Optical waveguides – Optical transmission cable – Ribbon cable
Reexamination Certificate
2000-11-22
2002-08-27
Sircus, Brian (Department: 2839)
Optical waveguides
Optical transmission cable
Ribbon cable
Reexamination Certificate
active
06442318
ABSTRACT:
BACKGROUND
The use of optical fiber ribbons as cables for the transmission of optical signals is well known in the communications industry. In a typical optical fiber ribbon, plural optical fiber waveguides are arranged and retained adjacent to one another in a generally planar orientation and encased in a common outer jacket. Until recently, the use of ribbonized optical fiber cables had been limited to long-haul trunking installations where the superior transmission efficiency and other transmission characteristics of optical fibers, as opposed to metallic conduits, for example, justified the greater expense and difficulties presented by their manufacture and installation in the field. As the demands on communications media continue to increase, more research and development effort is being dedicated to finding practical, simple and inexpensive ways to apply optical fiber cables, including ribbonized cables, to the transmission of signals over shorter distances for the interconnection of local devices, for example.
A weak link in the application of optical fiber ribbon cables generally has been the difficulty of splicing and connecting the individual fibers in a fiber ribbon cable with those of another, similar ribbon cable or and/or with signal-transmitting or signal-receiving equipment, for example. The industry has attempted to solve this problem by developing numerous prefabricated terminal connectors of various configurations for installation on the ends of optical fiber ribbon cables. Although these terminal connectors have alleviated some of the difficulties of interfacing two fiber ribbon cables in series once the connectors are installed on the ends of two ribbon cables to be joined, for example, practical difficulties still remain with attaching such terminal connectors to the ribbon cables themselves. The problem is particularly vexing for on-site field technicians attempting to repair and maintain previously installed ribbon cables. As a result, substantial research and development resources are still being expended to find better ways of fabricating optical fiber ribbon cables and terminal connectors, and of connecting prefabricated ribbon cables to prefabricated terminal connectors. The principal objective of these efforts is to create optical fiber ribbon cables and terminal connectors that are capable of easy and precise field connectorization. An important consideration in any such effort is that the end surfaces of the individual optical fibers within an optical fiber ribbon cable must align precisely with the signal-receiving or signal-emitting apparatus with which they are to interface to obtain a low-loss connection.
At present, there are two primary prefabricated multifiber terminal connectors: (1) AT&T's MAC™ and (2) the MT™ connector made by U.S. Conec. Of these two, only the MT™ connector lends itself to installation in the field, albeit, not simply. When a field technician desires to install an MT™ connector onto an existing fiber ribbon cable, the technician cuts the ribbon cable. The insulation jacket surrounding the ribbon cable is typically slit longitudinally to allow the insulation jacket to be peeled back. If the ribbon cable is cut too deeply at this point, the optical fibers could be damaged. After peeling back the insulation jacket, the technician is left with a fiber ribbon comprising a ribbon coating (e.g., plastic) encapsulating plural optical fibers.
Frequently, a hot blade stripper is used to strip the ribbon coating from the optical fiber. This tool heats the entire end of the ribbon and has two blades that move towards one another to cut the ribbon coating and pull the coating off the optical fibers. This step sometimes causes damage to the fibers because it is very easy to cut too deeply with the blades. Once the individual optical fibers are exposed and cleaned to remove any remaining coating residue or foreign particles, the connector must be filled with an appropriate quantity of adhesive and the individual fibers manually inserted through laterally spaced guide holes in the connector. Once this is done, the adhesive is cured to secure the fibers on the connector.
Although optical fiber ribbon cables have made the use of optical fibers in and as data conduits somewhat more ubiquitous, currently available methods of stripping and connecting (i.e., splicing) optical fiber ribbon cables are labor intensive and time consuming, require a great degree of skill and care and subject the optical fibers to potential damage due to the difficulty in stripping the protective jacket and buffer from the individual optical fibers.
Attempts have been made to alleviate the difficulty and time-intensiveness of optical fiber ribbon connectorization. One such attempt is discussed in U.S. Pat. No. 5,611,017 to Lee et al. for a Fiber Optic Ribbon Cable with Pre-installed Locations for Subsequent Connectorization. U.S. Pat. No. 5,611,017 teaches a fiber optic ribbon cable that has release elements manufactured in line with the ribbon cable. The release elements provide access points to the optical fibers contained therein to allow for simplified application of a connector in the field. A pair of adhesive tape layers is applied about the optical fibers to create a fiber optic ribbon cable. When it is desired to equip the ribbon cable with a connector, the cable is cut perpendicularly to the fiber axes near the midpoint of the access points. Once the cable is cut, the adhesive tape layers and the pieces of release element may be peeled back to expose the individual optical fibers. A connector is then installed onto the exposed optical fibers, the pieces of release element removed from the tape layers and the tape layers secured to the connector. Among the drawbacks of this technique are that it requires the inclusion of release elements in line with the ribbon cable. These release elements are described as being made of plastic or ceramic, but whatever the material from which they are fabricated, their presence may constitute irregular bulges along the length of the cable. Furthermore, the inclusion of the release elements introduces numerous stress points throughout the length of the cable that may result in damage to the individual optical fibers. Still further, because of the nature of the in-line access points, one needing to install a connector at such an access point will need to locate the midpoint of the release elements with a fair degree of accuracy for cutting of the cable.
SUMMARY
The present invention is directed to a prefabricated optical fiber cable for subsequent connectorization to a prefabricated connector, methods of fabricating the prefabricated optical fiber cable and methods of connectorizing a prefabricated optical fiber cable to a prefabricated multifiber terminal connector.
In one embodiment, an optical fiber ribbon cable comprises a plurality of elongated laterally spaced wave-transmitting optical fibers. The lateral center-to-center spacing of the optical fibers within the ribbon cable is maintained within predetermined tolerances by the inclusion of spacer fibers between adjacent optical fibers. The optical fibers and the spacer fibers are maintained in their desired positions, and protected from damage, by an encapsulation layer. The fabrication of the optical fiber ribbon cable may be such that the lateral spacing of the optical fibers is maintained by the spacer fibers along the entirety of a length of ribbon cable. The optical fibers are for transmitting signals, while the spacer fibers exist for the purpose of establishing and maintaining the lateral spacing of the optical fibers. The widths of the optical fibers and the spacer fibers are two parameters that may be varied in order to fabricate optical fiber ribbon cables for connectorization with prefabricated multifiber terminal connectors of various designs and dimensions, of which the MT™ Connector is only a single example.
The materials from which the encapsulation layer, the spacer fibers and the optical fibers are each comprised are chosen based on their relat
Franco Louis J.
Le Thanh-Tam
Schott Fiber Optics Inc.
Sircus Brian
LandOfFree
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