1. School of Physics , Harbin Institute of Technology , Harbin 150000 , People’s Republic of China
2. Heilongjiang Provincial Key Laboratory of Plasma Physics and Application Technology , Harbin 150000 , People’s Republic of China
3. Key Laboratory on In-Fiber Integrated Optics of Ministry of Education, College of Physics and Optoelectronic Engineering , Harbin Engineering University , Harbin 150001 , China
4. Department of Electronic and Electrical Engineering , University College London , Torrington Place , London WC1E 7JE , UK