1. College of Electronics and Information Engineering, Sichuan University, Chengdu 610064, China
2. Optical Nanostructures Laboratory, Columbia University, New York, New York 10027, USA
3. Department of Electrical Engineering, Columbia University, New York, New York 10027, USA
4. Department of Electrical and Computer Engineering, University of Delaware, Newark, Delaware 19716, USA
5. Department of Electrical, Computer, and Energy Engineering, University of Colorado Boulder, Boulder, Colorado 80309, USA
6. The Institute of Microelectronics, Singapore 117685, Singapore
7. Fang Lu Mesoscopic Optics and Quantum Electronics Laboratory, University of California, Los Angeles, California 90095, USA