1. University of Science and Technology of China, Hefei, 230026, P. R. China
2. Key Laboratory of Photonic Devices and Materials, Anhui Institute of Optics and Fine Mechanics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui Province, 230031, P. R. China
3. Advanced Laser Technology Laboratory of Anhui Province, Hefei, 230037, P. R. China