Graphene-based active slow surface plasmon polaritons.

Hua Lu,Philipp Reineck,Md Muntasir Hossain,Min Gu,Xueming Liu,Chao Zeng,Qiming Zhang

doi:10.1038/srep08443

Abstract

Finding new ways to control and slow down the group velocity of light in media remains a major challenge in the field of optics. For the design of plasmonic slow light structures, graphene represents an attractive alternative to metals due to its strong field confinement, comparably low ohmic loss and versatile tunability. Here we propose a novel nanostructure consisting of a monolayer graphene on a silicon based graded grating structure. An external gate voltage is applied to graphene and silicon, which are separated by a spacer layer of silica. Theoretical and numerical results demonstrate that the structure exhibits an ultra-high slowdown factor above 450 for the propagation of surface plasmon polaritons (SPPs) excited in graphene, which also enables the spatially resolved trapping of light. Slowdown and trapping occur in the mid-infrared wavelength region within a bandwidth of ~2.1 μm and on a length scale less than 1/6 of the operating wavelength. The slowdown factor can be precisely tuned simply by adjusting the external gate voltage, offering a dynamic pathway for the release of trapped SPPs at room temperature. The presented results will enable the development of highly tunable optoelectronic devices such as plasmonic switches and buffers.

Highlights

Finding new ways to control and slow down the group velocity of light in media remains a major challenge in the field of optics
These results show that graphene plasmonics (GPs) offers a range of design possibilities for photonic applications
A gate voltage is applied between the graphene sheet and Si substrate to set the doping level of graphene by the electric-field effect[34]

Summary

Introduction

Finding new ways to control and slow down the group velocity of light in media remains a major challenge in the field of optics. Theoretical and numerical results demonstrate that the structure exhibits an ultra-high slowdown factor above 450 for the propagation of surface plasmon polaritons (SPPs) excited in graphene, which enables the spatially resolved trapping of light. To broaden the slow light bandwidth, Gan et al proposed a graded grating structure to reduce the speed of light and realize a rainbow trapping effect on a metal surface[19,22]. Wang et al showed that graphene sheet arrays are capable of steering light efficiently through the SPP coupling between individual monolayers[30] These results show that graphene plasmonics (GPs) offers a range of design possibilities for photonic applications. We theoretically and numerically demonstrate that the SPP mode in graphene shows an exceptional slowdown factor above 450 with a broad bandwidth of ,2.1 mm in the mid-infrared optical region. The slowdown factor as well as the rainbow trapping performance of the system can be readily controlled via the external gate voltage, rendering the release of trapped waves feasible at room temperature

Methods

Results

Conclusion