Co-MOFs as Emerging Pulse Modulators for Femtosecond Ultrafast Fiber Laser

The metal organic framework (MOF) has attracted more and more attention due to its unique morphology, functional linkers, and orderly network structure. Zeolitio imidazolata frameworks (ZIFs), which are formed by bivalent transition metals (Zn, Co, etc.) and nitrogen-containing heterocyclic imidazole or purine organic ligands, are a very attractive subclass of MOFs. ZIF-67, obtained by the nucleation growth of dimethylimidazole and Co 2p, has been developed as a precursor for porous nanostructured cobalt-based metal oxides. During material preparation we add rGO because it can be used as a basic element to construct macroscopic three-dimensional carbon structural materials, which self-assemble into a 3D network structure with ZIF-67 through simple van der Waals forces or hydrogen bonds, and some samples contain specific functional groups that are added to the precursor. In this paper, we employ liquid-phase synthesis to generate rGO-ZIF-67 and calcine it at the temperature of 350 °C to obtain rGO-Co₃O₄. Then we fabricate rGO-Co₃O₄ and rGO-ZIF-67 modulators based on microfibers and test their nonlinear optical absorption in 1.5 μm range. The modulation depths of rGO-Co₃O₄ and rGO-ZIF-67 are measured as 10.41% and 6.61%, respectively. By using microfiber-based rGO-Co₃O₄ modulator, we have obtained a conventional soliton and a soliton molecule in Er³⁺-doped fiber lasers. The conventional soliton has a pulse width of 793.4 fs and a spectral width of 3.3 at 1558.9 nm, respectively. The obtained soliton molecule has a spectral modulation period of 1.65 nm and temporal separation of 4.94 ps at 1563.2 nm. By employing a microfiber-based rGO-ZIF-67 modulator, we obtain conventional solitons with a spectral width of 1.9 nm at the central wavelength of 1529.8 nm. Our research may expand the MOF-based materials for ultrafast photonics, blazing a new path for fiber laser, optical communications, and optoelectronics, etc.