U.S. patent application number 11/879633 was filed with the patent office on 2008-11-06 for optical fiber cables.
Invention is credited to Peter A. Weimann.
Application Number | 20080273845 11/879633 |
Document ID | / |
Family ID | 39939599 |
Filed Date | 2008-11-06 |
United States Patent
Application |
20080273845 |
Kind Code |
A1 |
Weimann; Peter A. |
November 6, 2008 |
Optical fiber cables
Abstract
Described is an optical fiber cable designed for drop cable
applications that has a compact profile, and is suitable for both
the indoor and outdoor portions of the installation. The new design
has three functional units, an optical fiber subunit, and two
strength members arranged side-by side on either side of the
optical fiber. The overall cable cross section round. In a
preferred embodiment, the optical fiber module of the cable has a
coupled fiber design.
Inventors: |
Weimann; Peter A.; (Atlanta,
GA) |
Correspondence
Address: |
Law Firm of Peter V.D. Wilde
301 East Landing
Williamsburg
VA
23185
US
|
Family ID: |
39939599 |
Appl. No.: |
11/879633 |
Filed: |
July 18, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60927475 |
May 3, 2007 |
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Current U.S.
Class: |
385/103 |
Current CPC
Class: |
G02B 6/4433
20130101 |
Class at
Publication: |
385/103 |
International
Class: |
G02B 6/44 20060101
G02B006/44 |
Claims
1. Method for installing optical fiber cable by running the cable
to both an outside installation and to an inside installation
wherein the optical fiber cable comprises: (a) an optical fiber
subassembly comprising at least one optical fiber encased in a
buffer encasement, (b) a layer of high-strength polymer yarn
surrounding the optical fiber subassembly, (c) a cable jacket
surrounding the polymer yarn layer, the cable jacket having a round
cross section, (d) a pair of protective rods extending linearly
along either side of the optical fiber subassembly.
2. The method of claim 1 wherein the protective rods comprise
fiberglass, and the polymer yarn is a polyaramid.
3. The method of claim 2 wherein the diameter of the cable jacket
cross section is less than 5 mm.
4. An optical fiber cable comprising: (a) an optical fiber
subassembly comprising at least one optical fiber encased in a
buffer encasement, (b) a layer of high-strength polymer yarn
surrounding the optical fiber subassembly, (c) a cable jacket
surrounding the polymer yarn layer, the cable jacket having a round
cross section, (d) a pair of protective rods extending linearly
along either side of the optical fiber subassembly.
5. The optical fiber cable of claim 4 wherein the optical fiber and
the protective rods are in-line.
6. The optical fiber cable of claim 5 wherein the protective rods
are embedded in the cable jacket.
7. The optical fiber cable of claim 5 wherein the protective rods
comprise fiber glass.
8. The optical fiber cable of claim 7 wherein the polymer yarn is
polyaramid.
9. The optical fiber cable of claim 5 wherein the protective rods
are embedded in the polymer yarn.
10. The optical fiber cable of claim 5 wherein the protective rods
are partly embedded in the polymer yarn and partly embedded in the
cable jacket.
11. The optical fiber cable of claim 5 wherein the aramid layer has
a racetrack shape.
12. The optical fiber cable of claim 5 wherein the cross section of
the cable jacket has a diameter of less than 5 mm.
13. The optical fiber cable of claim 5 wherein the cable has two or
more optical fibers wherein each of the optical fibers has a
separate buffer encasement to form a buffer encased optical fiber
subunit, and the two or more subunits are encased in a common
buffer.
14. The optical fiber cable of claim 13 wherein the separate buffer
encasements are color-coded.
15. The optical fiber cable of claim 5 further including a metal
armor layer.
16. The optical fiber cable of claim 5 further including a toning
wire.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of provisional
application 60/927,475 filed May 3, 2007, which is incorporated
herein by reference.
FIELD OF THE INVENTION
[0002] This invention relates to optical fiber cables specially
adapted for drop line applications.
BACKGROUND OF THE INVENTION
[0003] (Parts of this background may or may not constitute prior
art.) Fiber-to-the-premises (FTTP) from local telephone and cable
service providers is rapidly being implemented. This service
requires a broadband optical fiber distribution network comprising
local optical fiber distribution cables that are installed in
neighborhoods and city streets. The local distribution cable is a
large fiber count (multi-fiber) cable. Single fiber or few fiber
cables are used for the "drop" line from the street to the
premises. In many cases, aerial drop lines are used, and these have
special requirements. In other cases, buried drop lines are used,
and these have different requirements.
[0004] Optical fiber drop cables are made in several designs. Most
of these designs mimic earlier copper cable versions. In many
cases, physical resemblance is deliberate, so that the external
cable appearance matches that of existing copper versions, and
standard hardware and installation equipment may be used for both.
Thus "A-drop" optical fiber cable is an optical fiber version of
A-drop copper cable, and is made in the same flat or ribbon-like
configuration. Aerial drop cable typically has one or more strength
members for support. A common A-drop or flat cable design comprises
one or more optical fibers between two strength members. See for
example, U.S. Pat. Nos. 4,761,053, 6,836,603, and 6,501,888.
[0005] Optical fiber cables also commonly contain gel-filling
compounds for preventing water excursion in the cable. When water
enters a filled cable, flow of water along the length of the cable
is blocked by the gel. However, gel filled cables are time
consuming to install and repair, as the gel must be completely
removed from the optical fiber prior to fusion splicing operations.
Moreover, since the drop wire is typically attached to the side of
a customer's home or building, bleeding of ingredients in the cable
onto the customer's building may cause cosmetic or other problems.
Optical drop cables containing gel compounds may also be factory
preterminated or `connectorized` using `plug and play` optical
connectors. In this case the time and expense of field fusion
splicing may be avoided through factory installation of an outside
plant rated connector. However, factory assembly personnel
pre-installing the connectors face issues with time-consuming,
expensive complete removal of gel prior to connectorization.
[0006] Since aerial drop cables are subjected to considerable
stress and sag due to wind and ice build-up, these cables typically
have reinforcement members both to support the cable and to protect
the optical fiber module inside the cable. A common arrangement is
to center the optical fiber(s) between two strength members. The
optical fibers are contained within an optical fiber module,
bounded on each side by a round strength member. The centers of the
optical fiber module and the strength members are typically
arranged in-line. The resulting cable cross-section is typically
has a flattened, elongated, race-track shape.
[0007] Experience with installation and use of these cables has
revealed several disadvantages to the basic cable design. [0008] 1.
Stiffness. These cables are rigid and stiff and difficult to bend
or handle. [0009] 2. Size. The 300 lb. tensile requirement
(Telcordia GR-20 and ICEA-S-717 standards for Outside Plant optical
cables) leads to a large cable footprint, typically about 4.times.8
mm, often used to house a single optical fiber 0.25 mm in diameter.
[0010] 3. Non-circular cross-section. More difficult to manufacture
and handle [0011] 4. Not flame retardant. Typically terminated
outside the home and the signal must be transitioned to the indoor
network. Part of this is a function of size.
[0012] New designs for FTTP drop cable that offer compact size and
low cost are continually being sought. In many applications it is
desirable to use an optical drop cable indoors, for example to
transition from the outdoor network to an indoor `set-top box`
optical network unit that will receive the optical signal and
decode voice, data, and video signals. Alternately optical drop
cables may be used indoors to provide service to multi-dwelling
units (MDUs) such as condominums, townhouses, or multi-story
apartment buildings. One approach to design of optical cables for
this environment is to: omit large fiberglass strength members used
in outdoor cables, use instead aramid strength yarns; reduce the
tensile load rating of the cable; and jacket the cable with a
flame-retardant plastic compound, suitable for indoor use. This
results in a compact indoor cable, and is typically the option
chosen for current installations. For example, 3.0 mm diameter
indoor interconnect cordage with a tensile rating of 50 to 100 lbs.
is often used for this application. However, there are several
drawbacks to this also; the indoor cables are less robust than
outdoor cables, and the service provider must arrange for a
transition from the outdoor network to the indoor network for this
application.
[0013] Therefore, it would be desirable to have a single compact
cable design that is suitable for the drop (outside) portion of the
installation, and also for the indoor wiring, such that it may be
passed between the two environments with no transition
required.
[0014] In summary, existing drop cable designs are large and stiff,
and not suitable for use in both outside and inside installations.
Typical cable designs for inside wiring are not adequate for
outside service.
[0015] A single cable design that meets the criteria for both
inside and outside FTTH installations would represent a significant
advance in the art.
STATEMENT OF THE INVENTION
[0016] We have designed an optical fiber cable suitable for drop
cable applications that has a compact profile, and overcomes at
least in part the drawbacks just mentioned. The new design has
three functional units arranged side-by side, but the overall cable
cross section is essentially round. In a preferred embodiment, the
cable uses tight buffered optical fiber and aramid yarns that allow
for rapid connectorization using standard optical connectors.
Optical fiber cables with the construction of the invention may be
designed for use both indoors and outdoors, thus simplifying FTTH
installations.
BRIEF DESCRIPTION OF THE DRAWING
[0017] FIG. 1 is a sectional view of one embodiment of a
conventional optical fiber drop cable;
[0018] FIG. 2 is sectional view of a single or few fiber cable
designed for indoor installation:
[0019] FIG. 3 is a sectional view of one embodiment of the optical
fiber cable of the invention; and
[0020] FIGS. 4-7 are schematic views showing alternative
embodiments of the invention.
[0021] FIG. 8 is a schematic view of a preferred embodiment of a
multi-fiber cable;
[0022] FIG. 9 is a schematic view of an embodiment of the invention
wherein the cable is provided with a tone-detecting element;
[0023] FIG. 10 shows an embodiment wherein the cable is
armored.
DETAILED DESCRIPTION
[0024] Referring to FIG. 1, a flat optical fiber drop cable 11 is
shown with optical fiber module 15 and strength members 13 and 14.
The optical fiber tube 15 comprises two optical fibers 18, an
extruded plastic buffer tube 17, and a gelled filling compound 16.
The strength members 13 and 14 are typically glass fibers bonded
and encased in a rigid thermoset resin, forming a rod structure.
The three modules are encased in a common outer jacket or
encasement 12, with the centers of the optical fiber module and the
centers of the strength members in-line. The strength members 13
and 14 are preferably approximately the same size, as shown, which
imparts symmetry to the cable cross section.
[0025] FIG. 2 shows an optional cable design with strength members
omitted. The cable has optical fiber 21 with a conformal tight
buffer 22, an aramid protective layer 23, and outer sheath 24. This
design allows for a very flexible cable with a small form factor.
The overall size typically may be 2-4 mm. Moreover, in contrast
with the cable of FIG. 1, this cable is round in cross section,
thus easier to handle and install. This embodiment, sometimes
referred to as cordage, is suitable for inside installations.
However, it has these drawbacks: [0026] 1. Poor crush resistance.
The Telcordia GR-409 standard maximum compression load for this
sort of cable is 3.5 N/mm. The concern is that such a cable is not
robust enough for in-home installation by moderately skilled
craftspeople. For example, if this cable is run in a basement and
stapled to overhead floor joists, it must be sufficiently robust to
survive the pressure of a staple gun. [0027] 2. Too flexible.
Anything that is installed in the home environment is potentially
vulnerable to abuse or damage. Flexible cordage is vulnerable to
being bent in such a manner that fibers are broken or subjected to
high strain such that long-term mechanical reliability is at risk.
[0028] 3. Insufficiently robust for outdoor installations. These
cables can be made UV-resistant and waterblocking, but the basic
design is not adequate for outdoor aerial or buried portions of an
installation.
[0029] FIG. 3 depicts an embodiment of the invention. It is
suitable for use as both the inside and the outside (drop)-segments
of the installation. The cable comprises optical fiber 31 encased
in tight-buffered polymer encasement 32. This forms the optical
fiber module, which is typically 900 microns in diameter to meet
standard coupling and splicing equipment and techniques. Other
sizes may be used, e.g. 600 microns. The tight-buffer material 32
is preferably a stiff, robust dual-layer nylon/ethylene-acrylic
acid copolymer. Details of this buffer layer are given in U.S. Pat.
No. 5,684,910. In a preferred embodiment the outer layer is Degussa
"Vestamid L1670" nylon 12, the inner layer is Dow Chemical's
"Amplify EA 103" functional ethylene/acrylic acid copolymer.
However the buffer material can could be any suitable plastic
material, including PVC, thermoplastic elastomers such as DuPont's
"Hytrel" materials, fluoropolymers, nylon, poly(butylene
terephtalate), or UV-cured acrylate resins.
[0030] The encasement 32 is tightly fitting to the optical fiber
polymer coating. It will be recognized that this is in contrast to
the common approach to controlling microbending losses by
mechanically decoupling the optical fibers from the surrounding
cable. In decoupled structures, mechanical impacts and stresses on
the cable are not translated, or minimally translated, to the
optical fibers. However, a number of advantages result from using a
tight-buffered encasement that deliberately couples the optical
fiber to the surrounding cable medium. These are described in U.S.
Pat. No. 6,973,245, issued Dec. 6, 2005, which patent is also
incorporated herein by reference. This patent gives details of
coupled optical fiber encased systems for single or few fiber
cables. Among the advantages of coupled conformal encasements is
that they are inherently water blocking. A discussion of coatings
or encasements for optical fiber ribbon cables appears in U.S. Pat.
No. 6,317,542 issued Nov. 13, 2001. This patent describes a variety
of embodiments wherein conformal encasements are used for optical
fiber ribbon stacks, and this patent is incorporated herein by
reference.
[0031] The term "encasement" as used in this description is defined
as the primary medium that surrounds the optical fibers.
[0032] Referring again to FIG. 3, the tight-buffered optical fiber
is wrapped with a layer 33 of aramid yarns. Teijin Twaron BV's
Twaron Type 1055 waterswellable high modulus material is suitable.
Other high-strength polyaramid yarns, or other high strength
polymer yarns, can be used as well. The yarn is advantageously
coated with a waterswellable coating when the cable is to be used
for outdoor-indoor applications. Waterswellable coating is not
necessary for indoor-only applications. Waterswelling functionality
may also be incorporated through application of superabsorbent
polymer powders, spun yarns containing superabsorbent fibers, or
other filamentary material coated or impregnated with
waterswellable polymers.
[0033] According to an aspect of the invention, the optical fiber
subassembly is shielded with side protective members 35 and 36, and
the side members are placed in-line with the optical fiber 31,
i.e., the centers of the side protective members 35 and 36, and the
center of the optical fiber, lie approximately on the same axis.
Preferred for protective members 35, 36 are fiberglass rods
encapsulated in a stiff matrix of a thermoset resin so as to
provide high tensile and compressive stiffness. Positioning the two
rods as shown, i.e. with the centers of the rods and the center of
the optical fiber optical in-line offers favorable crush
resistance. Suitable rods are commercially available under the
brand name "Qualistrand" from CrWW & Associates, Hope Valley,
R.I. The rods 35 and 36 are preferably imbedded in the cable jacket
34 as shown in FIG. 3.
[0034] The cable jacket may be one or more of a wide variety of
materials depending on the application. For example, if the cable
is to be used outdoors only, the jacket may be made of polyethylene
containing carbon black. If the cable is to be used indoors, it may
be made of a flame-retardant PVC, fluoropolymer, flame-retardant
nylon, or a flame-retardant, polyolefin based nonhalogen material.
However, for indoor/outdoor applications the preferred cable jacket
is a UV-resistant resin that has good flame retardancy, such as Dow
Chemical DFDE-1638-NT EXP2 polyolefin-based FR nonhalogen resin, or
AlphaGary GW 2271-VW1 BLK.LA UV FG 2635 outdoor/indoor PVC. The
cable may be made riser or plenum rated as needed.
[0035] In the embodiments described, and specifically with two 0.7
mm diameter fiberglass rods and 6 strands of 2420 dTex Twaron Type
1055 waterswellable aramid yarn, the cable has a calculated tensile
rating of 220 lbs. (approximately 990 N). The small size and
reduced weight of this cable design allows for long span length in
aerial installations. In NESC heavy ice and wind loading zones, a
useful self-supporting span length is approximately 150 feet.
Conventional drop cables used in aerial installations typically
carry large steel or fiberglass strength members. The replacement
of these with aramid contributes to the reduction in weight and
size. The useful span length is inversely proportional to the cable
diameter. This is partly due to the fact that the amount of ice
that can form on a cable depends on the surface area of the cable.
Thus the very small size of this cable relative to conventional
drop cables contributes to long span lengths in aerial
installation. The calculated NESC heavy loading zone span length
for the cable depicted in FIG. 3 is approximately 165 feet.
[0036] The embodiment depicted in FIG. 3 is also suitable for use
in underground cable installations. If the optical drop cable is to
be installed in a small underground duct, or `microduct`, the rigid
fiberglass rods 35 and 36 provide compressive stiffness sufficient
to allow the cable to readily pushed or pulled through the duct,
especially through any areas where the duct changes direction in
the underground route. The prior art cable depicted in FIG. 1 can
be easily pushed through such a duct, but a duct with an inner
diameter of at least 10 mm is required to accommodate such a large
cable. The cable depicted in FIG. 3 can be installed in a duct with
an inner diameter as small as 5 mm. The prior art cable depicted in
FIG. 2 may not have the compressive resistance necessary to allow
it to be pushed through a duct, or easily pulled around a corner in
a duct route.
[0037] For use in direct-buried applications, the cable depicted in
FIG. 3 may also incorporate metallic members for location and/or
protection. The cable may be used as one component of a `figure 8`
design with a strippable copper toning wire that allows for use of
a locating device to detect the buried cable, in order to prevent
or limit the possibility of dig-ups and associated interruption in
service. In order to provide service either at the side of a
residence or in a residence, the copper toning wire may be stripped
away from the cable in the field, using common hand tools, thus
eliminating the need for grounding the copper wire at the
house.
[0038] Alternately the cable may be encased in corrugated or
interlocking metallic armor made from steel, stainless steel, or
aluminum to allow for detection as well as providing mechanical
protection against chewing rodents and accidental dig-ups. For the
case of outdoor/indoor cables, this armor may be stripped off the
cable at the point where the cable enters the residential unit.
[0039] The embodiment of FIG. 3 is a single fiber cable. Multiple
fiber cables also can be made according to the principles of the
invention. FIG. 4 shows a three-fiber cable, with three fibers 41
encased in tight-buffer 42. For FTTH applications, and small
business installations, cables with 1-3 fibers will normally be
used. In these figures, i.e. FIGS. 3-10, reference numbers
22,32,42, etc. denote similar elements.
[0040] FIGS. 3 and 4 show the rods 35, 36, 45, 46, fully embedded
in the jacket, but other arrangements are useful. FIGS. 5-7 show
alternative arrangements.
[0041] FIG. 5 shows rods 55, 56 embedded in aramid layer 53.
[0042] FIG. 6 shows rods 65, 66 partially embedded in aramid 63
layer and partially embedded in jacket 64.
[0043] FIG. 7 shows rods 75, 76 and tight-buffered optical fiber
71, 72, arranged in-line and wrapped with aramid layer 73. The
aramid layer has a racetrack shape, i.e. semi-circles separated by
straight side portions.
[0044] Various combinations of rigid rods and aramid yarns may be
used to optimize tensile strength, crush resistance, and bend
limiting for different applications. For example, for an indoor
only application a robust cable that resists stapling and sharp
bends may be made using 0.6 mm or 0.5 mm glass rods with 4 ends of
1610 dTex aramid yarn. [0045] Among many advantages of the cable
design described here are: Smaller size than conventional 300 lb.
drop cable. Cables made according to the invention are typically
less than 5 mm, e.g. 3-5 mm. Typical drop cables with steel armor
are approximately twice that size. [0046] Can be manufactured and
used as an indoor-outdoor cable, i.e. can be run into a residence
with no need for termination or transition from one cable design to
another. [0047] Compared to conventional indoor cordage it is more
robust. Glass rods provide a level of crush resistance not found in
conventional indoor cable. [0048] Round cross section. Easy to
package, route and handle. [0049] Naturally bend-limiting. Standard
cordage, with only aramid yarn, can be deformed into a knot--with
disastrous consequences for the fiber. The glass rods in this
design `push back` when the cable is bent tightly. [0050]
Compatibility with standard optical connectors. Use of buffered
fiber and aramid yarn makes this cable readily compatible with most
standard connector types. The 900 micron buffer naturally fits in
most connectors, and the aramid yarn is compatible with crimping
procedures with most common connectors.
[0051] FIG. 4 shows one embodiment of a multi-fiber cable wherein
the multiple fibers are encased in a common tight buffer. A
preferred embodiment of a multi-fiber cable is shown in FIG. 8
wherein four optical fibers are shown, each with a separate tight
buffer. The construction is adapted for efficient connectorization
wherein each buffered fiber is independently exposed when the cable
jacket is stripped, and each can be independently and conveniently
handled when the connector is applied. Moreover, the provision of
separate buffers allows these fibers to be color coded.
[0052] As mentioned above the cable depicted in FIG. 3 may also
incorporate metallic members for location and/or protection. These
expedients would be normally used for buried installations. FIG. 9
shows a cable similar in design to that of FIG. 3 but with a
locating accessory 97 added. The added accessory 97 carries a
"toning wire" 98, which is a copper wire or similar metallic member
used for locating a buried cable with an electrical locating
device. In order to provide service either at the side of a
residence or in a residence, the copper toning wire may be stripped
away from the cable in the field, using common hand tools, thus
eliminating the need for grounding the copper wire at the
house.
[0053] An alternative construction that allows for locating a
buried cable, and offers added protection for the buried cable is
shown in FIG. 10. Here the cable is encased in corrugated or
interlocking metallic armor 108. The armor may be made from steel,
stainless steel, or aluminum to allow for detection as well as
providing mechanical protection against chewing rodents and
accidental dig-ups. For the case of outdoor/indoor cables, this
armor may be stripped off the cable at the point where the cable
enters the residential unit.
[0054] Modifications in the geometry of the elements shown may be
made while still achieving the benefits of the invention. For
example, the strength members' are shown in the figures as having a
round cross section. Also the optical fiber system is shown with a
round cross section. Either of these shapes may be varied.
[0055] Various other modifications of this invention will occur to
those skilled in the art. All deviations from the specific
teachings of this specification that basically rely on the
principles and their equivalents through which the art has been
advanced are properly considered within the scope of the invention
as described and claimed.
* * * * *