350-W Coherent Beam Combining of Fiber Amplifiers With Tilt-Tip and Phase-Locking Control

We demonstrate the coherent beam combining (CBC) of a 350-W single-frequency fiber amplifier array with simultaneous tilt-tip control and phase-locking control. An adaptive fiber-optics collimator is employed to perform the tilt-tip control, and the phase-locking control is realized by the phase modulator. The fiber array in the CBC system consisted of two high-power fiber amplifiers, each with output power of about 175 W. Stochastic parallel gradient descent algorithm is employed in both tilt-tip and phase-locking control. The tilt-tip control makes two separate laser beams overlap with each other in the far field, while the phase-locking control compensates the piston phase differences between the fiber lasers. Normalized power in bucket increases from 0.27 in open loop to 0.99 in closed loop. The fringe contrast is improved from 0% to more than 97% correspondingly. The tilt-tip control bandwidth is higher than 5.4 Hz when the tilt-tip mean square error is 10 μrad.