NiSe-based all-fiber mode-locked lasers for generating dark soliton pulses and diverse soliton pulse pairs

Coherent optical structures exemplify how nonlinear effects can manipulate and control light properties. Bright soliton pulses (BSPs), dark soliton pulses (DSPs), breathers, and other stable coherent structures can help achieve specific desirable light temporal and spectral properties. Stable soliton pairs can be considered as fundamental building blocks of soliton molecules. Therefore, the physical mechanisms governing the formation of complex soliton pulse pairs through nonlinear interactions are of special interest. Here we study soliton pairs in an all-fiber erbium-doped mode-locked laser based on NiSe solid powder, a micrometer-sized material distinct from two-dimensional (2D) nanomaterials. We demonstrate switchable dark-bright (D-BSPPs), bright-dark (B-DSPPs) soliton pulse pairs as well as dark-bright-bright soliton pulse pairs (D-B-BSPPs) in an all-fiber erbium-doped fiber laser based on NiSe-saturable absorber, all featuring central wavelengths in the C-band and pulse durations of the nanosecond scale. To our knowledge, the fiber laser presented in this work exhibits richer, more diverse, and more complex dynamics than prior studies, along with excellent reproducibility. The experimental results show that the demonstrated laser design provides a simple test-bed for studying the interaction between DSPs and BSPs and developing laser systems exploiting their temporal-frequency properties for various potential applications.