Design of innovative photonic crystal fibers for high power lasers

Thanks to their superior properties in terms of output power, brightness, efficiency, compactness, and thermal management, fiber lasers are rapidly replacing other solid-state sources in many fields of application. In order to achieve further advancements of this technology, innovative active optical fibers are required, capable of allowing stable single-mode propagation in a large-area core. Photonic Crystal Fibers (PCFs) appear to be the most practical solution, thanks to their highly-tailorable guiding properties and well-established fabrication technology. The aim of this Thesis is to present the results on the design of innovative double cladding PCFs for high power fiber lasers, obtained during the Ph.D. course at the Information Engineering Department of the University of Parma. After a review of the most important issues related to power scaling of fiber laser systems and of the key features of photonic crystal fibers, the results of the analysis and optimization of different PCF designs are discussed, providing guidelines for the realization of active fibers for next-generation sources.