High-power ytterbium-doped multicore fibers

• Single-core fibers for amplification of light are facing performance limitations. • Parallelization of the amplification process can overcome these limitations. • Multicore fibers offer a compact way to realize parallelized amplification. • Average powers of more than 1 kW and pulse energies of more than 100 mJ achieved. • Beyond performance scaling, multicore fibers allow for beam and pulse shaping. Fiber lasers are nowadays one of the preferred coherent light sources when high average powers up to the multi-kW regime are targeted. Additionally, they are also widely employed for the generation of ultrashort pulses with moderate energy in the mJ-range. However, numerous physical limitations currently hinder a further performance scaling. One way to overcome these limitations is the coherent beam combination of parallel amplifiers. This approach has led to laser systems operating beyond the limits of a single amplifier, albeit at the cost of an increase in footprint and complexity. Amplifying multicore fibers hold the promise to combine the simplicity of fiber lasers with unprecedented performance scaling prospects and the additional benefit of enabling dynamic beam and pulse shaping. In this paper, basic considerations about design parameters of multicore fibers with non-coupling cores are given and the impact of physical effects on the output emission is discussed. State-of-the art results of multicore-fiber-based laser systems are reviewed with these fibers now being able to output kW-level average powers and nanosecond pulses with over 100 mJ pulse energies. Finally, an outlook regarding future performance targets and possible applications is given.