Efficient phase-locking of a tiled fiber array of 37 fiber lasers using SPGD

We present the laboratory experiments of phase locking of a 37-channel tiled fiber array using a stochastic parallel gradient descent (SPGD) feedback controller. The experimental setup comprises a hexagonally close-packed array of thirty-seven 23-mm-diameter fiber collimator sub-apertures. The fraction of the output laser power within a solid angle of 1.22λ/D was measured in open loop state and then in closed loop state. The results show that the power in the bucket was increased from 0.028 in open loop to 0.890 in closed loop. When the 37 beams were phase-locked, the residual phase error was λ/23. The power ratio in the bucket (PIB) was 28% that improved 32 times than the open loop state.