Optical waveguides – Optical transmission cable – Ribbon cable
Reexamination Certificate
1999-09-15
2001-04-10
Spyrou, Cassandra (Department: 2874)
Optical waveguides
Optical transmission cable
Ribbon cable
C385S109000, C385S110000, C385S112000
Reexamination Certificate
active
06215932
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to fiber optic cables and, more particularly, to protecting stacks of optical fiber ribbons within 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 to provide at least some protection for the optical fibers therein. It is important for optical fibers to be protected from stain because strain can degrade the performance of the optical fibers. For example, it is conventional for the above-referenced tubes 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 or inspection, for forming a splice between optical fibers, or the like. In addition, for a generally rectangular stack of optical fiber ribbons within a round tube, the optical fibers at the corners of the stack will often bear the brunt of any stresses.
Whereas there are several different conventional approaches for protecting stacks of optical fiber ribbons from stress by enclosing the stacks in tubes, further improvements in this area would be beneficial.
SUMMARY OF THE INVENTION
The present invention provides for the cushioned packaging of a stack of optical fiber ribbons by enclosing the stack in a buffer encasement having a relatively soft inner portion and an relatively hard outer portion. More specifically, the inner portion has an interior surface extends around and defines a longitudinally extending passage that contains the stack, and the interior surface closely bounds the stack. More specifically, the interior surface of the inner portion engages a substantial portion of the periphery of the stack. The outer portion extends around, closely bounds and contacts the inner portion, and has a modulus of elasticity that is greater than the modulus of elasticity of the inner portion.
In accordance with one aspect of the present invention, the inner portion has an exterior surface that extends around and is spaced apart from the passage, and the outer portion has an interior surface that extends around, closely bounds, and engages the exterior surface of the inner portion, whereby the buffer encasement has multiple plies. In contrast, in accordance with another aspect of the present invention, a surface is not defined between the inner portion and the outer portion.
In accordance with another aspect of the present invention, the buffer encasement is relatively thin. More specifically, each optical fiber ribbon includes 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 buffer encasement at least a majority of the buffer encasement has a thickness defined between the interior surface of the inner portion of the buffer encasement and an exterior surface of the outer portion of the buffer encasement, and the thickness of the buffer encasement is not substantially greater than the thickness of each of the optical fiber ribbons.
In accordance with another aspect of the present invention, the buffer encasement is 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 buffer encasement 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 another aspect of the present invention, the stack is longitudinally twisted, the buffer encasement is sufficiently rigid to hold the stack in the longitudinally twisted configuration, and the buffer encasement is thin such that an exterior surface of the outer portion of the buffer encasement defines ridges that correspond to the twist of the stack.
In accordance with another aspect of the present invention, the interior surface of the buffer encasement is unadhered to the stack and the stack is capable of moving relative to the buffer encasement.
In accordance with another aspect of the present invention, the periphery of the stack defines a shape in an end elevation view of the stack, and the interior surface of the inner portion of the buffer encasement defines a shape in an end elevation view of the buffer encasement that is substantially similar to the shape defined by the periphery of the stack in the end elevation view of the stack.
In accordance with another aspect of the present invention, in the end elevation view of the buffer encasement, the exterior surface of the outer portion of the buffer encasement defines a shape that is substantially similar to the shape defined by the periphery of the stack in the end elevation view of the stack.
In accordance with another aspect of the present invention, the buffer encasement is formed by coating the stack with an ultraviolet-curable material and thereafter exposing the ultraviolet-curable material to ultraviolet radiation for a predetermined period of time selected so that on a per unit basis more curing occurs in the outer portion than the inner portion.
In accordance with another aspect of the present invention, the buffer encasement is formed by extruding a first extrusion around the stack and extruding a second extrusion around the first extrusion so that the interior surface of the second extrusion comes into contact with the exterior surface of the first extrusion prior to solidification so that the interior and exterior surfaces become blended together.
In accordance with another aspect of the present invention, the buffer encasement is formed by applying a film around the stack and extrudi
Hardwick, III Nathan E.
Jackson Kenneth Wade
Lever Clyde Jefferson
Norris Richard Hartford
Sheu Jim Jenqtsong
Alston & Bird LLP
Boutsikaris Leo
Lucent Technologies - Inc.
Spyrou Cassandra
LandOfFree
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