High Power Cascaded Erbium Doped Fluoride Fiber Laser at Room Temperature

Abstract

We demonstrate a high power diode-cladding-pumped cascaded erbium doped fluoride fiber laser at room temperature with $^{4}\text{I}_{\mathrm {11/2}}\to ^{4}\text{I}_{\mathrm {13/2}}$ transition at $\sim 2.8~\mu \text{m}$ and $^{4}\text{I}_{\mathrm {13/2}}\to ^{4}\text{I}_{\mathrm {15/2}}$ transition at $\sim 1.6~\mu \text{m}$ . By simultaneously theoretically optimizing erbium ions dopant concentration and fiber length, maximum output power of 15.2 W centered at 2.885 $\mu \text{m}$ at a slope efficiency of 26.7% was achieved experimentally after the onset of cascaded transition centered at 1.613 $\mu \text{m}$ . Maximum output power and slope efficiency of 1.613 $\mu \text{m}$ 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- $\mu \text{m}$ waveband without any special active or passive cooling designs.