1. School of Physics and Optoelectronic Engineering, Guangdong University of Technology, Guangzhou 510006, P. R. China
2. Guangdong Provincial Key Laboratory of Information Photonics Technology, School of Materials and Energy, Guangdong University of Technology, Guangzhou, Guangdong 510006, P. R. China
3. Guangdong Provincial Key Laboratory of Nanophotonic Manipulation, Institute of Nanophotonics, Jinan University, Guangzhou 511443, P. R. China
4. State Key Laboratory of Optoelectronic Materials and Technologies, Nanotechnology Research Center, School of Materials Science & Engineering, Sun Yat-sen University, Guangzhou, Guangdong 510275, P. R. China
5. College of Optical Science and Engineering, Zhejiang University, Hangzhou, Zhejiang 310027, P. R. China