Supermode emission in four-core optical fiber amplifier doped with Yb³⁺

We demonstrate a high power four-core Yb-doped fiber amplifier both theoretically and experimentally. An all-fiber MOPA structure without mode selection components was utilized to amplify the 12 m long four-core fiber. An in-phase supermode laser operation was realized in this fiber. The laser slope efficiency is greater than 56.7% with a maximum output power of 11.47 W. The measured M ² factor of the amplified beam is 1.58, showing the high potential of the fiber. (letter)