Two pulse-shortening schemes based on the nonlinear propagation of picosecond pulses from a Nd: YAG laser in single-mode optical fibres are described. In the first experiment, a spectral-windowing technique was employed to compress self-phase modulated pulses exiting 100 m of optical fibre, and compression factors of 2.5 were recorded in good agreement with theoretical predictions. The technique was adapted to enable the time-dependent frequency shift occurring after pulse propagation through 2 km of fibre to be measured. In the second experiment, cascaded stimulated Raman generation, occurring when a high-power pump pulse propagated in 4 m of fibre, was studied. Lower-order components in the cascade were severely depleted through generation of higher-order Stokes signals, leaving negatively chirped pulse fragments. These were compressed with a dispersion-tunable Gires-Tournois interferometer and compression ratios of times 4 were obtained.