Coherent polarization beam combining of 16-channel femtosecond fiber lasers

Coherent beam combination (CBC) has been recognized as an effective way to break through the power limitation of single-channel femtosecond fiber lasers. Based on the stochastic parallel gradient descent (SPGD) algorithm and fiber stretcher for phase-locked control, we have achieved efficient filled aperture coherent polarization beam combination of sixteen-channel ultrafast fiber lasers. The combined output average power was 15 W, corresponding to a high combination efficiency of 94%. The phase residue error was estimated to be λ/21 in the closed loop state. In addition, the compressed output pulse duration was 633 fs. It is anticipated that higher power and combining efficiency can be realized by further introducing the beam pointing control for each channel.