  Rare-earth-doped fiber lasers are emerging as promising high-power
mid-infrared sources for the 2.6-3.0 {\mu}m and 3.3-3.8 {\mu}m regions based on
erbium and holmium ions. The intermediate wavelength range, however, remains
vastly underserved, despite prospects for important manufacturing and defense
applications. Here, we demonstrate the potential of dysprosium-doped fiber to
solve this problem, with a simple in-band pumped grating-stabilized linear
cavity generating up to 1.06 W at 3.15 {\mu}m. A slope efficiency of 73% with
respect to launched power (77% relative to absorbed power) is achieved: the
highest value for any mid-infrared fiber laser to date, to the best of our
knowledge. Opportunities for further power and efficiency scaling are also
discussed.
