Coherent addition of two dimensional array of fiber lasers
  Configurations for efficient free space coherent addition of four separate fiber lasers arranged in two dimensional array are presented. They include compact and robust interferometric combiners that can be inserted either inside or outside the cavity of the combined lasers system. The results reveal that over 85% combining efficiency can be obtained. 
Moti Fridman, Vardit Eckhouse, Nir Davidson, Asher A. Friesem, Elena   Luria, Vladimir Krupkin