2-µm laser beam quality improved by matched pedestal passive and active fibers

The geometry mismatch between active and passive fibers and particularly the presence of a pedestal around the core of active fibers creates a light coupling from this pedestal to the cladding of the passive fiber when spliced together. This signal light propagating in the cladding can results in a beam degradation that reduces the laser performances. We proposed a new solution consisting in using a perfectly matched couple of fibers by adding a pedestal around the core of the passive fiber. This pedestal maintains the coupling light in a quasi-single-mode pedestal area that will not lead to any power losses and not degrade the output beam.