1. Division of Physics and Applied Physics School of Physical and Mathematical Sciences Nanyang Technological University Singapore 637371 Singapore
2. Centre for Disruptive Photonic Technologies The Photonics Institute Nanyang Technological University Singapore 639798 Singapore
3. Agency for Science, Technology and Research Institute of Microelectronics 2 Fusionopolis Way Singapore 138634 Singapore
4. Institut d'Electronique de Microelectronique et de Nanotechnologie (IEMN) UMR CNRS 8520 Universite de Lille 1 Villeneuve d'Ascq CEDEX 59652 France