[1] Department of Electrical Electronic Engineering, Southern University of Science and Technology, Shenzhen, China
[2] Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore
[3] Key Laboratory of In-Fiber Integrated Optics of Ministry of Education, College of Physics and Optoelectronic Engineering, Harbin Engineering University, Harbin, China
[4] Center for Terahertz Waves, Key Laboratory of Optoelectronic Information Technology, Ministry of Education, College of Precision Instrument and Optoelectronics Engineering, Tianjin University, Tianjin, China