1. College of Science Huazhong Agricultural University Wuhan 430070 P. R. China
2. Henan Institute of Advanced Technology Zhengzhou University Zhengzhou 450001 P. R. China
3. School of Physics and Technology Wuhan University Wuhan 430072 P. R. China
4. School of Optoelectronic Engineering Guangdong Polytechnic Normal University Guangzhou 510665 P. R. China