1. Nanophotonics Technology Center, Universitat Politécnica de Valéncia, Camino de Vera s/n, 46022 Valencia, Spain
2. Institute of Solid State Physics, Friedrich Schiller University Jena, Max-Wien-Platz 1, 07743 Jena, Germany
3. Institute of Applied Physics, Abbe Center of Photonics, Friedrich Schiller University Jena, Albert-Einstein-Str. 15, 07745 Jena, Germany
4. MIND-IN2UB, Departament d’Enginyeria Electrònica i Biomédica, Facultat de Física, Universitat de Barcelona, Martí i Franqués 1, 08028 Barcelona, Spain
5. NEST Lab, CNR - Istituto di Nanoscienze and Scuola Normale Superiore, Piazza San Silvestro 12, 56217 Pisa, Italy