1. Key Laboratory of Communication and Information Systems, Beijing Municipal Commission of Education, School of Electronic and Information Engineering, Beijing Jiaotong University, Beijing, China
2. School of Physical Science and Engineering, Beijing Jiaotong University, Beijing, China
3. China Center for Information Industry Development, Beijing, China
4. Department of Physics, Department of Materials Science & Engineering, and Department of Biomedical Engineering, City University of Hong Kong, Hong Kong