Composite fiber optic cable

A composite cable for use in indoor or indoor/outdoor applications having a fiber optic core section includes at least one optical fiber. The composite cable includes a conductor and water blocking section, the conductor and water blocking section having a set of conductors providing mechanical strength and flame inhibiting characteristics to the composite cable. At least one interstice of the composite cable includes a water blocking member therein. An armor layer surrounds the conductor and water blocking section, and the armor layer is surrounded by a cable jacket with an interfacial zone defined therebetween. The interfacial zone includes a controlled bond layer so that during flame tests, as the jacket burns and forms a char barrier around the tape layer, the controlled bond layer supports the char barrier relative to the armor tape, thereby protecting the tape from flames and inhibiting the propagation of flame along the cable.

The present invention relates to a composite cable that combines the high 
bit-rate capacity of optical fiber conductors with the power/data 
transmitting capacity of electrical conductors, and meets flame, 
mechanical, and environmental cable performance standards allowing the 
cable to be used for indoor or indoor/outdoor applications. 
BACKGROUND OF THE INVENTION 
Conventional fiber optic cables comprise optical fibers that are used to 
transmit voice, video, and data information. Fiber optic cables may be 
required to meet mechanical and environmental tests, for example, as 
defined in Bellcore GR-409-Core, Issue 1, published May, 1994, and 
incorporated by reference herein. The mechanical tests of Bellcore 
GR-409-Core include, for example, tensile strength, compression 
resistance, cycle flex, and impact tests. In addition, the mechanical 
tests of Bellcore GR-409-Core include, for example, temperature cycling 
and cable aging. Fiber optic cables not able to withstand the rigors of 
the foregoing tests may be rejected by customers for certain applications. 
An example of a fiber optic cable that meets Bellcore GR-409-Core is 
disclosed in U.S. Pat. No. 5627932 assigned to the assignee hereof. In 
addition, fiber optic cables may be required to meet Bellcore GR-20-Core, 
which sets forth water penetration standards for optical cables intended 
for outdoor applications. 
Indoor fiber optic cables have been developed for installation in plenums 
and risers, and/or ducts of buildings. In order for a fiber optic cable to 
be rated for riser or plenum use, the cable must meet flame retardance 
standards as determined by means of vertical or horizontal flame tests. 
Exemplary requirements for such tests have been established by 
Underwriters Laboratories (UL). Since riser cables are typically installed 
in vertical shafts, the relevant standard for riser rated fiber optic 
cables is embodied in UL 1666, a flame test in a vertical shaft without a 
forced air draft in the shaft. UL 1666 does not include a smoke evolution 
requirement. UL has promulgated the riser rating requirements in a 
document entitled "Test for Flame Propagation Height of Electrical and 
Optical-Fiber Cables Installed Vertically in Shafts", wherein values for 
flame propagation height are set forth. Examples of riser rated fiber 
optic cables are disclosed in U.S. Pat. No. 5748823 and EP-A1-0410621. 
The relevant standard for plenum rated fiber optic cables is embodied in UL 
910, a horizontal flame test setting forth flame propagation and smoke 
evolution requirements. In the construction of many buildings, a plenum 
can include, for example, a space between a drop ceiling and a structural 
floor above the drop ceiling. A plenum typically serves as a conduit for 
forced air in an air handling system, and the plenum is oftentimes a 
convenient location for the installation of fiber optic cables. If, in the 
event of a fire, the fire reaches the plenum area, flames that would 
otherwise rapidly propagate along non-plenum rated cables are retarded by 
plenum rated cables. Moreover, plenum rated cables are designed to evolve 
limited amounts of smoke. Riser rated cables tested to UL 1666 
specifications typically do not exhibit acceptable flame spread and smoke 
evolution results and may be therefore unsuitable for plenum use. 
The UL 910 test is promulgated by UL in a document entitled: "Test for 
Flame Propagation and Smoke-Density Values for Electrical and 
Optical-Fiber Cables Used in Spaces Transporting Environmental Air". A key 
feature of the UL 910 test is the Steiner Tunnel test (horizontal forced 
air draft) as modified for communications cables. During the UL 910 test, 
flame spread values are observed for a predetermined time (20 minutes 
under the current standard), and smoke is measured by a photocell in an 
exhaust duct. Data from the photocell measurements are used to calculate 
peak and average optical density values. Specifically, according to UL 
910, the measured flame spread must not exceed five feet, peak smoke 
(optical) density must not exceed 0.5, and average smoke (optical) density 
must not exceed 0.15. In general, for UL 1666, the measured flame spread 
must not exceed 12 ft. or 850.degree. F. 
In order to meet the foregoing standards, various cable materials used in 
riser or plenum cables for the prevention, inhibition, and/or 
extinguishment of flame, may fall into two general categories. The first 
category includes inherently non-flammable, flame-resistant materials that 
are thermally stable, and may have high decomposition temperatures, for 
example, certain metals or high temperature rated plastics. The materials 
included in this first category can be useful as thermal/heat/flame 
barriers. Thermal/heat/flame barriers may have disadvantages, however, as 
they can be generally expensive and, because of limited burn-performance 
characteristics, they may be limited to a narrow range of applications. 
The second general category of materials used for the prevention, 
inhibition, and/or extinguishment of flame includes inherently flammable 
materials that have been chemically altered to include flame retardant 
additives. Such additives actively interfere with the chemical reactions 
associated with combustion. Examples of inherently flammable materials are 
polyethylene, polypropylene, polystyrene, polyesters, polyurethanes, and 
epoxy resins. Typical flame retardant additives include aluminum 
trihydrate, metal hydroxides, brominated and chlorinated organic 
compounds, and phosphate compounds. 
By comparison, thermal/heat/flame barriers typically do not include flame 
retardant additives, but rather are relied upon in flame protection 
designs for their resistance to decomposition at high temperatures, or 
their inherent heat dissipation properties. An example of a fiber optic 
cable that requires a thermal barrier, and is designed for use in plenum 
applications, is disclosed in U.S. Pat. No. 4941729, and is incorporated 
by reference herein. 
Exemplary known composite cables may not meet flame, water penetration, 
mechanical, and/or environmental cable performance standards, and may not 
be suitable for all indoor or indoor/outdoor applications. For example, 
U.S. Pat. No. 5544270 discloses a composite cable having multiple twisted 
pairs of electrical conductors in combination with optical fiber 
conductors. The cable has interstices between the twisted pair conductors 
and optical fiber conductors and, as none of the interstices include water 
blocking components, the cable may not meet water penetration standards. 
Another composite cable that may not be suitable for all indoor or 
indoor/outdoor applications is disclosed in U.S. Pat. No. 5539851. The 
cable includes a single central, tight buffered optical fiber surrounded 
by a ring of electrical conductors and a braided sheath RFI shield. The 
optical fiber is immediately surrounded by a KEVLAR sleeve and a TEFLON 
jacket. Because the composite cable has a single fiber, it has limited 
information carrying capacity. Additionally, the composite cable does not 
provide water blocking features in the interstices adjacent to the 
electrical conductors. Moreover, the combination of a KEVLAR sleeve, 
TEFLON jacket, a ring of electrical conductors, and a braided sheath 
results in a large, stiff composite cable that is not particularly suited 
to being routed through cable passageways. 
A cable that may be suitable for use in indoor applications is disclosed in 
U.S. Pat. No. 5481635. The cable includes a single large, central 
broadband coaxial cable, a set of voice-line twisted pair conductors, and 
a set of power conductors disposed around the coaxial conductor. Water 
blocking members are disposed about the coaxial cable. Compared to a fiber 
optic core, however, a coaxial core is disadvantageous because it has a 
smaller bandwidth capacity, and is subject to higher power loss. Moreover, 
the coaxial conductor is subject to electromagnetic interference, 
impedance, and electrical cross talk. Further, the coaxial conductor core 
is generally relatively heavier and larger, rendering it potentially 
difficult to route through cable passageways. Additionally, the coaxial 
conductor presents a spark hazard. Finally, because the coaxial conductor 
emits electromagnetic energy, it is easier to tap and is therefore less 
secure than a optical fiber core. 
OBJECTS OF THE INVENTION 
It is an object of the present invention to provide a low-cost composite 
cable that combines the high bit-rate capacity of optical fiber conductors 
with the power/data transmitting capacity of electrical conductors, and 
meets flame, water penetration, mechanical, and environmental cable 
performance standards allowing the cable to be used for indoor or 
indoor/outdoor applications. 
It is another object of the invention to provide a composite cable for 
indoor use comprising: a fiber optic core section, said core section 
including at least one optical fiber; a set of conductors with interstices 
adjacent to at least some of said conductors; and a flame retardant jacket 
surrounding said conductors. 
It is an object of the present invention to provide a composite cable for 
use in indoor/outdoor applications, comprising: a fiber optic core 
section, the core section including at least one optical fiber; a 
conductor and water blocking section, the conductor and water blocking 
section including a set of conductors providing mechanical strength 
characteristics to the composite cable, and a water blocking member 
therein; and an armor layer surrounding the conductor and water blocking 
section, the armor layer being surrounded by a cable jacket and defining 
an interfacial zone therebetween, the interfacial zone including a 
controlled bond layer so that, when the composite cable is subjected to 
flame tests, as the jacket burns and forms a char barrier around the tape 
layer, the controlled bond layer tends to support the char barrier 
relative to the armor tape, thereby protecting the tape from flames and 
inhibiting the propagation of flame along the cable. 
It is an object of the present invention to provide a composite cable for 
use in indoor/outdoor applications, comprising a fiber optic core section, 
the core section including at least one optical fiber; a conductor and 
water blocking section, the conductor and water blocking section including 
a set of conductors with interstices adjacent to at least some of the 
conductors, water blocking members being generally in or adjacent to at 
least some of the interstices, and a separate water blocking member 
surrounding the set of conductors; and a flame retardant jacket 
surrounding the conductor and water blocking section. 
It is an object of the present invention to provide a composite cable for 
use in indoor/outdoor applications, comprising a fiber optic core section, 
the core section including at least one optical fiber; a conductor and 
water blocking section, the conductor and water blocking section being 
multi-functional in that it contributes to flame, mechanical, and water 
penetration performance of the composite cable, the conductor and water 
blocking section including a set of conductors with interstices between at 
least some of the conductors, the conductors providing mechanical strength 
and flame inhibiting characteristics to the composite cable, with at least 
one of the interstices including a water blocking member therein, and a 
separate water blocking member surrounding the set of conductors. 
It is an object of the present invention to provide a fiber optic 
conductor, comprising: an optical fiber surrounded by a buffer layer 
including an aliphatic polyketone polymer. The buffer layer can be, for 
example, a tight buffer layer or a buffer tube.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIGS. 1-2, composite cables 10,10' according to the present 
invention will be described. Composite cables 10,10' combine the high 
bit-rate capacity of optical fiber conductors with the power/data 
transmitting capacity of electrical conductors, and meet flame, water 
penetration, mechanical, and environmental cable performance standards 
allowing the cables to be used for indoor or indoor/outdoor applications. 
Composite cables 10,10' can each include a core section 12, a conductor 
and water blocking section 30, an armor tape 50, and an outer jacket 60. 
Referring to fiber optic cable 10 (FIG. 1), core section 12 includes at 
least one fiber optic conductor 14 surrounded by a buffer layer. The 
buffer layer can be a buffer tube 18 having a water blocking material 16 
therein. Fiber optic conductor 14 may comprise, for example, one or more 
individual optical fibers, a group of optical fibers in a bundle, or one 
or more optical fiber ribbons. Core section 12 advantageously provides the 
high information carrying capacity of optical fibers to cable 10 without 
being subject to the disadvantages associated with electrical co-axial 
cables. Core section 12 is generally of a small size and has a light 
weight that facilitates routing of fiber optic cable 10 in cable 
passageways. 
Material 16 can be a thixotropic water blocking material, e.g., a silicone 
or a petroleum-based material, that permits movement of fiber optic 
conductor 14 during bending, expansion or contraction of cable 10. 
Alternatively, buffer tube 18 may include a dry water blocking material 
therein, for example, water blocking tape or yarn, or hydrophilic or 
superabsorbent powder loosely dispersed or impregnated in tube 18. 
For meeting plenum and/or riser flame tests, buffer tube 18 can be formed 
of an aliphatic polyketone polymer, used singly or in a polymer blend. 
Suitable aliphatic polyketone polymer compositions are described in U.S. 
Ser. No. 09/086,876, incorporated by reference herein. Halogenated and/or 
non-halogenated flame retardant additives may be added to the buffer layer 
material. As an alternative to the loose tube configuration of buffer tube 
18, the buffer layer can be a tight buffer layer 19, having one or more 
optical fibers therein, as embodied by fiber optic cable 10' (FIG. 2). 
Tight buffer layer 19 may comprise an aliphatic polyketone polymer used 
singly or blends thereof. In addition to flame test performance 
characteristics, the aliphatic polyketone polymer and blends thereof can 
be particularly advantageous in maintaining structural integrity of the 
buffer layer during high temperature connectorization processes. 
The conductor and water blocking section 30 of cables made in accordance 
with the present invention is multi-functional in that it contributes to 
the flame, mechanical, and water penetration performance of the cable. 
Conductor and water blocking section 30 includes a set of conductors, for 
example, twisted pair conductors 32 for electrical power, control, and/or 
data transmission. For flame retardance, conductors 32 can include an 
aliphatic polyketone insulating material surrounding a metallic conductor 
preferably in the range of AWG sizes 19 to 22, inclusive. Conductors 32 
can be stranded with an SZ or a counter-helical lay with respect to a 
center of the cable. Alternatively, conductors 32 can be disposed 
longitudinally with respect to the center of the cable. Although cables 
made in accordance with the present invention may include conventional 
strength members, this expense can be avoided, as the mechanical 
characteristics of conductors 32 impart sufficient tensile and crush 
strength to the cable thereby obviating the need for conventional strength 
members. More specifically, conductors 32 provide tensile strength, and 
buffer tube protection for meeting mechanical performance requirements of 
Bellcore GR-409-Core. In addition, conductor and water blocking section 30 
may include one or more buffered optical fibers 16. 
Water blocking is a feature of indoor/outdoor cables made according to the 
present invention, but is not required for indoor applications. As shown 
in FIGS. 1-2, conductors 32 are located in an annulus 40 defined between 
armor tape 50 and core section 12. Conductors 32 can be tightly or loosely 
placed adjacent to each other (as shown in the Figures), thereby forming 
interstices S of various sizes. Interstices S are simply any potential 
water penetration path between the cable components located within annulus 
40. To meet GR-20-Core water penetration requirements for outdoor 
applications, distinct water blocking members are provided in conductor 
and water blocking section 30, for example, one or more water blocking 
yarns 36 are generally disposed in or adjacent to interstices S. For ease 
of manufacturing, water blocking yarns 36 can be stranded with conductors 
32. 
A second water blocking member, for example, a water blocking tape 37, can 
be disposed inside armor tape 50 adjacent to interstices S. Water blocking 
tape 37 can be longitudinally wrapped about conductor and water blocking 
section 30 whereby respective conductors 32 are generally disposed between 
respective water blocking yarns 36 and water blocking tape 37. 
Alternatively, tape 37 may be helically wrapped about twisted pair 
conductors 32. As is conventional in the art, tape 37 may be wrapped with 
binders (not shown), and ripcords 38 can be provided for stripping jacket 
60 and armor tape 50. 
Moreover, the interface between armor tape 50 and outer jacket 60 can 
present a potential water penetration path, and can present mechanical 
and/or flame performance issues. Armor tape 50 comprises a metallic 
material, for example, a corrugated steel tape material, that is adequate 
to provide a ground path in the event of an electrical short. Jacket 60 is 
preferably formed of a robust flame retardant material, for example, an 
aliphatic polyketone composition, a flame retarded PE, or a PVC having a 
Limiting Oxygen Index (LOI) above about 40, preferably about 52 for plenum 
applications and about 30 or above for riser applications. In one aspect 
of the present invention, an interfacial zone is defined at the interface 
of armor tape 50 and jacket 60. The interfacial zone includes a controlled 
bond layer 52. Layer 52 is preferably formed of a polymeric compound that 
creates a bond between jacket 60 and tape 50 as jacket 60 is extruded 
thereover. Pressure extrusion is the preferred mode of cable jacket 
extrusion. The controlled bond permits stripping of jacket 60, but the 
adhesion provided by layer 52 between jacket 60 and tape 50 is 
mechanically robust enough to withstand cable flex tests, thereby 
inhibiting the formation of potential leak paths, armor tape cracking, and 
jacket zippering. In addition, controlled bond layer 52 is believed to 
enhance performance of cables 10,10' in flame tests. For example, although 
all cable components are evaluated for their respective impacts on flame 
test performance, the material of jacket 60 and adherence thereof to layer 
52 are believed to be effective in avoiding flame propagation in both UL 
910 (plenum) and UL 1666 (riser) flame tests. Layer 52 may also reduce 
smoke evolution in plenum flame tests. During flame tests, as jacket 60 
burns and forms a char barrier around tape 50, controlled bond layer 52 is 
believed to structurally support the coupled relationship between the char 
barrier and tape 50, thereby protecting the tape from heat/flames and 
inhibiting the propagation of flame along the cable. Layer 52 may also 
seal the armor seam thereby preventing the evolution of smoke from the 
cable core. 
The present invention has thus been described with reference to the 
foregoing embodiments, which embodiments are intended to be illustrative 
of the inventive concepts rather than limiting. Persons of skill in the 
art will appreciate that variations and modifications of the foregoing 
embodiments may be made without departing from the scope of the appended 
claims. Cables 10,10' made in accordance with the present invention can be 
adapted for indoor use (riser or plenum) in which case the need for 
waterblocking tape 37 and/or yarns 36 is obviated. Cables 10,10' can 
include one or more tensile strength members, for example, of the 
dielectric type. Fiber optic conductor 14 can include one or more single 
mode, multi-mode, or multi-core optical fibers. Armor tape 50 can include 
a seam guard as disclosed in U.S. Ser. No. 09/001,679 U.S. Pat. No. 
5,930,431, which is incorporated by reference herein. As an alternative to 
aliphatic polyketone polymers, buffer tube 18, tight buffer 19, and/or 
conductors 32 may comprise PVC blends, co-polyester elastomer, 
polyurethanes, a flouro compound, polyamide, or a PE material with or 
without the inclusion of flame retarding additives. Other alternative 
buffer materials may be, for example, polycarbonate, PBT, or polypropylene 
used singly, or in combination with the aforementioned aliphatic 
polyketone polymer. Buffer layers 18,19 can include various performance 
enhancing additives, for example, stabilizers. In addition, conductors 32 
can include one or more electrical co-axial conductors. Rather than the 
preferred pressure extrusion technique mentioned above, jacket 60 may be 
tubed on. Armor tape 50 can include various metallic materials, e.g., 
laminated aluminum, copper clad steel, bronze tape, or a non-metallic tape 
that bonds sufficiently with the material of controlled bond layer 52. 
Furthermore, controlled bond layer 52 can include a multi-laminate 
structure, for example, as disclosed in U.S. Pat. No. 4731504, 
incorporated by reference herein.