Fano resonance in double waveguides with graphene for ultrasensitive biosensor.

Fano resonance is realized in the multilayer structure consisting of two planar waveguides (PWGs) and few layer graphene, and the coupling mechanism between the two PWG modes with graphene is analyzed in detail. It is revealed that the Fano resonance originates from the different quality factors due to the different intrinsic losses of the graphene in the two waveguides, and the electric field distributions in the multilayer structure confirms our results. Fano resonance in our proposed structures can be applied in the ultrasensitive biosensor, and a significantly improved figure of merit (FOM) of 9340 RIU-1 has been obtained by optimizing the structure parameters, which has a 2~3 orders of magnitude enhancement compared to the traditional surface plasmon polaritons (SPR) sensor. Especially, it is found that both transverse magnetic (TM)-polarization and transverse electric (TE)-polarization can support the Fano resonance, and hence it can work as ultrasensitive biosensor for both polarizations.