Confining light at the nanoscale is very important for understanding fundamental emission and absorption processes and for applications, for instance, in quantum information technology, energy harvesting and sensing.
I will discuss two different approaches to enhance the light-matter interaction on a chip, based on highly engineered quantum photonic devices and disordered photonic crystals.
We have recently developed a photoluminescence imaging technique that allows to locate single emitters with nanometer-scale accuracy and to fabricate quantum photonic devices tailored to their emission properties . We have applied this technique to control and enhance the emission properties of single-photon sources, like InAs/GaAs quantum dots, by fabricating circular grating cavities and metallic nano-rings, centred around selected emitters [2,3]. To control the spontaneous emission via the coupling to plasmonic fields, we have also developed a new class of droplet quantum dots with ultrathin (few nanometers) capping layer .
Interestingly, a completely different approach can be followed to increase the light-matter interaction where, instead of highly engineered devices, disorder is used as a resource to efficiently trap light in the Anderson-localised regime. I will report on disordered photonic crystal waveguides in silicon nitride that confine visible light with quality factors exceeding highly engineered optical cavities . Even though the location where disorder-induced optical cavities appear is not controlled prior to device fabrication, we show that our imaging technique can be used to address specific cavity modes and that such devices can represent a novel platform for optical sensing .
 L. Sapienza, M. Davanco, A. Badolato, K. Srinivasan, Nanoscale optical positioning of single quantum dots for bright and pure single-photon emission, Nature Communications 6, 7833 (2015).
 O.J. Trojak, S.I. Park, J.D. Song, L. Sapienza, Metallic nanorings for broadband, enhanced extraction of light from solid-state emitters, Applied Physics Letters 111, 021109 (2017).
 O.J. Trojak, C. Woodhead, S.I. Park, J.D. Song, R.J. Young, L. Sapienza, Combined metallic nano-rings and solid-immersion lenses for bright emission from single InAs/GaAs quantum dots, arxiv.org/abs/1801.07210 (2018).
 S.I. Park, O.J. Trojak, E. Lee, J.D. Song, J. Kyhm, I. Han, J. Kim, G.-C. Yi, L. Sapienza, GaAs droplet quantum dots with nanometer-thin capping layer for plasmonic applications, Nanotechnology 29, 205602 (2018).
 T. Crane, O.J. Trojak, J.P. Vasco, S. Hughes, L. Sapienza, Anderson localisation of visible light on a nanophotonic chip, ACS Photonics 4, 2274 (2017).
 O.J. Trojak, T. Crane, L. Sapienza, Optical sensing with Anderson-localised light, Applied Physics Letters 111, 141103 (2017).