1. School of Physics and Material Science, Guangzhou University, Guangzhou 510006, China
2. School of Electronics and Communication Engineering, Guangzhou University, Guangzhou 510006, China
3. Key Laboratory of On-Chip Communication and Sensor Chip of Guangdong Higher Education Institutes, Guangzhou 510006, China
4. Department of Electrical Engineering, City University of Hong Kong, Kowloon, Hong Kong SAR 999077, China