Directional coupler based on metal-insulator-metal plasmonic waveguide

We present the power exchange dynamics between two closely kept metal-insulator-metal (MIM) structures that constitutes a surface plasmon polariton waveguide directional coupler. This composite MIM waveguide coupler is a miniature one. A comparative study of the power exchange and coupling dynamics is presented for Gold, Silver, Aluminium and Copper; the commonly used noble metals for MIM waveguides. Finite-difference-time domain method based full numerical experiments are performed to reveal the impact of the operating wavelength, refractive indices of the waveguides and other system parameters on the coupling profile of the plasmonic directional coupler. Unlike a conventional dielectric coupler MIM waveguide coupler shows linear increment in coupling length with increasing wavelength. Insertion of dielectric media in between the metal strips strengthens the coupling. The influence of nature of the metal-dielectric interfaces and waveguide asymmetry on the power coupling profile is demonstrated.