Study On Fiber Grating Characterization By Transverse Force And Torsion

In recent years, the axial strain response of fiber Bragg grating (FBG) has been fully investigated and used in measurement for strain, pressure, and thermal expansion coefficient. However, in previous related works, the effects of transverse force on the FBG and twisted characteristic on the high birefringence (HiBi) fiber grating are not discussed in detail. In this paper, the characteristics of FBG under transverse force and twisted HiBi fiber grating were studied. The primary content includes:Firstly, the paper introduces basic concepts on FBG. The characteristic of reflected spectra was deduced in detail based on coupled mold theory and transfer matrix method. Then the elementary model of sensing of FBG in stress and temperature was deduced.Secondly, the paper analyzes the spectra response of FBG under transverse force. The reason that the reflected spectra of FBG split under transverse force, the stress relation and the characteristic of reflected spectra were analyzed in detail. Based on this, the characteristic of FBG under local transverse force and inhomogeneous transverse force were studied. The characteristic of reflected spectra of FBG was analyzed based on transfer matrix method, when the FBG is subjected to transverse force. We can find that the spectrum split with the increase of local transverse force and the split point shift linearly and periodically. The change of stress position has no impact on the wavelength of split point, but the reflectivity of split point when the force is identical. The relationship between the reflectivity and the position of stress is hyperbolic tangent. In the case of plane stain, the reflected spectra response of FBG under inhomogeneous transverse force is analyzed. The relation between parameters of transverse force and bandwidth, symmetrical wavelength of spectra are deduced. Thereafter, the paper analyzes the spectra response of twisted HiBi fiber grating. Based on the characteristic of twisted HiBi fiber and coupled mold theory of FBG, the coupled equation of HiBi fiber grating is proposed and proved by transfer matrix method. The relation between reflected spectra response and twist angle is analyzed. Through employing latent root's form of HiBi fiber grating, the spectra response is analyzed in detail, and the mathematical models were established.At last, the paper carries out experiments on the characteristics of FBG under transverse force and twisted HiBi fiber grating. The theoretical analysis and numerical simulation are proved by the experimental results. Meanwhile, the paper analyzes experimental system and error, which makes theoretical basis for practical application in sensing fields of FBG under transverse force and torsion.