1Key Laboratory of In-Fibre Integrated Optics of Ministry of Education, College of Science, Harbin Engineering University, Harbin 150001, China
2Photonics Research Centre, Technological University Dublin, Kevin Street, Dublin 8, Ireland
3Optical Fibre Sensors Research Centre, Department of Electronic and Computer Engineering, University of Limerick, Limerick V94 T9PX, Ireland
4Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China