Coherent beam combining of pulsed fibre amplifiers with active phase control**Reported at the Conference ‘Laser Optics 2010’, Russia, St. Petersburg.

Abstract

Coherent beam combining of pulsed fibre lasers is a promising method for power scaling while simultaneously maintaining good beam quality. We propose and demonstrate a scalablearchitecture for coherent beam combining of all-fibre pulsed amplifiers with active phase control using the stochastic parallel gradient descent (SPGD) algorithm. A low-pass filter is introduced to eliminatethe fluctuation of the metric function caused by pulsed lasers and to extract the exact phase noise signal. Active control is thereby based on the SPGD algorithm, resulting in stable coherent beamcombining at the receiving plane even in a turbulent environment. Experimental results show that the fringe visibility of the long exposure pattern increases from 0 to 0.4, and the power encircled inthe main-lobe increases by 1.6 times when the system evolves from the open-loop phase-locking scheme to the closed-loop scheme. This architecture can be easily scaled up to a higher power by increasing the number of amplifying channels and the power of a single amplifier.