U.S. patent application number 09/941257 was filed with the patent office on 2002-02-28 for sub-miniature optical fiber cables, and apparatuses and methods for making the sub-miniature optical fiber cables.
Invention is credited to Graham, Loinell, Holman, James Robert, Mathis, Terry Don, Moss, Parry A., Viriyayuthakorn, Montri, Wilson, Carla G..
Application Number | 20020025127 09/941257 |
Document ID | / |
Family ID | 24029048 |
Filed Date | 2002-02-28 |
United States Patent
Application |
20020025127 |
Kind Code |
A1 |
Graham, Loinell ; et
al. |
February 28, 2002 |
Sub-miniature optical fiber cables, and apparatuses and methods for
making the sub-miniature optical fiber cables
Abstract
A simplex optical fiber cable of this invention includes an
optical fiber, a buffer preferably of nylon, surrounding and in
contact with the optical fiber, a yarn layer with strength fibers,
preferably aramid fibers, disposed about the buffer and a sheath
preferably formed of polyvinyl chloride (PVC) surrounding and in
contact with the yarn layer. [In cross-section, the simplex optical
fiber cable has a diameter less than 2.0 millimeters (mm), and thus
is much smaller in diameter than optical fiber cables presently
available Preferably, if the buffer is relatively thin providing
limited protection to the optical fiber, a slick substance such as
talc is applied to an outer surface of the buffer before the yarn
layer is disposed thereon. The slick substance allows the buffer of
the optical fiber to slide to a degree in contact with the yarn
layer and thus reduces fatigue caused by axial movement of a
ferrule of the connector terminating the optical fiber cable. On
the other hand, if the buffer is relatively thick, a
friction-reducing substance such as Modaflo.TM. can be applied to
the optical fiber to allow the buffer to be stripped relatively
easily]. A zip-cord duplex optical fiber cable of this invention
includes essentially two simplex optical fiber cables with their
respective sheaths joining at a middle portion along the axial
length of the simplex optical fiber cables. [Thus, in
cross-section, the zip-cord duplex optical fiber cable has a
figure-eight shape with a relatively thin portion in the middle
which can be manually pulled apart to separate the zip-cord duplex
optical fiber cable into separate simplex optical fiber cables.
This feature of the invention allows the zip-cord duplex optical
fiber cable to be split at its ends to allow connectors attached to
respective ends of the optical fiber cables for connection to
respective spaced connector receptacles]. A second duplex optical
fiber cable of this invention includes two simplex optical fiber
cables arranged side-by-side with an oversheath extruded about and
holding together the two simplex optical fiber cables. In
cross-section, the two duplex optical fiber cables of this
invention are less than 2.0 mm in height and 4.0 mm in width, and
thus are much smaller than currently available duplex optical fiber
cables. [The invention also includes die assemblies and methods for
making the simplex and duplex optical fiber cables].
Inventors: |
Graham, Loinell;
(Snellville, GA) ; Holman, James Robert; (Lilburn,
GA) ; Mathis, Terry Don; (Lilburn, GA) ;
Viriyayuthakorn, Montri; (Norcross, GA) ; Wilson,
Carla G.; (Conyers, GA) ; Moss, Parry A.;
(Stone Mountain, GA) |
Correspondence
Address: |
THOMAS, KAYDEN, HORSTEMEYER & RISLEY, LLP
100 GALLERIA PARKWAY, NW
STE 1750
ATLANTA
GA
30339-5948
US
|
Family ID: |
24029048 |
Appl. No.: |
09/941257 |
Filed: |
August 28, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09941257 |
Aug 28, 2001 |
|
|
|
08510021 |
Aug 1, 1995 |
|
|
|
Current U.S.
Class: |
385/102 ;
385/107 |
Current CPC
Class: |
G02B 6/443 20130101;
B29C 48/94 20190201; B29C 48/12 20190201; G02B 6/4479 20130101;
B29C 48/05 20190201; G02B 6/4403 20130101; B29C 48/06 20190201;
B29D 11/00663 20130101; G02B 6/4402 20130101; B29C 48/34 20190201;
G02B 6/4495 20130101 |
Class at
Publication: |
385/102 ;
385/107 |
International
Class: |
G02B 006/44 |
Claims
1. An optical fiber cable, comprising: a single optical waveguide
fiber having an outer coating, said outer coating having a diameter
of about 500 .mu.m; a layer of loose tensile fibers surrounding the
optical waveguide fiber outer coating; and a tubular jacket of
plastic material having an outer diameter D.sub.2 surrounding the
layer of loose tensile fibers, D.sub.2 not exceeding about 1500
.mu.m, said cable containing no gel like compounds.
2. An optical fiber cable qas set out in claim 1 wherein D.sub.2
does not exceed about 1400 .mu.m.
3. An optical fiber cable as set out in claim 1 wherein D.sub.2
does not exceed about 1200 .mu.m.
4. An optical fiber cable as set out in claim 1 wherein the optical
fiber cable outer jacket is formed of a flame retardant
material.
5. An optical fiber cable as set out in claim 1 wherein the tubular
jacket has an inner diameter D.sub.1 and D.sub.2-D.sub.1 is less
than or equal to about 300 .mu.m.
6. An optical fiber cable as set out in claim 1 which contains no
material comprising halogen compounds.
7. An optical fiber cable as claimed in claim 1 which contains no
materials containing leaded compounds.
8. An optical fiber cable comprising first and second optical
fibers; a first buffer composed of plastic material surrounding and
in contact with an outer surface of the first optical fiber; a
second buffer composed of plastic material surrounding and in
contact with an outer surface of the second optical fiber; each of
said buffers being surrounded by a yarn layer composed of strength
fibers; a sheath member surrounding and in contact with the yarn
layer; said cable having at least one transverse dimension in the
range of 1.25 mm. to 2.00 mm.
9. An optical fiber cable as claimed in claim 8 wherein said
transverse dimension is less than 2 mm.
10. An optical fiber cable, comprising: a single optical waveguide
fiber having an outer buffer, said outer buffer having an outer
diameter from about 500 .mu.m to about 900 .mu.m; a layer of loose
tensile fibers surrounding the optical waveguide fiber outer
buffer; and a tubular jacket of plastic material surrounding the
layer of loose tensile fibers, said tubular jacket having an outer
diameter not exceeding about 2000 .mu.m, said cable containing no
gel-like compounds.
11. The optical fiber cable of claim 10, wherein said outer buffer
has an outer diameter of about 900 .mu.m.
12. The optical fiber cable of claim 10, wherein said tubular
jacket of plastic material surrounding the layer of loose tensile
fibers has an outer diameter not exceeding about 1600 .mu.m.
13. An optical fiber cable, comprising: a single optical waveguide
fiber having an outer buffer, said outer buffer having an outer
diameter of about 900 .mu.m; a layer of loose tensile fibers
surrounding the optical waveguide fiber outer buffer; and a tubular
jacket of plastic material surrounding the layer of loose tensile
fibers, said tubular jacket having an outer diameter of about 1600
.mu.m, said cable containing no gel-like compounds.
14. An optical fiber cable comprising first and second optical
fibers; a first outer buffer composed of plastic material
surrounding and in contact with an outer surface of said first
optical fiber; a second outer buffer composed of plastic material
surrounding and in contact with an outer surface of said second
optical fiber; each of said outer buffers being surrounded by a
yarn layer composed of strength fibers; and a sheath member
surrounding and in contact with said yarn layer; said cable having
at least one outer transverse dimension not exceeding about 2000
.mu.m.
15. The optical fiber cable of claim 14, wherein said outer
transverse dimension does not exceed about 1600 .mu.m.
16. The optical fiber cable of claim 14, wherein said first and
second outer buffers have outer diameters from about 500 .mu.m to
about 900 .mu.m.
17. The optical fiber cable of claim 14, wherein said first and
second outer buffers have outer diameters of about 900 .mu.m.
18. An optical fiber cable comprising first and second optical
fibers; a first outer buffer composed of plastic material
surrounding and in contact with an outer surface of said first
optical fiber, said first outer buffer having an outer diameter of
about 900 .mu.m; a second outer buffer composed of plastic material
surrounding and in contact with an outer surface of said second
optical fiber, said second outer buffer having an outer diameter of
about 900 .mu.m; each of said outer buffers being surrounded by a
yarn layer composed of strength fibers; and a sheath member
surrounding and in contact with said yarn layer; said cable having
at least one outer transverse dimension of about 1600 .mu.m.
19. An optical fiber cable, comprising: a single optical waveguide
fiber having an outer buffer, said outer buffer having an outer
diameter from about 500 .mu.m to about 900 .mu.m; a layer of loose
tensile fibers surrounding said optical waveguide fiber outer
buffer; and a tubular jacket of plastic material surrounding said
layer of loose tensile fibers, said tubular jacket having an outer
diameter from about 1000 .mu.m to about 1800 .mu.m, said cable
containing no gel-like compounds.
20. The optical fiber cable of claim 19, wherein said outer buffer
has an outer diameter of about 500 .mu.m.
21. The optical fiber cable of claim 19, wherein said outer buffer
has an outer diameter of about 900 .mu.m.
22. The optical fiber cable of claim 19, wherein said tubular
jacket of plastic material surrounding said layer of loose tensile
fibers has an outer diameter not exceeding about 1600 .mu.m.
23. The optical fiber cable of claim 19, wherein said tubular
jacket of plastic material surrounding said layer of loose tensile
fibers has an outer diameter of about 1600 .mu.m.
24. An optical fiber cable, comprising: a single optical waveguide
fiber having an outer buffer, said outer buffer having an outer
diameter from about 500 .mu.m to about 900 .mu.m; a layer of loose
tensile fibers surrounding said optical waveguide fiber outer
buffer; and a tubular jacket of plastic material surrounding said
layer of loose tensile fibers, said tubular jacket having an outer
diameter from about 1200 .mu.m to about 1600 .mu.m, said cable
containing no gel-like compounds.
25. The optical fiber cable of claim 24, wherein said outer buffer
has an outer diameter of about 500 .mu.m.
26. The optical fiber cable of claim 24, wherein said outer buffer
has an outer diameter of about 900 .mu.m.
27. An optical fiber cable, comprising: a single optical waveguide
fiber having an outer buffer, said outer buffer having an outer
diameter of about 900 .mu.m; a layer of loose tensile fibers
surrounding said optical waveguide fiber outer buffer; and a
tubular jacket of plastic material surrounding said layer of loose
tensile fibers, said tubular jacket having an outer diameter of
about 1600 .mu.m, said cable containing no gel-like compounds.
28. An optical fiber cable comprising first and second optical
fibers; a first outer buffer composed of plastic material
surrounding and in contact with an outer surface of said first
optical fiber; a second outer buffer composed of plastic material
surrounding and in contact with an outer surface of said second
optical fiber; each of said outer buffers being surrounded by a
yarn layer composed of strength fibers; and a sheath member
surrounding and in contact with said yarn layer; said cable having
at least one outer transverse dimension from about 1250 .mu.m to
about 2000 .mu.m.
29. The optical fiber cable of claim 28, wherein said outer
transverse dimension does not exceed about 1680 .mu.m.
30. The optical fiber cable of claim 28, wherein said outer
transverse dimension is about 1600 .mu.m.
31. The optical fiber cable of claim 28, wherein said first and
second outer buffers have outer diameters from about 500 .mu.m to
about 900 .mu.m.
32. The optical fiber cable of claim 28, wherein said first and
second outer buffers have outer diameters of about 500 .mu.m.
33. The optical fiber cable of claim 28, wherein said first and
second outer buffers have outer diameters of about 900 .mu.m.
Description
RELATED APPLICATIONS
[0001] This application is a continuation application claiming
priority to application Ser. No. 08/510,021; filed Aug. 1,
1995.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention is directed to a sub-miniature optical fiber
cable, and to apparatuses and methods for making the sub-miniature
optical fiber cable.
[0004] 2. Description of the Related Art
[0005] Local exchange carriers are increasingly using optical fiber
signal transmission in central offices to accommodate the
increasing demand for optical fiber systems such as
fiber-to-the-home, fiber-to-the-curb, hybrid fiber-coax, digital
loop carrier and interoffice carrier systems. The central offices
are used to distribute optical fiber cables and to establish
cross-connections between optical fiber systems and/or exchanges.
At present, optical fiber cable is produced in standard sizes of
2.4 mm or 3 mm in diameter. Although these standard sizes may
appear to be relatively small in diameter, because they are used in
such large numbers in a central office, these standard sizes lead
to significant congestion, complication and expense in a central
office. In fact, to accommodate cross-connections between optical
fiber systems or exchanges, central offices require a relatively
large number of cabinets with troughs housing optical fiber jumper
cables, and racks housing connectors to join optical fiber jumper
cables together. The relatively large number of cabinets currently
required in a central office to accommodate cross-connections for
optical fibers increases the size and space requirements for
central offices and thus the expense of the central offices.
Moreover, the relatively large standard sizes of optical fiber
cables lead to congestion and complication in the central office
which requires significant time, and therefore expense, for service
persons to establish, replace, change or maintain cross-connections
in the central offices. Further, the size of the optical fiber
cable has a multiplicative effect on the size of the components
that are used with the cable in the central office. Thus, if the
optical fiber cable is relatively large, so must be the connectors
which terminate and attach the optical fiber cable to other optical
fiber cables, the size of the racks that house the connector
receptacles, the troughs which house the optical fiber jumper
cables, and the size of the cabinets used to house the racks and
troughs. If the size of the optical fiber cables can be reduced,
the connectors, racks, troughs and cabinets can be proportionally
decreased in size.
[0006] Also noteworthy is that the cost of the optical fiber
cables, connectors and cabinets is proportional to the amount of
materials used in the manufacture thereof. Therefore, by decreasing
the size of the optical fiber cables, connectors and cables,
significant cost-savings can be obtained. Thus, there is a need to
reduce the size of optical fiber cables.
SUMMARY OF THE INVENTION
[0007] This invention overcomes the disadvantages noted above. In
accordance with this invention, a simplex optical fiber cable
includes a jacketed optical fiber at its core. The optical fiber is
surrounded and contacted with a buffer made of plastic material
such as nylon, polyesters or polyvinyl chloride (PVC). About the
outer circumference of the buffer, aramid yarn is disposed. A
sheath of plastic material such as PVC surrounds and contacts the
aramid yarn.
[0008] A duplex optical fiber cable in accordance with this
invention includes two optical fibers with respective buffers and
aramid yarn layers, which are positioned side-by-side in a sheath,
preferably of PVC, covering and contacting the aramid yarn of both
optical fibers and integrated together to form a continuous
connection between portions of the sheath covering respective
aramid yarn layers, buffers and optical fibers. In an alternative
embodiment, a duplex optical fiber cable in accordance with this
invention includes two simplex optical fiber cables as previously
described, positioned side-by-side and having an oversheath,
preferably of PVC, enclosing the two simplex optical fiber
cables.
[0009] In cross-section, the diameter of the simplex optical fiber
cable can range from 1.0 mm through 1.8 mm, but is preferably
formed in standard sizes of about 1.2 mm and 1.6 mm. The simplex
optical fiber cable of this invention is thus significantly smaller
in diameter than the optical fiber cables presently available.
Likewise, in cross-section, the duplex optical fiber cable of this
invention ranges from 2.76 mm through 4.25 mm in width and from
1.60 mm through 2.10 mm in height, but preferably is formed in
standard sizes of about 2.76 mm in width and 1.68 mm in height, or
about 4.20 mm in width and 1.60 mm in height. Thus, the duplex
optical fiber cable of this invention is much smaller in
cross-section compared to duplex optical fiber cables presently
available.
[0010] Thus, the simplex and duplex optical fiber cables of this
invention are miniaturized relative to prior art optical fiber
cables, and make possible the reduction of congestion, complication
and size and space requirements presently required in central
offices. These features of the simplex and duplex optical fiber
cables of this invention considerably reduce the costs of
establishing, operating and maintaining central offices.
[0011] In accordance with this invention, if the buffer surrounding
the optical fiber is relatively thin in either the simplex or
duplex cable configuration, a slick substance such as talc can be
applied to the outer surface of the buffer. This feature of this
invention allows for the buffer to slide in contact with its aramid
yarn layer so that the optical fiber will not be overbent when the
ferrule of a connector attached to an end of the optical fiber,
forces the optical fiber in an axial direction along the length of
the optical fiber cable as the connector is connected to a
connector receptacle. Thus, the simplex and duplex optical fiber
cables of this invention reduce damage or breakage of optical
fibers caused by overbending or fatigue when a connector is coupled
to a connector receptacle.
[0012] Also, in either the simplex or duplex cable configuration,
if the buffer is relatively thick, a slick substance such as
Modaflo.TM. can be applied to the outer surface of a coated optical
fiber so that the relatively thick buffer can more readily be
stripped from the optical fiber.
[0013] In addition, the duplex optical fiber cables of this
invention are advantageous in that the respective buffers of the
two optical fibers in each duplex optical fiber cable of this
invention are individually wrapped with aramid yarn as opposed to
wrapping aramid yarn around the buffers of both optical fibers as
done in one type of optical fiber cable presently available. By
individually wrapping the two optical fiber buffers in the duplex
optical fiber cable of this invention, the need for bifurcation
kits to connect the duplex optical fiber cable to single
connectors, is eliminated. Because bifurcation kits have parts
which force the diameter of the optical fiber cable to increase
greatly, the elimination of the need for bifurcation kits
effectively reduces the size of the duplex optical fiber cable of
this invention relative to presently available duplex optical fiber
cables. Also, bifurcation kits are relatively expensive, so the
elimination of the need to use bifurcation kits in the duplex
optical fiber cables of this invention provides significant
cost-savings relative to duplex optical fiber cables which require
bifurcation kits.
[0014] The invention further includes die assemblies and methods
for making the simplex and duplex optical fiber cables of this
invention. The die assemblies have several component parts which
can easily be replaced if damaged, thus saving the cost of having
to replace an entire die as required in the prior art. The die
assemblies further split flows of molten plastic material and have
surfaces which cause the split flows to converge to increase
uniformity of the sheath or oversheath of the simplex or duplex
optical fiber cable.
[0015] These together with other objects and advantages, which will
become subsequently apparent, reside in the details of construction
and operation as more fully hereinafter described and claimed,
reference being had to the accompanying drawings, forming a part
hereof, wherein like numerals refer to like parts throughout.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The present invention can be better understood with
reference to the following drawings. The drawings are not
necessarily to scale, emphasis instead being placed upon clearly
illustrating principles of the present invention.
[0017] FIG. 1 is a diagram of an optical fiber jumper cable in
accordance with this invention with connectors at the terminal ends
thereof, showing the operation of connecting the connectors to
connector receptacles coupled to respective optical fiber
cables;
[0018] FIG. 2 is a perspective cutaway view of a simplex optical
fiber cable in accordance with this invention;
[0019] FIG. 3 is a cross-sectional view of the simplex optical
fiber cable;
[0020] FIG. 4 is an exploded perspective view of a crosshead
assembly for making the simplex optical fiber cable;
[0021] FIG. 5 is a cross-sectional diagram of the crosshead
assembly for making the simplex optical fiber cables, shown in its
assembled configuration;
[0022] FIG. 6 is a cross-sectional view of a duplex optical fiber
cable in accordance with this invention;
[0023] FIG. 7 is an exploded perspective view of a crosshead
assembly for making the duplex optical fiber cable of FIG. 6; FIG.
8 is a cross-sectional view of the crosshead assembly of FIG. 7,
shown in its assembled configuration; and
[0024] FIG. 9 is a cross-sectional view of a second embodiment of
the duplex optical fiber cable in accordance with this
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] In FIG. 1, an optical fiber cable 1 has connectors 2
attached to the terminal ends thereof. The connectors 2 can be ST,
FC, or SC connectors, for example. The connectors 2 can be
connected by insertion into respective connector receptacles 3. The
connector receptacles 3 are connected to respective optical fiber
cables 1 for distribution to remote locations.
[0026] In a central office, connector receptacles 3 are typically
housed in racks (not shown) in cabinets (not shown). Also, the
central office houses the optical fiber cables 1 in troughs (not
shown) in and running between the cabinets. Because a relatively
large number of cross-connections are required in a central office
to establish connections to transmit optical signals from various
remote locations to others, a correspondingly large number of
connector receptacles 3 and optical fiber cables 1 are housed in
the central office. The optical fiber cable 1 of this invention is
relatively small in diameter compared to currently-used optical
fiber cables, so the use of the optical fiber cables 1 of this
invention greatly reduce confusion, congestion, and complication in
establishing, organizing, replacing or maintaining
cross-connections in the central office. In addition, the
relatively reduced size of the optical fiber cable 1 of this
invention allows for a reduction in the size of the connectors 2
and the connector receptacles 3, a feature which allows for the
reduction of cabinet sizes relative to currently-used cabinets. In
turn, the reduction of the size of the cabinets used in the central
office leads to a reduction in the amount of floor space required
for the cabinets. Because the amount of floor space in a central
office determines the expense of building, leasing, and/or
operating a central office, this reduction in the cabinet sizes
used in a central office leads to a significant cost savings for
the central office.
[0027] In FIG. 2, a simplex optical fiber cable 1 of this invention
is shown in a perspective cutaway view. The simplex optical fiber
cable 1 includes at its core an optical fiber 4. Preferably, the
optical fiber 4 is coated with a plastic material such as
ultraviolet (UV)-curable acrylate, to provide a degree of
protection for the optical fiber 4. Typically, the coated optical
fiber 4 has a diameter of 0.254 mm (0.010"). Surrounding the
optical fiber 4 and in contact with the outer surface thereof, a
buffer 5 is formed. The buffer 5 is preferably formed of a plastic
material such as nylon, although other types of plastic material
can be used to form the buffer 5. Nylon material is preferred for
the buffer 5, however, because it has a degree of stiffness which
is relatively high for plastic materials. Therefore, the buffer 5
composed of nylon can be formed with a diameter which is relatively
thin, and yet the nylon buffer 5 is not inhibited by its relatively
thin diameter from providing significant protection from
overbending of the optical fiber 4. Thus, the use of nylon to form
the buffer 5 allows for miniaturization of the size of the optical
fiber cable 1 relative to other optical fiber cables.
[0028] If the buffer 5 is relatively thick (900 mm in diameter, for
example), a coating of Modaflo.TM. (a mixture of Teflon.TM. and
acetone) is applied to the coated optical fiber 4 before forming
the buffer 5 thereon. Because the hoop stress of the buffer 5 upon
the optical fiber 4 is relatively high if the buffer 5 is
relatively thick, the use of the Modaflo.TM. coating helps to
reduce friction between the buffer 5 and the optical fiber 4 so
that the buffer 5 can readily be stripped off of the optical fiber
4. For example, the Modaflo.TM. coating helps to strip off the
relatively thick buffer 5 when attaching a connector to the simplex
optical fiber cable 1.
[0029] On the other hand, if the buffer 5 is relatively thin (e.g.,
500 microns in diameter) a relatively slick substance 6 is applied
about the outer surface of the buffer 5. The substance 6 can be
talc, for example. The substance 6 facilitates sliding of the
buffer 5 relative to a yarn layer so that the buffer 5, and,
therefore the optical fiber 4, will not be overbent when the buffer
5 is forced to slide relative to the yarn layer 7, for example,
when connecting a connector attached to the end of the optical
fiber cable 1 to a connector receptacle. The substance 6 is not
necessary if the buffer 5 is relatively thick, because in this case
the buffer 5 is sufficiently strong to prevent the optical fiber 4
from being overbent. About the outer surface of the buffer 5, the
yarn layer 7 is composed of strands either laid straight (i.e.,
parallel with the optical fiber 4) or helically wrapped.
Preferably, the yarn layer 7 includes yarn strands with aramid
strength fibers which have relatively high strength and resistance
to stress and strain. The yarn layer 7 prevents the optical fiber 4
from being damaged by overbending. Also, because the yarn layer 7
is composed of relatively strong aramid fibers, the yarn layer 7 is
subject to relatively little fatigue over time. In addition, the
yarn layer 7 provides significant protection for the buffer 5 and
the optical fiber 4 from impact or shock with an object, or from
inadvertent cutting or tearing of the optical fiber cable 1. About
the outside surface and in contact with the outer surface of the
yarn layer 7, a sheath 8 is formed. The sheath 8 is formed from a
plastic material such as polyvinyl chloride (PVC) (or more
generally, plenum, riser and non-halogen rated plastics). The
sheath 8 provides structural strength for the optical fiber cable 1
and is flexible to a degree, but also is sufficiently resilient to
prevent the optical fiber 4 from being damaged by overbending.
[0030] In diameter, the simplex optical fiber cable of FIG. 2
ranges from 1.0 mm to 1.8 mm in diameter, and thus is much smaller
than the standard sizes of 2.4 mm or 3 mm in diameter for optical
fiber cables that are typically available. More specifically, the
optical fiber 4 has a diameter of 250 microns (.+-.15 microns) in
diameter, the buffer 5 ranges from 0.1 mm to 0.31 mm in radial
thickness, the yarn layer 7 ranges from 0.22 mm to 0.52 mm in
radial thickness, and the sheath 8 ranges in thickness from 0.15 mm
to 0.25 mm. Preferably, the simplex optical fiber cable 1 of this
invention has standard sizes of about 1.2 mm and 1.6 mm in
diameter. For the first standard size of about 1.2 mm, the coated
optical fiber 4 is about 0.250 mm in diameter, the buffer 5 is
about 0.13 mm in radial thickness, the yarn layer 7 is about 0.22
mm in radial thickness, and the sheath 8 is about 0.18 mm in
diameter. For the second standard size of the simplex optical fiber
cable 1 of this invention, the coated optical fiber 4 is about 0.25
mm in radial thickness, the buffer 5 is about 0.32 mm in diameter,
the yarn layer 7 is about 0.22 mm in radial thickness, and the
sheath 8 is about 0.18 mm in radial thickness.
[0031] In FIG. 3, the simplex optical fiber cable 1 of FIG. 2 is
shown in cross-section. The elements of FIG. 3 were previously
described with respect to FIG. 2, but the cross-sectional view of
FIG. 3 is provided to give an understanding of the simplex optical
fiber cable 1 of this invention in three-dimensions.
[0032] Importantly, if the nylon buffer 5 is formed with a diameter
of about 500 microns, the inventors have found that the buffer 5
can be stripped with a force of 3 pounds or less, a feature which
greatly eases the operation of attaching a connector to the optical
fiber cable 1, for example. The inventors have determined that a
diameter of about 900 microns for the buffer 5 is too great to
strip the buffer 5 without applying an intermediate layer of a
substance such as Modaflo.TM., which allows the 900 micron nylon
buffer to be stripped from the optical fiber 4. In any case, the
maximum diameter of the nylon buffer 5 for which the buffer 5 can
be stripped with a force of 3 pounds or less lies between 900 and
500 microns.
[0033] In FIG. 4, a crosshead assembly 9 for making the simplex
optical fiber cable 1 of this invention is shown. The crosshead
assembly 9 includes a crosshead 10 which can be a standard type of
crosshead widely used in the plastics extrusion industry. The
crosshead 10 defines an open cavity 11 and an aperture 12 at a
first end of the crosshead 10 which communicates with the cavity
11. Opposite its first end, the crosshead defines a second, open
end formed by the opening of the cavity 11. At the second end of
the crosshead 10 about the cavity 11, are defined threads 13 (not
shown in FIG. 4, but shown in FIG. 5). The crosshead 10 also
defines on its side surface an aperture 14 to receive an alignment
pin (not shown) to achieve proper orientation of the parts of the
crosshead assembly 9. The crosshead 10 further defines an aperture
15 on its side surface, to allow insertion of a temperature probe
(not shown) for monitoring the temperature of extruded plastic
material. The crosshead 10 also includes a flat surface 16 which
can be engaged with a support (not shown) with screws (not shown)
threaded through respective apertures 17 defined in flanges 18 of
the crosshead 10.
[0034] The aperture 12 is circular in cross-section and sized to
receive and hold, when inserted into the second open end and
through the cavity 11 defined in the crosshead 10, the cylindrical
surface 19 situated at a first end of a die holder 20. On a second
end opposite its first end, the die holder 20 also has a
cylindrical surface 21 with a diameter larger than that of the
cylindrical surface 19 and thus defining a ledge 22 which, when
inserted into the crosshead 10, engages with an inner surface of
the first end of the crosshead 10 in proximity to the aperture 12
to fix the die holder 20 in position against the inside surface of
the first end of the crosshead 10. The die holder 20 also defines
at its center an aperture 23 extending along an axial length of the
die holder 20 so that the die holder 20 is effectively ring- or
disc-like in shape. The aperture 23 is defined in the die holder 20
so that the die holder 20 has two cylindrical surfaces 24, 25 (only
surface 24 is visible in FIG. 4, but FIG. 5 shows both surfaces 24
and 25). The cylindrical surface 25 has a greater diameter than the
cylindrical surface 24, thus defining a step 26 (not shown in FIG.
4, but shown in FIG. 5) therebetween. About an outer periphery on
the second side of the die holder 20, a recessed portion 27 is
defined adjacent the cylindrical surface 21. The purpose of the
recessed portion 27 will be described later in this document. In
addition, the die holder 20 has a recess 28 for receiving an
alignment pin (not shown) inserted through the aperture 14 of the
crosshead 10, to orient and lock the die holder 20 in the crosshead
10.
[0035] The crosshead assembly 9 also includes a die 29. The die 29
defines an aperture 30 centered in and extending along the axial
length of the die 29. The aperture 30 is defined in the die 29 such
that it has a cylindrical surface 31 (not shown in FIG. 4, but
shown in FIG. 5) in proximity to a first end of the die 29, and
such that it has a funnel-like portion 32 (not shown in FIG. 4 but
shown in FIG. 5) in proximity to a second end of the die 29. The
funnel-like portion 32 is defined so that it narrows from the
second end toward the first end of the die 29 along an axial length
thereof until meeting with the cylindrical surface 31. The
cylindrical surface 31 of the die 29 shapes the molten plastic
material to form the outside surface of the sheath 8 of the simplex
optical fiber cable 1 of this invention, as will be explained later
in this document. The die 29 includes outer cylindrical surfaces
33, 34. When the die holder 20 is assembled with the die 29, the
surface 33 is inserted into the aperture 23 defined by the die
holder 20. The cylindrical surface 34 has a larger diameter than
that of the cylindrical surface 33, and thus defines a ledge 35
which engages with a second end of the die holder 20 when the die
holder 20 is assembled together with the die 29. Also, when the die
29 is inserted into the die holder 20, the second ends of the die
holder 20 and the die 29 are flush and define a substantially
enclose passages 37, 38 and annular recess 39 defined on the first
end face of the core tube 36. To hold the core tube 36 in position
relative to the die holder 20, the core tube 36 has a rim 40
disposed about an outer circumference of the core tube 36, which
engages with the recessed portion 27 defined about the outer
circumference of, and on the second end of, the die holder 20. The
first end of the core tube 36 defines a notch 41 which receives
molten plastic material such as nylon or PVC for the extrusion of
the sheath 8 of the simplex optical fiber cable 1. When enclosed by
the flat surfaces of the second ends of the die 29 and the die
holder 20, the notch 41 together with a portion of the cylindrical
surface 21 of the die holder 20 define an aperture to receive the
molten plastic material. The passages 37, 38 are U-shaped in
cross-section and together with the respective flat surfaces of the
second ends of the die holder 20 and the die 29, define channels
through which the molten plastic material flows. The passages 37,
38 split the molten plastic material flow from the notch 41 and
channel the split flows of molten plastic material to opposite
sides of a circular aperture 42 defined at a center axis of the
core tube 36. The passages 38 further split the flow from
respective passages 38 and direct the flow of plastic material to
the annular recess 39 at four spaced locations provided at 90
degree angular intervals about the edge of the circular aperture
42. The core tube 36 also has a rim 43 which extends from the
second end of the core tube 36. Defined symmetrically in the rims
40, 43 are opposing notches 44, 45 (not all of which are shown).
The notches 44, 45 allow insertion of the tip of a screwdriver, for
example, to disassemble the die holder 20 and the entry die 55 from
the core tube 36.
[0036] A core tube insert 46 has a tip 47 with an aperture 48
formed therein. The aperture 48 is defined by the core tube insert
46 such that it extends along the axial length of the core tube
insert 46. At a first end of the core tube insert 46, the aperture
48 has a cylindrical portion 49 (not shown in FIG. 4, but shown in
FIG. 5). At a second end of the core tube insert 46, the aperture
48 has a funnel-like portion 50 (not shown in FIG. 4, but shown in
FIG. 5) which converges in a direction from the first end to the
second end of the core tube insert 46 until meeting with an end of
the cylindrical portion 49 inside of the core tube insert 46.
Adjacent the tip 47, the core tube insert 46 has an outer conical
portion 51 about which molten plastic material is extruded by the
passages 37, 38 and the annular recess 39 of the core tube 36.
Also, the core tube insert 46 includes outer cylindrical surfaces
52, 53. The cylindrical surface 52 adjacent an end of conical
portion 51, has a diameter smaller than that of the cylindrical
surface 53 and thus defines a ledge 54 between the cylindrical
surfaces 52, 53. When the core tube insert 46 is assembled with
core tube 36, the ledge 54 engages with the second side of the core
tube 36, to hold the core tube insert 46 in position and prevent
the core tube insert 46 from moving in a direction toward the right
in FIG. 4. Also, the cylindrical surface 52 is sized to fit snugly
in the aperture 42 defined in the core tube 36 to hold the core
tube insert 46 firmly in position therein. When the core tube
insert 46 is assembled together with the core tube 36 and the die
29, the conical portion 51 extends through the aperture 42 and the
tip 47 extends into the aperture 30 at the second side of the die
29.
[0037] An entry die 55 defines a funnel-like aperture 56. The
funnel-like aperture 56 converges or tapers from the second end of
the entry die 55 to its first end, and so is relatively open at the
second end of the entry die 55, and relatively closed at the first
end of the entry die 55. The entry die 55 also has a recess 57
formed about the periphery of the entry die 55 on its first end,
which receives the rim 43 of the core tube 36 to aid in holding the
core tube 36, the- core tube insert 46 and the entry die 55
together when assembled. A crosshead nut 58 has at its first end
threads 59 and at its second end hexagonal surfaces 60. The threads
59 mate with corresponding threads 13 of the crosshead 10. When
threaded to the crosshead 10, the crosshead nut 58 holds the die
holder 20, the die 29, the core tube 36, the core tube insert 46,
and the entry die 55 in assembly inside of the cavity 11 of the
crosshead 10. The hexagonal surfaces 60 allow a wrench (not shown)
or the like to be used to screw the threads 59 of the crosshead nut
58 onto corresponding threads 13 of the crosshead 10. The crosshead
nut 58 defines an aperture 61 extending along the axial length
thereof. When assembled with the entry die 55, the aperture 61
communicates with the aperture 56 defined in the entry die 55.
[0038] The cross head 10, die holder 20, die 29, core tube 36, core
tube insert 46, the core guide 55 and the cross head nut 58 can all
be made of metal material such as stainless steel or tool
steel.
[0039] In FIG. 5, the crosshead assembly 9 for making the simplex
optical fiber cable 1 in accordance with this invention, is shown
in cross-section. The crosshead assembly 9 is assembled by
inserting the first side of the die 29 into the second side of the
die holder 20. When so inserted, the outer cylindrical surface 33
of the die 29 meets with the inner cylindrical surface 24 of the
die holder 20, the ledge 35 abuts step 26 and the outer cylindrical
surface 34 contacts the inner cylindrical surface 25. The step 26
and the ledge 35 fix the die 29 in position and prevent the die 29
from moving toward the right in FIG. 5. The core tube 36 is joined
with the die holder 20 so that the rim 40 meets with recessed
portion 27, thus holding the die 29 between the die holder 20 and
the core tube 36. The core tube insert 46 is inserted into the
second side of the core tube 36, so that tip 47 of the core tube
insert 46 is inserted through the core tube 36 and into the die 29
so that the tip 47 is situated at the first side of the die 29 in
the aperture 30. When so inserted, the conical portion 51 of the
core tube 46 opposes the funnel-like portion 32 and the cylindrical
surfaces 52, 53 and ledge 54 meet with respective surfaces defining
the aperture 42 in the core tube 36. The entry die 55 is joined
with the core tube 36 so that its recess 57 meets with the rim 43.
The assembled die holder 20, die 29, core tube 36, core tube insert
46 and entry die 55 are inserted into the cavity 11 of the
crosshead die 10 until the ledge 22 meets with an annular step 62
defined in the crosshead 10. The assembled die holder 20, die 29,
core tube 36, core tube insert 46 and entry die 55, are held in
position in the crosshead 10 by screwing the threads 59 of the
crosshead nut 58 into the threads 13 of the crosshead 10.
[0040] To make the optical fiber cable 1 of FIGS. 2 and 3, the
optical fiber 4 is manufactured and preferably coated using
well-known techniques. If the buffer 5 is to be relatively thick
(900 microns in diameter, for example), a coating of a
friction-reducing substance such as Modaflo.TM. is applied to the
optical fiber 4, for example, by drawing the optical fiber 4
through a container holding such substance. The buffer 5 is then
extruded onto the optical fiber 4 using well-known techniques. If
the buffer 5 is relatively thin (500 microns in diameter, for
example), the coating of the substance such as Modaflo.TM. can be
omitted. On the other hand, if the buffer 5 is relatively thick
(i.e., 900 microns in diameter) the slick substance 6 is applied to
the buffer 5 after extrusion of the buffer 5, either by spraying or
dusting the slick substance 6 on the buffer 5, or by running the
optical fiber 4 through a container holding the slick substance 6.
The straight-laying or helical wrapping of the yarn layer 7 on the
buffer 5 can be performed by an organizer (not shown) situated to
the left in FIG. 5 relative to the crosshead assembly 9. Such
organizers are well-known in the optical fiber cable industry. The
organizer can be a circular ring with holes formed therein to
receive strands of the yarn 7. If the strands of yarn are to be
laid straight (i.e., parallel with the optical fiber 4), the
strands of yarn are advanced through the organizer's holes and
guided into contact with the buffer 5 advanced by a motor through
the center of the organizer. Alternatively, if the yarn strands are
to be helically wrapped onto the buffer 5, the organizer ring is
rotated by a motor (not shown) which causes the strands of yarn 7
to be helically wrapped about the buffer 5 as it is drawn through
the center aperture of the circular ring. The optical fiber 4 with
buffer 5 and aramid yarn layer 7, are inserted from the left side
of FIG. 5 into apertures 61, 56, 48 and through apertures 23 and 12
of the crosshead assembly 9 of FIGS. 4 and 5. The apertures 56 and
48 define a funnel shape which tends to guide and ease insertion of
the end of the optical fiber 4, the buffer 5 with applied substance
6, and wrapped aramid yarn 7, through the crosshead assembly 9.
Thus, the funnel shape of the apertures 56, 48 greatly eases the
preparation of the crosshead assembly 9 for extrusion of the sheath
8 relative to previously-used crosshead dies.
[0041] The coated optical fiber 4, buffer 5 (with applied substance
6, if used), and yarn layer 7 are drawn through the apertures 61,
56, 48, 23 and 12 with a motor (not shown). Molten plastic material
is forced into the crosshead assembly 9 and through the notch 41
into passages 37, 38 which split the flow of molten plastic
material from the notch 41 into split flows supplied at separated
locations about the circumference of the annular recess 39 of the
core tube 36. The annular recess 39 evenly distributes the molten
plastic material about the annular surface 39 of the core tube
insert 46. The molten plastic material flows in a passage defined
by the outer surface of the conical portion 51 of the core tube
insert 46 and the inner surface of the aperture 30 defined in the
die 29. Advantageously, the channel defined between the outer
surface of the conical portions 51 of the core tube insert 36 and
the inner surface of the funnel-like portion 32 of the die 29 cause
the flow of molten material to converge toward the tip 47 of core
tube insert 46, a feature which ensures that the flow of molten
plastic material is uniformly distributed and continuous about the
circumference of the tip 47. The molten plastic material flows over
the outer surface of the tip 47 and the inner surface of the
cylindrical surface 31 defining the aperture 30 at the first side
of the die 29, forming a sheath 8, ring-like in cross-section,
about the optical fiber 4, the buffer 5, (with the applied
substance 6, if used), and the yarn layer 7 as they are drawn
through the crosshead assembly 9. When cooled sufficiently, the
sheath 8 constricts to a degree on the yarn layer 7 to form the
simplex optical fiber cable 1 of this invention.
[0042] The molten plastic material is extruded at a temperature of
about 360.degree. F. and cooled by immersion in
40.degree.-60.degree. F. water.
[0043] Importantly, should the die 20, the core tube 36 and/or the
core tube insert 46 become clogged with plastic material, they can
be readily replaced individually without the expense of replacing
the entire crosshead assembly 9, a feature which provides
significant cost-savings relative to previously-used dies.
[0044] FIG. 6 is a cross-sectional diagram of a first embodiment of
a duplex optical fiber cable 1 in accordance with this invention.
Essentially, the first embodiment of the duplex optical fiber cable
1 includes two simplex optical fiber cables 1 (as shown in FIGS. 2
and 3), but with the respective sheaths 8 of the two simplex
optical fiber cables 1 being formed such that they have a
continuous connection between the two simplex optical fiber cables
1. The first embodiment of the duplex optical fiber cable 1 is
called a zip-cord configuration and can be pulled apart at the
middle connecting portion of the sheath 8 to allow separation
between the two duplex optical fiber cables 1 so that respective
connectors can be attached to respective ends of each optical fiber
4. This separation of the ends of the optical fiber cable 1 into
two simplex optical fiber cables 1 allows the connector to be
connected to spaced connector receptacles. After splitting the end
of the duplex optical fiber cable 1 at the middle portion along a
length sufficient to connect the optical fibers 4 to respective
spaced connector receptacles 3, the duplex optical fiber 1 can be
taped with an adhesive tape about its circumference so that the
zip-cord duplex optical fiber cable 1 will not further split at its
middle portion. This feature of the invention eliminates the need
for bifurcation kits required to split the terminal end of
previously-used miniature duplex optical fiber cables for the
attachment of connectors thereto. Because a bifurcation kit has
components which greatly increase the diameter of a duplex optical
fiber cable to which the bifurcation kit is attached, the duplex
optical fiber cable 1 of this invention is substantially reduced in
size compared to previously-used optical fiber cables, a feature
which leads to reduced congestion in the racks and troughs of
central office cabinets.
[0045] In cross-section, the zip-cord duplex optical fiber cable 1
of this invention can range in size from 2.20 mm through 4.25 mm in
width and from 1.25 mm through 2.00 mm in height (with an optical
fiber of 0.254 mm in diameter, an optical fiber buffer of 0.1-0.34
mm in radial thickness, a yarn layer of 0.22-0.52 mm in radial
thickness and a sheath of 0.15-0.25 mm in radial thickness) but
preferably formed in standard sizes of about 2.7 mm in width and
1.68 mm in height, or about 3.55 mm in width and 1.60 mm in height.
For the first standard size, the optical fiber is 0.254 mm in
diameter, the buffer is 0.13 mm in radial thickness, the yarn layer
is 0.22 mm in radial thickness and the sheath is 0.18 mm in radial
thickness, and for the second standard size the optical fiber is
0.254 mm in diameter, the buffer is 0.32 mm in radial thickness,
the yarn layer is 0.22 mm in radial thickness and the sheath is
0.18 mm in radial thickness. Thus, the zip-cord duplex optical
fiber cable 1 of this invention is much smaller in cross-section
compared to duplex optical fiber cables presently available.
[0046] FIG. 7 is an exploded perspective view of a crosshead
assembly 9 for making the zip-cord duplex optical fiber cable 1 of
this invention. The crosshead 10 has similar components of those
explained previously with respect to FIG. 4, so an explanation of
these elements will be omitted here. The crosshead assembly 9 of
FIG. 7 also includes a die 65 defining a figure-eight-shaped
aperture 66 at a first end of the die 65. The aperture 66 has a
shape conforming to two tubes placed side-by-side such that the
tubes intersect and have an open space at the intersecting portion
thereof. The die 65 also defines outer cylindrical surfaces 67, 68.
The cylindrical surface 67 has a diameter less than that of the
cylindrical surface 68 so that the cylindrical surfaces 67, 68
define a ledge 69 therebetween. When inserted into the cavity 11 of
the crosshead die 10 of FIG. 7, the ledge 69 meets with the face of
annular step 62 (not shown in FIG. 7, but shown in FIG. 8) and thus
prevents the die 65 from moving toward the right in FIG. 7. The die
65 also has a rim 70 extending from a second end of the die 65 from
the outer periphery of the cylindrical surface 68. The die 65 also
defines slots 71, 72. The slot 71 receives an alignment pin
inserted through the aperture 14 of the crosshead 10, to align and
lock the position of the die 65 in the crosshead 10. The slot 72
allows for the tip of the screwdriver or the like to be inserted
into the slot 72 to separate the die 65 from other parts of the
crosshead assembly 9. Centered at its second side and extending
along the axial length thereof the die 65 defines a conical surface
73 (not shown in FIG. 7, but shown in FIG. 8) which converges from
the second side to the first side of the die 65. The conical
surface 73 defines an aperture 74 which communicates with the
figure-eight-shaped aperture 66.
[0047] The crosshead assembly 9 of FIG. 7 also includes a core tube
75 defining a notch 76 at one side thereof. The notch 76 receives
molten plastic material from the aperture 64 of the crosshead 10,
to extrude the sheath 8 of the zip-cord duplex optical fiber cable
1 of this invention. On its first end face, the core tube 75
defines passages 77 which split the flow of molten plastic material
from notch 76 and guide the split flows of molten plastic material
to opposite sides of a conical portion 78 disposed on the first end
of the core tube 75 and extending along the axial length thereof.
The conical portion 78 has recessed surfaces 79 which guide
respective split flows along the conical portion 78. Through the
center of the conical portion 78, an aperture 81 is defined which
runs from the tip end of the conical portion 78 along the axial
length of the core tube 75. The aperture 81 is defined at the first
end of the core tube 75, by a surface 82 (not shown in FIG. 7, but
shown in FIG. 8) which in cross-section has two parallel, opposing
sides with respective opposing semicircular ends meeting with
respective ends of the opposing sides. Communicating with the
aperture 81 defined at the first end of the core tube 75, a conical
surface 83 (not shown in FIG. 7, but shown in FIG. 8) is defined in
proximity to the second end of the core tube 75. Between the
adjoining ends of the surface 82 and the conical surface 83, a step
84 (not shown in FIG. 7, but shown in FIG. 8) is defined in the
core tube 75. The core tube 75 has a rim 85 extending from the
second end thereof from the outer periphery of cylindrical side
surface 86 of the core tube 75. The core tube 75 also includes
opposing notches 87 to allow the crosshead assembly 9 to be
disassembled using the tip of a screwdriver, for example.
[0048] The crosshead assembly 9 for making the zip-cord duplex
optical fiber cable 1 of this invention also includes a core tube
insert 88 including a conical portion 89 with an extension 90
protruding from and formed integrally therewith. In cross-section,
the extension 90 has outer surfaces with two opposing, parallel
sides and respective semicircular surfaces at the respective ends
of the opposing, parallel sides. Extending from the extension 90,
two parallel tubes 91 are disposed. The tubes 91 extend along the
axial length of the core tube insert 88 from its first end to a
location in near proximity to the second end of the core tube
insert 88. The tubes 91 have inner surfaces defining respective
apertures 92. In proximity to the second end of the core tube
insert 88, the core tube insert 88 defines conical surfaces 93
communicating with the apertures 92 defined by the tubes 91. The
conical surfaces 93 are relatively open at the second end of the
core tube insert 88, but converge in a direction toward the first
end of the core tube insert 88 until meeting with respective ends
of the tubes 91.
[0049] The crosshead assembly 9 of FIG. 7 also includes a core
guide 94 which is substantially cylindrical in shape and includes a
conical surface 95 protruding at the center of its first end. The
conical surface 95 has a flat end surface 96 defining a
figure-eight-shaped aperture 97 having a shape conforming to two
tubes with a spaced portion at the intersection of the two tubes.
The figure-eight-shaped aperture 97 extends along the axial length
of the core guide 94 and tapers inward from a second end to the
first end of the core guide 94 (as shown in FIG. 8). The core guide
94 also has a recessed portion 98 about its outer periphery at the
first end thereof. The crosshead assembly 9 of FIG. 7 also includes
a crosshead nut 99 having threads 100 defined at its first end, and
having hexagonal surfaces 101 defined at its second end. The
threads 100 can be threaded onto corresponding threads 13 defined
at the second end of the crosshead 10 by rotating the crosshead nut
99 relative to the crosshead 10. The hexagonal surfaces 101 allow a
wrench or the like to be fitted thereto for use in screwing the
crosshead nut 99 into the mating threads 13 of the crosshead 10.
The crosshead nut 99 also defines an aperture 102 extending along
the axial length thereof.
[0050] The cross head 19, die 65, core tube 75, core tube insert
88, core guide 94 and cross head nut 99, can all be made of metal
material such as stainless steel or tool steel.
[0051] FIG. 8 is a cross-sectional view of the crosshead assembly 9
in its assembled state. The crosshead assembly 9 is assembled by
joining the first end of the core tube 75 with the second end of
the die 65 so that the conical portion 78 of the core tube 75 is
inserted into and opposes the conical surface 73 of the die 65, and
so that the flat surface of the first end of the core tube 75
contacts the flat surface of the second end of the core die 65 to
enclose the passages 78 and a side of the notch 76. As so fitted
together, the rim 70 of the die 65 engages with the recessed
portion 80 of the core tube 75 to hold the die 65 and the core tube
75 together.
[0052] The first end of the core tube insert 88 is inserted through
the second end of the core tube 75 in the aperture 81, and into the
figure-eight-shaped aperture 66 of the die 65. As so inserted, the
end of the conical portion 89 abuts the step 84 of the core tube
75, the conical portion 89 of the core tube insert 88 contacts the
conical surface 83 inside of the core tube 75, and the surface of
the extension 90 contacts the surface 82 of the core tube 75. Also,
as so inserted, the tubes 91 extend into the figure-eight-shaped
aperture 66 of the die 65 so that the outer surfaces of the tubes
91 oppose respective circular surfaces defining the
figure-eight-shaped aperture 66.
[0053] The first end of the core guide 94 is joined with the second
end of the core tube 75 so that the conical portion 95 is inserted
into the aperture 81 of the core tube 75 and meets with the conical
surface 83 thereof. The flat surface 96 of the core tube insert 88
thus abuts the second end of the core tube insert 88 to hold the
core tube insert 88 inside of the core tube 75 and the die 65. The
aperture 97 of the core guide 94 thus communicates with the
apertures 92 of the core tube insert 88 at the second end thereof.
Also, the recessed portion 98 receives the rim 85 of the core tube
75 to hold the core guide 94 and the core tube 75 together.
[0054] The assembled die 65, core tube 75, core tube insert 88 and
core guide 94 are then inserted, with die 65 being inserted first,
into the cavity 11 defined in the crosshead 10 until the ledge 69
of the die 65 abuts the step 62 of the crosshead 10. The threads
100 of the crosshead nut 99 are then threaded to mating threads 13
of the crosshead 10, to hold the die 65, the core tube 75, the core
tube insert 88 and the core guide 94 in position inside of the
crosshead 10.
[0055] In preparation for making the zip-cord duplex optical fiber
cable 1 of this invention, the buffer 5 is extruded on the optical
fiber 4, which is preferably coated, using well-known techniques,
to make a buffered optical fiber. If the buffer 5 is to be
relatively thick (e.g., 900 mm in diameter), a substance such as
Modaflo.TM. is applied to the optical fiber 4 to aid in stripping
the buffer 5 when attaching a connector(s) for example, to the
zip-cord duplex optical fiber 1. The application of the substance
such as Modaflo.TM. can be applied to the outer surface of the
optical fiber 4 by drawing the optical fiber 4 through a container
holding such substance. On the other hand, if the buffer 5 is
relatively thin (e.g., 500 microns in diameter), the slick
substance 6 (such as talc) is applied to the outer surface of the
buffer 5 to allow it to slip relative to the yarn layer 7 to avoid
breakage of the optical fiber 4 which could occur, for example, if
the buffer 5 is unable to slip relative the yarn layer 7 during
connection of a connector(s) attached to the duplex optical fiber
cable 1, to a connector receptacle(s). The slick substance 6 can be
applied by spraying or dusting the optical fiber 6 with the
substance 6 as the optical fiber 4 and its buffer 5 are advanced in
a linear direction. Alternatively, the optical fiber 4 and the
buffer 5 can be advanced through a container containing the slick
substance 6 for the application of the substance 6 to the outer
surface of the buffer 5.
[0056] The optical fiber 4 with the buffer 5 are then advanced
through the center of an organizer (not shown) which can have a
shape conforming to a ring. The ring has apertures radially
arranged about the circumference thereof, which receive respective
strands to form the aramid yarn layer 7. The yarn strands can be
laid straight (i.e., parallel to the optical fiber 4) by advancing
the strands through respective holes in the organizer and guiding
the strands into contact with the buffer 5 to form the yarn layer
7. Alternatively, the aramid yarn strands can be helically wrapped
about the buffer 5 to form the yarn layer 7. As the optical fiber 4
with its buffer 5 are advanced through the center of the organizer,
a motor (not shown) drives the organizer to rotate and thus
helically wrap the yarn strands onto the outer surface of the
buffer 5, to form the yarn layer 7. The yarn strands can be
supplied from respective spools which unwind yarn strands as the
optical fiber 4 and its buffer 5 are advanced through the center of
the organizer. The above procedure is repeated for a second optical
fiber to be used in the pair of optical fibers 4 of the zip-cord
duplex optical fiber cable 1.
[0057] The above procedures result in two separate optical fibers 4
with respective buffers 5 and yarn layers 7.
[0058] The ends of the optical fibers 4 with respective buffers 5
and yarn layers 7 are inserted into the aperture 102 of the
crosshead nut 99 and also inserted into respective sides of the
figure-eight-shaped aperture 97. Importantly, as best seen in FIG.
8, the apertures 97 are tapered or funnel-like in shape and as such
allow for easy insertion of the ends of the optical fibers 4,
buffers 5 and yarn layers 7 therein. Upon further insertion, the
ends of the optical fibers 4, buffers 5 and yarn layers 7, are
inserted into respective apertures 92 and through the ends of the
tubes 91 of the core tube insert 88 and further through the
aperture 12 of the crosshead 10. At the left of the crosshead
assembly 9 in FIG. 8, the ends of the optical fibers 4, buffers 5
and yarn layers 7, are coupled to a motor (not shown) which draws
them through the crosshead assembly 9.
[0059] As the optical fibers 4, respective buffers 5 and yarn
layers 7, are drawn through the crosshead assembly 9 with the
motor, molten plastic material such as nylon or PVC, is forced
through the aperture 64 of the crosshead 10 and into the core tube
75 through the notch 76. The flow of molten plastic material is
split by passages 77 and uniformly distributed about the outside of
the conical portion 78 of the core tube insert 75 via recessed
surfaces 79 and the inner surfaces of conical surface 73 of the die
65. The opposing conical surfaces 78, 73 of the core tube 75 and
the die 65, respectively, cause the split flows of molten material
to converge as they flow toward the tip of the conical portion 78,
a feature of this invention which enhances the density, and
therefore uniformity, of the extruded sheath 8. The flow of molten
plastic material passes over the surfaces of the extension 90 and
tubes 91 and are shaped by the surfaces of the die 65 defining the
outer surface of the sheath 8. As the sheath 8 cools after
extrusion from the crosshead assembly 9 of FIG. 8, the sheath 8
constricts to a degree and contacts the yarn layers 7 to form a
zip-cord duplex optical fiber cable 1 as shown in FIG. 6.
Preferably, the molten plastic material forming the sheath 8 is PVC
extruded at a temperature of 180.degree. C. and cooled by immersion
in 40.degree. C.-60.degree. C. water.
[0060] FIG. 9 is a cross-section of a second embodiment of a duplex
optical fiber cable 1 of this invention. Essentially, the second
embodiment of the duplex optical fiber cable 1 includes two simplex
optical fiber cables 1 as shown in FIG. 3 which are positioned
side-by-side in a substantially parallel relationship. Extruded to
substantially surround and contact the two simplex optical fiber
cables 1, an oversheath 103 is formed. The oversheath 103 includes
opposing, on the substantially parallel sides 104 with ends joined
by respective semi-circular sides 105 which are rounded to conform
to respective outer surfaces of the sheath 8 of respective simplex
optical fiber cables 1.
[0061] To attach connectors to respective ends of the two simplex
optical fibers 1 contained in the oversheath 103, the oversheath
103 can be stripped from an end of the duplex optical fiber cable 1
to free the ends of the two simplex optical fiber cables 1.
Connectors can then be attached to the ends of each simplex optical
fiber cable 1.
[0062] Preferably, the duplex optical fiber cable 1 of FIG. 9 is in
cross-section about 1.6 mm to 2.1 mm in height and 2.76 mm to 4.2
mm in width, but preferably is in two standard sizes, one being
1.68 mm in height and 2.76 mm in width and the other being 1.6 mm
in height and 4.2 mm in width. In the first standard size, the
optical fibers 4 are about 0.250 mm in diameter, the buffers 5 are
about 0.13 mm in radial thickness, the yarn layers are about 0.22
mm in radial thickness and the sheaths 8 are about 0.18 mm in
radial thickness. In the second standard size, the optical fibers 4
are about 0.25 mm in diameter, the buffers 5 are about 0.32 mm in
radial thickness, the yarn layers are about 0.22 mm in radial
thickness and the sheaths 8 are about 0.18 mm in radial
thickness.
[0063] The die 9 used to make the second embodiment of the duplex
optical fiber cable 1 of this invention is substantially similar to
that shown in FIG. 7, except that the die 65 has an aperture 66
conforming in shape to the outer surface of the oversheath 103
shown in FIG. 9 rather than the figure-eight-shaped configuration
of FIG. 7, and the apertures 92 of the tubes 91 of the core tube
insert 88 are sized to receive respective simplex optical fiber
cables.
[0064] Advantageously, due to the application of the slick
substance 6, the simplex and duplex optical fiber cables 1 of this
invention allow the buffer 5 to slip relative to the yarn layer 7
when the ferrule of a connector at the terminal end of the optical
fiber cable 1 is connected to a connector receptacle. This feature
of this invention prevents fatigue or damage of the optical
fiber(s) 4 in the optical fiber cable 1 due to overbending which
would otherwise occur with relatively thin buffers 5 (e.g., 500
microns in diameter) in the absence of the slick substance 6. On
the other hand, if the buffer 5 is relatively thick (e.g., 900
microns in diameter), a slippery substance such as Modaflo.TM. is
applied to the outside of the optical fiber(s) 4 so that the
greater hoop stress of the relatively thick buffer 5 will not
impede the stripping of the buffers 5 to attach connectors, for
example. In addition, the crosshead assembly 9 used to manufacture
the simplex and duplex optical fiber cables 1 of this invention
extrude a relatively uniform sheath 8 or oversheath 103 which
provides increased protection for the optical fiber(s) 4 relative
to the nonuniform extrusions of sheath material of previously used
optical fiber cables. This advantage is derived from distributing
the molten plastic material in split flows using passages 37, 38 of
the core tube 36 of FIG. 4 or passages 77 of the core tube 75 of
FIG. 7 to extrude molten plastic material uniformly at various
points around the outer surfaces of the yarn(s) 7 of the simplex or
duplex optical fiber cables 1 of this invention. In addition, the
conical portion 51 and the funnel-like portion 32 (FIG. 4) or the
conical portion 78 and the conical surface 73 (FIG. 7) cause the
split flows of plastic material to converge, thus increasing the
uniformity of the extruded plastic sheath 8 or the oversheath 103.
Moreover, the crosshead assemblies 9 of this invention have
funnel-shaped apertures 56, 48 (see FIG. 5) or 97, 92 (see FIG. 8)
when assembled which allows the ends of the optical fiber(s) 4, the
buffer(s) 5 and yarn layer(s) 7, to be threaded relatively easily
into the crosshead assembly 9 in preparation for extruding the
sheath 8 or the oversheath 103. In addition, the die 29, the core
tube 36 and the core tube insert 46 of FIG. 4 and the die 65, core
tube 75 and the core tube insert 88 of FIG. 7 are relatively easy
to replace if they become fouled with extruded plastic, for
example, relative to previous crosshead dies which required the
replacement of the entire crosshead die rather than an individual
component such as the dies 29, 65, the core tubes 36, 75 or the
core tube inserts 46, 88 of this invention. In the first and second
embodiments of the duplex optical fiber cable 1 of this invention
shown in FIGS. 6 and 9, each optical fiber 4 and its buffer 5 are
individually wrapped with the yarn layer 7 as opposed to wrapping
yarn about side-by-side buffered optical fibers, as done in a
previous optical fiber cable. This feature of the invention
eliminates the need for bifurcation kits for connecting the end of
a duplex optical fiber cable to a pair of connectors, which require
components that greatly increase the diameter of a duplex optical
fiber cable using a bifurcation kit. The increased size of the
optical fiber cable using a bifurcation kit greatly increases the
complication and congestion in racks or troughs of cabinets, a
problem which is overcome by this invention.
[0065] Although the invention has been described with specific
illustrations and embodiments, it will be clear to those of
ordinary skill in the art that various modifications can be made
therein without departing from the scope and spirit of the
invention as outlined in the following claims. For example, the
buffer 5, the sheath 8, and the oversheath 103 can be made of other
materials than nylon or PVC as disclosed herein, such as halogen or
non-halogen or plenum-rated plastic materials. Also, although the
yarn 7 is preferably made of aramid fibers, other types of strength
yarns can be used without departing from the scope of this
invention. Moreover, the crosshead dies 9 of FIGS. 4 and 7 are
shown by way of illustration of the principles of this invention
only, and various modifications such as forming one or more parts
of the crosshead assembly 9 together or even forming the dies and
passageways of the core tubes or core tube inserts differently, can
be done without departing from the scope of this invention, the
important feature with respect to designing the crosshead assembly
9 being that the molten material is distributed at more than one
point leading into the die forming the outside of the sheath 8 or
the oversheath 103, and that the flow of molten material converges
to increase the uniformity of the sheath 8 or the oversheath 103.
All these modifications are intended to be included within the
scope of the invention as outlined in the following claims.
* * * * *