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We propose a modified Kretschmann-Raether configuration to realize the low threshold optical bistable devices at the terahertz frequencies. The metal layer is replaced by the dielectric sandwich structure with the insertion of graphene, and this configuration can support TM-polarization surface electromagnetic wave. The surface plasmon resonance is strongly dependent on the Fermi-level of graphene and the thickness of the sandwich structure. It is found that the switching-up and switching-down intensities required to observe the optical bistable behavior are lowered markedly due to the excitation of the graphene surface plasmons, thus making this configuration a prime candidate for experimental investigation at the terahertz range. And the switching threshold value can be further reduced by decreasing the Fermi-level or increasing the thickness of sandwich structure, hence providing a new way for realizing tunable optical bistable devices. Finally, the optical bistability at higher terahertz frequency and the influence of relaxation time under the actual experimental condition on Fermi-level are discussed.

In this article, we have theoretically demonstrated that the perfect absorption at infrared frequencies can be achieved and controlled by using a graphene-hexagonal Boron Nitride (hBN) hyper crystal. hBN, the latest natural hyperbolic material, can be regarded as an excellent substrate to form a hyper crystal with graphene. Although the perfect absorption by a half-space of hBN crystal can be achieved due to its high optical anisotropy, but the perfect absorption can only appear at certain fixed wavenumber and incidence angle. By introducing a graphene-hBN hyper crystal, we can get perfect absorption at different wavenumbers and incidence angles by varying the Fermi energy level of graphene sheets via electrostatic biasing. We show that the perfect absorption can be realized at different Fermi energies for TM waves.

We have established the theoretical relation of nonlinear optical response with respect to the dielectric/nonlinear graphene/dielectric heterostructures and further demonstrated the tunable optical bistability at terahertz frequencies. It is shown that the hysteretic behavior is strongly dependent on the Fermi energy of graphene, and the threshold electric fields could be correspondingly adjusted with the continuous tuning of Fermi Energy level. It is clear that the bistable thresholds can be lowered dramatically by decreasing the Fermi energy of graphene, at the same time the optical hysteresis width is narrowed. Moreover, we have confirmed that the optical bistability can be tuned by adjusting the incident illumination angle, or by varying the thickness and permittivity of the dielectric slabs. Our contribution might provide a new avenue of fabricating graphene based optical switching device that could even operate at terahertz regime.

We proposed and demonstrated a scheme to enhance and tune absorption properties of conventional microwave absorbing materials (MAMs) by metamaterials (MMs). By covering a MAM, say, carbonyl iron powder coating, with MMs composed of split ring resonators (SRRs) and wires, we show both by experiments and by simulations that the maximum reflection loss (RL) is increased significantly and the frequency region for absorption is shifted to lower frequency. The frequency region in which the maximum RL is less than −10 dB shifts from 5–7 to 4.2–6.2 GHz for perpendicular polarization electromagnetic waves and to 4–9 GHz for parallel polarization waves. Simulation results reveal that the magnetic resonance obtained by SRRs and the electric resonance obtained by copper wires are the main factors in enhancing and tuning microwave absorption properties.