1. Center for Terahertz Waves and College of Precision Instrument and Optoelectronics Engineering Key Laboratory of Optoelectronic Information Technology (Ministry of Education of China) Tianjin University Tianjin 300072 China
2. Physical Science and Engineering Division King Abdullah University of Science and Technology Thuwal 23955–6900 Saudi Arabia
3. College of Physics and Materials Science Tianjin Normal University Tianjin 300387 China
4. Guangxi Key Laboratory of Optoelectronic Information Processing School of Optoelectronic Engineering Guilin University of Electronic Technology Guilin 541004 China
5. School of Electrical and Computer Engineering Oklahoma State University Stillwater Oklahoma 74078 USA