1. Optoelectronics Research Centre, University of Southampton, Southampton SO17 1BJ, United Kingdom
2. nCAT, University of Southampton, Southampton SO17 1BJ, United Kingdom
3. National Physical Laboratory, Teddington, TW11 0LW, United Kingdom
4. School of Materials Science and Engineering, Harbin Institute of Technology, 150001 Harbin, China
5. National Key Laboratory of Science and Technology on Tunable Laser, Harbin Institute of Technology, 150001 Harbin, China
6. School of Physics and Electronic Engineering, Jiangsu Normal University, 221116 Xuzhou, China
7. Key Laboratory of In-Fiber Integrated Optics of Ministry of Education, College of Science, Harbin Engineering University, 150001 Harbin, China