Narrow-linewidth single-frequency single-polarization Er-doped fiber ring laser

In order to acquire a stable narrow-linewidth single-frequency polarized Er-doped fiber laser, the ring fiber laser with a saturable absorber was studied. In the experiments, an un-pumped Er-doped fiber was used as saturable absorber to form an optical narrow-bandwidth filter, a fiber Bragg grating with high reflectivity was adopted as coarse wavelength selective component, and a polarization-maintaining optical circulator with high extinction ratio was applied to acquire single polarization laser. The peak wavelength of the Er-doped ring fiber laser can be tuned from 1548 nm to 1552 nm by pulling the fiber Bragg grating. The maximum output power was 55.4 mW when the pump power arrived at 275 mW. The 20 dB linewidth of the Er-doped ring fiber laser was measured to be 3 kHz with the fiber delayed heterodyne method. It was found that the polarization of the Er-doped ring fiber laser was very stable for a long term, and the degree of polarization was 99.9%. This narrow-linewidth single-frequency single-polarization Er-doped fiber laser can be used as stable signal source for coherent laser radar.