Eur. Phys. J. D (2012) 66: 9
https://doi.org/10.1140/epjd/e2011-20502-8

Regular Article

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

¹ Center for Theoretical Physics, Department of Physics, Capital Normal University, Beijing 100048, P.R. China
² School of Mathematical Sciences, Capital Normal University, Beijing 100048, P.R. China
³ Department of Physics, Tsinghua University, Beijing 100084, P.R. China

^a e-mail: lichao19840621@163.com

Received: 29 August 2011
Published online: 11 January 2012

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 analysed. 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 occurring at the 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 [C. Li, Y.S. Zhou, H.Y. Wang, F.H. Wang, Opt. Express 19, 10073 (2011)]. In addition, some commonly used methods including FDTD, scattering matrix method and improved characteristic impedance method are compared with MEM to highlight the accuracy of these methods.