820 Hz linewidth short-linear-cavity single-frequency fiber laser at 1.5 μm

Abstract

We proposed a short-linear-cavity fiber laser with a virtual-folded-ring configuration, which combines the advantages of ring lasers and short-linear-cavity lasers. An all-fiber quarter-wave plate was used inside the cavity to introduce polarization retardation. By retarding the polarization of the travelling waves, the spatial-hole-burning effect was weakened and the efficient cavity length was extended to nearly twice its physical length. As a result, a single-frequency laser output with a linewidth of less than 820 Hz was obtained from the free-running fiber laser. The relaxation oscillation frequency was observed to be around 280 kHz and the signal to noise ratio of the laser output was >72 dB.