1. School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 Singapore
2. Centre for Disruptive Photonic Technologies, TPI and SPMS, Nanyang Technological University, 21 Nanyang Link, 637371 Singapore
3. Department of Electrical Engineering, National Cheng Kung University, Tainan City 701, Taiwan
4. College of Optoelectronic Engineering, Chongqing University, Chongqing 400044, China
5. School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, 637459 Singapore