On surface-plasmon-polariton waves guided by the interface of a metal and a rugate filter with a sinusoidal refractive-index profile. Part II: High-phase-speed solutions

In continuation of a previous paper [J. Opt. Soc. Am. B 27, 2218 (2010)], by solving a canonical boundary-value problem we found that the planar interface of a metal and a rugate filter can guide surface-plasmon-polariton (SPP) waves with phase speeds greater than the speed of light in free space. These SPP waves can be either p or s polarized, and can have extremely high phase speeds, but are very loosely bound to the metal/rugate-filter interface. In two practically implementable configurations with both partnering materials of finite thickness, both p- and s-polarized SPP waves with high phase speeds can be excited, provided that the thickness of the rugate filter is much larger than needed for SPP waves with low phase speeds.