Photonic bandgap structures for long-range surface plasmon polaritons

Propagation of long-range surface plasmon polaritons (LR-SPPs) along periodically thickness-modulated metal stripes embedded in dielectric is studied both theoretically and experimentally for light wavelengths in the telecom range. We demonstrate that symmetric (with respect to the film surface) nm-size thickness variations result in the pronounced band gap effect, and obtain very good agreement between measured and simulated (transmission and reflection) spectra. This effect is exploited to realize a compact wavelength add-drop filter with the bandwidth of ∼20 nm centered at 1550 nm. The possibilities of achieving a full bandgap (in the surface plane) for LR-SPPs are also discussed.