Negative dispersion: a backward wave or fast light? Nanoplasmonic examples

Propagation of light in a negative dispersion regime (antiparallel phase and group velocities) may be attributed to either fast light or a backward wave. We show that by applying causality, only one of these is valid for each scenario. A nanoplasmonic structure is shown to support both types of solution depending on the parameters. (C) 2009 Optical Society of America