Wideband Slow Surface Plasmons in Double Resonator Plasmonic Grating Waveguide

We propose a theoretical and numerical investigation of surface plasmon polaritons supported by a metal- insulator-metal (MIM) waveguide, periodically coupled to a series of adjacent resonators. The slow light characteristics of the MIM-coupled resonator is analyzed by controlling separation or displacement between resonators. By tailoring this displacement factor, group velocity of slow wave structures is reduced to a great extent with a large value of the normalized delay bandwidth product (NDBP = 0.667) that measures the capacity of the device. A low value of group velocity (V_g = c/7) is reported over an ultralarge bandwidth (Δf = 21 THz). An unusual U-shaped group index-frequency curves with a constant group index n_g is obtained, which leads to a nearly-zero value of group velocity dispersion followed by positive and negative peaks. The structure is also analyzed for changing the depth of the resonators. The structure can be further modified to suit different applications in optical switching device, dispersion compensating units, and nonlinear optics devices.