CrBi₂Te₄-based mode-locked fiber laser with three switchable operating states

In recent years, 2D materials have been widely used in the field of optoelectronics, and these 2D materials have further improved the performance of fiber lasers. CrBi₂Te₄ is a member of the 2D material family known as topological insulators, featuring unique ferromagnetic properties and potential for saturation absorption. In this paper, we study the saturation absorption characteristics of CrBi₂Te₄-PVA nanosheets and CrBi₂Te₄ D-type fibers, and verify their nonlinear absorption characteristics in erbium-doped fiber lasers. When CrBi₂Te₄-PVA nanosheets are used as SAs, 10th-order harmonic pulses with a pulse width of 765.1 fs are generated. Utilizing CrBi₂Te₄ D-type fibers as saturable absorbers (SAs) leads to the generation of dark solitons and bright-dark soliton pairs, with average output powers reaching a maximum of 2.38 mW and 3.12 mW, respectively. To the best of our knowledge, this is the first presentation of a mode-locked fiber laser with the CrBi₂Te₄-based SA, and also the first study of bright and dark soliton properties of a CrBi₂Te₄-based fiber laser. It is foreseeable that CrBi₂Te₄ will become an appealing candidate for bright and dark soliton fiber lasers.