1. Optoelectronics Research Centre (ORC), Physics Unit/Photonics, Faculty of Engineering and Natural Science, Tampere University, Korkeakoulunkatu 3, 33720 Tampere, Finland
2. Institut FOTON, UMR-CNRS 6082, Institut National des Sciences Appliquées de Rennes, University of Rennes, 35700 Rennes, France