Study On Fiber Bragg Grating Characterization By Local Transverse Force

The axial strain response of fiber Bragg grating (FBG) has been fullyinvestigated and used in measurement for strain, pressure, and thermalexpansion coefficient. On contrast, few study has been carried out on thetransverse load response of FBG.. In this paper, the characteristic of FBG underlocal transverse force based on characteristic of FBG under transverse forcewas studied. The primary content includes:1. The phase matching relation of FBG and characteristic of reflectedspectra was deduced in detail based on FBG module coupling theory in thispaper;the photoelastic effect was analyzed, and the elementary model ofsensing of FBG in transverse and axial direction was deduced.2. The reason that the reflected spectra of FBG split under transverseforce, the stress relation and the characteristic of reflected spectra wereanalyzed in detail. Based on this, the characteristic of FBG under localtransverse force was studied. The results are as following. (1) The characteristicof reflected spectra of FBG was analyzed based on transfer matrix method,when the center of FBG is subjected to transverse force. We can find that thespectrum split with the increase of local transverse force, and the split pointshift linearly and periodically. The characteristic of FBG subjected to transverseforce at center was theoretical analyzed using approximate matrix method;theexpression of period that the split point moved was deduced. It also analyzedthe split reason of reflected spectra, and the linear expression that the split spotshift in 3dB range was deduced. (2) After studying the characteristic ofreflected spectra of FBG subjected to local transverse force at different position,we can find the change of stress position has no impact on the wavelength ofsplit point, but the reflectivity of split point when the force is identical. Therelationship between the reflectivity and the position of stress is hyperbolictangent. (3) The phase character of FBG under local transverse force wasprimarily theoretical analyzed.3.The characteristic of FBG under local transverse force was carriedthrough experimental investigation. The result showed that the reflected spectrasplit when the center of FBG was subjected to transverse force, which is thesame as the simulation result;when the center wavelength of FBG is 1530.5 nm,the force that make the split spot shift one period is 11.06 N, this iscorrespondence with the result of the math expression;the spilt spot shift in oneperiodicity, its linearity is about 0.015 nm/N. The experiment of FBG undertransverse force in different position proved that the reflectance ratio is relatedwith the stress position. The data fitting curve prove that this relationship isapproximate hyperbolic tangent.