While the performance of mode-locked fiber lasers has been improved significantly, the limited gain bandwidth restricts them to generate ultrashort pulses approaching a few cycles or even shorter. Here we present a novel method to achieve few cycle pulses (~5 cycles) with ultra-broad spectrum (~400 nm). To our best knowledge, this is the shortest pulse width and broadest spectrum directly generated from fiber lasers. It is noteworthy that a dramatic ultrashort pulse evolution can be stabilized in a laser oscillator by the unique nonlinear processes of a self-similar evolution as a nonlinear attractor in the gain fiber and a perfect saturable absorber action of the Mamyshev oscillator.

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We report an experimental study of multipulsing states in an all-normal dispersion fiber laser using an all-fiber, tunable birefringent spectral filter. Various multipulsing states such as harmonic mode-locking and soliton bunches are observed by tuning the spectral filter. The multipulse evolution in this experiment relies only on the spectral filter characteristics, and it is independent of input pump power and saturable absorber effects. This laser provides an attractive option of controlling the pulse dynamics of a fiber laser with the use of a simple spectral filter.

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