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In this paper, a chiral metamaterial consisting of bilayered metasurface with double F-shaped resonators is investigated. We experimentally demonstrate that this new structure can realize multi-band asymmetric transmission of a linearly polarized wave in the microwave region. The simulated results also show that the structure can achieve multi-band 90°p olarization rotator for a y-polarized wave. The mechanisms of coupling modes are analyzed by the current distribution at different resonant frequencies, which indicates that the crosspolarized transmission is due to both the electric coupling and the magnetic coupling. Furthermore, the polarization conversion ratios (PCRs) with more than 90 % conversion efficiency of x-polarized and y-polarized waves are also studied based on the optical activity and electric field distributions.

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Recently, based on the selective excitation of the guided mode, researchers realized quasi-bound states in the continuum (quasi-BICs) in all-dielectric compound grating waveguide structures. In this paper, we introduce a graphene layer into an all-dielectric compound grating waveguide layer supporting quasi-BIC to achieve near-infrared perfect absorption of graphene. The underlying physical mechanism of perfect absorption can be clearly explained by the critical coupling theory derived from temporal coupled-mode theory in a single-mode, one-port system. By changing the Fermi level and the layer number of the graphene, the absorption rate of the system can be flexibly tuned. In addition, by changing the geometric parameter of the compound grating waveguide structure, the radiation coupling rate of the quasi-BIC can also be flexibly tuned. Therefore, the critical coupling condition can be maintained in a broad range of the Fermi level and the layer number of the graphene. The full width at half maximum of the near-infrared perfect absorption peak can be flexibly tuned from 5.7 to 187.1 nm. This bandwidth-tunable perfect absorber would possess potential applications in the design of 2D material-based optical sensors, electrical switchers, and solar thermophotovoltaic devices.