Dual-Band Light Focusing Using Stacked Graphene Metasurfaces

In this article, we theoretically study the optical properties of graphene metasurfaces consisting of layered graphene ribbons and their potential applications as multifunctional optical devices in the long-wavelength infrared region. By engineering the plasmonic resonance in graphene ribbons with different widths, the phase of reflected light can be tuned over a range of nearly 2π, while the reflectivity is kept relatively high at the target frequencies. Owing to the weak light–graphene interaction in the off-resonance region, independent control of the reflected light can be achieved by stacking multiple layers of graphene ribbons. Since the interlayer coupling between the ribbons is negligible, we have developed a transmission-line-based uncoupled model as a physical interpretation of the stacked metasurface. The modeled results show excellent agreement with numerical simulations. As a proof-of-principle demonstration, we have designed and demonstrated graphene metasurfaces as flat, dual-band focusing reflectors operating at 25 and 16 THz. Our work provides a general design scheme for multiband, multifunctional metasurfaces with various potential applications, including beam steering, optical communication, and information processing.