Research On Sensor Demodulation System Based On Tilted Fiber Grating

Tilted fiber grating(TFBG)is a kind of special short period fiber grating.Because of the angle between the grating plane and the fiber axis,part of the incident light is coupled to the cladding mode of backward conduction,and the other part of the incident light is coupled to the core mode of backward conduction,so it has a very rich transmission spectrum and reflection spectrum,which is widely used in the field of sensing and demodulation.In this paper,an edge filter based on TFBG is designed according to the spectral characteristics of the tilted fiber grating,so as to realize the wavelength demodulation of the sensor signal.The main work is as follows:1.First,the related knowledge of FBG is discussed,then some contents of tilted grating are introduced,mainly including the development,writing and application of FBG;finally,the demodulation technology of FBG is introduced.2.The basic structure of TFBG is analyzed.The expressions of TFBG core mode and cladding mode reflectivity,Bragg resonant wavelength and cladding mode resonant wavelength are derived.3.After studying the theory of TFBG,the influence of different structural parameters on the spectral characteristics of TFBG is analyzed,including the influence of grating parameters,core and cladding parameters andenvironmental refractive index on the transmission spectrum.Finally,themutual compensation effect between different structural parameters is summarized.4.The refractive index sensing characteristics of cascaded TFBG were studied,and it was found that cascaded TFBG has a very high sensitivity in the range of small environmental refractive index changes,which can reach the order of 10~5,and can be widely used in high precision refractive index sensing area.Compared with the performance of TFBG,it is found that cascade TFBG can improve the detection accuracy of refractive index by a factor of two.5.Based on TFBG and edge filtering demodulation technology,a sensor demodulation system based on tilted fiber grating is designed.This system can realize the wavelength demodulation of four temperature sensing signals with different center wavelengths at the same time.Under the condition that the detection sensitivity of the system is not reduced,the detection speed of the system is four times that of the single wavelength sensor demodulation system.