[1] Barcelona Inst Sci & Technol, ICFO Inst Ciencies Foton, Castelldefels 08860, Barcelona, Spain
[2] Poligon Cami Ral, Radiantis, Barcelona 08850, Spain
[3] BAE Syst Inc, MER15-1813,POB 868, Nashua, NH 03061 USA
[4] ICREA, Passeig Lluis Companys 23, Barcelona 08010, Spain