Modified BPM for plasmonic modeling

In this paper, we investigate the usefulness of the wide-angle Fast Fourier Transform-based Beam Propagation Method (FFT-BPM) in computational plasmonics. Major numerical difficulties associated with the singularity of the transverse derivative of the step-like refractive index at the interface plane, especially for the TM case, are circumvented using an equivalent-index formalism. A trigonometric function is used, for the first time to the authors' knowledge, to approximate the abrupt change of the refractive index at the interface. Accordingly, the TM problem is transformed to an equivalent TE one with no singular behavior.