1. Department
of Electrical and Computer Engineering, School of Engineering and
Applied Science, George Washington University, Washington, DC 20052, United States
2. The
Key Laboratory of Optoelectronics Technology, Ministry of Education,
College of Electronic Information and Control Engineering, Beijing University of Technology, Beijing 100124, People’s Republic of China
3. IBM T. J. Watson
Research Center, 1101 Kitchawan Road, Yorktown Heights, New York 10598, United States