1. Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
2. Centre for Disruptive Photonic Technologies, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
3. School of Electrical Engineering and Computer Science, Oklahoma State University, Stillwater, Oklahoma 87074, USA
4. Key Lab of All Optical Network and Advanced Telecommunication Network of EMC, Institute of Lightwave Technology, Beijing Jiaotong University, Beijing 100044, People's Republic of China
5. XLIM, Limoges University, CNRS, UMR 7252, 7 rue Jules Vallès, F-19100 Brive, France