Plasmonic Networks for Nanoscale Light Control (PINpOiNT)

Nanoscale quantum optics is a promising new field aimed at coherent control and manipulation of single photons emitted by individual quantum emitters in a nanostructured photonic environment. Single emitters have dimensions much smaller than the wavelength of light, and therefore interact slowly and omni-directionally with radiation, placing limits on photon absorption and emission. These intrinsic fluorescence limits can be overcome when the source is placed in a nanostructured photonic material.

Multi-scale (fractal) structures are a new class of particularly interesting photonic materials, since they lead to spatial localisation of the electromagnetic energy into subwavelength areas (hot spots of 10s of nm) over a wide spectral range, which are driven by optical excitations coupled to the network on different scales.

Here I propose to investigate collective plasmonic systems, based on plasmon multiple scattering and interference on metallic networks. I will study natural gold networks and artificially designed one. I will approach these structures using a network theory approach, a statistical method centred on the network topology, made of links and nodes. This method has the potentiality of describing the complex system with few robust parameters, extracted from the rich microscopic details, and thus provides much deeper understanding.

The study of network optical properties will focus on probing one of the most robust modal properties: the local density of optical states. This is a key fundamental quantity involved in light-matter interaction, as it provides a direct measure for the probability of spontaneous light emission (the Purcell effect), light absorption and scattering.

I propose to identify the emergent nature of the different optical modes of complex plasmonic networks by studying the statistics of the LDOS in artificial plasmonic networks. I plan to understand the inner character of the complex plasmonic modes, and to reveal subwavelength "hot-spots", critically localized states and chaotic mode signatures. This knowledge will be exploited to design and engineer the LDOS for local fluorescence enhancement and to exploit the network as an unconventional antenna to control the fluorescence of an individual colloidal quantum dot, enhance its radiation rate, boost and manipulate its directionality.
I will aim at demonstrating a strong link between the plasmonic network structures, their optical properties and their effect on a light emitter.

Generation and control of light in nano-devices will enter a broader world of practical applications only if miniaturised, highly efficient photonic devices will be achieved, which can boost light emitters to out-perform their natural properties.
Hybrid light-emitters and plasmonic networks have the potential to offer a new platform for light control and can therefore lead many applications at the industrial level. Enhancing and directing the fluorescence of an individual light source can largely benefit quantum technologies based on the exchange and manipulation of single photons. The proposed networks are very compact and can be implemented on a chip in an integrated platform and used to enhance the sensitivity of lab-on-chip biochemical sensing for healthcare, as transparent electrodes in many optoelectronic devices, including LEDs, electronic displays, and solar cells. Large-area optical antennas can be exploited for novel light-harvesting schemes relevant for photovoltaics. In this context, I expect to be able to provide direct guidelines for the optimum design of ultra-thin metallic electrodes to allow electrical conduction and at the same time enhance the optical properties of the device.

While the potential impact of some aspects of nano-plasmonic technologies will manifest itself on a >10 year timescale, establishing whether nanophotonics concepts based on complex photonic systems - an area which builds on nano-optics, plasmonics and quantum optics where the UK is internationally leading - are the route to follow is clearly a very timely and called-for endeavour, with immediate high impact on the future development of the field of photonics.

The project presented is strengthened by international collaborations, with ICFO (Barcelona) for the sample fabrication and ESPCI (Paris) for the theory, that are already active and that together with the resources of King's College London will ensure the success and high impact of the presented research. With respect to medium-term impact, the Physics Department at King's has strong ongoing partnerships with several major players in this industry, including INTEL, Seagate, Ericsson, Oxonica, and IMEC, with whom exchange and transfer of scientific and technical expertise take place on a continuous basis. In the longer term, in our global market the development of new disrupting technologies like complex nanophotonics is the key to win low-technology competition and to foster global economic performance and competitiveness of the UK at an international level.