1. College of Science, University of Shanghai for Science and Technology, Shanghai 200093, China.
2. School of Optical Electrical and Computer Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China (e-mail: tianengang@163.com)
3. College of Science, University of Shanghai for Science and Technology, Shanghai 200093, China, and also with the School of Automation Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China.