Lorenzo Rosa

Università degli studi di Modena e Reggio Emilia, Department of Engineering "Enzo Ferrari", Faculty Member

Swinburne University of Technology, Hawthorn, Centre for Micro-Photonics, Faculty Member

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Associate Professor of Electromagnetics, working on photonics, numerical methods for electromagnetism, and wireless systems.

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Papers by Lorenzo Rosa

Thermo-optical numerical modal analysis of multicore fibers for high power lasers and amplifiers

Optical Fiber Technology, May 1, 2022

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Polygonal Large-Mode-Area Leakage Channel Fibers with Reduced Mode Distortion

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Silver-gold nano-composites for photo-catalytic and sensing applications

xperimental results of photo-catalytic activity of Ag-Au nano-composites on different type of tit... more xperimental results of photo-catalytic activity of Ag-Au nano-composites on different type of titania are compared with numerical simulations. The action spectra of photo-catalyzed oxidation and the extinction (absorption together with scattering) spectra are compared for similar shape and size nanoparticles. Different shell-core composites using Ag and Au are numerically modeled for qualitative understanding of the light enhancement and its localization on the nanoparticle-titania substrate. We show that the electrical field component perpendicular to the interface between nanoparticle and substrate contributes the major field enhancement portion. Light enhancement at hot-spots and its scaling with gap size are revealed by surface enhanced Raman spectroscopy (SERS). Alloying of Ag and Au on nanoscale is demonstrated. The sp-to-d band transition of electrons in the plasmonic Ag and Au is proposed as a model of photo-catalysis at the wavelengths longer that the fundamental optical transition in titania (approximately 3.1 eV or 400 nm). Surface-enhanced infrared absorption (SEIRA) spectroscopy, is applied to highlyselective metal hole arrays (MHA), enhancing specific molecular vibrations for molecule fingerprinting, with up to 10 times enhancement of the absorption peaks within the 200-2000 cm 121 band. Selective IR band enhancement can be used for identification of specific molecules within complex mixtures and can be extended to longer wavelengths to probe the THz molecular bands. Discussed systems can bemodeled with a high fidelity using finite-difference timedomain (FDTD) methods. Sensing applications with microparticles can also be modeled providing insight in applications in far-IR (10-50 \u3bcm) and towards THz spectral range. The very same principles are applicable for broadband light energy harvesting

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Micro-manipulation of nanodiamonds containing NV centers for quantum applications

Diamond and Related Materials, Jun 1, 2020

Abstract Micro-manipulations of nanodiamonds (NDs) containing Nitrogen-Vacancy (NV) centers are h... more Abstract Micro-manipulations of nanodiamonds (NDs) containing Nitrogen-Vacancy (NV) centers are here reviewed. Various methods such as optical tweezers, electro-kinetic trap, ions traps, optofluidics and plasmonics applied to the specific nanomaterial are reviewed, focusing on the advantages and achievements in controlling the NDs positioning for magnetic sensing. These approaches are relevant to extend magnetic sensing and imaging in different fluid environments. Levitated NDs in vacuum using optical tweezers or ions traps are also reviewed for applications in cavity optomechanics towards establishing ultra-sensitive mechanical spin hybrid systems or nano-optomechanics devices. The current demonstrations of trapped or levitated NDs containing NV centers are relevant to fundamental studies of quantum spin-photon and mechanical systems coupling but have not yet been applied directly to biological systems, as these fields of applications present several challenges.

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Full-vector modeling of thermally-driven gain competition in Yb-doped reduced symmetry photonic-crystal fiber

Optical and Quantum Electronics, Mar 1, 2016

A new model to study gain competition in high-power fiber amplifiers, which accounts for the full... more A new model to study gain competition in high-power fiber amplifiers, which accounts for the full-vector nature of the propagating modes and thermal effects on core overlap, is applied to simulate the performance of an active rod-type fiber under severe heat load. Model tests on a Yb-doped large-pitch reduced symmetry photonic-crystal fiber show a successful analysis of gain competition.

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Nitrogen-vacancy centers in diamond for nanoscale magnetic resonance imaging applications

Beilstein Journal of Nanotechnology, Nov 4, 2019

The nitrogen-vacancy (NV) center is a point defect in diamond with unique properties for use in u... more The nitrogen-vacancy (NV) center is a point defect in diamond with unique properties for use in ultra-sensitive, high-resolution magnetometry. One of the most interesting and challenging applications is nanoscale magnetic resonance imaging (nano-MRI). While many review papers have covered other NV centers in diamond applications, there is no survey targeting the specific development of nano-MRI devices based on NV centers in diamond. Several different nano-MRI methods based on NV centers have been proposed with the goal of improving the spatial and temporal resolution, but without any coordinated effort. After summarizing the main NV magnetic imaging methods, this review presents a survey of the latest advances in NV center nano-MRI.

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Nanomagnetic Resonance Imaging (Nano-MRI) Gives Personalized Medicine a New Perspective

This paper reviews some of the major and most recent advances in nanoscale-magnetic resonance ima... more This paper reviews some of the major and most recent advances in nanoscale-magnetic resonance imaging (nano-MRI) for personalized medicine (PM). Nano-MRI may drastically expand the capabilities of the traditional magnetic resonance images (MRI), down to the nanometer scale and possibly, in the near future, at the atomic scale. Nano-MRI is potentially able to observe structures which cannot be seen using today's molecular imaging, with sensitivities of many billions of times better than MRI as currently used in hospitals, for example. The paper briefly reports on the foremost research themes in nano-MRI.

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Thermo-optic effects in multicore fibers for high-power lasers

Multi-core fibers (MCFs) are promising solutions for high power fiber based devices as they reduc... more Multi-core fibers (MCFs) are promising solutions for high power fiber based devices as they reduce nonlinearity and other unwanted detrimental effects, like transverse mode instability, by transporting, instead of a single high power beam, several low-powered ones to be coherently combined at the fiber output. This method relies on accurate evaluation of the phase differences between signals in different cores, which are significantly impacted by changes in the effective index of the propagating modes. For this to be effective, spatial heat generation must be accounted for. In particular, the heat flux from the doped cores to the external boundary causes a temperature gradient across the fiber, which affects the refractive index distribution, creating the chance for effective index change and thus dephasing of the output beams, which is harmful for beam combining. The results of in-depth numerical analysis on the performance of 9-core and 16-core MCFs under thermal effects are presented by studying the mode phase sensitivity to heat load and by introducing a coupled-mode theory model to study possible optical coupling effects. The effectively single-mode condition is also investigated by calculating the core modal overlap differences between fundamental and higher-order modes.

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Phase controlled SERS enhancement

Scientific Reports, Jan 24, 2019

Surface-enhanced Raman spectroscopy (SERS) has attracted increasing interest for chemical and bio... more Surface-enhanced Raman spectroscopy (SERS) has attracted increasing interest for chemical and biochemical sensing. Several studies have shown that SERS intensities are significantly increased when an optical interference substrate composed of a dielectric spacer and a reflector is used as a supporting substrate. However, the origin of this additional enhancement has not been systematically studied. In this paper, high sensitivity SERS substrates composed of self-assembled core-satellite nanostructures and silica-coated silicon interference layers have been developed. Their SERS enhancement is shown to be a function of the thickness of silica spacer on a more reflective silicon substrate. Finite difference time domain modeling is presented to show that the SERS enhancement is due to a spacer contribution via a sign change of the reflection coefficients at the interfaces. The magnitude of the local-field enhancement is defined by the interference of light reflected from the silica-air and silica-silicon interfaces, which constructively added at the hot spots providing a possibility to maximize intensity in the nanogaps between the self-assembled nanoparticles by changing the thickness of silica layer. The core-satellite assemblies on a 135 nm silica-coated silicon substrate exhibit a SERS activity of approximately 13 times higher than the glass substrate.

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Advances in diamond nanofabrication for ultrasensitive devices

Microsystems & Nanoengineering, Oct 23, 2017

This paper reviews some of the major recent advances in single-crystal diamond nanofabrication an... more This paper reviews some of the major recent advances in single-crystal diamond nanofabrication and its impact in nano-and micromechanical, nanophotonics and optomechanical components. These constituents of integrated devices incorporating specific dopants in the material provide the capacity to enhance the sensitivity in detecting mass and forces as well as magnetic field down to quantum mechanical limits and will lead pioneering innovations in ultrasensitive sensing and precision measurements in the realm of the medical sciences, quantum sciences and related technologies.

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Guidance properties and thermal effects in 9-core Yb-doped fiber for high power applications

In this abstract, the performance of optically uncoupled cores in 9-core multi core fibers for hi... more In this abstract, the performance of optically uncoupled cores in 9-core multi core fibers for high-power fiber lasers is evaluated by considering thermal effects due to the heat load originated by quantum defect between pump and laser radiation. For high power applications, thermal effects are currently seen as the main constraint to power scaling of fiber lasers. The finite-element method is employed to model the optical field distribution for optical amplification and lasing, in order to analyze the effect of heat load on the modes of ytterbium-doped multi-core fibers.

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Thermal induced dynamics of gain competition in Yb-doped Symmetry-Free Photonic Crystal Fibers

A fiber amplifier based on Yb-doped Symmetry-Free Photonic Crystal Fiber has been studied through... more A fiber amplifier based on Yb-doped Symmetry-Free Photonic Crystal Fiber has been studied through the use of a numerical tool. The amplification properties and the modal content of the amplifier have been investigated in conditions of severe heat load, in order to understand the effectiveness of amplification dynamics. The numerical tool, used for this study, is based on a FEM modal solver combined with a model which allows to evaluate amplification and thermal effects. Results depict a scenario where it is possible to obtain a good mode discrimination and a robust amplification under critical thermal condition.

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Improved performances of photonic crystal fibers for high power laser operation

In recent years fiber laser systems have shown a rapid evolution in terms of beam quality and pow... more In recent years fiber laser systems have shown a rapid evolution in terms of beam quality and power. High pulse energy and peak power require large effective area, so new photonic crystal fiber designs have been proposed. Thermo-optical effects can lead to transverse mode instability, a nonlinear effect that sets in at a threshold power level. The influence of thermal effects on fiber guiding properties is here investigated. Improved fiber designs are proposed.

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Thermally-Driven Mode Coupling in Multi-Core Optical Fibers

Advanced Photonics 2018 (BGPP, IPR, NP, NOMA, Sensors, Networks, SPPCom, SOF), 2018

We present results on multi-core fibers (MCFs) for optical amplification/lasing obtained by combi... more We present results on multi-core fibers (MCFs) for optical amplification/lasing obtained by combined thermal-optical finite-element method (FEM) simulations. Refractive index variation due to quantum defect caused heating is simulated to evaluate thermal dissipation-induced index gradients.

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Guidance properties and phase shift of a 9-core fiber amplifier for high power operation in presence of consistent thermal load

Multi-core fiber capability to deliver several independent beams in a single structure has been d... more Multi-core fiber capability to deliver several independent beams in a single structure has been deeply investigated to obtain spatial multiplexing in optical communication. Recently, the coherent beam multiplexing idea has been extended to high power fiber laser field, where multi-core fiber amplifiers, combining low power beams, promise to overcome thermal mode instability, which characterizes single-core fiber amplifiers. Although coherent output beam combination is advantaged in multi-core fiber, the understanding of core phase shifts is necessary to implement efficient beam combination. In presence of thermal load, induced by pump-to-signal conversion quantum defect, a refractive index gradient is formed on the multi-core fiber amplifier cross-section, thus changing core propagation properties and possibly creating unwanted core couplings. In this work a 9-core double-cladding fiber amplifier is numerically investigated by varying the core thermal load, from 2 to 15 W/m, in orde...

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A Preliminary Study of a Graphene Fractal Sierpinski Antenna

IOP Conference Series: Materials Science and Engineering, 2020

We provide a preliminary study of a Graphene fractal antenna operating at THz frequencies with th... more We provide a preliminary study of a Graphene fractal antenna operating at THz frequencies with the opportunity to modulate the emission. There are many advantages of the fractal design, namely multiband/wideband ability, and, a smaller, lighter and simpler configuration for higher gain, that can benefit from the coupling with Graphene, the thinnest and strongest of materials exhibiting very high electrical conductivity and tunability. This paper proposes a conceptual background for the study and presents some preliminary results on the electromagnetic emission simulations undertaken.

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Mode phase variation and sensitivity to thermal load in three-core optical fibers

Journal of Lightwave Technology, 2020

The phase of modes in three-core optical fibers under high thermal load is studied by means of th... more The phase of modes in three-core optical fibers under high thermal load is studied by means of the combined thermal and optical models. In particular, the effects of thermal dissipation in the doped cores, as a result of quantum defect heat generation, and the relative material refractive index variation are investigated. The induced index gradient can influence the guided mode propagation in multiple adjacent cores, even if their distance is enough to decouple them optically, showing a remarkable dephasing of the different fiber output beams. This effect brought by the thermal phenomenon inherent in the amplification process has to be carefully accounted for when designing multi-core high-power optical lasing and amplifying devices. The mode dephasing results also provide useful information for future evaluation of thermo-optic coupling effects that may occur along the fiber under high power regime.

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Reassessing the projections of the World Water Development Report

npj Clean Water, 2019

The 2018 edition of the United Nations World Water Development Report stated that nearly 6 billio... more The 2018 edition of the United Nations World Water Development Report stated that nearly 6 billion peoples will suffer from clean water scarcity by 2050. This is the result of increasing demand for water, reduction of water resources, and increasing pollution of water, driven by dramatic population and economic growth. It is suggested that this number may be an underestimation, and scarcity of clean water by 2050 may be worse as the effects of the three drivers of water scarcity, as well as of unequal growth, accessibility and needs, are underrated. While the report promotes the spontaneous adoption of nature-based-solutions within an unconstrained population and economic expansion, there is an urgent need to regulate demography and economy, while enforcing clear rules to limit pollution, preserve aquifers and save water, equally applying everywhere. The aim of this paper is to highlight the inter-linkage in between population and economic growth and water demand, resources and poll...

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Chlorination disadvantages and alternative routes for biofouling control in reverse osmosis desalination

npj Clean Water, 2019

With an ever-increasing human population, access to clean water for human use is a growing concer... more With an ever-increasing human population, access to clean water for human use is a growing concern across the world. Seawater desalination to produce usable water is essential to meet future clean water demand. Desalination processes, such as reverse osmosis and multi-stage flash have been implemented worldwide. Reverse osmosis is the most effective technology, which uses a semipermeable membrane to produce clean water under an applied pressure. However, membrane biofouling is the main issue faced by such plants, which requires continuous cleaning or regular replacement of the membranes. Chlorination is the most commonly used disinfection process to pretreat the water to reduce biofouling. Although chlorination is widely used, it has several disadvantages, such as formation of disinfection by-products and being ineffective against some types of microbes. This review aims to discuss the adverse effect of chlorination on reverse osmosis membranes and to identify other possible alterna...

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Size-controlled gold nanoparticles on octahedral anatase particles as efficient plasmonic photocatalyst

Applied Catalysis B: Environmental, 2017

Octahedral anatase particles (OAPs), prepared by ultrasonication-hydrothermal reaction (US-HT), w... more Octahedral anatase particles (OAPs), prepared by ultrasonication-hydrothermal reaction (US-HT), were modified with 2 wt% of gold by photodeposition. Conditions of US-HT process such as durations of US and durations of HT were varied to obtain OAPs products different by physicochemical and morphological properties. Au/OAPs samples were characterized by X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance spectroscopy (DRS). The photocatalytic activity was tested under UV irradiation for decomposition of acetic acid (CO 2 system) and dehydrogenation of methanol (H 2 system) under aerobic and anaerobic conditions, respectively, and for oxidation of 2-propanol under visible light irradiation. Photodeposition of gold was very fast for all OAPs samples (0.5-10 min) under Ar atmosphere, and the clear correlation between the content of electron traps (ETs) and the induction period, during which nanoparticles (NPs) of gold are formed, indicates that ETs in titania samples are a key-factor for rapidity of gold photodeposition on titania surface. It was found that better morphology of titania (larger content of faceted particles) resulted in formation of larger gold NPs, while small gold NPs were deposited on structural defects. Modification of OAPs with gold NPs resulted in significant enhancement of photocatalytic activity, being e.g., 1.5 (CO 2 system), 7.7 (H 2 system), and even more than 40 under vis irradiation. It was found that both the properties of titania and gold are crucial for resultant photocatalytic activity, but a direct correlation between one structural/physical property and photocatalytic activity could not be obtained since all structural properties changed simultaneously when conditions of photocatalyst preparation (US-HT) were changed. Therefore, gold NPs of controlled sizes were deposited on OAPs product with the best morphology by modified photodeposition method. Clear correlation between photocatalytic activity under visible light and the size of gold NPs indicates that gold properties are decisive for visible light activity rather than titania properties. 3D-FDTD simulations confirm that an increase in the size of gold NPs results in extended surface areas with field enhancement.

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Lorenzo Rosa

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