Metal Subwavelength Waveguide Transmittance

The rise and development of subwavelength optics provide a platform for the study of various subwavelength optical devices. Metal/dielectric/metal (MDM) waveguides have won more and more attention because of their unique advantages. Compared with other waveguides, their fabrication and numerical analysis are earier. In this paper, we investigated the transmission characteristics of one-dimensional ladder-shaped array structures, about which we focus on the relationship between the transmissivities and the light wavelength and the structure parameters.Firstly, this paper studies optical transmission of the interface in the ladder-shaped slit. It is assumed that the incident light source is set in the slit to ensure same incident condition. Our calculations show that there is a critical wavelength. When the light wavelength is below the critical wavelength, the two transmissivities corresponding to two incidence directions have big difference, that is to say, the transmission is unidirectional. The bigger difference between widths of the two slits is, the bigger difference between the two transmissivities is. When the light wavelength is above the critical wavelength, the two transmissivites are identical. The expression of the stable transmissivity as a function of the ratio of the widths of the two slits was obtained by analysis.Secondly, we calculated and discussed the transmissivities of one-dimensional ladder-shaped array structures when a TM polarized plane wave irradiate to the structure from a space. Our results show that the transmissive enery corresponding to two incidence directions are identical in subwavelength regime for a fixed structure, that is to say, the transmission is not unidirectional. There is a series of peaks in the transmissivity curves with wavelength. They can be divided into two groups. One is lower and the other is taller. The transmissivities of ladder-shaped double-slits and ladder-shaped gratings are also influenced by the distance between two ladder-shaped slits. With the distance, the transmissivities oscillate and decrease.