An optimum design of fused silica directional fiber coupler

A directional fiber coupler has been successfully fabricated by using fusion and elongation methods. Two or more single mode fibers (SMFs) were joined by injecting H2 gas at 1 bar and heating the coupling region while they are pulled for various pulling speeds. Coupling mode theory (CMT) in form of transfer matrix was involved to determine the transfer power propagation between fibers. However, coupling coefficient has been derived by using Henkel and Bessel function and assuming that cores of fibers are only touching each other. The periodical propagation of power transfer depends on the coupling coefficient and the coupling length. The increment of coupling coefficient has been exhibited as function of the separation distance between fibers axes and the degree of fusion. The coupling coefficient is also proportional with the increasing the degree of fusion. Good performance of the fiber couplers have been produced with typical of exertion loss is about 0.03 dB by pulling the coupling region at 1300 °C with the pulling speed of 150 μm/s.