Abstract
Active control of terahertz (THz) wave polarization state is of great significance for sensitive detection, imaging and communication. Here, a tunable THz quarter wave plate is designed by electronically controlling a composite metasurface consisting of the gold cross antennas and a monolayer graphene. The graphene composite metasurface acts as a quarter-wave plate when the chemical potential of graphene is 0 eV, by which the polarization state of the incident THz wave is converted from linear polarization to circular polarization. After the chemical potential of graphene is increased gradually, and to 0.5 eV, the transmitted polarization state of the THz wave is changed from right circular polarization to right elliptical polarization, and to linear polarization. Furthermore, the polarization state of the THz wave is able to be changed from left circular polarization to left elliptical polarization, and to linear polarization if the device is clockwise rotated by 90°. Therefore, the polarization state of THz wave could be actively controlled by the proposed tunable THz quarter wave plate. Our work will offer a new avenue for tunable THz polarization modulation devices.
Highlights
Tunable metasurfaces have attracted enormous research interests as a means to control the polarization state of THz wave
The conductivity of graphene can be controlled by changing the chemical potential in the simulation, and the resonance characters affected by conductivity of the composite metasurface are controlled
The transmission amplitudes of the two arms are about 0.60 except for some negligible differences between the two components at the frequency of 0.73 THz, but the phase delay is reduced to 0°, which means that the polarization of the transmission THz wave is back to the linear polarization state
Summary
Tunable metasurfaces have attracted enormous research interests as a means to control the polarization state of THz wave. More and more people have been committed to design metasurface structures, and proposed various functional devices including the anomalous reflection or refraction devices [2, 3], the holographic devices [4,5,6], the metasurface lenses [7,8,9], and the polarization-control devices [10,11,12,13,14,15,16,17], which mainly include the Active Control of THz Polarization half-wave plate [10, 11], the quarter-wave plate [12,13,14,15,16], and the retarders [17]. Polarization devices whose function is tunable in the THz band is still vary lacking
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