Note: Descriptions are shown in the official language in which they were submitted.
CA 02590758 2007-06-07
Tactical Flexible Fibre Optic Splice Enclosure
and Method of Installation
Field of Invention
[0001] The present invention relates to fibre optics and more particularly to
flexible,
durable, fibre optic splices, and methods of installing such splices.
Background
[0002] The world of optical fibre communications often requires that optical
fibres be
joined in order to obtain longer distances between optical transceivers. This
process is
known in the communications industry as splicing.
[0003] The military uses a system of communications known as tactical
communications.
This system utilizes special rugged fibre optic cables, having generally 2 to
4 optical
fibres per cable, which are stored on reels. The cable is deployed in the
field and
interfaced to fibre optic transceivers at each end thus providing
communications. During
field activities, the cable is often damaged and must be repaired on site.
[0004] Splicing fibre optic cables together is not an easy task because the
splice must be
rugged and yet flexible. Many splice systems lack tensile strength because the
splice
mechanism does not extend the continuity in the strength member of the cables.
Those
splices that show good compressive strength do so at the expensive of
bulkiness, which
interferes with retrieval and redeployment of the cable. Flexibility is also
beneficial
during retrieval and redeployment, which is a problem because most splice
systems are
very stiff.
[0005] While splice flexibility is desirable for practical reasons, there is a
problem in that
fibre optic cables will become damaged or performance will be impaired if the
fibres are
bent in too tight a radius. Thus, there is a need for a flexible splice that
nonetheless
prevents the fibres from being bent into dangerously tight radii.
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[0006] Tactical military cable systems are also required to tolerate harsh
environmental
conditions, which many splice systems cannot reliably endure.
[0007] Difficulties also arise while installing the splice itself. Most
splicing systems that
accommodate multi-fibre cables are not forgiving. That is, each of the splices
in the
multi-fibre cable must be approximately the same length because the splice
enclosure
cannot accommodate any excess fibre length. Thus, if the user happens to
damage a fibre
splice after having completed half of the splices in a multi-fibre cable, he
is generally
forced to abandon all of the completed splices and start again.
[0008] There is therefore a need for an improved fibre optic cable splice
enclosure and
method of installation, provided with consideration for the problems outlined
above.
Summary of the Invention
[0009] It is therefore an object of the invention to provide an improved fibre
optic splice
and method of assembly, which obviates or mitigates at least one of the
disadvantages
described above.
[0010] One aspect of the invention is broadly defined as a fibre optic splice
comprising:
a flexible central tensile member; a flexible helical wrapping positioned
about the flexible
central tensile member; and an outer protective jacket positioned about the
flexible
helical wrapping; the flexible central tensile member and the flexible helical
wrapping
defining a splice enclosure to accommodate optical fibres of the splice, at
least a portion
of the optical fibres being arranged in a generally helical orientation within
the splice
enclosure.
[0011] Another aspect of the invention is broadly defined as a method of
splicing a fibre
optic cable comprising the steps of: arranging at least a portion of the
optical fibres being
spliced, in a generally helical orientation about a flexible central tensile
member;
positioning a flexible helical wrapping about the optical fibres and the
flexible central
tensile member, the flexible central tensile member and the flexible helical
wrapping
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defining a splice enclosure to accommodate the optical fibres being spliced;
and
positioning an outer protective jacket about the flexible helical wrapping.
[0012] A further aspect of the invention is broadly defined as a pre-assembled
fibre optic
splice system comprising: a splice sleeve having generally axially-oriented
channels sized
to accommodate spliced optical fibres; a removable cover for the splice
sleeve; a flexible
central tensile member, the flexible central tensile member passing through
the splice
sleeve; and a pair of cable bonding clamps, one secured to each end of the
flexible central
tensile member.
[0013] This summary does not necessarily describe all features of the
invention.
Brief Description of the Drawings
[0014] These and other features of the invention will become more apparent
from the
following description in which reference is made to the appended drawings
wherein:
Figures la, lb and 2c present details of a splice sleeve cover in an
embodiment of the
invention;
Figures 2a, 2b and 2c present details of a splice sleeve in an embodiment of
the
invention;
Figures 3a, 3b and 3c present details of a cable bond clamp in an embodiment
of the
invention;
Figures 4a ¨ 4d present successive steps in the assembly of a fibre optic
splice in an
embodiment of the invention; and
Figures 5a ¨ 5d present successive steps in the termination of a fibre optic
cable to a
cable bond clamp in an embodiment of the invention.
Principles of Operation
[0015] This document describes an environmentally sealed, in-line fibre optic
cable,
flexible splice enclosure. Until now flexible inline splice enclosures have
been extremely
limited in their ability to achieve a tight bend radius. The main reason for
this is the
inability of inline splice enclosures to allow for excess fibre slack. The
flexible splice
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I.
described herein is able to achieve tight bend radius specifications and is
able to
accommodate different fibre lengths due to its unique method of accommodating
and
storing excess fibre slack.
[0016] As shown in Figures 4a ¨ 4d, the splice enclosure 10 is made up of the
following
major components: a pair of cable bond clamps 12, a splice sleeve / cover
combination
14, and a flexible, central length of neoprene 16. The cable bond clamps 12
(an example
of which is shown in Figures 3a ¨ 3c) are joined together by the flexible
central neoprene
tensile member 16, which passes through a splice sleeve 18 and a pair of
splice sleeve
covers 20 (examples of which are shown in Figures 2a ¨ 2c and Figures la ¨ lc
respectively). Other polymers or similar flexible materials with suitable
durability and
tensile strength could also be used for the central tensile member 16. The
cable bond
clamps 12, splice sleeve 18 and splice sleeve covers 20 are shown in the
figures as being
made from brass, but other materials such as aluminum could be used depending
on the
application and cost constraints (non-sparking, corrosion resistant, non-
magnetic, non-
electrical conducting and fire-resistant properties are often desirable for
such
components, depending on the application). All of the components of the system
preferably satisfy these requirements and also remain flexible and durable
over a
temperature range of ¨70 C to 100 C.
[0017] As will be explained in greater detail hereinafter, the role of the
splice sleeve /
cover combination 14 is simply to provide mechanical protection for the
optical fibre
splices themselves. As shown in Figures 1 a ¨ lc, the splice sleeve covers 20
include an
internal thread 46 to engage with the external thread 54 of the splice sleeve
18, and a
shoulder 48 to bear against the end of the splice sleeve 18. They also include
a knurled
or cross-hatched outer surface 50 to facilitate tightening by hand. Of course,
the splice
sleeve covers 20 also include a bore 52 that is wide enough to accommodate the
passage
of the optical fibres 24 and neoprene central member 16, and the dimensions of
the spiral
wrap fibre retainers 26, 26'. Finally, note that the outer edges of the splice
sleeve covers
20 are preferably rounded off or beveled as shown in Figure la, to remove
sharp or
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simply abrupt edges which might cause damage to the cable, splice, or other
components
of the system.
[0018] As shown in Figures 2a ¨ 2c, the splice sleeve 18 has an external
thread 54 that
engages with the internal threads 46 of the splice sleeve covers 20, and an
internal bore
56 to accommodate passage of the neoprene central member 16. It also includes
channels
or slots 64 running axially along its outer surface, sized to accommodate
individual,
spliced optical fibres. In this embodiment the splice sleeve 18 has six
channels 64 on its
outer surface, equally spaced apart around the circumference, but any number
and
arrangement may be used.
[0019] The cable bond clamps 12 are joined to the neoprene central member 16
both
chemically using epoxy, and mechanically with a press-fit stainless steel pin
applied
through a hole 22 in the cable bond clamps 12. Other chemical bonding
compounds
could also be used, and similarly, other mechanical pins, crimps or similar
fasteners could
also be used. All tensile forces are thereby transferred from the first cable
in the splice,
through the neoprene central member 16 to the second cable. The elastic
properties of
the neoprene central member 16 allows for fibre movement when the tensile
loads are
placed on the cable. The neoprene central member 16 also absorbs shock well
and allows
for immediate recovery in the case of momentary shock loads.
[0020] As shown in Figures 3a - 3c, the cable bond clamps 12 are generally
cylindrical
and include two bores 60 and 62 centered on the primary axis. The larger bore
60 is
sized to accommodate the neoprene central member 16, while the (typically)
smaller bore
62 is sized to accommodate the central strength member of the optical cable 28
being
spliced. The cable bond clamps 12 are drilled 22 to intersect with the larger
bore 60,
allowing a pin (or other fastener) to be insert through the cable bond clamps
12 and
neoprene central member 16. The cable bond clamps 12 are also drilled and
tapped 30 to
intersect with the smaller bore 62, so that a set screw 40 (see Figure 5a) can
be used to
secure the central strength member of the optical cable 28 after it is
inserted. The cable
bond clamps 12 also include a shoulder 38 that the heat shrink Kevlar
retainers 34 may
bear against (see Figure 5b), providing additional tensile strength. Finally,
the cable bond
CA 02590758 2007-06-07
clamps 12 also include a number of individual sub-cable holes 58 (see Figure
3b),
oriented in the axial direction and preferable equally spaced apart, through
which the sub-
cable units (i.e. individual optical fibres) of the optical cable 28 may pass.
[0021] Although the neoprene central member 16 is a significant reason for the
success
of the splice enclosure 10, the method of slack storage by helically winding
the optical
fibres 24 loosely around the neoprene central member 16 as shown in Figure 4b,
also
provides many advantages. By providing the optical fibres 24 with radial
support and
enough excess optical fibre within the splice enclosure 10, optical fibre
movement is
controlled without affecting optical loss or stability in a wide range of
travel.
[0022] The two lengths of spiral wrap 26, 26' shown in Figure 4c simply
provide a
conduit for the optical fibres 24 to move within while acting as a radius
limiter to avoid
any kinking of the optical fibres 24. The material of the spiral wrap 26 is
generally made
up of Teflon but can be made up of any flexible, non-metallic material that
presents no
sharp edges and has the ability to recover, and maintain its original shape
after being
exposed to compressive and tensile loads. It also provides impact resistance
for the
exposed optical fibres 24. The splice enclosure 10 is therefore able to
dynamically adjust
diameters and optical fibre slack according to the loads placed on the cable
28. The
storage of the excess optical fibre slack also removes the need to keep
spliced optical
fibres at the same length so long as the splices are kept central, and a
minimum of optical
fibre slack is maintained. This more forgiving method will allow field
technicians to
repeat a splice if required without the need to repeat all splices and cable
preparation.
[0023] As noted above, the central strength members of the fibre optic cables
28 are
bonded to the cable bond clamps 12 via mechanical means. Each cable bond clamp
12 is
drilled and tapped 30 (see Figure 3a) so that the central strength members of
the fibre
optic cables 28 can be bonded with a setscrew 40 (see Figure 5a). The cable
tensile
strength member (i.e. the outer Kevlar-stranded jacket 32 of the fibre optic
cable 28) is
also bonded to the cable bond clamp 12 via a pair of heat shrinks 34, 36 and a
shoulder
38 on the cable bond clamp 12. See Figures 5a ¨ 5d and the description
hereinafter for a
more detailed explanation of this arrangement.
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[0024] Figure 5a shows a fibre optic cable 28 with its central strength member
fastened
to the cable bond clamp 12 using the set screw 40, and the optical fibres 24
of the cable
28 passing through the sub-cable holes 58 of the cable bond clamp 12. Then, in
Figure
5b, a Kevlar retainer heat shrink 34 is installed over the outer layer of
Kevlar 32 (i.e. the
cable tensile strength member) that has been fanned out equally over the cable
bond
clamp 12 and is shrunk into place. Note that in breakout cable the outer
Kevlar is used
and the sub-cable Kevlar is discarded, while in distribution cable (where the
optical fibres
are surrounded by the cable tensile strength member) all of the Kevlar is
used.
[0025] The outer layer of Kevlar 32 is then folded back over the newly
installed Kevlar
retainer heat shrink 34, covering the entire bond clamp assembly and a portion
of the
cable outer jacket, as shown in Figure 5c. A heat shrink cable bond cover 36
is then
placed over the outer Kevlar-stranded jacket 32 which has been folded back,
and is heat-
shrunk into place as shown in Figure 5d. This effectively locks the outer
Kevlar-stranded
jacket 32 in place. All loads are thus transferred from one cable 28 to
another through the
neoprene central member 16. The optical fibres 24 are allowed enough movement
to
adjust to these loads.
[0026] The overall assembly is also covered with an adhesive lined heat shrink
material
44 as shown in Figure 4d that provides environmental sealing to the completed
splice.
The splice in its current form is designed to accommodate up to 6 fibres.
Larger versions
can be made to accommodate higher fibre counts.
Enclosure components
[0027] The splice structure includes the following components.
- two cable bond clamps 12
- one splice sleeve 18
- two splice covers 20
one Neoprene central member 16
one 0-ring retainer 46
two spiral wrap fibre retainers 26, 26'
- two heat shrink cable bond covers 36 (2" in length adhesive lined)
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two heat shrink Kevlar retainers 34 (0.5" in length)
one complete assembly heat shrink cover 44
twelve sub-cable heat shrink sleeves (depending on how many fibres are being
spliced in the single cable), which protect the optical fibres of distribution-
type
cables, where they pass through the cable bond clamps 12
twelve splice protection sleeves (again, depending on how many fibres are
being
spliced in the single cable), which consist of stainless steel rods and heat
shrink
material as known in the art.
Factory Pre-Assembly
[0028] In the pre-assembly process, the cable bond clamps 12 are installed
onto the
neoprene central member 16 in order to reduce the number of steps required for
field
termination and to simplify the overall installation process.
[0029] The pre-assembly consists of inserting the neoprene central member 16
through
the splice sleeve 18 with the two splice covers 20 and 0-ring 46 in place.
Once the splice
sleeve 18 is in place, the neoprene central member 16 is bonded to the cable
bond clamps
12 using an epoxy (though other adhesives, cements or resins could also be
used). The
cable bond clamps 12 are heat cured to insure a proper bond between the
neoprene
central member 16 and the cable bond clamps 12 (whether heat curing or some
other
treatment is required, of course, will depend on the nature of the adhesive or
cement
being used). Once the epoxy is cured and the retaining pin hole 22 on the
cable bond
clamp 12 is drilled out, a stainless steel retaining pin is pressed into place
using a
mechanical press. Once this is done the set screws 40 are installed in the
cable bond
clamps 12 and the product is inspected and packaged for field use.
Installation
[0030] For breakout style tactical cable, the cable 28 is prepared as follows:
1- On one
cable 28 to be spliced, insert the heat shrink cover 44, one heat shrink
cable bond clamp cover 36 and one heat shrink Kevlar retainer 34
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2- On the other cable 28, insert the remaining heat shrink cable bond clamp
cover 36 and the remaining heat shrink Kevlar retainer 34
3- Remove 12" of outer jacket of fibre optic cable 28
4- Cut the outer cable Kevlar 32 back to 2" from the outer jacket
5- Cut the cable central strength member (CSM) to 1/2" from outer jacket
6- Insure the set screw 40 in cable bond clamp 12 cannot be seen through
the
CSM receptacle
7- Insert sub-cable units through the individual sub-cable holes 58 in the
cable
bond clamp 12
8- Push the cable bond clamp 12 back until the CSM seats properly into the
bore
62 of the cable bond clamp 12 (as shown in Figures 3a and 3c, there are two
bores in the cable bond clamps 12 with a common axis ¨ the larger bore 60 is
to accommodate the neoprene central member 16, while the smaller bore 62 is
sized to accommodate the CSM)
9- Tighten the set screw 40 in cable bond clamp 12 to hold CSM in place.
Note
that the set screw 40 is merely intended to assist with assembly, and is not
intended to provide tensile strength to the splice.
10- Remove sub-cable jackets 1/4" from inside edge of cable bond clamp 12
and
cut sub-cable Kevlar 32 flush with jackets.
11- Fan the outer cable Kevlar 32 over, and evenly distribute around cable
bond
clamp 12 as shown in Figure 5a
12- Shrink the Kevlar retainer heat shrink 34 over the cable bond clamp 12
and
outer cable Kevlar 32 as shown in Figure 5b
13- Take excess outer cable Kevlar 32 and fold over the previously
installed
Kevlar retainer heat shrink 34 (per Figure 5c) and cover with the heat shrink
cable bond clamp cover 36 so that the Kevlar 32 is held between the Kevlar
retainer heat shrink 34 and the heat shrink cable bond clamp cover 36. The
heat shrink cable bond clamp cover 36 should overlap the cable outer jacket
by at least 3/1". Heat shrink when properly set in place (per Figure 5d)
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14- Remove the splice sleeve cover 20 and 0-ring retainer 46 from the
splice
sleeve 18 and insert the individual optical fibres 24 through these
components.
15- On one cable 28, insert one splice protection sleeve per optical fibre,
over
each optical fibre
16- Strip and cleave each optical fibre as per normal splicing practices
[0031] For distribution style tactical cable use the following instructions:
1- Follow instructions 1 ¨ 5 from the paragraph above
2- Insert on each optical fibre, one sub-cable heat shrink sleeve, push
sleeve back
to outer cable jacket and shrink into place
3- Continue with instructions 6 ¨ 16 from the paragraph above.
[0032] Regardless of which of the two processes above is followed, the balance
of the
steps may now be performed:
17 - Splice optical fibres of the cable as per standard practices using fusion-
splicing techniques.
18 - Protect each optical fibre splice with splice protection sleeves and heat
shrink
into place
19 - Once all of the optical splices have been completed and connectivity has
been
verified, insert the completed splices in the provided slots 64 in the splice
sleeve 18
and place the 0-ring retainer 46 over the splice centred on the splice sleeve
18 as
shown in Figure 4a. The purpose of the 0-ring retainer 46 is to hold the
optical
splices in place to facilitate the installation of the splice sleeve covers 20
20 - Thread on the splice sleeve covers 20 until they stop
21 - Starting on the left side of the splice, between the splice sleeve 18 and
the
cable bond clamp 12, wrap the optical fibres 24 loosely and helically around
the
neoprene central member 16 wrapping from the outside towards the centre as
shown
in Figure 4b
22 - Once the optical fibres 24 are in place, install the spiral wrap fibre
retainer 26,
26' over the optical fibres 24 as shown in Figure 4c, being careful not to
catch any of
the optical fibres 24 and insuring that the optical fibres 24 are moving
loosely under
CA 02590758 2014-06-03
the spiral wrap fibre retainer 26, 26'. The spiral wrap fibre retainer 26, 26'
will
terminate under the splice sleeve cover 20, the axial bore 52 of the splice
sleeve cover
20 being sized to accommodate
23 - Repeat the previous two steps for the right side of the splice.
24 - With both sides of the splice complete, cover the overall splice using
the
complete assembly heat shrink cover 44, as show in Figure 4d. Keep the splice
sleeve centred and shrink the cover 44 from the centre towards the outer edges
to
insure that no air is trapped in the splice.
25 - Allow the entire assembly to cool and deploy.
[0033] The present invention has been described with regard to one or more
embodiments. However, it will be apparent to persons skilled in the art that a
number of
variations and modifications can be made. The scope of the claims should not
be limited
by the preferred embodiments set forth in the examples, but should be given
the broadest
interpretation consistent with the description as a whole.
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