1. Centre for OptoElectronics and Biophotonics, School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore
2. School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, U.K.
3. Singapore Institute of Manufacturing Technology, 2 Fusionopolis Way, Singapore 138634, Singapore
4. School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371, Singapore