1. Guangdong Provincial Key Laboratory of Nanophotonic Functional Materials and Devices, School of Information and Optoelectronic Science and Engineering, South China Normal University, Guangzhou 510006, China
2. School of Optoelectronic Engineering, Guangdong Polytechnic Normal University, Guangzhou 510665, China
3. Department of Physics, The Hong Kong University of Science and Technology, Hong Kong 999077, China