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Research

We have a wide ranging portfolio of research, all focussed around the central theme of being able to have absolute control over light and its propagation. Below we have a few samples of our most recent research, and on the right is a list of all the themes we have worked on.

Integration of sub-micron semiconductor lasers in living cells

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In a paper published in Nature Communications, we report on the integration of sub-micron semiconductor lasers in living cells. In this work, fruit of the collaboration with Malte Gather and his group at the University of St Andrews, we demonstrate that lasers with dimensions much smaller than that of many cell nuclei can be used to tag individual cells and sense their environment. This research paves the way for a new bio-photonics platform that will provide new insight into cell biology, including research in immune cells, neutrons and cancer cells. A. H. Fikouras, M. Schubert, M. Karl, J. D. Kumar, S. J. Powis, A. Di… Read More »Integration of sub-micron semiconductor lasers in living cells

Photonic trimming of quantum emitters via direct fabrication of metallic nanofeatures

In a paper published in APL Photonics we demonstrate the control of the emission of a GaAs quantum dot (QD) embedded in a GaAs/AlGaAs nanowire (NW) by the post-fabrication of a plasmonic grating on its surface. We fabricated a sub-wavelength Pt grating directly on the NW surface, via electron beam induced deposition, to enhance the emission efficiency of QD for the polarization parallel to the NW of 45%, with a 17% reduction in the photon lifetime. These findings and EBID approach offer great opportunities for the development of nanopatterned QD emitters and new hybrid nanophotonic platforms for efficient single photon sources.

Flexible Holographic Metasurface with Surface Topology Dependent Functionality

In a paper published in ACS photonics, we present a flexible holographic metasurface with surface topology dependent functionality. We demonstrate that the phase contribution of the non-flat metasurface shape determines the symmetry properties of the far field holographic image. Here we also describe a framework to increase the sensitivity of the holographic image to the exact metasurface topology.   This work is of practical relevance for security printing technologies, as well as surface polarization and surface topology sensors.

Persistence and Lifelong Fidelity of Phase Singularities in Random Waves

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In this paper we show that Photonic Crystal chaotic resonators are a convenient platform to address the dynamic of optical phase singularities in random light landscapes. In particular, our collaborators at the Kavli Institute of Nanoscience of the Delft University of Technology have measured the fidelity and persistence of couples of singularities, as the wavelength is tuned within the bandgap of the resonator. The results unveil the non trivial statistical properties of singularities respect to their faithfulness.

Conformable Holographic Metasurfaces

In this work, published in Scientific Reports, we describe a conformable holographic metasurface operating in the visible range. We use gold nanoantennas to point-by-point tailor the Berry phase of a flexible membrane to create high fidelity images with helicity multiplexing. These membranes can then be applied to substrates which could not be nanopatterned directly. We demonstrate this experimentally with a glasses lens. The full article can be found here

Optothermal Nonlinearity of Silica Aerogel

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In a paper published in Appl. Phys. Lett., we report the first measurements of optothermal nonlinearity of silica aerogels. Silica based aerogels are ultra porous materials with refractive index close to unity. Their extreme porosity is responsible for very low thermal conductivity, which in turn leads to very peculiar optothermal properties. In this paper, in collaboration with researchers at the University Sapienza and CNR, we measured the optothermal nonlinear coefficient of silica based aerogels in the visible range. The full article can be found here.

Spatial Distribution of Phase Singularities in Optical Random Vector Waves

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In a paper published in Phys. Rev. Lett., we experimentally demonstrate that the distribution of phase singularities in vectorial random light fields is anisotropic.   Our collaborators at AMOLF, led by Prof. Kobus Kuipers, have measured the distribution of phase singularities supported by a chaotic electromagnetic landscape, reading the surface of a photonic crystal (PhC) cavity with a SNOM. PhC chaotic resonators in silicon on insulator technology are an ideal platform to prepare a random field with repeatable and well defined characteristics. Exploiting this feature, we were able to track the deep-subwavelength phase singularities supported in the cavity. Our results demonstrate that, due to the… Read More »Spatial Distribution of Phase Singularities in Optical Random Vector Waves

Optically Induced Metal-to-Dielectric Transition in Epsilon-Near-Zero Metamaterials

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Our work on the “Optically Induced Metal-to-Dielectric Transition in Epsilon-Near-Zero Metamaterials” has recently appeared in Scientific Reports. In this work we designed a metamaterial with epsilon-near-zero (ENZ) response, that is tuned all-optically from a metallic to dielectric behaviour. The transition is demonstrated using an ultrafast pump and probe scheme. The study unveils both analytically and experimentally the full associated nonlinear dynamics. The full article can be found here.

Enhanced Nonlinear Refractive Index in Epsilon-Near-Zero Materials

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In collaboration with Heriot-Watt University and Purdue University, we published a paper in Phys. Rev. Lett. demonstrating that epsilon-near-zero metamaterials (ENZ) exhibit an enhanced nonlinear response. In this study we demonstrated a six-fold enhancement of the Kerr nonlinear refractive index in proximity of the ENZ condition, in the near-infrared. The experiemtn was performed on Al-doped ZnO (AZO) thin film, and demonstrates a general behaviour of ENZ materials. The full paper can be found here.

Research

Ultrafast All-Optical Order-to-Chaos Transition in Silicon Photonic Crystal Chips

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In this work, published in Laser Photonics Review we report on the all-optical control of chaotic optical resonators based on a silicon on insulator (SOI) platform. We show that simple non-chaotic cavities can be tuned to exhibit chaotic behaviour via intense optical pumping, inducing a local change of refractive index. To this extent we have fabricated a number of devices and demonstrated experimentally and theoretically that chaos can be triggered on demand on an optical chip.   We show that the degree of chaos supported by a microcavity can be controlled dynamically using light itself. We start with a square (non-chaotic) cavity obtained on SOI.… Read More »Ultrafast All-Optical Order-to-Chaos Transition in Silicon Photonic Crystal Chips

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