An electrically tunable plasmonic optical modulator with high modulation depth based on graphene-wrapped silver nanowire

We report a systematic study of a graphene-wrapped plasmonic optical modulator with a high modulation depth. The optical modulator consists of a silver (Ag) nanowire as a single mode plasmonic waveguide being wrapped with a graphene monolayer as an electrically controllable absorbing material. While a thin dielectric spacing layer is used to electrically isolate the Ag nanowire from the graphene monolayer, we find it further promotes higher optical absorption by manipulating a strong electric field at its outer surface, where the graphene layer is located. By optimizing the dielectric layer thickness as well as the Ag nanowire radius, a strong optical modulation of 0.46 dB mu m(-1) with a high-speed characteristic at the operating wavelength of 785 nm is achieved. This design is further implemented at the telecommunication wavelength (1550 nm) with an optimized modulation depth of 1.07 dB mu m(-1).