Tunable terahertz absorption modulation in graphene nanoribbon-assisted dielectric metamaterial

Abstract

Designing metamaterial absorbers with tunable and broadband response with high modulation depth is crucial for application in switches, polarization sensitive devices, and optical filters. In this article, we report a tunable broadband metamaterial absorber in terahertz regime. The design comprises frustum shaped dielectric (SiO2) metamaterial structures on top of a one-dimensional period array of graphene nanoribbons (GNRs) deposited over the ultrathin metal-backed dielectric. For TM polarization, our design offers a near-perfect absorption in the range of 0.72 THz to 0.9 THz with 72.7 fractional bandwidth. On the contrary, we get a negligible absorption for the TE polarization of the incident light, thereby giving an absorption contrast ratio up to 20.5 dB. The excitation of plasmons in GNRs combined with resonance induced by the graphene-dielectric-metal cavity leads to nearly perfect broadband absorption for the TM polarized radiation. Further, modulation of the absorption spectrum has been achieved by changing graphene conductivity with the help of its Fermi energy. A theoretical model based on effective medium theory and transfer matrix method has been presented to validate absorption response for various Fermi energy values of the graphene. The figure of merit of our design can outperform some of the recently reported tunable metamaterial absorbers.