1. Institut Non-linéaire de Nice, Université de Nice Sophia, Antipolis—Centre Nationale de la Recherche Scientifique, 1361 route des Lucioles, 06560 Valbonne, France
2. SUPA, Department of Physics, University of Strathclyde, 107 Rottenrow, Glasgow G4 ONG, Scotland, United Kingdom
3. INFM-CNR and CNISM, Dipartimento di Matematica e Fisica, Università dell’Insubria, Via Valleggio 11, 22100 Como, Italy
4. ULM Photonics, Lise Meitner Str. 13, 89081 Ulm, Germany