Engineering light absorption at critical coupling via bound states in the continuum

Recent progress in nanophotonics is driven by the desire to engineer light–matter interaction in two-dimensional (2D) materials using high-quality resonances in plasmonic and dielectric structures. Here, we demonstrate a link between radiation control at critical coupling and metasurface-based bound states in the continuum (BIC) physics, and develop a generalized theory to engineer light absorption of 2D materials in coupling resonance metasurfaces. In a typical example of hybrid graphene–dielectric metasurfaces, we present manipulation of the absorption bandwidth by more than one order of magnitude by simultaneously adjusting the asymmetry parameter of silicon resonators governed by BIC and graphene surface conductivity while the absorption efficiency remains maximum. This work reveals the generalized role of BIC in radiation control at critical coupling, and provides promising strategies in engineering light absorption of 2D materials for high-efficiency optoelectronics device applications, e.g., light emission, detection, and modulation.