Managing Strain Relief Fibers in Fiber Optic Cables
Publication Date: 2003-Oct-08
The IP.com Prior Art Database
Disclosed herein is a convenient article and method of providing strain relief to fiber optic cables and of providing a convenient way to handle the fiber optic cables. Presently, commercially available fiber optic cables are constructed using arimid strands or other types materials to provide improved tensile strength to the fiber optic cables and to provide strain relief to the fiber optic cables. In use, the loose aramid strands are placed in such a manner that they surround the optical fibers within the cable's jacket. Figure 3 shows one exemplary prior art fiber optic cable where a fiber optic ribbon is surrounded by strain relief fibers (e.g., by aramid strands). In one application, a step in the preparation of the cables requires removing a portion of the cable's outer jacket, exposing the optical fibers and the strain relief fibers. In some known optical connector assemblies, the loose strain relief fibers are attached to the connector shell using items such as; metal crimp rings, binding posts, adhesives, or combinations thereof. The handling of the strain relief fibers can be difficult in that the manipulation of the loose strands is not conducive to either hand or automated assembly procedures. This article provides one approach to solving the above-mentioned problems by providing a means to easily organize the loose strain relief fibers and attaching them to a connector body. Figure 1 is a schematic perspective view of one exemplary embodiment having a cable jacket, optical fibers covered with a buffer layer, and bundles of spaced, strain relief fibers, encapsulated in a polymer matrix (herein after referred to as the "strength member"). Through encapsulation, the strain relief fibers are now ordered in a matrix polymer array that provides for convenient handling of the strain relief fibers. Encapsulation of the strain relief fibers into polymer matrix can be done by several conventional means, such as, e.g., melt extrusion. In the melt extrusion process, the strain relief fibers are drawn through a crosshead extrusion die where melted polymer is pressure fed about the strain relief fibers. Another encapsulation method include profile die coating the strain relief fibers with an ultraviolet light curable polymer followed curing the polymer to crosslink it. Yet another encapsulation method involves laminating the strain relief fibers between two polymer films and bonding the two films together using a heat fusing process, or a pressure sensitive adhesive, or solvent welding. In addition to providing increased tensile strength to the strength member the shape and form of the strength member can be provided with features that enhance its utility. Figure 2a illustrates an exemplary the strength member of the present invention with an opening punched through it. The opening is a feature in the strength member through which a protrusion on the connectors shell can be inserted thus allowing convenient attachment of the strength member to an optical connector shell. Figure 2b illustrates another exemplary strength member of the present invention. Here, the surface of the strength member has been provided with three-dimensional features. These features, in applications where the strength member is inserted into a cavity formed within the connector shell and potted with a polymer (such as epoxy), will substantially increase the amount of force required to remove the strength member from the connector shell. Figure 2c illustrates yet another exemplary strength member of the present invention. Here, the surface of the strength member has been provided with features that are shaped like ratchet teeth. In practice the strength member is inserted through an opening in the connector body. Located within this opening is a pawl or group of pawls that engage the ratchet teeth, thus preventing the strength member from being withdrawn from the opening. Figure 2d is an enlarged view of Figure 2c. Many methods can be used to provide the surface of the strength member with the desired three-dimensional features. One example is that of forming the features by pressing the strength member between two patterned chill rolls following the melt extrusion process. The features illustrated in Figure 2 are only a few of many possible feature shapes that may be formed on the surface of the strength member. Additionally, interactive structures may be formed on the surface of the strength member that interlock with shapes formed on the connector body to provide secure attachment of the strength member to the connector body. Examples of such feature can include mechanical interlocking devices or microreplicated interlocking devices.