1. School of Physics and Materials Science; Anhui University; Hefei 230601 China
2. State Key Laboratory of Infrared Physics; Shanghai Institute of Technical Physics; Chinese Academy of Sciences; Shanghai 200083 China
3. School of Optical and Electronic Information; Huazhong University of Science and Technology; 1037 Luoyu Road Wuhan Hubei 430074 China
4. Department of Electronic and Computer Engineering; The Hong Kong University of Science and Technology; Clear Water Bay Kowloon Hong Kong China SAR