GeAs2 Saturable Absorber for Ultrafast and Ultranarrow Photonic Applications

As a new IV-V group semiconductor, germanium-diarsenide (GeAs2) compounds have attracted considerable attention due to their outstanding optical and electrical properties, thickness-dependent bandgap, in-plane anisotropy, and excellent optical absorption. However, the potential of GeAs2 in the field of ultrafast and ultranarrow fiber laser has not been studied. In this article, a high-quality GeAs2 nanosheets saturable absorber (SA) is successfully prepared by liquid-phase exfoliation. The nonlinear optical characteristics of GeAs2 nanosheets have been investigated based on a balanced twin-detector measurement system. The modulation depth, nonsaturable loss, and saturation intensity are measured to be 5.2%, 24%, and 1.23 GW cm(-2), respectively. GeAs2 has been successfully applied as an SA in an ultrafast and single-frequency fiber laser. A stable mode-locked laser pulses operation with a duration as short as 371 fs and a repetition rate of 8.19 MHz at a wavelength of 1560 nm is achieved. Moreover, ultranarrow fiber lasers with a high signal-to-noise ratio of 80 dB and a linewidth of approximate to 678 Hz are obtained. The findings validate that 2D GeAs2 can be used as an SA and has promising applications in ultrafast and ultranarrow photonics.