We demonstrate passive combination of multiple beams in an optical fiber via stimulated Brillouin scattering (SBS). Four off-axis beams are combined in a long multimode optical fiber using a novel all-optical mount. The combined beam has the high spatial coherence properties of the mode owing to the beam cleanup properties of SBS. The threshold for SBS when off-axis pumps are used is shown to be a factor of 13 times higher than for on-axis pump beams. We propose this method would improve the brightness of an array of fiber amplifiers.
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