Utility optical fiber cable

An optical fiber cable (20) includes a core (22) which includes a plurality of bundles (31, 31 ) of optical fiber (24) and a yarn-like strength member system (35) which is wrapped with an oscillated or unidirectional lay about the optical fibers. The strength member system also provides impact resistance for the fibers. A jacket (40) which may include a flame-resistant plastic material encloses the core with the outer diameter of the jacket being substantially less than that of typical optical fiber cables. Portions of the strength member system contact an inner surface of the jacket, an outer surface of which is the outer surface of the cable.

TECHNICAL FIELD 
This invention relates to a utility optical fiber cable. More particularly, 
this invention relates to an optical fiber cable which may be used for 
temporary installations such as, for example, in restoring service across 
communication line damage locations. 
BACKGROUND OF THE INVENTION 
The use of communication cables which include a plurality of optical fibers 
is rapidly expanding. An optical fiber cable may comprise a plurality of 
glass fibers each of which is protected by at least one layer of a coating 
material. The optical fibers may be assembled into units in which the 
fibers are held together by binder ribbons to provide a core. In one 
manufacturer's line of cables, the core is enclosed by a plastic tube and 
a plastic jacket. 
Many different design optical fiber cables are available commercially. 
There are cables which include metallic shields, non-metallic or metallic 
longitudinally extending strength members and those which include 
grease-like filling material or superabsorbent polymer waterblocking 
materials. A typical optical fiber cable which is used between central 
offices has an outer diameter which is on the order of about 0.5 inch. 
Although the commercially available optical fiber cables fulfill specific 
needs, there is a demand for a simplistic optical fiber cable which may be 
used as a utility cable and which need not include some of the provisions 
included in the cables discussed hereinabove. For example, there is a need 
for a cable which may be used to restore service around a damage location 
in a communication line. 
During the service life of an optical fiber cable, the cable may become 
damaged. This may occur, for example, through unintentional contact by 
various kinds of excavation equipment, by lightning or by repeated attack 
by animals such as gophers, for example. Such damage may be partial in 
which case one or several optical fibers may be interrupted, or the damage 
may be total, such as a complete cable cut, for example. 
In any case, it becomes necessary to restore service as quickly as 
possible. This may be done through an expedited temporary arrangement 
while more work is under way to replace the damaged cable. Typically, the 
replacement is an equivalent or a cable having enhanced features. 
A temporary arrangement must be one which is easily installed and which is 
low in cost. Elements of the arrangement which must include a cable must 
be capable of being packaged in a carrying case which is portable and, 
desirably, in one which may be carried by an individual from a vehicle to 
a field location at which a disruption to service has occurred. 
The sought after cable of the temporary arrangement for restoring service 
which has been interrupted because of damage to an existing cable should 
be one which is simplistic in design yet is one which is capable of 
providing service at least on a temporary basis. It should be light in 
weight so as to render it portable and capable of being carried easily to 
damage locations. Also, inasmuch as it may be used on a temporary basis 
and may be discarded after such use, it should be one which is relatively 
low in cost. It should be flexible so that it may be installed easily 
without the need for mechanized installation equipment. And of course, 
because it includes optical fibers, it must be one which includes strength 
members so that the optical fibers are not overstressed. 
Accordingly, what is sought after and what seemingly is not available in 
the art is a lightweight, small, low-cost optical fiber cable which has 
sufficient strength to allow it to be installed without damage to the 
optical fiber therein. The sought after cable should be very flexible and 
smaller in outer diameter and lighter in weight than typical optical fiber 
cables. 
SUMMARY OF THE INVENTION 
The foregoing problems of the prior art have been overcome with cables of 
this invention. A cable of this invention includes a core which includes 
optical fiber transmission media and a jacket comprising a plastic 
material and having an outer surface which is the outer surface of the 
cable. A strength member system comprising yam-like material having a lay 
is disposed between the optical fiber transmission media and the jacket 
with a portion of the strength member system engaging an inner surface of 
the jacket. 
In a preferred embodiment, the core includes three bundles of optical 
fibers, each bundle including twelve optical fibers. The three bundles are 
stranded together and provided with a unidirectional or oscillating lay. 
The jacket of the preferred embodiment is a polyvinyl chloride plastic 
material. The outer diameter of the cable of the preferred embodiment is 
about 0.185 inch.

DETAILED DESCRIPTION 
Referring now to FIG. 1, there is shown an optical fiber cable of this 
invention which is designated generally by the numeral 20. The cable 20 
includes a core 22 which comprises optical fiber transmission media 24-24 
and which is shown generally by the broken line in FIG. 1. Each optical 
fiber transmission medium includes an optical fiber which is enclosed in 
one or more layers of coating material. For a description of a coating 
system for an optical fiber, see U.S. Pat. No. 4,962,992 which issued on 
Oct. 16, 1990, in the names of J. T. Chapin, A. G. Hardee, Jr., L. M. 
Larsen-Moss, C. M. Leshe, B. J. Overton, J. W. Shea, C. R. Taylor, and J. 
M. Turnipseed. 
Typically, the cable 20 includes a plurality of bundles of optical fiber 
24, each bundle being designated by the numeral 31. Also, typically, each 
bundle 31 includes a plurality of optical fibers 24-24 which are held 
together by two colored, thread-like binders 33-33 which are wrapped in 
opposite helical directions about the fibers. Binders typically are made 
of a plastic material and are well known in the art. The fibers extend 
longitudinally along the core without any intended stranding. The bundles 
are stranded together with a unidirectional twist lay or with what is 
referred to as an oscillated or S-Z lay in which the direction of the lay 
is reversed periodically. In order to provide an oscillated lay, the 
bundles 31-31 are fed through an oscillating face plate (not shown). The 
lay length of the assembled bundles 31-31 is in the range of about eight 
to fourteen inches. In a preferred embodiment, the cable 20 includes three 
bundles 31-31, each including twelve fibers. 
As can be seen in FIG. 1, the bundles 31-31 of optical fibers generally are 
in engagement with each other. Also, preferably, the bundles 31-31 are 
centered within the core 22. 
As can be seen in FIGS. 1 and 2, the core 22 also includes a strength 
system which is designated generally by the numeral 35. The strength 
system 35 includes a plurality of longitudinally extending yarn-like 
members 37-37. In a preferred embodiment, the strength system includes 
8.times.1420 denier aramid yams such as Kevlar.RTM. yarn. 
The yarn-like strength members are wrapped helically or wrapped with an 
oscillated lay about the bundles 31-31 of optical fibers 24-24. The lay 
length of the strength members 37-37 is about six to eight inches. If the 
strength members 37-37 are not provided with a helical wrap or an 
oscillated lay, the strength members most probably would kink when the 
cable is bent. The kinked strength members could impact the optical fibers 
which could lead to undesirable microbending. A preferred lay is about six 
inches and is unidirectional. 
About the core is disposed a jacket 40. The jacket 40 is made of a plastic 
material which in a preferred embodiment, is a flame-retardant plastic 
material such as a polyvinyl chloride (PVC) plastic material. The plastic 
material of the jacket 40 also may be a non-halogenated plastic material, 
for example. In a preferred embodiment, the outer diameter of the jacket 
40 is about 0.185.+-.0.005 inch whereas its inner diameter is about 
0.115.+-.0.005 inch. 
It should be observed that an outer surface 42 of the jacket 40 is an outer 
surface of the cable 20. Also, it should be observed that portions of the 
strength member system 35 contact an inner surface 44 of the jacket 40. 
Advantageously, the yarn-like strength members 37-37 which are disposed in 
the core 22 and which encase the optical fiber bundles perform another 
important function. The yarn-like strength members 37-37 provide 
protection of the optical fibers as the jacket 40 is being slit to provide 
access to the core. Also, not only does the yarn-like system provide 
tensile strength for the cable 20, it also provides impact resistance. As 
such, it cushions the optical fibers 24-24 in the core 22 from impact, 
thereby preventing damage to the optical fibers. 
As is apparent from the drawings, there is no core wrap interposed between 
the core 22 and the plastic jacket 40. Advantageously, the yarn-like 
strength members 37-37 prevent hot extruded plastic material which is to 
form the jacket 40 from sticking to the optical fibers 24-24. As a result, 
the outer jacket 40 may be easily stripped from the underlying yarn-like 
strength members 37-37 and the optical fiber transmission media. 
In the manufacture of the cable 20, the jacket 40 is tubed rather than 
pressure extruded onto the core 22. During such an operation, the jacket 
plastic is applied about the traveling assembly of optical fiber bundles 
31-31 and yarn-like strength members 37-37 so as to have an outer diameter 
which is larger than its desired size and then drawn down to form a loose 
fitting tubular member about the assembly of optical fiber bundles and 
yarn-like strength members. As a result, the tight fit of a pressure 
extruded jacket is avoided, permitting relatively easy removal of portions 
of the jacket 40 in the field. Such a structure results in a cable having 
enhanced flexibility and decreased sensitivity to microbending. 
Removal of the jacket 40 is facilitated further because of the absence of 
any strength members in the jacket. The tubed jacket is easily slit and 
removed to expose the yarn-like strength members 37-37 and the optical 
fiber bundles 31-31. 
Because of its structure, the cable 20 is very light in weight which allows 
substantial footage to be carried by a craftsperson in the field. Also, 
because of the material of the jacket and its thickness, the cable is very 
flexible and hence relatively easy to unwind and to rewind. 
Further, because the yarn-like strength members 37-37 are applied to the 
optical fiber bundles 31-31 using a relatively long lay length of about 
six to eight inches, it becomes relatively easy to separate the yarn-like 
strength members from the optical fiber bundles. Also, the use of an 
oscillated lay of the fiber bundles 31-31 appears to allow redistribution 
of stresses in the fibers during handling and installation, thereby 
reducing added loss due to packaging. 
There is a significantly higher packing ratio in cable cores of this 
invention than in the cable cores of many other optical fiber cables. By 
packing ratio is meant the ratio of the sum of transverse cross sectional 
areas of the optical fibers 24-24 in the core 22 to the transverse cross 
sectional area defined by an inner diameter of the jacket 40. That ratio 
is in the range of about 0.42. Although the yarn-like strength members are 
wrapped about the fiber bundles and the jacket plastic tubed about and 
drawn down on the core, there is little effect of the relatively high 
packing ratio on the performance of the cable 20 because the cable 
typically is in restoration use only a day or two until a permanent cable 
installation can be made and because the cable is of relatively short 
length. 
The cable 20 has several significant advantages. The cable is very flexible 
and provides a relatively large number of optical fibers in a relatively 
small core. The optical fibers 24-24 are unbuffered and the core is free 
of grease-like waterblocking material. The core is very easy to access, 
thus resulting in reduced times required for splicing and connecting. 
Because the cable is free of grease-like waterblocking material, because 
the optical fibers are not buffered and because the core is easy to 
access, the cable 20 is easy to install and connect to portions of the 
cable on each side of the damage location. As a result, service may be 
restored rapidly. 
A typical use of the cable 20 in restoring service to a customer or 
customers served by a cable 50 is depicted in FIG. 2. In the situation 
depicted in FIG. 2, the damage to the cable 50 is a complete break at a 
location 52 with end portions 54 and 56 of the cable newly formed by the 
break. The cable 20 may be included in a restoration kit such as that 
described and claimed in commonly assigned, copending application Ser. No. 
07/826,703 filed on even date herewith in the name of J. A. Aberson, Jr., 
E. Halupke, and W. C. Vicory, now U.S. Pat. No. 5,185,843 issued Feb. 9, 
1993 and which is incorporated by reference hereinto. One end 58 of the 
cable 20 is connected to the end portion 54 of the cable 50 in a closure 
61 which also is included in the restoration kit. The closure 61 may be 
one described and claimed in commonly assigned, copending application Ser. 
No. 07/826,711 filed on even date herewith in the names of W. Bensel and 
G. C. Cobb, now U.S. Pat. No. 5,189,725, issued on Feb. 23, 1993 and which 
is incorporated by reference hereinto. The cable 20 is unwound from the 
kit and an end portion 63 pulled to a location on an opposite side of the 
damage location and connected to the end portion 56 of the cable 50 in 
another closure 65. 
Although the cable 20 is ideally suited for use in providing temporary 
service around line breaks in outside plant, it has other uses. For 
example, it could be used as a riser cable. Typically a standard riser 
cable includes twelve fibers and has an outer diameter of about 0.225 to 
0.275 inch. In contrast, cable of this invention with an outer diameter of 
about 0.185 inch includes three bundles of twelve fibers each. Thus duct 
utilization may be maximized and in a vertical pull over several stories, 
less weight is involved. 
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.