Experimental study on partially coherent combination of a 2×2 all-fiber laser array

By using partially coherent combining technique, beam combining of a 22 all-fiber laser array was experimentally studied. The laser array consisted of two incoherent laser groups. Each group contained two all-fiber lasers which were phase-locked by using direct mode mutual injection method through a fiber Bragg grating with proper reflectivity. The four laser beams were arranged symmetrically. And they were placed as close as possible by using a four-right-angle prism. In the experiment, two groups of clear interfere strips with maximum visibility of about 43% and 38% were observed, respectively. The whole laser array finally generates 925 W output power when the total pump power was 1 624 W. The beam-quality value BQ of the combined beam emitting from the laser array was 1.95 when the fill factor of the laser array was 0.54. This fiber laser combining array was constructed by all-fiber components, thereby was monolithic with stable performance. During the long time of high power operation, the monolithic fiber laser array works with excellent stability, no thermal distortion and damage are observed.