1. Guangxi Key Laboratory of Optoelectronic Information Processing School of Optoelectronic Engineering Guilin University of Electronic Technology Guilin 541004 China
2. Center for Terahertz Waves and College of Precision Instrument and Optoelectronics Engineering Tianjin University Tianjin 300072 China
3. School of Electronic Engineering Tianjin University of Technology and Education Tianjin 300222 China
4. School of Electrical and Computer Engineering Oklahoma State University Stillwater OK 74078 USA