Study On High-speed And High-resolution Demodulation System Of Fiber Grating Based On Spectroscopy

As the key technology of "two aircraft" special project,the aero-engine has become a major engineering problem which related to national defense and civil aviation safety.As an indispensable part of it,aero-engine condition monitoring technology plays an important role.By monitoring the working state of the aero-engine,it is possible to detect faults in time,accurately locate fault points,and effectively predict the life of components for ensuring flight safety.Due to the complex environment such as high temperature,high pressure and string electromagnetic interference inside the aero-engine,the application of traditional electric measurement methods is limited or even unusable.Therefore,studying new types of sensors that can work in harsh environments such as high temperature and high pressure has great significance in structural state monitoring.With the advantages of high temperature resistance,high pressure resistance and electromagnetic interference resistance,the fiber Bragg grating sensor(sapphire)can measure the temperature and strain of the aero-engine.Based on the effective refractive index and grating period of the fiber grating affected by external parameters,the high-precision detection of physical quantities such as change and temperature is realized by demodulating the wavelength shift of the center of grating's reflected light.As most-used type of the commonly used demodulation methods,static demodulation is not sufficient to achieve dynamic real-time monitoring of aero-engines.This paper proposes a fiber grating demodulation system based on spectroscopy,which can realize high-speed high-resolution demodulation of small displacement of center wavelength.Firstly,the spectrometer structure based on double-transmission grating and high-speed InGaAs array was designed and its optical characteristics are analyzed in this paper.Based on this characteristic,the external dimensions and resolution of the spectrometer were calculated.By using the optical design software Zemax,the spectrometer's collimating,dispersion and imaging system was designed and analyzed to optimize the optical parameters and correct the system aberrations.And then,an FPGA-based demodulation system was designed,including power system,InGaAs drive timing,analog conditioning circuitry,and high-speed data interface.Finally,according to the processed lens and mechanical structure,the adjustment and performance test of the demodulation system was completed.In this paper,the wavelength range and resolution of the spectrometer were tested.At the same time,the pixel calibration experiment and stability test analysis of the instrument were completed.The actual test result shows that the demodulation system designed in this subject can work stably.The wavelength range of the dual-grating spectrometer is 1526nm~1565nm with the resolution of 63.6pm.The system demodulation speed can reach 10 KHz,which can effectively realize the high speed and high resolution demodulation of the fiber grating sensor.