Accuracy assessment of scalar wave propagation methods for diffractive optics design: from thin elements to thick binary grating

TL;DR

This paper systematically compares scalar wave propagation methods for diffractive optics against a rigorous reference, mapping their accuracy across different parameters to guide method selection.

Contribution

It provides a comprehensive accuracy assessment and practical guidelines for choosing wave propagation methods in diffractive optics design.

Findings

TEA, BPM, and WPM accuracy varies with grating parameters.

Accuracy maps identify valid domains for each method.

Guidelines improve reliability in diffractive optics inverse design.

Abstract

We present a systematic accuracy assessment of the thin-element approximation (TEA), the beam propagation method (BPM), and the wave propagation method (WPM) for binary diffractive gratings, using the rigorous Fourier modal method (FMM) as a reference. Random binary gratings are generated over a range of spatial frequency cutoffs and thicknesses, and the transmitted field overlap between each scalar method and the reference is measured. The results are summarized as accuracy maps in the spatial frequency-thickness parameter space, revealing the domain of validity of each method and providing practical guidelines for the choice of forward model in diffractive optics inverse design pipelines.