title: Negative dispersion: a backward wave or fast light? Nanoplasmonic examples.
abstract: 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.
authors.affiliation: Electrical Engineering Department, Technion, Haifa 32000, Israel.
authors.forename: Eyal
authors.initials: E
authors.lastname: Feigenbaum
authors.forename: Noam
authors.initials: N
authors.lastname: Kaminski
authors.forename: Meir
authors.initials: M
authors.lastname: Orenstein