Narrowband selection in a standing wave active fiber loop mirror for a single longitudinal mode L-band Er-doped fiber...

We demonstrate a simplified single longitudinal mode (SLM) L‑band erbium‑doped fiber laser using an active fiber loop mirror (AFLM). It requires no separate saturable absorber or circulator. Stable SLM operation is achieved with an output power of 3-4 mW and a wavelength drift <1 pm over 10 minutes. Reflectance measurements show that an absorption dynamic grating (ADG) in the unpumped fiber section provides narrowband selection, while a gain dynamic grating (GDG) in the pumped section reduces reflection contrast from 20% to 3% at high pump power. Nonetheless, the ADG remains strong enough to prevent mode hopping. The design offers a compact, low‑cost L‑band SLM laser.