Research Of High Precision Fiber Bragg Grating Demodulation System Based On F-P Filter

Fiber Bragg Grating Sensors(FBG)are widely used in aerospace field and civil market to measure temperature and strain physical quantities because of their great passive characteristics,high temperature resistance,corrosion resistance and electromagnetic interference resistance.The performance research of the demodulation system has good application value in engineering.At present,foreign demodulation systems and technologies are in a leading position,but their high-precision demodulation systems are costly;the performance of domestic demodulation systems need to be improved.This paper focuses on how to realize the low-cost and high-precision demodulation system,proposes factors that may affect the performance of the system.Based on the existing demodulation scheme,the optical solution is mainly improved,and the calibration algorithm for high precision is proposed.Key technologies and innovations are as follows:First,in the study of experiments about optical performance,it is found that the difference between the FP filter position,the coupler split ratio,and the SOA drive current affects the dynamic optical range and flatness of the wavelength tunable source.Based on the point factor,an optical solution for the wavelength tunable source with a flat spectrum and a large dynamic range is proposed.Second,during the data acquisition process,each signal has large noise interference after photoelectric conversion.According to the characteristics of this noise and the characteristics of the grating reflection spectrum,after analyzing two digital filtering algorithms FIR and IIR,and comparing three different data fittings,an optical solution for the tunable source with a flat spectrum and large dynamic range is proposed,which can improve the accuracy of the demodulation system and simplify the algorithm to improve the working efficiency.Third,aiming at the nonlinearity of the driving voltage and output wavelength caused by the creep characteristics of FP filter,a wavelength calibration algorithm based on standard sensor,etalon and acetylene chamber is proposed to set the threshold voltage of the triangular wave circuit to be dynamically adjustablele.Improve the accuracy of the etalon by calibrating the threshold voltage with the wavelength of the standard sensor.Fourth,on the basis of the basic demodulation function,the host computer software can set the tunable light source to a fixed wavelength output,which enhances the engineering value of the system.The fiber grating demodulation system designed in this paper is finally debugged and implemented on the FPGA-based embedded platform.The data processing algorithm is implemented based on the C language on the software development platform of LabWindows.After the system experiment,the system runs stablely,the software display well,the precision is ±1pm,the demodulation rate is 10 Hz,and the single channel can simultaneously demodulate 20 sensors,the working wavelength range is 1550±40nm,which verifies the design of the high-precision fiber grating wavelength demodulation system based on FP filter proposed in this paper is feasible.