Silicon-slot-mediated guiding of plasmonic modes: The realization of subwavelength optical confinement with low propagation loss

Waveguiding platforms consisting of metallic nano-wires embedded inside vertical-type dielectric slot waveguides are proposed and the guiding properties are investigated at the telecom wavelength. It is shown that the characteristics of the plasmonic modes can be strongly modified owing to the existence of the silicon rails in close proximity to the metallic nanowire, which enables low-loss light guiding with subdiffraction-limited mode area. Systematical analysis regarding the variation of key geometric parameters has revealed that the symmetric hybrid mode can exist within a wide-range of physical dimensions, and demonstrates improved optical performance over either the conventional hybrid plasmonic mode or the fundamental plasmonic mode supported by a single metal nanowire. Furthermore, we show numerically that the supported symmetric and asymmetric modes can be separately excited through controlling the polarization state of the Gaussian beam that illuminated onto the nanowire tip. The presented hybrid waveguides naturally extend the capabilities of both the silicon slot and metal nanowire structures, which could facilitate a number of potential applications at the subwavelength scale.