~2.1 um Tm 3+ -Ho 3+ co-doped tungsten tellurite single mode fiber laser

We investigate the spectroscopic and lasing performance of Tm 3+ -Ho 3+ co-doped tungsten tellurite single mode fiber operating around 2.1 μm with a commercial 800 nm diode laser pump source. The optimum doping concentration of Tm 2 O 3 and Ho 2 O 3 in Tm 3+ -Ho 3+ co-doped TeO 2 -WO 3 -La 2 O 3 (TWL) glass is 1 mol% and 0.5 mol%, respectively. The lifetime of Ho 3+ : 5 I 7 level is 3.3 ms in the bulk glass. The maximum stimulated emission cross-section of Ho 3+ in TWL is 10.0×10 -21 cm 2 . The tungsten tellurite single mode fibers are prepared by using rod-in-tube method. The infrared emission spectra are compared with varying fiber lengths. Tm 3+ -Ho 3+ co-doped fiber shows weak emission at ~1.9 μm very strong emission at ~2.1 μm, which indicates efficient energy transfer from Tm 3+ to Ho 3+ in the fiber. The 1.47 μm emission increases with the increment of the fiber length, which means a back energy transfer from Ho 3+ to Tm 3+ . A 106 mW continuous wave laser emission at ~2.1 μm is demonstrated from a 16 cm length of this fiber, the slope efficiency is 23%, corresponding to a 17% optical to optical efficiency. Lasing has also been achieved in <5 cm length of this fiber, making this material a promising candidate for single frequency ~2.1 μm laser sources.