In this study, we introduce a graphene-based plasmonic waveguide that consists of three layers including a nonlinear graphene nanoribbon (GNR), a stack of 6 layers of dielectric-like graphene and a Si layer. We compute the permittivity of the plasmonic GNR based on Kubo formalism considering the third-order nonlinear response of graphene medium. The thickness, width and Fermi level of GNR are considered to be 0.34 nm, 50 nm and 2.4 eV respectively. Excitation of surface plasmon resonance (SPR) in combination with Kerr effect establish a broad resonance mode that modify the reflectance characteristic at the wavelength range of 1400 ~1500 nm. Then we embed an array of graphene quantum dots (GQDs) with the diameter of 66 nm between GNRs. The permittivity of GQD is computed through Cole-cole model. The scattering effect of GQDs supports the establishment of narrow resonance mode. Coupling between the broad and narrow resonances results in Fano resonance at the reflectance characteristic. The characteristics of Fano resonance are highly sensitive to any change in refractive index of surrounding medium. These findings prove that the GQD/PNGN/MDG structure can be applied to detection of RI-induced characteristics as a biosensor. So we design a biosensor based on our waveguide where a 10 nm air gap is abandoned between two parts of biosensor. Replacing of the air gap with biomaterial medium having a RI of n=1.35 results in the amplitude change of Fano resonance. This finding proves the designed biosensor ability in detect of neurodegenerative disorders.
Baghbanzadeh et al. (Sun,) studied this question.