Abstract: In one aspect, the invention concerns fused fiber optic couplers of the type formed from fibers of transparent substance each having a circular cross-section of preselected diameter. The fibers include a central fiber and at least one ring of closely packed surrounding fibers with at least some of the fibers being optical fibers that have a core and a surrounding cladding. The coupler is formed by the processes of providing the fibers, assembling them in a close-packed relationship, and heating and drawing the assembly of fibers in the close-packed region.We have discovered that the steps involved in forming such a coupler, introduce slight size variations that can seriously affect the performance of the coupler, and that these slight variations can be accommodated by slight, controlled, under-sizing of one or more of the surrounding fibers or over-sizing of the central fiber.