1 Key Laboratory of Opto-Electronic Information Technology of Ministry of Education, School of Precision Instrument and Opto-Electronics Engineering, Tianjin University, Tianjin 300072, China
2 Key Laboratory of Integrated Opto-Electronic Technologies and Devices in Tianjin, School of Precision Instrument and Opto-Electronics Engineering, Tianjin University, Tianjin 300072, China
3 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
4 College of Optics and Photonics, CREOL and FPCE, University of Central Florida, Orlando, Florida 32816, USA