We investigate the impact of germanium oxide ( GeO2 ) doping on the linear and nonlinear properties of photonic crystal fibers. We propose some design rules allowing a strong enhancement of the Raman and Kerr nonlinearities with little impact on the fiber dispersive properties. It is experimentally and numerically demonstrated that using GeO2 -doped core photonic crystal fibers allows a significant enhancement of the soliton self-frequency shift as compared to pure silica photonic crystal fibers with comparable dispersion. We found that the high nonlinear coefficient (due to a good mode confinement) obtained in the GeO2 -doped core fiber plays a more important role on the soliton self-frequency shift enhancement than the intrinsic Raman gain.