Optical Near-Field Enhancement with Graphene Bowtie Antennas

Abstract

In this paper, the optical near-field enhancement of graphene bowtie antennas is numerically investigated at terahertz frequencies using boundary element method. The enhanced field intensity at the gap region is a result of the mutual coupling between two triangular elements upon the excitation of graphene plasmons. Firstly, wide plasmon frequency tunability is demonstrated by changing the chemical potential of graphene without the need to alter the antenna geometry. Secondly, by varying the tip angle and radius of curvature of the graphene antennas, the field intensity enhancement at the gap center of the two-element antennas is systematically studied. It is found that graphene bowtie antennas with two round-cornered equilateral triangles have superior performance to other two-element antennas, such as ribbon pair, sharp-cornered bowtie, and disk pair antennas. Last but not least, by applying a moderate chemical potential of 0.4 eV to graphene bowtie antennas, we found that the field intensity enhancement at gap center is about 220 times as much as using gold of comparable sizes. In short, graphene bowtie antennas of rounded corners give rise to considerable near-field enhancement and are promising for a wide range of applications such as molecular sensing at terahertz frequencies.