1. Guangdong Provincial Engineering Research Center of Crystal and Laser Technology, Guangzhou 510632, P. R. China
2. Guangdong Provincial Key Laboratory of Optical Fiber Sensing and Communications, Guangzhou 510632, P. R. China
3. Department of Optoelectronic Engineering, Jinan University, Guangzhou 510632, P. R. China
4. Guangdong Provincial Key Laboratory of Industrial, Ultrashort Pulse Laser Technology, Shenzhen 518055, P. R. China