Anisotropic dielectric waveguides

Abstract

The guided modes of anisotropic waveguides are known to be leaky when degenerate radiation modes of the orthogonal polarization exist. These losses can be quite large when the principal axes of the dielectric tensor are not aligned with the waveguide axis. We calculate the leakage rate in waveguides that have arbitrarily oriented dielectric tensors, using a perturbation expansion that is valid for weak guidance and weak anisotropy A relatively simple expression for the loss is obtained and is applied to model cases drawn from planar and fiber waveguides with step- and graded-index profiles. The scaling of the loss with profile height and anisotropy is discussed, including the practical case of strongly asymmetric planar waveguides.