Challenges in coherent beam combining of high power fiber amplifiers: a review

Coherent combining of light from multiple high power fiber amplifiers is a promising pathway to scaling the output power to hundreds of kiloWatts. In the last decade, substantial progress has been made in terms of scaling number of elements along with improvement in phase control techniques to achieve stable locking, resulting in tens of kiloWatts of output power. In this paper, we review the progress in coherent beam combining of fiber amplifiers in the master oscillator power amplifier configuration. We also discuss the challenges in power scaling as well as the current trends in the corresponding mitigation strategies. Specifically, the use of optimized phase modulation waveforms for mitigation of stimulated Brillouin scattering in high power amplifiers, scaling of the number of beam combining elements through deep-learning based phase control, and the use of micro-lens array for enhancing beam combination efficiency are discussed.