In this paper, a mode-locked Ytterbium-doped fiber laser based on nonlinear optical loop mirror (NOLM) is proposed. The laser generates a wide-spectrum dissipative soliton resonance mode-locked pulse with strong stimulated Raman scattering. The fiber laser is pumped forward, and the fiber ring cavity contains double-cladding Yb-doped fiber, output coupler, polarization controller, polarization independent isolator and other elements. NOLM is connected with the ring cavity by through a 3dB beam splitter and 25m single-mode fiber. The total length of the eight-shape cavity laser is about 60meters. By adjusting the intra-cavity polarization controller, a stable dissipative soliton resonance mode-locked spike pulse can be achieved. The repetition frequency of the pulse train is 3.44MHz, which is consistent with the cavity length. The 3dB bandwidth of the spectrum reaches 70.6nm, and the 10dB bandwidth is close to 147.11nm. In this experiment, dissipative soliton resonance mode-locked pulses with wide spectrum and high pulse energy are realized by a traditional mode-locking method, which has wide application in many fields such as laser spectral detection and terahertz wave generation.
We demonstrated a multi-dark soliton train generated from self-mode-locking ultra-long ring cavity fiber laser. The fiber laser used 10m double-clad Yb-doped fiber as gain medium, and used a polarization independent isolator to ensure the light propagation in one direction. The ring cavity of the laser was designed without any intra-cavity polarization controlling component. The cavity length is 1300 meters by insetting single mode fiber. When the pump power was increased to 2.75W, the multi-dark soliton trains were obtained. The stable pulse train has a repetition rate of 153.9 kHz corresponding to the cavity length. The number of sub-pulse continues to decrease during the increase of the incident pumping power until 3.39W. Stable three peaks appear in the spectra of our fiber laser due to the absence of the polarization controller in the cavity. The maximum peak wavelength locates around 1083.9nm with the 3dB bandwidth of 1.4nm. There are two sidebands with the central wavelength of 1086.3nm and 1090.1nm with a lower intensity. The occurrence of multi-dark soliton pulses train is relevant to the self-mode-locked operation at the cavity with a large amount of normal dispersion and accumulated nonlinearity.