1. School of Electrical and Electronic Engineering; Nanyang Technological University; 50 Nanyang Avenue Singapore 639798 Singapore
2. Laboratory of Optical Information Technology; Wuhan Institution of Technology; Wuhan 430205 China
3. School of Optical and Electronic Information; National Engineering Laboratory for Next Generation Internet Access System; Huazhong University of Science and Technology; Wuhan 430074 China
4. CINTRA CNRS/NTU/THALES; UMI3288; Research Techno Plaza; 50 Nanyang Drive Singapore 637553 Singapore