High precision phase control system in coherent combining of fiber laser based on stochastic parallel gradient descent algorithm

Abstract

Stochastic parallel gradient descent （SPGD） algorithm is one of the effective ways to realize high power fiber laser coherent combining of master oscillator power amplifier. The basic principle of the SPGD algorithm in the coherent combining is introduced, the SPGD phase controller has been designed and manufactured, and the representative experiment results are presented. Theoretical analysis shows that the iteration rate is 200000 per second, the average compensation bandwidth is about 12500 Hz, the minimal phase control error is 1/179 wavelength. Experiment shows that the SPGD controller can perform well in phase locking of two lasers, the average phase residual error is less than 1/25 wavelength when the amplitude of the phase noise is greater than λ/10, and the frequency is 3 kHz.