Fiber optics are used in many applications including telecommunications and instrumentation. Data is transmitted by pulsing light waves through the optical fibers. These fibers typically consist of a core surrounded by a cladding, and a protective jacket. The core and cladding are typically made of a silica material. Core diameters are typically in the range of 5 to 10 .mu.m with an outside fiber diameter of 125 .mu.m. The core has a higher refractive index than the cladding in order to achieve total internal reflection of the light beam propagating along the core. Optical fibers are also designed with multiple cores in order to increase the amount of information that can be transmitted by optical fibers.
One method for producing multiple core optical fibers consists of inserting a group of single cores, with their respective claddings, into a glass tube and then melting the claddings together forming what is referred to a multi-core preform. The preform is then mounted on a drawing machine and then drawn to fabricate the multiple core fiber. The resulting multiple core fiber consists of multiple cores with a single fused cladding material completely surrounding the cores.
One problem with such a method is that the positioning of the single core fibers, with their respective claddings, inside the tube may not be very accurate. This results in a fiber with cores that are not accurately aligned relative to one another. Inaccurate core alignment adds complexity to switcher and coupler designs utilizing the fiber. Another problem with drawn multiple core fibers is that since their claddings are joined along the entire length of the fiber, the light carried by the individual cores cannot be physically routed to different locations without the use of additional components.
Another prior art method for joining multiple cores involves the use of etching techniques. One problem with this method is that extensive chemical etching of the cladding material is required in order to bring the cores closer together. Such chemical etching may weaken the fiber and introduce stress defects that affect signal propagation through the fiber.
Other types of fibers containing multiple cores exist, known as coupled fibers. Fiber coupling machines fuse together multiple single core fibers to create a fiber section that couples light among the multiple cores. The fibers' jackets are removed along the section to be coupled. The fibers are twisted together, then heated and stretched to fuse the fibers together in order to achieve desired optical characteristics. The heating and stretching process reduces the diameter of the cores and cladding region of the fibers and brings the cores closer together. Such a process, however, may not be suitable for manufacturing multiple core fibers carrying non-coupled signals because the process results in cross-talk, or power coupling, between fiber cores.