Gourd-shaped subring resonator-based single longitudinal mode erbium-doped fiber laser

A gourd-shaped subring resonator (GSR)-based single longitudinal mode erbium-doped fiber laser (EDFL) is proposed and experimentally demonstrated. The GSR can effectively expand the free spectral range of the fiber laser due to the Vernier effect and eliminate the dense longitudinal modes greatly. At the same time, an unpumped erbium-doped fiber serves as a saturable absorber to suppress mode hopping and stabilize frequency effectively. The experimental results show that the linewidth of the produced EDFL is ∼1.84 kHz and the output stability of power variation is nearly 0.02 dB. It can be seen that the EDFL could be exploited in applications where narrow linewidth and high power stability are both required.