Optical waveguides – Accessories – Plug/termination device
Reexamination Certificate
2000-01-07
2001-08-21
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
Accessories
Plug/termination device
C385S100000, C385S103000
Reexamination Certificate
active
06278831
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to fiber optic cable assemblies and, in particular, to a furcation kit for fiber optic cables.
BACKGROUND OF THE INVENTION
Fiber optic transmission systems have been in commercial use for over 20 years. Fiber optic cable provides many performance advantages over commercial metallic copper-based wire. These advantages make optical fiber the most advanced transmission medium available today, offering a low-cost alternative to satellite systems for international communications. Optical fiber is also well suited to supporting emerging applications such as interactive multimedia services delivered to the home.
Fiber optic cables bundle and protect fiber optic strands which are generally manufactured from glass. The number of fiber optic strands in a cable is variable. One popular fiber optic cable construction is duplex fiber optic cable. Duplex fiber optic cable is generally of two types: 1) round, and 2) zip. Round duplex fiber optic cable generally sheathes two 900 &mgr;m buffer coated 125 &mgr;m fiber optic strands contained within an outer PVC coating with an overall total diameter of 3.6 mm. Zip duplex fiber optic cable typically include two 2.5 mm outer diameter PVC fiber optic cables joined by a narrow PVC bridge. Each 2.5 mm outer diameter PVC cable sheathes a separate 900 &mgr;m coated fiber optic strand with an overall total diameter of 5.3 mm.
The round duplex fiber optic cable requires a “breakout” or “furcation” kit in order to attach connectors to the individual fibers. The furcation kit reduces the probability of introducing “microbends”, which are sharp changes in direction in the connectorized fiber optic strands. Microbends are known to cause attenuation of light signals carried by the fiber strands.
Furcation kits for terminating fiber optic cables of various types are known in the art. For example, U.S. Pat. No. 5,231,688 which issued Jul. 27, 1992 to Zimmer teaches a furcation kit for a multiple optical cable. The cable end is secured by a mechanical compression fitting and optical fibers are routed into one or more plugs, each having a plurality of single optical fiber passages. A protective shell is mechanically secured around the area of furcation. The kit eliminates the need for adhesives and capsulants and thereby decreases the time required for installation.
U.S. Pat. Nos. 5,903,693 and 5,970,195 to Brown which issued respectively on May 11 and Oct. 19, 1999 describe a fiber optic cable furcation unit. The furcation unit has an outer heat shrink tube which encloses a protective sleeve. A spacer/fiber guide is located within the protective sleeve along with a sealant material. The furcation unit is designed expressly for loose tube fiber optic cables or tube ducts within Air Blown Fiber (ABF) cables to be furcated into multiple sheathed single fiber strands.
While the furcation kits known in the prior art have merit, they suffer from the disadvantage of being bulky and/or difficult to install without introducing microbends to the fiber strands. The furcation kit to Zimmer, for example, is generally too bulky for most indoor applications where limited space is available inside a patch cord panel or a patch cord tray. The furcation unit to Brown must be very carefully installed to avoid microbends in the fiber strands. Furthermore, the heat-shrink outer tube utilized to hold the furcation sleeve in the correct position does not stabilize the cable prior to heat treatment, and the heat exposure required to shrink the protective tube has potential for damaging the cable sheath and/or the fiber optic strands. Any damage induced in the fiber optic strands may result in increased signal attenuation.
Another furcation kit known in the art uses epoxy adhesives to secure a furcation tubing in place. Such furcation kits require significant curing times. Although curing can be accelerated by the application of heat, relatively long curing times are still required. Consequently, the assembly must remain isolated from outside influence that may cause a change in position of the furcation tubing or the fiber optic strands prior to the epoxy resin becoming adequately cured to support the components.
A need therefore exists for a simple furcation kit that is inexpensive to manufacture, easy to assemble, and occupies minimal space.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a furcation kit for a fiber optic cable that is easy to install and substantially eliminates a probability of introducing bends in the fiber strands during installation.
It is a further object of the invention to provide a furcation kit that occupies less space than prior art furcation kits.
The invention therefore provides a furcation kit for a fiber optic cable comprising a furcation body having a first hollow end for receiving an end of the fiber optic cable and a second hollow end for receiving a furcation plug. The furcation plug has a first end received in the furcation body and a second end having at least one passage that extends through the furcation plug, the at least one passage being adapted to receive and retain a furcation tube. The furcation kit further includes means for attaching the fiber optic cable to the second hollow end of the furcation body.
In accordance with a preferred embodiment of the invention, the means for attaching the fiber optic cable to the second hollow end of the furcation body comprises a crimp ring. The second hollow end of the furcation body includes a cylindrical backbone having a hollow interior sized to accept a stripped end of the fiber optic cable. An outer surface of the cylindrical backbone is sized to permit a fanned-out end of a strength member of the fiber optic cable to be overlaid on the backbone. The crimp ring is crimped over the fanned-out end of the strength member to attach the fiber optic cable to the furcation body. An adhesive may be applied between the fanned-out end of the strength member and the backbone before the crimp ring is crimped.
The furcation plug may be retained within the furcation body by clip members biased to engage notches in the second end of the furcation plug. Alternatively, the furcation plug may be retained within the furcation body by an adhesive.
The furcation body preferably includes a stop means for preventing the furcation plug from being inserted too far within the second end of the furcation body. This inhibits the formation of microbends in fiber optic strands pulled through the at least one furcation tube retained in the furcation plug.
The furcation body may be over-molded with a thermoplastic resin after the furcation plug is inserted in the furcation body.
The invention also provides a method of manufacturing a fiber optic cable having a furcated end. In accordance with the method, a crimp ring is placed over an end of the fiber optic cable and moved away from the end of the fiber optic cable. A cable sheath is stripped from the end of the fiber optic cable to expose a predetermined length of strength member and a buffer tube that surrounds at least one fiber optic strand. The strength member and the buffer tube are cut off a predetermined distance from an end of the cable sheath to expose a predetermined length of the at least one fiber optic strand. The cut end of the strength member is fanned-out and a backbone of the furcation body is slid over the cut end of the buffer tube. The fanned-out strength member is compressed over an outer surface of the backbone of the furcation body and the crimp ring is slid over the backbone and crimped to trap the fanned-out end of the strength member between the crimp ring and the backbone. Free ends of the at least one fiber optic strand are inserted into furcation tubes of the furcation plug, and the furcation plug is inserted into the end of the furcation body.
REFERENCES:
patent: 5231688 (1993-07-01), Zimmer
patent: 5838861 (1998-11-01), Bunde
patent: 5903693 (1999-05-01), Brown
patent: 5970195 (1999-10-01), Brown
Frith Kenton
Henderson Blaine
Palmer Phan T. H.
Pearne & Gordon LLP
Priority Electronics Inc.
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