Simulation method for analyzing mechanical long-period fiber gratings under high birefringence

A simulation model based on the finite-element method (FEM) and transfer matrix method (TMM) is developed for analyzing mechanical long-period fiber gratings (MLPFGs). The anisotropic characteristics of the cross section of a fiber are obtained using FEM and the non-rectangular distribution of refractive index of the stressed area is accounted for to analyze band-rejection filtering characteristics using TMM, both of which are neglected in the conventional coupled-mode method (CMM). The overall attenuation in the entire spectral range is successfully simulated by the proposed method. The deviations of the transmittance at resonance wavelength between theoretical values and the actual conditions are 11.39 dB and 1.18 dB for CMM and FEM-TMM, respectively, for a high-birefringence case under a high applied force such as F = 60 N.