Photonic lantern kW-class fiber amplifier.

Pump-limited kW-class operation in a multimode fiber amplifier using adaptive mode control and a photonic lantern front end was achieved. An array of three single-mode fiber inputs was used to adaptively inject the appropriate superposition of input modes in a three-mode gain fiber to achieve the desired mode at the output. Mode fluctuations at high power were compensated by adjusting the relative phase, amplitude, and polarization of the single-mode fiber inputs. The outlook for further power scaling and adaptive-optic compensation is described.