1 State Key Laboratory on Tunable Laser Technology, School of Electronic and Information Engineering, Harbin Institute of Technology, Shenzhen 518055, China
2 LTCI, Telecom Paris, Institut Polytechnique de Paris, 91120 Palaiseau, France
3 DTU Electro, Department of Electrical and Photonics Engineering, Technical University of Denmark, 2800 Lyngby, Denmark
4 School of Information Science and Technology, ShanghaiTech University, Shanghai 201210, China
5 Center for High Technology Materials, The University of New-Mexico, Albuquerque, New Mexico 87106, USA