Plasmonic metasurface with spatially modulated graphene. (a) Sketch of the monolayer graphene structure. The conductivity of the graphene sheet is periodically modulated along the x direction, σ(x), with period 2πγ. For radiation of wavelengths larger than the periodicity, the graphene appears as a homogeneous sheet with effective conductivity σ _eff. (b) Metasurface absorber: the graphene is placed on an asymmetric Fabry-Perot resonator of subwavelength dimensions. (c) Conductivity modulation profile for several values of the modulation strength, w ₀.