Long-range surface plasmon polariton modes with a large field localized in a nanoscale gap

A planar five-layer waveguide with a metal-insulator (with the low permittivity)-metal structure embedded in a high-permittivity dielectric is theoretically studied. A long-range surface mode draws special attention because of its superior properties of low attenuation and a large field localized inside the nanoscale middle gap provided with permittivity-contrast. Effects of the surrounding permittivity and the metal film thickness are investigated, and the electric field amplitude in the gap can be dozens of times higher than that at the outer interfaces. This plasmonic structure may have potential applications in integrated photonic devices.