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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 »

HIPPO – ERC Proof of Concept awarded

We are delighted to announce that our new ERC – Proof of Concept project on Holographic Integrated Photonics Platform for the Optical Analysis of Biological Samples (HIPPO) has been selected for funding. Innovative imaging project receives €150,000 grant  

On-Chip Optical Trapping with High NA Metasurfaces

Photonic metasurfaces can be used to create strongly focused beams for optical trapping applications. Here, we design and fabricate holographic metasurfaces with numerical aperture up to 1.2, and trapping stiffness greater than 400 pN/µm/W, which perform as well as a microscope objective with a comparable numerical aperture. In this work, we analyze how the trapping performance depends on the metasurface dimension, down to areas as small as 0.001 mm2. Finally, we demonstrate the photonic metasurfaces can create multi-site optical tweezers, for the trapping of extended objects, like photonic membranes.

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

All-optical manipulation of photonic membranes

In this paper, we demonstrate the all-optical manipulation of polymeric membranes in microfluidic environments. The membranes are decorated with handles for their use in holographic optical tweezers systems. Our results show that due to their form factor the membranes present a substantial increase in their mechanical stability, respect to micrometric dielectric particles. This intrinsic superior stability is expected to improve profoundly a wide range of bio-photonic applications that rely on the optical manipulation of micrometric objects.    

Perfect secrecy cryptography in photonic chips

We are very happy to share our new paper where we demonstrate that it is possible to create a perfect secrecy cryptographic protocol in classical channels. The system uses time varying integrated chips based on silicon on insulator technology and implements a working version of the One Time Pad protocol. The work was the result of the collaboration between our group, King Abdullah University of Science and Technology (KAUST) and the Center for Unconventional Processes of Sciences (CUP Sciences). You can access here the press release from the University of St Andrews.  

The Nonlinear Optical Memory Effect

Light propagating in random media produces characteristic speckle patterns, which remain correlated for small perturbations of the parameters of the incoming beam, including e.g. its angle and position. This behaviour is known as memory effect. In a paper published in Optics Letters, fruit of the collaboration of our group with Dr Tom Vettenburg (University of Dundee) and Prof. Claudio Conti (CNR, Italy), we generalise the memory effect to the case of light propagating in random nonlinear media. In particular, in a series of pump-probe experiments, we quantify the nonlinear memory effect produced by the opto-thermal response of silica aerogel. In this work, the memory effect… Read More »The Nonlinear Optical Memory Effect