Abstract: An overclad fiber optic coupler is formed from a coupler preform including a glass tube having a longitudinal aperture. The aperture is formed of a plurality of similarly shaped side walls, each of which includes a longitudinally extending, inwardly projecting protrusions. The region between each two adjacent protrusions constitutes a corner region. Disposed within the aperture are at least a portion of each of a plurality of glass optical fibers, one fiber being situated in each corner region. The midregion of the tube is collapsed onto the fibers, the protrusions maintaining the fibers in their relative positions. At least a portion of the midregion is stretched to reduce the tube midregion diameter.