Finite Element Analysis of Multi-axis Strain Sensitivities of Bragg Gratings in PM Fibers

This article presents a numerical analysis of the sensitivity of fiber Bragg grating (FBG) sensors written into polarization maintaining fibers to transverse and thermal loading. These sensors are typically applied for the measurement of multiple strain components for the monitoring of civil structures. The finite element analysis includes both the optical and mechanical variations in the optical fiber. Five fiber types typically used in FBG sensors (elliptical core, D-fiber, elliptical core SAP, Bow-Tie, and Panda) are compared. It is shown that when only the fiber geometry is considered while the material parameters are approximately the same, the D-fiber demonstrates the highest sensitivity to transverse loading. In addition, it is shown that reducing the fiber cladding diameter significantly improves the sensitivities of the FBG sensor to transverse loads. All fiber types exhibit approximately the same sensitivity to thermal loading.