1. Optoelectronics Research Centre and Centre for Photonic MetamaterialsUniversity of Southampton Southampton SO17 1BJ UK
2. Department of ChemistryUniversity of Southampton Southampton SO17 1BJ UK
3. Department of Electrical and Computer EngineeringUniversity of Alberta Edmonton Canada
4. Centre for Disruptive Photonic Technologies and The Photonics InstituteSchool of Physical and Mathematical SciencesNanyang Technological University Singapore 637371 Singapore