Narrow linewidth single mode fiber laser with double unpumped EDF Sagnac loops filter

摘要

In this paper, we proposed a narrow linewidth single longitudinal mode (SLM) fiber laser, which was realized by employing a double unpumped erbium doped fiber (EDF) Sagnac loops structure. The Sagnac loops formed self-injected fiber Bragg gratings (FBG) and helped SLM selection, while the saturable absorption in unpumped EDF was used to compress the output laser linewidth. Connecting two unpumped EDF Sagnac loops in sequence was analyzed theoretically and tested experimentally, which would lead to narrower output laser linewidth. Under a pump power of 200 mW, we obtained an output linewidth of 858 Hz and a power stability of 0.32 dB/30 min. This structure provided a simple and low-cost way of generating narrow linewidth stable SLM laser.