High Power Cascaded Erbium Doped Fluoride Fiber Laser at Room Temperature

We demonstrate a high power diode-cladding-pumped cascaded erbium doped fluoride fiber laser at room temperature with ⁴I_11/2 →⁴I_13/2 transition at ~2.8 μm and ⁴I_13/2 →⁴I_15/2 transition at ~1.6 μm. By simultaneously theoretically optimizing erbium ions dopant concentration and fiber length, maximum output power of 15.2 W centered at 2.885 μm at a slope efficiency of 26.7% was achieved experimentally after the onset of cascaded transition centered at 1.613 μm. Maximum output power and slope efficiency of 1.613 μm cascaded laser were 3.2 W and 7.1%, respectively. In our case, no cooling designs were employed on the fiber owing to the use of lowly erbium doped fiber and cascaded laser cavity that weakened the cascaded multiphonon relaxation processes while improving the optical-to-optical conversion efficiency. To the best of our knowledge, this is the first 10-W level fiber laser at 3-μm waveband without any special active or passive cooling designs.