title: Direct observation of Bloch harmonics and negative phase velocity in photonic crystal waveguides.
abstract: The eigenfield distribution and the band structure of a photonic crystal waveguide have been measured with a phase-sensitive near-field scanning optical microscope. Bloch modes, which consist of more than one spatial frequency, are visualized in the waveguide. In the band structure, multiple Brillouin zones due to zone folding are observed, in which positive and negative dispersion is seen. The negative slopes are shown to correspond to a negative phase velocity but a positive group velocity. The lateral mode profile for modes separated by one reciprocal lattice vector is found to be different.
authors.affiliation: Applied Optics Group, Department of Science and Technology and MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands.
authors.forename: H
authors.initials: H
authors.lastname: Gersen
authors.forename: T J
authors.initials: TJ
authors.lastname: Karle
authors.forename: R J P
authors.initials: RJ
authors.lastname: Engelen
authors.forename: W
authors.initials: W
authors.lastname: Bogaerts
authors.forename: J P
authors.initials: JP
authors.lastname: Korterik
authors.forename: N F
authors.initials: NF
authors.lastname: van Hulst
authors.forename: T F
authors.initials: TF
authors.lastname: Krauss
authors.forename: L
authors.initials: L
authors.lastname: Kuipers