1 State Key Laboratory of Advanced Optical Communications System and Networks, School of Electronics, Peking University, Beijing 100871, China
2 Key Laboratory of Information and Communication Systems, Ministry of Information Industry, Beijing Information Science and Technology University, Beijing 100192, China
3 Peng Cheng Laboratory, Shenzhen 518055, China
4 Frontiers Science Center for Nano-optoelectronics, Peking University, Beijing 100871, China
5 Peking University Yangtze Delta Institute of Optoelectronics, Nantong 226010, China
6 e-mail: haowenshu@pku.edu.cn
7 e-mail: xjwang@pku.edu.cn