1. Instituto de Telecomunicações, Instituto Superior Técnico, University of Lisbon, Avenida Rovisco Pais 1, Lisboa, 1049001 Portugal
2. Instituto de Física, Universidade Federal do Rio de Janeiro, Caixa Postal 68528, 21941-972 Rio de Janeiro, RJ, Brazil
3. Department and Centre of Physics, and QuantaLab, University of Minho, Campus of Gualtar, 4710-057 Braga, Portugal
4. ICFO−Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), Spain
5. ICREA−Institució Catalana de Recerca i Estudis Avançats, Passeig Lluís Companys 23, 08010 Barcelona, Spain
6. International Iberian Nanotechnology Laboratory (INL), Av. Mestre José Veiga, 4715-330 Braga, Portugal