1. Singapore−MIT Alliance for Research and Technology, 138602 Singapore
2. Department of Materials Science and Engineering, National University of Singapore, 117575 Singapore
3. Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
4. Centre for Disruptive Photonic Technologies, School of Physical and Mathematical Sciences and The Photonics Institute, Nanyang Technological University, 637371 Singapore