1. Optoelectronics Research Centre and Centre for Photonic Metamaterials, University of Southampton, Southampton SO17 1BJ, UK
2. Data Storage Institute, Agency for Science, Technology and Research (A*STAR), Singapore 117608, Singapore
3. School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore
4. The Photonics Institute and Centre for Disruptive Photonic Technologies, Nanyang Technological University, Singapore 637371, Singapore