1. Materials and Microsystems Laboratory χLab, Politecnico di Torino, C.so Duca degli Abruzzi 24, IT-10129 Torino, Italy
2. Optics and Photonics Technology Laboratory, Ecole Polytechnique Fédérale de Lausanne EPFL-STI-OPT, A.-L. Breguet 2, CH-2000 Neuchâtel, Switzerland
3. IIT - Italian Institute of Technology @ POLITO, Corso Trento 21, 10129 Torino, Italy
4. Nanophotonics and Metrology Laboratory, Swiss Federal Institute of Technology Lausanne EPFL-STI-NAM, ELG Station 11, CH-1015 Lausanne, Switzerland
5. Dipartimento di Energetica, SAPIENZA Università di Roma and CNISM, Via A. Scarpa 16, IT-00161 Roma, Italy