1. State Key Laboratory of Integrated Optoelectronics College of Electronic Science and Engineering Jilin University Changchun 130012 China
2. Department of Nano Engineering University of California San Diego San Diego CA 92093‐0448 USA
3. State Key Lab of Precision Measurement Technology and Instruments Department of Precision Instrument Tsinghua University Beijing 100084 China
4. Department of Physics, Applied Physics, and Astronomy Rensselaer Polytechnic Institute Troy NY 12180 USA