1. Wuhan Research Institute of Posts and Telecommunications, Wuhan, Hubei 430074, PR China
2. Wuhan National Laboratory for Optoelectronics (WNLO), Huazhong University of Science and Technology, Wuhan, Hubei 430074, PR China
3. Hunan Provincial Key Laboratory of Girds Operation and Control on Multi-Power Sources Area, Shaoyang University, Shaoyang, Hunan 422000, PR China
4. Department of Physics, City University of Hong Kong, Kowloon, Hong Kong 999077, PR China