Abstract: A multimode to low-mode optical fiber is constructed by forming a plurality of multimode optical fibers into a fiber bundle. The bundle is then selectively heated and drawn to form a bi-tapered fiber bundle having a central straight portion in which the multimode fibers are fused into a single length of fiber. During the drawing step, measures are taken to provide an aperture extending through the bi-tapered bundle, including the single straight portion of the bundle. An optical fiber having a low-mode or single-mode core is inserted through the aperture into the straight section of the bi-tapered bundle. The bi-tapered bundle and the low-mode core fiber are heated to a temperature at which cladding of the low-mode core fiber fuses to the straight portion of the bi-tapered bundle. The bi-tapered bundle is then cleaved in the straight portion to provide the multimode to low-mode optical fiber combiner. In one example, the multimode fiber bundle is formed around a metal wire before the drawing operation.