"Fast" Plasmons Propagating in Graphene Plasmonic Waveguides with Negative Index Metamaterial Claddings.

Zeyang Zhao,Qiang Kan,Pingping Qiu,Shaojian Su,Weibin Qiu,Hengjie Zhou

doi:10.3390/nano10091637

Abstract

We propose the monolayer graphene plasmonic waveguide (MGPW), which is composed of graphene core sandwiched by two graphene metamaterial (GMM) claddings and investigate the properties of plasmonic modes propagating in the waveguide. The effective refraction index of the GMMs claddings takes negative (or positive) at the vicinity of the Dirac-like point in the band structure. We show that when the effective refraction index of the GMMs is positive, the plasmons travel forward in the MGPW with a positive group velocity (vg > 0, vp > 0). In contrast—for the negative refraction index GMM claddings—a negative group velocity of the fundamental mode (vg < 0, vp > 0) appears in the proposed waveguide structure when the core is sufficiently narrow. A forbidden band appears between the negative and positive group velocity regions, which is enhanced gradually as the width of the core increases. On the other hand, one can overcome this limitation and even make the forbidden band disappear by increasing the chemical potential difference between the nanodisks and the ambient graphene of the GMM claddings. The proposed structure offers a novel scheme of on-chip electromagnetic field and may find significant applications in the future high density plasmonic integrated circuit technique.

Highlights

Negative-index materials (NIMs)—a class of photonic structures with simultaneously negative effective dielectric constant and permeability [1,2]—provide novel prospects for manipulating light
We propose a monolayer graphene plasmonic waveguide (MGPW) made up of a graphene core embedded in the graphene plasmonic metamaterial(s) (GMMs) claddings
The thickness of the graphene core is set as δ and the graphene plasmonic metamaterial(s) considered in this work is constructed by monolayer graphene, where two periodically arranged graphene nanodisks are surrounded by the same sheet of graphene with different chemical potential

Summary

Introduction

Negative-index materials (NIMs)—a class of photonic structures with simultaneously negative effective dielectric constant and permeability [1,2]—provide novel prospects for manipulating light. Photonic crystals with a negative refractive index are commonly implemented by periodically varying parameters such as the dielectric constant [8], and further enable the exquisite control of light propagation in integrated optical circuits. Graphene plasmonic metamaterials, which consist of a continuous graphene monolayer with an array of periodic distribution of chemical potentials, overcome this limitation and demonstrate broadband turnability [9] These electrostatically tunable periodic structures may be derived by the standard complementary metal oxide semiconductor (CMOS) technology and offer a practical method for on-chip electromagnetic field manipulation in nanoscale [9,10]. In contrast to the conventional materials ‘fast-light’ media, the proposed broadly tunable two-dimensional ‘fast’ plasmon device offers the practical on-chip plasmon manipulation, ultracompact footprint and two- dimensional integratively [12] and may find broad applications in the field of light-matter interaction and high-density plasmonic integrated circuits in the future

Calculation Methods and the Models

The Monolayer Graphene Plasmonic Waveguide and Dispersion Relation

Conclusions