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Multi-wavelength square pulses are generated in the dissipative soliton resonance (DSR) regime by a Yb-doped fiber laser (YDFL) with a long cavity configuration. The spectral filter effect provided by a passive fiber with low-stress birefringence facilitates the establishment of multi-wavelength operation. Through appropriate control of the cavity parameters, a multi-wavelength DSR pulse can be generated in single- and dual-waveband regions. When the multi-wavelength DSR works in the 1038 nm waveband, the pulse duration can broaden from 2 ns to 37.7 ns. The maximum intra-cavity pulse energy is 152.7 nJ. When the DSR works in the 1038 nm and 1080 nm wavebands, the pulse duration can be tuned from 2.3 ns to 10.5 ns with rising pump power. The emergence of the 1080 nm waveband is attributed to the stimulated Raman scattering (SRS) effect. Our work might help a deeper insight to be gained into DSR pulses in all-normal-dispersion YDFLs. [ABSTRACT FROM AUTHOR]

We report on the observation of quasi-trapezoid noise-like pulses (NLPs) in a fiber laser with a large anomalous dispersion regime based on nonlinear polarization rotation. Trapezoidal NLPs operate at 1568 nm with a fundamental repetition rate of 946.14 kHz. The pulse width can widen from 12.54 to 32.17 ns, and the pulse energy can be increased from 8.81 to 25.84 nJ by increasing the pump power from 77.4 to 244.4 mW. The maximum intracavity energy of a trapezoidal pulse can reach ~258.4 nJ. Furthermore, stable high-order harmonics are obtained by regulating the pump power and polarization state. In the harmonic mode-locking regime, the second- to the tenth-order harmonic trapezoidal pulses can be achieved in the fiber laser. [ABSTRACT FROM AUTHOR]