Research On Sensing Detection Based On Tapered Dense Grating

With the development of sensing technology,Fiber Bragg Gratings(FBGs)as sensing elements have advantages over traditional sensors and have a trend to replace it.However,the strain temperature cross-sensitivity issues of FBG sensors still restricts their development.If this key problem can be properly solved,it will bring tremendous economic benefits.In recent years,a variety of techniques have also been proposed to solve cross-sensitivity issues,such as two FBGs,the design based on special structures,and the solution based on special gratings.Through the comparative analysis of these techniques,this article has a research work on the characteristics,fabrication techniques and demodulation methods of sensors.Based on the study of characteristics and demodulation methods of sensors,an improved structure of sensors,which is named as Tapered Dense Grating(TDG),as well as the new demodulation method are proposed.The main research work is as follows:(1)An improved sensor named TDG is proposed.Applying transmission matrix method and coupled mode theory,which is used to analyze the spectral characteristics of non-uniform periodic gratings,to derive the transmission principle and sensing characteristics influenced by temperature and strain of TDG.(2)According to theoretical analysis,the numerical analysis of reflection spectral in TDGs is shown.A few simulations are made for different configurations of TDG,including the grating length,the position of grating,the length of the tapered region and the grating spacing.Using horizontal stretching and heating method as well as the phase mask method,it is to design and make TDGs with desired spectral characteristics.(3)An improved demodulation method based on Optical Frequency Domain Reflectance(OFDR)for TDG is proposed.According to research on the location and reflection peak demodulation techniques of TDG,the peak wavelength and the bandwidth of the reflection spectrum are measured by the segment demodulation with OFDR.By experimentally verifying the theoretical analysis,the new demodulation approach is feasible.(4)Temperature and strain sensing experiments are performed on the prepared TDG to measure the sensitivity of the grating bandwidths/peak wavelengths to temperature and strain.Using TDG for the simultaneous measurement of temperature and strain,the unmodified demodulation and improved demodulation methods are used to decouple the temperature and strain in this case,respectively.Sensing performances of TDG compare with Tapered Fiber Bragg Grating(TFBG)sensing performances among existing research.