Towards loss compensated and lasing terahertz metamaterials based on optically pumped graphene

P Weis,J L Garcia-Pomar,M Rahm

doi:10.1364/oe.22.008473

Abstract

We evidence by numerical calculations that optically pumped graphene is suitable for compensating inherent loss in terahertz (THz) metamaterials. We calculate the complex conductivity of graphene under optical pumping and determine the proper conditions for terahertz amplification in single layer graphene. It is shown that amplification in graphene occurs up to room temperature for moderate pump intensities at telecommunication wavelength λ = 1.5 μm. Furthermore, we investigate the coupling between a plasmonic split ring resonator (SRR) metamaterial and optically pumped graphene at a temperature T = 77 K and a pump intensity I = 300 mW/mm(2). We find that the loss of a SRR metamaterial can be compensated by optically stimulated amplification in graphene. Moreover, we show that a hybrid material consisting of asymmetric split-ring resonators and optically pumped graphene can emit coherent THz radiation at minimum output power levels of 60 nW/mm(2).

Highlights

In the last decade, metamaterials have intensively been subject to fundamental physical studies and have been developed to an advanced level of maturity which opens up new exciting routes to industrial applications
Comparing the impact of pure dielectric loss on the amplification in an optically pumped a-split ring resonator (SRR)/graphene metamaterial with perfect electrical conductor (PEC) resonators to the influence of pure ohmic loss in such an optically pumped asymmetric splitring resonator (a-SRR)/graphene material without dielectric substrate we found that the dielectric loss has only a weaker degradation effect on the resonator quality (see Fig. 5(b))
We numerically studied amplification of terahertz (THz) radiation in optically pumped split ring resonator (SRR)/graphene and asymmetric split ring resonator/graphene hybrid systems in the constant gain limit at a temperature of T=77 K and an optical pump wavelength of 1.5 μm

Summary

INTRODUCTION

Metamaterials have intensively been subject to fundamental physical studies and have been developed to an advanced level of maturity which opens up new exciting routes to industrial applications. Rhyzii and Otsuji et al [31,32,33,34,35,36,37] suggested and demonstrated the phenomenon of negative conductivity in optically pumped graphene, which leads to an amplification of radiation in the THz-regime This is an interesting finding with the potential to dramatically change the state-of-the-art of THz-technology, which until the present day has significantly suffered from the deficit in high power radiation sources which presume the existence of suitable gain media. Equivalent for both structures we start with the strongly approximated case where we assume the absence of ohmic and dielectric loss. Based on our numerical calculations we estimate that an optically pumped a-SRR/graphene metamaterial can provide coherent THz radiation of at least 60 nW and can prospectively serve as an ultrathin, robust alternative to existing THz sources

OPTICALLY PUMPED GRAPHENE

LOSS COMPENSATED AND LASING METAMATERIALS

CONSTANT GAIN RESTRICTION

Findings

CONCLUSION