An Efficient Scalar, Non-Paraxial Beam Propagation Method

A fast non-paraxial beam propagation method (BPM) is developed. Our method is based on expanding the field and the refractive index distributions in azimuthal harmonics, thus replacing a 3-D wave equation with a small number of 2-D wave equations. The method is shown to be substantially faster than standard 3-D finite-difference methods with comparable accuracy and works well with wide-angle waves.