Transversely anisotropic curved optical fibers: variational analysis of a nonstandard eigenproblem

A novel variational functional is introduced for the analysis of curved open and closed waveguides. The theory is based on the variational principle for nonstandard eigenvalue problems. The present method is valid for the arbitrary waveguide cross section and arbitrary radius of curvature for closed waveguides; for open guides, the radius should be sufficiently large, because the method predicts the real part of the propagation constant, not the imaginary part, which gives the attenuation in curved open structures. The dielectric medium can be homogeneous or nonhomogeneous with transverse and/or longitudinal anisotropy. As an example of the method, curved isotropic and anisotropic single-mode fibers with two different kinds of anisotropy models are studied. The analysis includes field distributions, changes in the dispersion curves due to reformed geometry, and birefringence characteristics in curved anisotropic fibres.>