1. Institute of Fundamental and Frontier Sciences University of Electronic Science and Technology of China Chengdu 610054 China
2. Department of Photonics and Institute of Electro‐Optical Engineering College of Electrical and Computer Engineering National Chiao Tung University Hsinchu 30010 Taiwan
3. Department of Physics and Astronomy Ohio University Athens OH 45701 USA
4. Microsystem and Terahertz Research Center China Academy of Engineering Physics Chengdu 610200 China
5. Institute of Electronic Engineering China Academy of Engineering Physics Mianyang 621999 China