Tunable infrared Fano resonance from graphene based hybrid grating structure with germanium substrate

Fano resonance (FR) spectra from graphene based hybrid structure in the infrared region have been obtained and the related mechanisms are demonstrated by simulation method. By changing geometrical parameters, the interaction between graphene surface plasmon polariton (GSPP) and Fabry Perot (FP) mode can be dramatically tuned, resulting in an interesting asymmetric FR spectrum curve. Combing with the electric field distribution at a certain wavelength, the FR spectrum is ascribed to the coupling of the GSPP mode and FP mode. By applying different gate-voltage, the FR spectrum from this hybrid structure exhibits a continuous tunability in the range of 4.5–15.5 um. A high refractive index sensitivity of this hybrid structure working in the mid-infrared is theoretically demonstrated, and the sensitivity of which reaches 1000 nm per refractive index unit. This tunable hybrid structure exhibits great potential application in optoelectronic devices and high performance sensor. Graphic abstract