Research On Sensing Characteristics Based On Tilted Fiber Grating

Tilted fiber Bragg grating(TFBG)is a kind of fiber grating with special structure.Because there is a tilt angle between the fiber core axis and the grating plane,the coupling mode of TFBG is changed.It not only has the advantages of ordinary FBG,but also has its own unique advantages.Ordinary FBG is not sensitive to the refractive index of the external environment,while TFBG is very sensitive to the refractive index of the external environment due to the existence of cladding mode.A single FBG can not solve the cross-sensitivity problems such as temperature stress,while TFBG can use the characteristics of the cladding mode to solve this problem.Therefore,TFBG has been widely concerned by researchers in sensing and other fields.In this paper,the coupled mode theory of TFBG,spectral characteristics change under different structural parameters and sensing characteristics are studied.On the basis of these studies,a method for monitoring the leakage of liquid pipeline is further proposed and the idea of multi-parameter measurement based on TFBG is simply put forward.The main contents are as follows:1.The development,classification and application of fiber Bragg grating are introduced,On the basis of fiber grating,the development status and application fields of tilted fiber grating at home and abroad are briefly described.2.The writing methods of fiber gratings and tilted fiber gratings are introduced,and then the coupled mode theory of fiber gratings is explained in detail,and the coupled mode theory of tilted fiber gratings is deduced by analogy.3.The influence of different structural parameters of TFBG on its transmission spectrum characteristics is simulated by using the fiber grating simulation software optigrating,including the influence of tilt angle,grating length,core radius,grating period and grating modulation depth on the transmission spectrum.The mutual compensation between the structural parameters is summarized,which provides some theoretical guidance for writing qualified TFBG.4.By means of theoretical derivation,simulation analysis and experimental verification,the sensing characteristics of TFBG,including temperature,stress and external environment refractive index sensing,are studied.The study found that the resonance peaks of each mode of TFBG have a linear drift with the change of temperature or stress,and the sensitivity of each cladding mode to temperature or stress is basically the same.For temperature sensing,the core mode is more sensitive than each the cladding mode.For stress sensing,the opposite is true.At this time,the sensitivity of the cladding mode is significantly higher than that of the core mode;for the refractive index sensing characteristics,the resonant peak wavelength of each mode of TFBG will increase with the increase of the refractive index gradually shifts to the long wavelength direction.In addition,the continued increase of the refractive index of the external environment will cause the TFBG to start to cut off from the highest order cladding mode.The research results have certain reference significance for the development of TFBG sensors.5.A TFBG sensor which can be used for pipeline leak monitoring(the refractive index of the transport liquid should be greater than or equal to the refractive index of the cladding mode)is proposed,and the feasibility of this method is further verified by simulation and experiment.In the fourth chapter,a multi-parameter measurement method based on TFBG is proposed based on the research of TFBG sensing characteristics.6.Finally,this paper summarizes the research content of this paper,and puts forward some improvement ideas for the shortcomings of this paper,and prospects the future work.