Properties of coupled surface plasmon-polaritons in metal-dielectric-metal structures

The properties of surface plasmon-polaritons (SPPs) in symmetrical metal-dielectric-metal (MDM) structures were theoretically investigated and experimentally demonstrated. These SPPs exhibit several intriguing properties that are not observed in single-interface SPPs: they can directly couple to radiation outside the MDM structure; their frequency may fall within the plasmon gap; their group velocities can be positive, negative, or even zero, and their density of states can be tuned. All of these properties are favorable in devices that exploit the Purcell effect of SPPs to improve performance. Analytical descriptions of the dispersion curves in some important regions are presented.