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Plasmon-based Functional and Quantum Nanophotonics

Final Report Summary - PLAQNAP (Plasmon-based Functional and Quantum Nanophotonics)

The project PLAQNAP has been dealing with grand challenges in plasmon-based nanophotonics, the research field concerned with surface plasmon waveguides and circuitry. It was oriented towards exploiting the unique characteristic of radiation guiding by plasmonic modes along metal surfaces, viz., extreme mode confinement within dimensions orders of magnitude smaller than the light wavelength: (i) development of ultra-compact plasmonic configurations and (ii) realization of quantum plasmonic components.

Pursuing the project objectives, we have realized extremely confined plasmonic modes with lateral dimensions of only 25 nm using slot waveguides with air gaps between metal layers and demonstrated branched resonators as elementary building blocks of ultra-dense plasmonic circuitry. We have developed novel approaches to on-chip electrical photovoltaic detection of radiation guided by plasmonic modes in nanophotonic components, with the possibility of precisely fabricating µm-sized photodetectors within plasmonic elements. Furthermore, utilizing very strong confinement of plasmonic modes, we have realized compact and efficient hybrid graphene–plasmonic electro-absorption modulators and plasmonic lithium niobate based electro-optic modulators operating at telecom wavelengths and allowing for subsequent miniaturization of plasmon-based nanophotonic circuitry made of plasmonic waveguides, resonators, modulators and detectors.

We have further exploited unique properties of plasmonic modes for constructing efficient plasmon-based resonators and used their arrays to develop optical metasurfaces producing spatial gradients in the phase of reflected radiation so as to realize ultra-thin flat optical components for molding the reflected radiation flow. Thus, we have realized the first metasurfaces for mathematical operations (differentiation and integration) on incident electromagnetic waves and for simultaneous analysis of states of light polarization along with the determination of the incident light wavelength. Overall, we have developed the whole family of multifunctional components, for example, for simultaneous polarization splitting, conversion and focusing at different focal points. The developed ultra-thin flat optical multifunctional components far exceed the possibilities offered by conventional optical design, while being light weighted and ultra-compact as well as amenable to planar industrial scale fabrication.

In quantum optical technologies, one of the key issues is the development of efficient and bright single-photons sources by advantageously exploiting strong field enhancement and confinement that can be achieved both with localized and propagating plasmonic modes. Considering speeding up the emission rates from single-photon sources so as to satisfy ever increasing demands of tele-communications, we have uncovered the fundamental limitations to emission rate enhancement by the Purcell effect and shown that judiciously engineered plasmonic nanostructures are superior to purely dielectric ones by two orders of magnitude. Motivated even stronger by this argument, we have vigorously implemented the project research program and developed novel experimental procedures for deterministic arrangement of individual quantum emitters, such as color centers in nano-diamonds and quantum dots, within plasmonic nanostructures supporting localized or propagating plasmon modes and constituting plasmonic nanocircuitry.

Overall, the research work performed during the reporting period has generated significant knowledge within the field of plasmon-based nanophotonics by successfully dealing with several scientific and technological challenges. The obtained results, which are documented in 87 peer-reviewed publications, including 8 highly cited papers, enable further progress in our understanding of complicated physical phenomena involved and stimulate further developments towards exploitation of enormous potential of this field.