U.S. patent application number 16/129481 was filed with the patent office on 2020-03-12 for optical cables for harsh environments.
The applicant listed for this patent is Prysmian S.p.A.. Invention is credited to Matias Campillo Sanchez, Ester Castillo Lopez, Josep Maria Martin Regalado, Josep Oriol Vidal Casanas.
Application Number | 20200081209 16/129481 |
Document ID | / |
Family ID | 67875310 |
Filed Date | 2020-03-12 |
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United States Patent
Application |
20200081209 |
Kind Code |
A1 |
Martin Regalado; Josep Maria ;
et al. |
March 12, 2020 |
Optical Cables for Harsh Environments
Abstract
An optical cable includes a plurality of optical fibers sealed
within a metal tube, a polymer inner sheath surrounding the metal
tube and operatively connected to the metal tube, and an outer
sheath disposed over the polymer inner sheath.
Inventors: |
Martin Regalado; Josep Maria;
(Barcelona, ES) ; Vidal Casanas; Josep Oriol;
(Barcelona, ES) ; Campillo Sanchez; Matias;
(Barcelona, ES) ; Castillo Lopez; Ester;
(Barcelona, ES) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Prysmian S.p.A. |
Milano |
|
IT |
|
|
Family ID: |
67875310 |
Appl. No.: |
16/129481 |
Filed: |
September 12, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 6/4488 20130101;
G02B 6/4494 20130101; G02B 6/4416 20130101; H01B 13/22 20130101;
G02B 6/4436 20130101; H01B 9/005 20130101; G02B 6/443 20130101;
H01B 9/02 20130101 |
International
Class: |
G02B 6/44 20060101
G02B006/44; H01B 9/02 20060101 H01B009/02; H01B 9/00 20060101
H01B009/00; H01B 13/22 20060101 H01B013/22 |
Claims
1. An optical cable comprising: a plurality of optical fibers
sealed within a metal tube, the metal tube being sealed by welding
or extrusion; polyamide inner sheath surrounding and directly
adjacent to the metal tube, the polyamide inner sheath being a
single homogeneous polyamide layer; a metal layer surrounding and
directly adjacent to the polyamide inner sheath; and an outer
sheath surrounding the metal layer, the outer sheath comprising an
external surface of the optical cable.
2. The optical cable according to claim 1, wherein the metal layer
is a single layer of armor disposed between the polyamide inner
sheath and the outer sheath.
3-5. (canceled)
6. The optical cable according to claim 1, wherein the outer sheath
is made of a material selected from a group consisting of a
polyvinylchloride (PVC) material and a low smoke zero halogen
(LSoH) polymer material.
7. The optical cable according to claim 1, further comprising: a
single layer of armor disposed over the polyamide inner sheath; and
an intermediate sheath disposed between the metal layer and the
single layer of armor, the metal layer being an electrically
conductive layer, wherein the optical cable is configured to
transmit optical signals through the plurality of optical fibers,
and wherein the optical cable is further configured to conduct
electrical current through the electrically conductive layer.
8. The optical cable according to claim 7 wherein the intermediate
sheath comprises polyethylene or ceramifying silicone rubber.
9-10. (canceled)
11. An optical cable comprising: an optical core comprising a metal
tube enclosing a plurality of loose optical fibers and configured
to resist water penetration; a single layer homogeneous polyamide
inner sheath disposed over and directly attached to the optical
core, the single layer homogeneous polyamide inner sheath being
configured to be chemically resistant; and an outer sheath
surrounding the single layer homogeneous polyamide inner sheath,
the outer sheath being configured to be flame retardant.
12. The optical cable according to claim 11 further comprising an
armor layer disposed between and physically contacting both the
single layer homogeneous polyamide inner sheath and the outer
sheath.
13. The optical cable according to claim 11, further comprising: a
conductive layer disposed over and physically contacting the single
layer homogeneous polyamide inner sheath; an armor layer; and an
intermediate sheath disposed between the conductive layer and the
armor layer, wherein the optical cable is configured to transmit
optical signals through the plurality of loose optical fibers, and
wherein the optical cable is further configured to conduct
electrical current through the conductive layer.
14. The optical cable according to claim 11, wherein the total
quantity of optical fibers enclosed by the metal tube divided by
the diameter of the optical cable is greater than 3 fibers/mm.
15. The optical cable according to claim 11, wherein the optical
core is sealed to prevent water penetration.
16. The optical cable according to claim 11, wherein the single
layer homogeneous polyamide inner sheath surrounds the optical core
so that the optical cable is protected from chemicals.
17-22. (canceled)
23. The optical cable according to claim 11, wherein the outer
sheath comprises one or more of: a crystalline propylene
homopolymer or copolymer; a copolymer of ethylene with at least one
alpha-olefin; and natural magnesium hydroxide so that the optical
cable is fire resistant and flame retardant.
24. A hybrid cable comprising: a plurality of optical fibers sealed
within a metal tube; a polyamide inner sheath surrounding the metal
tube, wherein the polyamide inner sheath is directly attached to
the metal tube; a conductive layer disposed over and physically
contacting the polyamide inner sheath; an intermediate sheath
disposed over the conductive layer; and an outer sheath surrounding
the intermediate sheath, wherein the hybrid cable is configured to
transmit optical signals through the plurality of optical fibers,
and wherein the hybrid cable is further configured to conduct
electrical current through the conductive layer.
25. The hybrid cable according to claim 24 further comprising an
armor layer disposed between the intermediate sheath and the outer
sheath.
26. The hybrid cable according to claim 24, wherein the polyamide
inner sheath is a single homogeneous polyamide layer.
27. The hybrid cable according to claim 24, wherein the conductive
layer is further configured to transmit electrical power through
the hybrid cable.
28. The hybrid cable according to claim 24, wherein the polyamide
inner sheath surrounds the metal tube so that the plurality of
optical fibers are protected from heat, oil and gasoline.
29. The hybrid cable according to claim 24, wherein the metal tube
is sealed so that the plurality of optical fibers are protected
from fire.
30. The optical cable according to claim 1, wherein the metal tube
is sealed so that the plurality of optical fibers are protected
from fire.
31. The optical cable according to claim 1, wherein the polyamide
inner sheath surrounds the metal tube so that the plurality of
optical fibers are protected from heat, oil and gasoline.
32. The optical cable according to claim 1, wherein the polyamide
inner sheath is between about 0.3 mm and 1.0 mm thick.
33. The optical cable according to claim 1, wherein the polyamide
inner sheath is directly attached to the metal tube using an
adhesion layer.
34. The optical cable according to claim 1, wherein the thickness
of the polyamide inner sheath along a radius of the optical cable
is between about 0.3 mm and about 1.5 mm.
Description
TECHNICAL FIELD
[0001] The present invention relates generally to optical cables,
and, in particular embodiments, to optical cables capable of
maintaining operation in harsh environments.
BACKGROUND
[0002] Optical fibers are glass strands capable of transmitting an
optical signal over great distances, at very high speeds, and with
relatively low signal loss relative to standard copper wire
networks. Optical cables are therefore widely used in long distance
communication and have replaced other technologies such as
satellite communication, standard wire communication etc. Besides
long distance communication, optical fibers are also used in many
applications such as medicine, aviation, computer data servers,
etc.
[0003] Due to the broad range of applications for optical fibers,
optical cables may need to be capable of operation in harsh
environments. For example, optical cables may be used in harsh
environments where high chemical resistance is needed such as in
ducts, refineries such as oils and gas plants, mining operations,
and the like. Optical cables may also be relied upon to maintain
functionality for safety reasons during disaster events. For
instance, optical cables may need to be flame retardant, fire
resistant, and maintain circuit integrity for as long as possible
during a fire. In addition, the performance of optical cables may
be adversely affected by pressure events such as bending, buckling,
and compressive stresses. For these reasons, optical cables that
are resistant to chemicals, fire, and/or mechanical stresses may be
desirable.
[0004] Optical cables may also be used in applications where
electrical signals and/or electrical power are desirable in
addition to an optical signal. A hybrid cable may include
electrically conductive pathways as well as optical pathways in an
integrated cable solution. For example, optical devices and
electronic equipment such as machinery, sensors, communication
devices, and others may be fed by a hybrid cable. Hybrid cables
have been described previously in the art.
[0005] A fiber-optic transmission cable for high-stress
environments and especially undersea applications is described by
Stamnitz in European Patent Publication No. EP0371660A1. The
fiber-optic transmission cable comprises one to a large number of
optical fibers, electrical conductors, and metallic wire strength
members contained within a single cable structure. A specific
example is an electro-opto-mechanical cable that includes at least
one thin-wall steel alloy tube containing at least one single mode
fiber and a void filling gel. A dielectric annulus includes an
electrically conductive layer disposed therein. An optional
double-layer contrahelical or three or four layer, torque balanced,
steel wire strength member provides additional protection as well
as capability to be towed, deployed and recovered from the seafloor
at abysmal depths.
[0006] An undersea telecommunications cable is described by Marlier
et al. in U.S. Pat. No. 5,125,061. The undersea telecommunications
cable has optical fibers embedded in a material filling a tube
which itself lies inside a helical lay of metal wires having high
mechanical strength and in which the interstices are filled with a
sealing material. The cable includes a first extruded sheath
between the tube and the helical lay, and the helical lay is itself
covered by a second extruded sheath which is insulating and
abrasion resistant, and if the cable is for a remotely-powered
link, it includes a conductive strip on the tube or on the first
sheath.
SUMMARY
[0007] In accordance with an embodiment of the invention, an
optical cable includes a plurality of optical fibers sealed within
a metal tube, a polymer inner sheath surrounding the metal tube and
operatively connected to the metal tube, and an outer sheath
surrounding disposed over the polymer inner sheath. In an
embodiment, a single layer of armor is disposed between the polymer
inner sheath and the outer sheath.
[0008] In accordance with another embodiment of the invention, an
optical cable includes an optical core comprising a metal tube
enclosing a plurality of loose optical fibers. The optical core is
configured to resist water penetration. The optical cable further
includes a single layer homogeneous inner sheath disposed over and
operatively connected to the optical core and an outer sheath. The
single layer homogeneous inner sheath is configured to be
chemically resistant. The optical cable may also include an armor
layer disposed over and physically contacting the single layer
homogeneous inner sheath, and the outer sheath disposed over the
armor layer. The outer sheath is configured to be flame
retardant.
[0009] In accordance with still another embodiment of the
invention, a hybrid cable includes a plurality of optical fibers
sealed within a metal tube and a polyamide inner sheath surrounding
the metal tube. The polyamide inner sheath is directly attached to
the metal tube. The hybrid cable further includes a conductive
layer disposed over and physically contacting the polyamide inner
sheath, an intermediate sheath disposed over the conductive layer,
and an outer sheath surrounding the intermediate sheath. An armor
layer may be disposed between the intermediate sheath and the outer
sheath. The hybrid cable is configured to transmit optical signals
through the plurality of optical fibers. The hybrid cable is
further configured to conduct electrical current through the
conductive layer.
[0010] In accordance with yet another embodiment of the invention,
a method of fabricating an optical cable includes providing a
plurality of optical fibers, sealing the plurality of optical
fibers within a metal tube, forming a polymer inner sheath
surrounding the metal tube and operatively connected to the metal
tube, and forming an outer sheath to surround over the polymer
inner sheath. In an embodiment, the method further comprises
forming a single layer of armor over the polymer inner sheath
before forming the outer sheath.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] For a more complete understanding of the present invention,
and the advantages thereof, reference is now made to the following
descriptions taken in conjunction with the accompanying drawings,
in which:
[0012] FIG. 1 illustrates a conventional optical cable;
[0013] FIG. 2 illustrates another conventional optical cable;
[0014] FIG. 3 illustrates an exemplary optical cable including a
single layer inner sheath directly adjacent to a sealed metal tube
containing a plurality of optical fibers in accordance with an
embodiment of the invention;
[0015] FIG. 4 illustrates an exemplary optical cable including a
single layer inner sheath directly adjacent to a sealed metal tube
containing two or more fiber tubes each containing a plurality of
optical fibers in accordance with an embodiment of the
invention;
[0016] FIG. 5 illustrates an exemplary hybrid cable including a
single layer inner sheath directly adjacent to a sealed metal tube
containing a plurality of optical fibers as well as an electrically
conductive layer in accordance with an embodiment of the
invention;
[0017] FIG. 6 illustrates an exemplary hybrid cable including a
single layer inner sheath directly adjacent to a sealed metal tube
containing two or more fiber tubes each containing a plurality of
optical fibers as well as an electrically conductive layer in
accordance with an embodiment of the invention;
[0018] FIG. 7 illustrates an exemplary method of fabricating an
optical cable in accordance with an embodiment of the
invention;
[0019] FIG. 8 illustrates another exemplary method of fabricating
an optical in accordance with an embodiment of the invention;
and
[0020] FIG. 9 illustrates an exemplary method of fabricating a
hybrid cable in accordance with an embodiment of the invention.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0021] The making and using of the presently preferred embodiments
are discussed in detail below. It should be appreciated, however,
that the present invention provides many applicable inventive
concepts that can be embodied in a wide variety of specific
contexts. The specific embodiments discussed are merely
illustrative of specific ways to make and use the invention, and do
not limit the scope of the invention.
[0022] In various embodiments, an optical cable with high chemical
resistance, fire resistance, flame retardancy, circuit integrity,
and mechanical strength will be described. The optical cable
achieves these and other properties by including a chemically
resistant layer directly contacting a metal tube that houses
optical fibers. The following description describes the exemplary
embodiments.
[0023] Two conventional optical cables will first be described
using FIGS. 1 and 2. Two embodiment optical cables will then be
described using FIGS. 3 and 4. Two embodiment hybrid cables will
then be described using FIGS. 5 and 6. Several exemplary methods of
fabricating embodiment cables will then be described using FIGS.
7-9. A selection of possible cable diameters and cable diameter
ranges will be summarized in Table I.
[0024] FIG. 1 illustrates a conventional optical cable.
[0025] Referring to FIG. 1, a conventional optical cable 100
includes a glass fiber reinforced plastic (GFRP) central element
150. Thermoplastic polyester tubes 152 are arranged around the GFRP
central element 150. Each of the thermoplastic polyester tubes 152
contains a plurality of optical fibers no and a gel compound 122.
The conventional optical cable has 72 optical fibers no contained
in six thermoplastic polyester tubes 152 as illustrated in FIG.
1.
[0026] The thermoplastic polyester tubes 152 are surrounded by a
heat resistant and swellable core covering 124. The heat resistant
and swellable core covering 124 comprises a mica tape for heat
resistance and an absorbent powder for water protection. The heat
resistant and swellable core covering 124 is surrounded by a low
smoke zero halogen (LSoH) layer 154. The GFRP central element 150,
thermoplastic polyester tubes 152, the heat resistant and swellable
core covering 124, and the LSoH layer 154 make up a cable core 140
of the conventional optical cable 100.
[0027] The cable core 140 has a conventional core diameter 190
determined as a function of the number and arrangement of the
optical fibers within the thermoplastic polyester tubes 152. The
total number of optical fibers typically ranges from 6 to 96. The
conventional core diameter 190 has a minimum diameter 6.5 mm for 6
to 36 optical fibers. The diameter increases as the number of
optical fibers increases. A conventional optical cable 100
including 72 optical fibers has a conventional core diameter 190 of
7.4 mm. Similarly, a conventional optical cable 100 including 96
optical fibers has a conventional core diameter 190 of 9 mm.
[0028] The cable core 140 is covered by a multilayer inner sheath
142 in a radially outer position with respect to LSoH layer 154.
The multilayer inner sheath 142 has an aluminum foil 132, a high
density polyethylene (HDPE) layer 156, and a polyamide (PA) layer
158. The PA layer 158 is made of polyamide 12 (also referred to as
PA12). The multilayer inner sheath 142 has a conventional inner
sheath diameter 192 which is limited by the number of layers
included in multilayer inner sheath 142 as well as minimum
protection requirements. In order to protect the conventional
optical cable 100, the conventional inner sheath diameter 192
cannot be less than 6.9 mm.
[0029] An armor layer 146 is disposed on the multilayer inner
sheath 142. The armor layer 146 consists of one layer of galvanized
steel wires 136. An LSoH outer sheath 148 covers the armor layer
146. Conventional optical cable 100 has a conventional optical
cable diameter 199 which includes the LSoH outer sheath 148. Since
the cable core 140 is also included, the conventional optical cable
diameter 199 is subject to the same limitations as the conventional
core diameter 190. A conventional optical cable 100 with a total
number of optical fibers in the range of 6 to 36 optical fibers has
a conventional optical cable diameter 199 of 19.8 mm. A
conventional optical cable 100 with 72 optical fibers has a
conventional optical cable diameter 199 of 20.7 mm. Similarly, a
conventional optical cable 100 with 96 optical fibers has a
conventional optical cable diameter 199 of 22.3 mm.
[0030] FIG. 2 illustrates another conventional optical cable.
[0031] Referring to FIG. 2, a conventional optical cable 200 has a
central strength member 250. Fibers 210 are protected in gel-filled
loose tubes 252 stranded around the central strength member 250. A
moisture barrier 232 is made of aluminum copolymer tape that is
longitudinally folded around the loose tubes 252. A subunit jacket
256 made of high density polyethylene (HDPE) is arranged over the
moisture barrier 232. A polyamide jacket 258 is arranged around the
subunit jacket 256. An armor 246 consisting of steel wires, steel
wire braids, or corrugated steel tape is formed around the
polyamide jacket 258. A sheath 248 consisting of low smoke, zero
halogen, flame retardant material or PVC flame retardant and heat
and oil resistant material is formed around the armor 246.
[0032] The conventional optical cable 200 has a conventional
optical cable diameter 299 subject to the same limitations as the
optical core 240 in a manner similar to conventional optical cable
100. The conventional optical cable diameter 299 cannot be less
than 18.0 mm when the conventional optical cable 200 has a total
number of optical fibers in the range of 2 to 72 optical fibers. A
conventional optical cable 200 with 96 optical fibers has a
conventional optical cable diameter 299 of 19.6 mm. A conventional
optical cable 200 with 144 optical fibers has a conventional
optical cable diameter 299 of 23.4 mm.
[0033] Several disadvantages may be associated with conventional
optical cables. For example, conventional optical cables are
relatively thick. Both conventional optical cable 100 and
conventional optical cable 200 need to have a GFRP central strength
member which increases the diameter of the optical core and
consequently the diameter of the conventional optical cable. This
is because filler tubes containing no optical fibers are included
to maintain structural integrity of the cable even when fewer tubes
containing optical fibers are needed. Additionally, the multilayer
inner sheath of conventional optical cable 100 and conventional
optical cable 200 increases the total diameter of the cable.
[0034] Another disadvantage of conventional optical cables like
cable 100 is the use of mica tape to provide fire resistance. Mica
tape complicates manufacturing process flows by requiring that the
conventional optical cable be moved to another line to wind the
mica tape. The additional processing increases manufacturing costs
by increasing manufacturing time and requiring additional
machinery. Mica tape is formed by gluing mica flakes onto a glass
fiber substrate, and is therefore very fragile. Mica flakes easily
peel off during processing which disadvantageously pollutes the
working environment. In addition, mica tape is relatively expensive
which further increases costs. Cable 200, not comprising mica
tapes, is not suitable for maintaining circuit integrity under fire
according to IEC 60331-25 (1999).
[0035] Conventional optical cables also cannot meet all of the
protection requirements for certain harsh environments such as
those found in the oil and gas industry. For example, optical
cables designed for chemically challenging environments such as
mines and oil wells have to be simultaneously water resistant, fire
resistant, flame retardant, chemically resistant, mechanically
stable, and maintaining circuit integrity during a fire.
Conventional optical cables disadvantageously lack one or more
protection requirements so as to render them unsuitable for use in
these harsh environments such as in the oil and gas industry.
[0036] Furthermore, it may be desirable to provide electrical
connectivity in addition to optical connectivity within a single
cable. For example, electrical signals and/or power may be
transmitted concurrently within a single optical cable. Electrical
power may be advantageous to power remote machinery or sensors, for
example. However, conventional optical cables disadvantageously
only provide optical connectivity.
[0037] The inventors of the present application have found that
conventional optical cables fail to meet protection requirements
such as fire resistance and circuit integrity in the presence of
fire. Furthermore, the inventors of the present application have
found that conventional optical cables cannot be made thinner and
less expensive while still meeting the protection requirements for
harsh environments such as those found in the oil and gas industry.
The inventors of the present application also recognize an unmet
need in the industry of providing electrical signals and/or power
in addition to optical signals using a single cable suitable for
use in these harsh environments.
[0038] FIG. 3 illustrates an exemplary optical cable according to
the present disclosure including a single layer inner sheath
directly adjacent to a sealed metal tube containing a plurality of
optical fibers in accordance with an embodiment of the
invention.
[0039] Referring to FIG. 3, an optical cable 300 includes a
plurality of optical fibers 10 sealed within a metal tube 30. Any
conceivable number of optical fibers may be sealed within the metal
tube 30. In various embodiments, the number of optical fibers 10
within the metal tube 30 is less than 150. However, the number of
optical fibers 10 within the metal tube 30 may also equal or exceed
150. In one embodiment, the number of optical fibers 10 within the
metal tube 30 is 48. In another embodiment, the number of optical
fibers 10 within the metal tube 30 is 12. In still another
embodiment, the number of optical fibers 10 within the metal tube
30 is 96.
[0040] A fill material 20 may be included to fill empty space and
partially or completely immobilize the optical fibers 10 within the
metal tube 30. The fill material 20 may be configured to prevent
the propagation of moisture in a longitudinal direction along the
optical cable 300. For example, the fill material 20 may include a
waterblocking compound. The fill material may also include a
hydrogen scavenger. In various embodiments, the fill material 20
includes an absorbent material for absorbing moisture and water,
and includes a super absorbent powder in some embodiments. In other
embodiments, the fill material 20 includes a gel and is a
thixotropic gel in some embodiments. In various embodiments, the
fill material 20 is a flooding compound for preventing longitudinal
moisture propagation within the metal tube 30. Examples of
materials suitable as fill material according to the present
disclosure are hydrotreated heavy paraffines, hydrotreated neutral
C20-50 oils, and polydimethylsiloxane oils. Water-blocking yarns
bearing, for example polyacrylate and/or polyacrylamide powder, may
also or alternatively be used.
[0041] In various embodiments, the metal tube 30 may be welded or
extruded, if possible. The metal tube 30 may be of steel, for
example of stainless steel such as 304 or 304L stainless steel, or
316 or 316L stainless steel. The metal tube 30 may also be
implemented using other metals or metal alloys. In one alternative
embodiment, the metal tube 30 is elemental copper (Cu) and is a
welded copper tube in one embodiment. In other embodiments, the
metal tube 30 is a copper alloy and is a welded copper alloy tube
in one embodiment. In various embodiments, the metal tube 30 is
aluminum and is a welded aluminum tube in one embodiment.
Alternatively, metal tube 30 may be formed from extruded aluminum.
When the metal tube 30 is made of copper, copper alloy or aluminum,
it can also carry electric current, as requested by the specific
cable application.
[0042] The metal tube 30, fill material 20, and plurality of
optical fibers 10 comprise an optical core 40 of the optical cable
300. Although the plurality of optical fibers 10 may be partially
or completely immobilized by the fill material 20, the
configuration as illustrated in FIG. 3 may be referred to as a
loose tube core configuration. A possible advantage of this
configuration is that the metal tube 30 may provide mechanical
stability so that a central strength member is unnecessary. Since
the metal tube 30 is sealed by welding or extrusion, it may also
function to prevent water ingress into the optical core 40.
Specifically, the metal tube 30 may prevent radial water
penetration into optical core 40.
[0043] Still referring to FIG. 3, the optical cable 300 further
includes an inner sheath 42 surrounding the metal tube 30. In
various embodiments, the inner sheath 42 is formed from a single
layer of homogeneous polymer material and is a polyamide material
in some embodiments. In other embodiments, inner sheath 42 may
include two or more layers. Inner sheath 42 may also be implemented
using other materials such as polyethylene (PE), as an example.
Inner sheath 42 may be configured to protect optical core 40 from
harsh chemicals. A possible advantage of inner sheath 42 is that
sufficient protection from chemicals such as oil, fuel, toluene,
water, and others may be obtained using a single layer of material.
Consequently, inner sheath 42 may advantageously be thinner, less
expensive, and simpler to fabricate than conventional layers
configured to protect an optical core.
[0044] When made of polyamide, the inner sheath of the cable of the
disclosure was found to be resistant to chemicals such as sodium
hydroxide at room temperature, toluene at 50.degree. C., benzene at
50.degree. C., diesel fuel at 50.degree. C., ASTM reference oil 902
at 75.degree. C. and 100.degree. C., ASTM reference oil 903 at
100.degree. C. and 140.degree. C., the inner sheath being tested
according to IEC 60811-2-1 (2001).
[0045] In one embodiment, inner sheath 42 is implemented using a
single homogeneous layer of nylon 6 (also referred to as PA6).
Specifically, nylon 6 has the chemical formula
[NH--(CH.sub.2).sub.5--CO].sub.n as a repeated unit. For example,
as described below, the inventors have found that nylon 6 may be
used to form inner sheath 42 in order to advantageously provide
chemical protection while minimizing the thickness of inner sheath
42. In another embodiment, inner sheath 42 is implemented using a
single homogeneous layer of nylon 12 (also referred to as PA12).
Specifically, nylon 12 has the chemical formula
[NH--(CH.sub.2).sub.11--CO].sub.n as a repeated unit. Other types
of nylon may also be used for inner sheath 42 such as nylon 6,6.
Similarly, other polyamide materials may also be used for inner
sheath 42. In some applications, other materials such as other
polymer materials may also be included in inner sheath 42.
[0046] An optional adhesion layer 26 may be disposed between the
metal tube 30 and the inner sheath 42. The adhesion layer 26 may be
configured to facilitate bonding of the inner sheath 42 directly to
the metal tube 30. The adhesion layer 26 may also be configured to
act as a primer by preparing the outer surface of the metal tube 30
to be bonded to the inner sheath 42. In various embodiments, the
adhesion layer 26 completely fills the space between metal tube 30
and inner sheath 42. As a result, adhesion layer 26 may also
function to prevent or reduce longitudinal water penetration.
Suitable adhesives for the cables of the present disclosure are
based, for example, on polyamide or polyethylene, optionally
admixed with acrylic acid or acrylate polymers.
[0047] Optical cable 300 also includes an armor layer 46
surrounding the inner sheath 42. The armor layer 46 includes a
metal in various embodiments. In one embodiment, armor layer 46 is
a single layer of armor. Implementing armor layer 46 as a single
layer of armor may advantageously enable a smaller overall diameter
of optical cable 300. Armor layer 46 may be implemented using a
plurality of round wires 34. In some embodiments, armor layer 46
includes stainless steel and in one embodiment is implemented using
round galvanized steel wires (SWA) wound in a closed helix around
inner sheath 42. Alternatively, armor layer 46 may comprise other
types of metal such as steel phosphate, stainless steel, aluminum
clad steel, elemental copper (Cu), elemental aluminum (Al), metal
alloys, and the like.
[0048] The shape of the elementary components of armor layer 46 is
not limited to round wires. Armor layer 46 may also be implemented
using corrugated tape, trapezoidal wires, or flat wires. Further,
armor layer 46 may also be implemented using dielectric strength
members such as round glass strength members or flat glass strength
members or round aramid wires. Armor layer 46 may also include
additional layers.
[0049] Referring again to FIG. 3, the optical cable 300 further
includes an outer sheath 48 around the armor layer 46. The outer
sheath 48 may be advantageously configured to provide substantial
fire resistance and flame retardancy. The outer sheath 48 may also
advantageously be heat, oil, and UV resistant. The outer sheath 48
may optionally produce low smoke and zero halogens in the presence
of fire. In some embodiments, the outer sheath 48 is implemented
using an LSoH material as described, for example, in U.S. Pat. No.
6,552,112 which is incorporated herein by reference in its
entirety. Specifically, the LSoH material may comprise, for
example, (a) a crystalline propylene homopolymer or copolymer; (b)
a copolymer of ethylene with at least one alpha-olefin, and
optionally with a diene; and (c) natural magnesium hydroxide in an
amount such as to impart flame-retardant properties. In other
embodiments, the outer sheath 48 maybe implemented using a PVC
material or an HDPE material.
[0050] Several representative dimensions of the optical cable 300
are shown in FIG. 3. The optical core 40, which includes the metal
tube 30, the plurality of optical fibers 10, and optionally the
fill material 20, has a first optical core diameter 90. The first
optical core diameter 90 may depend on the number of optical fibers
10 contained within. First optical core diameter 90 may further
depend on the thickness of metal tube 30 as well as the presence of
additional structural and organizational components included to
arrange the plurality of optical fibers 10. For example, the
thickness of metal tube 30 may be between 0.1 mm and 0.5 mm and is
0.4 mm in one embodiment. A possible benefit of the metal tube 30
including loose packed optical fibers 10 is that the first optical
core diameter 90 is decreased in comparison to conventional optical
cores because of reasons described below in more detail.
[0051] In various embodiments, the first optical core diameter 90
is between 1.5 mm and 5.5 mm. In one embodiment, the first optical
core diameter 90 is about 2 mm. As a specific example, an optical
core 40 including 12 optical fibers may have a first optical core
diameter 90 of 2 mm. In other embodiments, the first optical core
diameter 90 is about 3.5 mm. As a specific example, an optical core
40 including 13 to 48 optical fibers may have a first optical core
diameter 90 of 3.5 mm. In still other embodiments, the first
optical core diameter 90 is about 4.8 mm. As a specific example, an
optical core 40 including 49 to 96 optical fibers may have a first
optical core diameter 90 of 4.8 mm. Other combinations of optical
core diameters and numbers of optical fibers are possible. The
first optical core diameter 90 may generally increase as the number
of optical fibers increases, but this is not necessarily true in
all cases.
[0052] In contrast to conventional optical cables designed to be
fire resistant and maintain circuit integrity in the presence of
fire, optical cable 300 may not include any fire resistant layer
other than metal tube 30 around the optical core 40. For example,
conventional optical cables typically utilize a fire resistant tape
such as mica tape to achieve the requirements of fire resistant
circuit integrity standards such as International Electrotechnical
Commission (IEC) 60331-25 (1999). Conventional cables that do not
employ some type of heat resistant tape do not pass the IEC
60331-25 (1999) standard.
[0053] The inventors of the present application have found that a
metal tube such as the metal tube 30 provides sufficient protection
for the optical fibers to maintain circuit integrity during a fire.
Specifically, the inventors have conducted circuit integrity tests
on cables comprising stainless steel tubes containing unbuffered
optical fibers with good results. The cable of the present
disclosure successfully passed the circuit integrity tests at
750.degree. C. for 90 min and at 1000.degree. C. for 180 min
according to IE C 60331-25 (1999) and at 830.degree. C. for 120 min
under impacts according to CEI EN50200 (2015). This finding may be
counterintuitive based on known methods and configurations because
the optical fibers may be expected to become overheated because of
the high thermal conductivity of most metals. Advantageously, using
a metal tube containing loose optical fibers may decrease the
optical core diameter of embodiment optical and hybrid cables while
still maintaining high levels of fire resistance and circuit
integrity in the presence of fire.
[0054] The inner sheath 42 has a first inner sheath thickness 92.
In various embodiments, the first inner sheath thickness 92 is
between 0.4 mm and 3 mm and may range from about 0.3 mm to about
1.5 mm is some embodiments. In one embodiment, the first inner
sheath thickness 92 is about 0.5 mm. As a specific example, an
inner sheath 42 implemented using a homogeneous PA material such as
nylon 6 may have a first inner sheath thickness 92 of about 0.5 mm.
In another embodiment, the first inner sheath thickness 92 is about
1.3 mm. As a specific example, an inner sheath 42 implemented using
a homogeneous PE material may have a first inner sheath thickness
92 of about 1.3 mm. It should be noted that while the thickness of
the adhesion layer 26 is nonzero it may be made very thin (having a
thickness equal to or lower than 0.2 mm) so as to be much smaller
than the first optical core diameter 90 and the first inner sheath
thickness 92.
[0055] The thickness of the inner sheath 42 may advantageously be
made thin in comparison to conventional inner sheath thicknesses.
For example, conventional inner sheaths may include multiple layers
which increase the thickness of the inner sheath. Conventional
inner sheaths used for chemical resistance may employ composite
layers made of a PE layer, an aluminum layer, and a PA layer
altogether. Other conventional inner sheaths may be made very thick
in order to use certain materials which may have reduced
effectiveness when made thin, especially when used in harsh
environments, such as environments where high chemical resistance
is important.
[0056] The inventors of the present application have found that a
single layer of appropriate thickness may be used for the inner
sheath 42 of optical cable 300 while still maintaining a high level
of chemical resistance. For example, the inventors have exposed PE,
nylon 6, and nylon 12 to various compounds such as water, oil (IRM
902), fuel (IRM 903), and toluene at various temperatures, as
already mentioned above. The inventors have determined, among other
results, that a relatively thin layer of polyamide, for example
nylon 6 or nylon 12, may be used to protect a metal tube in harsh
chemical environments. For example, the thin layer of nylon 6 may
range from a thickness of about 0.3 mm to about 1.0 mm. Based on
the test results, an inner sheath implemented using a homogeneous
PE layer is less efficient in providing protection in harsh
chemical environments, particularly environments where oil and gas
are present.
[0057] Still referring to FIG. 3, the armor layer 46 of optical
cable 300 has an armor layer thickness 96. The armor layer
thickness 96 may be dependent on the mechanical requirements of a
given application. In cases where armor layer 46 is implemented
using a single layer of round wires 34, the diameter of the round
wires 34 may determine the value of armor layer thickness 96. In
various embodiments, the armor layer thickness 96 is between about
0.5 mm and about 3.6 mm. In one embodiment, the armor layer
thickness 96 is about 1.0 mm. For certain applications where very
high mechanical strength is desired, armor layer 46 may be
implemented using multiple layers. Armor layer thickness 96 may
exceed 3.6 mm for certain applications.
[0058] The outer sheath 48 has an outer sheath thickness 97. The
outer sheath thickness 97 may depend on various desired protection
levels such as chemical resistance, heat resistance, flame
retardancy, circuit integrity, mechanical stability, and others.
The outer sheath thickness 97 is between about 1.0 mm and about 5.0
mm in various embodiments. In one embodiment, the outer sheath
thickness 97 is 2.2 mm. In another embodiment, the outer sheath
thickness 97 is about 3.0 mm.
[0059] The optical cable 300 has a first optical cable diameter 399
which depends on the combination of first optical core diameter 90,
first inner sheath thickness 92, armor layer thickness 96, and
outer sheath thickness 97. In various embodiments, the first
optical cable diameter 399 is between 5 mm and 25 mm and ranges
from about 5.6 mm to about 21 mm in some embodiments. In one
embodiment, the first optical cable diameter 399 is about 12.5 mm
for an optical cable 300 including 48 optical fibers.
[0060] Since the first optical cable diameter 399 is often
primarily dependent on the number of optical fibers 10, it may be
useful to consider the ratio of the number of included optical
fibers to the optical cable diameter. For example, in the preceding
example of a first optical cable diameter 399 of 12.5 mm for an
optical cable 300 including 48 optical fibers, the fiber/diameter
ratio is about 3.84 fibers/mm. In general, a higher fiber/diameter
ratio indicates a smaller cable and may be desirable in
applications for the space devoted to cabling is limited. A table
listing various exemplary optical cable diameters and corresponding
numbers of optical fibers is shown below in Table I.
[0061] The first optical cable diameter 399 may be much thinner for
a given number of optical fibers 10 than conventional optical
cables. In the above example, an optical cable including 48 optical
fibers has a fiber/diameter ratio of about 3.84 fibers/mm.
Conventional optical cables have a fiber/diameter ratio that is
much lower. For example, as previously described in reference to
FIG. 1, a conventional optical cable including 36 optical fibers
typically has a fiber/diameter ratio of 1.81 fibers/mm. In
contrast, embodiments of the present can achieve fiber/diameter
ratio greater than 3 fibers/mm and between about 3 fibers/mm to
about 8 fibers/mm.
[0062] A further advantage of the cable of the present disclosure
may be the amount of organic materials contained therein, such
amount being largely reduced as compared with a conventional cable.
Consequently, the smoke performance and the flame performance may
be significantly improved. As a specific example, a cable of the
present disclosure has been made that has a transmittivity >90%
(98% with a 48 optical fiber cable, and 95% with a 96 optical fiber
cable, both having a LSoH outer layer) under smoke test according
to IEC 61034-2 (2005), and has successfully passed flame
propagation tests according to IEC 60332-1-2 (2004), IEC 60332-3-24
(2000) Cat C, and 60332-3-22 (2009) Cat A.
[0063] A cable according to the present disclosure, containing up
to 96 optical fibers and having an LSoH outer layer has been
classified B2ca-s1a,d2,a1 CPR Class according to Commission
Delegated Regulation (EU) 2016/364 of 1 Jul. 2015.
[0064] FIG. 4 illustrates an exemplary optical cable including a
single layer inner sheath directly adjacent to a sealed metal tube
containing two or more fiber tubes each containing a plurality of
optical fibers in accordance with an embodiment of the
invention.
[0065] Referring to FIG. 4, an optical cable 400 includes an
optical core 41, an inner sheath 42, an armor layer 46, and an
outer sheath 48. The optical cable 400 may be similar to optical
cable 300 as previously described in reference to FIG. 3 except for
the inclusion of optical core 41 which includes a multiple set of
optical fibers contained within fiber tubes 18. Similarly labeled
elements may be as previously described and will not be described
here in the interest of brevity.
[0066] The optical core 41 may include any number of fiber tubes
18, each containing a set of optical fibers 10. The fiber tubes 18
may comprise a polymer material. In various embodiments, the fiber
tubes 18 include a polyester material and are implemented using a
thermoplastic polyester material in one embodiment. The fiber tubes
18 may be configured to organize the optical fibers 10 within the
optical core 41. The fiber tubes 18 may also provide additional
mechanical stability and confine an optional fiber tube filler
material 21. The fiber tube filler material 21 may be a gel
material similar to fill material 20, for example. In the cable
configuration of FIG. 4, a silicone based fiber tube filler
material 21 can be employed.
[0067] Respective sets of optical fibers 10 may be the same or
different from other sets of optical fibers 10. A set of optical
fibers 10 may be a single optical fiber 10 in some embodiments.
There is not theoretical limit to the quantity of optical fibers 10
in a set of optical fibers. However, practical considerations may
limit the number of optical fibers 10 in a single fiber tube 18. As
illustrated in FIG. 4, optical core 41 may include three fiber
tubes 18 containing first, second, and third sets of optical fibers
11, 12, 13. In one embodiment, each of the sets of optical fibers
11, 12, 13 consists of twelve optical fibers 10. In other
embodiments, some or all of the sets of optical fibers 11, 12, 13
consist of more or less than twelve optical fibers 10.
[0068] The optical core 41 has a second optical core diameter 91
which may be similar or different from the first optical core
diameter 90 of optical cable 300. For example, due to the addition
of fiber tubes 18, the second optical core diameter 91 may be
larger than first optical core diameter 90 for a given number of
optical fibers 10, but this is not necessarily true for all cases.
As a result, the second optical cable diameter 499 of optical cable
400 may be larger than the first optical cable diameter 399 of
optical cable 300 for a given number of optical fibers 10, but
again, this is merely a general guideline rather than a strict
requirement.
[0069] FIG. 5 illustrates an exemplary hybrid cable including a
single layer inner sheath directly adjacent to a sealed metal tube
containing a plurality of optical fibers as well as an electrically
conductive layer in accordance with an embodiment of the
invention.
[0070] Referring to FIG. 5, a hybrid cable 500 includes an optical
core 40, a hybrid inner sheath 43, an armor layer 46, and an outer
sheath 48. The hybrid cable 500 may be similar to embodiment
optical cables such as optical cable 300 as previously described in
reference to FIG. 3 except that hybrid cable 500 includes a
conductive layer 44 disposed between a hybrid inner sheath 43, made
of PA or PE, and an intermediate sheath 45, made of PE or
ceramifying silicone rubber, insulating the conductive layer 44
from the armor layer 46. Similarly labeled elements may be as
previously described and will not be described here in the interest
of brevity.
[0071] The hybrid cable 500 may be configured to feed electrical
signals and/or power using conductive layer 44. The electrical
signals and/or power may be either direct current (DC) or
alternating current (AC). For example, the hybrid cable 500 may
carry direct current (DC) at 48V at most, and alternate current
(AC) at 380V at most, thus qualifying as a low voltage cable. In
some cases, the armor layer 46 may be grounded and utilized as a
return path for a power feeding system using hybrid cable 500. In
various embodiments, conductive layer 44 is implemented using a
plurality of electrically conductive wires 38.
[0072] In some embodiments, the electrically conductive wires 38
have a round, solid cross-section. In one embodiment, the
electrically conductive wires 38 are implemented using elemental
copper (Cu). In another embodiment, the electrically conductive
wires 38 are implemented using elemental aluminum (Al). The
material composition of electrically conductive wires 38 is not
limited to elemental metals and may also be formed from metal
alloys, and the like.
[0073] The hybrid inner sheath 43 may be similar to inner sheath 42
as previously described. Alternatively, hybrid inner sheath 43 may
be different to account for electrical considerations of conductive
layer 44. The thickness and material composition of optical core 41
may be dependent on electrical isolation requirements of the
optical core 41. For example, conventional hybrid cables may
utilize multilayered inner sheaths or thick homogeneous PE layers
to provide electrical isolation between a conventional conductive
layer and a conventional optical core.
[0074] Therefore, it may not be immediately apparent to one of
ordinary skill in the art whether a thin single layer inner sheath
implemented using a material other than a PE material will be
sufficient to provide the require electrical isolation. The
inventors of the present application have performed tests to verify
that thin single layer inner sheaths implemented using alternative
materials such as polyamide (PA) materials provide sufficient
electrical isolation between an optical core and a conductive
layer. In one embodiment, the hybrid inner sheath 43 comprises
nylon 6. A possible benefit of hybrid cable 500 is that hybrid
inner sheath 43 may be made thinner than conventional inner sheaths
as provided by CEI EN 50363-0 (2006) while still maintaining
electrical isolation of conductive layer 44. The thickness of this
layer depends on the level of isolation required by the specific
current transported. As an example, for a 12 or 24V DC, a 0.5
mm-thick inner sheath 43 shall be sufficient.
[0075] In various embodiments, intermediate sheath 45 comprises a
PE material such as HDPE. In other embodiments, especially when
fire resistance is sought, intermediate sheath 45 may comprises a
PE material and fiber glass or mica tape(s), or fiber glass or mica
tape(s) alone, or a ceramifying silicone rubber
[0076] In addition to similarly labeled dimensions which may be as
previously described, hybrid cable 500 includes a second inner
sheath thickness 93, a conductive layer thickness 94, and an
intermediate sheath thickness 95. The second inner sheath thickness
93 may be similar to the first inner sheath thickness 92 as
previously described with the added possible consideration of
electrical isolation between the optical core 40 and conductive
layer 44. The intermediate sheath thickness 95 may be similar to
the previously described second inner sheath thickness 93. However,
there is no strict requirement that the intermediate sheath
thickness 95 be the same, greater than, or less than second inner
sheath thickness 93 for a given application.
[0077] In various embodiments, the conductive layer thickness 94 is
between 0.5 mm and 6 mm and ranges from about 0.6 mm to 3.6 mm in
some embodiments. For example, the full range conductors may be
used from 85 mm.sup.2 (AWG 3/0) to 2.08 mm.sup.2 (AWG 14). In one
embodiment, the conductive layer thickness 94 is about 0.6 mm. In
another embodiment, the conductive layer thickness 94 is about 1
mm. For example, if conductive layer 44 is implemented using 20
copper (Cu) wires with a 1 mm diameter, the copper cross-sectional
area may be about 15 mm.sup.2.
[0078] It should be noted the material composition of conductive
layer 44 may impact the required cross-sectional area of conductive
layer 44. For example, a conductive layer 44 that is implemented
using aluminum may require aluminum wires that have a diameter
about 1.65 times larger than an electrically equivalent conductive
layer 44 implemented using copper wires.
[0079] The hybrid cable 500 has a first hybrid cable diameter 599
which depends on the combination of first optical core diameter 90,
second inner sheath thickness 93, conductive layer thickness 94,
intermediate sheath thickness 95, armor layer thickness 96, and
outer sheath thickness 97. In various embodiments, the first hybrid
cable diameter 599 is between 7 mm and 35 mm and ranges from about
7.4 mm to about 31.2 mm in some embodiments. In one embodiment, the
first hybrid cable diameter 599 is about 15.5 mm for a hybrid cable
500 including 48 optical fibers.
[0080] As with previous embodiment optical cables, the first hybrid
cable diameter 599 of hybrid cable 500 may be significantly smaller
than conventional hybrid cable diameters. Similarly, hybrid cable
500 may be uniquely suitable for harsh environments and may meet a
large number of protection standards.
[0081] FIG. 6 illustrates an exemplary hybrid cable including a
single layer inner sheath directly adjacent to a sealed metal tube
containing two or more fiber tubes each containing a plurality of
optical fibers as well as an electrically conductive layer in
accordance with an embodiment of the invention.
[0082] Referring to FIG. 6, a hybrid cable 600 includes an optical
core 41, a hybrid inner sheath 43, a conductive layer 44, an
intermediate sheath 45, an armor layer 46, and an outer sheath 48.
The hybrid cable 600 may be similar to hybrid cable 500 as
previously described in reference to FIG. 5 except for the
inclusion of an optical core 41 which includes multiple sets of
optical fibers contained within fiber tubes 18. The optical core 41
of hybrid cable 600 may be as previously described, such as in
reference to FIG. 4, for example. Similarly labeled elements may be
as previously described and will not be described here in the
interest of brevity.
[0083] As before, the second optical core diameter 91 may be
similar or different from the first optical core diameter 90 of
hybrid cable 500, for example. As a result, the second hybrid cable
diameter 699 of hybrid cable 600 may be larger than the first
hybrid cable diameter 599 of hybrid cable 500 for a given number of
optical fibers 10. As previously described, this is merely a
general guideline rather than a strict requirement.
[0084] It should be noted that in some embodiment cables, the armor
layer may advantageously have a decreased thickness or be removed
entirely because of the metal tube of the optical core. For
example, a metal tube of sufficient thickness may improve the
structural properties of the optical core so that a thinner armor
layer or no armor layer may be used to achieve the same overall
properties. This may beneficially result in a reduction of the
overall thickness of embodiment cables while maintaining desirable
structural properties and levels of fire, water, and chemical
protection when compared to conventional cables.
[0085] FIG. 7 illustrates an exemplary method of fabricating an
optical cable in accordance with an embodiment of the invention.
The method 700 may be used to fabricate any of the optical cables
or hybrid cables described herein. For example, method 700 may be
used to fabricate embodiment optical cables as described in
reference to FIG. 3 such as optical cable 300. The following steps
of method 700 may be performed in any order and are not intended to
be exhaustive. Additional steps may be added to method 700 and one
or more steps may be removed from method 700 as may be apparent to
one of ordinary skill in the art. The steps of method 700 are not
necessarily performed sequentially and any number of steps of
method 700 may be performed concurrently.
[0086] Step 701 of fabricating the optical cable includes providing
a plurality of optical fibers which are then sealed within a metal
tube in step 702. The spaces in the metal tube between optical
fibers are optionally filled for a fill material in step 703. The
fill material may be applied before, during, or after step 702. In
one embodiment, steps 702 and 703 are performed concurrently.
[0087] The method 700 of fabricating the optical cable further
includes an optional step 704 of applying an adhesion layer over
the outer surface of the metal tube. For example, the adhesion
layer may be a primer that prepares the outer surface of the metal
tube for direct bonding with a subsequent layer. The outer surface
of the metal tube is a major outer surface of the metal tube and
the adhesion layer may be applied so that the major outer surface
is substantially entirely covered by the adhesion layer and a
subsequent bonded layer such as an inner sheath.
[0088] Step 705 of fabricating the optical cable includes forming
an inner sheath over the adhesion layer and the outer surface of
the metal tube. If step 704 is omitted, then step 705 includes
forming the inner sheath over only the outer surface of the metal
tube. The inner sheath may be formed using an extrusion process. If
the inner sheath is a multilayer inner sheath, then a co-extrusion
process may be used. If the inner sheath comprises a mixture of
materials then a compound extrusion process may be used.
[0089] Step 706 of fabricating the optical cable includes forming
an armor layer over the inner sheath. The armor layer may be formed
by winding a plurality of strength components in to form closed
helix around the inner sheath. As previously described, the
strength components may be round metal wires, trapezoidal metal
wires, polymer wires, dielectric rods, and the like. Alternatively,
the armor layer may be formed from corrugated metal tape which may
be applied longitudinally. In some embodiments, the armor layer
comprises multiple layers is formed in several steps.
[0090] The method 700 of fabricating the optical cable further
includes an optional step 707 of filling the voids in the armor
layer with a fill material. Step 708 includes forming an outer
sheath over the armor layer and the armor fill material if optional
step 707 is included. The outer sheath may be formed using an
extrusion process. Similar to step 705, the outer sheath may also
be formed using a coextrusion or compound extrusion process where
applicable.
[0091] FIG. 8 illustrates another exemplary method of fabricating
an optical in accordance with an embodiment of the invention. The
method 800 may be used to fabricate any of the optical cables or
hybrid cables described herein. For example, method 800 may be used
to fabricate embodiment optical cables as described in reference to
FIG. 4 such as optical cable 400. The following steps of method 800
may be performed in any order and are not intended to be
exhaustive. Additional steps may be added to method 800 and one or
more steps may be removed from method 800 as may be apparent to one
of ordinary skill in the art. The steps of method 800 are not
necessarily performed sequentially and any number of steps of
method 800 may be performed concurrently.
[0092] Step 801 of fabricating the optical cable includes providing
a plurality of sets of optical fibers when are then sealed in
respective fiber tubes in step 802. The spaces between optical
fibers in each of the fiber tubes may optionally be filled with a
fiber tube fill material in step 803. The fiber tubes may be formed
using an extrusion process. Steps 802 and 803 may be performed
concurrently in some embodiments. In one embodiment, steps 802 and
803 are performed concurrently using a co-extrusion process.
[0093] Step 804 of fabricating the optical fiber includes sealing
the fiber tubes within a metal tube. An optional step 805 includes
filling the spaces between fiber tubes with a fill material. As
with steps 702 and 703 of method 700, steps 804 and 804 may be
performed in any order and are performed concurrently in one
embodiment. The remaining steps of method 800 mirror steps 704-708
of method 700.
[0094] FIG. 9 illustrates an exemplary method of fabricating a
hybrid cable in accordance with an embodiment of the invention. The
method 900 may be used to fabricate any of the hybrid cables
described herein. For example, method 900 may be used to fabricate
embodiment hybrid cables as described in reference to FIGS. 5 and 6
such as hybrid cable 500 and hybrid cable 600. The following steps
of method 900 may be performed in any order and are not intended to
be exhaustive. Additional steps may be added to method 900 and one
or more steps may be removed from method 900 as may be apparent to
one of ordinary skill in the art. The steps of method 900 are not
necessarily performed sequentially and any number of steps of
method 900 may be performed concurrently.
[0095] The first steps of method 900 mirror steps 701-705 of method
700. Alternatively, steps 801-805 of method 800 may be performed
followed by steps 704 and 705 of method 700. Step 905 is performed
after performing step 705 in either case and includes forming a
conductive layer over the inner sheath. The conductive layer may be
formed in a manner similar to the armor layer as previously
described. An optional step 907 includes filling the voids in the
conductive layer with a fill material.
[0096] Step 908 of forming the hybrid cable includes forming an
intermediate sheath over the conductive layer. The intermediate
sheath may be formed in a manner similar to the inner sheath as
previously described. Step 909 includes forming an armor layer over
the intermediate sheath and is similar in concept to step 706 of
method 700 except that the armor layer is being formed over a
different sheath. The remaining steps of method 900 mirror steps
707-708 of method 700.
[0097] Table I in the following summarizes several cable diameters
and fiber/diameter ratios which may be associated with a specific
number of included optical fibers. For example, as described in the
above embodiments, some variation in the chosen thicknesses of each
of the layers is possible due to specific design considerations.
Table I summarizes possible ranges of diameters (and consequently
fiber/diameter ratios) corresponding to the number of included
optical fibers. The values presented in Table I represent several
exemplary configurations of embodiment optical cables and
embodiment hybrid cables. However, the given values are not
intended to be limiting as it is conceivable that the values may be
outside of these ranges in practice.
TABLE-US-00001 TABLE I Possible Diameters Possible Fiber/Diameter
Ratios Type No. of Fibers Min. Max. Max. Min. Optical 12 5.6 mm
18.2 mm 2.14 fibers/mm 0.66 fibers/mm 13 to 48 7.1 mm 19.7 mm 6.76
fibers/mm 0.66 fibers/mm 49 to 96 8.4 mm 21.0 mm 11.43 fibers/mm
2.33 fibers/mm Hybrid 12 7.4 mm 28.4 mm 1.62 fibers/mm 0.42
fibers/mm 13 to 48 8.9 mm 29.9 mm 5.39 fibers/mm 0.43 fibers/mm 49
to 96 10.2 mm 31.2 mm 9.41 fibers/mm 1.57 fibers/mm
[0098] It should also be noted that, although embodiment cables
advantageously provide increased fiber/diameter ratios over
conventional cables, some of the possible fiber diameter ratios
shown in table 1101 are lower than those of a conventional cable.
For some particularly demanding applications, the thicknesses of
the various layers of embodiment cables may be increased in order
to improve protection and/or structural properties of the cable
which may in turn result in a lower fiber/diameter ratio.
Therefore, in these demanding applications, embodiment cables may
not be thinner than conventional cables, but may provide improved
properties over conventional cables.
[0099] Example embodiments of the invention are summarized here.
Other embodiments can also be understood from the entirety of the
specification as well as the claims filed herein.
[0100] While this invention has been described with reference to
illustrative embodiments, this description is not intended to be
construed in a limiting sense. Various modifications and
combinations of the illustrative embodiments, as well as other
embodiments of the invention, will be apparent to persons skilled
in the art upon reference to the description. It is therefore
intended that the appended claims encompass any such modifications
or embodiments.
* * * * *