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Multistate transformations of a femtosecond fiber laser based on a pure fiber saturable absorber.

The graded index multimode-fiber step-index multimode fiber-graded index multimode fiber (GIMF-SIMF-GIMF) structure was designed as a saturable absorber (SA). To obtain optical pulses that meet the requirements of different applications, the multistate transformations of a femtosecond fiber laser based on GIMF-SIMF-GIMF SA were numerically and experimentally researched. The fiber laser can self-start mode-locking; its fundamental repetition rate of fiber laser is 10.35 MHz. The fiber laser can deliver three different optical pulses, namely, the conventional soliton, second-order bound state, and noise-like pulse. The duration of soliton is 421.2 fs; the energy of noise-like pulse is 197.10 pJ. The experimental and simulated results show that the output states of the fiber laser can be switched by adjusting the pump power.