High density fiber optic cable

Details High density fiber optic cable High density fiber optic cable

2001-06-25

2004-10-19

Hyeon, Hae Moon (Department: 2839)

Optical waveguides

Optical transmission cable

Tightly confined

C385S102000

Reexamination Certificate

active

06807347

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to fiber optic cables and, more particularly, to high density fiber optic cables.
BACKGROUND OF THE INVENTION
In many applications, it is desirable for a fiber optic cable to include a plurality of optical fibers. With the increased demand for optical communications, there has been a corresponding demand to increase the number of optical fibers, i.e., the fiber count, of a fiber optic cable. By increasing the fiber count of a fiber optic cable, a single fiber optic cable would be able to support additional optical communications channels.
In order to increase the fiber count of fiber optic cables, unitized fiber optic cables have been developed. As shown in
FIG. 1
, a unitized fiber optic cable
10
includes a number of bundles
12
of optical fibers
14
that are stranded about a common central strength member
16
. A unitized fiber optic cable
10
also includes a cable jacket
18
extruded about the bundles
12
of optical fibers
14
, and an optional ripcord
22
for facilitating removal of cable jacket
18
. As shown in
FIG. 1
, each bundle
12
of optical fibers
14
includes at least two and, more commonly, six or twelve optical fibers that are stranded together.
Optical fibers
14
are typically tight buffered optical fibers. A tight buffered optical fiber
14
includes a single mode or multi-mode optical fiber surrounded by an interfacial layer. The interfacial layer can be formed of a Teflon® containing material and is surrounded by a tight buffer layer. The tight buffer layer is typically formed of a plastic, such as polyvinyl chloride (PVC). As an alternative to PVC, the tight buffer layer can be formed of a non-halogenated polyolefin, such as a polyethylene or a polypropylene. Still further, the tight buffer layer can be formed of EVA, nylon or polyester.
Each bundle
12
of optical fibers
14
also generally includes a central strength member
26
about which the plurality of tight buffered optical fibers are stranded. Each bundle
12
of optical fibers
14
further includes a jacket
28
that surrounds the plurality of optical fibers, and an optional ripcord
20
for facilitating removal of jacket
28
. Jacket
28
serves to protect optical fibers
14
and to maintain the bundle of optical fibers in a stranded relationship about central strength member
26
. Jacket
28
is typically formed of a polymer, such as PVC. As an alternative to PVC, jacket
28
may be formed of a fluoro-plastic, such as polyvinylidene fluoride (PVDF), a fluoro-compound as disclosed by U.S. Pat. No. 4,963,609 or blends of PVC and PVDF or PVC and polyethylene (PE). Jacket
28
is typically relatively thick and, in one embodiment, has a thickness of about 0.8 millimeters.
During fabrication, a bundle
12
of optical fibers
14
is passed through an extruder cross head and jacket
28
is extruded thereabout in order to maintain the optical fibers in position within the bundle. Since the tight buffer layer of the tight buffered optical fibers
14
is typically formed of a plastic, the plastic that is extruded to form jacket
28
will tend to adhere to the tight buffer layer of the tight buffered optical fibers
14
in the absence of a barrier therebetween. In this regard, the plastic that is extruded to form jacket
28
of a bundle
12
of optical fibers
14
may partially melt the outermost portion of the tight buffer layer of the tight buffered optical fibers
14
such that jacket
28
and the tight buffered optical fibers will adhere to one another as the plastic cools. Unfortunately, the adherence of the tight buffered optical fibers
14
to the surrounding jacket
28
generally decreases the performance of the optical fibers. In this regard, signals propagating along optical fibers
14
generally experience greater attenuation as fiber optic cable
10
is bent or flexed in instances in which the tight buffered optical fibers are adhered to jacket
28
since the optical fibers will no longer be free to move relative to jacket
28
in order to accommodate bending or flexure of fiber optic cable
10
.
Each bundle
12
of optical fibers
14
therefore also generally includes a barrier
30
disposed between the plurality of tight buffered optical fibers and jacket
28
in order to separate the tight buffered optical fibers from jacket
28
and to prevent adherence therebetween that otherwise would result from the extension of jacket
28
about optical fibers
14
. As such, optical fibers
14
can move somewhat relative to jacket
28
as fiber optic cable
10
is flexed. Barrier
30
is typically formed of a layer of strength members, such as aramid yarn, that are typically stranded about the optical fibers. The layer of strength members is also generally relatively thick and may have a thickness of about 0.2 mm in one embodiment.
Each bundle
12
of optical fibers
14
is typically stranded about common central strength member
16
of fiber optic cable
10
. Like central strength member
26
of each bundle
12
of optical fibers
14
, common central strength member
16
of fiber optic cable
10
is typically formed of a relatively stiff fiber or glass reinforced plastic, or a relatively flexible combination of aramid fibers that may or may not be overcoated with a plastic material. Fiber optic cable
10
also includes a protective cable jacket
18
that surrounds each of the bundles
12
of optical fibers
14
. Cable jacket
18
is typically formed of a plastic, such as PVC. As an alternative to PVC, cable jacket
18
may be formed of a fluoro-plastic, such as PVDF, a fluoride-compound or blends of PVC and PVDF or PVC and PE.
As described above in conjunction with jacket
28
that surrounds each bundle
12
of optical fibers
14
, cable jacket
18
is also typically extruded over the plurality of bundles of optical fibers. As a result of the plastic materials that form cable jacket
18
and the jackets
28
that surround the respective bundles
12
of optical fibers
14
, cable jacket
18
and the jackets that surround the respective bundles of optical fibers may also adhere to one another following the extrusion of cable jacket
18
about the bundles of optical fibers. While the adherence of cable jacket
18
to the jackets
28
of the respective bundles
12
of optical fibers
14
does not impair the performance of fiber optic cable
10
as significantly as adherence between jacket
28
of a bundle
12
of optical fibers
14
and the tight buffer layer of the tight buffered optical fibers, the adherence of cable jacket
18
and the jackets of the respective bundles of optical fibers does disadvantageously impair the flexibility of fiber optic cable
10
somewhat.
Accordingly, fiber optic cable
10
can also include a surface coating on at least that portion of the exterior surface of jacket
28
of each bundle
12
of optical fibers
14
that otherwise would be in contact with cable jacket
18
. The surface coating is typically formed of powdered talc that serves to prevent or reduce adhesion between cable jacket
18
and the jackets
28
of the respective bundles
12
of optical fibers
14
.
Unitized fiber optic cable
10
as depicted in
FIG. 1
is generally relatively large. For example, unitized fiber optic cable
10
depicted in
FIG. 1
having six bundles
12
of optical fibers
14
stranded about a central strength member
16
with each bundle of optical fibers having six tight buffered optical fibers stranded about a respective strength member
26
generally has a diameter of about 18.8 millimeters. In many applications, it is desirable to minimize the size of fiber optic cable
10
while maintaining or increasing the number of optical fibers
14
within fiber optic cable
10
. As such, it would be advantageous to develop a unitized fiber optic cable having a relatively high fiber count while also being somewhat smaller.
SUMMARY OF THE INVENTION
A fiber optic cable is provided according to one aspect of the present invention that includes at least one non-jacketed bundle of optical fibers having a plurality of optica

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