Loss of longitudinal coherence as a result of the birefringence effect

The longitudinal coherence properties of waves propagating through a birefringent optical fiber are described theoretically and experimentally. A significant loss of longitudinal coherence is clearly observed for interference between two orthogonally polarized HE11 modes traversing an optical fiber with highly stress-induced anisotropy. It is verified that coherence degradation is due to the difference in magnitude of the chromatic-dispersion difference between the two eigenpolarization modes, even when the optical-path difference between the two polarizations is zero. The theoretically predicted results closely match experimentally obtained results with respect to both the modulus of the longitudinal coherence and its curved shape against the optical-path difference in the wavelength region from 0.8 to 1.55 μm.