| 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. |
