∼2.1 μm Tm 3+-Ho 3+ co-doped tungsten tellurite single mode fiber laser

We investigate the spectroscopic and lasing performance of Tm3+-Ho3+ co-doped tungsten tellurite single mode fiber operating around 2.1 mu m with a commercial 800 nm diode laser pump source. The optimum doping concentration of Tm2O3 and Ho2O3 in Tm3+-Ho3+ co-doped TeO2-WO3-La2O3 (TWL) glass is 1 mol% and 0.5 mol%, respectively. The lifetime of Ho3+:I-5(7) level is 3.3 ms in the bulk glass. The maximum stimulated emission cross-section of Ho3+ in TWL is 10.0x10(-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. Tm3+-Ho3+ co-doped fiber shows weak emission at similar to 1.9 mu m very strong emission at similar to 2.1 mu m, which indicates efficient energy transfer from Tm3+ to Ho3+ in the fiber. The 1.47 mu m emission increases with the increment of the fiber length, which means a back energy transfer from Ho3+ to Tm3+. A 106 mW continuous wave laser emission at similar to 2.1 mu m 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 similar to 2.1 mu m laser sources.