Figure 3. Schematic illustration of the graphene plasmonic graded grating structure.

The groove depth d increases gradually along the direction of light propagation. p, w and t are the grating period, the groove width and the thickness of SiO₂ spacer, respectively. The inset shows cross-sectional contour plots of the field distribution |E_y|² along the graphene at the wavelength of 9.0 μm for different gate voltages. |E₀| is the maximum value of |E_y|. In the simulation, the parameters are set as t = 100 nm, p = 2w = 40 nm, T = 300 K and μ = 20000 cm²V⁻¹s⁻¹. d increases linearly from 100 nm to 400 nm with an increment of 10 nm.