1. Photonics Research Group, Department of Information Technology, Ghent University - imec, Technologiepark-Zwijnaarde 126, 9052 Ghent, Belgium
2. Center for Nano- and Biophotonics (NB-Photonics), Ghent University, Technologiepark-Zwijnaarde 126, 9052 Ghent, Belgium
3. imec, Kapeldreef 75, 3001 Leuven, Belgium
4. Technology Division, Panasonic Corporation, 1006 Kadoma, Kadoma City, Osaka 571-8508, Japan