1. Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371, Singapore
2. Centre for Disruptive Photonic Technologies, The Photonics Institute, Nanyang Technological University, Singapore 639798, Singapore
3. Institute of Microelectronics, Agency for Science, Technology and Research, 2 Fusionopolis Way, Singapore 138634, Singapore
4. Agency for Science, Technology and Research, 1 Fusionopolis Way, Connexis North Tower, Singapore 138632, Singapore