1. Institute of Materials Research and Engineering Agency for Science Technology and Research (A*STAR) 2 Fusionopolis Way Singapore 138634 Singapore
2. Division of Physics and Applied Physics School of Physical and Mathematical Sciences Nanyang Technological University 50 Nanyang Avenue Singapore 637371 Singapore
3. The Photonics Institute and Center for Disruptive Photonic Technologies Nanyang Technological University 50 Nanyang Avenue Singapore 639798 Singapore