Stable hybrid plasmonic directional coupler based on an embedded silver nanostructure waveguide

In this paper, a stable hybrid plasmonic optical directional coupler based on an embedded silver nanostructure that can offer a power transfer up to 95% is presented. This optimum power transfer is obtained at an outer edge-to-edge separation of 0.58 µm between the two waveguides. The obtained propagation loss is as low as 0.0863 dB/µm. The electric field distributions of the symmetric and antisymmetric modes of the coupler are compared, and the transmission characteristics are studied in detail using the finite element method. The performances of the directional coupler have been further characterized in terms of excess loss, coupling degree, and directionality. The shortest coupling length at which the maximum power coupling occurs is obtained as 2.488 µm. The proposed compact directional coupler features good field confinement and low propagation loss, which opens the door for many device applications in photonic-integrated circuits and optoelectronic industries.