Key Laboratory of Broadband Fiber Transmission and Communication Networks, University of Electronic Science and Technology of China, Chengdu 610054, CHN
1 Fujian Provincial Key Laboratory of Photonic Technology, Institute of Laser & Optoelectronic Technology, Fujian Normal University, Fuzhou 350007, CHN
2 Department of Information Science & Electronic Engineering, Zhejiang University, Hangzhou 310027, CHN