Finite-difference beam-propagation method for anisotropic waveguides with torsional birefringence.

A new three-dimensional finite-difference (FD)-based beam propagation method (BPM) is proposed for simulating optical propagation in weakly guiding waveguides with torsional birefringence, which cannot be simulated by existing FD-BPM algorithms. We also demonstrate that this new BPM algorithm is capable of obtaining eigenmode solutions in a helically-symmetric z-dependent waveguide structure with torsional birefringence.