All-fiber 50 W coherently combined passive laser array

We experimentally demonstrate 50 W of spontaneously phase-locked two-laser array in an all-fiber and all-passive configuration using large-mode-area (LMA) polarization-maintaining fiber laser cavities and an LMA fiber coupler. We show that both laser cavity length difference and fiber nonlinearity play an important role in achieving efficient and stable coherent beam combining. In addition, we compare the difference in coherent combining efficiency by using fibers with different mode-field diameters and discuss the underlying phase-locking mechanism and its power scalability.