1. Photonics Research Group, Department of Information Technology (INTEC), Ghent University-imec 1 , 9052 Ghent, Belgium
2. Liquid Crystal & Photonics Group, Department of Electronics and Information Systems (ELIS), Ghent University 2 , 9052 Ghent, Belgium
3. Centre for Nano and Bio-photonics, Ghent University 3 , 9052 Ghent, Belgium
4. 4 Sol-gel Centre for Research on Inorganic Powders and Thin Films, Department of Chemistry, Ghent University, 9000 Ghent, Belgium