Single frequency fiber laser with sub-kHz linewidth based on ultra narrowband nonlinear filtering using fiber loop mirror and silver indium phosphorus sulfide

This article demonstrates a linear cavity single frequency fiber laser (SFFL) implemented using a transient grating composed of AgInP₂S₆ and a fiber loop mirror as a filter. We first studied the optical properties such as transient absorption and nonlinear absorption of AgInP₂S₆ nanomaterials. Based on this, a SFFL with a center wavelength of 1550.12 nm and a linewidth of 0.92 kHz has been achieved. The signal-to-noise ratio is 64 dB and the maximum output power reaches 12.6 mW. Further research is conducted on the stability of the output single frequency laser within 6 h, with wavelength and power fluctuations of less than 20 pm and 1.51 %, and the side mode suppression ratio of the self-heterodyne beat signal and spectral linewidth fluctuations being less than 0.8 dB and 4.2 %, respectively. It is worth noting that we use AgInP₂S₆ materials combined with fiber loop mirrors to form fiber filters with ultra narrow bandwidth. Compared with ultra short cavity distributed feedback fiber lasers and distributed Bragg reflector fiber lasers, it has a longer cavity length, which is very desirable for achieving laser linewidth compression and output power improvement. Therefore, this study provides valuable strategies and guidance for the development of nonlinear optical materials based on AgInP₂S₆ and opens up new path for advanced photonic devices for SFFLs.