Long-term stable 850-Hz linewidth single-longitudinal-mode ring cavity fiber laser using polarization-maintaining fiber

A long-term stable single-longitudinal-mode (SLM) all polarization-maintaining (PM) compound-ring cavity fiber laser is reported. The results show that the PM fiber's strong ability to resist the environment disturbance allows finely designing the length of each secondary cavity in real time according to the main cavity under the laboratory environment, and then the effective longitudinal mode spacing can be sufficiently increased by accurately using the Vernier effect, so that the mode-hopping can be effectively suppressed. Furthermore, the temperature compensation is used for asynchronously fine-adjusting each cavity length to follow the Vernier effect requirement more strictly. The mode-hopping-free SLM operation time of the packaged laser reaches 11 h. As far as we know, this is the longest SLM free running time of ring cavity fiber laser to date. The optical signal to noise ratio of the laser reaches 77 dB and the linewidth is less than 850 Hz with up to 50 mW maximum output power.