Research And Implementation Of On-line Quality Monitoring System For Large-scale Weak Fiber Bragg Grating Array

Weak Fiber Bragg Grating sensor has been widely used in the measurement fields of temperature,stress and vibration due to their special sensing characteristics.There,as an important carrier for constructing a large-capacity fiber Bragg grating sensing networks,FBG sensor has its own special performances,and these performances will directly affects the function of the sensing network.At present,the quality detection of large-scale fiber grating arrays is performed by OSA after the whole FBG arrays are completed.However,this method cann't immediately detect the quality of fibber Bragg grating fabricated,and effectively analyze the quality of the fibber Bragg grating in time.If a large number of grating quality is not up to standard in the grating array,it will result in poor performance of the sensing system and economic loss.In order to ensure the quality of the weak fiber grating array is qualified,it should be strictly controlled from the grating preparation source.Therefore,it is very important to analyze the grating spectral information and stop loss in real time during the on-line preparation of the grating.In order to solve the above problems,this paper designs a fast fiber grating demodulation system and a FBG quality analysis system,to achieve a high precision and accurate classification quality monitoring system of large capacity identical weak FBG.The main research works of this paper are as follows :(1)Aiming at the poor signal-to-noise ratio of end signal in long-distance propagation in large-scale long-distance weak fiber grating,the denoising method based on coded optical pulse according to Golay complementary is studied.On this basis,a variety of coding methods and corresponding demodulation methods based are studied to realize the construction of optical system construction and demodulation algorithm.In order to realize the appropriate optical pulse coding scheme,the influence of the linewidth of the laser source on different optical pulse coding methods and the influence of key components in the optical system on the coding system are studied.In order to realize the optical pulse demodulation algorithm based on Golay complementary code,the demodulation algorithm based on complementary correlation is studied to determine the corresponding demodulation rules and the correctness of the simulation verification demodulation rules.(2)Aiming at the requirements of real-time fast,non-interferometric demodulation for on-line weak fiber grating array spectrum,fiber grating demodulation system based on FPGA is researched and designed.In order to achieve fast demodulation,combined with the characteristics of the grating optical system,a positioning method and a precise signal acquisition method for the weak fiber grating are designed in the FPGA module.Aiming at the multiple reflection problem in long-distance weak fiber grating arrays,based on the weak fiber grating sensing principle,wavelength migration method is analyzed,and the scheme of non-interferometric demodulation of each weak fiber grating is obtained.Aiming at the problem of interaction between FPGA demodulation system and fiber grating writing device(drawing tower),the working mode of writing the grating in the drawing tower is studied,and the synchronous working method of two devices and the mechanical connecting device of two devices are analyzed.(3)Aiming at the requirement of spectral quality analysis of weak fiber grating,the weak fiber grating quality analysis method is studied to realize the classification and identification of weak fiber grating spectrum.Based on this,the spectral characteristics of weak fiber gratings are studied,the characteristic information of weak fiber grating spectrum is extracted,and the spectral analysis system is built to realize spectral classification and quality analysis of weak fiber grating.(4)The experimental platform was built to verify the improvement of the signal-to-noise ratio of the complementary coded pulse.The narrow-band weak grating array with a total length of 9.03 km and a spacing of 3m,and the chirped fiber grating array with a total length of 5km and a spacing of 3m were used as online monitoring targets to verify the stability and effectiveness of the demodulation system,as well as the reliability of the grating quality analysis system.