1. School of Optical and Electronic Information and Suzhou Key Laboratory of Biophotonics, Suzhou City University, Suzhou 215104, P. R. China
2. School of Physical Science and Technology and Jiangsu Key Laboratory of Thin Film, Soochow University, Suzhou 215006, P. R. China
3. School of Mathematics and Physics, Queen’s University Belfast, Belfast BT7 1NN, Northern Ireland, United Kingdom