Finite element model for embedded fiber Bragg grating sensor

Abstract

This paper presents an integrated formulation for the calculation of the spectral response ofa fiber Bragg grating sensor embedded in a host material system, as a function of theloading applied to the host structure. In particular, the calculation of the transverse strainsensitivity of a fiber Bragg grating sensor through the calculation of the change in effectiveindex (or indices) of refraction of the fiber cross-section due to the applied load is presentedin detail. For the calculation of the fiber propagation constants, a two-step finiteelement formulation is used incorporating the optical, geometric and materialproperties of the cross-section. Once the propagation constants and principaloptical axes are known along the fiber, a modified transfer matrix method isapplied to calculate the spectral response of the FBG. It is shown that the FEformulation yields close agreement with previous methods for benchmark diametricalcompression cases. However, the current method provides the potential to evaluate theeffects of high strain gradients across the optical fiber core present in some loadingapplications.