Pulsed Four-Wave Mixing at Telecom Wavelengths in Si3N4 Waveguides Locally Covered by Graphene.

Recently, the nonlinear optical response of graphene has been widely investigated, as has the integration of this 2D material onto dielectric waveguides so as to enhance the various nonlinear phenomena that underpin all-optical signal processing applications at telecom wavelengths. However, a great disparity continues to exist from these experimental reports, depending on the used conditions or the hybrid devices under test. Most importantly, hybrid graphene-based waveguides were tested under relatively low powers, and/or combined with waveguide materials that already exhibited a nonnegligible nonlinear contribution, thereby limiting the practical use of graphene for nonlinear applications. Here, we experimentally investigate the nonlinear response of Si3N4 waveguides that are locally covered by submillimeter-long graphene patches by means of pulsed degenerate four-wave mixing at telecom wavelength under 7 W peak powers. Our measurements and comparison with simulations allow us to estimate a local change of the nonlinearity sign as well as a moderate increase of the nonlinear waveguide parameter (γ∼-10 m-1W-1) provided by graphene. Our analysis also clarifies the tradeoff associated with the loss penalty and nonlinear benefit afforded by graphene patches integrated onto passive photonic circuits, thereby providing some guidelines for the design of hybrid integrated nonlinear devices, coated with graphene, or, more generally, any other 2D material.

Programmable frequency-bin quantum states in a nano-engineered silicon device.

Photonic qubits should be controllable on-chip and noise-tolerant when transmitted over optical networks for practical applications. Furthermore, qubit sources should be programmable and have high brightness to be useful for quantum algorithms and grant resilience to losses. However, widespread encoding schemes only combine at most two of these properties. Here, we overcome this hurdle by demonstrating a programmable silicon nano-photonic chip generating frequency-bin entangled photons, an encoding scheme compatible with long-range transmission over optical links. The emitted quantum states can be manipulated using existing telecommunication components, including active devices that can be integrated in silicon photonics. As a demonstration, we show our chip can be programmed to generate the four computational basis states, and the four maximally-entangled Bell states, of a two-qubits system. Our device combines all the key properties of on-chip state reconfigurability and dense integration, while ensuring high brightness, fidelity, and purity.

Photo-Thermal Tuning of Graphene Oxide Coated Integrated Optical Waveguides.

We experimentally investigate power-sensitive photo-thermal tuning (PTT) of two-dimensional (2D) graphene oxide (GO) films coated on integrated optical waveguides. We measure the light power thresholds for reversible and permanent GO reduction in silicon nitride (SiN) waveguides integrated with one and two layers of GO. For the device with one layer of GO, the power threshold for reversible and permanent GO reduction are ~20 and ~22 dBm, respectively. For the device with two layers of GO, the corresponding results are ~13 and ~18 dBm, respectively. Raman spectra at different positions of a hybrid waveguide with permanently reduced GO are characterized, verifying the inhomogeneous GO reduction along the direction of light propagation through the waveguide. The differences between the PTT induced by a continuous-wave laser and a pulsed laser are also compared, confirming that the PTT mainly depend on the average input power. These results reveal interesting features for 2D GO films coated on integrated optical waveguides, which are of fundamental importance for the control and engineering of GO's properties in hybrid integrated photonic devices.

Flexible PBAT-Based Composite Filaments for Tunable FDM 3D Printing.

Biobased composites with peculiar properties offer an attractive route for producing environmentally friendly materials. The reinforcement for poly(butylene adipate-co-terephthalate) (PBAT), based on zein-titanium dioxide (TiO2) complex (ZTC) microparticles, is presented and used to produce composite filaments, successfully 3-dimensionally (3D) printed by fused deposition modeling (FDM). The outcome of ZTC addition, ranging from 5 to 40 wt %, on the thermo-mechanical properties of composite materials was analyzed. Results reveal that storage modulus increased with increasing the ZTC content, leading to a slight increase in the glass transition temperature. The creep compliance varies with the ZTC concentration, denoting a better resistance to deformation under constant stress conditions for composites with higher complex content. Scanning electron microscopy was used to assess the quality of interphase adhesion between PBAT and ZTC, showing good dispersion and distribution of complex microparticles in the polymer matrix. Infrared spectroscopy confirmed the formation of a valid interface due to the formation of hydrogen bonds between filler and polymer matrix. Preliminary tests on the biocompatibility of these materials were also performed, showing no cytotoxic effects on cell viability. Finally, the 3D printability of biobased composites was demonstrated by realizing complex structures with a commercial FDM printer.

Microfabrication of polymer microneedle arrays using two-photon polymerization.

Three dimensional (3D) printing technology has pushed state-of-the-art manufacturing towards more advanced processing methods through its ability to produce complex computer-designed 3D structures in a wide range of materials. Two-photon polymerization applied to the fabrication of ultraprecise 3D microstructures is one of the various innovative approaches to cutting-edge 3D printing. The integration of an ultrashort pulsed laser source and an appropriate photoresist has made it an attractive candidate for advanced photonics and biomedical applications. This paper presents the development of 3D solid microneedle arrays as a novel transdermal drug delivery system via two-photon polymerization in a single manufacturing step. Through a series of experiments, the best fabrication parameters are identified. Finite element simulations are then performed to investigate the interaction between a single microneedle and human skin. The results of this study highlight the influence of fabrication parameters such as laser power, scanning speed, hatch distance and layer height on the structural resolution and fabrication time of microneedles, as well as human skin deformation caused through application of force to a single polymer microneedle.

"Re-engineering of a food oven for thermal sanitization of Personal Protective Equipment against Sars-CoV-2 virus".

One of the main issues addressed by the recent COVID-19 pandemic which affected the whole world is the availability of Personal Protective Equipment (PPE) (e.g., face masks, white coats, or disposable gloves). This issue impacts on sustainability from different perspectives, such as more generated waste or environmental pollution, both for manufacturing and disposal, or more inequalities deriving from who can afford and access PPE and who cannot, since many shortages were recorded during the pandemic as well as fluctuating unit prices. Moreover, quite often PPE intended for single use are improperly used more times, thus generating a biological risk of infection. In an attempt to propose an innovative solution to face this problem, in this paper the re-design of an oven originally intended for food purposes is presented, with the aim of operating a thermal sanitization of PPE. The machinery and its components are detailed, together with physical and microbiological tests performed on non-woven PPE to assess the effect of treatment on mechanical properties and viral load. The pilot machinery turned out to be effective in destroying a bovine coronavirus at 95 °C and thus reducing contaminating risk in one hour without compromising the main properties of PPE, opening perspectives for the commercialization of the solution in the near future.

Suppression of Parasitic Nonlinear Processes in Spontaneous Four-Wave Mixing with Linearly Uncoupled Resonators.

We report on a signal-to-noise ratio characterizing the generation of identical photon pairs of more than 4 orders of magnitude in a ring resonator system. Parasitic noise, associated with single-pump spontaneous four-wave mixing, is essentially eliminated by employing a novel system design involving two resonators that are linearly uncoupled but nonlinearly coupled. This opens the way to a new class of integrated devices exploiting the unique properties of identical photon pairs in the same optical mode.

Author Correction: In-vivo vascular application via ultra-fast bioprinting for future 5D personalised nanomedicine.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

In-vivo vascular application via ultra-fast bioprinting for future 5D personalised nanomedicine.

The design of 3D complex structures enables new correlation studies between the engineering parameters and the biological activity. Moreover, additive manufacturing technology could revolutionise the personalised medical pre-operative management due to its possibility to interplay with computer tomography. Here we present a method based on rapid freeze prototyping (RFP) 3D printer, reconstruction cutting, nano dry formulation, fast freeze gelation, disinfection and partial processes for the 5D digital models functionalisation. We elaborated the high-resolution computer tomography scan derived from a complex human peripheral artery and we reconstructed the 3D model of the vessel in order to obtain and verify the additive manufacturing processes. Then, based on the drug-eluting balloon selected for the percutaneous intervention, we reconstructed the biocompatible eluting-freeform coating containing 40 nm fluorescent nanoparticles (NPs) by means of RFP printer and we tested the in-vivo feasibility. We introduced the NPs-loaded 5D device in a rat's vena cava. The coating dissolved in a few minutes releasing NPs which were rapidly absorbed in vascular smooth muscle cell (VSMC) and human umbilical vein endothelial cell (HUVEC) in-vitro. We developed 5D high-resolution self-dissolving devices incorporating NPs with the perspective to apply this method to the personalised medicine.

Ultralow-loss tightly confining Si3N4 waveguides and high-Q microresonators.

Efficient nonlinear phenomena in integrated waveguides imply the realization in a nonlinear material of tightly confining waveguides sustaining guided modes with a small effective area with ultra-low propagation losses as well as high-power damage thresholds. However, when the waveguide cross-sectional dimensions keep shrinking, propagation losses and the probability of failure events tend to increase dramatically. In this work, we report both the fabrication and testing of high-confinement, ultralow-loss silicon nitride waveguides and resonators showing average attenuation coefficients as low as ∼3 dB/m across the S-, C-, and L bands for 1.6-µm-width × 800-nm-height dimensions, with intrinsic quality factors approaching ∼107 in the C band. The present technology results in very high cross-wafer device performance uniformities, low thermal susceptibility, and high power damage thresholds. In particular, we developed here an optimized fully subtractive process introducing a novel chemical-physical multistep annealing and encapsulation fabrication method, resulting in high quality Si3N4-based photonic integrated circuits for energy-efficient nonlinear photonics and quantum optics.

Solid-State Phase Transformations in Thermally Treated Ti-6Al-4V Alloy Fabricated via Laser Powder Bed Fusion.

Laser Powder Bed Fusion (LPBF) technology was used to produce samples based on the Ti-6Al-4V alloy for biomedical applications. Solid-state phase transformations induced by thermal treatments were studied by neutron diffraction (ND), X-ray diffraction (XRD), scanning transmission electron microscopy (STEM) and energy-dispersive spectroscopy (EDS). Although, ND analysis is rather uncommon in such studies, this technique allowed evidencing the presence of retained ß in α' martensite of the as-produced (#AP) sample. The retained ß was not detectable by XRD analysis, nor by STEM observations. Martensite contains a high number of defects, mainly dislocations, that anneal during the thermal treatment. Element diffusion and partitioning are the main mechanisms in the α ↔ ß transformation that causes lattice expansion during heating and determines the final shape and size of phases. The retained ß phase plays a key role in the α' → ß transformation kinetics.

3D printing processes for photocurable polymeric materials: technologies, materials, and future trends.

The aim of this review is a faithful report of the panorama of solutions adopted to fabricate a component using vat photopolymerization (VP) processes. A general overview on additive manufacturing and on the different technologies available for polymers is given. A comparison between stereolithography and digital light processing is also presented, with attention to different aspects and to the advantages and limitations of both technologies. Afterward, a quick overview of the process parameters is given, with an emphasis on the necessities and the issues associated with the VP process. The materials are then explored, starting from base matrix materials to composites and nanocomposites, with attention to examples of applications and explanations of the main factors involved.

Special Resins for Stereolithography: In Situ Generation of Silver Nanoparticles.

The limited availability of materials with special properties represents one of the main limitations to a wider application of polymer-based additive manufacturing technologies. Filled resins are usually not suitable for vat photo-polymerization techniques such as stereolithography (SLA) or digital light processing (DLP) due to a strong increment of viscosity derived from the presence of rigid particles within the reactive suspension. In the present paper, the possibility to in situ generate silver nanoparticles (AgNPs) starting from a homogeneous liquid system containing a well dispersed silver salt, which is subsequently reduced to metallic silver during stereolithographic process, is reported. The simultaneous photo-induced cross-linking of the acrylic resin produces a filled thermoset resin with thermal-mechanical properties significantly enhanced with respect to the unfilled resin, even at very low AgNPs concentrations. With this approach, the use of silver salts having carbon-carbon double bonds, such as silver acrylate and silver methacrylate, allows the formation of a nanocomposite structure in which the release of by-products is minimized due to the active role of all the reactive components in the three dimensional (3D)-printing processes. The synergy, between this nano-technology and the geometrical freedom offered by SLA, could open up a wide spectrum of potential applications for such a material, for example in the field of food packaging and medical and healthcare sectors, considering the well-known antimicrobial effects of silver nanoparticles.

Toward athermal silicon-on-insulator (de)multiplexers in the O-band.

We report on the design, fabrication, and characterization of a 1×4 silicon-on-insulator (SOI) demultiplexer exhibiting a significant reduction of its thermo-optical sensitivity in the O-band. The optical filtering is achieved by cascading several Mach-Zehnder interferometers (MZIs) fabricated on a 300-nm-thick SOI platform. Owing to an asymmetric design of the confinement for each MZIs, we found an athermal criterium that satisfies the spectral requirements. The thermal sensitivity of the structure is analyzed by a semi-analytical model in order to create an athermal multiplexer. Fiber-to-fiber thermo-optical testing reveals a thermal sensitivity of around 17 pm/°C reduced by 75% compared to the standard devices with promising performances for both the crosstalk (15 dB), the insertion losses (4 dB), and absolute lambda registration (<0.25 nm).

1310 nm hybrid InP/InGaAsP on silicon distributed feedback laser with high side-mode suppression ratio.

We report on the design, fabrication and performance of a hetero-integrated III-V on silicon distributed feedback lasers (DFB) at 1310 nm based on direct bonding and adiabatic coupling. The continuous wave (CW) regime is achieved up to 55 °C as well as mode-hop-free operation with side-mode suppression ratio (SMSR) above 55 dB. At room temperature, the current threshold is 36 mA and the maximum coupled power in the silicon waveguide is 22 mW.

Magnetic memory of a single-molecule quantum magnet wired to a gold surface.

In the field of molecular spintronics, the use of magnetic molecules for information technology is a main target and the observation of magnetic hysteresis on individual molecules organized on surfaces is a necessary step to develop molecular memory arrays. Although simple paramagnetic molecules can show surface-induced magnetic ordering and hysteresis when deposited on ferromagnetic surfaces, information storage at the molecular level requires molecules exhibiting an intrinsic remnant magnetization, like the so-called single-molecule magnets (SMMs). These have been intensively investigated for their rich quantum behaviour but no magnetic hysteresis has been so far reported for monolayers of SMMs on various non-magnetic substrates, most probably owing to the chemical instability of clusters on surfaces. Using X-ray absorption spectroscopy and X-ray magnetic circular dichroism synchrotron-based techniques, pushed to the limits in sensitivity and operated at sub-kelvin temperatures, we have now found that robust, tailor-made Fe(4) complexes retain magnetic hysteresis at gold surfaces. Our results demonstrate that isolated SMMs can be used for storing information. The road is now open to address individual molecules wired to a conducting surface in their blocked magnetization state, thereby enabling investigation of the elementary interactions between electron transport and magnetism degrees of freedom at the molecular scale.