Random Quasi-Phae-Matching in Tantalatio di Litio: origine del fenomeno, confronto tra propagazione bulk e guidata.

We observe second harmonic generation via random quasi phase matching in a 1.5μm periodically poled lithium tantalate. The presence of a slab waveguides allows the comparison between bulk and guided wave configurations.

NEAR INFRARED PICOSECOND PULSED BACKWARD SECOND-HARMONIC-GENERATION IN PERIODICALLY-POLED LITHIUM NIOBATE

We report on backward second-harmonic-generation in bulk periodically-poled congruent lithium niobate with a 3.2μm period. A picosecond pulsed laser allowed us exciting a resonance at 1722nm. The resonances were also resolved by temperature tuning.

Preliminary Analysis on Correlations between Spatial Distribution of Chlorophyll-a and Experimental Data of Biomass in the Strait of Sicily

This study, using both remotely sensed and measured in situ data, is directed to the analysis of the correlations between the chlorophyll-a concentration and the biomass of sardines and anchovies acoustically evaluated in the Strait of Sicily. This work, inter alia, shows the usefulness of remote observation of seas in determining possible relationships between fish stocks and some oceanographic parameters (Sea Surface Temperature, Chlorophyll-a, Zooplankton).

Rateless codes mitigation technique in a turbulent indoor Free Space Optics link

Free Space Optics (FSO) links are affected by several impairments and, among them, optical turbulence is the most important factor that can degrade the link quality. Due to the presence of this phenomenon, the signal irradiance detected by the receiver fluctuates, thus causing erasure errors and fading events. In this work, we present an indoor Free Space Optics link, in which several turbulence conditions are generated by using two heating elements. We show that the generated turbulence causes erasure errors and packet losses during the data transmission, and we also compare the statistical distribution of the samples with the theoretical models. Moreover, we demonstrate how the applicatio…

Fabrication and Characterization of Dye-Sensitized Solar Cells

Among the next-generation solar cells, a predominant role is played by Dye sensitized solar cells (DSSC) based on ruthenium complexes as sensitizers. They take advantage of a photoelectrochemical system to transform solar radiation into electric energy. In fact, DSSCs represent a cost-effective alternative to traditional silicon-based photovoltaic devices and they do not require expensive and sophisticated apparatus for their fabrication. In this work, we have produced and tested ruthenium DSSCs. In particular, we have measured the main parameters of these cells, such as the electrical and power performances and the efficiency levels, at different irradiance levels and at different incident…

Analysis of Lithium Niobate Surface Layer after Electric Field Periodic Poling and Proton Exchange

Optical wireless GEO satellite-to-ground downlinks: rateless codes as solution for scintillation fading

Scintillation fading can corrupt a satellite-to-ground optical wireless links with burst errors. Rateless codes, suitable for erasure channel, are able to eliminate or to reduce these communication errors. We analyzed the performances of three different rateless codes in a simulated Geo satellite-to-ground downlink.

A Simple Cardiovascular Model for the Study of Hemorrhagic Shock

Hemorrhagic shock is the number one cause of death on the battlefield and in civilian trauma as well. Mathematical modeling has been applied in this context for decades; however, the formulation of a satisfactory model that is both practical and effective has yet to be achieved. This paper introduces an upgraded version of the 2007 Zenker model for hemorrhagic shock termed the ZenCur model that allows for a better description of the time course of relevant observations. Our study provides a simple but realistic mathematical description of cardiovascular dynamics that may be useful in the assessment and prognosis of hemorrhagic shock. This model is capable of replicating the changes in mean …

Backward frequency doubling of near infrared picosecond pulses.

We report on backward second-harmonic generation using ps laser pulses in congruent lithium niobate with 3.2 µm periodic poling. Three resonant peaks were measured between 1530 and 1730 nm, corresponding to 16th, 17th and 18th quasi-phase-matching orders in the backward configuration, with a conversion efficiency of 4.75 x 10(-5%)/W for the 16th order. We could also discriminate the contributions from inverted domains randomized in duty-cycle.

Studio della Nonlinearità Quadratica di Zincoblende per la Generazione di TeraHertz in Guida d'Onda: un Confronto di Cristalli Differenti

DFG TeraHertz generation can approach the quantum efficiency limit with much lower peak powers than bulk experiments. We give details on the model and on the waveguide geometry.

Soft proton exchanged channel waveguides in congruent lithium tantalate for frequency doubling

We report on stable optical waveguides fabricated by soft-proton exchange in periodically-poled congruent lithium tantalate in the a-phase. The channel waveguides are characterized in the telecom wavelength range in terms of both linear properties and frequency doubling. The measurements yield a nonlinear coefficient of about 9.5pm/V, demonstrating that the nonlinear optical properties of lithium tantalate are left nearly unaltered by the process. (C) 2010 Optical Society of America

Random quasi-phase matching in congruent lithium tantalate waveguides by proton exchange

A report is presented on broadband second-harmonic generation in the range between 930 and 970 nm using random quasi-phase matching in a planar waveguide fabricated by soft proton exchange in congruent lithium tantalate. Bulk and waveguide measurements are compared, outlining the averaging role of guided-wave modes and their interactions with respect to spectral acceptance and near-field profile.

Continuous-Wave Backward Frequency Doubling in Periodically Poled Lithium Niobate

Surface Plasmon Resonance Optical Biosensors for Mannoproteins Detection

CulnSe2/Zn(S,O,OH) junction on Mo foil by electrochemical and chemical route for photovoltaic applications

Electrodeposition is a convenient technique for the development of low cost materials for photovoltaic (PV) device processing. Using a single step electrodeposition route, several groups have fabricated CIS (CuInSe) and CIGS (CuInGaSe) films [1]. One of the most important requirements for successful application of one-step electrodeposition film formation, is the ability to control composition of the deposited films and to develop polycrystalline microstructures with a low surface roughness and high sintered density. In this preliminary work, CIS films were produced by single bath electrodeposition finding the optimal conditions in order to achieve a dense film with high crystallinity and u…

Responsivity measurements of SiC photodiodes

We investigated the technical features of three novel classes of 4H-SiC vertical Schottky UV photodiodes (henceforth, named SiC8, SiC10, SiC20) employing Ni2Si interdigitated strips whose pitch size is 8, 10 and 20 µm respectively [1] and based on the pinch-off surface effect.

Integrated optic Surface Plasmon Resonance Measurements in Glass substrates

The surface plasmon resonance (SPR) technique is an optical method that can be used to measure the refractive index of organic nano-layers adsorbed on a thin metal film. Although there are many techniques for measuring biomolecular interactions, SPR-based techniques play a central role in many current biosensing experiments, since they are most suited to sensitive and quantitative kinetic measurements. Here we give some results from the analysis and numerical elaboration of SPR data regarding the flow of different solutions with refractive indexes in the range of interest (1-1.4). After a brief discussion of the principles of SPR and of waveguide fabrication technique, we give a description…

Environmental Noise and Nonlinear Relaxation in Biological Systems

We analyse the effects of environmental noise in three different biological systems: (i) mating behaviour of individuals of 'Nezara viridula' (L.) (Heteroptera Pentatomidae); (ii) polymer translocation in crowded solution; (iii) an ecosystem described by a Verhulst model with a multiplicative Lèvy noise. Specifically, we report on experiments on the behavioural response of 'N. viridula' individuals to sub-threshold deterministic signals in the presence of noise. We analyse the insect response by directionality tests performed on a group of male individuals at different noise intensities. The percentage of insects which react to the sub-threshold signal shows a non-monotonic behavior, charac…

MODELLISTICA MATEMATICA E PIATTAFORME INFORMATICHE A SUPPORTO DELLA RICERCA AMBIENTALE

La modellizzazione matematica è diventata ormai uno strumento essenziale nell’avanzamento delle conoscenze in qualsiasi campo della scienza, dall’econometria alla psicologia, dalla chimica all’epidemiologia, come vissuto di recente nella pandemia da SARS-coV-2. Anche quelle che erano una volta discipline “soft” come la biomedicina o l’ecologia possono ora usufruire di tecniche di rappresentazione ed esplicazione dei processi estremamente utili alla comprensione delle dinamiche in gioco. Questa evoluzione, dovuta in non piccola parte all’attuale disponibilità di abbondante potenza di calcolo elettronico a costi ridotti, non è però opera ed appannaggio soltanto della nostra generazione. Lo st…

Analytical Model for wideband THz sources and detectors based on Optical Rectification and Electro-Optic Sampling

An analytical model describing a laser based set-up for wideband THz generation and detection is presented. Particular attention is focused on the main broadband phenomena, which occur when THz radiations have to be handled.

Signal to noise ratio measurements of silicon photomultipliers in the continuous wave regime

We report on our signal to noise ratio (SNR) measurements carried out, in the continuous wave regime, on a novel class of silicon photomultipliers (SiPMs) fabricated in planar technology on silicon p-type substrate.

Noise Induced Phenomena in the Dynamics of Two Competing Species

Noise through its interaction with the nonlinearity of the living systems can give rise to counter-intuitive phenomena. In this paper we shortly review noise induced effects in different ecosystems, in which two populations compete for the same resources. We also present new results on spatial patterns of two populations, while modeling real distributions of anchovies and sardines. The transient dynamics of these ecosystems are analyzed through generalized Lotka-Volterra equations in the presence of multiplicative noise, which models the interaction between the species and the environment. We find noise induced phenomena such as quasi-deterministic oscillations, stochastic resonance, noise …

Graded Carrier Concentration Absorber Profile for High Efficiency CIGS Solar Cells

We demonstrate an innovative CIGS-based solar cells model with a graded doping concentration absorber profile, capable of achieving high efficiency values. In detail, we start with an in-depth discussion concerning the parametrical study of conventional CIGS solar cells structures. We have used the wxAMPS software in order to numerically simulate cell electrical behaviour. By means of simulations, we have studied the variation of relevant physical and chemical parameters-characteristic of such devices-with changing energy gap and doping density of the absorber layer. Our results show that, in uniform CIGS cell, the efficiency, the open circuit voltage, and short circuit current heavily depe…

Electrochemical and chemical synthesis of CIS/Zn(S,O,OH) for thin film solar cells

In this work, we are reporting results on the electrodeposition of the CuInSe2 thin films on molybdenum thin foil substrates. We have used an aqueous non-buffered electrolyte and a careful choice of deposition parameters to ensure a good quality and composition of the deposited films. In addition, CdS was replaced in the buffer layer with a wider bandgap Zn(S,O,OH) film obtained by chemical bath deposition. The deposited films were annealed in inert atmosphere at different temperatures. The influence of annealing temperature on the properties of the films is briefly discussed. Films were also characterized by photoelectrochemical and I-V measurements. Structural characterization was carried…

Generazione di Seconda Armonica per Quasi-Phase-Matching Random in Tantalato di Litio con Poling Periodico

We experimentally observed and explained bulk Second Harmonic Generation via Random Quasi-Phase-Matching, derived from a periodically poled Lithium Tantalate sample with a randomly patterned mark-to-space-ratio.

A mathematical model of cardiovascular dynamics for the diagnosis and prognosis of hemorrhagic shock

Abstract A variety of mathematical models of the cardiovascular system have been suggested over several years in order to describe the time-course of a series of physiological variables (i.e. heart rate, cardiac output, arterial pressure) relevant for the compensation mechanisms to perturbations, such as severe haemorrhage. The current study provides a simple but realistic mathematical description of cardiovascular dynamics that may be useful in the assessment and prognosis of hemorrhagic shock. The present work proposes a first version of a differential-algebraic equations model, the model dynamical ODE model for haemorrhage (dODEg). The model consists of 10 differential and 14 algebraic e…

GENERAZIONE DI SECONDA ARMONICA IN GUIDA D’ONDA IN TANTALATO DI LITIO CONGRUENTE CON POLING PERIODICO E CONVERSIONE DI LUNGHEZZA D’ONDA IN BANDA C + L

Here we show the results obtained by the characterization of a lithium-tantalate based device for second-harmonic-generation and all-optical wavelength conversion. The waveguides have been obtained by proton-exchange in a periodically-poled congruent lithium tantalate substrate.

Signal to noise ratio measurements of silicon photomultipliers

We report on our signal to noise ratio (SNR) measurements carried out, in the continuous wave regime, on a novel class of silicon photomultipliers (SiPMs) fabricated in planar technology on silicon p-type substrate. SiPMs are large area detectors consisting of a parallel array of Geiger Mode APDs with individual integrated quenching resistors. Each photodiode is an independent photon counting microcell and is connected to a common analog output to produce a summation signal proportional to the number of detected photons [1], [2]. SNR of SiPMs is expressed by the ratio of the SiPM average signal current and the RMS deviation of the overall current (i.e., the overall shot noise current). The …

Responsivity measurements of SiC Schottky photodiodes

We investigated the technical features of three novel classes of 4H-SiC vertical Schottky UV detectors employing Ni2Si interdigitated strips whose pitch size is 8, 10 and 20 µm, respectively, based on the pinch-off surface effect.

Signal to Noise Ratio of Silicon Photomultipliers measured in the Continuous Wave Regime

We performed a Signal to Noise Ratio characterization, in the continuous wave regime, at different bias voltages, frequencies and temperatures, on a novel class of silicon photomultipliers fabricated in planar technology on silicon p-type substrate. Signal to Noise Ratio has been measured as the ratio of the photogenerated current, filtered and averaged by a lock-in amplifier, and the Root Mean Square deviation of the overall current flowing to the device. The measured noise takes into account the shot noise, resulting from the photocurrent and the dark current. We have also performed a comparison between our SiPMs and a photomultiplier tube in terms of Signal to Noise Ratio, as a function …

Statistical analysis of RaptorQ failure probability applied to a data recovery software

In this work, we have implemented a data recovery software integrating the most recent rateless codes, i.e., RaptorQ codes. Thanks to the above-mentioned software, it is possible to recover data loss occurring on several kinds of network conditions. We have performed a statistical analysis of failure probabilities at several configurations of RaptorQ parameters. We have found a good agreement with the theoretical values of a random linear fountain code over Galois Field GF(256). Moreover, we have shown that the probability of having a certain number of failed decoded source blocks - when sending a fixed size file - follows a Poisson distribution.

Packet loss recovery in an indoor Free Space Optics link using rateless codes

Free Space Optics (FSO) systems present some important advantages if compared to Radio Frequency links, but they can be affected by several impairments that degrade the link quality and availability. In particular, due to temporary interruptions of the line-of-sight condition between the transmitter and the receiver, packet loss can occur during data transmission. In this work, we present an indoor Free Space Optics link, in which we have systematically generated interruptions of the beam. We demonstrate how the application of the most recent rateless codes, i.e., RaptorQ codes, can strongly improve the link quality by reducing packet loss. In particular, results show that the Packet Error …

Noise effects in biological systems

Responsivity measurements of silicon carbide Schottky photodiodes in the UV range

We report on the design and the electro-optical characterization of new classes of 4H-SiC Schottky UV detectors, fabricated employing Ni 2 Si interdigitated strips. We have measured, in dark conditions, the forward and reverse I-V characteristics as a function of temperature and C-V characteristics. Responsivity measurements of the devices, as function of wavelength in the UV range, of package temperature and of applied reverse bias are reported. We also compared devices featuring different strip pitch sizes, discussing their performances, and found the device exhibiting best results.

Optical turbulence measurements and channel modeling of an indoor Free Space Optics link (Abstract)

CIGS PV Module Characteristic Curves Under Chemical Composition and Thickness Variations

This paper analyzes how the electrical characteristics of a CIGS photovoltaic module are affected by the chemical composition and by the thickness variations of the CIGS absorber. The electrical characteristics here considered are the short circuit current, the open circuit voltage, the efficiency and the power peak. The chemical composition is varied by tuning the ratio between gallium and indium. This analysis has been performed by means of the wxAMPS software, developed by the University of Illinois. The above variations have been taken into account on a PV module made of 72 cells. This analysis has been carried out employing a PV module mathematical model developed and implemented by th…

Design and realization of a portable multichannel continuous wave fNIRS

A design and implementation of a portable functional Near InfraRed Spectroscopy embedded system prototype is described. In this theoretical and experimental work, we present an embedded system hosting 64 LED sources and 128 Silicon PhotoMultiplier detectors (SiPM). The elementary part of the structure is a flexible probe “leaf” consisting of 16 SiPMs, 4 couples of LEDs, each operating at two wavelengths, and a temperature sensor. The hardware system is based on an ARM main microcontroller that allows to perform both the switching time of LEDs and the acquisition of the SiPM outputs. The performed preliminary experimental tests achieved very promising results, thus demonstrating the effectiv…

Design and development of a fNIRS system prototype based on SiPM detectors

Functional Near Infrared Spectroscopy (fNIRS) uses near infrared sources and detectors to measure changes in absorption due to neurovascular dynamics in response to brain activation. The use of Silicon Photomultipliers (SiPMs) in a fNIRS system has been estimated potentially able to increase the spatial resolution. Dedicated SiPM sensors have been designed and fabricated by using an optimized process. Electrical and optical characterizations are presented. The design and implementation of a portable fNIRS embedded system, hosting up to 64 IR-LED sources and 128 SiPM sensors, has been carried out. The system has been based on a scalable architecture whose elementary leaf is a flexible board …

Design and implementation of a portable fNIRS embedded system

We report on the design, development and operation of a portable, low cost, battery-operated, multi-channel, functional Near Infrared Spectroscopy embedded system, hosting up to 64 optical sources and 128 Silicon PhotoMultiplier optical detectors. The system is realized as a scalable architecture, whose elementary leaf consists of a probe board provided with 16 SiPMs, 4 couples of bi-color LED, and a temperature sensor, built on a flexible stand. The hardware structure is very versatile because it is possible to handle both the switching time of the LED and the acquisition of the photodetectors, via an ARM based microcontroller.

Performance Investigation of Fountaine Codes on a Simulated Terrestrial Free Space Optical Channel

Analysis of Lithium Niobate Surface after Electric Field Periodic Poling and Proton Exchange

Correlated channel model for terrestrial Free Space Optics: performance analysis of rateless codes

We describe a novel correlated channel model able to predict random temporal fluctuations of optical signal irradiance caused by scintillation. With regards to the same channel, we also report simulation results on the error mitigation performance of Luby-Transform and Raptor codes.

Backward second-harmonic generation of near infrared picosecond pulses

We report on backward second-harmonic generation using picosecond laser pulses in congruent lithium niobate with 3.2 µm periodic poling. By tuning both the pump wavelength and the sample temperature, we observed three resonant peaks in the range 1530-1730 nm, corresponding to 16th, 17th and 18th quasi-phase-matching orders, respectively. A maximum conversion efficiency of 0.475% was achieved at the 16th order with a 10 kW peak pump power. The latter is the highest conversion reported in bulk to date, for the backward configuration, with an improvement greater than 50% with respect to those previously achieved with nanosecond pulses for the same order of resonance.

Responsivity measurements of 4H-SiC Schottky photodiodes for UV light monitoring

We report on the design and the electro-optical characterization of a novel class of 4H-SiC vertical Schottky UV detectors, based on the pinch-off surface effect and obtained employing Ni2Si interdigitated strips. We have measured, in dark conditions, the forward and reverse I–V characteristics as a function of the temperature and the C–V characteristics. Responsivity measurements of the devices, as a function of the wavelength (in the 200 – 400 nm range), of the package temperature and of the applied reverse bias are reported. We compared devices featured by different strip pitch size, and found that the 10 μm device pitch exhibits the best results, being the best compromise in terms of fu…

Comparison between two different cardiovascular models during a hemorrhagic shock scenario

Hemorrhagic shock is a form of hypovolemic shock determined by rapid and large loss of intravascular blood volume and represents the first cause of death in the world, whether on the battlefield or in civilian traumatology. For this, the ability to prevent hemorrhagic shock remains one of the greatest challenges in the medical and engineering fields. The use of mathematical models of the cardiocirculatory system has improved the capacity, on one hand, to predict the risk of hemorrhagic shock and, on the other, to determine efficient treatment strategies. In this paper, a comparison between two mathematical models that simulate several hemorrhagic scenarios is presented. The models considere…

Characterization of PP-cLT Waveguides for phase conjugation in the C + L band of Optical Communications

5th EOS Topical Meeting on Optical Microsystems, Poster OμS13_1569798553: Analytical Model for wideband THz sources and detectors based on Optical Rectification and Electro-Optic Sampling

All-Optical frequency Shifter in a Periodically Poled Lithium Tantalate Waveguide

A frequency shifting device is fabricated and tested in a congruent Lithium Tantalate waveguide. Periodic poling for quasi-phase-matching and channels for operation in the near-infrared C-band were obtained, demonstrating a two-stage parametric conversion.

Correlated Channel Model for terrestrial Free Space Optics and project specifications evaluation of LT code in OOK modulation

Free Space Optics is a wireless line-of-sight communication system able to offer good bandwidth performance as well as straightforward installation and relocation. So that it represents a modern technology that allow to realize large bandwidth communication particularly when it is not possible to employ physical cable or radio technologies. Examples of FSO applications are: wireless backaul, fiber backup, temporary links, metro network extension and last mile access[1]. FSO is based on optical signals propagation in air and that is why it suffers of impairments which depend on atmospheric conditions. In detail, FSO suffers of scattering (i. e. Rayleigh and Mie) losses, absorption and scinti…

Parametrical study of multilayer structures for CIGS solar cells

In this paper, a numerical analysis of relevant electrical parameters of multilayer structures for CIGS-based solar cells was carried out, employing the simulation software wxAMPS. In particular, we have focused on thin film cells having a ZnO:Al/ZnO/CdS/CIGS structure with a Molybdenum back contact. The aim of this work is to establish good theoretical reference values for an ongoing experimental activity, where our technology of choice is the single-step electrodeposition. In detail, we have analyzed how the main electrical properties change with the bang gap and the thickness of the absorber layer, for such a type of solar cell structure. Our results show that both efficiency and fill fa…

Continuous-Wave Backward Frequency Doubling in Periodically Poled Lithium Niobate

We report on backward second-harmonic- generation in periodically poled lithium niobate with a 3.2 micron QPM period. A tunable continuous-wave Ti:Sapphire laser allowed us exciting two resonant orders. Experimental data compared well with standard theory.

Electro-Optical characterization of Silicon Carbide Schottky photodiodes

Continuous-wave backward frequency doubling in periodically poled lithium niobate

We report on backward second-harmonic-generation in bulk periodically poled congruent lithium niobate with a 3.2 microns period. A tunable continuous-wave Ti:sapphire laser allowed us exciting two resonant quasi-phase-matching orders in the backward configuration. The resonances were also resolved by temperature tuning and interpolated with standard theory to extract relevant information on the sample.

High resolution x-ray investigation of periodically poled lithium tantalate crystals with short periodicity

Domain engineering technology in lithium tantalate is a well studied approach for nonlinear optical applications. However, for several cases of interest, the realization of short period structures (< 2 ��m) is required, which make their characterization difficult with standard techniques. In this work, we show that high resolution x-ray diffraction is a convenient approach for the characterization of such structures, allowing us to obtain in a nondestructive fashion information such as the average domain period, the domain wall inclination, and the overall structure quality.

Parametric conversion in micrometer and sub-micrometer structured ferroelectric crystals by surface poling

We report on recent technological improvements concerning nonlinear patterning of lithium niobate and lithium tantalate in the micrometer and submicrometer scales using surface periodic poling for ferroelectric domain inversion. The fabricated samples were employed for frequency doubling via quasiphase-matching both in bulk and guided wave geometries, including forward and backward configurations and wavelength conversion in bands C and L. We also investigated short-period quasiperiodic samples with randomly distributed mark-to-space ratios.

Characterization of PP-cLT Waveguides for Second-Harmonic-Generation and Wavelength-Conversion in the C + L Band of Optical Communications

We report the characterization of single-mode optical waveguides at telecom wavelength, realized in congruent lithium-tantalate. We demonstrate that waveguides realized by proton-exchange show a nonlinear coefficient matching that expected in a bulk crystal.

Rateless Codes Performance Analysis in Correlated Channel Model for GEO Free Space Optics Downlinks

Silicon Photomultipliers Signal-to-Noise Ratio in the Continuous Wave Regime

 Abstract— We report on Signal-to-Noise Ratio measurements carried out, in the continuous wave regime, at different bias voltages, frequencies and temperatures, on a class of silicon photomultipliers fabricated in planar technology on silicon p- type substrate. Signal-to-Noise Ratio has been measured as the ratio of the photogenerated current, filtered and averaged by a lock-in amplifier, and the Root Mean Square deviation of the same current. The measured noise takes into account the shot noise, resulting from the photocurrent and the dark current. We have also performed a comparison between our SiPMs and a photomultiplier tube in terms of Signal-to-Noise Ratio, as a function of the tempe…

Electro-optical characterization of new classes of Silicon Carbide UV photodetectors

In this paper, we present the fabrication process steps and the characterization of 4H-SiC vertical Schottky UV detectors, where interdigitated strips, acting as top metal contacts, have been realized in $\hbox{Ni}_{2}\hbox{Si}$ . These devices exploit the pinch-off surface effect. $I$ – $V$ and $C$ – $V$ characteristics, as functions of temperature, were measured in dark conditions. In addition, we have carried out responsivity measurements, for wavelengths ranging from 200 to 400 nm, at varying package temperature and applied reverse bias. A comparison among devices having different strip pitch sizes has been performed, thus finding out that the 10- $\mu\hbox{m}$ pitch class demonstrates …

Rateless Codes Performance Tests On Terrestrial FSO Time-Correlated Channel Model

Free Space Optics (FSO) links are affected by several impairments: optical turbulence, scattering, absorption, and pointing. In particular, atmospheric optical turbulence generates optical power fluctuations at the receiver that can degrade communications with fading events, especially, in high data rate links. A way to mitigate FSO link outages can be to add a coding to communications. Nevertheless, in order to study innovative solutions (software or hardware) and to improve the FSO link performance it needs accurate testing models. In this paper we describe an accurate time-correlated channel model able to predict random temporal fluctuations of optical signal irradiance caused by optical…

Indoor free space optics link under the weak turbulence regime: Measurements and model validation

In this study, the authors present the measurements performed on a free space optics (FSO) communications link using an indoor atmospheric chamber. In particular, the authors have generated several different optical turbulence conditions, demonstrating how even the weak turbulence regime can strongly affect the FSO link performance. The authors have carried out an in-depth analysis of the data collected during the measurements, and calculated the turbulence strength (i.e. scintillation index and Rytov variance) and the important performance metrics (i.e. the Q-factor and bit error rate) to evaluate the FSO link quality. Moreover, the authors have tested, for the first time, an appositely de…

MAPPATURA DEL DISORDINE NON LINEARE MEDIANTE INTERAZIONE PARAMETRICA A TRE ONDE

We introduce a simple approach for characterizing the ferroelectric domain distribution in bulk quadratic crystals. The approach is demonstrated in a lithium tantalate sample with periodic electric field poling and random mark-to-space ratio.

Fading mitigation coding techniques for space to ground free space optical communications (Euro Med Telco 2014)

In this manuscript, a Geostationary satellite-toground Free Space Optics (FSO) downlink channel model has been implemented, which is able to predict temporal irradiance fluctuations caused by scintillation at a wide range of turbulence conditions and for different values of the zenith angle. In order to mitigate fading events that occur in FSO communications, we have also tested the performance of three different families of Rateless Codes (Luby Transform, Raptor and RaptorQ) into our model and found that RaptorQ is the best candidate to mitigate errors in FSO links.

Analysis of the vertical distribution in a model of phytoplankton dynamics

Phytoplankton often faces the dilemma of living in contrasting gradients of two essential resources: the light that comes from above and nutrients that are often supplied from below. In poorly mixed water columns, algae can be heterogeneously distributed, with thin layers of biomass found on the surface, in depth, or on the sediment surface. Here, we show that these patterns can result from intraspecific competition between light and nutrients. First, we present numerical solutions of a reaction-diffusion-taxis model for phytoplankton, nutrients and light. We argue that motile phytoplankton can form a thin layer under poorly mixed conditions. The numerical solution of this model indicates t…

GENERAZIONE DI SECONDA ARMONICA RETRO-PROPAGANTE IN NIOBATO DI LITIO CON POLING PERIODICO

We report on backward second-harmonic-generation in bulk periodically poled congruent lithium niobate with a 3.2 micron period. A tunable continuous-wave Ti:Sapphire laser allowed us exciting two resonant quasi-phase-matched orders. Resonances were also resolved by temperature tuning.

Recovery Capabilities of Rateless Codes on Simulated Turbulent Terrestrial Free Space Optics Channel Model

Free Space Optics (FSO) links are affected by several impairments: optical turbulence, scattering, absorption, and pointing. In particular, atmospheric optical turbulence generates optical power fluctuations at the receiver that can degrade communications with fading events, especially in high data rate links. Innovative solutions require an improvement of FSO link performances, together with testing models and appropriate channel codes. In this paper, we describe a high-resolution time-correlated channel model able to predict random temporal fluctuations of optical signal irradiance caused by optical turbulence. Concerning the same channel, we also report simulation results on the error mi…

Evidence of stochastic resonance in the mating behavior of Nezara viridula (L.)

We investigate the role of the noise in the mating behavior between individuals of Nezara viridula (L.), by analyzing the temporal and spectral features of the non-pulsed type female calling song emitted by single individuals. We have measured the threshold level for the signal detection, by performing experiments with the calling signal at different intensities and analyzing the insect response by directionality tests performed on a group of male individuals. By using a sub-threshold signal and an acoustic Gaussian noise source, we have investigated the insect response for different levels of noise, finding behavioral activation for suitable noise intensities. In particular, the percentage…

Elaborazione parametrica di segnali ottici

Questa tesi presenta una panoramica dell‘attività di ricerca da me svolta in questo triennio di dottorato, avente come oggetto la progettazione, la fabbricazione e la caratterizzazione di dispositivi non lineari in ottica integrata per l‘elaborazione parametrica dei segnali. Gli aspetti funzionali di questi dispositivi, le proprietà non lineari del secondo ordine dei materiali di cui sono composti così come i risultati dei processi di fabbricazione necessitano di un‘analisi teorica approfondita che ne consenta l‘effettiva applicazione alle comunicazioni ottiche. Il primo capitolo è un‘attenta disamina del metodo del Quasi-Phase-Matching mediante il quale si ha l‘implementazione del fenomeno…

CIGS THIN FILM BY ONE-STEP ELECTRODEPOSITION FOR SOLAR CELLS

In this work, we present a cost-effective technique to produce CIGS thin films for solar cells by means of a single-step electrodeposition. In fact, electrodeposition is known as an easy technique for building low cost materials for photovoltaic device processing. Morphological, structural and optical characterization of these films has been performed.

Fading mitigation coding techniques for space to ground free space optical communications

Seven Mathematical Models of Hemorrhagic Shock

Although mathematical modelling of pressure-flow dynamics in the cardiocirculatory system has a lengthy history, readily finding the appropriate model for the experimental situation at hand is often a challenge in and of itself. An ideal model would be relatively easy to use and reliable, besides being ethically acceptable. Furthermore, it would address the pathogenic features of the cardiovascular disease that one seeks to investigate. No universally valid model has been identified, even though a host of models have been developed. The object of this review is to describe several of the most relevant mathematical models of the cardiovascular system: the physiological features of circulator…

Luby Transform Performance Tests on Time-Correlated Channel Model for Geo Free Space Optics Downlinks

Integrated frequency shifter in periodically poled lithium tantalate waveguide

A frequency shifting device is fabricated and tested in a ferroelectric waveguide in a low-photorefractivity crystal. Periodic poling for quasi-phase-matching and channels for operation in the near-infrared C-band were obtained in congruent lithium tantalate, demonstrating for the first time both wave confinement and two-stage parametric conversion in such waveguides.

Thin Film CIGS Solar Cells, Photovoltaic Modules, and the Problems of Modeling

Starting from the results regarding a nonvacuum technique to fabricate CIGS thin films for solar cells by means of single-step electrodeposition, we focus on the methodological problems of modeling at cell structure and photovoltaic module levels. As a matter of fact, electrodeposition is known as a practical alternative to costly vacuum-based technologies for semiconductor processing in the photovoltaic device sector, but it can lead to quite different structural and electrical properties. For this reason, a greater effort is required to ensure that the perspectives of the electrical engineer and the material scientist are given an opportunity for a closer comparison and a common language.…

Second Harmonic Generation via Random Quasi-phase Matching in a Periodically Poled Lithium Tantalate Waveguide

We observe second harmonic generation via random quasi phase matching in a 1.5μm periodically poled lithium tantalate. The presence of a slab waveguide allows the comparison between bulk and guided wave configurations.

Signal to Noise Ratio of Silicon Photomultipliers: a study in the Continuous Wave Regime

We report on Signal to Noise Ratio measurements carried out, in the continuous wave regime, at different bias voltages, frequencies and temperatures, on a novel class of silicon photomultipliers fabricated in planar technology on silicon p-type substrate. Signal to Noise Ratio has been measured as the ratio of the photogenerated current, filtered and averaged by a lock-in amplifier, and the Root Mean Square deviation of the same current. The measured noise takes into account the shot noise, resulting from the photocurrent and the dark current. We have also performed a comparison between our SiPMs and a photomultiplier tube in terms of Signal to Noise Ratio, as a function of the temperature …

CIGS Thin Film by One-Step Electrodeposition Deposition for Solar Cells

Photovoltaic module characteristics from CIGS solar cell modelling

We describe our approach to the task of modelling, both at single cell structure and complete module levels, during the solar cell technology development process. This can give very helpful indications, in terms of global photovoltaic module characteristics, for the assessment of intermediate research results and planning of further experiments. We make reference specifically to the fabrication of thin film CIGS solar cells by means of single-step electrodeposition, a technique which appears fairly easy and low-cost but, at the same time, can lead to quite different structural and electrical properties.

Interference-Based Chromatic Coatings by Ion Plating Plasma Assisted Deposition Technology

The goal of replacing widespread and inexpensive galvanic treatments with suitable vacuum deposition techniques, in order to eliminate the environmental hazards and their polluting effects, is becoming, in some cases, more tangible. Shorter cleaning cycles, shorter pump-down times, reduced heating times of substrates and higher deposition rates allow the costs of new plasma-assisted processes to become competitive with respect to galvanic ones. Moreover, vacuum treatments offer superior mechanical and optical properties and non-conductive substrates (like glass, ceramics, plastics) can be more easily coated. This work describes the results obtained with Ion Plating Plasma Assisted depositio…

Noise effects in two different biological systems

We investigate the role of the colored noise in two biological systems: (i) adults of Nezara viridula (L.) (Heteroptera: Pentatomidae), and (ii) polymer translocation. In the first system we analyze, by directionality tests, the response of N. viridula individuals to subthreshold signals plus noise in their mating behaviour. The percentage of insects that react to the subthreshold signal shows a nonmonotonic behaviour, characterized by the presence of a maximum, as a function of the noise intensity. This is the signature of the non-dynamical stochastic resonance phenomenon. By using a “soft” threshold model we find that the maximum of the input-output cross correlation occurs in the same ra…

Features of randomized electric-field assisted domain inversion in lithium tantalate

We report on bulk and guided-wave second-harmonic generation via random Quasi-Phase-Matching in Lithium Tantalate. By acquiring the far-field profiles at several wavelengths, we extract statistical information on the distribution of the quadratic nonlinearity as well as its average period, both at the surface and in the bulk of the sample. By investigating the distribution in the two regions we demonstrate a non-invasive approach to the study of poling dynamics.

CuInSe2/Zn(S,O,OH) junction by electrochemical and chemical route for photovoltaic applications (GE 2014)

Electrodeposition is a convenient technique for the development of low cost materials for photovoltaic (PV) device processing. Using a single step electrodeposition route, several groups have fabricated CIS (CuInSe) and CIGS (CuInGaSe) films. One of the most important requirements for successful application of one-step electrodeposition film formation is the ability to control composition of the deposited films and to develop polycrystalline microstructures with a low surface roughness and high sintered density.

Optical turbulence measurements and channel modeling of an indoor Free Space Optics link

Backward Frequency Doubling in Periodically Poled Lithium Niobate in the Pulsed Regime

Two-species model for spatial distributions of sardine and anchovy: A comparison with real data

We present a study of pattern formation in a set of two coupled equations modeling two competing species. We consider generalized Lotka-Volterra equations in the presence of a multiplicative noise which models the interaction between the species and the environment. The interaction parameter between the species is a random process which obeys a stochastic differential equation with a generalized bistable potential in the presence of a periodic driving term, which accounts for the environment temperature variation.We find noise-induced spatial patterns with strong anti-correlation between the two species. We compare our theoretical results with the experimental data of the spatial distributi…

Numerical Model of THz sources and detectors based on Optical Rectification and Electro-Optic Sampling

A model describing a laser based set-up for wideband THz generation and detection is presented. Particular attention is focused on the main broadband phenomena, which occur when THz radiations have to be handled.

Optical turbulence measurements and channel modeling of an indoor Free Space Optics link (Versione estesa)

In this work, we propose an indoor experimental set-up able to generate several optical turbulence conditions in a Free Space Optics link. Using this set-up, we prove the effectiveness of an irradiance time-series generator based on the Gamma-Gamma model and able to predict the irradiance fluctuations at the receiver, under both weak and moderate turbulence conditions.

Fading mitigation coding techniques for space to ground free space optical communications

In this manuscript, a Geostationary satellite-toground Free Space Optics (FSO) downlink channel model has been implemented, which is able to predict temporal irradiance fluctuations caused by scintillation at a wide range of turbulence conditions and for different values of the zenith angle. In order to mitigate fading events that occur in FSO communications, we have also tested the performance of three different families of Rateless Codes (Luby Transform, Raptor and RaptorQ) into our model and found that RaptorQ is the best candidate to mitigate errors in FSO links. Keywords— Optical Wireless Communications; Space-toGround FSO links, time-series, rateless codes; fading mitigation