1. Division of Physics and Applied Physics; School of Physical and Mathematical Sciences; Nanyang Technological University; 21 Nanyang Link Singapore 637371 Singapore
2. Center for Disruptive Photonic Technologies; The Photonics Institute; Nanyang Technological University; 50 Nanyang Avenue Singapore 639798 Singapore
3. School of Materials Science and Engineering; Nanyang Technological University; Singapore 639798 Singapore