Efficient watt-level fluoride fiber laser beyond 3 μm enabled by direct diode pumping

Rare-earth-ion-doped fluoride fiber laser enabled by direct diode pumping provides a compact and robust platform for mid-infrared production, thereby serving a number of real-world applications. Nowadays, the power of such an architecture beyond 3 μm, however, has been clamped at < 1 W due to lack of readily available laser diode and/or efficient operation mechanism. In this work, we experimentally present efficient watt-level power output beyond 3 μm from an Er/Dy codoped fluoride fiber laser, clad-pumped by a cost-effective 974 nm diode, for the first time. In a free-running F-P scheme with an optimized output coupler reflectivity of 33 %, a maximum output power of 3.03 W at ∼3210 nm has been achieved with a slope efficiency of up to 19.1 % (with respect to the coupled pump), representing the first > 1 W diode-pumped rare-earth-ion-doped fiber laser beyond 3 µm with the highest efficiency. Then the numerical model, validated by our experimental data, has been built up, in which the previously ignored processes (i.e., ∼2.8 µm emission of Er and absorption of Dy) have been considered as an equivalent cross relaxation process, and confirmed probably to be the dominant role in determining efficient operation of this system. Using the model, the numerical optimization and performance prediction have been performed. Numerical comparison with the state-of-the-art Dy-doped fluoride fiber laser in this band based on tandem pumping approach indicates great potential of Er/Dy codoped system in high-power operation and its merits of compactness and high cost effectiveness as a promising alternative scheme.