Stable single transverse mode excitation in 50 µm core fiber using a photonic-lantern-based adaptive control system.

We report on the generation of single transverse mode output in large-mode-area fiber with a core diameter of 50 µm using a 3×1 photonic-lantern-based adaptive spatial mode control system. We have designed and fabricated the photonic lantern composed of a single mode fibers bundle taper region and a multi-segment multimode fiber splicing region. From simulation and experiments, we demonstrate that the quality of the output beam is significantly influenced by the size of the fibers bundle's waist and the segmented splicing scheme of the multimode fiber. Stable single transverse mode output is achieved at 1064 nm with M ∼1.4, which will provide a possible technical solution to increase the mode instability threshold in high power large-mode-area fiber systems.