1. State Key Laboratory on Integrated Optoelectronics College of Electronic Science and Engineering Jilin University 2699 Qianjin Street Changchun 130012 China
2. Department of Applied Physics The Hong Kong Polytechnic University Hung Hom Hong Kong China
3. State Key Lab of Precision Measurement Technology and Instruments, Department of Precision Instrument Tsinghua University Haidian Beijing 100084 China