Random numbers are fundamental elements in different fields of science and technology such as computer simulation like Monte Carlo-method simulation, statistical sampling, cryptography, games and gambling, and other areas where unpredictable results are necessary. Random number generators (RNG) are generally classified as “pseudo”-random number generators (PRNG) and "truly" random number generators (TRNG). Pseudo random numbers are generated by computer algorithms with a (random) seed and a specific formula. The random numbers produced in this way (with a small degree of unpredictability) are good enough for some applications such as computer simulation. However, for some other applications like cryptography they are not completely reliable. When the seed is revealed, the entire sequence of numbers can be produced. The periodicity is also an undesirable property of PRNGs that can be disregarded for most practical purposes if the sequence recurs after a very long period. However, the predictability still remains a tremendous disadvantage of this type of generators. Truly random numbers, on the other hand, can be generated through physical sources of randomness like flipping a coin. However, the approaches exploiting classical motion and classical physics to generate random numbers possess a deterministic nature that is transferred to the generated random numbers. The best solution is to benefit from the assets of indeterminacy and randomness in quantum physics. Based on the quantum theory, the properties of a particle cannot be determined with arbitrary precision until a measurement is carried out. The result of a measurement, therefore, remains unpredictable and random. Optical phenomena including photons as the quanta of light have various random, non-deterministic properties. These properties include the polarization of the photons, the exact number of photons impinging a detector and the photon arrival times. Such intrinsically random properties can be exploited to generate truly random numbers. Silicon (Si) is considered as an interesting material in integrated optics. Microelectronic chips made from Si are cheap and easy to mass-fabricate, and can be densely integrated. Si integrated optical chips, that can generate, modulate, process and detect light signals, exploit the benefits of Si while also being fully compatible with electronic. Since many electronic components can be integrated into a single chip, Si is an ideal candidate for the production of small, powerful devices. By complementary metal-oxide-semiconductor (CMOS) technology, the fabrication of compact and mass manufacturable devices with integrated components on the Si platform is achievable. In this thesis we aim to model, study and fabricate a compact photonic quantum random number generator (QRNG) on the Si platform that is able to generate high quality, "truly" random numbers. The proposed QRNG is based on a Si light source (LED) coupled with a Si single photon avalanche diode (SPAD) or an array of SPADs which is called Si photomultiplier (SiPM). Various implementations of QRNG have been developed reaching an ultimate geometry where both the source and the SPAD are integrated on the same chip and fabricated by the same process. This activity was performed within the project SiQuro—on Si chip quantum optics for quantum computing and secure communications—which aims to bring the quantum world into integrated photonics. By using the same successful paradigm of microelectronics—the study and design of very small electronic devices typically made from semiconductor materials—, the vision is to have low cost and mass manufacturable integrated quantum photonic circuits for a variety of different applications in quantum computing, measure, sensing, secure communications and services. The Si platform permits, in a natural way, the integration of quantum photonics with electronics. Two methodologies are presented to generate random numbers: one is based on photon counting measurements and another one is based on photon arrival time measurements. The latter is robust, masks all the drawbacks of afterpulsing, dead time and jitter of the Si SPAD and is effectively insensitive to ageing of the LED and to its emission drifts related to temperature variations. The raw data pass all the statistical tests in national institute of standards and technology (NIST) tests suite and TestU01 Alphabit battery without a post processing algorithm. The maximum demonstrated bit rate is 1.68 Mbps with the efficiency of 4-bits per detected photon. In order to realize a small, portable QRNG, we have produced a compact configuration consisting of a Si nanocrystals (Si-NCs) LED and a SiPM. All the statistical test in the NIST tests suite pass for the raw data with the maximum bit rate of 0.5 Mbps. We also prepared and studied a compact chip consisting of a Si-NCs LED and an array of detectors. An integrated chip, composed of Si p+/n junction working in avalanche region and a Si SPAD, was produced as well. High quality random numbers are produced through our robust methodology at the highest speed of 100 kcps. Integration of the source of entropy and the detector on a single chip is an efficient way to produce a compact RNG. A small RNG is an essential element to guarantee the security of our everyday life. It can be readily implemented into electronic devices for data encryption. The idea of "utmost security" would no longer be limited to particular organs owning sensitive information. It would be accessible to every one in everyday life.

The laser, whose name stands for Light Amplification by Stimulated Emission of Radiation, in less than a century has became a fundamental tool in several applications and technological processes, such as metrology, telecommunications, medicine and industry, because of their peculiar properties. More in details, they are spatially and temporally coherent, they exhibit a low divergence and can offer high power density and monochromaticity. The work of this thesis can be placed within the framework of laser assisted industrial processes. Material processing exploits the interaction between a high power laser beam and the matter. The interaction happens in the surface of the material where the extreme heat transferred by the laser source can cause a local phase change, without affecting in a significant way the bulk properties of the treated medium. Typically high brightness laser sources are used. The most used solution is represented by fiber lasers. In the last years the research moved towards the semiconductor laser sources because of the numerous advantages that they o↵er with respects to the other types of sources, like a higher conversion efficiency, a smaller size and the possibility of a mass production. Nevertheless, the maximum output power that can be extracted from a single diode laser is relatively small. The adopted strategies for power scaling rely on beam combining. Here we propose a novel architecture for the implementation of passive coherent beam combining, into a single resonant cavity. The main block of the scheme is an Interferometric Semiconductor Amplifier (ISA). In an ISA, the optical amplifier is placed in one arm of a Mach-Zehnder Interferometer. A sequence of ISA, placed into a common resonant cavity, is used for the power scaling. The theoretical model is presented, and the experimental results are discussed.

My research in these three years has been mainly focused on the characterization of structural and optical properties of three kinds of Si-based materials and devices. The first one is the study of SiOC thin films, carried within the TMR-POLYCERNET project financed by the European community. The scientific objective of this project is to create molecularly-tailored, nanostructured SiOC ceramics with unusual multifunctional properties, including photoluminescence. In addition these novel, polymer-derived ceramics, or PDCs, will have high resistance to oxidation, degradation, corrosion and deformation at temperatures above 1400°C. The aim of our work is focused on the optical characterization of PDCs. The PDCs are constituted from polymeric precursors which can be tailored and designed at the molecular level. These multifunctional properties are then carried over into the ceramic phase by self-assembly and controlled pyrolysis. Thus, these novel materials are apparently polymer-like in their structure (for example, they are seemingly amorphous but contain nanodomains) but have the chemical, mechanical and functional properties of high temperature ceramics. The photoluminescence will be the most important property that will be studied and optimized. The specific objective of this work is to optimize chemistry and processing to achieve bright emission and high external quantum efficiency in high-quality thin film. In the second chapter of the thesis, starting from a brief description of SiOC glasses and the sol-gel process to introduce our work, we explained how the thin films were prepared and characterised. A study on the absorption coefficient of the films is reported, in order to compare it with results in literature of similar samples. The major part of this chapter was focalized on our work on the photoluminescence of the films. At high annealing temperature, we observed a very high yellow luminescence from the films, most notably due to the presence of SiC nanoclusters and C clusters in our samples. A well detailed discussion on the origin of the strong emission is reported. A study of the effects of Boron addition on the photoluminescence of our thin films was also effectuated and by comparing the evolution of the B-free (SiOC) and B-containing samples (SiBOC), the important role of boron in promoting the evolution of nanostructure in our thin films is described. Finally, to have an idea of the potential of our films, their external quantum efficiency (E.Q.E.) was measured. A detailed description of the measurement technique is reported and the results are compared with Si-nc samples whose EQE is well-known. Very high EQE were found for TH films pyrolysed at 1200 °C (11.5 %) and THDH2 films pyrolysed at 1200 °C (5%). These external quantum efficiency values are very promising and make SiOC a very interesting material for LED applications. Another part of the work was devoted to the study of Si-based waveguides, and more particularly Silicon on Insulator (SOI) waveguides and Slot SOI waveguides. This work was carried out within the European project PHOLOGIC. The general objective of the PHOLOGIC project is to explore the mass-manufacturing feasibility of Silicon Nanocrystals inside SiO2 matrix in terms of CMOS technology compatibility for a highly scalable photonic logic gate structure. A XOR gate was chosen as functional validation device. The third and fourth chapters of this thesis are dedicated to this work. In the third chapter, we characterized various building blocks like splitters, MMI and bends made in Silicon on Insulator technology. The loss figures found for these building blocks were useful as a benchmark for further development of silicon microphotonics components and circuits on SOI platform like photonic crystals and ring resonators. In effect, the results of this chapter are basic to the development of the SCISSOR structures based on SOI technology, described in chapter five. In the fourth chapter, we studied nano-Si slot waveguides. Horizontal slot waveguides filled with Si-nc have been realized and characterized in terms of propagation losses as a function of the layer deposition conditions (i.e. Si excess and annealing temperature). We were able to reach propagation losses as low as 3 dB/cm which is the best result reported so far for slot waveguides of very small width (50 nm). We presented also experimental results of resonant optical cavities such single and double ring resonators coupled to the horizontal slot waveguides with very high quality factors. The importance of this works relies on the fact that by optimizing the annealed SRSO (i.e. Si-nc) in the slot, we have significantly reduced the propagation losses and at the same time we can add new functionalities related to the Si-nc optical properties (i.e. light emission and/or non-linear optical effects). Finally, a one-dimensional photonic crystal structure based on horizontal slot waveguide with a photonic band gap around 1.55 μm has also been designed and optically characterized. Finally, the last part of this thesis will be devoted to the characterization of Silicon on Insulators Multi-Resonators. This work is a continuation of the study of SOI building blocks described above, and was carried within the European project WADIMOS. The main goal of the WADIMOS project is to build a complex photonic interconnect layer incorporating multi-channel microsources, microdetectors and different advanced wavelength routing functions directly integrated with electronic driver circuits. Our work in this project is to test innovative optical waveguide division multiplexing circuits based on coupled ring resonators. In the last part of this thesis, we will characterize various coupled ring/disks resonators structures, from simple double coupled rings until eight coupled ring SCISSOR. In the last chapter, we measured and compared the characteristic of the light propagation of different connection geometries for sequences of microrings (or microdisks) resonators. In this work, we studied various configurations of coupled disk/ring resonators. With these various structures, we observed the differences in the transmission spectrum between rings and disks resonators, we noticed the whispering gallery modes and the effect of the gap in the CRIT effect for a serially double-disks resonator. On a first time, we studied the serially coupled configuration CROW where each ring resonator is coupled to one another. For this structure, we restrict our attention to two ring/disk based units. We observed the differences in the transmission spectrum between rings and disks resonators and we noticed the whispering gallery modes and the effect of the gap in the electromagnetically induced transparency effect for a serially double-disks resonator. The second configuration that was studied is the SCISSOR configuration. In this case, all resonators are coupled to both the input and drop port waveguides. We characterized the behaviour of complex eight-resonators SCISSOR devices in the case of microdisks and microrings resonators. In order to facilitate the characterization of these complex structures, a new set-up was also build up, which allowed us to study the scattered light of the resonators from the top as a function of the wavelength. Finally, with this technique, for the first time, we demonstrated the presence of EIT-like band even in complex structures. Extremely small differences between adjacent rings can give rise to the appearance of EIT states, delocalized over only few rings and with a great Q-factor and strong out-of-plane scattering.

The work in this thesis has been centred on the light emitting properties of silicon nanocrystals and the possible applications of this particular material platform to various topics ranging from bio-imaging to erbium ion sensitization. Silicon nanocrystals as bio-imaging agent have been investigated by employing colloidal dispersion of individual silicon nanocrystals where surface properties could be controlled to a great extent. By using a suitable functionalization scheme, high quality hydrophilic luminescent nanoparticles were produced. Using the improvements in the physical coating, bio-imaging on living cells (in vitro) was demonstrated showing that silicon nanocrystals have a great potential in bio-imaging and offer a promising alternative to commonly used fluorescence dyes. A part from being good light emitters, silicon nanocrystals could also amplify the light. This is a reason why the part of the work in this thesis has been dedicated to the investigation of silicon nanocrystals as a gain material. While most of the studies on this topic are concentrated on the nanocrystal surface as a driving mechanism behind the optical amplification, the work presented in this thesis concerns the study of a zero phonon (direct) optical transition as a possible source of optical amplification in this material system. To this scope, investigation of the dynamics of the system on a nanosecond time-scale and under high excitation conditions has been employed. Additional insight on ultrafast dynamics has been obtained by using optical cavities in the form of optically active free-standing micro-disk resonators. Finally, in the last part of this thesis a study of Er3+-doped Silicon-Rich-Oxide (SRO) materials and Er3+-doped SRO based devices is presented. This part of the work differs from the rest of the work reported in this thesis as is not focused on the light emitting properties of silicon nanocrystals but mostly on their non-radiative process engineering (energy transfer to erbium ions). Er3+ doped SRO opens the route towards compact waveguide amplifiers and lasers and allows for the possibility of electrical injection schemes, which are not realizable in standard erbium amplifiers used in EDFA for telecom applications. To that end, novel opto-electronic structures were proposed, modeled and manufactured and preliminary results of their performance were presented. The sensitization mechanism between silicon nanoparticles and erbium ions was studied and its complex nature was illustrated. Although, the acquired knowledge of physics involved was not sufficient for formulation of a complete working theory of the energy transfer process, some important physical aspects of this process have been elucidated paving the way towards its complete understanding.

Realizzazione di un sistema in concentrazione: inseguitore, ottica primaria, ricevitore. Al fine di massimizzare la potenza elettrica trasferita al carico, è stata posta particolare attenzione al tipo di connessioni fra le celle che costituiscono l'array.

There is a rising concern about energy and environment for future. Transition from current fossil fuels to green fuels and building of cleaner environment to lead sustainable life is at enormous task. Hydrogen gas is recognized as a clean fuel and may be a sustainable solution. Hydrogen can be directly used as clean fuel in fuel cells with no harmful by-products. Chemical hydrides with high hydrogen storage capacity in terms of gravimetric and volumetric efficiencies are the most promising candidates to supply pure hydrogen at room temperature. Among them, Ammonia Borane (NH3BH3, AB) and Sodium borohydride (NaBH4, SBH) have drawn a lot of interest as they are stable, non-flammable, and nontoxic. Large amount of pure hydrogen gas is released during the hydrolysis of these hydrides in presence of certain catalysts and the by-products are non-toxic, environmentally safe and can be recycled. Co based catalysts are considered as good candidates for catalyzed hydrolysis owing to their good catalytic activity, low cost and effortless synthesis. In favor of environmental concern, especially the air pollution (conversion of CO to CO2) and water pollutions (organic pollutants) are vital problems and there is a serious need to mitigate these problems. Cobalt (Co) based materials are with high catalytic activity for hydrolysis, organic pollutants degradation and CO oxidation. So, a single Co based catalysts as powders and as immobilized coatings prepared by chemical reduction method and pulsed laser deposition (PLD) were studied for hydrogen production by hydrolysis of AB and SBH and thin film coatings Co3O4 were studied for CO oxidation and organic pollutants degradation. On the basis of characterization results, the role of catalyst to enhance catalytic activity is discussed in hydrolysis, CO oxidation and pollutants degradation reactions. The stability and re-usability of these catalysts have also been investigated.

Catalysts are of great importance in many different fields, including the energy and the environmental sectors. It is important to produce them with simple preparation technique and to enhance the catalysts surface-to-volume ratio. The work undertaken in this thesis concerns the synthesis of nanostructures by Pulsed Laser Deposition (PLD) and R.F. sputtering deposition and the tailoring of their structures by varying deposition parameters. We synthesized Cobalt oxide nanoparticles (NPs) by PLD and studied the influence of the deposition parameters (i.e. substrate temperature, target-to-substrate distance and partial pressure of Oxygen in the chamber) on the final structure and crystalline phase of the NPs. The deposited NPs can be divided in two main categories: small NPs having a diameter of about 5 nm, and big NPs of size ranging from 50 to 400 nm. Depending on the value chosen for the deposition parameters, small NPs have CoO- or Co3O4 crystalline phase, and NPs can have a core/shell structure. The phase composition of the core and of the shell also vary according to the deposition conditions. We synthesized thin film of Co-B NPs by PLD. Depending on the energy density, the laser process is able to produce well-dispersed spherical Co NPs partially embedded within B-based film matrix in a single-step deposition. The small size, the polycrystalline nature of Co NPs, and the presence of Boron matrix is important for catalytic performance of the Co-B film. The catalytic activity of the Co-B has been tested in hydrolysis of chemical hydrides (ammonia borane and sodium borohydride). PLD deposition of C-film, to serve as support for Co-B NPs, was performed at different Ar pressures (from 10 to 50 Pa) to tailor film roughness in order to investigate the role of porous and irregular C- surface on supporting Co-B NPs acting as catalysts. The measured hydrogen generation rate attained with C-supported Co-B catalyst film is higher than both unsupported-Co-B film and conventional Co-B powder. Multilayer ITO/Cr-doped-TiO2 thin films have been synthesized by radiofrequency magnetron sputtering in order to sensitize TiO2 in visible light and to lower the charge recombination rate in the Cr-doped-TiO2. When the multilayer films were exposed to visible light, we observed that the photocurrent increases as function of the number of bilayers by reaching the maximum with 6-bilayers of ITO/Cr-doped- TiO2. The superior photocatalytic efficiency of the 6-bilayers film implies higher hydrogen production rate through water-splitting. Spontaneous growth of Lead nanowires (NWs) have been observed in composite Al-Pb film deposited by R.F. sputtering deposition. The parameters of deposition and the storage of the Al-Pb films after deposition has been changed in order to understand the growth process of NWs. Evolution of NWs growth was also observed inside a SEM chamber. We propose that a stress-driven mechanism and the corrosion occurring on the films surface in environment atmosphere are the cause of NWs growth.

A century after the prediction of the existence of gravitational waves by A. Einstein and after over fifty years of experimental efforts, gravitational waves have been detected at Earth directly. This result is a major achievement and opens new prospectives for the exploration of our universe. Gravitational waves carry different and complementary information about the source with respect to electromagnetic signals. In particular the first detection demonstrated the existence of stellar-mass black holes, binary systems of black holes and their coalescence. The detection was made by the LIGO instruments which are twin kilometer-scale Michelson interferometers in the US. These detectors represent the second generation of gravitational wave interferometers and, for the first time, they achieved the outstanding strain sensitivity of 10^(-23) Hz^(-1/2) between 90Hz and 400Hz. In the next months the LIGO network will be joined by another second generation detector: Advanced Virgo located near Pisa, Italy. The sensitivity of these advanced detectors is set by different noise sources. In particular, in the low frequency range (below 100Hz) major contributions come from thermal noises, gravity gradient noise and radiation pressure noise; instead, the high frequency band (above 100-200Hz) is dominated by shot noise. Quantum noise (radiation pressure and shot noise) is expected to dominate the detector sensitivity in the whole frequency band at the final target laser input power. To decrease the shot noise while increasing the radiation-pressure noise, or vice-versa, Caves \cite{Caves1981} proposed in 1981 the idea of the squeezed-state technique. The LIGO collaboration demonstrated for the first time in 2011 that the injection of a squeezed vacuum state into the dark port of the interferometer can reduce the shot noise due to the quantum nature of light. This result was achieved with the German-British interferometer GEO600 and was replicated in 2013 with the LIGO interferometer at Livingston. After these results, the LIGO collaboration have pursued further the research in the squeezed-state technique which is considered mandatory for third generation of ground based interferometric detectors. In 2013, the Virgo collaboration started developing the squeezed-state technique. The subject of my thesis is the realization of a prototype of frequency independent squeezed vacuum state source to be injected in Advanced Virgo. This prototype is developed in collaboration with other Virgo groups.

In this work we have proposed a PSi based flow through bio-sensor able to perform fast and sensitive real time analysis. The present work is summarized as: 1. We have presented a simple fabrication method for n-type PSi free-standing membranes with straight and smooth pores of up to ~100nm of diameter. 2. A two solution method is presented to fabricate free standing porous membranes. 3. Our process maintains a very good planarity of the interface as demonstrated by the fabrication of very thin and large area free standing membranes. No HF concentration gradient effect is noticed. 4. We found that membranes detachment does not require a high current burst but it is a self-limited process that involves a thin transitional layer at the bottom of the porous region. 5. Covalent functionalization of silicon surface is found to be suitable used to stabilize the porous surface and to act as intermediate layer for binding of other bio-molecules. 6. Role of non-specific binding in sensing efficiency is analyzed by comparing flow over and flow-through sensing for sensor fabricated on silicon substrate and sensor in freestanding nature. 7. Real time sensitivity per unit length of 0.0053degree/NaCl% and 0.0148degree/NaCl% was observed respectively for porous alumina and PSi membranes and PSi was found more suitable and sensitive for bio-sensing applications.

In the past several years there has been a growing commercial interest in Concentration PhotoVoltaics (CPV) thanks to its promise of low cost electrical power generation. While the technology of CPV using point-focus Fresnel-like optical elements is reaching maturity, the systems based on dense array receivers still need further scientific progress. This thesis explores the field of CPV applied to a parabolic concentrator prototype and to a dense array receiver made of multijunction solar cells. The solar concentrator, completely designed and built at the University of Trento, is characterized, in order to get the illumination distribution on the PV receiver. The non-uniformity in incident flux results in a current mismatch among cells and strongly impacts the system performance. In order to solve this issue, we have proposed a new type of electrical connection by fitting each cell of the array with an individual DC-DC converter. This method is shown to increase the power transfer efficiency with respect to classical series connection, at least for the tested illumination levels and unbalances. The other main problem with dense array systems is the reliability of the PV receiver, with special attention to the high thermal flux to be dissipated. Several types of water-cooled receivers have been built, with different material configurations that were previously studied with 3D thermal modeling. In particular the building of a multi-cell receiver has required the design of the insulation/interconnection between the cells, the tuning of the cell soldering and the realization of front contact connections.