Abstract
Backward wave with anti-parallel phase and group velocities is one of the basic properties associated with negative refraction and sub-diffraction image that have attracted considerable interest in the context of photonic metamaterials. It has been predicted theoretically that some plasmonic structures can also support backward wave propagation of surface plasmon polaritons (SPPs), however direct experimental demonstration has not been reported, to the best of our knowledge. In this paper, a specially designed plasmonic metamaterial of corrugated metallic strip has been proposed that can support backward spoof SPP wave propagation. The dispersion analysis, the full electromagnetic field simulation and the transmission measurement of the plasmonic metamaterial waveguide have clearly validated the backward wave propagation with dispersion relation possessing negative slope and opposite directions of group and phase velocities. As a further verification and application, a contra-directional coupler is designed and tested that can route the microwave signal to opposite terminals at different operating frequencies, indicating new application opportunities of plasmonic metamaterial in integrated functional devices and circuits for microwave and terahertz radiation.
Highlights
Possess the similar dispersion relations and field properties of optical SPPs, but work at lower frequency down to microwave or terahertz regimes
We propose a new design of plasmonic metamaterial to construct a symmetric conformal surface plasmons (CSPs) waveguide mimicking an IMI system, which can support backward wave propagation with its odd guiding mode
We focus on the plasmonic metamaterial of symmetric CSP structure which has same corrugated grooves on both sides of the strip, as showed in top part of Fig. 1a
Summary
Possess the similar dispersion relations and field properties of optical SPPs, but work at lower frequency down to microwave or terahertz regimes. Thanks to the low loss and large propagation length of the new spoof SPPs waveguide, we achieve the dispersion relation of the odd mode with a negative slope from both the full wave simulation and direct measurement of the transmission through the waveguide. Such results insure anti-parallel phase and group velocities, and the backward wave propagation can be clearly verified by the phase evolution in the simulation. Experimental test on the fabricated prototype coupler have validated the design principle based on the backward wave propagation in the plasmonic metamaterial waveguide We believe these results could contribute to the development of more complicated surface circuitry for microwave and terahertz wave
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