1. School of Electrical and Electronic Engineering; Nanyang Technological University; 50 Nanyang Avenue Singapore 639798 Singapore
2. Department of Chemical and Biomolecular Engineering; National University of Singapore; 4 Science Drive 4 Singapore 117585 Singapore
3. Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province; College of Optoelectronic Engineering; Shenzhen University; Shenzhen 518060 China
4. School of Chemical Biology and Biotechnology; Peking University Shenzhen Graduate School; Shenzhen 518055 China
5. Department of Electrical and Electronic Engineering; Auckland University of Technology; Auckland 92006 New Zealand