Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This application is a divisional of our copending
Canadian Patent Application 308,103 filed July 25, 1978. The
present invention relates to optical fiber cable constructions
and to methods and apparatus for fabricating same.
2. Description of the Prior Art
. . .
Conventional optical fiber cables typically utilize the
construction shown in cross-section in Fig. 1. As shown in Fig.
1, a plurality of fiber units 2, each consisting of a plurality
of optical fibers 1, are ~athered and stranded around a core
member 3. Core member 3 is usually fabricated from a material
that exhi,bits a high tensile strength. An outer roll or sheath
4 made of plastic material or the like is typically formed over
the outer surfaces of fiber units 2 so as to form an outer
covering. It should be noted that this. construction inherently
- subjects the optical fibers 1 to s,ubs~tantial lateral or com-
pression forces..
The construction o~ Fig. 1 exhibits a low ratio of
~ opti,cal fibers per cross-sectional unit area because of the dead
spaces between adjacent cable units 2 and between adjacent cable
units 2 and the outer s:heath.4. ~n order to i,ncrease the ratio
of optical fibers per cross,-sectional unit area, other con-
ventional opt~,cal fiber cable structures include additional
optical fibers 1 in the above-descr~bed dead spaces. Howeyer,
thes.e conventional optical fiber cable structures inherently
subject the optical fibers 1 in the cable units 2 as well as the
:~ optical fibers 1 in the dead spaces to subs.tantial lateral or
compressi:on forces,
As is: known in the art, lateral or compress,ion forces
have a deleterious effect on the opti,cal performance and, thus,
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1 the transmission character~stics. of the optical fibers. Specific-
ally, such lateral or compression forces substantially increase
transmission losses and substantially change the transmission
- pass band of the optical fibers.
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1 One conventional approach directed at reducing the
lateral or compression forces applied to the optical fibers in an
optical fiber cable utili~es a rigid or semi-rigid support member
disposed within the outer covering of the cable. The support
member typically is fabricated using a plastic material or the
like, and is provided wi$h a plurality of extruded ribs which
extend radially outwardly from the center-line of the cable and
thus define a plurality of compartments which extend longitudin-
ally in a substantially parallel fashion along the center-line of
the cable. The optical fibers are accommodated into loosely-
fitting fashion in the compartments. Because of the loose fitting
that is provided by this construction, the optical fibers are not
subjected to substantial lateral or compression forces, and, thus,
do not exhibit increased transmission losses and changed trans-
mission bandwidth caused by such forces, as described above.
The use of the rigid or semi-rigid support member,
however, results in several major deficiencies. For example,
such a support member is difficult and expensive to fabricate and
also makes the insertion of the optical fibers into the compart-
ments very difficult, especially when an optical cable having asubstantial length is involved. In addition, the support member
must be specially fabricated when a different number of ribs, and,
thus, compartments are desired, which inherently increases fabri-
cation cost and manufacturing time. Furthermore, the use of a
support member inherently produces an optical cable having a rigid
or a semi-rigid characteristic, which often makes it difficult to
install the optical cable. In this connection, it should be
noted that the rigid or semi-rigid characteristic also makes it
difficult to assemble the optical cable at a location different
from the installation location because of the required transport-
ation of the fabricated cable. Splicing of optical fibers is a
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1 complicated and expensiye operation that inherently increase
transmission loss and changes trnamission bandwidth, Thus, it
is desirable to be able economically to manufacture and ins.tall
the optical fiber cable without having to provide any undesired
- cable splices.
SU~ARY OF THE :INVENTION
The present invention discloses several optical fiber
eable eonstructions which basically dispose the optical fibers
in a loosely-fitting fashion in respective longitudinal compart-
ments provided by splicing tapes ~olded or shaped to a desi.gnated
transverse cross-seetional shape, The loose fitting of the
optical fibers overcomes the increas,ed transmission loss,es and
changed transmis.s.ion bandwidth.caused by l~teral or co~pression
forces inherently applied to the optical fibers of conventional
; optieal fiber eable eonstructions. Two methods and apparatus
for fabricating the optical fiber cable construetions are also
diselosed. In an e~bodiment, the assemblage die i.s stationary
; with respeet to a rotary cage and a guide plate, whereas in
the second embodiment the assemblage die i,s mounted to rotate
with.the rotary cage and the guide plate.
In one aspeet the present inYention provides~ an ap=
- paratus, for producing an optical fiber cable having a plurality
of optieal fibers disposed in a plurality of corresponding com-
partments defined by a plurality of longitudlnally folded splieing
tapes:, compri.sing:
a) rotary cage means for provi.ding in a desi~gnated
spacial relationship the plurality of optical fibers ~nd the
plurality of spl~eing tapes;
b) folding means disposed adjacent the rotary cage
means. for folding each spli,cing tape to a desi~red eross~
sectional shape so as to form a reces.sed porti~on; and
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1 c~ assemblage die means disposed adjacent the folding
means for gathering and stranding the folded splicing tapes with
the optical fibers disposed therein.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a transverse cross-sectional view-of the
construction of a conventional optical fiber cable;
Fig~ 2 is a transvers-e cross-sectional view-of the
construction of a first embodiment of the optical fiber cable
of the present invention,
Fig. 3 is a transverse cross-sectional Yiew-of the
construction of a modification of the first embodiment of the
optical fiber cable of the present invnetion as shown in Fig. 2;
Fig. 4 is- a transverse cross-sectional Yiew-of the
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1 construction of a second embodiment of the optical fiber cable
of the present invention;
Fig. 5 is a transverse cross-sectional view of the
construction of a third embodiment of the optical fiber cable
of the present invention;
Fig. 6 is a tra~sverse cross-sectional view of the
construction of a fourth embodiment of the optical fiber cable
of the present invention;
Fig. 7 is a transverse cross-sectional view of the ~-
construction of a fifth embodiment of the optical fiber cable
of the present invention;
Fig. 8 is a perspective view showing the apparatus and
basic method for providing the various optical fiber cable con-
structions of the present invention;
` Fig. 9 is a plan view of one embodiment of the guide
plate 56 used in the method and apparatus of the present invention
shown in Fig. 8; and
Fig. 10 is a schematic view showing a second embodiment
of the method and apparatus for providing the various optical
fiber cable constructions of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The optical fiber cable constructions according to the
present invention will now be described.
Referring now to Fig. 2, the first embodiment of the
optical fiber ca~le construction of the present invention will
now be described. A plurality of optical ~ibers 10 are accommo-
dated in the recesses provided in a plurality of V-shaped folded
splicing tapes 11. It should be noted that optical fibers 10
can be provided with an appropriate coating if desired. Because
of the recesses provided by folding splicing tapes 11 into a
1 V-shape in the longitudinal direction, the optical fibers 10 can
be accommodated in a loosely-fitted fashion therein. As shown
in Fig. 2, each of the fibers 10 is accommodated in a separate
recess provided by a folded splicing tape 11. Of course, more
than one fiber 10 could be accommodated in each recess. Because
of the loose fitting, the optical fibers 10 are not subjected by
the folded splicing tapes 11 to any appreciable lateral or
compression forces.
In the construction of Fig. 2, each of the splicing
tapes 11 is shaped or folded to have a groove in the longitudinal
direction and each splicing tape so shaped or folded has a
symmetrical transverse cross-section. Splicing tapes 11 are
arranged, as shown in Fig. 2, in a radial fashion with respect to
the center-line of the optical fiber cable formed thereby.
The material for splicing tapes 11 is preferably a
rather rigid material that is easily shaped or folded but which
retains the shape or fold provided thereby. One example of a
suitable material for splicing tape 11 is a thick polyester having
; a thickness, for example, of about 0.1 mm. Another suitable
material for splicing tape 11 is aluminum. Of course, additional
materials are equally suitable for splicing tape 11.
It should be noted that a high tension rod (not shown)
can be provided along with one of the optical fibers 10 in the
compartment defined by the associated folded splicing tape 11.
This high tension rod acts to increase the tensile strength of
the optical fiber cable. Of course, more than one such high
tension rod can be provided.
Similarly, it should be noted that~cushioning rod or
material (not shown) can be provided along with one of the optical
fibers 10 in the compartment defined by the associated folded
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1 splicing tape 11. The cushioning rod or material acts to cushion
the associated optical fiber 10 from physical shock. One suitable
material for the cushioning rod or material is rope or jute. Of
course, more than one such cushioning rod or material can be
provided.
It should be noted that a colored member (not shown)
can be provided along with one of the optical fibers 10 in the
compartment defined by the associated folded splicing tape ll.
This colored member provides a capability of identification of a
designated optical fiber 10 or a designated compartment. It
should be realized that the colored function could be added to
either the high tension rod or to the cushioning rod. Alterna-
tively, at least one of the tapes is colored to realize this
function. Of course, more than one such colored membér can be
provided.
As shown in Fig. 2, a tape 12 is spirally wound or
spliced in a longitudinal fashion along the outer peripheral
ends of the folded spliced tapes ll so as to form the outer
covering of the optical fiber cable formed thereby. Any suitable
material, such as polyester or polyethylene tape, can be used for
tape 12. It should be noted that tape 12 can be bonded or
fastened, if desired, to sele~ted areas along the outer peripheral
ends of the folded spliced tapes ll. An adhesive agent or
ultrasonic bonding is used for bonding. The bonding is advanta-
geous in developing the end portion of the cable to identify the
fiber or to connect fibers.
Referring now to Fig. 3, a variation on the construc-
tion of the first embodiment of Fig. 2 is shown. Like numbers
between Figs. 2 and 3 refer to like components. The differences
between Figs 2 and 3 is that in Fig. 3 the spliced tapes ll are
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1 folded or shaped so as to assume more of a U-shape than the
V-shape of Fig. 2. It should also be noted that five optical
fibers 10 and associated compartments defined by folded splicing
tapes 11 are provided in the cable of Fig. 3, whereas there are
six such optical fibers 10 and associated compartments defined
by folded splicing tapes 11 in the cable of Fig. 2.
A second embodiment of the construction of the optical
fiber cable of the present invention is shown in Fig. 4. Like
reference numerals in Figs. 2 and 4 designate like elements.
It should be noted that splicing tapes 11' are folded so as to
have a flattened U-shape in the transverse cross-section. The
flattened U-shape of splicing tapes 11' creates a compartment
along the center-line of the cable. As shown in Fig. 4, a core
member 14 is disposed in the center-like compartment. Core
member 14 can exhibit a high tensile strength or can also be an
optical fiber 10.
- An actual cable has been constructed with the configura-
tion shown in Fig. 2, but the dimensions are equally applicable
to the configurations of Figs. 3 and 4. In the actual cable,
the optical fibers 10 had diameters of 0.9 mm, and the outer
diameter of the optical fiber cable was 4.0 mm. Even this cable,
with its very small dimensions, subjects the optical fibers 10
to extremely small lateral and compression forces since each of
the optical fibers 10 are loosely accommodated in the associated
compartment. The actual cable exhibited a low transmission loss
and a stable transmission bandwidth.
A third embodiment of the cable structure of the
present invention is shown in Fig. 5. A plurality of cable units
20 are disposed within an outer cover 12 made in the same fashion
as outer cover 12 of Fi~s. 2 - 4 described above. A small number
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1 of optical ~ibers 24 are disposed within each cable unit 20 and
are accommodated in a loosely-fitted manner as shown in Figs. 2
through 4. Thus, only a very small lateral or compression force
is applied to each optical fiber 24 due to the loosely-fitted
manner in which the fibers are arranged in the cable units 20.
As shown in Fig. 5, reference numeral 22 designates a
central member, which is preferably a tension member having high
tensile strength. However, central member 22 can be replaced
with a cable unit 20. Thus, as shown in Fig. 5, there are six
cable units 20 if the central member 22 is a tension member,
or there are seven cable units 20 if the central member 22 is
a unit cable 20.
Fig. 6 shows a fourth embodiment of the optical fiber
cable of the present invention. The fourth embodiment of Fig. 6
is a combination of the second embodiment shown in Fig. 4 and
the third embodiment shown in Fig. 5. As shown in Fig. 6, a
plurality of cable units 20 having a cross-section shown in Figs.
2 through 4 are accommodated in U-shaped grooves of folded spliced
tapes 11'. Cable units 20 and folded spliced tapes 11' are dis-
posed around a central member 22, and the outer peripheralsurfaces thereof are covered with an outer tape 12. In the
fourth embodiment, because the optical fibers 24 are disposed in
the cable units 20 and the cable units 20 are loosely supported
in the cable assembly, the optical fibers 24 are not subjected
to any appreciable lateral or compression pressure. In this
embodiment, cables having a cross-section shown in Fig. 1 are
usable as cable units 20.
The remarkable advantage of the present invention is
that in the above-described optical fiber cable structures, the
stranding pitch of the optical fibers 10, the folded splicing
tapes 11, 11' and the cable units 20 can be selected to be any
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1 value in accordance with the flexibility of these elements.
Of course, for special purposes, no stranding need be
provided.
The construction of a fifth embodiment of the optical
fiber cable of the present invention is shown in Fig. 7. The
fifth embodiment of the present invention provides unit-type
optical fiber cable wherein V-shaped compartments defined by
V-shaped folded spliced tapes 11 are disposed in the gaps defined
between adjacent cable units 20 and an outer sheath 12. The
optical fibers 10 are accommodated in the V-shaped compartments
defined by the folded spliced tapes 11. It should be noted that
like reference numerals in Fig. 7 refer to like elements in
Figs. 2 - 6.
In the optical fiber cable of the fifth embodiment,
because the optical fibers 10 are accommodated in V-shaped grooves
formed by the V-shaped tapes 11, which are disposed in gaps
defined between the adjacent units 20 and the outer sheath 12,
the lateral and compression pressure applied to the optical
fibers 10 is very small. In an actual cable having a construction
as shown in Fig. 7, it was possible to accommodate 48 optical
fibers 10, with each optical fiber 10 having a diameter of 0.9 mm,
in a cable sheath having an outer diameter of about 15 mm, if a
central member 22 is replaced by a cable unit 20.
The methods and apparatus for constructing the optical
fiber cable constructions according to the present invention will
now be described.
The basic method for producing the above-described
optical fiber cable according to the present invention will now
be described. As shown in Fig. 8, a plurality of bobbins 50
around which a corresponding pluralit~ of optical fibers 10 are
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:~ 1 wound~ and a plurality of rolls of splicing tape 54 for supplying
- unfolded splicing tapes 11, are mounted for rotation in a rotatiny
cage 52 The rolls 54 are disposed to prevent the splicing tapes
.~ 11 from being twisted or stranded, while the bobbins are disposed
either to strand or not to strand the optical fiber 10.
However, in order to prevent the optical fiber 10 from
: exhi~iting mechanical distortion, the bobbins 50 should be disposed
to strand the optical fibers 10. As shown in Fig 2, the number
of the optical fiber bobbins 50 is equal to the number of tape
rolls 54
The optical fibers 10 and unfolded splicing tapes 11
are fed from the rotary cage 52 to a folding means, which folds
each splicing tape 11 to a desired cross-sectional shape, for
example~ either a V, U or flattened U shape. Various methods can
` be employed to fold or shape the splicing tapes 11 into the
desired shape For exa~ple~ a pair of rollers can be used (not
shown~. Alternately, the unfolded splicing tapes 11 can bé passed
through a plurality of corresponding slits or openings of prede-
termined shape formed in a guide plate 56. The guide plate 56 is
preferably proYided with additional holes for passing the optical
fi~ers 10 therethrough, Fig 9 shows the plan view of one embod-
iment of the guide plate 56 that is provided with a plurality of
slits 6Q for folding the unfolded splicing tapes 11 ta the desired
shape~ with a plurality of holes 62 for passing said optical
fibers lQ therethrough, and with a hole 64 for passing a center
memher therethrough. Thus, guide plate 56 acts both to fold the
unfolded splicing tapes 11 to the desired shape, and also to orient
: the folded splicing tapes 11 with respect to the corresponding
. optical fi~ers 10.
; 30 It should be noted that the guide plate 56 should be
integrally mounted for rotation with the rotary cage 52. A pair
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Z
1 f rollers can be provisionally used, if desired, to fold the
unfolded splicing tapes 11 even in the case when a guide plate 56
~` is also used to fold the unfolded splicing tapes 11. The guide
plate 56 should be used in order to control the positional
relationship between the optical fibers 10 and folded splicing
tapes 11, and to accurately introduce the optical fibers 10 into
grooves of the folded splicing tapes 11.
The folded splicing tapes 11 together with optical
fibers 10 disposed therein are gathered and stranded in an
assemblage die 70. Normally, the assemblage die 70 is not mounted
for rotation.
The stranding pitch of the optical fiber cable is
determined by the rotational angular velocity of the cage 52 with
respect to the take-up speed of the optical fiber cable.
The assembled cable core is preferably covered with an
outer tape 12. Tape 12 can either be spirally wound or spliced
in a longitudinal direction to the assembled cable core. In Fig.
8, the cable core is spliced in the longitudinal direction by a
tape 12, and the tape 12 is wrapped over the cable core by means
of a forming means 74. Reference numeral 72 designates string or
tape spirally wound on the outer surface of tape 12 to prevent
the tape 12 from separating from the optical fiber cable.
The second embodiment of the method and apparatus of
the present invention is shown in Fig. 10. It should be noted
that like reference numbers designate like elements in Figs. 8,
9 and 10~
In the first embodiment of the method and apparatus
discussed above, it was stated that guide plate 56 was preferably
integrally mounted for rotation with rotary cage 52 so that both
have the same rotational angular velocity. However, in that
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1 embodiment, it was stated that the assemblage die 70 was main-
tained fixed, and that the stranding pitch was determined by the
ratio of the ro~ation of rotary cage 52 with respect to the take-
up speed of the cable.
The second embodiment of the method and apparatus of
the present invention, as shown in Fig. 10, produces a stranded
core which is superior to that produced by the first embodiment.
Specifically, the stranded core produced by the second embodiment
exhibits a more uniform shape in the shape of the compartments,
and also exhibits an improved dimensional accuracy. This improve-
ment is due to the rotation of the assemblage die 70 together with
guide plate 56 and rotary cage 52.
In the second embodiment of the method and apparatus of
the present invention the system surrounded by the dotted chain
line 90 of Fig. 10 is integrally rotated. The rotation of the
assemblage die 70 can be easily realized by a mechanical and
integral connection between the die 70 to the guide plate 56 and
the rotary cage 52. Alternatively, instead of the mechanical
linkage therebetween, the die 70 can be integrally rotated with
the rotary cage 52 by supporting the die 70 by means of a bearing
to permit free rotation thereof. Incidentally, the system
surrounded by the broken line shows a conventional rotation
system.
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