We report the experimental generation of two-soliton molecules in an all-polarization-maintaining ytterbium-doped fiber laser operating in the normal dispersion regime. These molecules exhibit an independently evolving phase and are characterized by a regular spectral modulation pattern with a modulation depth of 80% measured as an averaged value. Moreover, the numerical modeling confirms that the limited modulation depth of the spectrum is caused by the evolution of the phase difference between the pulses.

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 $\sim 70\mathrm{dB}$ 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.

We report on high-energy ultrashort pulse generation from an all-normal-dispersion large-mode-area fiber laser by exploiting an efficient combination of nonlinear polarization evolution (NPE) and a semiconductor-based saturable absorber mode-locking mechanism. The watt-level laser directly emits chirped pulses with a duration of $1\mathrm{ps}$ and $163\mathrm{nJ}$ of pulse energy. These can be compressed to $77\mathrm{fs}$, generating megawatt-level peak power. Intracavity dynamics are discussed by numerical simulation, and the intracavity pulse evolution reveals that NPE plays a key role in pulse shaping.

A new method to generate multi-watt-level, octave-spanning, spectrally flat supercontinua stemmed from cascaded Raman scattering in graded-index multimode fibers is reported. Formation dynamics of supercontinua are investigated by studying the effect of fiber length and core size. High power handling capacity of the graded-index multimode fibers is demonstrated by power scaling experiments. Pump pulse repetition rate is scaled from kHz to MHz while pump pulse peak power remains same and ~4 W supercontinuum is achieved with 2 MHz pump repetition rate. To the best of our knowledge, this is the highest average power and repetition supercontinuum source ever reported based on a graded-index multimode silica fiber. Spatial properties of the generated supercontinua are measured and Gaussian-like beam profiles obtained for different wavelength ranges. Numerical simulations are performed to investigate underlying nonlinear dynamics in details and well-aligned with experimental observations.

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