Compact Bragg gratings for long-range surface plasmon polaritons

By introducing periodic thickness modulation of thin metal stripes embedded in a dielectric, compact and efficient Bragg gratings for long-range surface plasmon polaritons (LR-SPPs) operating around 1550 nm are realized. Reflection and transmission spectra of the gratings having different lengths (from 20 to 160 μm), heights (tens of nanometers), and widths of the metal ridges forming the grating were measured, and the reflectivity of up to 60% and bandwidths ranging from 5 to 40 nm are demonstrated. By using a simple lossless-uniform-grating description, the effective refractive-index modulation in LR-SPP gratings is estimated to be of the order of 10^-2, and two different approaches for these calculations are compared. The LR-SPP loss incurred in the investigated gratings is also discussed.