Topological birefringence and combined Rytov-Magnus effect

It is shown that the symmetry properties of the locally isotropic inhomogen eous medium of an optical fiber cause circular and linear topological biref ringence. The circular birefringence delta n(C) in graded- index fibers is similar to(lambda/rho)(2) (where lambda is the wavelength and rho is the co re radius), while the linear birefringence is delta n(L)similar to(lambda/r ho)(3). This topological birefringence is characterized not only by the pol arization basis (as in crystals for example) but also by the magnitude and sign of the topological charge of the guided vortex. This topological biref ringence forms the basis of the instability of the fiber IV vortex and is o bserved experimentally as the combined Rytov-Magnus effect. (C) 1999 Americ an Institute of Physics. [S1063-7850(99)00803-4].