1. Center for Information Photonics and Communications; School of Information Science and Technology; Southwest Jiaotong University; Chengdu 611756 China
2. Institute of Optoelectronics; University of Duisburg-Essen; Duisburg 47057 Germany
3. Microwave Photonics Research Laboratory; School of Electrical Engineering and Computer Science; University of Ottawa; Ottawa K1N 6N5 Canada