Abstract
Graphene has been recently proposed as a promising alternative to support surface plasmons with its superior performances in terahertz and mid-infrared range. Here, we propose a graphene-coated elliptical nanowire (GCENW) structure for subwavelength terahertz waveguiding. The mode properties and their dependence on frequency, nanowire size, permittivity and chemical potential of graphene are studied in detail by using a finite element method, they are also compared with the graphene-coated circular nanowires (GCCNWs). Results showed that the ratio of the long and short axes (b/a) of the elliptical nanowire had significant influence on mode properties, they also showed that a propagation length over 200 μm and a normalized mode area of approximately 10−4~10−3 could be obtained. Increasing b/a could simultaneously achieve both long propagation length and very small full width at half maximum (FWHM) of the focal spots. When b/a = 10, a pair of focal spots about 40 nm could be obtained. Results also showed that the GCENW had a better waveguiding performance when compared with the corresponding GCCNWs. The manipulation of Terahertz (THz) waves at a subwavelength scale using graphene plasmon (GP) may lead to applications in tunable THz components, imaging, and nanophotonics.
Highlights
Terahertz (THz) waves, located between millimeter radio waves and far infrared waves, have been widely investigated in the fields of spectroscopy, imaging, and communications [1,2,3,4]
We considered the graphene-coated elliptical nanowire (GCENW) waveguide to be surrounded by a dielectric medium (ε2 )
For the2.lowest eff order mode, propagation length increased with b increasing, and LP is about 83 μm and 107.7 μm for b/a = 0.5 and b/a = 3, respectively
Summary
Terahertz (THz) waves, located between millimeter radio waves and far infrared waves, have been widely investigated in the fields of spectroscopy, imaging, and communications [1,2,3,4]. To further downscale the mode area, He et al [34,35] proposed two graphene-based hybrid plasmonic waveguides, which could simultaneously achieve a very small normalized modal area of approximately 10−4 ~10−3 and a propagation length of approximately several hundreds of micrometers at 3 THz. Recently, graphene-coated nanowires have attracted lots of research interest and been investigated mainly in the mid-infrared band [37,38,39,40,41,42,43,44]. We present that a simple graphene-coated elliptical nanowire (GCENW) could simultaneously achieve a very small normalized modal area of approximately 10−4 ~10−3 and a propagation length of several hundreds of micrometers. By adjusting the chemical potential of graphene, the waveguiding properties could be tuned to achieve better performance
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