Beam propagation method

Summary

The beam propagation method computes how a light beam evolves along a waveguide or another slowly varying structure. It replaces the Helmholtz equation by the paraxial wave equation for a slowly varying envelope, which is first order in the direction of propagation. The field is then marched step by step along that direction, for example by the split-step Fourier method or by finite differences. It is a standard tool for optical fibres and integrated optics.