Research On Distributed FBG Sensing System And Spectrum Correlation Demodulation Techniques

There is universal attention to fiber gratings and its application in fiber sensors. Fiber gratings offer many outstanding advantages. And they are very suitable for forming the grating array, by means of writing them into a fiber continuously. By pasting them on or into the material, the fiber grating array can measured the properties of the material, such as temperature, strain and so on. And how to enhance the accuracy of demodulation technology is a key to make the FBG sensors promising in industry. In the dissertation, the multiplexing and wavelength demodulation technology of distributed FBG strain-sensing system are researched. We propose that Spectrum Correlation (SC) and Digital Filter (DF) techniques in fiber Bragg grating sensors can enhance the accuracy of wavelength shift detection.In this thesis, the history, domestic and abroad research status and development trend for the future of FBG sensing technology are briefly introduced. The classification of FBG, the advantages of FBG sensors and its applications are presented.After the basic theory of FBG and FBG sensors are described, strain-sensing and temperature-sensing model are analyzed. The physical mechanics of the cross sensitivity is discussed. And then we introduce the process compensation of temperature and the result compensation of temperature. Base on the theory of FBG sensor and its principle, the experimental analysis on the strain sensing principle is explained.On the basis of analyzing advantages and disadvantages of several multiplexing and wavelength demodulation technologies, a mixture multiplexing method that combines wavelength division multiplexing (WDM) and space division multiplexing (SDM) is proposed to address 8×10 FBG sensing arrays and the tunable Fabry-Perot cavity wavelength filter method is proposed to demodulate the shift of wavelength. And we use LabVIEW to process the signal and design the interface.Because of the shortage of Conventional Peak Detection (CPD) technique, Spectrum Correlation (SC) and Digital Filter (DF) techniques are analyzed in theory, and it is testified that the two techniques could be applied to wavelength shift detection in fiber Bragg grating sensors system. The simulation and experiment results of CPD, DF (Chebychev Low pass Filter and Ideal Low pass Filter) and SC techniques are given separately. After analyzing the experiment data, it is validated that the experiment results accorded with the theory results well. Using Spectrum Correlation (SC) and Digital Filter (DF) techniques in fiber Bragg grating sensors can enhance the accuracy of wavelength shift detection by analyzing the simulation and experiment results. And Spectrum Correlation and Ideal Filter techniques nearly have the same effect.