Design of a Reconfigurable Ultra-Wideband Terahertz Polarization Rotator Based on Graphene Metamaterial

Abstract

In this work, a reconfigurable ultra-wideband transmissive terahertz polarization rotator based on graphene metamaterial is proposed that can switch between two states of polarization rotation within a broad terahertz band by changing the Fermi level of graphene. The proposed reconfigurable polarization rotator is based on a two-dimensional periodic array of multilayer graphene metamaterial structure, which is composed of metal grating, graphene grating, silicon dioxide thin film, and a dielectric substrate. The graphene metamaterial can achieve high co-polarized transmission of a linearly polarized incident wave at the off-state of the graphene grating without applying the bias voltage. Once the specially designed bias voltage is applied to change the Fermi level of graphene, the polarization rotation angle of linearly polarized waves is switched to 45° by the graphene metamaterial at the on-state. The working frequency band with 45-degree linear polarized transmission remaining above 0.7 and the polarization conversion ratio (PCR) above 90% is from 0.35 to 1.75 THz, and the relative bandwidth reaches 133.3% of the central working frequency. Furthermore, even with oblique incidence at large angles, the proposed device retains high-efficiency conversion in a broad band. The proposed graphene metamaterial offers a novel approach for the design of a terahertz tunable polarization rotator and is expected to be applied in the applications of terahertz wireless communication, imaging, and sensing.

Active control of an electromagnetically induced transparency analogue in a coupled dual bound states in the continuum system integrated with graphene

“…In this study, we achieve modulation of BIC without altering structural parameters by placing a single layer of graphene beneath the BIC structure and actively adjusting its Fermi level E F through an external gate voltage. The relationship between graphene's Fermi level E F and the applied bias voltage V g can be described by the following equation: 37,38 Here, ν f represents the Fermi velocity in graphene, ε 0 is the vacuum permittivity, ε r is the relative permittivity of silicon, and h 0 is the length between the two electrodes (corresponding to the height of the silicon strip). By applying a bias voltage to change the carrier concentration in graphene, the E F can be artificially modulated.…”