Abstract
The surface plasmon polaritons (SPPs) have many potential application due to their local field enhancement and sub-wavelength characteristics. Recently, the gradient metasurface is introduced to couple the spoof SPPs in microwave frequency band. One of the most important issue which should be solved is the narrowband of spoof SPPs coupling on the gradient metasurface. Here, the metasurface is proposed to achieve the wideband helicity dependent directional spoof SPPs coupling for circular polarized light. Our research show that the coupling frequency of spoof SPPs on the gradient metasurface is determined by the dispersion of the metasurface, so the coupling frequency can be controlled by dispersion design. The careful design of each cell geometric parameters has provided many appropriate dispersion relations possessed by just one metasurface. The wave vector matching between the propagating wave and the spoof SPPs has been achieved at several frequencies for certain wave vector provided by the metasurface, which leads to wideband spoof SPPs coupling. This work has shown that wideband helicity dependent directional spoof SPPs coupling has been achieved with a high efficiency. Hence, the proposed wideband spoof SPPs coupling presents the improvement in practice applications.
Highlights
Coupling for linear polarized waves[15,30]
The previous works[15,28,29,30] related to the spoof SPPs excitation on the gradient metasurface are focused on the metasurface gradient phase design, while our work studies the dispersion relation for the spoof SPPs excitation on the gradient metasurface, and it has been shown that the spoof SPPs coupling frequency point is determined by the dispersion relation of the metasurface under given wave vector
The spoof SPPs supported by the metasurface has a lager wave vector kx than the free space wave at a given frequency, which indicates that the wave vector of the incident free space wave should be increased to couple the incident free space wave into spoof SPPs on the metasurface
Summary
The generalized Snell’s law indicates that the incident free space wave with normal incident angle[15] can convert into the spoof SPPs, when the wave vector provided by the gradient metasurface is greater than the wave vector of incident free space wave Wideband spoof SPPs coupling can be excited on the gradient metasurface, which can provide a larger wave vector in a wide frequency band and have multiple appropriate dispersion relations in this band range, simultaneity. This is due to the fact that the dispersion properties are related to the geometrical parameters of cell
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