Plasmonic waveguiding properties of the gap plasmon mode with a dielectric substrate

•We propose a structure of plasmonic waveguiding.•This plasmonic waveguiding has a combination of high confinement and long propagation length.•There is a critical distance between silver nanowires that the influence of a silica substrate can be neglected when the distance is smaller than it.•The conclusion is applicable considering the roughness of the substrate surface.

The plasmonic waveguiding properties of the gap plasmon mode between two adjacent silver nanowires with a substrate are theoretically investigated using finite element method. The results show that there is a critical gap distance between two silver nanowires which approximately equals to the radius of the nanowires. When the gap distance is less than the critical distance, the influence of the substrate on the gap plasmon mode can be neglected. The gap plasmon mode has a combination of high confinement and long propagation length. Moreover, the plasmonic waveguiding properties of the gap plasmon mode are not sensitive to the wire-to-substrate distance between silver nanowires and the substrate.