[1] Institute of Photonic Sciences (ICFO), ICREA, Mediterranean Technology Park, Avenue del Canal Olímpic s/n, 08860 Castelldefels (Barcelona), Spain
[2] Photonics for Nanoapplications Laboratory, Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation (NHRF), 48 Vassileos Constantinou Avenue, 11635 Athens, Greece
[3] Optoelectronics Research Centre, University of Southampton, Southampton SO17 1BJ, United Kingdom
[4] Department of Electrical and Computer Engineering, National Technical University of Athens, 15780 Athens, Greece