1. State Key Laboratory of Luminescent Materials and Devices School of Materials Science and Engineering South China University of Technology Guangzhou 510640 P. R. China
2. Guangdong Provincial Key Laboratory of Fiber Laser Materials and Applied Techniques Guangdong Engineering Technology Research Center of Special Optical Fiber Materials and Devices Guangzhou 510640 P. R. China
3. Nuclear Power Institute of China Chengdu 610000 P. R. China
4. Department of Engineering Physics Tsinghua University Beijing 100084 P. R. China
5. Shanghai Hapstar Mechanical and Electrical Equipment Co., Ltd. Shanghai 210100 P. R. China
6. College of Optical Science and Engineering State Key Laboratory of Modern Optical Instrumentation Zhejiang University Hangzhou 310027 P. R. China