Propagation of long-range surface plasmon polaritons in photonic crystals

We study the interaction of long-range surface plasmon polaritons (LR-SPPs), excited at telecommunication wavelengths, with photonic crystals (PCs) formed by periodic arrays of gold bumps that are arranged in a triangular lattice and placed symmetrically on both sides of a thin gold film embedded in polymer. Radiation is delivered to and from the PC structures with the help of LR-SPP guides that consist of 8 mu m wide and 15 nm thick gold stripes attached to wide film sections (of the same thickness) covered with bumps (diameter similar to 300 nm, height up to 150 nm on each side of the film). We investigate the LR-SPP transmission through and reflection from the PC structures of different lengths and lattice periods as well as the LR-SPP propagation along line defects of different widths. The reflection measurements indicate a large penetration depth of LR-SPPs (tens of micrometers) into the investigated PC structures. Using a self-consistent description based on the Green'S function formalism, we simulate numerically the LR-SPP transmission through and reflection from finite-size PC structures consisting of finite-size scatterers, as well as the LR-SPP guiding along line defects in these structures. Calculation results are found to be in good agreement with experimental findings, showing, e.g., deep penetration of LR-SPPs in the PC structures and good confinement of the radiation inside the channels. Our results indicate that the multiple LR-SPP scattering, occurring in the investigated PC structures, is rather weak, so that the photonic bandgap effect might be expected to take place only for some particular propagation directions. Preliminary experiments on LR-SPP bending and splitting at large angles are reported, and further research directions are discussed.