Research Of High-speed Fiber Bragg Grating Demodulation System Based On Distributed Feedback Laser

Fiber Bragg Grating(FBG)sensor has the characteristics of minute extension,low cost,high sensitivity,and so on.It is widely used in detection of structural health and mechanical equipment in the fields of civil engineering,space technology,marine shipping industry,and others.At present,fiber grating demodulation technology in low speed at home and abroad is very mature,but demodulation speed of fiber grating demodulation technology in low speed cannot meet the requirements in some fields like blade inspection of rotating machinery,which should enforce the key information acquisition such as multi-parameter dynamic,transient.This paper uses high-speed sweep frequency laser source made up by distributed feedback(DFB)laser and high-speed modulating current drive to carry on research of high-speed data acquisition,and finally developed a high-speed fiber grating demodulation system based on DFB laser focused on the wavelength demodulation demands of high-speed and high precision demodulation.The main work is as follow.(1)Proposed solutions of high-speed fiber grating sense demodulation based on DFB laser.Use the DFB laser drove by high-speed modulating current to form scanned-laser of 100 kHz.Use FBG sensor combined with circulator,phototube,and other optical devices to make up optical path modules.Use high-speed AD sampling to accomplish real-time acquisition of FBG reflection spectrum data.Use FPGA as an embedded control system to implement signal processing.Made up a high-speed fiber grating demodulation system to implement the high-speed demodulation of 100 kHz for fiber grating.(2)Study the wavelength demodulation method for high-speed fiber grating.Use peak searching algorithm of half-peak detection to do peak searching for FBG reflective spectrum to ensure the accuracy and high speed of peak value judgment for demodulation system design plan.Use system calibration and piecewise linear demodulation algorithm to do wavelength demodulation to FBG reflective spectrum,which improves the wavelength demodulation accuracy of the system.Propose the deleted waveform repair method in order to increase the wavelength demodulation range of the demodulation system,and repair the incomplete FBG reflective spectrum when mass data lose at the edge scanning of the laser,which implements wavelength demodulation of the incomplete FBG reflective spectrum.(3)Study the FBG Multiplexing of demodulation system.Use identical weak FBG to replace strong grating in order to increase the detection capacity of the demodulation system,and implement multipoint distributed detection.Use optical multiplexing technology to implement the demodulation of the multi gratings sensor network.(4)Test the demodulation system performance based on experiments of static temperature and dynamic vibration.Validate the incomplete waveform repair algorithm.The multiplexing capability of identical weak FBG of the demodulation system is validated based on the temperature experiment.Experimental results show that the system has excellent static and dynamic demodulation ability.Increase 40 % of the system demodulation range by waveform repairing algorithm.Comparison of the existing demodulation technology,demodulation system proposed by this paper can be used in 100 kHz high-speed fiber grating demodulation,and has the characteristics of high demodulation precision,simple structure and low cost,which can implement multiplex of identical weak FBG sensor network,and cannot be affected by external environment light intensity disturbance.The system has high stability and adaptive ability to application scenarios,which has greatly practical utility value.