Narrow linewidth fiber laser with multiple unpumped EDF fiber loops and self-injection feedback

Abstract

In this paper, we proposed a narrow linewidth single-longitudinal-mode (SLM) fiber laser, which was realized by employing a triple-cascaded unpumped erbium doped fiber (EDF) Sagnac loops structure with Rayleigh backscattering (RBS) feedback. Narrow linewidth SLM laser output can be achieved by using the unpumped EDF loops. However, it is generally difficult to achieve laser emission with a linewidth below 1 kHz and a power of tens of milliwatts. In this paper, we propose a fiber laser with multiple unpumped Er-doped fiber loops and self-injection feedback. The cascade of multi-unpumped Er-doped fiber rings is employed to reduce the linewidth of the laser, while the self-injection feedback based on RBS is used to improve the stability of the laser and further compress the laser linewidth. By only utilizing three unpumped Er-doped fiber rings cascaded, we obtain an output beam with a linewidth of 723.05 Hz and laser power of 21.52 mW with 0.30 dB fluctuation during a period time of 30 min at the pump power of 170.6 mW. After introducing the feedback mechanism based on RBS into the fiber laser, an output laser with a linewidth of 530.11 Hz and a laser power of 8.57 mW with 0.23 dB fluctuation in 30 min can be obtained at the pump power of 268.68 mW. Compared with the fiber laser with one unpumped Er-doped fiber ring, the linewidth is reduced more than two times.