1. Institute of Photonics and Quantum Sciences, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom
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 Mathematics and Physics, North China Electric Power University, Baoding 071003, China
4. College of Material Science and Engineering, Kunming University of Science and Technology, Kunming 650093, China
5. School of Science, Harbin Institute of Technology, Shenzhen 518055, China
6. Department of Physics, University of Hong Kong, Hong Kong, China
7. Department of Electronic & Electrical Engineering, University of Hong Kong, Hong Kong, China