1. School of Physics and Electronic Information, Henan Polytechnic University, Jiaozuo 454000, P. R. China
2. School of Physics and Electronics Engineering, Jiangsu Normal University, Xuzhou 221116, P. R. China
3. Jiangsu Xiyi Advanced Materials Research Institute of Industrial Technology, Xuzhou 221400, P. R. China
4. College of Physics and Engineering, Henan University of Science and Technology, Luoyang 471000, P. R. China
5. Diode Lasers and LED Systems Group, Department of Electrical and Photonics Engineering, Technical University of Denmark, Roskilde 4000, Denmark