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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.

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.

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.

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 measured noise takes into account the shot noise, resulting from the photocurrent and the dark current, while background light is not present in our setup. Unlike the shot noise, SiPM average dark current is an offset term and it can be filtered through a simple external DC removal circuit and, for this reason, we discarded it.

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 of the SiPM package and at different bias voltages. Our results show the outstanding performance of this novel class of SiPMs even without the need of any cooling system.

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 out by XRD and Raman spectroscopy. Results show the growth of good quality films with very uniform morphology and good chemical composition.

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.

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 wavelengths. Our results show a maximum conversion efficiency between 11% and 12% in the range within 540 and 550 nm. The results are in a fairly good agreement with theoretical predictions, especially with regard to the dependence of the parameters on the irradiance levels. Nevertheless, there are some aspects that suggest the need for further and more detailed studies on the deterioration mechanisms and fabrication processes.

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 uniform, flat surfaces, which are of critical importance for photovoltaic applications. Electrodeposition was carried out in the potentiostatic mode using a conventional three-electrode configuration.

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.

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.

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.

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.

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 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.

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 di generazione efficiente e il mantenimento della radiazione elettromagnetica di seconda armonica all‘interno di un mezzo non lineare. Il secondo capitolo tratta della teoria e della tecnica dei complessi processi fisici che governano il bulk e surface poling nei cristalli di Niobato e di Tantalato Litio. Nel terzo capitolo si descrivono le caratteristiche peculiari del Surface Periodic Poling e si riportano i risultati conseguiti nell‘indagine, effettuata mediante diffrazione di raggi X, di strutture periodiche fabbricate con questa tecnica. L‘analisi strumentale è focalizzata sulla periodicità e sull‘uniformità dei reticoli sub-micrometrici implementati. Il quarto capitolo descrive le fasi di progettazione, fabbricazione e caratterizzazione di un dispositivo costruito per la generazione di seconda armonica in configurazione retro-propagante. Trattandosi di un fenomeno estremamente difficile da esaminare, lo studio ed il lavoro di ricerca si sono concentrati principalmente sugli aspetti di Tutor Ch.mo Prof. Alessandro C. Busacca Sommario III fabbricazione e di caratterizzazione del componente, portando a risultati originali, ed interessanti soprattutto da un punto di vista fisico. Nel quinto capitolo si descrivono i passi tecnologici che hanno portato alla costruzione di un dispositivo per il random Quasi-Phase-Matching e si discute delle misure realizzate durante le osservazioni sperimentali in bulk ed in guida d‘onda planare, cercando di darne una spiegazione chiara e, per quanto possibile, dettagliata alla luce della caratterizzazione del dispositivo stesso. L‘approccio seguito, oltre ad essere estremamente utile per svariate applicazioni, permette, al contempo, di evidenziare interessanti proprietà fisiche proprie di questo processo. Nel sesto ed ultimo capitolo, infine, viene presentato, per la prima volta, un frequency shifter in guida d‘onda a canale per scambio protonico in fase α, su substrato di Tantalato di Litio con poling periodico, in grado di confinare la radiazione elettromagnetica e permettere la conversione parametrica a due stadi in cascata (Generazione di Seconda Armonica-Generazione di Frequenza Differenza) operante nel range della banda C delle telecomunicazioni ottiche.

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.

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.

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 scintillation. The former two impairments depend on a attenuation coefficient that is larger under hard atmospheric conditions, the latter is a random phenomena mainly noticeable also under clear sky. Scintillation phenomena depends on turbulence which is described by a local variations of the mean index of refraction and finally converted in a fluctuation of the signal optical irradiance. In this paper we describe for the first time a correlated channel model that predicts the temporal behavior of optical signal irradiance. We give also details on LT coding for OOK modulation.

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.

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.

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.

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).

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.

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.

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 deposition processes, using thermal sources, to realise special decorative chromatic effects with multilayer interferential thin films. Special attention was dedicated to the study of mechanical properties of the deposited layers in relation to the energy of condensing particles and bombarding ions, and to the measurement of their chromatic characteristics. Finally, some considerations about the practical applications of the described processes are presented.