The Extraordinary-Transmission Of Subwavelength Structure Based On FDTD Method

The reflection that occurs when light passes the interface between materials with different refractive index result in trouble in industrial applications. Such as in solar cells, the introduction of a substrate will result in an increase in reflection and a decrease in solar energy utilization rate. There are many ways to reduce the reflection from a substrate, which have been investigated so far, including dielectric interference coatings, surface texturing, adiabatic index matching, and scattering from plasmonic nanoparticles etc. Since Ebbesen group first observed the Extraordinary optical Transmission(EoT) phenomenon on sub-wavelength hole arrays in a metal thin film, the hidden mechanism of the structure have been explored by many researchers. One widely accepted theory is that incident energy have stimulated the surface plasmon polartions on metal surface, so that the light energy is coupled to the other side of the structure and radiate out by a coupling among the apertures. This help provide a reference to research low surface reflection device.With respect to the deep observation on subwavelength metal aperture array structure and the EoT phenomenon, it can find that when light is incident to the surface of metal sub-wavelength size structure etched with emboss, the incident and reflected light will produce an resonant transmission or absorption phenomenon. As substrate for industrial applications are non-metallic dielectric material, this paper suggest a new structure that is composed of dielectric substrate and sub-wavelength periodical emboss. This paper combined Auxiliary Differential Equation (ADE), Finite Difference of Time Domain(FDTD) method and iterative FDTD method together to study its scattering properties, the details as follows:Firstly, since the material used here is dispersive media, so we introduce dispersion medium to the simulation of ADE-FDTD method. Then one can derives the ADE-FDTD difference scheme in dispersion medium out and one can get the combination of some key technologies in ADE-FDTD with dispersion medium. And some numerical examples have carried out to show the effectiveness of the algorithm.Secondly, this sub-wavelength structure is periodical. It is necessary to link up the basic theory of periodic structures with ADE-FDTD method together, to make sure it can be applied in numerical calculations of periodic structures. So that we can get the ADE-FDTD method with periodical boundary condition.Finally, above ADE-FDTD method and iterative FDTD method can be used for dielectric sub-wavelength emboss structure analysis. And we change some structure variables, such as emboss material, emboss structure, to explore its impact on resonant peaks of the results.