Active phasing a nine-element 114 kW all-fiber two-tone MOPA array using SPGD algorithm

Abstract

We demonstrated active phase locking a nine-element 1.1 kW all-fiber master-oscillator power amplifier (MOPA) array using the stochastic parallel gradient descent (SPGD) blind optimization algorithm. Two spectrally combined single-frequency seed lasers, which provide potential ability to suppress the stimulated Brillouin scattering effect, are employed as a master oscillator for the nine MOPA channels. The nine laser beams are tiled side by side into a 3×3 laser array with a fill factor of 40% in the near field. When the SPGD controller is enabled, the metric function is increased 4.1 times, and a visibility more than 90% of the interference pattern at the receiving plane is obtained. The computed phase residual error is less than λ/15, despite the phase fluctuation of each channel.