A mode-preserving perfectly matched layer for optical waveguides

For numerical simulation of wave propagation in optical waveguides, we develop a mode-preserving boundary condition for the popular perfectly matched layer, which truncates the unbounded transverse plane. The method is particularly useful for single-mode longitudinally varying wave-guiding structures and it is easy to use for step-index planar waveguides. With this boundary condition, accurate numerical solutions can be obtained in a much smaller computational window. Numerical results based on the beam propagation method for a tapered waveguide are used to demonstrate the capacity of this boundary condition.