1. College of Electronic Information and Optical Engineering; Nankai University; Tianjin 300071 China
2. Microsystem and Terahertz Research Center; China Academy of Engineering Physics; Chengdu 610200 China
3. Institute of Electronic Engineering; China Academy of Engineering Physics; Mianyang 621999 China
4. Municipal Key Laboratory of Photo-electronic Thin Film Devices and Technology; Nankai University; Tianjin 300071 China