We demonstrate a passively $Q$-switched ytterbium-doped fiber laser based on black phosphorus (BP) flakes covered microfiber. The BP saturable absorber is fabricated by sandwiching a microfiber between two pieces of polydimethylsiloxane supported BP flakes film, which is prepared by the mechanical exfoliation method. In this case the BP flakes can be well protected from the action of air and moisture. By incorporating BP flakes covered microfiber into a ytterbium-doped ring fiber laser, stable and reliable $Q$-switched operation at 1064 nm can be realized via interaction between few-layers BP flakes and the evanescent field of the laser. The laser allows $Q$-switched pulse generation with a repetition rate in the range of 26–76 kHz and a pulse duration in the range of 5.5–2.0 μs, by varying the pump power from 38 mW to 100 mW.

We demonstrate for the first time, to our knowledge, an all-fiber erbium-doped mode-locked laser in which mode-locking (ML) is realized by the combination of nonlinear polarization rotation and a saturable dynamic filtering effect, thereby generating nearly transform-limited ultrashort pulses with a pulse duration and spectral width of 45.2 ps and 0.0775 nm, respectively. The laser achieves both ML and harmonic ML by increasing the pump power. Simultaneously, the filtering function is maintained by the saturable dynamic induced grating (SDIG) throughout the power-modulation process. Furthermore, numerical simulations are used to analyze the pulse energy evolution in the cavity, revealing the advantages of hybrid ML in decreasing the pulse duration and time-bandwidth product under narrow filtering status. This work proposes a practical method to achieve ultrafast laser pulses with a narrow bandwidth, solving the problem that the SDIG has a hard time realizing a stable ML sequence.

We investigate numerically the impact of spectral filtering on pulse characteristics in anomalous dispersion erbium-doped fiber laser mode-locked with carbon nanotube-based saturable absorber. The laser can operate only in a single-pulse state without a filter, while it will transit to bound soliton states once the saturation energy of the gain fiber and the bandwidth of the filter are carefully chosen, respectively. Further analyzation shows that the operation of a single-pulse lasing from dissipative soliton to conventional soliton can be selectively targeted by changing the bandwidth of the filter through the loss and frequency narrowing effects. Laser performances, such as spectrum structure, pulse duration, pulse energy and peak power in both the frequency and the time domains, will all be affected. This paper provides a guidance for the mode-locked fiber laser and proposes a feasible way to control the pulse dynamics.

In this Letter, a single-frequency fiber laser using a molybdenum disulfide (MoS2) thin film as a saturable absorber is demonstrated. We use a short length of highly Yb-doped fiber as the gain medium and a fiber ferrule with MoS2 film adhered to it by index matching gel (IMG) that acts as the saturable absorber. The saturable absorber can be used to discriminate and select the single longitudinal modes. The maximum output power of the single-frequency fiber laser is 15.3 mW at a pump power of 130 mW and the slope efficiency is 15.3%. The optical signal-to-noise ratio and the laser linewidths are ～60dB and 5.89 kHz, respectively.

Generally speaking, the self-sweeping effect relies on the dynamical grating formed in active fiber. Here, the normal self-sweeping was generated in a ytterbium-doped fiber which serves as a fiber saturable absorber and is introduced to the laser cavity by a circulator in this experiment. The sweeping rate and the sweeping range alter as usual, both of which can be controlled by the pump power. Further, a new self-pulse signal is observed and discussed, which shows both the grating feature and saturable absorption of YDFSA. Our work provides a new self-sweeping way and can act as a platform to further deeply study this effect.

We investigate the mechanism of changing the polarization state to generate noise-like pulses (NLPs) in the all-normal dispersion (ANDi) all-fiber laser based on nonlinear polarization rotation (NPR). Numerical simulations show that the intracavity positive and negative feedback states change with the polarization state, the peak power of the pulse will be clamped when the negative feedback comes into play, thus facilitating the transition from dissipative soliton (DS) to NLP. Experimentally, the observation of wavelength switching and transition between DS and NLP by simply adjusting the polarization state matches the numerical simulation results. This study contributes to a deeper understanding of the mechanism for generating NLP by changing the intracavity polarization state in ANDi all-fiber lasers based on NPR and offers new possibilities for pulse-switchable light sources.