Ultrafast Plasmonics on Gold Nanowires: Confinement, Dispersion, and Pulse Propagation

We explore the potential of plasmonic nanowires for ultrafast photonics by comparing the properties of the guided surface plasmon polariton (SPP) to that of the mode guided in a silicon nanowire. For this purpose, we combine ultrafast near-field microscope measurements of gold nanowires with mode simulations to study modal properties such as mode width, propagation length, fundamental mode cutoff, group velocity dispersion, and third-order dispersion coefficients. Using this information we show that, for ultrashort-pulse propagation, plasmonic waveguides can outperform their dielectric counterparts. In particular, we demonstrate that the ohmic losses, which are unavoidable in the gold nanowire, cause less peak amplitude decay as ultrashort pulses propagate than do the high dispersion and the presence of a mode cutoff.