Phase Change of Electromagnetic Wave Induced by Static Strain

Abstract

The electromagnetic wave in a deformable body such as optical fibers will be affected by applying mechanical disturbance. Some previous investigators have focused on the phase change of the electromagnetic wave caused by strain and then applied the photoelastic theory to explain the experimental results. In this paper, we develop another approach based on coupled electromagnetic and mechanical equations for deformable electrodynamics to study the same phenomena. Constitutive equations which are derived from rational mechanics rather than measured by experiments are used to fit the coupled equations mentioned above. Because there are three sources for deformations - predeformation, applied electromagnetic wave, and perturbed strain-we consider the whole process of deformation as four states, i.e., natural, initial, intermediate, and final states. The equations under consideration are highly nonlinear and the strain due to the applied electromagnetic wave is much smaller than the others, the linearization and rigid body state approximation are necessary to estimate the main part of the phase change of the electromagnetic wave induced by perturbed strain. The relationships between electrostriction constants and elasto-optical coefficients, which are very important and valuable to make the result derived from deformable electrodynamics comparable to that from the photoelastic theory, are developed and discussed. From the comparison made, it is evident that results from the two approaches present satisfactory features.