The dependence of the output characteristics of a regeneratively and harmonically FM mode-locked erbium-doped fiber laser on intracavity dispersion have been investigated by changing the group velocity dispersion (GVD) of the fiber. It is shown that a stable pulse train can be obtained only when the GVD of the cavity is anomalous in the presence of self-phase modulation (SPM). The shortest pulse obtained was 2. 0 ps at a repetition rate of 10 GHz.

The effects of forced phase modulation (FPM) and self phase modulation (SPM) in dispersion tuned fiber lasers (DTFL) are examined. We show that FPM, such as chirp in the modulator, plays an important role in the pulse shaping because of the important role of dispersion in the cavity. In particular, compared to the case of zero FPM, significant pulse shortening can be obtained by using up-chirp modulation. The results suggest that modulators with large chirp parameters are desirable for DTFLs. When SPM is introduced, the pulse shapes differ greatly depending on the direction of the FPM. Significant deviations from Gaussian profiles are observed.