Graphene based tunable metamaterial absorber and polarization modulation in terahertz frequency

TLDR

Graphene’s tunable sheet conductivity enables the design of tunable terahertz devices. The study aims to realize a polarization‑independent terahertz absorber with spectral tuning and to propose a polarization modulation scheme using cross‑shaped resonators and double‑layer graphene. The absorber employs a cross‑shaped metallic resonator coupled to double‑layer graphene wires, modeled by a transmission line model where gate‑bias‑induced changes in graphene inductance tune the resonance. The device achieves a 15 % tunable peak absorption with near‑perfect efficiency by adjusting graphene Fermi energy, and the polarization modulator can electrically rotate the reflected wave’s linear polarization from 0° to 90°, demonstrating flexible control of terahertz absorption and polarization.

Abstract

Graphene can be utilized in designing tunable terahertz devices due to its tunability of sheet conductivity. In this paper, we combine the metamaterial having unit cell of cross-shaped metallic resonator with the double layer graphene wires to realize polarization independent absorber with spectral tuning at terahertz frequency. The absorption performance with a peak frequency tuning range of 15% and almost perfect peak absorption has been demonstrated by controlling the Fermi energy of the graphene that can be conveniently achieved by adjusting the bias voltage on the graphene double layers. The mechanism of the proposed absorber has been explored by a transmission line model and the tuning is explained by the changing of the effective inductance of the graphene wires under gate voltage biasing. Further more, we also propose a polarization modulation scheme of terahertz wave by applying similar polarization dependent absorbers. Through the proposed polarization modulator, it is able to electrically control the reflected wave with a linear polarization of continuously tunable azimuth angle of the major axis from 0° to 90° at the working frequency. These design approaches enable us to electrically control the absorption spectrum and the polarization state of terahertz waves more flexibly.