ABSTRACT
Tangent conical refraction may occur in an inhomogeneously deformed crystal, in an inhomogeneously deformed glass whose optical anisotropy is caused by the elastic-optical effect, and also in a moving fluid with an inhomogeneous velocity field, where the anisotropy is due to the Maxwell effect. If a birefringent medium with parameters admitting an appreciable wave transformation is placed between crossed polarizers, one may discern the transformation by observing the alterations in the interference pattern on a screen. The photoelastic effect usually leads to a weak optical anisotropy in elastic bodies. Liquid crystals are also characterized by a relatively weak anisotropy. In the approximation of independent normal waves the polarization vector of the extraordinary electromagnetic wave is tied to the direction of the optical axis and follows its rotation. Electromagnetic waves in axisymmetric optical fibers are characterized by a two-fold polarization degeneracy, similar to transverse waves in an isotropic medium.
