1. Key Laboratory of E&M, Ministry of Education, Zhejiang University of Technology, Hangzhou 310014, People's Republic of China
2. Center for Optoelectronics Materials and Devices, Zhejiang Sci-Tech University, Hangzhou 310018, People's Republic of China
3. State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China