1Centre for Disruptive Photonic Technologies, The Photonic Institute, 50 Nanyang Avenue, Singapore 639798, Singapore
2Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371, Singapore
3Natural Sciences and Science Education, National Institute of Education, Nanyang Technological University, Singapore 637616, Singapore
4CINTRA CNRS/NTU/THALES, UMI 3288, Research Techno Plaza, 50 Nanyang Drive, Nanyang Technological University, Singapore, 637553, Singapore
5School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore
6School of Biomedical Engineering, The University of Sydney, Sydney, New South Wales 2006, Australia
7The University of Sydney Nano Institute, The University of Sydney, Sydney, New South Wales 2006, Australia