[1
]State Key Laboratory of Luminescent Materials and Devices Guangdong Provincial Key
Laboratory of Fiber Laser Materials and Applied Techniques Guangdong Engineering Technology
Research and Development Center of Special Optical Fiber Materials and Devices School
of Materials Science and Engineering South China University of Technology Guangzhou
510641 China
[2
]School of Physics and Optoelectronics South China University of Technology Guangzhou
510641 China