Molybdenum Carbide Buried in D-Shaped Fibers as a Novel Saturable Absorber Device for Ultrafast Photonics Applications.

Study of nonlinear laser-matter interactions in 2D materials has promoted development of photonics applications. As a typical MXene material, molybdenum carbide (MoC) has attracted much attention because of its graphene-like structure. Here, a type of D-shaped fiber (DF)-buried MoC saturable absorber (SA) fabricated by magnetron-sputtering deposition (MSD) and sol-gel technique is reported. The MoC material was buried between the bottom DF and the upper amorphous silica fabricated by sol-gel technology. Therefore, the DF-based SA effectively solves the problem of material shedding and aging, thus improving the stability and damage threshold of the fiber laser. Application of the SA in erbium-doped fiber laser and stable passive Q-switched operation with a maximum pulse energy of 430.47 nJ is realized. By adjusting the polarization state and pump power, high-power mode-locked pulses are generated with a pulse duration and output power of 199 fs and 54.13 mW, respectively. Further, bound-state soliton pulses are obtained with a pulse width of 312 fs and soliton interval of 1.26 ps for the first time based on MXene materials. Moreover, by application of the SA in ytterbium-doped fiber lasers, a stable dissipative soliton mode-locked pulse is obtained with a pulse width of 23 ps. These results indicate that the DF-based buried MoC as a novel SA provides a reliable method for all-fiber and multifunctional high-power ultrafast laser.