Widely-tunable harmonic mode-locked fiber laser by the combination of spectral filtering and gain management

•The widely-tunable harmonic mode-locked fiber laser with a fixed repetition rate.•Pulse width is tunable by exploiting the combination of spectral filtering and gain management.•The broadband CNT SA and TF play an important role in the pulse width tunability. Controlled flexible ultrafast pulses are of great importance in many application fields, such as metrology. Here, we report a compact pulse width tunable passively harmonic mode-locked fiber laser by exploiting the combination effect of spectral filtering and gain management. The spectral filtering is achieved by adopting a bandwidth tunable filter, resulting in pulse width tunable and changing the harmonic order (i.e., repetition rate). On the other hand, gain management can tune the harmonic order, while the emission pulse width typically remains the same. Thus, a combination of these two effects can make the pulse width tunable in a broad range at a fixed repetition rate. At the 6th-order harmonic mode-locking (76.8 MHz), the pulse width can be tuned from ∼ 0.8 ps to 4.3 ps by adjusting the bandwidth and pump strength. The development of pulse width tunable laser sources at a high-repetition rate would find potential applications in fields such as optical sensing and biomedical imaging.