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We report on improvements of mode-locked soliton pulse energy and peak power in a thulium-doped fiber laser. At the pump power of 370 mW, conventional soliton can be first generated using nonlinear polarization rotation technology. By increasing the pump power to 550 mW and appropriately adjusting cavity polarization state, the conventional soliton pulse can be converted into the Gaussian pulse. Due to dispersion management, excess accumulation of nonlinear phase shifts in the cavity can be avoided. In this case, the pulse energy and peak power can be increased from 77 pJ to 1.38 nJ and from 106.9 W to 2.67 kW, respectively. These improvements indicate that the Gaussian pulse operation can effectively enhance the pulse energy and peak power of the thulium-doped fiber laser.

We report on the experimental observations of stable single soliton and soliton molecules in an anomalous-dispersion thulium-doped passively mode-locked fiber laser by using the nonlinear polarization rotation technology. The stable single soliton operation can convert to the soliton pair operation by cautiously adjusting the PCs, at the pump power of 350 mW. It is experimentally demonstrated that the formation of stationary soliton pairs is related to the interaction between solitons and dispersive waves. By appropriately adjusting the cavity parameters, more complex soliton molecules composed of three, four, and five bound solitons can be observed. Meanwhile, we experimentally analyze complex nonlinear dynamics of soliton molecules around 2- ${\mu }\text{m}$ .

We propose and demonstrate a multi-wavelength actively mode-locked fiber laser around $2.07~\mu \text{m}$ . A holmium-doped fiber is used as the gain medium which is pumped by a 1.93- $\mu \text{m}$ fiber laser. The multi-wavelength laser is achieved by employing a fiber Lyot filter in cavity, and actively mode-locking is achieved by driving a sinusoidal radio frequency signal on the electro-optic modulator. Stable actively mode-locked pulses can be obtained with up to 10.078-GHz repetition rate. The shortest measured pulse width is 16 ps. The wavelength channels can be accurately tuned under a fixed pump power by adjusting the polarization controllers and the BIAS voltage. Up to 27 channels can be obtained under a stable mode-locked operation. However, the increase of output channels leads to a significant increase in the threshold, and the maximum output channels have a strong dependence on the repetition rate.