1. State Key Laboratory of Optical Technologies on Nano-Fabrication and Micro-Engineering, Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, China.
2. Centre for Micro-Photonics and CUDOS (Centre for Ultrahigh Bandwidth Devices for Optical Systems), Faculty of Science, Engineering and Technology, Swinburne University of Technology, P.O. Box 218, Hawthorn, Victoria 3122, Australia.
3. Department of Electrical & Computer Engineering, National University of Singapore, Engineering Drive 3, Singapore 117576, Singapore.