Family of graphene-assisted resonant surface optical excitations for terahertz devices.

I-Tan Lin,Jheng-Yuan Syu,Ching-Yuan Su,Jia-Ming Liu,Hsin-Cheng Tsai,Kaung-Hsiung Wu

doi:10.1038/srep35467

Abstract

The majority of the proposed graphene-based THz devices consist of a metamaterial that can optically interact with graphene. This coupled graphene-metamaterial system gives rise to a family of resonant modes such as the surface plasmon polariton (SPP) modes of graphene, the geometrically induced SPPs, also known as the spoof SPP modes, and the Fabry-Perot (FP) modes. In the literature, these modes are usually considered separately as if each could only exist in one structure. By contrast, in this paper, we show that even in a simple metamaterial structure such as a one-dimensional (1D) metallic slit grating, these modes all exist and can potentially interact with each other. A graphene SPP-based THz device is also fabricated and measured. Despite the high scattering rate, the effective SPP resonances can still be observed and show a consistent trend between the effective frequency and the grating period, as predicted by the theory. We also find that the excitation of the graphene SPP mode is most efficient in the terahertz spectral region due to the Drude conductivity of graphene in this spectral region.

Highlights

Of the FP cavity is modified, and the corresponding resonance frequency of the FP mode changes as shown in the inset of Fig. 1c
Compared to the devices based on other types of surface excitation, the device shown in Fig. 1d has the smallest footprint because of the strong confinement of the graphene SPPs
We mainly focus on the devices based on the excitation of graphene SPPs

Summary

Introduction

Of the FP cavity is modified, and the corresponding resonance frequency of the FP mode changes as shown in the inset of Fig. 1c. By increasing the chemical potential, the electron density and the conductance increase, and the resonance frequency of a graphene SPP mode, corresponding to the transmittance trough, is blue-shifted, as shown in the inset of Fig. 1d where the chemical potential μ2 >μ1. For a scattering rate of 1 ps−1, the modulation depth is around 90% at 0.6 THz, as shown in the inset of Fig. 1d. This value is larger than that of devices based on Fig. 1c11,12, and much larger than the experimentally measured values, which are 15% or below, for devices based on SRR or monolayer graphene on a flat substrate[10,13,14]. We mainly focus on the devices based on the excitation of graphene SPPs

Methods

Results

Conclusion