Using graphene-covered-microfiber (GCM) as a saturable absorber, the generation and evolution of multiple operation states are proposed and demonstrated in passively mode-locked thulium-doped fiber laser. The microfiber was fabricated using the flame brushing method to an interaction length of ∼ 1.2 cm with a waist diameter of ∼ 10 µm. Graphene layers were grown on copper foils by chemical vapor deposition and transferred onto the polydimethylsiloxane (PDMS) to form a PDMS/graphene film, which allowed light-graphene interaction via evanescent field. With the increase of the pump power from 1.25 W to 2.15 W, five different lasing regimes, including continuous-wave, conventional soliton mode-locking, multisoliton mode-locking, a period of transition, and noise-like mode-locking, were achieved in a fiber ring cavity. To the best of our knowledge, it is the first report of the generation and evolution of multiple operation states by covering graphene on the microfiber in the 2-µm region. The results demonstrate that GCM can be a promising method for fabricating all fiber SA, and the switchable operation states can provide more portability in complex application domain.

We demonstrated a 2-µm passively mode-locked nanosecond fiber laser based on a MoS 2 saturable absorber (SA). Owing to the effect of nonlinear absorption in the MoS 2 SA, the pulse width decreased from 64.7 to 13.8 ns with increasing pump power from 1.10 to 1.45 W. The use of a narrow-bandwidth fiber Bragg grating resulted in a central wavelength and 3-dB spectral bandwidth of 2010.16 and 0.15 nm, respectively. Experimental results show that MoS 2 is a promising material for a 2-µm mode-locked fiber laser.

In this paper, a multistate passively mode-locked thulium-doped fiber laser with nonlinear amplifying loop mirror is reported. An ultra-high numerical aperture fiber is employed to compensate the cavity abnormal dispersion, and the net cavity dispersion value is fixed at -0.046  ps. By changing the pump power, three different mode-locked regions, namely Q-switched mode-locking operation, mode-locking operation, and dual-wavelength mode-locking operation, are observed sequentially. When the pump power is raised to the threshold of 1.60 W, the transition state of the Q-switched mode locking begins to be observed. When the pump power increases from 2.88 W to 8.75 W, stable single-wavelength mode-locking operation is obtained. And the center wavelength is 1988.73 nm corresponding to the 3 dB spectral bandwidth of 11.21 nm. As the pump power is raised beyond 8.75 W, dual-wavelength mode-locking operation is developed, where the dual wavelengths are 1969.70 nm and 1984.12 nm with the 3 dB spectral bandwidth of ∼4.11  nm and ∼6.14  nm, respectively.

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