1. School of Electronic Engineering, Beijing University of Posts and Telecommunications, Beijing, China
2. Center for Terahertz Waves and College of Precision Instrument and Optoelectronics Engineering, Key Laboratory of Opto-Electronics Information and Technical Science, Ministry of Education, Tianjin University, Tianjin, China
3. College of Electronic and Information Engineering, Shandong University of Science and Technology, Qingdao, China
4. Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China
5. National Institute of Metrology, Beijing, China