  The lack of high power integrated lasers have been limiting silicon
photonics. Despite much progress made in chip-scale laser integration, power
remains below the level required for key applications. The main inhibiting
factor for high power is the low energy efficiency at high pumping currents,
dictated by the small size of the active device. Here we break this power
limitation by demonstrating a platform that relies on the coupling of a
broad-area multimode gain to a silicon-nitride feedback chip, which acts as an
external cavity. The feedback provided by the silicon-nitride chip is routed
through a ring resonator and a single-mode filter, thus causing the otherwise
multimode-gain chip to concentrate its power into a single highly-coherent
mode. Our device produces more than 150 mW of power and 400 kHz linewidth. We
achieve these high-performance metrics while maintaining a small footprint of 3
mm^2.
