1 kW average power emission from an in-house 4x4 multicore rod-type fiber

Multicore fibers have the potential to combine the advantages of optical fibers (such as their high average power capability, high efficiency and well-defined beam quality) with those stemming from the large beam areas commonly used in other laser architectures. Coherent combination can then be employed to achieve one single, high-quality, output beam [1] , [2] . To match and even surpass the performance of state-of-the-art lasers systems comprising multiple separate fiber amplifiers, multicore fibers need to leverage the same technological advancements. One example is the use of a rod-type geometry with large core diameters to mitigate detrimental nonlinear effects. In this contribution, we present our high power laser results achieved with an in-house, all-glass, rod-type multicore fiber, whose basic structure is shown in figure 1 . The fiber contains 16 ytterbium-doped cores in a rectangular arrangement with a diameter of 22 µm each, operating at near single-mode output. The core-to-core pitch is 58 µm. An embedded octagonal fluoride ring is used as the guiding mechanism for the pump with a diameter of 310 µm and a NA of 0.22. A device length of 1.1 m was chosen to provide sufficient pump absorption.