Controllable Soliton Pairs in Few-Layer FePSe₃ Nanosheets-Based Optical-Intensity Modulators

Optical-intensity modulators based on two-dimensional (2D) materials play a significant role in the realization of ultrashort pulses. FePSe3, as a new 2D material, has shown great potential in this field because it has a suitable band gap (indirect, ∼1.3 eV) and stronger linear absorption in the middle infrared region compared with homologous compounds. However, the research of its nonlinear absorption has not been reported yet. In this work, the saturable absorption intensity (312 MW/cm2) and modulation depth (33.7%) of few-layer FePSe3 nanosheets, synthesized by an inorganic salt templated method, have been measured by a stable femtosecond laser. Most importantly, controllable bright-dark soliton pairs in the time domain and 40th-order harmonic mode locking have been experimentally achieved based on an optical-intensity modulator made by few-layer FePSe3 nanosheets. This work has proven that few-layer FePSe3 nanosheets can be used as a high-performance optical-intensity modulator in many fields, such as ultrafast optics.