Frequency-Tunable Mid-Infrared Cross Polarization Converters Based on Graphene Metasurface

We have proposed two designs of graphene-enabled cross polarization converters, which are capable of high-efficiency polarization conversion rate and can work equally well for a wide range of incident wave angles. The first type is carefully constructed by an ellipse-shaped graphene sheet printed on a dielectric material backed up by a gold ground plane, while the second one comprises a graphene ring embedded an ellipse resonator. Numerical results demonstrate that the polarization conversion rate of the first polarizer reaches 99.38 % at 22.541 THz when the Fermi energy is fixed at 0.9 eV. The second one can simultaneously work at two frequencies with its polarization conversion rate being 96.74 and 95.88 %, respectively. Therefore, for two devices, the incident linearly polarized beams are almost completely rotated to its orthogonal counterpart after reflection in the mid-infrared spectral range. More importantly, the cross polarization amplitude and resonant frequencies can be dynamically tuned by shifting the Fermi energy without changing the nanostructure, which will exhibit enormous potential applications in photonics field.