Graphene-based hybrid plasmonic waveguide for highly efficient broadband mid-infrared propagation and modulation.

In this paper, a graphene-based hybrid plasmonic waveguide is proposed for highly efficient broadband surface plasmon polariton (SPP) propagation and modulation at mid-infrared (mid-IR) spectrum. The hybrid plasmonic waveguide is composed of a monolayer graphene sheet in the center, a polysilicon gating layer, and two inner dielectric buffer layers and two outer parabolic-ridged silicon substrates symmetrically placed on both sides of the graphene. Owing to the unique parabolic-ridged waveguide structure, the light-graphene interaction and subwavelength SPPs confinement of the fundamental SPP mode for the hybrid waveguide can be significantly increased. Under the graphene chemical potential of 1.0 eV, the proposed waveguide can achieve outstanding SPP propagation performance with long propagation length of 12.1-16.7 μm and small normalized mode area of ~10-4 in the frequency range of 10-20 THz, exhibiting more than one order smaller in the normalized mode area while remaining the propagation length almost the same level with respect to the hybrid plasmonic waveguide without parabolic ridges. By tuning the graphene chemical potential from 0.1 to 1.0 eV, we demonstrate the waveguide has a modulation depth greater than 51% for the frequency ranging from 10 to 20 THz and reaches a maximum of nearly 100% at the frequency higher than 18 THz. Benefitting from the excellent broadband mid-IR propagation and modulation performance, the graphene-based hybrid plasmonic waveguide may open up a new way for various mid-IR waveguides, modulators, interconnects and optoelectronic devices.