Hollow MoS2-Co3S4 heterostructures derived from ZIF-67 as saturable absorber for generating gigahertz repetition frequency mode-locked fiber lasers

In practical applications, high repetition frequency (HRF) lasers are widely used in the fields of material processing, laser communication and medical therapy. In this work, the passive harmonic mode-locked (HML) technique is used to realize a HRF fiber laser in GHz level, effectively overcoming the limitations of traditional fiber laser structures. In order to maximize the advantages of nanomaterials, we synthesized high-purity hollow MoS 2 -Co 3 S 4 heterojunction materials by hydrothermal method. Then, a “sandwich” structure saturable absorber (SA) was prepared by photodeposition, and its nonlinear optical properties were investigated. The results demonstrate that the modulation depth and saturation intensity of MoS 2 -Co 3 S 4 SA are 24 % and 4.53 MW/cm 2 , respectively. The fiber laser based on MoS 2 -Co 3 S 4 SA could realize the fundamental frequency mode-locked at 23.11 MHz with a pulse width of 0.99 ps. In addition, various high-order HML are realized with this laser system capable of stable operation for extended periods up to the highest repetition frequency of 1.109 GHz achieved thus far in this field. This research provides strong support to promote the development and commercialization of HRF fiber lasers.