1. Division of Physics and Applied Physics; School of Physical and Mathematical Sciences; Nanyang Technological University; Singapore 637371 Singapore
2. School of Electrical and Electronic Engineering; Nanyang Technological University; Nanyang Avenue Singapore 639798 Singapore
3. Centre for Disruptive Photonic Technologies (CDPT); Nanyang Technological University; Singapore 637371 Singapore
4. Department of Electrical and Electronics Engineering; Department of Physics, UNAM - Institute of Materials Science and Nanotechnology; Ankara Turkey 06800