BPM (Beam Propagation Method)

BPM is a numerical method used to simulate the propagation of a light beam along long waveguide structures, such as optical waveguides, splitters, and directional couplers.

How does BPM work?

Unlike FDTD, which solves the full Maxwell's equations at every grid point, BPM assumes light propagates mainly in one direction (usually along the waveguide axis) and calculates the changes to the field profile along that axis step by step. Thanks to this simplification, BPM is much faster than FDTD for long structures, though less accurate for strongly backward or resonant phenomena.

Applications

BPM is used to design long optical waveguides, Y-splitters, directional couplers, WDM multiplexers, and taper structures in silicon photonics and fiber-optic systems.

Related terms

FDTD

Optical waveguide

Mode solver