Yb-free Er-doped all-fiber amplifier cladding-pumped at 976 nm with output power in excess of 100 W

Abstract

Power scaling of Yb-free Er-doped fiber lasers is extremely challenging due to low Er ion absorption cross-section and growth of unbleachable loss at high Er concentrations because of clustering effects. Hence, usual double-clad Er-doped fibers suffer from low efficiency. We present an efficient high power all-fiber amplifier based on our newly developed Yb-free Er-doped fiber. Proper core composition and relatively low Er3+ concentration mitigates clustering effect. Furthermore, large single-mode core diameter of 34 um increases the pump absorption and decreases the fiber length. Our amplifier consists in the specialty Er fiber pumped through a commercially available pump combiner by means of 6 pigtailed multimode diodes (D=105 um, NA=0.15, input pump power of 275W). The signal source is a low power continuous wave fiber laser spliced to the amplifier. Therefore we built truly all-fiber laser without any free space coupling. We obtained 103 W of amplified signal limited only by the available pump power. Pump conversion efficiency is as high as 37 %. To the best of our knowledge this is the highest power ever demonstrated for Yb-free Er-doped lasers pumped at 976 nm. This power level is similar to that obtained in resonantly pumped Er-doped fiber lasers.