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