Résumé : We investigate femtosecond pulse propagation in photonic crystal fiber, reporting the generation of tunable femtosecond soliton pulses. For sufficiently broad spectral content, stimulated Raman scattering transfers energy from the higher frequency spectral components to lower frequencies, resulting in a continuous self-frequency shift to longer wavelengths. Power dependent spectral analysis reveals a well-formed soliton at peak powers exceeding 100 W. Background-free intensity autocorrelation measurements confirm soliton formation with a duration of < 90 fs and with an energy conversion efficiency of 60%. Numerical solutions were performed based on a generalized nonlinear Schrödinger equation that included the effects of dispersion, self-steepening, optical shock formation, self-phase modulation and stimulated Raman scattering. The resulting spectra from the simulations are in excellent agreement with the measured spectra, and are consistent with the intensity autocorrelation measurements.