1. Center for Optoelectronics Materials and Devices & Key Laboratory of Optical Field Manipulation of Zhejiang Province Department of Physics Zhejiang Sci-Tech University Hangzhou 310018 China
2. College of Materials Science and Engineering Xiangtan University Xiangtan 411105 Hunan Province China
3. State Key Laboratory of Information Photonics and Optical Communications & Laboratory of Information Functional Materials and Devices School of Science Beijing University of Posts and Telecommunications Beijing 100876 China
4. College of Electronic and Optical Engineering & College of Microelectronics Nanjing University of Posts and Telecommunications Nanjing 210046 China