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We propose and validate an approach to obtain an ultra-broadband terahertz absorber by taking the advantages of the absorption of the surface plasmon resonance in combination with the absorption of the intrinsic mode. The absorber is composed of a gold (Au) bottom layer and a patterned graphene embedded in TOPAS polymer, exhibiting ultra-broadband absorption by coupling the surface plasmon resonance and the intrinsic modes. The single-layer graphene is patterned to C4 symmetric regular polygons which are arranged in circle circumscribed polygons (CUPs) or circle inscribed polygons (CIPs) at the same periodicity for comparison. With the increase of the side number (N), the strongest and weakest coupling of the surface plasmon resonance and the intrinsic modes was achieved at N = 4 (square) and ∞ (circle) for CUP and CIP arrangements, respectively. The optimum absorption bandwidth of 2.54 THz with relative absorption bandwidth of 109.5% above 90% absorption efficiency has been achieved for the circles with a diameter of 12.4 μm arranged at a gap distance of 1.0 μm. This design shows broader relative absorption bandwidth than previously reported single-layer graphene THz absorbers. Therefore, the proposed method would be highly valuable to design and manufacture ultra-broadband THz absorbers. [ABSTRACT FROM AUTHOR]

In this paper, we numerically and theoretically study the tunable plasmonically induced transparency (PIT) effect based on the graphene metasurface structure consisting of a graphene cut wire (CW) resonator and double split-ring resonators (SRRs) in the middle infrared region (MIR). Both the theoretical calculations according to the coupled harmonic oscillator model and simulation results indicate that the realization of the PIT effect significantly depends on the coupling distance and the coupling strength between the CW resonator and SRRs. In addition, the geometrical parameters of the CW resonator and the number of the graphene layers can alter the optical response of the graphene structure. Particularly, compared with the metal-based metamaterial, the PIT effect realized in the proposed metasurface can be flexibly modulated without adding other actively controlled materials and reconstructing the structure by taking advantage of the tunable complex surface conductivity of the graphene. These results could find significant applications in ultrafast variable optical attenuators, sensors and slow light devices. [ABSTRACT FROM AUTHOR]

In this paper, we propose a metamaterial structure for realizing the electromagnetically induced transparency effect in the MIR region, which consists of a gold split-ring and a graphene split-ring. The simulated results indicate that a single tunable transparency window can be realized in the structure due to the hybridization between the two rings. The transparency window can be tuned individually by the coupling distance and/or the Fermi level of the graphene split-ring via electrostatic gating. These results could find significant applications in nanoscale light control and functional devices operating such as sensors and modulators. [ABSTRACT FROM AUTHOR]