Coherent beam combination of ten fiber arrays via stochastic parallel gradient descent algorithm

Coherent beam combination of ten fiber arrays using a stochastic parallel gradient descent (SPGD) algorithm is demonstrated. A high speed phase controller has been designed and manufactured based on the SPGD algorithm and a field programmable gate array (FPGA). The signal processing speed of the FPGA circuit is 50 MHz and its iteration rate is more than 200 kHz. Experimental investigation on coherent beam combination of 10 fiber laser beams is successfully demonstrated, with imposing additional phase disturbances to mimic the phase noises in the high power fiber amplifiers. The combining efficiency is about 96.4% and 92.6% without/with additional phase distortion, corresponding to the RMS phase error of λ/35 and λ/23.