All-fiber passive coherent combining of high power lasers

We report >100 W output power by coherently combining two, three, and four high power lasers in all-fiber and all-passive configurations using Yb fiber laser cavities operating at a wavelength of 1080 nm with polarization maintaining fibers and 2×2 fused fiber couplers. We present the power and number scaling characteristics of the laser arrays and compare their beam combining efficiencies in different array configurations. We experimentally show beam combining efficiency degradation with increase of laser power and number of lasers. In addition, we discuss the effect of fiber nonlinearity on beam combining efficiency.