Graphene-spacer-grating-based structure to realize tunable mid-infrared narrow-band plasmonically induced transparency and slow light effect

Tunable narrow-band plasmonically induced transparency (PIT) effect at mid-infrared region is realized in a graphene-spacer-grating-based (GSG-based) hybrid system. A silicon/SiO 2 grating is used to compensate wave-vector mismatches between graphene surface plasmons (GSPs) and free space optical waves. The PIT effect can be quickly tuned by small changes in the Fermi energy levels of the graphene sheets. A quality-factor (Q-factor) over 108 of the PIT peak with a group time delay over 0.44 ps within the PIT window can be achieved by setting suitable parameters of the graphene sheets and manipulating desirable geometric parameters of the Silicon/SiO 2 grating and the SiO 2 spacer. A GSG-based device with graded periods of the silicon/SiO 2 grating is further proposed to achieve a slowdown factor over 350 at certain cut-off wavelength and a trapping bandwidth of ∼ 0.7 μm (from λ ∼ 7.55 to λ ∼ 8.25 μm) corresponding to ∼ 3.3 THz via dynamically tuning the Fermi level of the graphene sheet. The proposed GSG-based structure has potential applications in graphene-based optical devices such as tunable optical filters, plasmonic switches, and buffers.