Propagazione ed effetti nonlineari in fibre ottiche a pochi modi

Since their birth in the mid-twentieth century, optical fibers' role in the global technological and economical landscape has become exponentially larger and more diverse, going from becoming the backbone of today's internet infrastructure, to enabling high-resolution medical imaging, or permitting the discovery of novel light sources. In each of these applications, nonlinear optical effects play an important role: in certain cases they can be the spark that lights the fire of innovation, while in others they can impose significant limitations. In this thesis, the main results of my three-year period as a Ph.D student are presented. The first part of my research has focused on the nonlinear effect known as Raman scattering in the context of next-generation space-division multiplexed transmissions. Firstly, machine learning techniques have been applied to spectrally and spatially optimize the design of Raman amplifiers. Secondly, through the development of a theoretical model and the use of numerical simulations, the effect of fiber imperfections, such as birefringence and core ellipticity, on the gain of Raman amplifiers has been studied. The second and last part of the thesis is dedicated to the topic of Supercontinuum Generation: some early results on the characterization of novel microstructured optical fibers, achieved in collaboration with the Institute of Applied Physics (IAP) of the University of Bern, are presented.