Figure 4

Effective refractive indices (n_eff) of fundamental SPP mode of a TiO₂-Au-air-Au-TiO₂ multilayer plasmonic waveguide with air spacing, s = 10 (red) and 14 (green) nm. The real parts of the refractive index of Au (n_Au)³⁷ is also plotted as a blue curve.