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Andrea Di Falco

Engineering Waveguide Nonlinear Effective Length via Low Index Thin Films

The nonlinear response of an integrated optical device should take into account the propagation distance relevant to the device. In this paper, we present a CMOS-compatible integrated optical platform with an optimized nonlinear response for propagation lengths of tens of microns. The platform is based on a low-index thin film, interfaced with a silicon-on-insulator guiding layer. The experimental results enable the development of integrated optical networks with low-power nonlinear activation functions.

Self-calibrated flexible holographic curvature sensor

Optical curvature sensors find regular use in deformation analysis, typically requiring pre-calibration and post–processing of gathered data. In this paper, we present a self-calibrated curvature sensor based on flexible holographic metasurfaces operating in the visible range. In contrast to existing solutions, the sensor can be fabricated independently from target objects and provides an immediate readout of their curvature. The sensor consists of distinct patterned areas that create images of a reference scale and of a position indicator, which shift with respect to each other, as the metasurface is deformed. We validate the results of our sensor with an external calibration and critically discuss the types… Read More »Self-calibrated flexible holographic curvature sensor

ZrO2 metasurface

ZrO2 Holographic Metasurfaces for Efficient Optical Trapping in The Visible Range

In this paper, we introduce a new material platform for holographic metasurfaces. Ceramic-based metasurfaces are ideally suited for biophotonic applications, where the operating wavelength goes down to the blue region of the visible range and below. Here, we exploit the unique properties of this platform by demonstrating the first on-chip trapping using blue light.

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

Thin-film polymeric metasurfaces for visible wavelengths

Photonic Metasurfaces (MSs) have now become one of the key platforms to encode multiplexed holographic information, using e.g. wavelength, angular momentum, angle of incidence and polarization of the light source. Traditionally, the meta-atoms composing the MSs are made structuring at subwavelength scales composite materials. However, while this enables a variety of interesting scattering properties that can be used to add functionalities to MSs, using a single material would often be preferable, to facilitate the design and fabrication of the devices. In this paper, we demonstrate a new class of holographic metasurfaces made by a simple polymeric membrane for holographic applications. Our devices retain good efficiency… Read More »Thin-film polymeric metasurfaces for visible wavelengths

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

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.