Dispersion shifts in optical nanowires with thin dielectric coatings.

Based on exact solutions of Maxwell's equations of a 3-layer-structured cylindrical waveguide, we calculated dispersion shifts in thin-dielectric-coated optical nanowires. Typical parameters of silica and silicon nanowires are used for numerical simulations. It shows that, the dispersion of a nanowire waveguide can be made highly sensitive to the thickness and index of the coating layer, and a thin coat may lead to considerable dispersion shift of the guided light. For example, in a 300-nm-diameter silicon nanowire, a 1% decrease in diameter of the silicon core by oxidation of silicon into silica shell leads to a 34% decrease in dispersion at 1450-nm wavelength. Results presented in this work suggest the possibility of tuning waveguide dispersions of optical nanowires by coating thin dielectric layers.