The Study Of Demodulation System Of Fiber Bragg Grating Sensor Based On Tunable Laser

With the rapid development of detection technology,sensor measurements are widely used to monitoring mine,temperature,pressure,vibration and civil structural.Most of traditional electronic sensors have good detection accuracy and work efficiency.However,they are limited to apply in harsh working environments because of charging and poor anti-electromagnetic interference ability.The fiber grating sensor widely concerned and applied in engineering practice because it has the advantages such as small volume,high precision and strong anti-interference ability.The fiber bragg grating mainly judges the change of physical quantity measured by detecting wavelength drift.Therefore,the fast and accurate demodulation of center wavelength of spectrum is significantly important in high precision monitoring of the system of fiber bragg grating.Firstly,the thesis expounds the research background and significance of the subject and discusses the development status and demodulation technology of fiber bragg grating at home and abroad.To overcome the disadvantages of traditional demodulation algorithms of wavelength such as low detection accuracy and efficiency,a high-precision wavelength demodulation algorithm of fiber bragg grating based on wavelet denoising is proposed and it is applied to engineering project.Secondly,the basic theory and sensing properties of fiber grating is exposed as well as the demodulation methods of fiber grating are analyzed.Then the thesis compares and analyzes the demodulation methods in terms of demodulation precision,demodulation stability,demodulation capability,demodulation speed,measurement range and system cost.Finally,the tunable laser method is determined as the demodulation method of this subject.Furthermore,the hardware design modules,chip and circuit of the demodulation system of fiber grating are proposed in terms of drive module of laser,current control module,temperature control module,photoelectric detection module,voltage regulator and data acquisition module in detail.Then the high-precision demodulation algorithm of fiber bragg grating based on wavelet denoising is put forward.And the algorithm is verified by computer simulation.Comparing wavelet denoised algorithm with finding-peak directly algorithm,polynomial fitting algorithm and Gaussian fitting algorithm by simulation,the result shows that features of wavelet denoised algorithm are highly speed and excellent stability.The temperature accuracy can reach ±0.04℃ and the maximum standard deviation after wavelength demodulation is better than 1.67 pm in the range of 70℃ to90℃.Operational efficiency of wavelet denoising algorithm is twice that of Gaussian fitting algorithm.Finally,a demodulation system of fiber grating sensor based on Vertical Cavity Surface Emitting Laser is built,and the demodulation algorithm adopts the high-precision wavelength demodulation algorithm of fiber bragg grating based on wavelet denoising.The result declares the system can measure the temperature of the water tank that its temperature is constant from hypothermia to megathermal and the temperature error is less than ±0.04℃.Simultaneously the temperature error is better than ±0.04℃ in the dynamic range of 70℃ to 90℃ of transformer windings.The experiences verify the feasibility and reliability of wavelet denoising algorithm and the algorithm can apply to high precision demodulate fiber grating in industry rapidly.