The development of ultrafast lasers has enabled a wide range of applications such as time-resolved spectroscopy, micro-machining and non-linear microscopy. For the past 20 years, solid-state lasers have been the workhorses of ultrafast science. However, they remain bulky and sensitive tools requiring careful alignment. Thus, rare-earth doped fiber lasers have generated significant interest. They can be monolithically integrated and use simple power scalable diode pumping. Thanks to recent advances in the understanding of non-linear pulse evolution in optical fiber, as well as the development of large-core fiber technologies, fiber lasers have achieved performance matching conventional solid-state lasers. This thesis explores the non-linear propagation and parametric conversion of high energy short pulses in normal dispersion optical fibers. A laser source for coherent anti-Stokes Raman scattering microscopy is demonstrated based on frequency conversion of picosecond pulses through four-wave mixing in photonic crystal fiber. The effects of vibrational dephasing on the coherence and compressibility of Raman Stokes pulses generated in chirped-pulse fiber amplifiers are investigated. Finally, all-normal-dispersion fiber lasers are scaled to high pulse energies using large-core fibers. The performance of multimode step-index fiber, chirally-coupled core fiber and photonic crystal fiber is compared. Using fibers with robust modefiltering, fibers lasers delivering up to a megawatt of peak power are demonstrated.