Ultra-narrow linewidth Tm3+-doped fiber laser based on intra-core fiber Bragg gratings

A 74 pm ultra-narrow linewidth diode laser (LD) claddingding-pumped Tm 3+ -doped fiber laser was reported. The maximal continuous wave (CW) output power was 14.5 W at 1946 nm, with a slope efficiency of 37.5% and the threshold of 5.3 W. The single-mode double-cladding Tm 3+ -doped fiber had a core diameter of 15 μm (NA:0.1), and the regular hexagonal inner-cladding diameter was 200 μm (NA:0.46). The high reflection coupler was based on the intra-core fiber Bragg gratings (FBGs), which were directly written into the Tm 3+ -doped non-photosensitive fiber core by the 800 nm femtosecond laser and a phase mask. The output coupler was the other fiber end with 3.6% Fresnel reflection, and the pump source was a high power 792 nm LD with a 200 μm pigtail fiber output. According to our knowledge, this was the first report on the ultra-narrow linewidth Tm 3+ -doped fiber laser using intra-core FBGs approximately 2 μm.