Coherent beam combining of fiber amplifiers

In this paper, we demonstrate the coherent superposition of fiber amplifiers in a Michelson-type setup with active amplifying arms. The diffraction limited beam quality from the amplifiers is not reduced by imposing the beams and combining efficiencies exceeds 95%. The output of this basic active interferometer is coherently added to additional amplifier stages. Amplifier performance and further details on the locking technique are also presented.