Accurate near-field calculation in the rigorous coupled-wave analysis method

TL;DR

This paper investigates the accuracy of near-field calculations in RCWA, identifies issues like slow convergence and artifacts, and proposes a mathematical formulation to improve near-field accuracy for various diffraction gratings.

Contribution

The paper introduces a new mathematical formulation for accurate near-field computation in RCWA, addressing convergence issues and artifacts in existing methods.

Findings

Improved near-field accuracy demonstrated on test structures

Reduction of unphysical oscillations at material boundaries

Enhanced convergence properties of the modified RCWA

Abstract

The rigorous coupled-wave analysis (RCWA) is one of the most successful and widely used methods for modeling periodic optical structures. It yields fast convergence of the electromagnetic far-field and has been adapted to model various optical devices and wave configurations. In this article, we investigate the accuracy with which the electromagnetic near-field can be calculated by using RCWA and explain the observed slow convergence and numerical artifacts from which it suffers, namely unphysical oscillations at material boundaries due to the Gibb's phenomenon. In order to alleviate these shortcomings, we also introduce a mathematical formulation for accurate near-field calculation in RCWA, for one- and two-dimensional straight and slanted diffraction gratings. This accurate near-field computational approach is tested and evaluated for several representative test-structures and configurations in order to illustrate the advantages provided by the proposed modified formulation of the RCWA.