CW and Q-switched 2.1 μm Tm3+/Ho3+/Yb 3+-triply-doped tellurite fibre lasers

We present efficient CW lasing Tm3+/Ho3+/Yb3+-triply-doped tellurite fibre at ∼2.1 μm. Two different pump schemes have been demonstrated for this laser: a 1.088 μm Yb3+-doped silica fibre laser simultaneously pumping the Tm3+:3H5, Ho3+:5I6and Yb3+:2F5/2levels, and a 1.6 μm Er3+/Yb3+-doped silica fibre laser directly pumping the Tm3+:3F4level. For the 1.6 μm pumping, a slope efficiency of 62% has been achieved in a 76 cm long fibre which is close to the Stokes efficiency limit of ∼75%. An output power of 160 mW has also been achieved, but with no signs of saturation or fibre damage suggesting that higher output powers should be possible. For the 1.088 μm pumping there is very strong pump ESA resulting in bright blue (480 nm) and near-IR (800 nm) fluorescence due to the1G4→3H6and3H4→3H6transitions of Tm3+, respectively, and this limits the achievable slope efficiency, which in this case was a maximum of 25% for a 17 cm long fibre. With this pump scheme, the highest observed output power was 60 mW, and further power scaling was limited due to the intense ESA and thermal damage to the pump end of the fibre. We also present results on the active Q-switching of the 1.6 μm pumped fibre laser using a mechanical chopper operating at 19.4 kHz. Average powers of 26 mW and pulse energies of 0.65 μJ were measured with pulse widths in the range 100-160 ns.