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Plasmonics and Metamaterials

Optically Manipulated Micromirrors for Precise Excitation of WGM Microlasers

Whispering gallery mode microlasers are highly-sensitive refractive index sensors that are widely explored for biophotonic and biomedical applications. These microlasers are used for excitation and collection of the emitted light, typically utilizing microscope objectives at normal incidence. However, this limits the choice of the oscillation plane of the modes. To overcome this limitation, in this paper, we present a new platform that enables the excitation of microlasers from various directions using an optically manipulated micromirror. This scheme enables precise sensing of the environment surrounding the microlasers along different well-controlled planes. Furthermore, the platform’s capability to perform a time-resolved experiment of dynamic sensing using a polystyrene… Read More »Optically Manipulated Micromirrors for Precise Excitation of WGM Microlasers

Laser writing of parabolic micromirrors with a high numerical aperture for optical trapping and rotation

In this paper, we present a fast and customisable technique for creating trapping arrays with high numerical aperture. Using a continuous wave CO2 laser, we write micromirror structures through ablation. First, we expose the glass substrate for ∼100 ms to a focused laser, resulting in a nearly parabolic mirror profile. The glass is then coated with a thin gold layer to achieve a smooth reflective surface. We show that through tuning the ablation parameters, the diameter and depth of the micromirrors can be controlled accurately. To demonstrate the platform’s viability, we use a high NA micromirror to trap 5 μm vaterite and 2 μm silica… Read More »Laser writing of parabolic micromirrors with a high numerical aperture for optical trapping and rotation

Shape Dependent Conformable Holographic Metasurfaces

In this paper, we report on the design, fabrication, and experimental demonstration of conformable holographic metasurfaces. Here, we show that the produced holographic image changes as the metasurface is applied to targets with different shapes. The demonstration is based on a reflective type metasurface, where the reflected polarization is perpendicular to that of the incident light. In addition, we discuss critically how the parameters of the metasurface determine the quality of the images produced and the ability to produce independent images.

Anti-reflection coatings for epsilon-near-zero materials

In this article we design and fabricate an anti-reflection layer for a multilayer epsilon-near-zero metamaterials. The layer is designed using a Multi-Objective-Grey-Wolf-Optimizer (MOGWO), using the same constituent materials of the ENZ stack. The anti-reflection layer yields a transmission enhancement of 20% over a 150 nm range and reflection minimization of 50% over a 200 nm range, respect to the uncoated sample.

Two-tier manipulation of holographic information

In this paper, published in Optics Express, we design and experimentally demonstrate the two-tier manipulation of optical information using holographic metasurfaces. Our devices encodes different information that can be retrieved if two keys are simultaneously used. Here, one key is the wavelength used to probe the holographic metasurfaces. The other key is the medium in which the metasurface is held. Specifically, one image is obtained for visible light at 705nm and air and a different, uncorrelated image is obtained for a wavelength of 750nm in water. The key element that enables our technology is the use of resonant meta-atoms (the unit cell of the  metasurface)… Read More »Two-tier manipulation of holographic information

ERC PoC – Holophrase

[Edit February 2023: Holophrase is now funded by the EPSRC, due to the UK-EU ongoing negotiations.] We are happy to share the news that the group has been awarded an ERC Proof of Concept grant, to develop an integrated on-chip pH sensor. HolopHrase is based on the ERC consolidator grant AMPHIBIANS, which introduces the metasurfaces technology in microfluidic environments. With HolopHrase, we will develop a flexible solution for the real time, label free, quantitative optical imaging readout of the pH level of a liquid solution. Our approach brings together the ease of access, simplicity, and cost of bulkier solutions, with the accuracy and level of… Read More »ERC PoC – Holophrase

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.

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

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.