Flat drop cable with medial bump

An example fiber optic cable includes an outer jacket having an elongated transverse cross-sectional profile defining a bowtie shape. The outer jacket defines at least first and second separate passages that extend through the outer jacket along a lengthwise axis of the outer jacket. The fiber optic cable includes a plurality of optical fibers positioned within the first passage and a tensile strength member positioned within the second passage. The tensile strength member has a highly flexible construction and a transverse cross-sectional profile that is elongated in the orientation extending along the major axis.

BACKGROUND

A fiber optic cable typically includes: (1) an optical fiber; (2) a buffer layer that surrounds the optical fiber; (3) a plurality of reinforcing members loosely surrounding the buffer layer; and (4) an outer jacket. Optical fibers function to carry optical signals. A typical optical fiber includes an inner core surrounded by a cladding that is protected by a coating. The buffer layer functions to surround and protect the coated optical fibers. Reinforcing members add mechanical reinforcement to fiber optic cables to protect the internal optical fibers against stresses applied to the cables during installation and thereafter. Outer jackets also provide protection against chemical damage.

Drop cables used in fiber optic networks can be constructed having a jacket with a flat transverse profile. Such cables typically include a central buffer tube containing a plurality of optical fibers, and reinforcing members such as rods made of glass reinforced epoxy embedded in the jacket on opposite sides of the buffer tube. U.S. Pat. No. 6,542,674 discloses a drop cable of a type described above. Flat drop cables of the type described above are designed to be quite robust. However, as a result of such cables being strong and robust, such cables are typically quite stiff, inflexible and difficult to handle. Additionally, such cables can be expensive to manufacture.

SUMMARY

The present disclosure relates to a fiber optic cable including an outer jacket having an elongated transverse cross-sectional profile. The transverse cross-sectional profile has a medial bump region located two outer contour regions. In some implementations, pinched regions separate the medial bump region from the outer contour regions. The outer jacket also defines first and second separate passages that extend through the outer jacket along a lengthwise axis of the outer jacket. The fiber optic cable also includes a plurality of optical fibers positioned within the first passage a tensile strength member positioned within the second passage. The tensile strength member has a highly flexible construction and a transverse cross-sectional profile that is elongated in the orientation extending along the major axis.

A variety of additional aspects will be set forth in the description that follows. These aspects can relate to individual features and to combinations of features. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restricted of the broad concepts upon which the embodiments disclosed herein are based.

DETAILED DESCRIPTION

FIGS. 1 and 2show a fiber optic cable500(e.g., a drop cable) in accordance with the principles of the present disclosure. The drop cable500includes an outer jacket502surrounding at least one optical fiber512. At least one strength member507also is embedded in the outer jacket502. In the example shown, the optical fiber512is positioned between two strength members507. The outer jacket502has a non-circular outer profile.

In some implementations, the fibers512are routed through a passage506defined in the outer jacket502without a buffer. For example, in one implementation, strands of the optical fibers512are loosely routed through the passage506defined in the outer jacket502. In another implementation, ribbonized optical fibers512are routed through the passage506. In other implementations, however, the optical fiber512is contained within a buffer tube504routed axially through the passage506. In one implementation, the buffer tube504includes a tight buffer around a single optical fiber512. In another implementation, the buffer tube504includes a loose buffer around one or more strands of optical fibers512. In another implementation, the buffer tube504includes a loose buffer around ribbonized optical fibers512.

The outer jacket502is longer along a major axis530than along a minor axis531. The major and minor axes530,531are perpendicular to one another and intersect at a center of the outer jacket502. The width of the outer jacket502is taken along the major axis530and the thickness of the outer jacket502is taken along the minor axis531. In the example shown, the transverse cross-sectional profile of the cable500is generally symmetrical about the major and minor axes530,531. In other implementations, however, the cable500can be asymmetrical.

For example, as shown atFIG. 2, when viewed in transverse cross-section, the outer profile of the outer jacket502has a generally obround shape with two intermediate pinched regions520. The pinched regions520define a medial bump region526between two outer contour regions522,524on each side of the flat cable500. The optical fibers512are routed axially along the medial bump section526of the cable500. The reinforcing members507are routed along the outer contour sections522,524. In one example implementation, the medial bump region526peaks along the minor axis531.

As shown inFIG. 2, the cable500has a first thickness A at the outer contour regions522,524, a second thickness B at the pinched regions520, and a third thickness C at the medial bump region526(e.g., along the minor axis531). In general, the pinched regions520define the minimum thickness of the cable500. Accordingly, the second thickness B is less than the first thickness A and the second thickness B is less than the third thickness C. In accordance with some aspects, the third thickness C of the medial bump region526defines the maximum thickness of the cable500. Accordingly, the third thickness C is at least as large as the first thickness A of the contour regions522,524. In some implementations, the third thickness C is greater than the first thickness A.

It will be appreciated that the outer jacket502can be made of any number of different types of polymeric materials. In one embodiment, the outer jacket16is made of a medium density ultra-high molecular weight polyethylene.

The buffer tube504can also be made of any number of different polymeric materials. For example, the buffer tube14can be made of a polymeric material such as polyvinyl chloride (PVC). Other polymeric materials (e.g., polyethylenes, polyurethanes, polypropylenes, polyvinylidene fluorides, ethylene vinyl acetate, nylon, polyester, or other materials) may also be used.

It will be appreciated that one or more optical fibers512can be positioned within the cable500. In a preferred embodiment, the cable500contains at least twelve optical fibers12. It will be appreciated that the optical fibers512can have any number of different types of configurations. In an embodiment shown atFIG. 3, an example structure for one of the fibers512is shown. The optical fiber512includes a core32. The core32is made of a glass material, such as a silica-based material, having an index of refraction. In the subject embodiment, the core32has an outer diameter D1of less than or equal to about 10 μm.

The core32of each optical fiber512is surrounded by a first cladding layer34that is also made of a glass material, such as a silica based-material. The first cladding layer34has an index of refraction that is less than the index of refraction of the core32. This difference between the index of refraction of the first cladding layer34and the index of refraction of the core32allows an optical signal that is transmitted through the optical fiber12to be confined to the core32.

A trench layer36surrounds the first cladding layer34. The trench layer36has an index of refraction that is less than the index of refraction of the first cladding layer34. In the subject embodiment, the trench layer36is immediately adjacent to the first cladding layer34.

A second cladding layer38surrounds the trench layer36. The second cladding layer38has an index of refraction. In the subject embodiment, the index of refraction of the second cladding layer38is about equal to the index of refraction of the first cladding layer34. The second cladding layer38is immediately adjacent to the trench layer36. In the subject embodiment, the second cladding layer38has an outer diameter D2of less than or equal to 125 μm.

A coating, generally designated40, surrounds the second cladding layer38. The coating40includes an inner layer42and an outer layer44. In the subject embodiment, the inner layer42of the coating40is immediately adjacent to the second cladding layer38such that the inner layer42surrounds the second cladding layer38. The inner layer42is a polymeric material (e.g., polyvinyl chloride, polyethylenes, polyurethanes, polypropylenes, polyvinylidene fluorides, ethylene vinyl acetate, nylon, polyester, or other materials) having a low modulus of elasticity. The low modulus of elasticity of the inner layer42functions to protect the optical fiber512from microbending.

The outer layer44of the coating40is a polymeric material having a higher modulus of elasticity than the inner layer42. In the subject embodiment, the outer layer44of the coating40is immediately adjacent to the inner layer42such that the outer layer44surrounds the inner layer42. The higher modulus of elasticity of the outer layer44functions to mechanically protect and retain the shape of optical fiber12during handling. In the subject embodiment, the outer layer44defines an outer diameter D3of less than or equal to 500 μm. In another embodiment, the outer layer44has an outer diameter D3of less than or equal to 250 μm.

In the subject embodiment, the optical fiber512is manufactured to reduce the sensitivity of the optical fiber12to micro or macro-bending (hereinafter referred to as “bend-insensitive”). An exemplary bend insensitive optical fiber has been described in U.S. Pat. Application Publication Nos. 2007/0127878 and 2007/0280615 that are hereby incorporated by reference in their entirety. An exemplary bend-insensitive optical fiber is commercially available from Draka Comteq under the name BendBright XS.

It will be appreciated that the cable ofFIGS. 1 and 2can be used as drop cables in a fiber optic network. For example, the fiber optic cable can be used as drop cables in fiber optic networks such as the networks disclosed in U.S. Provisional Patent Application Ser. No. 61/098,494, entitled “Methods and Systems for Distributing Fiber Optic Telecommunications Services to a Local Area,” filed on Sep. 19, 2008 and hereby incorporated by reference in its entirety.

The cable500has an elongated transverse cross-sectional profile (e.g., a flattened cross-sectional profile, an oblong cross-sectional profile, an obround cross-sectional profile, etc.) defined by the outer jacket502. A width W1of the outer jacket profile extends along the major axis530and the thicknesses A, B and C of the outer jacket profile extends along the minor axis531. The width W1is longer than the thicknesses A, B and C. In certain embodiments, the width W1is at least 50% longer than the thickness C. As depicted inFIG. 5, the width W1is a maximum width of the outer jacket profile and the thickness C is a maximum thickness of the outer jacket profile.

In the depicted embodiment ofFIG. 2, the transverse cross-sectional profile defined by the outer jacket502of is generally rectangular with rounded ends. The major axis530and the minor axis531intersect perpendicularly at a central lengthwise axis of the cable500.

The construction of the cable500allows the cable500to be bent more easily along a plane P1that coincides with the minor axis531than along a plane P2that coincides with the major axis. Thus, when the cable500is wrapped around a spool or guide, the cable500is preferably bent along the plane P1.

As indicated above, the outer jacket502defines the elongate transverse cross-sectional profile of the cable500. The central passage506and the strength members507are aligned along the major axis530of the cable500. The passage506has a generally circular transverse cross-sectional profile while the strength members507and their corresponding passages within the jacket502have elongate transverse cross-sectional profiles. For example, the strength members507have transverse cross-sectional profiles that are elongated in an orientation that extends along the major axis530of the cable500.

It will be appreciated that the outer jacket502of the cable500can be shaped through an extrusion process and can be made by any number of different types of polymeric materials. In certain embodiments, the outer jacket502can have a construction the resists post-extrusion shrinkage of the outer jacket502. For example, the outer jacket502can include a shrinkage reduction material disposed within a polymeric base material (e.g., polyethylene). U.S. Pat. No. 7,379,642, which is hereby incorporated by reference in its entirety, describes an exemplary use of shrinkage reduction material within the base material of a fiber optic cable jacket.

In one embodiment, the shrinkage reduction material is a liquid crystal polymer (LCP). Examples of liquid crystal polymers suitable for use in fiber-optic cables are described in U.S. Pat. Nos. 3,911,041; 4,067,852; 4,083,829; 4,130,545; 4,161,470; 4,318,842; and 4,468,364 which are hereby incorporated by reference in their entireties. To promote flexibility of the cable500, the concentration of shrinkage material (e.g. LCP) is relatively small as compared to the base material. In one embodiment, and by way of example only, the shrinkage reduction material constitutes less than about 10% of the total weight of the outer jacket502. In another embodiment, and by way of example only, the shrinkage reduction material constitutes less than about 5% of the total weight of the outer jacket502. In another embodiment, the shrinkage reduction material constitutes less than about 2% of the total weight of the outer jacket502. In another embodiment, shrinkage reduction material constitutes less than about 1.9%, less than about 1.8%, less than 1.7%, less than about 1.6%, less than about 1.5%, less than about 1.4%, less than about 1.3%, less than about 1.2%, less than about 1.1%, or less than about 1.0% of the total weight of the outer jacket502.

Example base materials for the outer jacket502include low-smoke zero halogen materials such as low-smoke zero halogen polyolefin and polycarbon. In other embodiments, the base material can include thermal plastic materials such as polyethylene, polypropylene, ethylene-propylene, copolymers, polystyrene and styrene copolymers, polyvinyl chloride, polyamide (nylon), polyesters such as polyethylene terephthalate, polyetheretherketone, polyphenylene sulfide, polyetherimide, polybutylene terephthalate, as well as other plastic materials. In still other embodiments, the outer jacket502can be made of low density, medium density or high density polyethylene materials. Such polyethylene materials can include low density, medium density or high density ultra-high molecular weight polyethylene materials.

The passage506of the outer jacket502is sized to receive one or more of the bend insensitive fibers512. The bend insensitive fibers are preferably unbuffered and in certain embodiments have outer diameters in the range of 230-270 μm. In one embodiment, the passage506is sized to receive at least 12 of the bend insensitive fibers512. When the fibers512are positioned within the passage506, it is preferred for the fibers512to occupy less than 60% of the total transverse cross-sectional area defined by the passage506.

It is preferred for the passage506to be dry and not to be filled with a water-blocking gel. Instead, to prevent water from migrating along the first passage104, structures such water-swellable fibers, water-swellable tape, or water-swellable yarn can be provided within the passage506along with the fibers512. However, in certain embodiments water-blocking gel may be used.

The strength members507of the cable500preferably each have a transverse cross-sectional profile that matches the transverse cross-sectional profile of their corresponding passage defined by the jacket502. As shown atFIG. 2, the strength members507have a transverse cross-sectional width W2that is greater than a transverse cross-sectional thickness T2of the strength members507. The width W2extends along the major axis530of the cable while the thickness T2extends along the minor axis531of the cable100. In the depicted embodiment, the thickness T2is bisected by the major axis530. In certain embodiments, the width W2of each strength member507is at least 50% longer than the thickness T2, or the width W2of each strength member507is at least 75% longer than the thickness T2, or the width W2of each strength member507is at least 100% longer than the thickness T2, or the width W2of each strength member507is at least 200% longer than the thickness T2, or the width W2of each strength member507is at least 300% longer than the thickness T2, or the width W2of each strength member507is at least 400% longer than the thickness T2. As depicted inFIG. 2, the width W2is a maximum width of each strength member507and the thickness T2is a maximum thickness of each strength member507.

In certain embodiments, the strength members507are bonded to the outer jacket502. The bonding between the strength members507and the outer jacket502can be chemical bonding or thermal bonding. In one embodiment, the strength members507may be coated with or otherwise provided with a material having bonding characteristics (e.g., ethylene acetate) to bond the strength members507to the outer jacket502.

The strength members507preferably have a construction that is highly flexible and highly strong in tension. For example, in certain embodiments, the strength members507provide the vast majority of the tensile load capacity of the cable500. For example, in one embodiment, the strength members507carry at least 95% of a 150 pound tensile load applied to the cable500in a direction along the lengthwise axis of the cable. In one embodiment, the strength members507can carry a 150 pound tensile load applied in an orientation extending along a central longitudinal axis of each strength member507without undergoing meaningful deterioration of the tensile properties of the strength members507. In another embodiment, the strength members507can carry a 200 pound tensile load applied in an orientation extending along central longitudinal axes of the strength members507without undergoing meaningful deterioration of the tensile properties of the strength members. In still another embodiment, the strength members507can carry a 300 pound tensile load applied in an orientation that extends along the central longitudinal axes of the strength members507without experiencing meaningful deterioration of their tensile properties.

It is preferred for the strength members507to be able to provide the tensile strengths described above while concurrently being highly flexible. In determining the tensile strength of the cable500, tensile load is applied to the cable500in a direction that extends along the lengthwise axis of the cable100. Similarly, to determine the tensile strength of the strength members507, tensile load is applied to the strength members507in a direction that extends along central longitudinal axes of the strength members507. In one embodiment, a strength member507having tensile strength characteristics as described above also has a flexibility that allows the strength member507to be wrapped at least 360 degrees around a mandrel300(seeFIGS. 4 and 5) having a 10 millimeter outer diameter for one hour without undergoing/experiencing meaningful deterioration/degradation of the tensile strength properties of the strength member507. As shown atFIGS. 4 and 5, the 360 degree wrap is aligned generally along a single plane P3(i.e., the 360 degree wrap does not form a helix having an extended axial length). In this way, the strength member507conforms to the outer diameter of the mandrel and generally forms a circle having an inner diameter of 10 millimeters. This test can be referred to as the “mandrel wrap” test. In certain embodiments, the strength member507maintains at least 95% of its pre-mandrel wrap test tensile strength after having been subjected to the mandrel wrap test. In certain embodiments, the strength member507does not “broom stick” when subjected to the mandrel wrap test described. As used herein, the term “broom stick” means to have reinforcing elements of the strength member visually separate from the main body of the strength member507. In certain embodiments, the strength member507does not generate any audible cracking when exposed to the mandrel wrap test.

In certain embodiments, each strength member507is formed by a generally flat layer of reinforcing elements (e.g., fibers or yarns such as aramid fibers or yarns) embedded or otherwise integrated within a binder to form a flat reinforcing structure (e.g., a structure such as a sheet-like structure, a film-like structure, or a tape-like structure). In one example embodiment, the binder is a polymeric material such ethylene acetate acrylite (e.g., UV-cured, etc.), silicon (e.g., RTV, etc.), polyester films (e.g., biaxially oriented polyethylene terephthalate polyester film, etc.), and polyisobutylene. In other example instances, the binder may be a matrix material, an adhesive material, a finish material, or another type of material that binds, couples or otherwise mechanically links together reinforcing elements.

In other embodiments, each strength member507can have a glass reinforced polymer (GRP) construction. The glass reinforced polymer can include a polymer base material reinforced by a plurality of glass fibers such as E-glass, S-glass or other types of glass fiber. The polymer used in the glass reinforced polymer is preferably relatively soft and flexible after curing. For example, in one embodiment, the polymer has a Shore A hardness less than 50 after curing. In other embodiments, the polymer has a Shore A hardness less than 46 after curing. In certain other embodiments, the polymer has a Shore A hardness in the range of about 34-46.

In one embodiment, each strength member507can have a width of about 0.085 inches and a thickness of about 0.045 inches. In another embodiment, such a strength member may have a width of about 0.125 inches and a thickness of about 0.030 inches. In still further embodiments, the strength member has a thickness in the range of 0.020-0.040 inches, or in the range of 0.010-0.040 inches, or in the range of 0.025-0.035 inches. Of course, other dimensions could be used as well. In additional embodiments, the strength member may have a width in the range of 0.070-0.150 inches. Of course, other sizes could be used as well.

In certain embodiments, the strength member507preferably does not provide the cable100with meaningful resistance to compression loading in an orientation extending along the lengthwise axis of the cable500. For example, in certain embodiments, the outer jacket502provides greater resistance to compression than the strength member507in an orientation extending along the lengthwise cable axis. Thus, in certain embodiments, the reinforcing members507do not provide the cable500with meaningful compressive reinforcement in an orientation that extends along the lengthwise axis. Rather, resistance to shrinkage or other compression of the cable500along the lengthwise axis can be provided by the outer jacket502itself through the provision of the shrinkage reduction material within the base material of the outer jacket502. In this type of embodiment, when a compressive load is applied to the cable500along the lengthwise axis, a vast majority of the compressive load will be carried by the outer jacket502as compared to the strength members507.

The above specification provides examples of how certain inventive aspects may be put into practice. It will be appreciated that the inventive aspects can be practiced in other ways than those specifically shown and described herein without departing from the spirit and scope of the inventive aspects of the present disclosure. For example, the cable500having the medial bump region526is described in combination with strength members507. In other implementations, however, the medial bump design can be used with other types of cables including other types of strength members (e.g., more rigid strength members capable of supporting compression loading such as relatively stiff rods formed by a resin (e.g., epoxy) that is reinforced with glass fibers (e.g., fiberglass rovings)).