Core-confined beam propagation method for guiding and leaky structures

We propose a beam propagation method variant, which only requires the computational grid to span the core region of a waveguiding structure. Optical fields outside are accounted for through semitransparent boundary conditions. The method is fast, simple to implement, and accurate over a wide range of wavelengths. It is applicable to both guiding and leaky structures, with sufficiently strong contrast between refractive indices in the core, substrate, and cladding.