1 College of Electronic and Optical Engineering & College of Microelectronics, Institute of Advanced Photonics Technology, Nanjing University of Posts and Telecommunications, Nanjing 210023, China
2 College of Physics, National Laboratory of Solid State Microstructures, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
3 College of Physics Science and Technology, Yangzhou University, Yangzhou 225002, China
4 College of Science, Nanjing Forestry University, Nanjing 210037, China
5 College of Science, Zhejiang University of Technology, Hangzhou 310023, China
6 e-mail: chaojuntang@126.com
7 e-mail: zchen@nju.edu.cn