Abstract: Apparatus and methods allow fused bi-conical couplers to be pulled to reduced diameters to exposes more of the evanescent field in the coupled region. First and second stages hold the fibers on either side of the fused region, with at least one of the stages being moveable relative to the other. A furnace positioned relative to the fused region, and a tensometer is used to determine the tension of the fibers between the stages. A controller is provided to monitor the tension on the fibers and increase the distance between the stages when the tension falls to a predetermined threshold. As the fibers are pulled, light begins to couple from one fiber to the next, leading to five distinct crossover regions. The tension is continuously monitored, and when the tension drops below each threshold, the furnace is slowly pushed back to maintain the tension by decreasing the heat on the fiber from the furnace. As the fiber is pulled through these crossover areas, the coupling region decreases in diameter.