1. Guangxi Key Laboratory of Optoelectronic Information Processing, School of Optoelectronic Engineering, Guilin University of Electronic Technology 1 , Guilin 541004, China
2. School of Physics and Optoelectronic Engineering, Guangdong University of Technology 2 , Guangzhou 510006, China
3. Center for Terahertz Waves and College of Precision Instrument and Optoelectronics Engineering, Tianjin University 3 , Tianjin 3000072, China