Optical waveguides – Optical transmission cable – Ribbon cable
Reexamination Certificate
1999-09-15
2001-11-20
Schuberg, Darren (Department: 2872)
Optical waveguides
Optical transmission cable
Ribbon cable
C385S109000, C385S110000, C385S112000, C385S113000
Reexamination Certificate
active
06321013
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to fiber optic cables and, more particularly, to stacks of optical fiber ribbons contained in respective buffer encasements.
BACKGROUND OF THE INVENTION
Optical fiber is a very popular medium for large bandwidth applications, and as a result there is a demand for fiber optic cables with greater numbers of optical fibers. In response to demands for increased optical fiber count in fiber optic cables, optical fiber ribbons have been developed. Optical fiber ribbons are planar arrays of optical fibers that are bonded together as a unit. Optical fiber ribbons are advantageous because many ribbons can be stacked on top of each other to form a stack of optical fiber ribbons.
It is conventional for stacks of optical fiber ribbons to be incorporated into two different types of fiber optic cables that are generally referred to as “central-core” and “loose-tube” cables. In the central-core design, a stack of optical fiber ribbons is contained within a central tube that is located at the center of the fiber optic cable. Strength members are positioned between the central tube and an outer plastic jacket of the cable. In contrast, loose-tube fiber optic cables typically include a number of relatively small buffer tubes that are positioned around a central strength member, and each buffer tube encloses a stack of optical fiber ribbons. The buffer tubes are longitudinally stranded around the central strength member, meaning that the buffer tubes are rotated around the central strength member along the length of the fiber optic cable.
It is conventional for the above-referenced tubes that contain respective stacks of optical fiber ribbons to be round, and for the stacks of optical fiber ribbons to be generally rectangular. Therefore, for each tube and the stack of optical fiber ribbons it contains, there is space defined between the interior surface of the tube and the periphery of the stack. In some applications that space is utilized to allow for relative movement between the stack of optical fiber ribbons and the tube, and that relative movement diminishes the stresses to which the optical fibers are exposed. However, in some applications that space can be characterized as wasted space. In some applications that space is filled with a gel, such as a thixotropic gel, that cushions the stack of optical fiber ribbons to diminish the stresses to which the optical fibers are exposed. However, in some applications those gels are considered a nuisance because they are messy and must be dealt with when entering a fiber optic cable for the purpose of forming a splice between optical fibers or inspecting optical fibers. In addition, for a generally rectangular stack of optical fibers within a round tube, the optical fibers at the corners of the stack will often bear the brunt of any stresses caused by contact between the optical fibers and the interior of the tube, even if a gel is within the tube.
As the numbers of optical fibers within fiber optic cables increases, the likelihood of a cable having inoperative optical fibers increases. Often the operability of optical fibers within an fiber optic cable is evaluated after the fiber optic cable has been fully manufactured. Determining that a fiber optic cable with a large number of optical fibers has an unacceptable number of inoperative optical fibers is very disadvantageous, because it is expensive to repair or rebuild such a cable.
SUMMARY OF THE INVENTION
The present invention solves the above problems, and other problems, by providing an optical module that is in the form of a stack of optical fiber ribbons that are within a buffer encasement, which is preferably a thin sheath, that closely bounds the periphery of the stack. Because the sheath closely bounds the periphery of the stack, the sheath cushions all of the sides of the stack. Accordingly, it is preferred that the sheath not contain any thixotropic gels, or the like.
In accordance with one aspect of the present invention, the sheath is relatively thin. More specifically, each optical fiber ribbon has a pair of longitudinally extending opposite edges and a pair of longitudinally extending opposite surfaces that extend laterally between the edges, and each optical fiber ribbon has a thickness defined between its opposite surfaces. In an end elevation view of the sheath at least a majority of the sheath has a thickness defined between interior and exterior surfaces of the sheath. The thickness of the sheath is not substantially greater than the thickness of each of the optical fiber ribbons.
Whereas the interior surface of the sheath can be adhered to the stack, in accordance with one aspect of the present invention the interior surface of the sheath is not adhered to the stack so that the stack is capable of moving relative to the sheath. It is preferred for a lubricant to enhance the moveability of the stack relative to the sheath and the moveability of the optical fiber ribbons relative to one another. Further, the sheath is preferably sufficiently rigid to maintain the stack in a stacked configuration, and sufficiently flexible to allow the optical fiber ribbons to slide laterally relative to one another so that, in an end elevation view of the stack, the stack and the sheath can transition from a non-skewed configuration to a skewed configuration. The lateral displacement between the optical fiber ribbons in the skewed configuration is different from the lateral displacement between the optical fiber ribbons in the non-skewed configuration. In accordance with a method of the present invention, at least one optical module is transitioned from the non-skewed configuration to the skewed configuration when being enclosed within a fiber optic cable.
In accordance with another aspect of the present invention, the stack of optical fiber ribbons and the sheath of an optical module are both generally rectangular, so that the optical modules can be readily stacked in a manner that results in a very space efficient fiber optic cable. Further, the optical modules can be tested prior to being incorporated into the fiber optic cable so as to maximize the probability of the fiber optic cable being fully operable.
In accordance with another aspect of the present invention, the stack is in a longitudinally twisted configuration, and the sheath is sufficiently rigid to hold the stack in the longitudinally twisted configuration. Further, the sheath is preferably thin such that the exterior surface of the sheath defines ridges that correspond to the twist of the stack.
In accordance with another aspect of the present invention, in an end elevation view of the stack, the periphery of the stack defines a shape, and in an end elevation view of the sheath the interior surface of the sheath defines a shape. The shape defined by the interior surface of the sheath is substantially similar to the shape defined by the periphery of the stack. In addition, it is preferred for the exterior surface of the sheath to define a shape, in an end elevation view thereof, that is substantially similar to the shape defined by the periphery of the stack in the end elevation view of the stack. More specifically, the periphery of the stack bounds a first area in the end elevation view of the stack, the interior surface of the sheath bounds a second area in the end elevation view of the sheath, and the first and second areas are approximately equal.
In accordance with another aspect of the present invention, in the end elevation view of the sheath the exterior surface of the sheath defines generally polygon-like shape, and the sheath comprises thickened or bulbous-like portions proximate to the corners of the polygon-like shape.
In accordance with another aspect of the present invention, one or more of the optical modules are longitudinally stranded around a central member, which can be a strength member or a spacer, with the optical modules and the central member enclosed within a jacket.
REFERENCES:
patent: 4078853 (1978-03-01), Kempf et al.
patent: 4744631 (1988-05-01),
Hardwick, III Nathan E.
Jackson Kenneth Wade
Lever Clyde Jefferson
Norris Richard Hartford
Sheu Jim Jenqtsong
Boutsikaris Leo
Lucent Technologies - Inc.
Schuberg Darren
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