1. Hubei Key Laboratory of Optical Information and Pattern Recognition, Wuhan Institute of Technology, Wuhan 430205, P. R. China
2. Hubei Key Laboratory of Micro-Nanoelectronic Materials and Devices, School of Microelectronics, Hubei University, Wuhan 430062, China
3. College of Physics and Telecommunication Engineering, Zhoukou Normal University, Zhoukou 466001, PR China