Single-frequency fiber lasers based on metal thiophosphites with sub-kHz linewidths.

Metal thiophosphites (CrPX) (X = S and Se), emerging layered metal chalcogenophosphate materials, have found extensive utility in the fields of advanced electronic devices, magnetic technologies, and electrochemical systems. However, their applications in single-frequency fiber lasers have been relatively limited. Here, liquid phase exfoliation technology is used to exfoliate the CrPX into few-layered samples. Subsequently, we explored the application of CrPX-based saturable absorbers (CrPX-SA) by precisely depositing CrPX nanosheets onto the surface of D-shaped fibers. This led to the successful creation of two stable single-frequency fiber lasers (SFFLs) based on CrPS and CrPSe with center wavelengths of 1550.068 nm and 1550.092 nm, respectively. The linewidth of CrPSe was tested and determined to be roughly 375 Hz, which is the narrowest ever value attained for an SFFL based on its structure, and its signal-to-noise ratio (SNR) was 74.17 dB. The maximum output power of each oscillator was 0.796 mW and 0.963 mW, and their corresponding power fluctuations were 2.5% and 1.4%, respectively.