1. Centre for Silicon Photonics for Optical Communications (SPOC), Department of Electrical and Photonics Engineering, Technical University of Denmark 1 , Kgs. Lyngby, Denmark
2. Istituto Nazionale di Ottica del Consiglio Nazionale delle Ricerche (CNR-INO) 2 , 50125 Firenze, Italy
3. Università degli Studi di Napoli Federico II 3 , Napoli, Italy
4. QTI S.r.l 4 ., 50125 Firenze, Italy
5. Department of Physics and Astronomy, University of Florence 5 , 50019 Firenze, Italy