1. School of Physics and Electronic-Electrical Engineering, Xiangnan University, Chenzhou 423000, P. R. China
2. Microelectronics and Optoelectronics Technology Key Laboratory of Hunan Higher Education, School of Physics and Electronic Electrical Engineering, Xiangnan University, Chenzhou 423000, P. R. China
3. School of Physics and Optoelectronics & Hunan Institute of Advanced Sensing and Information Technology, Xiangtan University, Xiangtan 411105, P. R. China