1. Key Laboratory of Optoelectronic Device and Systems of Ministry of Education and Guangdong Province College of Optoelectronic Engineering Shenzhen University Shenzhen 518060 P. R. China
2. School of Electrical and Electronic Engineering Nanyang Technological University 50 Nanyang Avenue Singapore 639798 Singapore
3. Department of Electrical and Electronic Engineering Southern University of Science and Technology Shenzhen 518055 P. R. China
4. CNRS/NTU/THALES UMI3288 Research Techno Plaza 50 Nanyang Drive Singapore 637553 Singapore