Research On Sensing Demodulation Based On Tilted Fiber Grating

Fiber Bragg grating(FBG)which is an indispensable member of optical passive devices has been widely used in optical communication networks and sensing fields.The grating surface of tilted fiber grating(TFBG)and the fiber axis are not parallel to each other.It is this special structure that makes the spectrum of TFBG richer.TFBG is often used in sensing demodulation as a sensor in recent years.After the theoretical derivation of TFBG,this paper explores the refractive index,temperature sensing characteristics and demodulation system of TFBG from the experimental process referring to its spectral characteristics in the simulation process.The relevant contents are as follows:1.This paper introduces the relevant aspects of TFBG starting from the classification,development and application of FBG.Then it describes the writing process and demodulation technology of TFBG.2.The structure of TFBG is theoretically explored,and its core and cladding modes are analyzed by using the coupled mode theory;Then the transfer matrix method which can be used to analyze inhomogeneous fiber gratings is introduced.3.The spectral characteristics of TFBG are studied by using simulation software and the spectral changes of TFBG are explored when the grating period,length,inclination and other parameters change.The influence of different parameters on the transmission spectrum of TFBG is analyzed and the effect of parameter compensation is discussed.Then the sensing characteristics of TFBG for temperature and refractive index are analyzed.4.The refractive index sensing characteristics of TFBG are explored,and the variation law of its spectrum with the refractive index of the external environment is detected.It is found that the transmission spectrum of TFBG will drift by 0.1840 nm when the external refractive index increases from 1 to 1.4.The traditional refractive index sensing system is improved,and a new refractive index sensing system is designed.The sensitivity of the two systems are 2.532mw/riu and 3.95mw/riu respectively.The improved system does not cause excess loss,and the sensitivity is greatly improved,which can better realize the refractive index measurement in a certain range.5.A four wavelength channel FBG temperature sensing demodulation system is proposed which uses TFBG as the edge filter.In order to ensure the accuracy of data and suppress the instability of light source,the FBG is encapsulated,which greatly increases the sensitivity of the demodulation system.The sensitivities of the four channels are 0.1072 nw/℃,0.1937 nw/℃,0.2323 nw/℃ and0.2987 nw/℃.On this basis,a new demodulation system is proposed.The system is based on 3d B coupler cascaded TFBG and deep transmission spectrum,which greatly increases the sensitivity of the system again.The experimental results show that the sensitivity of the new system is 0.1756nw/ ℃,0.4468 nw/ ℃,0.4988 nw/ ℃ and 0.7318 nw/ ℃ respectively.The system has simple structure,greatly improved sensitivity and greatly improved demodulation rate.