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A magnetically tunable multi-band switchable frequency terahertz (THz) absorber based on graphene is proposed, and its absorption performance is analyzed using the 4 × 4 transfer matrix method. The results indicate that the proposed absorber achieves absorption amplitude tuning across multiple switchable THz frequencies by adjusting the static bias magnetic field. Moreover, both absorption and modulation depths exceed 90% for the left-handed circularly polarized wave. This performance can be attributed to the unequal Landau levels distribution of graphene in the quantum domain and the properties of photonic crystals, which include photonic bandgaps and optical localization. This study may have significant potential in various frequency-switchable components, such as circular polarization sensors, circular polarizers, and magnetic circular dichroism optical detectors. [ABSTRACT FROM AUTHOR]

Based on graphene metasurface, this paper proposes a broadband multifunctional reflective polarization converter in the terahertz regime. This converter was formed of periodic unit cells, and each cell comprises two gold resonant ribbons, two-layer graphene sheets, a dielectric spacer, and a ground plane. The results demonstrated that the converter presented dynamical multiple polarization-manipulating functions, such as linear-to-circular conversion and linear-to-linear conversion, by varying the Fermi energy of the graphene. For example, in the frequency range from 0.92 to 1.47 THz, the ultra-broadband cross-polarization conversion was obtained with a Fermi energy of 0 eV, and in the range from 0.55 to 1.26 THz, the ultra-broadband linear-to-circular polarization conversion was achieved by varying the Fermi energy with a tunable relative bandwidth of 78.5%. Finally, the physical mechanisms were determined by analyzing the equivalent circuits and current distributions. This polarization converter has the potential for future applications in electronic measurements, photonic design, and other optoelectronic systems. [ABSTRACT FROM AUTHOR]

Metasurface, with the ultrathin thickness, has been extensively investigated in the past few years. A specific branch, the metasurface-based absorber, has generated considerable interest as a result of its high absorptivity of electromagnetic waves. In this paper, an ultra-wideband absorber based on patterned phosphorene metasurface is proposed in terahertz range and can overstep the bandwidth limitation of the conventional metasurface-based absorber. This absorber comprises 4-group phosphorene/dielectric pairs with various widths and regular spaces, which forms frustum pyramid stack on a gold ground. In this design, the surface plasmonic waves are excited on phosphorene and the wide bandwidth from 3.4 to 9.6 THz with the absorptivity ≥90% is obtained. Attributing to the electric dipolar resonance, the incident plane waves with various frequencies are absorbed at phosphorene with corresponding widths, which results in the ultra-wideband absorption. Moreover, it remains ultra-wideband and high absorption over a wide angular range of incidence around 40°, and an absorption band above 90% even for 70° incident angle. The proposed phosphorene-based absorber has potentials in THz detectors, thermal emitters, etc. [ABSTRACT FROM AUTHOR]