Tension-induced modal birefringence in a single-fiber interferometric strain gauge

The sensitivity of a fiber-optic strain gauge that makes use of interference between the orthogonal linearly polarized eigen-modes propagated in a length of highly birefringent single-mode fiber is primarily determined by tension-induced modal birefiringence ΔB. This ΔB is in a close relationship with the ellipticity of the jacket surrounding the core, on which anisotropic residual stresses are imposed, but ΔB does not depend definitely on the beat length of fiber. Dependence of AB on Young's modulus and the Poisson ratio are computed and discussed in association with the measured results.