1. Photonics Research Group; Ghent University - imec; Technologiepark Zwijnaarde 126 B-9052 Ghent Belgium
2. Center for Nano- and Biophotonics (NB-Photonics); Ghent University; Technologiepark Zwijnaarde 126 B-9052 Ghent Belgium
3. Walter Schottky Institute; Technical University of Munich; Am Coulombwall 4 D-85748 Garching Germany