1. Center for Terahertz Waves and College of Precision Instruments and Optoelectronics Engineering, Tianjin University, No. 92 Weijin Road, Tianjin 300072, People’s Republic of China
2. Department of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Hong Kong 999077, People’s Republic of China
3. The Hong Kong Polytechnic University Shenzhen Research Institute, Shenzhen 518057, People’s Republic of China