High Figure of Merit Graphene Modulator Based on Long-Range Hybrid Plasmonic Slot Waveguide

By exploiting the electro-absorption effect of graphene, we present a graphene-based long-range hybrid plasmonic slot (LRHPS) waveguide modulator. The waveguide structure consists of a silica substrate, two high-index silicon strips, two low-index slots, two graphene layers, and a metal. The modes are confined within the two horizontal slot regions, which make graphene layer close to the maximum of tightly confined electric field. The designed LRHPS waveguide takes advantages of both the traditional long-range surface plasmon polariton waveguide and the hybrid plasmonic waveguide. The combined effects of long-range surface plasmon polaritons and discontinuity of electric field at the interface between two dielectrics with highcontrast refractive index enable low insertion loss together with high modulation depth for potential high-density nanophotonic integration. The modulator performance is comprehensively studied in terms of attenuation, insertion loss, modulation depth, and figure of merit (FoM). The designed graphene-based LRHPS waveguide modulator shows a 3-dB modulation depth with only ~363-nm-long waveguide, a 3-dB optical bandwidth of 15 THz with a center wavelength of 1550 nm, a low energy per bit consumption of 0.008 fJ/b, and a high FoM of 218 improved by more than one order of magnitude. Moreover, gate-variable broadband operation is also available covering the entire O, E, S, C, L, and U telecommunication bands.