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

• Ultrathin VSe 2 nanosheets with thickness less than 5 nm are prepared by liquid phase exfoliation. • Two-dimensional metallic layered VSe 2 exhibits saturable absorption properties. • Single- and Dual-wavelength mode-locked fiber lasers are realized using VSe 2 -based saturable absorber, respectively. Vanadium selenide (VSe 2) 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, VSe 2 has advantage of ultrafast carrier recovery time and broadband optical response range. However, the potential application of VSe 2 in the field of ultrafast photonics has not been fully developed so far. In this work, the as-prepared VSe 2 nanosheets were deposited on tapered fiber by optical deposition to obtain VSe 2 SA. By inserting VSe 2 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 VSe 2 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 VSe 2 is of great potential value in ultrafast fiber laser. [ABSTRACT FROM AUTHOR]