Supramolecular isomeric Co-CPs as saturable absorbers in erbium-doped fiber lasers

Abstract

Metal-organic frameworks (MOFs) are notable for their tunable pore structures, high surface areas, and diverse optical properties, making them promising candidates for ultrashort pulsed laser applications. In this study, we synthesized two MOF materials, {[Co₂(L)(dmbpy)₂(H₂O)₂]·DMF}_n (referred to as CoCP-1) and {[Co(L)_0.5(dmbpy)(H₂O)]·0.5H₂O·0.75DMF}_n (referred to as CoCP-2), with similar one-dimensional chain structures, using an F-containing tetracarboxylic acid ligand. Despite the similarity in their chain structures, variations in the bending of the aromatic ring linkages result in the formation of distinct supramolecular architectures. In our experimental investigation, CoCP-1 showed a relatively higher modulation depth of 12.57% and a saturation intensity of 77.03 MW/cm², while CoCP-2 exhibited a modulation depth of 9.82% and a saturation intensity of 59.28 MW/cm². Upon integration into an erbium-doped fiber laser system, both materials demonstrated the capability to generate stable mode-locked and Q-switched mode-locked (QML) pulses. At a pump power of 193 mW, the CoCP-1-based fiber laser generated a fundamental mode-locked pulse with a pulse width of 1.19 ps and a repetition rate of 4.363 MHz. In comparison, the CoCP-2-based fiber laser achieved a 1.16 ps pulse width with a repetition rate of 4.407 MHz. As pump power increased, QML pulses emerged in both systems. Both systems maintained an SNR above 45 dB for QML pulses. This work demonstrates that CoCP-1 and CoCP-2 possess outstanding optical properties, broadening the application scope of MOFs. These findings offer new insights and possibilities for designing and optimizing saturable absorbers in nonlinear optics and ultrashort pulsed laser technology.