Few-Layer Bismuthene for Coexistence of Harmonic and Dual Wavelength in a Mode-Locked Fiber Laser

Bismuthene, as a novel two-dimensional (2D) material, has attracted extensive attention because of its outstanding properties including narrow band gap, stability at room temperature, nonlinear optical transmission, and so on. In this paper, the physical characteristic, nonlinear optical response, and ultrafast photonics application of few-layer bismuthene are studied experimentally. By the balanced twin-detector measurement method, the saturable absorption property of few-layer bismuthene with a modulation depth of 2.5% and saturable intensity of 110 MW/cm2 at the optical communication band (C-band) is illustrated. Dependent on a few-layer bismuthene saturable absorber, an all-fiber ultrashort pulse laser is fabricated and the proposed fiber laser can operate with coexistence of harmonic mode-locking and dual-wavelength mode-locking. The different laser generations of harmonic and dual wavelength depend on the saturable absorption of few-layer bismuthene, the suitable birefringence and nonlinearity strength in the laser cavity. The results suggest that the ultrashort pulse laser obtained based on few-layer bismuthene could be applied to the field of pump–probe experiments and tunable terahertz radiation generation potentially.