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, 21 Nanyang Link, Singapore 637371, Singapore.
3. School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Ave, Singapore 639798, Singapore.
4. Laboratoire de Physique des Lasers, Atomes et Molécules, PhLAM, UMR 8523, Université de Lille, CNRS, 59655 Villeneuve d'Ascq, France.
5. Institut d’Electronique de Microélectronique et de Nanotechnologie, Université de Lille 1, Lille, France.