Modeling of coupling parameters of directional fiber coupler based on degree of fusion

A directional fiber coupler with exertion loss 0.03-dB has been successfully fabricated using fusion technique with typical coupling ratio 1%-90%. The coupling region of two twisted single mode fiber is heated by injecting Hydrogen gas at 2.5 Bar. During fusion process, both two sides of fiber are pulled by stages that are automatically motorized in range of 800-4800μm, and stopped when the preset coupling ratio is reached. The parameters of automated mechanical motion of pulling stages and coupling parameters at fusion region have been calculated by using kinetic model. The effect of heating and elongation reduces the diameter of cross section tapered region with a diameter is 6.35 micrometer. Since the fabrication of fiber couplers described by degree of fusion which is function of heating and pulling length, it can be seen clearly that the coupling coefficient between the fibers increases exponentially with increasing the degree of fusion. However, by knowing coupling power and mechanical motion parameters, the fabrication of directional fiber coupler can be optimized.