1Key Laboratory of All Optical Network & Advanced Telecommunication of EMC, Institute of Lightwave Technology, Beijing Jiaotong University, Beijing 100044, China
2Department of Electronics, Information and Communication Engineering, Osaka Institute of Technology, 5-16-1 Omiya, Asahi-ku, Osaka 535-8585, Japan
3Graduate School of Natural Science and Technology, Okayama University, 1-1-1 Tsushimanaka, Kita Ward, Okayama Prefecture 700-8530, Japan