Optically pumped semiconductor vertical external cavity surface emitting lasers (VECSEL) were first demonstrated in the mid 1990's. Due to the unique design properties of extended cavity lasers VECSELs have been able to provide tunable, high-output powers while maintaining excellent beam quality. These features offer a wide range of possible applications in areas such as medicine, spectroscopy, defense, imaging, communications and entertainment. Nowadays, newly developed VECSELs, cover the spectral regions from red (600 nm) to around 5 µm. By taking the advantage of the open cavity design, the emission can be further expanded to UV or THz regions by the means of intracavity nonlinear frequency generation. The objective of this dissertation is to investigate and extend the capabilities of high-power VECSELs by utilizing novel nonlinear conversion techniques. Optically pumped VECSELs based on GaAs semiconductor heterostructures have been demonstrated to provide exceptionally high output powers covering the 900 to 1200 nm spectral region with diffraction limited beam quality. The free space cavity design allows for access to the high intracavity circulating powers where high efficiency nonlinear frequency conversions and wavelength tuning can be obtained. As an introduction, this dissertation consists of a brief history of the development of VECSELs as well as wafer design, chip fabrication and resonator cavity design for optimal frequency conversion. Specifically, the different types of laser cavities such as: linear cavity, V-shaped cavity and patented T-shaped cavity are described, since their optimization is crucial for transverse mode quality, stability, tunability and efficient frequency conversion. All types of nonlinear conversions such as second harmonic, sum frequency and difference frequency generation are discussed in extensive detail. The theoretical simulation and the development of the high-power, tunable blue and green VECSEL by the means of type I second harmonic generation in a V- cavity is presented. Tens of watts of output power for both blue and green wavelengths prove the viability for VECSELs to replace the other types of lasers currently used for applications in laser light shows, for Ti:Sapphire pumping, and for medical applications such as laser skin resurfacing. The novel, recently patented, two-chip T-cavity configuration allowing for spatial overlap of two, separate VECSEL cavities is described in detail. This type of setup is further used to demonstrate type II sum frequency generation to green with multi-watt output, and the full potential of the T-cavity is utilized by achieving type II difference frequency generation to the mid-IR spectral region. The tunable output around 5.4 µm with over 10 mW power is showcased. In the same manner the first attempts to generate THz radiation are discussed. Finally, a slightly modified T-cavity VECSEL is used to reach the UV spectral regions thanks to type I fourth harmonic generation. Over 100 mW at around 265 nm is obtained in a setup which utilizes no stabilization techniques. The dissertation demonstrates the flexibility of the VECSEL in achieving broad spectral coverage and thus its potential for a wide range of applications.

La prise en compte des couplages dynamiques entre les différents organes constituant une turbomachine s’inscrit dans le processus d’optimisation des designs moteur. L’amélioration des performances des turboréacteurs passe souvent par l’utilisation d’architectures multi-rotors. Dans le contexte des moteurs avec une architecture bi-rotor, des résultats d’essais expérimentaux montrent qu’il est nécessaire de considérer, dès la conception, l’influence de la dynamique de l’arbre Haute Pression (HP) sur les aubages de l’arbre Basse Pression (BP). Dans ce cadre d’étude, un premier modèle simplifié de bi-rotor aubagé est développé dans le repère tournant lié au rotor BP. Ce modèle est composé de deux rotors modélisés par des équivalents poutres - masses - ressorts et d’une roue aubagée constituée d’aubes souples modélisées par des poutres encastrées sur un disque rigide. Desnon-linéarités de type jeu radial avec contact au niveau des paliers sont également considérées et la réponse des aubes soumises à des excitations multi-fréquentielles de type balourd BP et HP est analysée. La présence de non-linéarités dans le système conduit à mettre en oeuvre des algorithmes adaptés, basés sur des techniques de résolution dans le domaine fréquentiel avec l’évaluation des efforts non-linéaires dans le domaine temporel. Afin d’avoir une meilleure description de la dynamique de la roue aubagée, une méthode spécifique de couplage est proposée, permettant de coupler un modèle réduit de roue aubagée 3D à un modèle simplifié de bi-rotor. Une démarche adaptée à la modélisation de la roue aubagée en symétrie cyclique est implémentée afin de considérer des non-linéarités de type contact en tête d’aube. La méthode de couplage proposée est ensuite illustrée sur un exemple simple puis validée dans un cadre linéaire et non-linéaire. Enfin, cette méthode de couplage est appliquée au cas d’une structure industrielle, constituée d’un modèle d’ensemble simplifié représentatif d’un moteur et d’un modèle éléments finis d’une roue de turbine BP. Les résultats obtenus mettent en évidence le couplage entre la dynamique d’ensemble et la dynamique de la roue aubagée et permettent de prédire la réponse non-linéaire des aubes de turbine BP en présence d’une excitation multi-fréquentielle, dans des configurations de co-rotation et de contra-rotation. / The design and optimization process of high efficiency turbomachinery has become a major challenge and a topical issue at both industrial and research levels. Performance improvement has motivated the use of multi-shaft architecture in engines. In the context of dual-shaft aircraft engines, the interaction between dynamics occurring within shafts and bladed disks seems to play an important role at the design stage. The present research work deals with the coupling of these components involving several unbalances in the dynamic response of blades. Within this framework, a simplified analytical model of a bladed dual-shaft developed in the rotating frame is presented. The dual-shaft is modelled by spring - mass- beam systems and connected to a bladed disk composed of a set of flexible blades modelled by Euler-Bernoulli beams clamped in a rigid disk. Nonlinearities coming from bearings are also considered and modelled as a radial clearance and contact stiffness. Considering nonlinearities requires the implementation of dedicated algorithms and specific resolution techniques in the frequency domain as well as the computation of nonlinear forces in the time domain. The nonlinear response of blades subjected to unbalances excitations is investigated and analysed. To have a finer description of the bladed disk dynamics, a specific coupling method is proposed allowing to connect a bladed disk finite element model with the simplified dual-shaft model. A cyclic symmetry approach well-suited to the nonlinear dynamics of bladed disks is developed in order to consider blade tip contact nonlinearities. Performances of the proposed method are illustrated through an academic example and validated in both linear and nonlinear settings. Eventually, the coupling technique is applied to a complex industrial case involving a classical simplified dual-shaft model and a finite element model of the low pressure turbine bladed disk. Numerical results clearly demonstrate the coupling between dynamics and enable to predict the nonlinear response of low pressure turbine blades to several unbalances, for both co-rotating and counter-rotating engines.

In the field of second harmonic (SH) generation most studies have been concerned with maximizing conversion efficiencies, generally achievable at the phase matching (PM) condition. Outside of the PM the conversion efficiency drastically decreases. This has caused that the possible working conditions out of PM to remain largely unexplored. In this thesis work we initiated a systematic study of the SH behavior in under conditions of large phase mismatch. When a pump pulse crosses an interface between a linear and a nonlinear medium there are always two generated SH components. These components may be understood on the basis of the mathematical solution of the inhomogeneous wave equations at the SH frequency. The homogeneous (HOM) solution is a component with wave-vector k(2¿) as expected from the dispersion relation and exchanges energy with the pump until the inevitable walk-off. The inhomogeneous (INH) solution is a component with a wave-vector 2k(¿), twice the pump wave-vector, and travels locked to the pump pulse. We divide our work in two parts, one for each generated component. Inhomogeneous component. We start a systematic study of the behavior of the generated INH component, phase locked to the pump. The consequences of phase locking (PL) can guide us towards new scenarios by allowing working conditions hitherto assumed inaccessible for absorbing materials. We show that while the HOM component travels with the group velocity given by material dispersion, the IHN component is captured by the pump pulse and experiences the same effective dispersion of the pump. It does not follow the PM condition. It naturally follows that the suppression of absorption at the SH wavelengths will occur if the pump is tuned to a region of transparency. We extended the same theory for the generated third harmonic (TH). We then studied the surprising behavior of SH and TH INH components with frequencies above the absorption edge when the material is placed inside a cavity resonant only at the fundamental frequency. We have shown that the PL mechanism not only inhibits absorption but also fosters the enhancement of harmonic generation by several orders of magnitude compared to the no-cavity case. Finally, we tested the INH SH and TH behaviors in metallic frequency regime of material. Homogeneous component. The techniques used to PM the nonlinear interaction enable efficient nonlinear interactions but drastically limit the spectral bandwidth of the nonlinear optical process, making the designed frequency converter only suitable for a fixed input wavelength and single interaction only. It has been shown that the use of disordered nonlinear media relaxes the PM condition thus allowing one to achieve relatively efficient broad bandwidth regime of the frequency conversion. An example of a quadratic nonlinear medium with a disordered domain structure is an un-poled Strontium Barium Niobate (SBN) crystal. It is composed of a system of random size anti parallel ferroelectric domains that allow to phase-match any second-order parametric process over a broad range of wavelengths without any poling. We have initiated an experimental and theoretical investigation of the properties of the SH waves generated in SBN crystals, with an extension to the generated TH. This study covers the coherence and polarization properties of the generated signal, as well as its spatial distribution. In addition, we have made an experimental study of the noncollinear interaction of short optical pulses in a SBN crystal by using two fundamental waves intersecting inside the crystal. We have shown that this effect may be employed as a simple tool for monitoring both the pulse duration and initial chirp. This method offers a simple and economic alternative to the existing methods for pulse characterization.

Quantum cascade lasers (QCLs) operate due to population inversion on intersubband in unipolar mutiple-quantum-well (MQW) heterostructure. QCLs are considered one of the most flexible and powerful light semiconductor sources in the mid- and far-infrared (IR) wavelength range, covering most of the critical spectral regions relevant to IR applications. InGaAs/InAlAs/InP QCLs are the only semiconductor lasers capable of continuous wave (CW) operation at room temperature (RT) in the spectral range 3.4-12 micron. This dissertation details the development of RT QCLs based on passive nonlinear coupled-quantum-well structures monolithically integrated into mid-IR QCLs to provide a giant nonlinear response for the pumping frequency. The primary focus of short-wavelength approach in this dissertation is to develop of RT InGaAs/InAlAs/InP QCLs for lamda=2.5-3.7 micron region, based on quasi-phase-matched intracavity second harmonic generation (SHG) associated with intersubband transition. Intersubband optical transition can be engineered by the choice of quantum well and barrier thicknesses to provide the appropriate energy levels, optical dipole matrix elements, and electron scattering rates amongst other parameters. Thus, aside from their linear optical properties, resonant intersubband transitions in coupled QW's can also be designed to produce nonlinear optical medium with giant nonlinear optical susceptibilities. In long-wavelength region, at high temperature, the population inversion is reduced between the upper and lower laser levels due to the longitudinal optical (LO) phonon scattering of thermal carriers in the upper laser state and the thermal backfilling of carriers into the lower laser level from the injector state. This dissertation aims to improve an alternative approach for THz QCL sources based on intra-cavity difference frequency generation (DFG) in dual-wavelength mid-IR QCLs with a passive nonlinear structure, designed for giant optical nonlinearity. Further studies describe that Cerenkov DFG scheme allows for extraction of THz radiation along the whole length of the laser waveguide and provides directional THz emission in 1.2-4.5 THz range. An important requirement for many applications, like chemical sensing and molecular spectroscopy, is single-mode emission. We demonstrate single-mode RT DFG THz QCLs operation in 1-5 THz region by employing devices as integrated dual-period DFB lasers, where efficient solid state RT sources do not exist. / text

Purpose: To evaluate sound quality preferences of participants wearing hearing aids with different strengths of nonlinear frequency compression (NFC) processing versus no NFC processing. Two analysis methods, one without and one with a qualifier as to the magnitude of preferences, were compared for their percent agreement to differentiate a small difference in perceived sound quality as a result of applied NFC processing. Research Design: A single-blind design was used with participants unaware of the presence or strength of NFC processing (independent variable). The National Acoustic Laboratories-Nonlinear 2 (NAL-NL2) prescription of amplification was chosen because audibility is intentionally not prescribed in the presence of larger sensorineural hearing loss thresholds. A lack of prescribed audibility, when present, was deemed an objective qualifier for NFC. NFC is known to improve the input bandwidth available to listeners when high-frequency audibility is not otherwise available and increasing strengths of NFC were examined. Experimental condition 3 (EC3) was stronger than the manufacturer default (EC2). More aggressive strengths (e.g., EC4 and EC5), however, were expected to include excessive distortion and even reduce the output bandwidth that had been prescribed as audible by NAL-NL2 (EC1). Study Sample: A total of 14 male Veterans with severe high-frequency sensorineural hearing loss. Data Collection and Analysis: Participant sound quality preference ratings (dependent variable) without a qualifier as to the magnitude of preference were analyzed based on binomial probability theory, as is traditional with paired comparison data. The ratings with a qualifier as to the magnitude of preference were analyzed based on the nonparametric statistic of the Wilcoxon signed rank test. Results: The binomial probability analysis method identified a sound quality preference as well as the nonparametric probability test method. As the strength of NFC increased, more participants preferred the EC with less NFC. Fourteen of 14 participants showed equal preference between EC1 and EC2 perhaps, in part, because EC2 showed no objective improvement in audibility for six of the 14 participants (42%). Thirteen of the 14 participants showed no preference between NAL-NL2 and EC3, but all participants had an objective improvement in audibility. With more NFC than EC3, more and more participants preferred the other EC with less NFC in the paired comparison. Conclusions: By referencing the recommended sensation levels of amplitude compression (e.g., NAL-NL2) in the ear canal of hearing aid wearers, the targeting of NFC parameters can likely be optimized with respect to improvements in effective audibility that may contribute to speech recognition without adversely impacting sound quality. After targeting of NFC parameters, providers can facilitate decisions about the use of NFC parameters (strengths of processing) via sound quality preference judgments using paired comparisons.

This thesis presents the results and analyses of computational studies on certain problems of combustion instability in solid propellants. Specifically, effects of relaxing certain assumptions made in previous models of unsteady burning of solid propellants are investigated. Knowledge of unsteady burning of solid propellants is essential in studying the phenomenon of combustion instability in solid propellant rocket motors. In Chapter 1, an introduction to different types of unsteady combustion investigated in this thesis, such as 1) intrinsic instability, 2) pressure-driven dynamic burning, 3) extinction by depressurization, and 4) L* -instability, is given. Also, a review of previous experimental and theoretical studies of these phenomena is presented. From this review it is concluded that all the previous studies, which investigated the unsteady combustion of solid propellants, made one or more of the following assumptions: 1) quasi-steady gas-phase (QSG), 2) quasi-steady condensed phase reaction zone (QSC), 3) small perturbations, and 4) unity Lewis number. These assumptions limit the validity of the results obtained with such models to: 1) relatively low frequencies (< 1 kHz) of pressure oscillations and 2) small deviations in pressure from its steady state or mean values. The objectives of the present thesis are formulated based on the above conclusions. These are: 1) to develop a nonlinear numerical model of unsteady solid propellant combustion, 2) to relax the assumptions of QSG and QSC, 3) to study the consequent effects on the intrinsic instability and pressure-driven dynamic burning, and 4) to investigate the L* -instability in solid propellant rocket motors. In Chapter 2, a nonlinear numerical model, which relaxes the QSG and QSC assumptions, is set up. The transformation and nondimensionalization of the governing equations are presented. The numerical technique based on the method of operator-splitting, used to solve the governing equations is described. In Chapter 3, the effect of relaxing the QSG assumption on the intrinsic instability is investigated. The stable and unstable solutions are obtained for parameters corresponding to a typical composite propellant. The stability boundary, in terms of the nondimensional parameters identified by Denison and Baum (1961), is predicted using the present model. This is compared with the stability boundary obtained by previous linear stability theories, based on activation energy asymptotics in the gas-phase, which employed QSC and/or QSG assumptions. It is found that in the limit of large activation energy and low frequencies, present result approaches the previous theoretical results. This serves as a validation of the present method of solution. It is confirmed that relaxing the QSG assumption widens the stable region. However, it is found that a distributed reaction in the gas-phase destabilizes the burning. The effect of non-unity Lewis number on the stability boundary is also investigated. It is found that at parametric values corresponding to low pressures and large flame stand-off distances, small amplitude, high frequency (at frequencies near the characteristic frequency of the gas-phase) oscillations in burning rate appear when the Lewis number is greater than one. In Chapter 4, the effect of relaxing the QSG assumption is further investigated with respect to the pressure-driven dynamic burning. Comparison of the pressure-driven frequency response function, Rp, obtained with the present model, both in the QSG and non-QSG framework, with those obtained with previous linear stability theories invoking QSG and QSC assumptions are made. As the frequency of pressure oscillations approaches zero, |RP| predicted using present models approached the value obtained by previous theoretical studies. Also, it is confirmed that the effect of relaxing QSG is to decrease the |Rp| at frequencies near the first resonant frequency. Moreover, relaxing QSG assumption produces a second resonant peak in |Rp| at a frequency near the characteristic frequency of the gas-phase. Further, Rp calculated using the present model is compared with that obtained by a previous linear theory which relaxed the QSG assumption. The two models predicted the same resonant frequencies in the limit of small amplitudes of pressure oscillations. Finally, it is found that the effect of large amplitude of pressure oscillations is to introduce higher harmonics in the burning rate and to reduce the mean burning rate. In Chapter 5, first the present non-QSC model is validated by comparing its results with that of a previous non-QSC model for radiation-driven burning. The model is further validated for steady burning results by comparing with experimental data for a double base propellant (DBP). Then, the effect of relaxing the QSC assumption on steady state solution is investigated. It is found that, even in the presence of a strong gas-phase heat feedback, QSC assumption is valid for moderately large values of condensed phase Zel'dovich number, as far as steady state solution is concerned. However, for pressure-driven dynamic burning, relaxing the QSC assumption is found to increase |RP| at all frequencies. The error due to QSC assumption is found to become significant, either when |Rp| is large or as the driving frequency approaches the characteristic frequency of the condensed phase reaction zone. The predicted real part of the response function is quantitatively compared with experimental data for DBP. The comparison seems to be better with a value of condensed phase activation energy higher than that suggested by Zenin (1992). In Chapter 6, burning rate transients for a DBP during exponential depressurization are computed using non-QSG and non-QSC models. Salient features of extinction and combustion recovery are predicted. The predicted critical initial depressurization rate, (dp/dt)i, is found to decrease markedly when the QSC assumption is relaxed. The effect of initial pressure level on critical (dp/dt)i is studied. It is found that the critical (dp/dt)i decreases with the initial pressure. Also, the overshoot of burning rate during combustion recovery is found to be relatively large with low initial pressures. However as the initial pressure approached the final pressure, the reduction in initial pressure causes a large increase in the critical (dp/dt)i. No extinction is found to occur when the initial pressure is very close to the final pressure. In Chapter 7, a numerical model is developed to simulate the L* -instability in solid propellant motors. This model includes a) the propellant burning model that takes into account nonlinear pressure oscillations and that takes into account an unsteady gas- and condensed phase, and b) a combustor model that allows pressure and temperature oscillations of finite amplitude. Various regimes of L* -burning of a motor, with a typical composite propellant, namely 1) steady burning, 2) oscillatory burning leading to steady state, 3) oscillatory burning leading to extinction, 4) reignition and 5) chuffing are predicted. The predicted dependence of frequency of L* -oscillations on mean pressure is compared with one set of available experimental data. It is found that proper modeling of the radiation heat flux from the chamber walls to the burning surface may be important to predict the re-ignition. In Chapter 8, the main conclusions of the present study are summarized. Certain suggestions for possible future studies to enhance the understanding of dynamic combustion of solid propellants are also given.

Les parties tournantes des turbomachines aéronautiques sont composées d’une succession de roues aubagées qui permettent le transfert de l’énergie entre l’air et le rotor. Ces roues aubagées constituent des pièces particulièrement sensibles car elles doivent répondre en termes de dimensionnement à des impératifs de performances aérodynamiques, d’aéroacoustique et de tenue mécanique à la rotation,à la température et à la charge aérodynamique. Le contact avec frottement existant au niveau des attaches aube-disque joue un rôle important sur les niveaux vibratoires.Ce travail porte sur l’étude de l’usure par fretting sous chargements dynamiques dans les interfaces frottantes. En effet, les vibrations de l’aube peuvent produire des micro-glissements en pied d’aubequi peuvent entraîner un phénomène d’usure par fretting. Les connaissances sur le comportement de l’usure sous sollicitations dynamiques sont faibles. Seuls existent des outils numériques pour modéliser l’usure dans le cas de sollicitations quasi-statiques. Nous proposons dans cette thèse des méthodes pour calculer l’évolution de l’usure au cours des cycles de chargement dynamique basées sur une approche multi-échelle en temps. La réponse vibratoire de la structure est liée à une échelle de temps rapide qui est calculée par une méthode d’équilibrage harmonique, dans laquelle les déplacements et les efforts sont projetés sur la base de Fourier. Différentes approches temps-fréquence de calcul des coefficients de Fourier des forces de contact sont présentées. La cinétique d’usure est liée à une échelle lente et différentes méthodes sont proposées pour l’intégrer. La prise en compte des géométries usées dans le modèle éléments finis se fait par l’ajout d’un vecteur des profondeurs d’usure dans le terme de pénalité des lagrangiens dynamiques. Des exemples académiques valident et illustrent les méthodes proposées. Ces méthodes sont ensuite appliquées à l’étude de l’usure par fretting en pied d’aube de soufflante. L’étude numérique met en lumière le couplage entre vibration et usure par fretting aux interfaces de contact. La modification du comportement dynamique global de la roue aubagée est aussi observée. / The rotating parts of aeronautical turbomachineries are made of bladed disks which enable the transfer of energy from the air to the rotor. These bladed disks are especially critical parts because their dimensioning has to meet strict requirements in terms of aerodynamical performance, aeroacoustics and mechanical resistance to rotation, temperature and aerodynamical loads. The frictional contact at the interface between blade and disk has an important influence on the vibratory levels.This work deals with the study of fretting-wear in frictional interfaces under dynamical loading. Indeed,the blade’s vibrations can produce micro-slidings in blade’s root which may entail fretting-wear. Wear under dynamical loading is a badly known phenomenon. Numerical tools exist for quasic-static conditions only. Here,methods are proposed to quantify the evolution of wear along dynamical loadingcycles based on a time-multiscale approach. The vibratory response of the structure is linked with a fasttime scale which is calculated by a harmonic balance method : displacements and forces are expressed through Fourier series. Different frequency-time approaches are presented to compute the Fourier coefficients of contact forces. Wear kinetics is linked with a slow time scale and different methods are proposed to integrate it.Worn geometries are taken into account in the finite elements model by a wear depth vector included in the penalty term of dynamic lagrangians. Academic examples validate and illustrate the proposed methods. These methods are then used to study fretting-wear in a fan’s bladeroot. The numerical results highlight the coupling between vibration and fretting-wear in frictional interfaces.The modification of the global dynamical behaviour of the bladed disk is also observed.

La capacité ultime du canal dans les systèmes de transmission optique à longue distance est limitée par les effets non linéaires liés à la propagation dans les fibres optiques. Des techniques de compensation des effets non-linéaires, tel que la DBP (Digital Back Propagation), ont été proposées pour surmonter ces limitations et accroître la capacité. Compte tenu de leur complexité d’implémentation, leur gain en performance reste très limité. Cela a déclenché très récemment la recherche de nouvelles techniques de communication prenant en compte la non-linéarité de la fibre. Une nouvelle méthode de communication en régime non-linéaire, basée sur la théorie de la transformation spectrale inverse (IST pour Inverse Spectral Transform), a été proposée pour surmonter la limitation induite par ces effets. Cette méthode, proposée à l'origine par Hasegawa en 1993, encore appelée communication aux valeurs propres (ou multi-solitons), est basée sur l'observation fondamentale selon laquelle le spectre non linéaire d'un signal optique est invariant (à l'exception d'un déphasage linéaire trivial) lors de la propagation dans la fibre optique, comme décrit par l’équation non linéaire de Schrödinger (NLSE pour Non-Linear Schrödinger Equation). Cela signifie que si la transformée spectrale directe (DST) (également appelée NFT pour Nonlinear Fourier Transform) du signal reçu peut être calculée, le spectre de valeurs propres peut être entièrement récupéré.Cette thèse porte sur une technique de communication de type NFT connue sous le nom de multiplexage non linéaire en fréquence (NFDM pour Non-Linear Fourier Transform). Différentes configurations de systèmes optiques NFDM ont été évalués numériquement et validés expérimentalement. Dans un premier temps, la structure d’un système NFDM en mono-polarisation utilisant le spectre continu des fréquences non-linéaires dans une fibre en régime de dispersion normale est décrite. Pour ce faire, une forme NFT du vecteur NLSE, encore appelé système de Manakov, a été développé numériquement. Sur la base de ces algorithmes, la méthode NFDM a été étendue aux systèmes multiplexés par division de polarisation (PMD) et validée expérimentalement pour la première fois en utilisant le spectre continu. Finalement, l’expérience a été répliquée en régime de dispersion anormale. Afin d'étudier les contraintes de mise en œuvre, des études numériques supplémentaires ont été effectués pour la transmission de signaux NFDM utilisant la modulation du spectre continu. / Nonlinear effects in optical fiber set the ultimate limit to the channel capacity in long-haul optical transmission systems. Advanced nonlinear compensation techniques such as digital backpropagation (DBP) have been proposed as a solution to overcome the channel capacity crunch. However, given theircomputational complexity, in a practical environment their performance gainremains very limited. This triggered a search for a novel communication system design that takes fiber nonlinearity into consideration. A new nonlinearcommunication method, based on the theory of the inverse spectral transform, has been proposed to overcome the nonlinear capacity crunch. Thismethod, originally proposed by Hasegawa in 1993 and called eigenvalue (ormulti-soliton) communication, is based on the fundamental observation thatthe nonlinear spectrum of an optical signal is invariant (except for a triviallinear phase shift) upon propagation in the fiber channel, as described bythe nonlinear Schrödinger equation (NLSE). This means that if the directspectral transform (also known as nonlinear Fourier transform (NFT)) ofthe received signal can be computed, the eigenvalue spectrum can be fullyrecovered.This thesis focuses on a NFT-based communication technique known as nonlinear frequency division multiplexing (NFDM). The NFDM optical systemis numerically assessed and experimentally demonstrated. First, the structure of the proposed single-polarization NFDM system using the continuousspectrum in the normal dispersion regime is presented. To that end, theNFT of the vector NLSE, or Manakov system, was numerically developed.Based on these algorithms the NFDM method was extended to polarizationdivision multiplexed (PMD) systems, and experimentally validated for thefirst time using the continuous spectrum. Finally, the experiment will bereplicated in the anomalous dispersion regime.Additional numerical studies are presented, in order to investigate the implementation challenges of the proposed NFDM techniques for the continuousspectrum modulation.