1. Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
2. Materials Processing Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
3. The Key Laboratory of Optoelectronic Technology and System, Education Ministry of China, Chongqing University, Chongqing 400044, China
4. School of Precision Instruments and Optoelectronics Engineering, Tianjin University, Tianjin 300072, China
5. CREOL, The College of Optics and Photonics, University of Central Florida, Orlando, Florida 32816, USA
6. Photonics Devices and Systems Group, Singapore University of Technology and Design, Singapore 487372, Singapore