Fantasies using optical fibers

The activity carried out during the PhD course has concerned special optical fibers with particular refractive index profiles, from Photonic Crystal Fibers (PCFs) to Plastic Optical Fibers (POFs), which is a research topic in continuous evolution and characterized by a great scientific excitement. The aim of the research of the three year PhD course has been to accurately study, and thus to deeply understand the light guiding mechanisms exploited in these kinds of optical fibers. The unusual guiding properties of PCFs with different air-hole arrangements in the fiber cross-section have been investigated both numerically, through a full-vector modal solver based on the Finite Element Method, and experimentally, by considering samples of large mode area PCFs, as well as of nonlinear fibers. Moreover, the properties of Erbium-Doped Fibers (EDFs) with a particular refractive index profile, that is with a depressed-cladding, have been experimentally characterized. By exploiting the bending loss of these active fibers, amplifiers with different configurations have been realized, which cover larger bandwidths with respect to conventional ones, as well as tunable lasers in S, C and L band. Then, in order to design and realize the pre-amplifier stage for a pulsed high power laser useful for industrial applications, single-mode ytterbium-doped fibers with different doping concentrations, with either a single or a double-cladding, have been considered with the aim to optimize the gain performances. Finally, low cost sensors based on the inexpensive plastic fibers have been proposed as an effective solution to the problem of the liquid level measurement. Sensors for both point and continuous measurements of the liquid level, which can be also exploited to distinguish fluids according to their refractive index.