1. School of Mechanical Engineering and Automation, Wuhan Textile University, Wuhan, Hubei 430074, P. R. China
2. Wuhan National Laboratory for Optoelectronics (WNLO), Huazhong University of Science and Technology (HUST), Wuhan, Hubei 430074, P. R. China
3. School of Physics and Electronics Science, Hunan University of Science and Technology, Xiangtan 411201, China