1. Institute of Mathematics and Physics, Central South University of Forestry and Technology, Changsha 410004, People's Republic of China
2. College of Science, Jiujiang University, Jiujiang 332005, People's Republic of China
3. Key Laboratory for Micro-Nano Optoelectronic Devices of Ministry of Education, Hunan University, Changsha 410082, People's Republic of China
4. National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Science, Shanghai 200083, People's Republic of China