 |
Description  |
|
|
FIELD OF THE INVENTION
The present invention relates generally to optical fiber transmission media
and, more particularly, to fiber optic ribbon cable assemblies having the
fiber optic ribbon manufactured with arbitrary spacing between optical
fibers, having the connectors manufactured in line with the ribbon cable
assembly, and having with the ribbon cable assembly manufactured with or
without an outside jacket or reinforcing shell.
BACKGROUND OF THE INVENTION
Optical fiber ribbon cables are well known for the transmission of optical
signals. Use of optical cables, including optical fiber ribbon cables, has
generally been limited to long-haul trunking installations where the
improved transmission characteristics of the optical fibers justify the
greater expense and difficulty associated with their manufacture and
installation. As the demands on communication media continue to increase,
the advantages of using optical cable for transmission of signals across
shorter distances or, for interconnecting local devices, continues to
grow. Unfortunately, the costs associated with the production of optical
fiber cable assemblies, and in particular with the installation of
connectors on optical fiber ribbon cables, continue to limit the wide
spread application of optical fiber transmission media for these
applications.
Traditionally, a single fiber optical cable is assembled by coating an
optical fiber with a buffer layer and then encasing the buffered optical
fiber within a Kevlar.RTM. sheath that provides tensile strength and a
vinyl outer jacket that serves as an environmental shield. Multi-fiber
optical cables are assembled in a similar manner by bundling multiple
buffered optical fibers within the center of a Kevlar.RTM. sheath and
corresponding outer jacket. The difficulty with a multi-fiber bundled
optical cable is in providing an economic, convenient and reliable system
for installing a connector on the ends of the optical fibers so as to
provide a finished fiber optic cable assembly.
As an alternative to a multi-fiber bundled optical cable, optical fiber
ribbons have been developed in which multiple optical fibers are aligned
and maintained in a planar configuration. U.S. Pat. No. 3,920,432, issued
to Smith describes an early method of fabricating an optical fiber ribbon
cable in which a plurality of glass optical fibers are carried by a
grooved holder with a plurality of spacing fibers of triangular
cross-section continuously fed into the spaces between adjacent optical
fibers in the holder. The spacing fibers are then melted to secure the
optical fibers within the holder. The advantage of this technique is that
the optical fibers are accurately aligned within the holder, thereby
aiding in the ability to easily interface the fiber optic ribbon with an
optical connector. The disadvantage is that this technique limits the
mechanical performance of the fiber optic ribbon by requiring that the
holder be provided for the entire length of the ribbon and that the holder
have sufficient structural integrity to accurately maintain the
positioning of the optical fibers within the holder. In addition, the
requirement that the fiber optic ribbon be heated in order to melt the
triangular-type spacing fibers to secure the optical fibers within the
holder subjects the fiber optic ribbon to thermal stress.
U.S. Pat. Nos. 4,289,558 issued to Eichenbaum et al. and 4,980,007, issued
to Ferguson describe improved methods of fabricating a fiber optic ribbon
in which buffered optical fibers are positioned adjacent one another in a
planar orientation and then sandwiched between the adhesive layers of a
pair of thin binding tapes. The resulting fiber optic ribbon is then
encased in Kevlar.RTM. fibers and a plastic sheath, for example, to
provide tensile strain relief and environmental protection for the optical
fibers. In this technique, the alignment of the optical fibers within the
ribbon is created and maintained by abutting adjacent fibers and then
relying on the dimensional characteristics of the buffer layer surrounding
the optical fibers so as to achieve a uniform spacing across a cross
sectional width of the fiber optic ribbon. While these techniques provide
a clear manufacturing advantages to the technique disclosed by Smith in
U.S. Pat. No. 3,920,432, the problems which are created by utilizing these
techniques are an increased difficulty in attaching, aligning and
installing optical connectors on the ends of the fiber optic ribbon in
order to create a finished fiber optic ribbon cable assembly.
Numerous optical connectors have been developed to aid in the connection
and splicing of fiber optic ribbons. Examples of connectors which are
designed to terminate an end of a fiber optic ribbon are shown and
described in U.S. Pat. Nos. 3,864,018, issued to Miller, 4,793,683, issued
to Cannon, Jr., et al., and 5,309,537, issued to Chun, et al. In contrast,
U.S. Pat. No. 3,871,935, issued to Cloge, et al. and European Patent Publ.
No. 0 613 031 81 both describe methods for encapsulating a middle portion
of a fiber optic ribbon within an optical connector assembly that is then
severed in half to form opposed ends of a pair of optical connectors. In
both of these references, the protective jacket and buffer surrounding the
optical fibers are chemically removed in a middle portion of the ribbon
and the resulting bare optical fibers are positioned within an
encapsulating mold into which a bonding material is injected to secure the
optical fibers. Once secured, the molded assembly is divided in half along
a plain perpendicular to the axis of the optical fibers, thereby exposing
ends of the fibers which can be polished for alignment and/or abutment to
other optical fiber ends. The advantages of these encapsulation connector
techniques are that they involve less manipulation and mechanical stress
of the optical fibers than the technique taught by Smith. The
disadvantages are that the stripping step subjects the optical fibers to
potential damage and that the alignment of optical fibers in the molded
assembly is not certain due to the potential movement of optical fibers
during the encapsulating process. In any event, these techniques are still
post-production techniques applied after the fiber optic ribbon has been
assembled.
Although existing techniques for the manufacture of fiber optic ribbon
cable assemblies having optical connectors at one or both ends of a fiber
optic ribbon cable are capable of producing optical transmission media
that are well suited for certain applications, it would be desirable to
provide a method of fabrication of fiber optic ribbon cable assemblies
which was more cost effective and allowed for easier manufacture and
assembly of fiber optical ribbon cable assemblies so as to broaden the
potential applications for use of fiber optic ribbon cables.
SUMMARY OF THE INVENTION
The present invention is a fiber optic ribbon cable assembly having optical
connector assemblies manufactured in line with the ribbon cable assembly
so as to provide a fixed, lateral spacing of the optical fibers relative
to each other within the connector assembly and having the remaining
portion of the fiber optic ribbon cable manufactured within an arbitrary
lateral spacing of the optical fibers relative to each other. A pair of
adhesive tape layers are sandwiched around the optical fibers and the
in-line optical connector assemblies. By having the connector assemblies
manufactured in line with the fiber optic ribbon cable, the resulting
ribbon cable assembly is easier to manufacture, has a higher alignment
accuracy, and is more cost effective than existing techniques for
manufacturing ribbon cable assemblies. Additionally, the pair of adhesive
tape layers preferably encapsulate the optical fibers and may serve as the
outermost jacket for the ribbon cable assembly, thereby reducing the
number of components associated with the ribbon cable assembly.
In a first embodiment of the present invention, a fiber optic ribbon cable
assembly includes a pair of adhesive tape layers. A plurality of optical
fibers are arranged in a generally longitudinal orientation between a pair
of adhesive tape layers with adjacent optical fibers positioned with an
arbitrary lateral spacing relative to each other. At least a portion of at
least one connector assembly is also disposed between the pair of adhesive
tape layers. The plurality of optical fibers are disposed within the
connector assembly with adjacent optical fibers positioned with a fixed
lateral spacing relative to each other.
In accordance with the second embodiment of the present invention, a method
of manufacturing a fiber optic ribbon cable assembly involves the steps of
providing a plurality of optical fibers oriented in a generally
longitudinal manner. Adjacent ones of the plurality of optical fibers are
then arranged in a fixed lateral spacing relative to each other and a
connector assembly is applied onto a first longitudinal segment of the
plurality of optical fibers. At least a second longitudinal segment of the
plurality of optical fibers separate from the first longitudinal segment
are sandwiched between a pair of adhesive tape layers to form a ribbon
cable assembly. Adjacent ones of the plurality of optical fibers are
maintained in an arbitrary lateral spacing relative to each other in the
second longitudinal segment.
In a preferred embodiment, the plurality of optical fibers are fed from
spools of continuous optical fiber. The connector assembly comprises an
upper connector component and a lower connector component with structure
defined therein so that when the plurality of optical fibers are
sandwiched between the upper connector component and the lower connector
component, the fixed lateral inter-fiber spacing is established. The
arbitrary lateral inter-fiber spacing within the non-connector portion of
the ribbon cable may range from 0.0 to 2.0 centimeters. Preferably,
in-line connector assemblies include structure defining a center portion
such that the center portion may be cut generally perpendicular to the
longitudinal orientation of the optical fibers, thereby exposing ends of
the plurality of optical fibers with a lateral cross section of the
connector assembly and in the fixed lateral spacing. The pair of adhesive
tape layers may include a pair of margin portions that extend laterally
beyond a planar orientation of the plurality of optical fibers and are
adhered to each other to form a seal along at least a portion of the
longitudinal edge of the ribbon cable assembly.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic illustration of the method of manufacturing a fiber
optic ribbon cable assembly having integrated in-line connector assemblies
in accordance with the present invention.
FIG. 2 is a cross sectional view of a fiber optic ribbon cable of the prior
art.
FIG. 3 is a cross sectional view of a fiber optic ribbon cable of the
present invention.
FIG. 4 is an exploded cross sectional view of the fiber optic ribbon cable
of the present invention showing the layered details of the adhesive tape
and optical fibers.
FIG. 5 is a cross sectional view of the fiber optic ribbon cable of FIG. 4
as assembled in accordance with the preferred embodiment of the present
invention.
FIG. 6 is a schematic side view of the process of the present invention
showing the application of the integrated in-line connector assemblies
onto the fiber optic ribbon cable.
FIG. 7 is a series of side views of a fiber optic ribbon cable assembly
produced in accordance with the present invention demonstrating a
preferred finishing technique for the integrated in-line connector
assembly.
FIG. 8 is a side view of a preferred embodiment of the integrated in-line
connector assembly.
FIG. 9 is an top view of the lower connector component of the connector
assembly of FIG. 8.
FIG. 10 is an end view of the connector assembly of FIG. 8.
FIG. 11 is a top view of an alternate embodiment of the connector assembly
of the present invention including mechanical attachment features.
FIG. 12 is a side view of the alternate embodiment of the connector
assembly shown in FIG. 11.
FIG. 13 is an end view of an alternate embodiment of a connector assembly.
FIG. 14 is an end view of another alternate embodiment of a connector
assembly.
FIG. 15 is a side view of another alternate embodiment of a connector
assembly.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, the method of producing a fiber optic ribbon cable
assembly 20 in accordance with the present invention will be described. A
plurality of optical fibers 30 are drawn from a corresponding series of
spools 32 holding such optical fibers 30 through a guiding comb 34.
Guiding comb 34 is provided with structure to establish a fixed, lateral
inter-fiber spacing between optical fibers 30. Preferably, this spacing
corresponds with a fixed, lateral inter-fiber spacing of a connector
assembly 22 which is preferably comprised of a pair of upper and lower
connector components 23, 24. After optical fibers 30 are brought through
guiding comb 34, the connector components 23, 24 are positioned so as to
sandwich optical fibers 30 therebetween, thereby fixing the lateral
inter-fiber dimension within connector assembly 22. At a point farther
down stream in the process, a lower adhesive tape 26 and an upper adhesive
tape 27 are introduced to sandwich optical fibers 30 therebetween creating
a fiber optic ribbon cable 28. A pair of compression rollers 36, 38 are
preferably used to supply the force necessary to secure lower adhesive
tape 26 to upper adhesive tape 27 with optical fibers 30 being held
therebetween and having an arbitrary and non-fixed, lateral inter-fiber
separation distance, except for in those locations of optical fiber ribbon
20 where connector components 23, 24 have been located. When present,
optical connector components 23, 24 are also sandwiched between upper and
lower adhesive tapes 26, 27.
In describing the present invention, the term connector assembly is used to
describe structure which typically creates a pair of optical connectors on
opposing ends of fiber optic ribbon segments when the structure is
severed, although it is possible to have a connector assembly which
results in only a single useable optical connector. In a preferred
embodiment, connector assembly 22 is comprised of a pair of connector
components 23, 24, although it will be understood that other arrangements
of connector assembly 22 are possible, such as four connector components
(as shown in FIG. 15) or a unitary connector assembly having an aperture
through which optical fibers 30 are threaded. It will be recognized that
connector assembly 22 is usually cut along at least one axis that is
generally perpendicular to the longitudinal orientation of optical fibers
30, however, it is possible to make this cut a small angle to
perpendicular, for example, in order to aid in the prevention of
reflections. Connector assembly 22 is preferably made of plastic, but may
also be manufactured from ceramic or metal materials and may, for example,
be comprised of a plastic body having a ceramic or metal insert
corresponding to the portion of connector assembly 22 which interfaes with
optical fibers 30.
In conventional installation of fiber optic cables, an optical connector on
an end of one cable is joined to an optical connector on an end of another
cable using an optical coupler. While an optical coupler is normally
required in order to complete an interconnetion between two cables, it
should be recognized that it would be possible to include the mating
structure of an optical coupler as part of a connector assembly in
accordance with the present ivnention. It also will be recognized that
numerous combinations and configurations of mechanical connector members
and connector orientation configurations can be accomplished with the
present invention.
One of the advantages of the present invention is that, by assembling
optical fibers 30 within connector components 23, 24 prior to completing
the remaining assembly of optical fiber ribbon cable assembly 20, it is
not necessary to maintain specific inter-fiber distances or tolerances
throughout the entire length of ribbon cable 28. As shown in FIG. 2, the
prior art technique of assembling a fiber optic ribbon cable 40 relies on
positioning adjacent optical fibers 42 in a contiguous planar, abutting
relationship. By doing so, the prior art relies on the thicknesses of a
buffer layer 44 surrounding each adjacent optical fiber 42 to establish a
fixed inter-fiber optical separation d shown at 46. While this process
works to define inter-fiber spaces 46 along a longitudinal length of fiber
optic ribbon cable 40, it does not work well enough to provide for
consistent, accurate inter-fiber spacings 46 which could be used for
optical alignment within an optical connector.
In contrast to fiber optic ribbon cable 40, fiber optic ribbon cable 28 of
the present invention as shown in FIG. 3 does not attempt to maintain a
precisely fixed, lateral relation among optical fibers 30 when sandwiched
between tape layers 26, 27. As a result, distance is d' shown at 50 and d"
shown at 52 between adjacent optical fibers 30 may or may not be
identical. Each distance d' and d" will generally include a space between
laterally-adjacent optical fibers, .DELTA..sub.1 shown at 54 and
.DELTA..sub.2 shown at 56, although it will be recognized that because no
fixed lateral, inter-fiber spacing is dictated when optical fibers 30 are
positioned within tape layers 26, 27, it would also be possible for
adjacent optical fibers 30 to, in some situations, be in an abutting
relationship.
Another advantage of the present invention is that, by assembling optical
fibers 30 within connector assembly 22 prior to completing the remaining
assembly of optical fiber ribbon cable assembly 20, significant time and
money are saved with the installation of optical connectors on the optical
fibers. The fixed, lateral inter-fiber spacing within connector components
23, 24 establishes a fixed pitch of optical fibers 30. Unlike the prior
art techniques, optical fibers 30 are not subjected to either thermal or
chemical stresses during the process of installing the optical connector
assembly. In addition, there is absolute certainty of the relative
position of the optical fibers 30 within connector components 23, 24.
Finally, the manufacture of the integrated, in-line optical connector
assembly 22 can be incorporated into a continuous manufacturing process,
thereby significantly reducing the production costs of fiber optic ribbon
cable assembly 20 as compared to prior techniques for the manufacture or
field-installation of optical connectors on fiber optic ribbons.
Referring now to FIG. 4, a preferred embodiment of tape layers 26, 27 and
optical fibers 30 will be described. FIG. 4 shows an exploded
cross-sectional view of ribbon cable 28 prior to sandwich assembly of tape
layers 26, 27 with optical fibers 30 therebetween. In a preferred
embodiment, optical fibers 30 are comprised of an optical core 60 composed
of a material selected from the set of glass, plastic or air. Fiber optic
core 60 is surrounded by a cladding layer 62 composed of a material
selected from the set comprising glass, plastic or metal.
The optical fiber 30 may also include a buffer layer 64 composed of a
material selected from the set of plastic, metal, carbon, ceramic or any
combination thereof. In a preferred embodiment, optical fibers 30 are
TECS.TM. hard clad fiber FT-200-EMA, available from 3M Company, St. Paul,
Minn., although it will be recognized that the present invention is
equally applicable to fiber optic ribbon cable assemblies 20 utilizing a
variety of different optical fibers.
In a preferred embodiment, tape layers 26, 27 are each three-layer planar
tape assemblies comprised of an inner encapsulating layer 70, an adhesive
layer 72 and an outer protective layer 74. Encapsulating layer 70 serves
to encapsulate optical fibers 30 and is preferably comprised of a
deformable material such as pressure sensitive adhesive, thermoset
adhesive, thermoplastic adhesive, radiation-curable adhesive, gel, foam,
fibrous material, deformable plastic or any combination thereof. Adhesive
layer 72 is interposed between inner layer 70 and 74 to secure each to the
other and is preferably comprised of a material such as pressure sensitive
adhesive, thermoset adhesive, thermoplastic adhesive, radiation-curable
adhesive, mechanically interlocking structures or any combination thereof.
Outer protective layer 74 serves as the outer jacket for fiber optic
ribbon cable assembly 20 and is preferably comprised of a vinyl or plastic
material which is suitable for a variety of environmental applications, or
may be comprised of plastic, metal, fabric or any combination thereof.
Preferably layers 72 and 74 are comprised of Scotch.RTM. brand tape No.
471 and layer 70 is comprised of VHB.TM. brand tape No. F-9469PC, both of
which are available from 3M Company, St. Paul, Minn.
In an alternate embodiment shown in FIG. 5, protective layer 74 and
adhesive layer 72 are extended beyond encapsulating layer 70 in an area
shown at 76, for example, such that the lateral edges of fiber optical
ribbon cable 28 are effectively sealed from environmental contamination.
While it is understood that, for economic reasons, in a preferred
embodiment outer layer 74 is intended to serve as an outermost jacket of
ribbon cable assembly 20, it would also be possible to enclose one or more
ribbon cable assemblies 20 within an additional outer jacket layer, such
as in the case where a larger fiber optic cable bundle is required for a
long haul transmission application. In such an embodiment, it would also
be possible to arrange the fiber optic cable assembly 20 within an
additional outer jacket such that the final cable assembly would offer
more structural integrity so as to prevent, for example, bending or
crimping of optical fibers 30. One such embodiment would involve folding
the generally planar orientation of cable assembly 20 into an S-shaped
configuration. Another alternate configuration would provide for a stacked
orientation of multiples ones of cable assembly 20. Still another
embodiment would include an additional core member around which cable
assembly 20 could be wrapped, with the core member having a circular cross
section, for example, to simulate a more traditional tubular shape for the
final cable assembly.
Referring now to FIG. 6, a side view of the assembly process of fiber optic
ribbon cable assembly 20 is shown in which it is demonstrated how
connector components 23, 24 are inserted at discrete locations along the
longitudinal length of optical fibers 30 during the process of the present
invention. It will be seen by controlling the positioning and number of
connector assemblies 22, it is possible to produce a continuous run of
cable assembly 20 having a series of cable segments 80 (as shown in FIG.
7), each with a length effectively determined by the positioning of
sequential connector assemblies 22.
FIG. 7 shows how cable segments 80 | | |
