Black phosphorus, a newly emerged two-dimensional material, has attracted wide attention as novel photonic material. Here, multilayer black phosphorus is successfully fabricated by liquid phase exfoliation method. By employing black phosphorus as saturable absorber, we demonstrate a passively Q-switched Er-doped ZBLAN fiber laser at the wavelength of 2.8 μm. The modulation depth and saturation fluence of the black phosphorus saturable absorber are measured to be 15% and 9 μJ/cm², respectively. The Q-switched fiber laser delivers a maximum average power of 485 mW with corresponding pulse energy of 7.7 μJ and pulse width of 1.18 μs at repetition rate of 63 kHz. To the best of our knowledge, this is the first time to demonstrate that black phosphorus can realize Q-switching of 2.8-μm fiber laser. Our research results show that black phosphorus is a promising saturable absorber for mid-infrared pulsed lasers.

Ultrafast fiber lasers are in great demand for various applications, such as optical communication, spectroscopy, biomedical diagnosis, and industrial fabrication. Here, we report the highly stable femtosecond pulse generation from a MXene mode-locked fiber laser. We have prepared the high-quality ${\mathrm{Ti}}_3{\mathrm{C}}_2{\mathrm{T}}_{\mathrm{x}}$ nanosheets via the etching method, and characterized their ultrafast dynamics and broadband nonlinear optical responses. The obvious intensity- and wavelength-dependent nonlinear responses have been observed and investigated. In addition, a highly stable femtosecond fiber laser with signal-to-noise ratio up to 70.7 dB and central wavelength of 1567.3 nm has been delivered. The study may provide some valuable design guidelines for the development of ultrafast, broadband nonlinear optical modulators, and open new avenues toward advanced photonic devices based on MXenes.

The strong light–matter interaction in two dimensional (2D) materials portends an untapped potential for fiber lasers in the long sought-after terahertz to mid-infrared spectral range. Here, the broadband nonlinear optical properties of zero-gap 2D Ti ₂ CT _x MXene—a class of 2D transition metal carbides that exhibit high laser damage threshold—is discussed. Using the open aperture Z -scan method, for the first time the broadband saturable absorption properties of Ti ₂ CT _x in the 800–1560 nm spectral range are demonstrated. Specifically, it is shown that the high absorption and low saturation intensity of Ti ₂ CT _x make it an ideal saturable absorber for mode-locked fiber lasers operating at 1565 and 1051 nm, which exhibited pulse widths of 5.3 ps and 164 ps, respectively. Additionally, a Ti ₂ CT _x saturable absorber was used as a Q-switcher to realize a pulsed fiber laser operating at 2.8 µ m, which showed excellent nonlinear absorption performance in the mid-infrared regime. This study significantly broadens the scope of materials available for non-linear optical applications in the near and mid-infrared regimes.

We experimentally demonstrated a stable, high-average-power, continuous-wave (CW) passively mode-locked ${\mathrm{Er}}^{3+}$-doped ZBLAN fiber laser at 2.8 μm based on a semiconductor saturable absorber mirror. A stable mode-locked laser with a signal-to-noise ratio of 52 dB and a slope efficiency of 14% was obtained. The highest average output power in excess of 1 W was generated at the incident pump power of 8.2 W, with a pulse repetition rate of 22.56 MHz and pulse duration of 25 ps. To the best of our knowledge, this is the highest average output power of a CW mode-locked ZBLAN fiber laser in the mid-infrared wavelength regime up to now.

The third-order nonlinear optical properties of CH₃NH₃PbI₃ perovskite film have been investigated by the Z-scan technique in the mid-infrared (mid-IR) region. We prepared the high-quality CH₃NH₃PbI₃ films with the precursor solutions, and experimentally observed its broadband saturable absorption behavior and large Kerr nonlinearity. The CH₃NH₃PbI₃ perovskite film exhibited a large nonlinear refractive index (~10⁻¹² m²/W) in the mid-IR regime. Our study indicates the great potential of the organic-inorganic perovskite material in the mid-IR nonlinear optics, and might provide some new sights for Kerr nonlinearity based mid-IR nonlinear optical application.

We demonstrated a passively Q-switched 2.8-μm Er ^3± -doped ZBLAN fiber laser with topological insulator Bi ₂ Te ₃ nanosheets prepared by the solvothermal method. Enabled by the gold mirror with self-assembled Bi ₂ Te ₃ nanosheets film sandwiched by polymethyl methacrylate polymer, the Q-switched fiber laser can deliver a maximum average power of 856 mW with corresponding pulse energy of 9.3 μJ and a pulse width of 1.3 μs at a repetition rate of 92 kHz under the pump power 5.9 W. To the best of our knowledge, this is the highest output power for the pulsed fluoride fiber laser around 2.8 μm modulated by the two-dimensional Dirac material. This letter reveals that the topological insulator can be a kind of promising nonlinear modulator for a mid-infrared laser.