Hybrid metal-insulator plasmonic slab directional coupler

A new two-dimensional plasmonic directional coupler is proposed based on the hybrid metal-insulator slab waveguide (HMISW). It is analyzed using the super mode theory (SMT) based on solving the symmetrical and antisymmetrical modes with the aim of transfer matrix method (TMM). The hybrid slab waveguide is composed of a metallic layer of silver and two dielectric layers of silica (SiO₂) and silicon (Si). Analysis is performed at the telecommunication wavelength of 1550 nm. Optimization of the coupling length according to layer thicknesses is mainly considered. Maximum transferred power (P_max) and the spatial extent of the coupler (L_s) are calculated as two additional performance criteria. It is shown that coupling lengths as low as 0.5 μm could be achieved resulting in a coupler much smaller than conventional directional couplers. In this case, percentage of transferred power is 90, coupler thickness is about 200 nm and the spatial length is 700 nm.