This study presents propagation properties of plasmonic slab waveguides based on graphene compared with noble metals. Transfer matrix theory as an analytical method and finite element method as a numerical approach are applied for analysis of one-dimensional plasmonic structures. Calculating the guided mode propagation constants of the waveguides, characteristics of the waveguides are compared by three factors: propagation length, spatial length, and electromagnetic field profile. The results obtained here are very helpful to the guidedwave applications in terahertz and infrared frequencies.
Index Terms-Graphene, Noble metals, Plasmonic slab waveguides, and Terahertz,Recently, graphene, a one-atom-thick material consisting of carbon atoms bonded in a hexagonal lattice, is introduced as a planar plasmonic (metal-like) material [9-10]. The significant characteristics of graphene compared to noble metals (e.g. silver and gold) include low losses in THz and mid-infrared regimes, extreme confinement, mechanical strength, tunability of its complex conductivity by means of chemical doping, electric and magnetic fields. The unique properties of graphene make it a novel platform to implement highly integrated plasmonic devices [11][12][13][14][15][16][17].
An ultrashort plasmonic directional coupler based on the hybrid metal-insulator slab waveguide is proposed and analyzed at the telecommunication wavelength of 1550 nm. It is first analyzed using the supermode theory based on mode analysis via the transfer matrix method in the interaction region. Then the 2D model of the coupler, including transition arms, is analyzed using a commercial finite-element method simulator. The hybrid slab waveguide is composed of a metallic layer of silver and two dielectric layers of silica (SiO2) and silicon (Si). The coupler is optimized to have a minimum coupling length and to transfer maximum power considering the layer thicknesses as optimization variables. The resulting coupling length in the submicrometer region along with a noticeable power transfer efficiency are advantages of the proposed coupler compared to previously reported plasmonic couplers.
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