The molecular structure of solvent and adsorbates at naturally occurring solid–liquid interfaces is a feature that defines much of the chemistry of the natural environment. Because of its importance, this chemistry has been studied for many decades. More recently, nonlinear optical techniques have emerged as a valuable tool for non-invasive investigation of environmental interfaces, in part because of their inherent surface specificity. Solid–aqueous interfaces are complex regions in which chemical and electrostatic forces combine to drive adsorption processes. Second-harmonic generation and sum-frequency generation (SFG) spectroscopies have been employed by many groups to investigate water structure at these interfaces over a range of pH and ionic strength environments. In this thesis, I report results of further investigation of water structure adjacent silica, fluorite, polystyrene, and poly (methyl methacrylate) surfaces in the presence of varying concentrations of Na+ and Cl– . A model is developed to describe the SFG response from the fused silica–solution interface as ionic strength is increased. This model reveals both details of interfacial water structure and the interplay between second- and third-order optical responses present at charged interfaces. In context of this model, water structure at the three other interfaces is discussed. Knowledge of the phase of the SFG response provides additional surface structural information that can be related to the polar orientation of a molecule or functional group, for example, a flip in the orientation of water at an interface. Methods to capture the phase information at exposed interfaces are well established, but buried interface phase measurement remains a challenge. Therefore, I focused on development of a systematic method for buried interface phase measurement. In this thesis, I demonstrate improvements in the precision and accuracy of two phase-sensitive SFG techniques for measurement of exposed interfaces. Results from efforts to extend the theory to the buried interface are presented, along with an examination of the challenges encountered along the way. / Graduate

Inversion Recovery (IR) is a powerful tool for contrast manipulation in Mag- netic Resonance Imaging (MRI). IR can provide strong contrast between tissues with different values of T1 relaxation times. The tissue magnetization stored at an IR image pixel can take positive as well as negative values. The corresponding polarity information is contained in the phase of the complex image. Due to numerous factors associated with the Magnetic Resonance (MR) scanner and the associated acquisition system, the acquired complex image is modulated by a spatially varying background phase which makes the retrieval of polarity information non-trivial. Many commercial MR scanners perform magnitude-only reconstruction which, due to loss of polarity information, reduces the dynamic contrast range. Phase sensitive IR (PSIR) can provide enhanced image contrast by estimating and removing the background phase and retrieving the correct polarity information. In this thesis, the background phase of complex MR image is modeled using a statistical model based on Markov Ran- dom Fields (MRF). Two model optimization methods have been developed. The first method is a computationally effcient algorithm for finding semi-optimal solutions satisfying the proposed model. Using an adaptive model neighborhood, it can recon- struct low SNR images with slow phase variations. The second method presents a region growing approach which can handle images with rapid phase variations. Ex- perimental results using computer simulations and in vivo experiments show that the proposed method is robust and can perform successful reconstruction even in adverse cases of low signal to noise ratios (SNRs) and high phase variations.

Fluorescence lifetime determination and allied studies find application in spectroscopy in general and fiber optic biosensors in particular. Instruments and sensors cited in literature however use open loop, intensity based techniques with sophisticated detectors and components. We propose phase sensitive signal processing schemes to estimate the fluorescence lifetime using simple detectors and components, without compromising on accuracy. The performance of the schemes proposed is analysed and contrasted from a communications (signals and systems) point of view. The resolution and sensitivity limits imposed in processing the signal, by systematic errors and additive noise, are derived for the schemes suggested. It is found that systematic errors impose a phase resolution limit of about 2°. We then study the suitability of different detectors and channels for application in phase sensitive fluorescence biosensors we analyse the effect of systematic limitations as well as additive noise, in the detection/transmission process, from the point of view of the components used. Certain fundamental limits of operation in terms of excitation intensities are derived for different detector-channel combinations, with a view to obtain a given resolution. A photodiode used with a fiber bundle is found to be sufficient for accurate phase read outs with 10"4 radians resolution. A PMT used in conjunction with a multimode fiber serves as a very good device for microsensing applications Lastly, the biosensor for oxygen sensing, the ruthenium complex, is studied for standardisation of the sensor. We examine the quenching of fluorescence, the repeatability and reusability of the sensor, the stability of the instrument and such.

In this thesis, the work focuses on developing distributed optical fiber vibration sensors based on phase-sensitive optical time domain reflectometry (Φ-OTDR). Three works have been accomplished to improve the performances of Φ-OTDR for distributed vibration sensing. Firstly, Φ-OTDR based on a polarization diversity scheme is demonstrated to mitigate the polarization mismatch effect occurring in traditional systems. A theoretical analysis is performed in different polarization cases corresponding to coherent and polarization diversity detection. Φ-OTDR based polarization diversity shows a great potential in the multi-events sensing application. Two vibration events are simultaneously detected and their signal to noise ratios are improved by 10.9 dB and 8.65 dB, respectively, compared to the results obtained by a conventional coherent scheme. Intensity fluctuation in a phase-sensitive optical-time domain reflectometry (Φ-OTDR) system caused by stochastic characteristics of Rayleigh backscattering has limited relative vibration strength measurement, which is proportional to dynamic strain. A trace-to-trace correlation coefficient is thus proposed to quantify the Φ-OTDR system stability and a novel approach of measuring the dynamic strain induced by various driving voltages of lead zicronate titanate (PZT) is demonstrated. Piezoelectric vibration signals are evaluated through analyzing peak values of the fast Fourier transform spectra at fundamental frequency and high-order harmonics based on Bessel functions. Experimental results show high correlation coefficients and good stability of our Φ-OTDR system, as well as the small measurement uncertainty of measured peak values. To reduce the intra-band noise caused by the finite extinction ratio of optical pulses, Φ-OTDR based on high extinction ratio generation is studied. Two methods are developed for achieving high extinction ratio of optical pulse generation. One of the approaches is to synchronize two cascaded electro-optic modulators to achieve high extinction ratio operation. The other one is to use the nonlinear optical fiber loop mirror as an optical switch to suppress the continuous wave portion of optical pulse. The sensing range of 1.8 km and 8.4 km with corresponding spatial resolution of 0.5 m and 2 m have been demonstrated based on cascaded two electro-optic modulators and nonlinear optical fiber loop mirror setup, respectively.

Accurate, non-invasive determination of multiphase fluids distribution in reservoir rock can greatly help the evaluation and monitoring of oil reservoirs. This laboratory thesis research, carried but utilizing the biomedical engineering concepts and measurement facilities, is an important step in developing a novel magnetic field-based oil detection method. When paramagnetic nanoparticles are either adsorbed oil/water interface or dispersed in a fluid phase in reservoir rock pores, and exposed to external magnetic field, the resultant particle movements displace the interface. Interfacial tension acts as a restoring force, leading to interfacial fluctuation and a pressure (sound) save. As the first step, the motion of the interface between a suspension of paramagnetic nanoparticles and a non-magnetized fluid (placed in a cylindrical dish) is measured by phase-sensitive optical coherence tomography (PS-OCT). Experiments were carried out with a range of iron-oxide nanoparticles that were synthesized and surface-coated by our Chemical Engineering collaborators. The numerical method was improved to be volume conserving, and extended to 3D, for more quantitative matching. The measurements of interfacial motion by PS-OCT confirm theoretical predictions of the frequency doubling and importance of material properties, such as the particle size, for the interface displacements. The relative densities of the fluid phase(air/aqueous and dodecane/aqueous) strongly affect the interfacial displacement. Next, the acoustic responses to the external magnetic oscillation, from the rock samples into which different aqueous dispersions of nanoparticles were injected, were measured in terms of the magnetic frequency, nanoparticle concentration, and other process parameters. Subsequently, the PS-OCT displacements in response to the external magnetic oscillation, from the rock samples into which different aqueous dispersions of nanoparticles were injected, were also measured in terms of the magnetic frequency, nanoparticle concentration, and other process parameters. Conclusions and the recommendations for further study are then given. / text

No description available.

La capacité et les performances des systèmes à fibres optiques et photoniques dépendent fortement du bruit et des non-linéarités des amplificateurs optiques. Dans ce contexte, les amplificateurs paramétriques à fibre optique (PS-FOPA), reposant sur le mélange à quatre ondes dans les fibres optiques, surpassent les amplificateurs conventionnels insensibles à la phase. En effet, leur sensibilité à la phase peut être exploitée pour l'amplification sans bruit et al compensation de la distortion non-linéaire. En conjonction avec leur large spectre de gain et d'autres fonctionnalités telles que la conversion de longueur d'onde, ils sont considérés comme des candidats prometteurs pour la prochaine génération d'amplificateurs optiques pour les communications et le traitement de signal tout optiques.Le PS-FOPA est classiquement décrit par les équations d'ondes couplées, dérivées de l'équation de Schrödinger non-linéaire qui ne contiennent que trois ou quatre ondes en interaction. Cependant, dans un cas plus général, l'apparition de fréquences supplementaires d’ordre plus élevé affectera inévitablement la sensibilité en phase.L’objectif de cette thèse est d'étudier de manière approfondie les propriétés non-linéaires, en termes de gain et de sensibilité en phase d'un PS-FOPA dégénéré à double pompe pour différentes configurations. Une analyse numérique plus précise est obtenue en utilisant le modèle à 7 ondes qui incorpore les ondes supplémentaires issues de processus de mélange à quatre ondes d’ordre élevé. Ce modèle permet de donner une interprétation physique plus précise des interactions multi-ondes en fonction des conditions d'accord de phase, révélant les relations sous-jacentes entre la dispersion et la sensibilité de phase. De plus, la capacité de régénération simultanée de phase et d'amplitude d'un PS-FOPA basique est évaluée pour l'optimisation globale. Il permet d'exploiter pleinement la capacité potentielle d'un PS-FOPA de base agissant comme un bloc de construction fondamental des futures fonctionnalités tout optiques. L’approche basée sur ce modèle permet une optimisation orientée vers l’application et revêt une importance particulière pour la conception et l'optimisation de tels PS-FOPAs dans divers scénarios. / The capability and performance of the widely deployed fiber-optic and photonic systems strongly depend on the noise and nonlinearities of the optical amplifiers. In this context, phase-sensitive fiber-optic parametric amplifiers (PS-FOPAs), relying on four-wave mixing in optical fibers, outperforms conventional phase-insensitive amplifier thanks to the unique phase-sensitivity that can be exploited for noiseless amplification and mitigation of the nonlinear impairment. In conjunction with the vast gain spectrum and other functionality such as wavelength conversion, they have been regarded as a promising candidate for the next generation optical amplifiers towards all-optical communication and processing.The PS-FOPA is conventionally described by the fundamental coupled wave equations derived from the nonlinear Schrödinger equation that contains only three or four interacting waves. However, for a more general case, the emergence of high-order waves will inevitably affect the phase-sensitivity. The objective of this thesis aims at the thorough investigation of the nonlinear properties in terms of the gain properties and the phase sensitivities with respect to different configurations of a dual-pump signal-idler degenerate PS-FOPA. The more accurate numerical analysis is obtained by using the 7-wave model that incorporates the first order high-order waves stemming from the high-order four-wave mixing processing. This model permits to assess a more precise physical interpretation of the multi-wave interactions based on phase matching conditions, revealing the underlying relations between the dispersion and the phase-sensitivity. Moreover, the simultaneous phase and amplitude regenerative capability of a basic PS-FOPA is evaluated for the overall optimization. It allows fully exploiting the potential ability of a basic PS-FOPA acting as a fundamental building block of the future all-optical functionalities. The analysis approach based on this model permits application-oriented optimization and is of particular guiding significance for design and optimization of PS-FOPA in various scenarios.

All-optical signal processing techniques for phase-shift keyed (PSK) systems were developed theoretically and demonstrated experimentally. Nonlinear optical effects in fibers, in particular four-wave mixing (FWM) that occurs via the ultra-fast Kerr nonlinearity, offer a flexible framework within which numerous signal processing functions can be accomplished. This research has focused on the regenerative capabilities of various FWM configurations in the context of processing PSK signals. Phase-preserving amplitude regeneration, phase regeneration, and phase-regenerative wavelength conversion are analyzed and demonstrated experimentally. The single-pump phase-conjugation process was used to regenerate RZ-DPSK pulse amplitudes with different input noise distributions, and the impact on output phase characteristics was studied. Experiments revealed a limited range over which amplitude noise could effectively be suppressed without introduction of phase noise, particularly for signals with intensity pattern effects. Phase regeneration requires use of phase-sensitive amplification (PSA), which occurs in nonlinear interferometers when the pump and signal frequencies are degenerate (NI-PSA), or in fiber directly through single-stage (degenerate) or cascaded (non-degenerate) FWM processes. A PSA based on a Sagnac interferometer provided the first experimental demonstration of DPSK phase and amplitude regeneration. The phase-regenerative capabilities of the NI-PSA are limited in practice by intrinsic noise conversion (amplitude to phase noise) and to a lesser extent by the requirement to modulate the pump wave to suppress stimulated Brillouin scattering (SBS). These limitations are relaxed in novel materials with higher SBS thresholds and nonlinearities. Degenerate FWM provides PSA in a traveling-wave configuration that intrinsically suppresses the noise conversion affecting the NI-PSA, while providing stronger phase-matched gain. Experiments confirmed superior phase-regenerative behavior to the NI-PSA with simultaneous reduction of amplitude noise for NRZ-DPSK signals. Phase-regenerative wavelength conversion (PR-WC) provides the regenerative properties of PSA at a new wavelength, and was proposed and demonstrated for the first time in this research. The parallel implementation of two FWM processes, phase-conjugation and frequency conversion, provides two idlers which exhibit interesting and useful regenerative properties. These were investigated theoretically and experimentally. Ideal phase-regenerative behavior is predicted when the contributing FWM processes are equally phase-matched, which can be maintained over any interaction length or wavelength shift provided the pump powers are properly adjusted. Depleted-pump regime PR-WC provides simultaneous phase and amplitude regeneration. Experiments confirmed regenerative behavior for wavelength shifts of the idlers up to 5 nm. Two techniques for phase regeneration of 4-level PSK signals were developed and evaluated. The first is based on parallel operation of PSAs suitable for processing 2-level PSK signals, where phase projection and regeneration are combined to recover the input data. Analysis of this scheme outlined the conditions required for effective phase regeneration and for practical implementation using known PSAs. A novel process based on FWM (parallel phase-conjugation followed by PSA) was developed and analyzed, and demonstrated using numerical simulations. These studies provide a basis for further work in this area.

Resolver, due to its reliability and durability, has been used for the aim of shaft position sensing of military rotary systems such as tank turrets and gun stabilization platforms for decades. Ready-to-use resolver-to-digital converter integrated circuits which convert the resolver signals into position and speed measurements are utilized in servo systems most commonly. However, the ready-to-use integrated circuits increase the dependency of the servo system to hardware components which in turn decrease the efficiency and flexibility of the servo system for changing system structures such as for changing resolver carrier frequency or changing position and speed sensors. The proposed solution to increase the efficiency and flexibility of the servo system is a software-based resolver-to-digital converter which does not require aforesaid special hardware components and presents a complete software-based solution for the conversion. The proposed software-based resolver-to-digital converter makes use of common programmable hardware v components, that is, FPGA and DSP which form the heart of the servo controller technology in recent years. The proposed structure for the conversion has three components. The first component is the signal conditioner which minimizes the disturbances coming from the resolver signals as harmonic distortions and noise. The second component, the phase-sensitive demodulator, as the name implies, is responsible for phase-sensitive demodulation of resolver signals. The third component is the estimator filter. In order to determine the optimal estimator filter, five different estimator filters with the aforesaid two components are implemented in ASELSAN&rsquo / s stabilized gun system STAMP and they are compared in terms of both estimation performance and computational complexity. The implemented filters include nonlinear observer type filter which is already proposed in the literature for resolver conversion, tracking differentiator adapted to resolver conversion and kalman filters adapted to resolver conversion in different forms such as linear kalman filter, extended kalman filter and unscented kalman filter. At the end of the study, stability and sensitivity analyses are also performed for the proposed system.

The master’s thesis describes known methods of signal measurement using principle of synchronous detection. Various methods are presented, their principles are examined and the problems when using them are analyzed. Further, procedures for reduction of adverse effects are described also. Second part of this thesis is focused on the instrument design. The instrument is intended for detection and processing of the output signals in a given optometric system. The proposed device is designed to operate on the principle of synchronous detection method using a vector signal evaluation. Advantages and disadvantages are discussed below.