US Patent 7933479 Multimode fiber outer cladding coupler for multi-clad fibers

A multimode fiber coupler has a structure in which a plurality of tapered pump fibers are coupled laterally to a multi-clad fiber, such as a double clad fiber (DCF). Such coupler is produced by first forming a plurality of tapered pump fibers and positioning them around the multi-clad fiber, thus forming a fiber bundle. Then, the fiber bundle is twisted and fused so that the input pump fibers converge towards a waist and then diverge from it. The diverging portions of the pump fibers may be removed from the structure. Also, at the waist, the structure may be cleaved and the portion with the converging pump fibers is then spliced with a multi-clad fiber which is similar or identical to the one in the middle of the bundle.