All-fiber highly efficient delivery of 2 kW laser over 2.45 km hollow-core fiber

Anti-resonant hollow-core fibers have emerged as an important medium for high-power laser delivery due to their low optical nonlinearity and high damage threshold. However, current delivery systems of high-power laser based on anti-resonant hollow-core fibers mainly rely on free-space optical components, which limits long-term stability. Here, we report an all-fiber delivery of 2 kW laser with 85.4% transmission efficiency over 2.45 km, using a self-fabricated hollow-core fiber with a record low transmission loss of 0.168 dB/km at 1080 nm. Notably, we observed the phenomenon of stimulated Raman scattering amplified within the silica nested tubes for the first time. By effectively suppressing the Raman noise from the laser source, we achieve an all-fiber laser delivery without stimulated Raman scattering of silica glass. This work marks a significant breakthrough in multi-kilometer and multi-kilowatt power delivery that is potentially useful for industrial manufacturing, nuclear decommissioning, laser drilling in oil and so on.