Investigating the behavior of an atom in response to the applied electric field when the latter frequency is in resonance with the natural frequency of the atom is an interesting subject. Near resonance, some of the most interesting optical phenomena such as dispersion, and absorption are more pronounced. Moreover, considering resonant and near resonant interaction of light with two-level atoms, uncovers fascinating physical phenomena such as area theorem and self-induced transparency describing stable pulse propagation regimes in which the pulses maintain their identity. Existence of these optical structures in on-resonance optical media has not been investigated in detail. In this thesis, the on-resonance interaction of optical field with atoms is considered and the formation of several novel self-similar and kink waves in linear and nonlinear resonant media is discovered and theoretically explored. First, self-similar pulse formation in homogeneous broadened linear amplifiers in a vicinity of an optical resonance is analyzed. It is demonstrated that the self-similar pulses serve as universal asymptotics of any near resonance short pulses propagating in coherent linear amplifiers. Second, ultrashort self-similar pulse propagation in coherent linear absorbers near optical resonance is investigated. Third, existence of self-similar optical waves with kink structure in resonant optical systems is discovered. Fourth, it is found that self-induced transparency quadratic solitons are realizable in the media with quadratic optical nonlinearities, doped with resonant impurities. Finally, stable spatial similaritons supported by homogeneous conservative optical media with quintic nonlinearities are explored. To experimentally realize the presented results, physical models are presented for all systems under consideration. The stability of the proposed near resonance optical systems is demonstrated through a series of numerical case studies.

The main objective of the thesis is to understand the parameters that contribute in limiting the pulse energy and spectral bandwidth of the mode-locked femtosecond fiber lasers. I have focused on studying the impact of the parameters of the saturable absorber and the bandwidth of the lumped spectral filter on the temporal and spectral profiles of the pulse. Therefore, I developed two models that can help us to optimize the pulse characteristics such as the pulse energy, spectral bandwidth and de-chirped pulse width. I also introduce two techniques that result in increasing the pulse peak power and spectral bandwidth. The nonlinear transmission coefficient of the saturable absorber is one of the main limitations to achieving high-energy pulses. Throughout my research, I have used two types of saturable absorbers. The first is a lumped semiconductor saturable absorber mirror (SESAM) and the second is based on the nonlinear polarization rotation (NPR) that is considered an artificial saturable absorber with distributed effect. The first model introduced in this thesis is an analytical model, which provides closed form relations for the pulse characteristics of all-normal dispersion fiber laser. It shows how the spectral bandwidth of the lumped filter inserted inside the cavity affects the pulse characteristics. Also, it illustrates the influence of the saturable absorber parameters on the pulse characteristics. I show that increasing the small signal saturable absorber loss and decreasing the saturation power leads to the increase in pulse energy and spectral bandwidth. Numerical simulation and experimental results are in agreement with the results of the analytical models. The second model, which is called the semi-vector model, is applicable to all-normal dispersion mode-locked fiber laser with high output coupling ratio. Nonlinear polarization rotation is employed for mode-locking. The model shows the relationship between the location of the overdriving point of the saturable absorber and the output pulse energy. The results of this model are in agreement with those of the full-vector model, but with a much reduced simulation time. In addition, the experimental results show the accuracy of the proposed model. In this thesis, I mitigate the peak power limitation, caused by the accumulated nonlinear phase shift, by replacing the short high-doped Yb3+ fiber with a long low-doped one. This results in an increase of the peak power by a factor that depends on the ratio between the gain coefficient of the high- and low-doped Yb3+ fiber. The length of the nonlinear section is kept unchanged by reducing the length of the single mode fiber after the long low-doped Yb3+ fiber. Numerical simulation and experimental results validate the idea. The location of narrow bandwidth lumped spectral filter, in an active Similariton laser, has proved to have a distinct effect on the pulse energy, spectral bandwidth and de-chirped pulse width and peak power. The proximity of the spectral filter to the input of the Yb3+-doped fiber leads to increasing the pulse spectral bandwidth and peak power of the de-chirped pulse as well as shortening the de-chirped pulse, but at the expense of reducing the pulse energy.

L'autosimilarité et l'évolution asymptotique intermédiaire sont des caractéristiques fondamentales de divers phénomènes physiques. Les recherches dans le domaine de l'optique ont mené à la prévision et à l'observation du similariton, nouvelle classe d'impulsions optiques ultracourtes présentant un profil d'intensité parabolique et développé par celles-ci au cours de leur propagation dans un amplificateur fibré à dispersion normale. Au delà de leur intérêt scientifique, les similaritons optiques sont d'une importance pratique primordiale du fait que leur profil peut être maintenu sans distorsion dans toute fibre à dispersion normale active ou passive et parce qu'ils possèdent un chirp strictement linéaire facilitant leur compression. Ce mémoire s'attache à mettre en évidence les possibilités d'obtention de ce profil dans un amplificateur à fibre dopée erbium. Les impulsions expérimentales caractérisées à l'aide d'un dispositif FROG présentent un profil d'intensité ainsi qu'une dérive fréquentielle en accord avec les résultats issus d'un modèle numérique. Nous avons aussi été en mesure d'étudier la formation des ailes du similariton durant son régime asymptotique intermédiaire. Une application typique des similaritons consiste dans le développement de sources impulsionnelles ultracourtes; expérimentalement nous avons développé un dispositif femtoseconde totalement fibré combinant un amplificateur à similaritons et une fibre à bandes interdites photoniques.

Ce mémoire présente la génération de similaritons dans un amplificateur Raman à dispersion normale aux longueurs d'onde des télécommunications optiques. Les profils temporels expérimentaux obtenus par caractérisation FROG mettent en évidence un profil d'intensité parabolique associé à une dérive de fréquence linéaire, en accord avec les résultats d'un modèle numérique.<br />Différentes propriétés théoriques des similaritons sont ensuite vérifiées expérimentalement. La dynamique de deux impulsions similaritons à des longueurs d'ondes centrales identiques ou différentes est également étudiée : les similaritons sont robustes vis-à-vis des collisions alors que l'interaction de deux similaritons entraîne la génération d'un train de solitons noirs à haut-débit.<br />Dans une dernière partie, nous évoquons l'application des similaritons à trois domaines : la génération d'impulsions ultracourtes, la mise en forme d'impulsions et enfin la régénération optique de signaux télécom à haut-débit.

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