title: What is the direction followed by a beam in a photonic medium?
abstract: The direction of propagation followed by a monochromatic beam in a periodic structure is generally deduced from the isofrequency diagram, which is related to the group velocity. However, the group velocity is the derivative of omega with respect to the wavenumber, while the behavior of the beam should depend on omega only. In the subwavelength regime, a method for choosing the relevant branch of the isofrequency diagram and relying on the behavior of the system at omega only is described.
authors.affiliation: University of Montpellier II, GES UMR 5650, Bat. 21 CC074 Place E. Bataillon, 34095 Montpellier Cedex 05, France. felbacq@ges.univ-montp2.fr
authors.forename: Didier
authors.initials: D
authors.lastname: Felbacq
authors.forename: Brahim
authors.initials: B
authors.lastname: Guizal