Composite service and distribution communications media

A cable (20) which may be used in an aerial or buried installation to serve customers' premises and which is a composite optical fiber-copper conductor type serves present customer needs but has the capability to fulfill the service requirements predicted in the communications market of tomorrow. The cable includes one or more reinforced optical fiber units (22--22) and one or more metallic conductor pairs enclosed in a sheath system. Each optical fiber unit is reinforced to include a plurality of strength members (40--40) arrayed about a buffered optical fiber (36) to enclose the optical fiber and to provide columnar strength to resist compressive forces. A filling compound (52) is disposed within the unit between a jacket (50) which encloses the strength members and the buffered optical fiber.

TECHNICAL FIELD 
This invention relates to composite service and distribution communications 
media. More particularly, it relates to a cable which includes a 
reinforced optical fiber unit and metallic conductors and which may be 
strung up in an aerial or plowed in a buried mode or introduced into an 
earlier placed conduit to provide service and distribution media. 
BACKGROUND OF THE INVENTION 
Telephone service to the home has been provided by aerial or buried service 
wire. Typically each of these has included a pair of metallic conductors 
such as cooper wires enclosed in a jacket. For purposes of self-support, 
the aerial wire also has included at least one strength member. 
The use of optical fibers in communications has grown significantly over 
the past few years. It is anticipated that its use will reach into the 
residential loop distribution system in the near future. For now, loop 
distribution cables which include insulated metallic conductors continue 
to be installed. 
Nevertheless, operating telephone companies have expressed a desire to 
install cables which include optical fibers as well as metallic 
conductors. Such a course of action of early placement of optical fibers 
in aerial or buried installations to customers' premises will facilitate 
the later transition from a metallic to an optical fiber operating system. 
Obviously, the first cost of installing optical fiber to customers' 
premises is minimized by such an approach. With such a cable, optical 
fiber can be provided to customers' premises awaiting the arrival of the 
optical fiber network and development of associated hardware and 
electronics. 
Such composite cables will be placed by the same methods and apparatus as 
are used for all-copper cables. Accordingly, the optical fiber portion 
thereof must be robust enough to withstand plowing and trenching or aerial 
stringing of a host structure and to be capable of survival outside the 
host structure in a separate run to an optical fiber storage or 
termination point. 
With such a cable structure in place, service will evolve from the metallic 
pairs to the optical fibers. Simple telephone service can begin 
immediately over a metallic pair of conductors. Other metallic conductor 
pairs of the distribution and service cable can serve as secondary lines 
or alarm circuits. Initially, the optical fiber unit may be used to 
provide cable television or retained for later use. 
At a later date, more sophisticated offerings which require increased 
bandwidth and customer interaction such as, for example, electronic 
newspapers and mail, catalogs and shopping, banking and business 
activities and data and computer functions may be served through a remote 
terminal. For this application, metallic conductor pairs may provide power 
to on-premise electronics or serve as control circuits. Still later, all 
offerings may be provided over the optical fiber media, but power still 
will have to be provided for on-site electronics by the power or telephone 
operating company. Providing power from a central office source through 
these structures should result in reliable telecommunications during power 
outages. Also, the copper conductor pairs may have other uses such as 
circuit maintenance, for example. 
The sought-after cable should have desired properties. For example, it 
should have a relatively high tensile and compressive axial loading 
capability, a relatively low minimum bend radius, stiffness against bend 
losses in order to insure that the optical fiber unit does not follow the 
twists and turns of neighboring twisted pairs and should remain as 
straight as possible to minimize bend losses, an operating temperature 
range of about -40.degree. to +160.degree. F., single mode capability and 
low cost. The cable should be properly cushioned to withstand repeated 
impacts by vehicles on structures routed across roadways during 
installation. Also, the structure must not be affected adversely by cable 
filling compounds. The cable must be water-resistant to prevent damage due 
to water-induced crack propagation or freezing. Inasmuch as in some 
instances it will connect to customers' premises, the cable must be 
capable of being made flame retardant. 
Seemingly, the prior art is devoid of such a cable which provides both 
metallic and optical fiber conductors along with the desired properties. 
Single optical fiber cables having an optical fiber and strength member 
yarn disposed between the optical fiber and a plastic jacket are available 
commercially. However, such a cable does not provide columnar strength in 
compression and is not suitable for outside plant, particularly at 
relatively low temperatures. The sought-after cable will fill a need in 
the marketplace as services to the home are expanded. 
SUMMARY OF THE INVENTION 
The foregoing problem has been solved by the cable of this invention. The 
cable of this invention includes at least one reinforced optical fiber 
unit which includes at least one optical fiber and which may or may not 
include a buffer layer of plastic material that encloses the optical 
fiber. The reinforced optical fiber unit may be referred to as a 
lightguide reinforced unit. Also, the unit includes a plurality of 
impregnated fiber glass strength members each having a cross section which 
includes two generally parallel sides which are joined at their ends by 
arcuate portions. The strength members enclose the optical fiber in a 
manner which allows the fiber to float within the strength members and 
which provides columnar strength to resist compressive forces. A jacket 
which is made of a plastic material encloses the array of strength 
members. Disposed in the interstices between the jacket and the strength 
members and between the strength members and the optical fiber is a 
waterblocking material. In one embodiment, the cable also includes at 
least one insulated metallic conductor. A sheath system encloses the 
optical fiber unit and any metallic conductors. In a preferred embodiment 
the cable includes at least one pair of insulated metallic conductors. The 
sheath system includes an outer plastic jacket and in some instances a 
metallic shield which is disposed between the jacket and the core. For 
some applications, a flame-retardant waterblocking material is disposed 
within the sheath system about the reinforced optical fiber unit and any 
metallic conductors.

DETAILED DESCRIPTION 
Referring now to FIGS. 1 and 2, there is shown a cable being designated 
generally by the numeral 20 and having a core 21 which includes one or 
more reinforced optical fiber units each of which is designated generally 
by the numeral 22. The cable 20 is a composite cable which is suitable for 
distribution service to customer premises and includes the at least one 
reinforced optical fiber unit as well as one or more conductors. In 
another embodiment, the cable 20 may include at least one reinforced 
optical fiber unit and at least one or more pairs of insulated metallic 
conductors 24--24. 
Referring now to FIGS. 3-5 there is shown in detail one of the reinforced 
optical fiber units 22--22. The reinforced optical fiber unit 22 includes 
an optical fiber which is designated generally by the numeral 30 and which 
includes a coating. In a preferred embodiment, the optical fiber 30 is 
provided with a buffer coating 34. The buffer coating 34 typically 
comprises a polyester elastomer or polyvinyl chloride (PVC) plastic which 
has been extruded over the coated optical fiber. Typically the buffered 
optical fiber which is designated by the numeral 36 has an outer diameter 
of about 0.035 inch. 
The buffered optical fiber 36 is enclosed by a plurality of fiber glass 
strength members each designated by the numeral 40. As can be seen in FIG. 
3, each of the fiber glass strength members has an elongate cross section 
transverse of its longitudinal axis with the cross section defined by 
parallel sides 42--42 and by arcuately shaped ends 44--44. 
The strength members 40--40 must have suitable strength characteristics to 
prevent tensile load failure. Tensile load failure is caused by filament 
abrasion, flaws and tensile load imbalance. Filaments are abraded by 
neighboring filaments in the environment of use and by particles in a 
subsequently extruded jacket and is most severe under some conditions. 
Flaws occur with the probability that increases with the filament length 
and cause tensile load failures in a length of time which is approximately 
inversely proportional to the cable length. Uneven sharing of the tensile 
load results when the filaments are not coupled to share the tensile loads 
evenly. As some filaments break, others accept the load until the total 
cross section of the strength member fails. 
Generally as a solution to these problems, impregnated rovings or yarns are 
used as strength members. Impregnating material may be formed by 
condensation or addition polymerization reactions and may include, for 
example, urethanes, acrylic acid or acrylate-based materials, epoxies, 
polyesters, and polyvinyl chloride or other vinyl based materials. For 
strength member materials such as fiber glass, a coupling agent or sizing 
such as silane must be used to couple the impregnating material to the 
filaments; for material such as KEVLAR.RTM. fiber, a coupling agent may 
not be required. 
In a preferred embodiment, impregnated fiber glass rovings or yarns are 
used as strength members. Impregnating material coats each filament with a 
layer which protects against abrasion and couples each filament to its 
neighbor to bridge flaws and establish tensile load balance. 
Fiber glass impregnation is customarily accomplished by fiber glass 
suppliers. Glass filaments are drawn from a furnace bushing and cooled by 
water spray followed by the application of a water dispersion of silane. 
Drying removes excess water and alcohol, which formed as the silane bonds 
the glass and leaves silane-coated filament with organo functional groups 
positioned to couple with the impregnating material. Each strength member 
is impregnated in a bath with the sized fibers being spaced apart to 
enhance the impregnation. For an example of a method of impregnating a 
bundle of filaments, see U.S. Pat. No. 4,479,984 which issued on Oct. 30, 
1984 in the names of N. Levy and P. D. Patel and which is incorporated by 
reference hereinto. 
Impregnating roving or yarn overcomes a disadvantage of plain roving or 
yarn for the strength members. Unlike plain roving or yarn, any flaws in 
any of the filaments are bridged by the impregnating material which also 
prevents abrasion. Impregnation increases the flex life of the completed 
structure over that of unimpregnated roving. The impregnating material 
also serves as part of the waterblocking system for the reinforced optical 
fiber unit. 
The strength members are of a flattened shape because of the manner in 
which they are manufactured. The rovings or yarn are spread over a bar so 
that the roving afterwards appears flat. This design is beneficial in that 
it enhances the protection for the buffered optical fiber 36. Further as 
can be seen in FIG. 4, the strength members 40--40 are assembled to the 
optical fiber in such a manner as to have a lay along the length of the 
lightguide reinforced unit 22. In a preferred embodiment, the lay length 
is about 4 inches. 
It also should be observed that the strength members are arranged in a 
particular fashion about the buffered optical fiber 36. They are arranged 
so as have a generally triangular configuration with one of the parallel 
sides of each being adjacent to the buffered optical fiber which is 
enclosed by the three strength members. A light touching of the strength 
members to the optical fiber is permissible, but anything more could cause 
a loading of the optical fiber and may result in microbending losses. 
Other arrangements are within the scope of this invention. For example, 
two or more arcuately shaped strength members could be disposed about the 
optical fiber as could four strength members which form a square cross 
section. 
What is important is that the strength members are organized to provide a 
composite columnar strength member which resists compressive forces 
applied axially. Advantageously, the strength members also provide 
transverse compressive strength which prevents collapse of the unit as it 
is moved through the extruder or experiences bending. Also, the array of 
strength members function as a heat barrier during extrusion. The strength 
members must be decoupled sufficiently from the optical fiber to prevent 
the transfer of forces thereto. Decoupling also is important because of 
the relationship of the tightness between the sheath components and the 
optical fiber to the response time required for the optical fiber to 
return to a low stress state after having been stressed during bending or 
thermal cycling, for example. 
The reinforced optical fiber unit 22 also includes a jacket which is 
designated generally by the numeral 50. The jacket may be made of a 
material such as PVC which has suitable resistance to flame spread and 
smoke evolution. Typically, the jacket comprises a nylon material, for 
example, in order to provide it with toughness and resistance to abrasion, 
impact and compression. 
The reinforced optical fiber unit 22 is sized so that it may be an 
approximate size replacement for a copper distribution pair in a cable. 
The outside diameter of the jacket 50 is about 0.130 inch. The reinforced 
optical fiber unit 22 has been shown to include one optical fiber which is 
buffered. However, the unit may still have its same outer diameter, and 
the buffered fiber may be replaced with two or more unbuffered optical 
fibers. Or the buffer 34 which typically has an outer diameter of 0.035 
inch may be replaced with one or more optical fibers each of which is 
enclosed by a thinner buffer layer. 
Interposed between the jacket 50 and the strength members 40--40 of the 
reinforced optical fiber unit 22 and between the strength members and the 
buffered optical fiber 36 is a filling composition of matter 52. This 
composition of matter provides suitable waterblocking characteristics for 
the reinforced optical fiber unit 22. The filling material 52 must possess 
certain properties. It has been determined that in an optical fiber cable, 
a filling composition must also function to maintain the optical fibers in 
a relatively low state of stress. Such a material is a colloidal 
particle-filled grease composition disclosed in patent application Ser. 
No. 697,054 which was filed Jan. 31, 1985, and which is incorporated by 
reference hereinto. The composition of the waterblocking material 52 is 
intended to block effectively entry of water into the core while 
minimizing the added loss to the cable in order to provide excellent 
optical performance. 
A grease typically is a solid or semiliquid substance comprising a 
thickening or gelling agent in a liquid carrier. The gelling agents used 
in greases frequently are fatty acid soaps, but high melting point 
materials, such as clays, silicas, organic dyes, aromatic amides, and urea 
derivatives also may be used. 
When a low stress is applied to a grease, the material acts substantially 
as a solid-like material. If the stress is above a critical value, then 
the viscosity decreases rapidly and the material flows. The decrease in 
viscosity is largely reversible because typically it is caused by the 
rupture of network junctions between filler particles, and these junctions 
can reform following the removal of the supercritical stress. 
A cable filling or waterproofing material, especially an optical fiber 
cable filling compound, should meet a variety of requirements. Among them 
is the requirement that the physical properties of the cable remain within 
acceptable limits over a rather wide temperature range, e.g. from about 
-40.degree. to about 160.degree. F. It is also desirable that the filling 
material be relatively free of syneresis over the aforementioned 
temperature range. Syneresis is the separation of oil from the gel under 
applied stress. Filling materials for use in optical fiber cables also 
should have a relatively low shear modulus. According to the prior art, 
the shear modulus is a critical material parameter of optical fiber cable 
filling materials because it is believed to be directly related to the 
amount of microbending loss. For a discussion of microbending loss, see S. 
E. Miller et, al., Optical Fiber Telecommunications, Academic Press, New 
York (1979), pp. 158-161. Typically, microbending loss is more difficult 
to control at long wavelengths than at short ones. Thus, it is important 
to be able to produce optical fiber cable that has no significant 
cabling-induced losses at long wavelengths such as, for example, 1.55 
.mu.m. 
The preferred waterblocking material is a composition which comprises two 
major constituents, namely oil, and a gelling agent such as colloidal 
particles, and, optically, a bleed inhibitor. Preferably, the 
waterblocking composition includes a thermal oxidative stabilizer. 
Among the oils useful in the waterblocking material are polybutene oils 
having a minimum specific gravity of about 0.83 and a maximum pour point, 
as per ASTM D97, of less than about 18.degree. C., or ASTM type 103, 104A, 
or 104B, or mixtures thereof, per ASTM D-226 test, of naphthenic or 
paraffinic oils having a minimum specific gravity of about 0.86, and a 
maximum pour point, per ASTM D97, of less than about -4.degree. C. 
Specific examples of oils useful in the cable of the invention are a 
polybutene oil, which is a synthetic hydrocarbon oil having a pour point 
per ASTM D97 of -35.degree. C., an SUS viscosity of 1005 at 99.degree. C., 
a specific gravity of 0.8509, and an average molecular weight of 460. It 
is available from the Amoco Chemical Corporation, Texas City, Tex., under 
the trade designation L-100. Another example oil is a white mineral oil, 
having a pour point per ASTM D97 of -25.degree. C., an SUS viscosity of 
53.7 at 99.degree. C., an average specific gravity of 0.884, and maximum 
aromatic oils 1% by weight (b.w.). The latter is available from Penreco of 
Butler, Pa., under the designation Drakeol 35. Other oils include 
triglyceride-based vegetable oils such as castor oil and other synthetic 
hydrocarbon oils such as polypropylene oils. For applications requiring 
fire-retardant properties, chlorinated paraffin oils having a chlorine 
content of about 30-75% b.w. and a viscosity at 25.degree. C. of between 
100 and 10,000 cps are useful. An example of such oil is Paroil 152, which 
is available from the Dover Chemical Company of Dover, Ohio. 
Oil-retention of the inventive greases may be improved by the addition of 
one or more bleed inhibitors to the composition. The bleed inhibitor can 
be a rubber block copolymer, a relatively high viscosity semiliquid, 
sometimes referred to as semisolid, rubber, or other appropriate rubber. 
Block copolymers and semiliquid rubbers will be referred to collectively 
as rubber polymers. Incorporating a rubber polymer into the grease 
composition allows a reduction in the amount of colloidal particles that 
must be added to the mixture to prevent syneresis of the gel. This 
reduction can result in cost savings. Furthermore, it makes possible the 
formulation of nonbleeding compositions having a relatively low critical 
yield stress. 
Among the rubber block copolymers that can be used in waterblocking 
compositions for the cable of the invention are styrene-rubber and 
styrene-rubber-styrene block copolymers having a styrene/rubber ratio 
between approximately 0.1 and 0.8 and a molecular weight, as indicated by 
viscosity in toluene at 25.degree. C., of from about 100 cps in a 20% b.w. 
rubber solution to about 2000 cps in a 15% b.w. rubber solution. Exemplary 
block rubbers are (a) a styrene-ethylene-propylene block copolymer (SEP), 
unplasticized, having a styrene/rubber ratio of about 0.59, a specific 
gravity of about 0.93, a breaking strength per ASTM D-412 of 300 psi, and 
being available from the Shell Chemical Company of Houston, Tex., under 
the trade designation Kraton G1701; (b) styrene-ethylene-butylene block 
copolymer (SEB), having a styrene/rubber ratio about 0.41, and being 
available from the Shell Chemical Company under the designation 
TRW-7-1511; (c) styrene/ethylene-butylene-styrene block copolymer (SEBS), 
unplasticized, and having a styrene/rubber ratio of about 0.41, a specific 
gravity of about 0.91, 500% elongation, 300% modulus per ASTM D-412 of 700 
psi, and being available from the Shell Chemical Corporation under the 
trade designation Kraton G1652. Other styrene-rubber of 
styrene-rubber-styrene block coploymers are styrene-isoprene rubber (SI) 
and styrene-isoprene-styrene (SIS) rubber, styrene-butadiene (SB) and 
styrene-butadiene-styrene (SBS) rubber. An example of SIS is Kraton D1107, 
and an example of SBS is Kraton D1102, both available from the Shell 
Chemical Company. 
Among the semiliquid rubbers found useful are high viscosity 
polyisobutylenes having a Flory molecular weight between about 20,000 and 
70,000. Exemplary thereof is a polyisobutylene having a Flory molecular 
weight of about 42,600-46,100, a specific gravity of about 0.91, and a 
Brookfield viscosity at 350.degree. F. (about 177.degree. C.) of about 
26,000-35,000 cps, and available from the Exxon Chemical Company of 
Houston, Tex., under the trade designation Vistanex LM-MS. Other rubbers 
which are considered to be useful are butyl rubber, ethylene-propylene 
rubber (EPR), ethylene-propylene dimer rubber (EPDM), and chlorinated 
butyl rubber having a Monney viscosity ML 1+8 at 100.degree. C. per ASTM 
D-1646 of between about 20 and 90. Examples of the above are Butyl 077, 
Vistalon 404, Vistalon 3708, and Chlorobutyl 1066, respectively, all 
available from the Exxon Chemical Company. Also useful are depolymerized 
rubbers having a viscosity of between about 40,000 and 400,000 cps at 
38.degree. C. An example thereof is DPR 75 available from Hardman, Inc. of 
Belleville, N.J. 
Colloidal filler particles in oil gel the oil by bonding surface hydroxyl 
groups to form a network. Such gels are capable of supporting a load below 
a critical value of stress. Above this stress level, the network is 
disrupted, and the material assumes a liquid-like character and flows 
under stress. Such behavior is often referred to as thixotropic. 
Colloidal fillers useful in the cable of the invention include colloidal 
silica, either hydrophilic of hydrophobic, preferably a hydrophobic fumed 
silica having a BET surface area between about 50 and about 400 m.sup.2 
/gm. An example of a hydrophobic fumed silica is a 
polydimethylsiloxane-coated fumed silica having a BET surface area of 
about 80-120 m.sup.2 /gm, containing about 5% b.w. carbon, and being 
available from the Cabot Corporation of Tuscola, Ill. under the trade 
designation Cab-O-Sil N70-TS. An exemplary hydrophilic colloidal material 
is fumed silica with a BET surface area of about 175-225 m.sup.2 /gm, 
nominal particle size of 0.012 .mu.m, and a specific gravity of 2.2, 
available from the Cabot Corporation under the designation Cab-O-Sil M-15. 
Other colloidal fillers useful in the practice of the invention are 
precipitated silicas and clays such as bentonites, with or without surface 
treatment. 
FIG. 6 shows a generalized stress-strain curve 53 at constant strain rate 
for a thixotropic material such as that used as the waterblocking material 
52, and identifies several important parameters. In segment 55 of the 
stress-strain curve 53, the material acts essentially an an elastic solid. 
The segment 55 extends from zero stress to the critical yield stress 
.sigma.c. The strain corresponding to .sigma.c is identified as .gamma.c, 
the critical shear strain. By definition, the coordinates indicate the 
onset of yielding and the quantity .sigma.c/.gamma.c (or d.sigma./d.gamma. 
for .sigma.&lt;.sigma.c) is known as the shear modulus (Ge) of the material. 
The prior art teaches that filling materials for optical fiber cable need 
to have low values of Ge. However, it has been determined that, at least 
for some applications, a low value of Ge of the filling material is not 
sufficient to assure low cabling loss, and that a further parameter, the 
critical yield stress, .sigma.c, also needs to be controlled. Typically, 
the critical yield stress of material according to the invention is not 
greater than about 70 Pa, measured at 20.degree. C. whereas the shear 
modulus is less than about 13 kPa at 20.degree. C. 
A segment 56 of the stress-strain curve of FIG. 6 represents increasing 
values of the incremental strain for increasing stress. The stress 
.sigma.y is the maximum value of stress sustainable by the material at a 
given strain rate with .gamma.y being the corresponding strain. For 
strains in excess of .gamma.y, the stess at first decreases as shown by 
segment 58, becoming substantially independent of strain for still greater 
values of strain as shown by the segment 59. The waterblocking material 
thus exhibits a liquid like behavior for .gamma.&gt;.gamma.y. 
A preferred filling composition 52 for the unit 22 typically comprises 
about 91.4 to 94.0% by weight (b.w.) oil and preferably about 92.8 to 93% 
by weight (b.w.) Drakeol 35 oil and about 6 to 8.5% b.w. colloidal filler 
and preferably about 6.9 to 7.1% of b.w. N70-TS hydrophobic fumed silica. 
The preferred composition also includes about 0.1% b.w. of an oxidative 
stabilizer. An exemplary stabilizer is tetrakis methane, available from 
CIBA-GEIGY under the trade designation Irganox 1010. Another composition 
which may be suitable for filling the unit 22 provides about 92.5 to 93.5% 
b.w. of an extender oil such as Drakeol 35, about 6.5 to 7.5% b.w. of a 
rubber such as Kraton G 1652 and 0.2% b.w. of an antioxidant such as 
Irganox 1010 or 1035 material. For the preferred composition, the 
following test values were obtained: (a) .sigma.c (Pa)=10, Ge (kPa)=1.8; 
(b).sigma.c(Pa) =10 and Ge (kPa)=1.8, time in hours=16. 
The compositions were prepared by known methods, typically comprising the 
constituent materials first at ambient temperature and pressure, then at 
ambient temperature under a partial vacuum (typically less than about 300 
Torr). The resulting compositions were evaluated, including a 
determination of .sigma.c and Ge of some by cone-and-plate rheometry. An 
exemplary summary of the properties also is presented hereinabove with all 
measurements of .sigma.c and Ge being at 20.degree. C. The stress values 
designated (a) were determined without aging while those designated (b) 
were aged for the time indicated. 
Advantageously, the waterblocking material 52 which is used to fill the 
core of the unit of this invention yields at a low enough stress so that 
the optical fiber 30 is capable of moving within the unit 22 when the unit 
is loaded or bent. Because the yielding filling material 52 allows the 
optical fiber to move within the unit 22, the stress therein is reduced, 
microbending is minimized and the life of the optical fiber is lengthened. 
The filling material 52 for the reinforced optical fiber unit 22 also may 
be flame-retardant. This may be accomplished by including in the 
hereinbefore described composition a flame-retardant constituent such as 
chlorinated paraffin and/or Al.sub.2 O.sub.3 .multidot.3H.sub.2 O. 
As indicated hereinbefore, the distribution cable 20 includes one or more 
reinforced optical fiber units 22--22 and one or more metallic conductors 
and/or one or more twisted pairs of insulated metallic conductors 24--24 
(see FIGS. 1 and 2). Viewing again FIGS. 1 and 2 it can be seen that each 
of the insulated conductors 24--24 includes a metallic portion 62 and 
insulation 64 which has been extruded thereover. Typically, each of the 
metallic conductor portions 62--62 is 22 AWG wire and is insulated with 
polyethylene plastic material, for example. The diameter-over-dielectric 
(DOD) of each insulated conductor 24 is such that the mutual capacitance 
of a pair of conductors insulated with the polyethylene is 0.083 
.mu.F/mile. As a result, the circuit length of the metallic pair can be 
about 7 miles which does not unduly limit the optical fiber length. Also, 
advantageously, each reinforced optical fiber unit 22 having an outer 
diameter of 0.130 inch can replace a conductor pair each of which has an 
outer diameter of 0.057 inch. 
The distribution cable of this invention may include any of several sheath 
systems depending on the requirements of the environment of use. For 
example in FIG. 2, there is shown a distribution cable which includes the 
reinforced optical fiber unit and twisted metallic conductor pairs 
enclosed by a gopher-resistant sheath system designated 70 which includes 
a helically wrapped laminate 72 comprising copper and stainless steel. The 
copper-stainless steel, helically wrapped laminate 72 overlies an inner 
jacket 75 which may be made of high density polyethylene. Covering the 
outside of the copper-stainless steel laminate is an outer jacket of 76 
which in a preferred embodiment is made of flame retardant polyvinyl 
chloride (PVC) plastic material. The outer diameter of the cable 20 is 
about 0.350 inch. 
In an alternate embodiment designated generally by the numeral 80 (see 
FIGS. 7 and 8), the core which comprises the reinforced optical fiber unit 
or units 22--22 and the twisted metallic conductor pairs 24--24 includes 
an inner polyester plastic wrap 82 which is used to enclose the core. Over 
the polyester plastic core wrap 82 is disclosed a metallic shield 84 
comprising in a preferred embodiment corrugated bronze having a 
longitudinal seam. Finally, the corrugated bronze shield 84 is enclosed in 
an outer jacket 85 which comprises a flame retardant PVC plastic material. 
For all buried applications, the core is filled with a waterblocking 
composition of matter 89 (see FIGS. 2 and 8). Such a material may comprise 
Flexgel.RTM. material which is disclosed and claimed in U.S. Pat. No. 
4,176,240 which issued on November 1979 in the name of R. Sabia and which 
is incorporated by reference hereinto. As can be seen in aforementioned 
U.S. Pat. No. 4,176,240, the Flexgel filling compound comprises a mineral 
oil, styrene block copolymer rubber and polyethylene. Should the buried 
cable be routed adjacent to a customer's premises, the composition of 
matter should also include a chlorinated paraffin material comprising 
about 70% chlorine. 
The distribution cable of this invention also may be used in an aerial 
fashion. Aerial cables which may be of the self-support style are well 
known. An aerial cable 90 (see FIG. 9) in accordance with this invention 
includes a core which comprises at least one reinforced optical fiber unit 
22 and at least one pair of twisted insulated metallic copper conductors 
24--24. The core is enclosed in a self-support arrangement which includes 
a plastic jacket 91 which includes a large diameter portion 92 that 
encloses the core and a smaller diameter portion 94 connected by a web 95. 
The smaller diameter portion 94 encloses a steel strength member 96 which 
is strung up between poles. Typically the plastic of the jacket which is 
sometimes referred to as a "figure 8" configuration is made of a flame 
retardant PVC plastic material. In this embodiment, the core need not be 
filled with a waterblocking material. 
Another embodiment of an aerial service lightguide cable is depicted in 
FIG. 10 and is designated generally by the numeral 100. In it, a core may 
comprise a reinforced optical fiber unit which is enclosed in a jacket 
102. The jacket configuration 102 is similar to that shown in the 
copending application Ser. No. 770,041 which was filed on Aug. 28, 1985 in 
the names of N. J. Cogelia, et al. 
The aerial service cable 100 also includes a pair of strength members or 
support strands 106--106 which extend longitudinally. Each of the strength 
members 106--106 in the preferred embodiment of FIG. 10 comprises a 
fibrous strand material which is impregnated with a plastic material and 
is essentially the same as each of the strength members 40--40 except for 
the configuration. Each strength member 106 comprises a plurality of 
filaments which are gathered together. The filaments may be a material 
such as fiber glass of an organic material such as KEVLAR.RTM. aramid 
fiber. Further, the filaments may be assembled together so that they 
extend generally parallel to the longitudinal axis of the strength member 
in which case they comprise a roving or twisted together to form a yarn. 
In a preferred embodiment, the members 106--106 which provide strength for 
the aerial service cable 100 each are comprised of a plurality of E-glass 
fibers. E-glass fibers comprise a borosilicate composition with the fibers 
having a minimum tensile strength of 200,000 psi. In a preferred 
embodiment, each strength member comprises about 8000 fibers. 
As can be seen in FIG. 10, the reinforced optical fiber unit and the 
strength members 106--106 are enclosed in the jacket 102 comprising a 
plastic material which in a preferred embodiment is flame retardant 
polyvinyl chloride (PVC). The jacket 102 is generally rectangular in cross 
section and includes a first or neutral axis 112 which extends 
horizontally in FIG. 10 and a second axis 114 which is normal thereto. The 
jacket cross section has a width as measured in a direction parallel to 
the first axis 112 and a height as measured in a direction parallel to the 
second axis 114. Further, the jacket 102 is provided with enlarged end 
portions 116--116 at opposite ends of the axis 112. The enlarged portions 
116--116 created troughs 118--118 which extend longitudinally of the wire. 
Also, the corners of the jacket are provided with chamfers 119--119. 
The arrangement of the reinforced optical fiber unit 22 and of the strength 
members 106--106 within the jacket 102 is important. As is seen in FIG. 
10, the reinforced optical fiber unit 22 is generally disposed adjacent to 
a longitudinal axis 120 of the jacket which passes through a geometric 
center of each jacket cross section through which the first axis 112 also 
passes. 
Also of importance is the disposition of the strength members 106--106 with 
respect to the reinforced optical fiber unit 22 and the jacket 102. As 
shown, they are disposed along the axis 112 and outboard of the optical 
fiber unit 22. Each strength member 106 is disposed along the axis 112 
between the reinforced optical fiber unit 22 and the outer surface of the 
jacket. Because the strength members and the longitudinal axis intersect 
the axis 112 of each jacket cross section, the strength members and the 
longitudinal axis which is interposed therebetween are aligned. Further, 
each strength member 106 is disposed within one of the enlarged end 
portions 116--116, which are referred to as support columns. As a result, 
compressive forces provided by a support clamp are aligned with the 
support columns 116--116 and the strength members 116--116 therein. The 
reinforced optical fiber unit 22 is further protected against compressive 
loading of the support clamp by the troughs 118--118. 
The aerial service cable 100 forms generally a catenary between two 
wedge-type support clamps (not shown). The load due to the weight of the 
length of the aerial service cable in the catenary causes forces to be 
exerted between the clamps and the ends of the aerial service cable. Each 
clamp engages the outer surface of the jacket 102. It should be apparent 
that if there is insufficient adhesion between the jacket 102 and the 
strength members 106--106, the reaction of the clamp on the aerial service 
cable due to combined effects of cable weight and any ice and wind loading 
could cause the jacketing material to be pulled therefrom leaving the 
optical fiber unit unprotected and perhaps causing the cable to fall. It 
follows that the jacketing composition must have at least a sufficient 
minimum adhesion to the strength members 106--106. Not only must the 
strength members 106--106 be suitably adhered to the jacket 102, they must 
also have suitable strength characteristics to prevent static load failure 
discussed hereinbefore with respect to the strength members for the 
reinforced optical fiber unit 22. 
As a solution to these problems, impregnated rovings or yarns are used as 
strength members. The material which is used to impregnate the strength 
members must be such that the strength members are coupled to the jacket 
sufficiently so that there is no rupture, nor slippage after a 290 pound 
tensile load has been applied to the aerial service transmission medium 
through support clamps for a 24 hour period at room temperature. Also, the 
material used to impregnate the strength members must be a material that 
will couple to the jacket 102. Also, it must exhibit a relatively high 
coefficient of static friction with the material of the jacket 102. 
Further it must have hydrolytic stability. The impregnating material may 
be the same as that used to impregnate the optical fiber unit 22. 
In the impregnated roving or yarn for the strength members 106--106, unlike 
plain roving or yarn, any flaws in any of the filaments are bridged by the 
impregnating material which also prevents abrasion. There is sufficient 
adhesion of the jacket 102 to the strength members 106--106 to allow 
suitable transfer of forces to the strength members from the clamps. 
Further, the flex life of an aerial service cable which includes 
impregnated strength members is, at expected maximum surface temperatures, 
about ten times that of one which includes strength members that are not 
impregnated. 
The aerial service cable 100 provides other advantages. It has a 
flame-retardant jacket. Reinforced optical fiber units are positioned for 
protection against impact and abrasion. Another advantage relates to 
handling criteria. The unprotected hands of a craftsperson preparing the 
cable for termination are not exposed to the filaments as the jacket is 
removed to access the optical fiber unit. 
The use of a nylon jacketed reinforced optical fiber unit avoids problems 
with a prior art aerial service wire wherein a single plastic material was 
used to provide insulation for copper-clad steel conductors and a jacket. 
The plastic material had to be tough, have adequate low temperature 
flexibility, acceptable resistance to compression, ultra-violet 
resistance, acceptable weatherability, adequate flame-retardance because 
of the installation adjacent to customer's premises and high insulation 
resistance to insulate the conductors. Inasmuch as each function, 
insulating and jacketing, was required to provide particular properties, 
comprises were made to accomodate both functions with a single material. 
In the aerial service cable 100, the nylon material is a jacket for the 
reinforced optical fiber unit and the polyvinyl chloride an excellent 
jacketing material. Furthermore, the nylon does not bond to the polyvinyl 
chloride and thereby allows slippage between the reinforced optical fiber 
unit and the jacket. 
It should also be pointed out that another advantage of the aerial service 
cable which is shown in FIG. 10 is that the reinforced optical fiber unit 
may be accessed by one of several methods. For example, it may be accessed 
by a split method at normal temperatures or a clip-twist method at 
relatively low temperatures such as those in the range of 0.degree. to 
-20.degree.0 F. In the split method, a craftsman makes a cut with diagonal 
pliers into a jacket between the support columns. Afterwards the 
craftsperson grasps a support column in each hand and applies forces to 
separate one support column from the other which is effective to separate 
out the reinforced optical fiber unit 22. In the clip-twist method, the 
craftsperson uses the pliers to cut the jacket from each of its sides to 
the troughs which are centered over the unit 22. Then the craftsperson 
twists the wire to break any connection to the center portion of the 
jacket, pulls the separated jacket portion away leaving the reinforced 
optical fiber unit. 
Although the foregoing embodiments depict a reinforced optical fiber unit 
22 disposed in a distribution or service cable, it should be noted that it 
also may be used as a stand-alone unit in outside telephone plant or in 
buildings, or one or more such units may be used in outside telephone 
plant exchange cable or in multi-pair building cable. For use in a 
building, the unit 22 need not be filled with a waterblocking material but 
it must be flame retardant. This may be accomplished with a flame 
retardant buffer coating and a flame retardant jacket 50 and any one of 
several underlying tapes, if necessary, which retard flame spread and 
smoke evolution. On the other hand, for outside plant, the unit 22 
preferably is filled with a waterblocking material and if it becomes 
disposed adjacent to a building, must be flame retardant. The reinforced 
optical fiber unit also may be used as inside wiring in a customer's 
premises. Further, because of its size and robustness, a reinforced 
optical fiber unit 22 may be incorporated into a presently used copper or 
optical fiber exchange cable. 
FIGS. 11 and 12 depict other embodiments of the cable of this invention. In 
FIG. 11 there is shown a cable 130 which includes a plurality of the 
reinforced optical fiber units 22--22 enclosed in a sheath system such as 
the sheath system shown in FIG. 8. The cable 130 also includes a 
waterblocking material which may be the waterblocking material 89. In FIG. 
12, a cable 140 includes a plurality of reinforced optical fiber units 
22--22 enclosed in a sheath system such as that of the cable in FIG. 8 
without waterblocking material within the core among the optical fiber 
units. 
It is to be understood that the above-described arrangements are simply 
illustrative of the invention. Other arrangements may be devised by those 
skilled in the art which will embody the principles of the invention and 
fall within the spirit and scope thereof.