Broadband near-unity light absorption with anti-hermitian coupled stacked graphene metasurfaces

Enhancement of the interaction between monolayer or few-layers graphene and light is crucial to the potential applications of graphene-based optoelectronic devices. Recently, various nanostructured graphene has been proposed to achieve efficient optical absorption, whereas the bandwidth of the enhanced spectral absorption is always fairly narrow, which might be disadvantageous to their opt-electrical applications relying on light harvesting. In this work, we propose an effective method of constructing a stacked graphene-based metasurface to achieve broadband unity absorption. The main concept of the design is to realize the near-zero mutual coupling among graphene resonators based on the idea of anti-Hermitian coupling. This coupling will restrain the mode splitting due to the effect of direct near-field coupling between the neighboring graphene resonators, and thus facilitate the realization of a broadband absorption through the superposition of the individual resonance. In principle, the absorption bandwidth could be expanded further, and the proposed idea might also be used to design broadband absorber of other sub-wavelength nano-resonators.