1. State Key Laboratory of Luminescent Materials and Devices, Institute of Optical Communication Materials, Guangdong Engineering Technology Research and Development Center of Special Optical Fiber Materials and Devices, and Guangdong Provincial Key Laboratory of Fiber Laser Materials and Applied Techniques, South China University of Technology, Guangzhou 510641, China
2. School of Physics and Optoelectronics, South China University of Technology, Guangzhou 510640, China