A relevant contribution in the explosion of the silicon photonics derives from its nonlinear optics branch, also called nonlinear silicon photonics. This research area exploits the tight confinement of the light, which is allowed by the high contrast index in the silicon sub-micron-structures, and the nonlinearity of silicon to produce (fabricate, develop) novel active devices on the chip scale. Despite of the plenty of third order nonlinear optical phenomena, silicon lacks the second order nonlinearity, which is an essential component of nonlinear optics. In fact, due to the inversion symmetry of its crystalline structure, silicon is characterized by a zero bulk second order nonlinear susceptibility in electric-dipole approximation. Hence, this thesis had the general goal to demonstrate the possibility to perform an all optical experiment of frequency conversion by making use of the second order nonlinear response induced in strained silicon waveguides. The necessary condition to have a bulk second order nonlinear response in silicon is the breaking of its centrosymmetry. This can be obtained by deforming the crystalline structure, for example, by means of a mechanical strain. Based on this approach, this thesis presents and discusses the results achieved in the characterization of the mechanical properties and the strain-induced second order nonlinearity of silicon-on-insulator (SOI) waveguides mechanically strained by using a stressing cladding layer deposited on the waveguide. In particular, the mechanical characterization has been performed by micro-Raman spectroscopy allowing to reconstruct for the first time the two dimensional spatial distribution of the strain across the waveguide cross-section and study its inhomogeneity by varying the stress applied by the cladding overlayer. The second order nonlinear response and the influence of the strain field on it have been experimentally investigated through Second Harmonic Generation (SHG) experiments in transmission configuration and theoretically analyzed, pointing out the strict dependence of the second order nonlinear susceptibility on the extent and inhomogeneity of the strain field.

LISA is the proposed ESA-NASA space-based gravitational wave detector in the 0.1 mHz - 0.1 Hz band. LISA Pathfinder is the down-scaled version of a single LISA arm. In this thesis it is shown that the arm -- named Doppler link -- can be treated as a differential accelerometer, measuring the relative acceleration between test masses. LISA Pathfinder -- the in-flight test of the LISA instrumentation -- is currently in the final implementation and planned to be launched in 2014. It will set stringent constraints, with unprecedented pureness, on the ability to put test masses in geodesic motion to within the required differential acceleration of 3\times10^{-14} m s^{-2} Hz^{-1/2} and track their relative motion to within the required differential displacement measurement noise of 9\times10^{-12} m Hz^{-1/2}, at frequencies relevant for the detection of gravitational waves. Given the scientific objectives, it will carry out -- for the first time with such high accuracy required for gravitational wave detection -- the science of spacetime metrology, in which the Doppler link between two free-falling test masses measures the spacetime curvature. This thesis contains a novel approach to the calculation of the Doppler response to gravitational waves. It shows that the parallel transport of 4-vectors records the history of gravitational wave signals passing through photons exchanged between an emitter and a receiver. In practice, the Doppler link is implemented with 4 bodies (two test masses and two spacecrafts) in LISA and 3 bodies (two test masses within a spacecraft) in LISA Pathfinder. Different non-idealities may originate in the measurement process and noise sources couple the motion of the test masses with that of the spacecraft. To compensate for such disturbances and stabilize the system a control logic is implemented during the measurement. The complex closed-loop dynamics of LISA Pathfinder can be condensed into operators acting on the physical coordinates describing the relative motion. The formalism can handle the couplings between the test masses and the spacecraft, the sensing noise, as well as the cross-talk, and allows for the system calibration. It suppresses the transients in the estimated residual acceleration noise between the test masses. The scope of system identification is indeed the calibration of the instrument and the compensation of different effects. After introducing a model for LISA Pathfinder along the optical axis and an example of cross-talk from other degrees of freedom to the optical axis, this thesis describes some data analysis procedures applied to synthetic experiments and tested on a realistic simulator provided by ESA. The same procedures will also be adopted during the mission. Those identification experiments can also be optimized to get an improvement in precision of the noise parameters that the performances of the mission depend on. This thesis demonstrates the fundamental relevance of system identification for the success of LISA Pathfinder in demonstrating the principles of spacetime metrology needed for all future space-based missions.

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This thesis work covers both classical and quantum aspects of nonlinear propagation of photons in nanophotonic Silicon waveguides. The work has been carried out within the framework of the project SIQURO, which aims to bring the quantum world into integrated photonics by using the Silicon platform and, therefore, permitting in a natural way the integration of quantum photonics with electronics. The research towards on chip bright quantum sources of photon pairs has been done by investigating Multi Modal Four Wave Mixing in micrometer-size waveguides, thus exploiting the large third order nonlinearity of Silicon. The possibility to induce second order nonlinearities by straining its unit cell has been also analyzed through the study of the electro-optic effect. This has been done with the aim to promote Silicon as a platform for the integration of quantum sources of entangled photons based on Spontaneous Parametric Down Conversion. New quantum interference effects have been reported in a free space unbalanced Mach Zehnder interferometer asymmetrically excited by colour entangled photon pairs. Innovative designs of integrated quantum circuits have been proposed, which extend the capabilities of the quantum circuits demonstrated so far and provide additional functionalities. This work represents a step forward to the realization of self subsistent integrated devices for quantum enhanced measurement, quantum computation and quantum crypthography.

This thesis presents experimental work developing silicon nanocrystal based light emitting devices for silicon photonics. The chapters are organized as follows: In chapter 2, fabrication and characterization of silicon nanocrystal based devices are presented. In collaboration with Intel Corporation and Bruno Kessler Foundation and thanks to the support of European Commission through the project No. ICT-FP7-224312 HELIOS and through the project No. ICT-FP7-248909 LIMA, it is shown that layers and devices containing silicon nanocrystals can be formed in a production silicon-fab on 4 and 8 inch silicon substrates via PECVD and subsequent thermal annealing. Devices produced by single layer and multilayer deposition are studied and compared in terms of structural properties, conduction mechanisms and electroluminescence properties. Power efficiency is evaluated and studied in order to understand the relation between exciton recombination and electrical conduction. A band gap engineering method is proposed in order to better control carrier injection and light emission in order to enhance the electroluminescence power efficiency. In chapter 3, the power efficiency of silicon nanocrystal light-emitting devices is studied in alternating current regime. An experimental method based on impedance spectroscopy is proposed and an electrical model based on the constant phase element (CPE) is derived. It is, then, given a physical interpretation of the electrical model proposed by considering the disordered composition of the active material. The electrical model is further generalized for many kinds of waveforms applied and it is generalized for the direct current regime. At the end, time-resolved electroluminescence and carrier injection in alternate current regime are presented. In chapter 4, erbium implanted silicon rich oxide based devices are presented. The investigation of opto-electrical properties of LED in direct current and alternate current regime are studied in order to understand the injection mechanism and estimate the energy transfer between silicon nanocrystals and erbium. At the end a device layout and process flow for an erbium doped silicon nanocrystal based laser structure are shown. In chapter 5, some other applications of silicon nanocrystal are presented. An example of all-silicon solar cell is shown. The photovoltaic properties and carrier transport of silicon nanocrystal based solar are studied. At the end, the combination of emitting and absorbing properties of silicon nanocrystal based LED are used to develop an all-silicon based optical transceiver.

Porous silicon (Psi) and nanocellulose (NC) hydrogels are nanostructured materials with several properties that make them promising for drug delivery applications. In this work, Î2-carotene (BC) and clofazimine (CFZ) are used as model molecules to investigate the physical and chemical processes governing the interactions of hydrophobic molecules with both inorganic (Psi) and organic (NC) nanostructured carriers. Despite the large number of advantages, Psi does not perform well as carrier for BC, since it stimulates the molecule degradation even if its surface is carefully passivated. Furthermore, during the release experiments, BC tends to nucleate on Psi surface forming aggregates whose dissolution is much slower than the BC molecules release, thus they negatively impact on the control over the drug release. On the other hand NC hydrogels do not pose heavy issues to the release of lipophilic drugs, provided that a suitable surfactant (either Tween-20 or Tween-80) mediates the molecule solvation and its subsequent release into aqueous media. Moreover, NC gels protect BC from degradation much better than its storage in freezer or in organic solvent, making these carriers interesting for DD.

This thesis work presents the results of experimental studies on the gas transport properties of three polymer-based membrane systems: (i) amine-modified epoxy resins, (ii) epoxy resin nanocomposites containing Few Layer Graphene (FLG) nanoplatelets as dispersed fillers and (iii) nanocellulose-based membranes. The gas transport properties of the present membrane systems were studied by gas phase permeation techniques changing sample temperature and penetrant molecules; results were discussed in the framework of the free volume theory of diffusion, using information on the samples’ free volume structure as experimentally obtained by Positron Annihilation Lifetime Spectroscopy (PALS). Results evidenced that the transport properties of small penetrant molecules are controlled by the membranes’ free volume structure, which determines, in fact, the penetrant diffusion kinetics. The free volume of epoxy resins was changed by changing their crosslink density but maintaining same chemical environment for penetrant molecules: it was observed that, reducing the free volume structure, the gas diffusivity decreases but no relevant changes in the gas solubility occurred. The experimentally obtained fractional free volume values permitted to reproduce the measured diffusivity values and their variation with temperature, using equations provided by the free volume theory of diffusion. Increasing the amount of FLG fillers in epoxy-based nanocomposites, we observed a progressive gas permeability decrease, which was accompanied by a progressive reduction of their free volume. This correlation was attributed to the formation of constrained, gas-impermeable polymer regions at the filler-matrix interfaces. The thickness of these regions was evaluated by the reduction of the nanocomposites’ fractional free volume with respect to the free volume of the pure polymer matrix; its value permits to reproduce quantitatively the experimental permeation data of the nanocomposites at all examined temperatures, filler concentrations and test gases. Few micrometers thick nanocellulose films deposited on polylactic acid substrates act as impermeable barriers for CO2, O2, and N2 and reduce the D2 (deuterium) and He permeation flux by a factor of approx. 10^3. Penetrant transport through this biopolymer is controlled by the solution-diffusion mechanism and barrier properties are due to the extremely low penetrant diffusivity. The free volume in the nanocellulose coatings consists of interconnected elongated cavities with sub-nanometer cross-sectional size where the selective transport of the small size penetrants is due to sieving effects. D2 and He diffusion has thermally activated character and occurs in configurational regime.

Optical biosensors, and in particular label-free optical biosensors have become one of the most active and attractive fields within the biosensing devices. The portability and the possibility to set free from the laboratory settings gave a new hint for integrated photonic biosensors development and use in numerous applications. Integrated photonic sensors have shown very promising results, and in particular, devices like WGM resonators and interferometers are showing high sensitivities and miniaturization abilities, which allow the realization of an integrated complete lab-on-chip device. The main goal of this thesis is the development of an optical biosensor for the fast and comprehensive detection of carcinogenic Aflatoxin M1 (AFM1) mycotoxin. The acceptable maximum level of AFM1 in milk according to European Union regulations is 50 ng/L equivalent to 152 pM for the adults and 25 ng/L equivalent to 76 pM for the infants, respectively. Within a European Project named SYMPHONY, we develop an integrated silicon-photonic biosensor based on the optical microring resonators (MRR) and the asymmetric Mach-Zehnder Interferometers (aMZI). The sensing is performed by measuring the resonance wavelength shift in the MRR transmission or the phase shift of aMZI caused by the binding of the analyte to the ligand immobilized on the sensor surface. The experimental characterization of the bulk refractometric sensing of the devices is performed in a continuous flow. This characterization assesses the high resolution of both device types, which are able to resolve variations in the refractive index of the liquids with a limit of detection down to 10E-6 refractive index units (RIU). Furthermore, the SYMPHONY sensor optimization based on the Fab' and DNA-aptamer functionalization strategies is realized. It is therefore demonstrated, that the Fab' functionalization strategy provides more reproducible results with respect to the DNA-aptamer one. However, for both strategies, the specificity of the sensor functionalization to detect AFM1 molecules is achieved with respect to non-specific Ochratoxin molecules at high concentrations. In the final stage of the SYMPHONY project, the Fab'-based functionalized aMZI sensor is tested with real milk samples (eluates) prepared in the SYMPHONY system that consists of the three main modules: the defatting module, the concentrator module and the sensor module. The system calibration yields the minimum concentration of AFM1 at 40 pM to be detectable. The detection of the ligand-analyte binding in real-time enabled the study of the kinetics of the binding reaction, and we measured for the first time the kinetic rate constants of the Fab'-AFM1 interaction with our sensors. Finally, a MRR based affinity biosensor is developed dedicated to the biotinylated BSA - anti-biotin binding study. An affinity constant of 10E6 1/M is measured. The sensor is successfully regenerated up to eight times by applying a longer incubation period.

X-ray photon correlation is used to probe the dynamics of the strong glass former boron trioxide and of a series of alkali borate glasses, (M2O)x(B2O3)1-x where M is the alkali modifier (M=Li, Na and K). The decay times τ of the obtained correlation functions in B2O3 are consistent with visible light scattering results and independent of the incoming beam intensity in the undercooled liquid phase; are instead temperature independent and show a definite dependence on the X-ray beam intensity in the glass. We are therefore witnessing an atomic dynamics induced by the X-ray beam. Furthermore, we clearly demonstrate that the value of τ is related to absorption by investigating a series of alkali borate glass with the same molar ratio and as a function of the alkali modifier. Finally, we highlight the role played by the structure in the X-ray induced dynamics by studying a series of lithium borate glasses with different molar ratios, and by investigating the wave vector dependence. Despite the observed dynamics is clearly intensity dependent, we obtain very interesting information on glasses not available with other experimental techniques.

In this thesis, second order optical nonlinearities in silicon waveguides are studied. At the beginning, the strained silicon platform is investigated in detail. In recent years, second order nonlinearities have been demonstrated on this platform. However, the origin of these nonlinearities was not clear. This thesis offers a clear answer to this question, demonstrating that this nonlinearity does not originate on the applied strain, but on the presence of trapped charges that induce a static electric field inside the waveguide. Based on this outcome, a way to induce larger electric fields in silicon waveguide is studied. Using lateral p-n junctions, strong electric fields are introduced in the waveguides, demonstrating both electro-optic effects and second-harmonic generation. These results, together with a detailed modeling of the system, pave the way through the demonstration of spontaneous parametric down-conversion in silicon.