1 Key Laboratory of Photonic Materials and Devices Physics for Oceanic Applications, Ministry of Industry and Information Technology, College of Physics and Optoelectronic Engineering, Harbin Engineering University, Harbin 150001, China
2 Key Laboratory of In-Fiber Integrated Optics of Ministry of Education, College of Physics and Optoelectronic Engineering, Harbin Engineering University, Harbin 150001, China
3 School of Physics and Engineering, ITMO University, St. Petersburg 197101, Russia
4 School of Information Engineering, Guangdong University of Technology, Guangzhou 510008, China
5 Qingdao Innovation and Development Center, Harbin Engineering University, Qingdao 266000, China
6 e-mail: yangj@gdut.edu.cn