1 Department of Optoelectrics Information Science and Engineering, School of Physics and Electronics, Central South University, Changsha 410012, China
2 State Key Laboratory of Optoelectronic Materials and Technologies, School of Electronics and Information Technology, Sun Yat-sen University, Guangzhou 510275, China
3 School of Electrical Engineering and Computer Science, Louisiana State University, Baton Rouge, Louisiana 70803, USA
4 Center for Computation and Technology, Louisiana State University, Baton Rouge, Louisiana 70803, USA
5 e-mail: yhuan15@csu.edu.cn
6 e-mail: shenyuecheng@mail.sysu.edu.cn