Efficient 1.9 μm Tm3+/Yb3+-doped tellurite fibre laser

We report a Tm3+/Yb3+-doped tellurite fibre laser operating at wavelengths in the range 1879-1994 nm. Two different pump schemes have been demonstrated for this laser: a 1088 nm Yb3+-doped silica fibre laser simultaneously pumping the Tm3+: H-3(5) and Yb3+: F-2(5/2) levels, and a 1610 tun Er3+Nb3+-doped silica fibre laser directly pumping the Tm3+: F-3(4) upper laser level. For the 1610 rim pumping, a slope efficiency of 76% has been achieved in a 32 cm long fibre which is very close to the Stoke efficiency limit of similar to 80%. An output power of 283 mW has also been achieved, but with no signs of saturation or fibre damage suggesting that higher output powers should be possible. For the 1088 nm pumping there is very strong pump ESA resulting in bright blue (480 nm) and near-IR (800 nm) emission and this limits the achievable slope efficiency, which in this case was a maximum of 10% for a 16 cm long fibre. With this pump scheme, the highest observed output power was 67 mW, and further power scaling was limited due to the intense ESA and thermal damage to the pump end of the fibre. Lasing has been achieved in <10 cm lengths of this fibre making this material a promising candidate for ultra compact medium power mid-IR laser sources for range-finding, medical and atmospheric monitoring and sensing applications.