Abstract
The highly unidirectional excitation of graphene plasmons (GPs) through near-field interference of orthogonally polarized dipoles is investigated. The preferred excitation direction of GPs by a circularly polarized dipole can be simply understood with the angular momentum conservation law. Moreover, the propagation direction of GPs can be switched not only by changing the phase difference between dipoles, but also by placing the z-polarized dipole to its image position, whereas the handedness of the background field remains the same. The unidirectional excitation of GPs can be extended into arc graphene surface as well. Furthermore, our proposal on directional generation of GPs can be realized in a semiconductor nanowire/graphene system, where a semiconductor nanowire can mimic a circularly polarized dipole when illuminated by two orthogonally polarized plane waves.
Highlights
Graphene plasmons (GPs), the intrinsic collective oscillations of electrons coupled with electromagnetic waves in doped graphene, have attracted enormous interests for their unique properties, including such as inherently highly controllable, long-lived and extremely electromagnetic field confinement and enhancement in midinfrared and terahertz spectral regimes[1,2,3]
We demonstrated here that near field interference of a circularly polarized dipole and two mirror image symmetric dipoles with orthogonally polarizations can directional generate propagating graphene plasmons (GPs)
The viewpoint of angular momentum conservation is very efficient to determine the preferred direction of exited GPs
Summary
Graphene plasmons (GPs), the intrinsic collective oscillations of electrons coupled with electromagnetic waves in doped graphene, have attracted enormous interests for their unique properties, including such as inherently highly controllable, long-lived and extremely electromagnetic field confinement and enhancement in midinfrared and terahertz spectral regimes[1,2,3]. Due to large wavevector mismatch between GPs and free light field, propagating GPs are usually excited by deep sub-wavelength point-like sources[11]. In these cases, the sources such as emitters, absorbers and scatterers serve as dipoles perpendicular or parallel to the propagation plane of GPs[12]. Two orthogonally oriented dipoles are employed to efficiently excite symmetric and anti-symmetric charge ordering modes in flat and arc graphene planes. The circularly polarized dipole can be efficiently mimicked by a semiconductor nanowire illuminated by two orthogonally polarized plane waves in experiments, and the problem about magnetic induction currents induced by oblique incidence can be solved in our considered system. We believe our findings should be found applications in compact plasmonic circuits in mid-infrared and terahertz regimes
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