Optimum Design Of Fiber Bragg Grating Demodulator Based On Tunable F-P Cavity

With the development of society and the continuous growth of global economy,structural health monitoring for various large and super large projects is becoming more and more important.Compared to traditional electrical sensors,Fiber Bragg Grating(FBG)has the characteristics of light mass,corrosion resistance,radiation resistance and anti-electromagnetic interference.It can be used to measure various physical quantities such as stress,temperature,vibration,gas concentration and so on.Therefore,it is widely used in the fields of aviation,ship,electricity and petroleum.The main work is as follows:Firstly,aiming at the low sensitivity of common base chip packaging structure,a new type of base chip packaging structure has been designed on the basis of common base chip packaging structure.At the same time,the key parameters of the sensitized structure are simulated and analyzed,and the experimental verification is carried out on the basis of the simulation analysis results.The strain sensitivity of the fiber Bragg grating strain sensor can be increased by 50% compared with the common base chip package after packaging the fiber Bragg grating with a new sensitizing structure.Secondly,based on the principle of fiber Bragg grating(FBG),this paper optimizes the performance of the demodulator on the basis of the demodulation method of the tunable Fabri-Perot(Fabry-Perot,F-P)filter.The reasons for the poor stability of the demodulation results are analyzed,a data acquisition and processing module,a power module and a photoelectric conversion module with FPGA as the main control chip are designed to effectively reduce the noise of the hardware circuit and enhance the signal to noise ratio of the signal so as to improve the stability of the demodulation results.Then,the factors that affect the real-time performance of the demodulator are analyzed,a half wave peak seeking algorithm with faster operation speed is adopted in the system data acquisition and processing module.The realization process of the algorithm is analyzed and the actual verification is carried out inside the FPGA.At the same time,the data communication between the lower computer and the upper computer is completed.The real-time demodulation of the center wavelength of the fiber Bragg grating is realized,and the demodulation rate is improved.Finally,by comparing the influence of the linear fitting and the secondary curve fitting on the demodulation results,the secondary curve fitting method is used to determine the central wavelength of the fiber Bragg grating,and the demodulation error caused by the hysteresis characteristic of the tunable F-P filter is reduced and the accuracy of measurementis improved.At the same time,a temperature compensation scheme is designed and the strain measurement is carried out according to the fiber Bragg grating strain sensor designed in this paper.The test results show that the demodulator works steadily,the central wavelength drift is ?pm3,the mean of measurement error is 2pm,and the demodulation rate is 30 Hz.