1. School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, UK.
2. SZU-NUS Collaborative Innovation Center for Optoelectronic Science and Technology, Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China.
3. Key Laboratory of In-Fiber Integrated Optics of Ministry of Education, College of Science, Harbin Engineering University, Harbin 150001, China.
4. School of Electronic Information, Wuhan University, Wuhan 430072, China.
5. Department of Physics, University of Paderborn, Warburger Straße 100, Paderborn D-33098, Germany.
6. Department of Materials Science and Engineering, Southern University of Science and Technology, Shenzhen 518055, China.