1. School of Materials Science and Engineering University of Shanghai for Science and Technology Shanghai 200093 China
2. State Key Laboratory of Infrared Physics Shanghai Institute of Technical Physics Chinese Academy of Sciences Shanghai 200083 China
3. State Key Laboratory of Functional Materials for Informatics Shanghai Institute of Microsystem and Information Technology Shanghai 200050 China
4. School of Electrical and Electronic Engineering Nanyang Technological University Singapore 639798 Singapore
5. Engineering Research Center for Nanophotonics & Advanced Instrument Ministry of Education East China Normal University Shanghai 200062 China
6. Photonic Laboratory Department of Microtechnology and Nanoscience Chalmers University of Technology S-412 96 Göteborg Sweden