1. School of Physics, Harbin Institute of Technology, Harbin 15001, China
2. Department of Optoelectronics Science, Harbin Institute of Technology at Weihai, Weihai 264209, China
3. State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130012, China
4. Photonics Research Center, School of Electronic Engineering and Automation, Guilin University of Electronic Technology, Guilin 541004, China