1. Centre of Photonics and Photonic Materials, University of Bath, Bath BA2 7AY, U.K.
2. Centre of Nanoscience and Nanotechnology, University of Bath, Bath BA2 7AY, U.K.
3. SBAI Department, La Sapienza University of Rome, Rome 00161, Italy
4. Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States
5. Solid State Physics and NanoLund, Lund University, Box 118, Lund, Skane 22100, Sweden
6. Department of Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16803, United States
7. Department of Chemistry, University of Bath, Bath BA2 7AY, U.K.
8. Centre for Photonics and Quantum Science, University of East Anglia, Norwich NR4 7TJ, U.K.