Figure 4:

Dynamic control of phase, polarization, and beam steering. (A) Schematic of the graphene-based metasurface integrating a one-port resonator design. (B) Gate-dependent phase spectra showing the transition from underdamped to overdamped regimes through critical damping. (C) Smith curves illustrating the evolution of the reflection coefficient, showing critical damping between underdamped and overdamped behavior [78] (Copyright 2015, American Physical Society). (D) Schematic of the graphene plasmonic metamolecule designed for mid-infrared phase and amplitude modulation. (E) Amplitude (left) and phase (right) maps of the reflection coefficient, showing dual-parametric control via independent Fermi-level tuning of the graphene plasmonic ribbons [66] (Copyright 2020, American Chemical Society). (F) Schematic of the graphene-based metasurface designed to achieve phase modulation. (G) Complex reflection coefficients as the Fermi level is tuned from 0 to 1 eV. (H) Plot of the frequency dependence of the reflected phase, derived from the reflection coefficients shown in (G) [79] (Copyright 2022, Springer Nature). (I) Fabricated supercell image of graphene-based metasurfaces for electrically tunable anomalous refraction. (J) Simulated electric field distribution of THz waves at two gate voltages (2.2 V and 0 V). (K) Measured cross-polarized transmission intensity at 1.15 THz as a function of refraction angle with two gate voltages. (L) Simulated electric field (left) and energy density distributions (right) at 1.15 THz [83] (Copyright 2017, John Wiley and Sons). (M) Schematic of a gate-tuned graphene-based metasurface designed for dynamic THz beam steering. By adjusting the gate voltage, the metasurface can switch between ON (anomalous reflection) and OFF (normal reflection) states, leveraging critical coupling and PB phase gradients. (N) Experimental demonstration of ON/OFF switching in a gate-tuned graphene-based metasurface with an incident angle of −50°. The left panel shows the scattered electric field intensity of the reflected wave, while the right panel illustrates the deflection efficiency. ON state shows anomalous reflection at −7.3°, and OFF state exhibits normal reflection at 50° [84] (Copyright 2022, De Gruyter). (O) Schematic of a gate-controlled graphene-based chiral metamaterial. (P) Gate-controlled circular dichroism at the resonance frequency (left) and optical activity at an off-resonance frequency (right) [85] (Copyright 2017, The American Association for the Advancement of Science). (Q) Schematic of the graphene-based metasurfaces for electrically tunable polarization control and microscopic image. (R) Experimental and simulated polarization state evolution on the Poincaré sphere, showing voltage-dependent polarization control with mono- (left) and bilayer (right) graphene-based metasurfaces [86] (Copyright 2023, De Gruyter).