A Three-Dimensional-FEM Model With Experimentally Determined Material Parameters of an FBG Sensor Element in a Panda-Type Fiber

Abstract

A 20-mm-long 3D-FEM model of a Panda fiber was developed to improve the understanding of multiparameter sensing in attached or embedded polarization maintaining (PM) fibers. Previously unknown but for FEM modeling critical material parameters of the fiber's stress applying parts (SAP) were determined by a combination of measurements and simulations. The methodology gave evidence of a doping concentration of about 24 mole-% B2O3 in the SAPs for the specific type of PM fiber used. The model was evaluated for axial strains up to 1600 μstrain, axial stress up to 170 MPa, and in a temperature range from –40 to 160 °C. The simulated changes in the Bragg wavelengths of the slow and the fast axes and the change of their separation due to applied axial strain, stress, and temperature variations were in good agreement with measured data. A reliable 3D-FEM model of an FBG in a Panda fiber is now available that can be integrated into larger FEM models of embedded or surface-glued sensors fibers of type Panda. The model can be used to predict the influences of any arbitrary mechanical loads on an FBG in a Panda-type fiber at different temperatures.