severely affected by transmission loss, optical powerfluctuations and other factors. The direct wavelength demodulation systems are less,expensive and low integrative, which hinder the FBG used in practical engineeringapplication. Therefore, a direct FBG wavelength demodulation system with theadvantages of ease integration, low cost and good stability was established, whichcould satisfy the requirements of potential practical application.Firstly, a FBG demodulation system based on the dynamic scanning ofdistributed feedback (DFB) laser was established by using the basic principle FBGsensors, the wavelength-tuning characteristic of DFB laser and wavelength-selectiveproperty of fixed Fabry-Perot etalon. The demodulation principle and feasibility ofthe scheme were illustrated theoretically. Secondly, an experiment platform of FBGdemodulation system based on the dynamic scanning of DFB laser was set up. Thewavelength scanning properties of tunable DFB laser and the specific wavelengthtransmission characteristics of fixed Fabry-Perot etalon were investigated. Theresults show that the spectral peaks intervals of Fabry-Perot etalon transmissionspectrum are unequal because of the nonlinearity of DFB laser wavelength scanning.The quadratic polynomial was used to fit the wavelength and the scanning time point,and the fitting degree is more than0.999. Meanwhile, for the spectral characteristicsof FBG and fixed Fabry-Perot etalon, as well as the existing Peak-Detectionalgorithm, a complete demodulation algorithm of the system is proposed, combining a Peak-Detection algorithm that deals with the time-domain signals of FBG andfixed Fabry-Perot etalon by the direct Peak-Detection first and Gaussian fittingPeak-Detection afterward with the binomial fitting algorithm; The next, using the Cprogramming language and LabVIEW compile the data processing procedure of thesystem to deal with the time-domain signal acquired by the experimental platform,including the data reading, algorithm calling and result showing, for algorithmprocessing, the program has an interactive data processing interface easy to operate,and is easy to subsequently the develop and optimize. Finally, the calibration testgives the four system parameters: resolution is1pm, measurement accuracy is±10pm,the measurement range is1547~1552nm, the relative error is0.26%, so the systemcan meet the industry standard of FBG applications.