Metallic layered VSe2 saturable absorber based single- and dual-wavelength ultrafast fiber laser

•Ultrathin VSe2 nanosheets with thickness less than 5 nm are prepared by liquid phase exfoliation.•Two-dimensional metallic layered VSe2 exhibits saturable absorption properties.•Single- and Dual-wavelength mode-locked fiber lasers are realized using VSe2-based saturable absorber, respectively. Vanadium selenide (VSe2) is a special two-dimensional (2D) transition metal dichalcogenide (TMD) material with metallic properties similar to graphene, which has been proved to have saturable absorption properties and used in mode-locked fiber lasers. As an excellent saturable absorber (SA) material, VSe2 has advantage of ultrafast carrier recovery time and broadband optical response range. However, the potential application of VSe2 in the field of ultrafast photonics has not been fully developed so far. In this work, the as-prepared VSe2 nanosheets were deposited on tapered fiber by optical deposition to obtain VSe2 SA. By inserting VSe2 SA into an Er-doped fiber laser, the mode-locked pulses with a central wavelength of 1574.4 nm can be obtained. The pulse width of the laser is measured to be ∼680 fs which is narrowest in the reported VSe2 SA-based lasers. In addition, the unique dual-wavelength mode-locked pulse is also obtained by further adjusting intracavity dispersion and polarization. This kind of dual-wavelength pulse is valuable in high order harmonic generation enhancement, terahertz wave generation, dense wavelength division multiplexing, dual-frequency comb and other applications. Our results show that metallic VSe2 is of great potential value in ultrafast fiber laser.