Three-transition cascade erbium laser at 1.7, 2.7, and 1.6 µm

We report on an upconversion cascade laser in an erbium-doped ZBLAN fiber emitting simultaneously on the three transitions 4S3/2 -> 4I9/2 at 1.7 um, 4I11/2 -> 4I13/2 at 2.7 um, and 4I13/2 -> 4I15/2 at 1.6 um. At moderate pump powers, the laser transition at 1.6 um supports 2.7-um lasing and permits a slope efficiency at 2.7 um of 15% versus launched pump power. Above the threshold of upconversion lasing at 1.7 um, the slope efficiency at 2.7 um increases to 25.4%. Taking pump excited-state absorption into account, this value represents more than 90% of the theoretical slope efficiency. A transversely single-mode output power of 99 mW is achieved at 2.7 um.