Near-unity absorption of graphene monolayer with a triple-layer waveguide coupled grating

In order to achieve the enhancement and manipulation of light absorption in graphene monolayer within the visible (Vis) and near infrared (NIR) regions, a design of absorber inspired by contact coupled gratings with an absentee layer is demonstrated. It is proved that the absorptance of monolayer graphene can be greatly enhanced to near unity through rigorous coupled-wave analysis (RCWA) numerical calculation. The thickness of grating and homogeneous absentee layers can significantly change the linewidth and resonant mode position in absorption spectrum. Furthermore, the lateral shift of the contact coupled gratings changes the magnetic field distributions in the grating cavity and the surface-confined mode at the cover/grating interface, thus facilitating the dynamic control of the spectral bandwidth of the graphene absorber. The proposed devices could be efficiently exploited as tunable and selective absorbers, allowing to realize other two-dimensional (2D) materials-based selective photo-detectors.