An Opto-Mechanical FBG Model in Polarization-Maintaining Optical Fibers With Photoelastic Anisotropy

This work presents a comprehensive three dimensional opto-mechanical model of a fiber Bragg grating (FBG) in a polarization-maintaining (PM) optical fiber. The model integrates solid-element finite element analysis with a polarization-resolved FBG formulation that accounts for polarization cross-coupling resulting from mechanical shear strains in the transverse optical fiber plane. Unlike previous approaches, an anisotropic photoelastic behavior is introduced to represent the full strain tensor of a weakly guiding optical fiber and demonstrated on a bow-tie PM fiber with an inscribed FBG. Experimental validation was performed using longitudinal tensile loading, diametric transverse loading, and temperature characterization. The model predicts the experimental load cases and temperature variations. The results provide a validated strain and temperature basis for designing PM optical fiber-based sensors with FBGs and sensor systems, especially when embedded in a host material.