ESTIMATION OF COUPLING PARAMETERS FOR AUTO-MOTORIZED FABRICATION OF DIRECTIONAL FIBER COUPLER Dedi Irawan 1 , Saktioto 1,2 , Jalil Ali 1 , Iwantono 2 1 APSI, Physics Dept. Faculty of Science, Universiti Teknologi Malaysia, Johore, Malaysia 2 Physics Dept. Math and Science Faculty, University of Riau, Pekanbaru, Indonesia ABSTRACT 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 fibers are pulled by stages that are automatically motorized in range of 800-4800 m μ , and stopped when the desired 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 micro meter scale. 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. Keyword: Fiber Coupler, Coupling region, Coupling coefficient, and degree of fusion. 1. INTRODUCTION The use of optical devices on network communication system has been widely expanded. It provides an optical circuit that can carry out data in term of audio, video, data processing, etc. with big capacity low loss and faster. Optical directional fiber coupler is a passive device and main component of optical networking system (Hosseini, et al., 2010). It is used to split, to combine, or to switch optical signal. Since the networking system is built by using optical components, a directional fiber coupler with various coupling ratio is always needed. The fiber coupler can be fabricated using twist-etching techniques, polishing Technique, and Fusion Technique (Daniel, et al., 1994). Fusion and elongation is an easier technique that has been used to fabricate fiber coupler. In 2005, Fused biconical Tapered (FBT) coupler was fabricated by this this technique. The coupling region was heated by CO 2 laser, and resulting good FBT couplers with 3 dB splitting ratio (Saktioto, et al., 2008). Because of CO 2 laser beam is a high cost technology, fusion technique by injecting H 2 Gas to the torch flame was purposed for hearting the coupling region (Saktioto, et al., 2009). During fusion, fibers are elongated in micro meter scale until the coupling ratio is reached. Since that fabrication results high coupling loss, the study of the automated fiber coupler fabrication system based on fusion technique becomes necessary to determine coupling parameters. In this paper, coupler machine (Acupler-2000) is used to fabricate a basic 2X2 fiber coupler. The parameter of pulling stages, and coupling power are determined from the kinetic model of automated mechanical motion of coupler machine. 2. THEORETICAL CONSIDERATION The propagation of an optical signal in the coupled waveguide medium was determined clearly from the Maxwell equation using coupling-mode theory (CMT) method (Snyder, 1972). The modelling and experiment of power parameters SMF coupler were also studied (Snyder, 1983). It showed the coupling ratio as function of coupling coefficient between the fibers. Since the refractive indices of coupled fibers are constant, and geometrical fibers are also identical as shown in Fig. 1, the amplitude of power exchanges between two fibers given by Eq. 1, (a) L Pb(0) Pa(0) Pb(z) Pa(z) Tapered region