Research On Fiber Bragg Grating Magnetic Field Sensing Technology Based On Microwave Photonics

The optical fiber magnetic field sensor has the advantages of small size,low cost and anti-chemical corrosion.It has broad application prospects in navigation,vehicles,and medical instrument systems.Among the existing optical fiber-based sensing solutions,optical spectrum analyzers are widely used in traditional optical sensing systems.Because the resolution and detection speed of the spectrum analyzer cannot be achieved at the same time.The traditional optical fiber magnetic field sensor also has the problem of mutual restriction between the resolution and the detection speed.Therefore,it is necessary to propose an optical fiber magnetic sensor with high resolution and low cost to meet the needs of high-performance sensing applications.In this paper,a new magnetic field sensor system based on microwave photonic is proposed for FBG array.Microwave photonic technology is used to convert the optical domain sensing information to the microwave domain,and the dispersive element and the linear frequency modulation signal is used to convert the wavelength information of the grating in the optical domain to the frequency information in the microwave domain.Measurement by mature and high precision microwave equipment can further improve the interrogation performance.Thus,a fiber grating array magnetic field sensing system based on microwave photonics is realized.The work of this article is mainly divided into the following three aspects:(1)We have studied the coupled-mode theory and sensing principles of fiber Bragg gratings.The factors affecting the multiplexing capacity of the identical weak reflection fiber grating array,including backward Rayleigh scattering,multipath reflection and the limit of photodetector sensitivity,have also been investigated using theoretical derivation and simulation analysis.(2)We summarize the magnetic field sensor,including the causes of magnetostriction,the mechanism of the action of magnetic field on fiber grating and the strain transfer analysis of the sticky fiber grating magnetic field sensor.The magnetic field generating device is simulated and analyzed by ANSYS software.(3)A fiber grating magnetic field sensing system based on microwave photonics was proposed,and the design principle of the grating array for magnetic field sensing was analyzed.A magnetic field sensing grating array with temperature compensation is designed.In the demodulation system,the linear frequency modulation signal is used to drive the intensity modulator to modulate the broadband light emitted by the wide spectrum light source,and the chirped grating is used as the dispersive element to realize the mapping from wavelength to time domain.The beat signal is collected through mixers,photodetectors.Besides,the principle of wavelength demodulation is deduced in detail.Finally,20,50 and 100 identical weak reflection fiber grating cascade magnetic field sensing systems are simulated by MATLAB,and the influence of magnetic field and temperature on magnetic field sensor array is also analyzed.