The manufacturing of an optical fiber coupler by the fusion elongation method

An optical fiber coupler is used for joining or splitting optical signals at optical fiber branch points. It is an essential component for optical communication systems. Nowadays, telecommunication systems providers such as AT&T in America and NTT in Japan are in the process of implementing Fiber To The Home and Fiber To The Curb and therefore optical coupler will be in high demand in the near future. Special optical fibers such as polarization maintaining (PM) fiber also enjoy ever increasing popularity as communication systems and fiber sensor become more sophisticated. Consequently optical fiber couplers made of PM fiber will be in great demand. The fabrication of PM fiber couplers is either by the polishing method or by the fusion and elongation method. The fabrication technique for the polishing type PM fiber coupler has well been developed. However, the properties of the epoxy resin used in a polishing type PM fiber coupler change with temperature and humidity. Consequently, the characteristics of such coupler are also dependent on temperature. This undesired characteristics has imposed severe limitations of the use of the PM polishing type coupler. It is believed that PM couplers made by the fusion and elongation method have a steady characteristics over a wide temperature range. This paper reports a method for the fabrication of Polarization-Maintaining (PM) Optical Fiber Couplers using the fusion and elongation method and confirms that the characteristics of such PM couplers are stable over a temperature range of 110°C. Moreover, the manufacturing time for the fusion and elongation type coupler is reduced tremendously compared with that for the polishing type coupler. As the manufacturing time is reduced, the cost of production should proportionally be decreased. By applying this method, the manufacturing process could be fully automated and a high reliability product would be produced.