1. Institute of Microelectronics, Agency for Science Technology and Research (A*STAR) 2 Fusionopolis Way Singapore 138634 Singapore
2. Department of Physics and Center for Metamaterials Research The Hong Kong University of Science and Technology Hong Kong 999077 China
3. School of Science and Engineering The Chinese University of Hong Kong Shenzhen 518060 P. R. China
4. College of Physics and Optoelectronic Engineering Shenzhen University Shenzhen 518060 P. R. China
5. Department of Biomedical Engineering The Chinese University of Hong Kong Shatin, NT Hong Kong SAR 852 China