Three-dimensional Ag₂S cubes for switchable multi-wavelength ultrashort pulse application

Three-dimensional (3D) materials are widely used in optoelectronics, thermodynamics and ultrafast fiber lasers because of their excellent nonlinear optical properties. Silver sulfide (Ag₂S) is a kind of 3D material with a unique cubic structure and large absorption coefficient. In this paper, a double-balance detection system is used to measure the saturation absorption intensity of Ag₂S as 226.6 MW cm^-2and the modulation depth as 13.9%. In the ring fiber laser, Ag₂S is used as a saturable absorber (SA) to obtain a stable dual-wavelength mode locking. The center wavelengths of the mode locking are 1536.9 and 1544.5 nm, and the corresponding 3 dB bandwidths are 1.3 and 1.5. nm. By adjusting the polarization controller, a tuning process from two wavelengths to multiple wavelengths is realized, and the tunable width is 13.1 nm. This phenomenon is due to the combined effect of birefringence and nonlinear effects in the cavity. To our knowledge, this is the first report of a multiplexed fiber laser with Ag₂S as a SA. The emergence of this result provides a valuable reference information for the multifunctional compact fiber laser, and the formed system can be applied in the fields of fiber sensing, telecommunications and optical communication.