1. Centre for Optical and Electromagnetic Research, State Key Laboratory of Modern Optical Instrumentations, JORCEP [Joint Research Center of Photonics of the Royal Institute of Technology (Sweden), Lund University (Sweden), and Zhejiang University], Zhejiang University, Zhijingang Campus, 310058 Hangzhou, China
2. ZJU-SCNU Joint Research Center of Photonics, South China Normal University, 510006 Guangzhou, China
3. Department of Physics, Harbin Institute of Technology, 150001 Harbin, China
4. Department of Physics, Lund University, P.O. Box 118, 22100 Lund, Sweden