Study And Design Of Transversal Strain Sensor Based On Polarization Characteristics Of Linearly Chirped Fiber Bragg Grating With Transversal Strain In Small Applying Scale

There will be some axial extension in the applying scale of linearly chirped fiber bragg(LCFBG)with transversal strain.The effect of the axial one should be considered on condition that the length of the applying scale is sharp to the same order of magnitude compared with the diameter of fiber.Based on the analysis method of spatial elasticity,phase shift in the modulated refractive index distribution of LCFBG is obtained because of the axial extension.And a transmission spectrum peak is created which is related to the value and the position of phase shift.Furthermore,the radial refractive index of LCFBG is also changed for the birefringence with transversal strain.Considered with the conditions above,the theoretical sensing model of transversal strain in small applying scale is introduced in this paper,in which the polarization dependent loss(PDL)characteristics and Stokes parameters of LCFBG are very important and useful.The results of simulation and analysis are shown that the transmission coefficient grows exponentially with transversal strain but the peak value of transmission PDL spectrum is linearly dependent to the value of transversal strain applying in LCFBG.There is a one-to-one correspondence between the peak wavelength of transmission PDL spectrum and the applying position of transversal strain.And the peak wavelength of transmission PDL spectrum grows linearly with the value of transversal strain.And the peak value of transmission Stokes-s1 parameters is linearly dependent to the value of transversal strain applying in LCFBG.The peak wavelength of transmission Stokes-s1 parameters grows linearly with the value of transversal strain.So the position and value of transversal strain in small applying scale can be converted through the analysis method of measuring the transmission PDL spectrum of LCFBG.The linear relationship between Stokes-s1 parameters and the transversal strain has been measure by experiment.The sensitivity has grown better because the applying scale of linearly chirped fiber bragg is much smaller than tradition transversal strain measurement applying to the whole fiber grating area.There will be other uses of LCFBG because of the one-to-one correspondence between the peak wavelength of transmission PDL or Stokes-s1 spectrum and the applying position of transversal strain.Because of the extra phase-shift features,there is a relevance between the strain applying position and the peak of polarization parameters,and there will be of some theoretical and practical value.In practical application,the applying scale of LCFBG can be fixed for transversal strain sensor.And applying position can be different for a group of sensor to sensors network use.