All-fiber all-normal-dispersion femtosecond laser with a nonlinear multimodal interference-based saturable absorber.

In this Letter, we demonstrate, to the best of our knowledge, the first all-fiber all-normal-dispersion ytterbium-doped oscillator with a nonlinear multimodal interference-based saturable absorber capable of generating ultrashort dissipative soliton pulses. Additional to functioning as a saturable absorber, the use of multimode fiber segments between single-mode fibers also ensures the bandpass filtering via multimode interference reimaging necessary to obtain dissipative soliton mode locking. The oscillator generates dissipative soliton pulses at 1030 nm with 5.8 mW average power, 5 ps duration, and 44.25 MHz repetition rate. Pulses are dechirped to 276 fs via an external grating compressor. All-fiber cavity design ensures high stability, and ∼70  dB sideband suppression is measured in the radio frequency spectrum. Numerical simulations are performed to investigate cavity dynamics, and obtained results are well matched with experimental observations. The proposed cavity presents an alternative approach to achieve all-fiber dissipative soliton mode locking with a simple and low-cost design.