Scattering mechanism in a step-modulated subwavelength metal slit: a multi-mode multi-reflection analysis

TL;DR

This paper investigates the scattering and transmission mechanisms in a step-modulated subwavelength metal slit using a multi-mode multi-reflection model based on ray theory, providing detailed analysis and comparison with other methods.

Contribution

It introduces an improved modal expansion method (MEM) for analyzing scattering in subwavelength metal slits, enhancing efficiency and accuracy over previous models.

Findings

The multi-mode multi-reflection model accurately predicts transmission behavior.

MEM outperforms traditional methods in efficiency and precision.

Comparison validates the model's effectiveness.

Abstract

In this paper, the scattering/transmission inside a step-modulated subwavelength metal slit is investigated in detail. We firstly investigate the scattering in a junction structure by two types of structural changes. The variation of transmission and reflection coefficients depending on structural parameters are analyzed. Then a multi-mode multi-reflection model based on ray theory is proposed to illustrate the transmission in the step-modulated slit explicitly. The key parts of this model are the multi-mode excitation and the superposition procedure of the scatterings from all possible modes, which represent the interference and energy transfer happened at interfaces. The method we use is an improved modal expansion method (MEM), which is a more practical and efficient version compared with the previous one [Opt. Express 19, 10073 (2011)]. In addition, some commonly used methods, FDTD, scattering matrix method, and improved characteristic impedance method, are compared with MEM to highlight the preciseness of these methods.