OPTICAL FIBER CABLE WITH DROP CABLES HAVING PREATTACHED OPTICAL CONNECTORS AND METHOD TO STRAND THE SAME

An optical fiber carrying structure and a method of making are disclosed. The structure comprises a central core extending from a first end to a second end, and subunits wound around a portion of the central core. The subunits include one or more optical fiber subunits having at least one optical fiber, a connector is attached to an end of the optical fiber subunit, and a filler rod is coupled to the optical fiber subunit.

BACKGROUND

The present disclosure relates to optical fiber cables and more particularly to optical fiber cables that have drop cables that run along at least a portion of a central core. Optical fiber cables are used to transmit data over distance. Generally, large distribution cables that carry a multitude of optical fibers from a hub are sub-divided at network nodes, which are further sub-divided, e.g., to the premises of individual subscribers. Generally, these subdivisions involve splicing a cable tether into a main distribution line. Cable splicing at specific locations along a main distribution line is a delicate and time consuming process that requires precise placement of the cable tether and involves the risks of cutting the wrong fibers and providing environmental exposure to the cable interior.

SUMMARY

One embodiment of the disclosure relates to an optical fiber carrying structure, such as an optical fiber cable, including a central core, an optical fiber carrying subunit, a connector coupled to an end of the subunit, and a filler rod. The subunit is wound around the central core and extends a first length of the optical fiber cable. The connector is optically coupled to one end of the subunit that extends laterally outward away from the central core. The filler rod is wound around the central core and extends a second portion of the optical fiber cable. The filler rod does not comprise an optical fiber and the filler rod is coupled to an outer surface of the optical fiber carrying subunit.

In another embodiment the disclosure relates to an optical fiber cable including a central core, an optical fiber carrying subunit, a connector and a filler rod. The subunit is wound around the central core and extends a portion of a distance from the first end of the optical fiber cable to the second end of the optical fiber cable. The connector is optically coupled to one end of the subunit that extends laterally outward away from the central core. The filler rod is coupled to the section of the subunit adjacent to the portion that extends away from the central core. The filler rod and the subunit exert a tensile force on each other.

In yet another embodiment the disclosure relates to a method of manufacturing an optical fiber carrying structure that includes unspooling a central core from a first spool and unspooling a first subunit from a second spool. The first subunit includes an optical fiber carrying subunit, a connector and a filler rod. The connector is optically coupled to one end of the subunit that extends laterally outward away from the central core. The filler rod is coupled to the optical fiber carrying subunit. The first subunit is wound around the central core for at least a portion of the length of the central core.

DETAILED DESCRIPTION

Referring generally to the figures, various embodiments of a bundled optical fiber cable are provided. The bundled optical fiber cable includes a central core, such as an optical fiber carrying structure, and at least one subunit cable wound around the central core. Unlike other cable tethers, one or more of the subunit cables include a pre-connected connector that is spooled into the bundled optical fiber cable during manufacture. In this way connectorized subunit cables can be stranded with connectors at selected locations along the length of the bundled optical fiber. Filler rods are coupled to the subunit cables adjacent to the end of the subunit cable where the connector is coupled. When forming the bundled optical fiber cable, the filler rod exerts a tensile force on the subunit cable. This approach permits the bundled optical fiber cable to be formed easier and more quickly by enabling the connector to be biased away from the central core during spooling of the subunit cable onto the central core. This biasing of the connector away from the central core reduces the likelihood of the connector interfering with the desired formation of the bundled optical fiber cable.

FIG. 1depicts an embodiment of a bundled optical fiber cable10in a perspective cross-sectional view taken perpendicular to a longitudinal axis of the bundled optical fiber cable10. As can be seen, the bundled optical fiber cable10includes a central core, shown as central cable unit12, and a plurality of optical fiber carrying subunits, shown drop cables14, that are wound around the outside of the central cable unit12. In various embodiments, the drop cables14are helically wound around the central cable unit12. For example, in embodiments, the drop cables14may have an S winding or a Z winding around the central cable unit12. Additionally, in embodiments, the drop cables14may have an SZ winding around the central cable unit12.

In various embodiments a section of drop cable14, shown as connection leg38, extends outwardly from central cable unit12at transition point81towards connector66. First end76of drop cable14is coupled to connector66such that connector66is in optical communication with one or more optical fibers20within drop cable14.

Filler rod48is helically wound around central cable unit12and is coupled to the drop cable14adjacent to first end76of drop cable14. The drop cable14is wound around central cable unit12from second end70to transition point81, and filler rod48is wound around central cable unit12from transition point81to first end68. Thus, drop cable14extends a first portion from first end68to second end70and filler rod48extends a second portion from first end68to second end70, so both drop cable14and filler rod48extend less than the full distance from first end68to second end70. In one embodiment the first portion over which drop cable14extends is distinct from the second portion over which filler rod48extends. In one embodiment, one or more filler rods48extend from first end68of bundled optical fiber cable10to second end70of bundled optical fiber cable10.

In embodiments, the drop cables14are held to the central cable unit12only via the winding, which allows the drop cables14some degree of movement longitudinally along the length of the central cable unit12during bending of the bundled optical fiber cable10. In embodiments, the laylength of the winding (i.e., the length required for the drop cable14to make a complete revolution around the central cable unit12) is a function of the ratio between the laylength LL and a pitch circle PC (as shown inFIG. 2). With reference toFIG. 2, the pitch circle runs through the center of each drop cable14and, thus, has a diameter extending from the center of a first drop cable14to the center of a second drop cable14directly opposite the first drop cable14. Therefore, the diameter of the pitch circle is equal to the outer diameter D bundled optical fiber cable10minus the outer diameter d of one drop cable14. In embodiments, the laylength of the drop cables14is selected such that the ratio LL/PC is20or less. In other embodiments, the laylength of the drop cables14is selected such that the ratio LL/PC is 17.5 or less, and in still other embodiments, the laylength is selected such that the ratio LL/PC is 15 or less. A lower laylength corresponds to tighter coils of the drop cables14around the central cable unit12, which increases the length of the drop cables14necessary for a given length of the central cable unit. Further, processing line speed is slower at lower laylengths because of the tighter coiling. Thus, in embodiments, the laylength is maintained close to the allowable LL/PC ratio to reduce extra fiber length and to maintain a higher processing line speed.

In embodiments, bands are placed at various intervals along the length of the bundled optical fiber cable10to keep the drop cables14wrapped around the central cable unit12. In certain embodiments, the bands are welded polyethylene bands. In another embodiment, webbing, such as a polyethylene web ribbon, is provided around the drop cables14to keep the drop cables14wrapped around the central cable unit12.

As will be appreciated from the discussion provided later herein, in embodiments, the drop cables14each have different lengths and run only so far as to reach their desired drop location. The central cable unit12spans at least as long as the longest drop cable14. However, each of the drop cables14and the central cable unit12has substantially the same beginning point. In an embodiment as shown inFIG. 1, drop cables14define an outermost surface64of cable10, and in contrast to other cable designs that include an outer cable jacket, cable10provides each branching and routing access to drop cables14by not including an outer cable jacket.

FIG. 2provides a detailed cross-sectional view of the bundled optical fiber cable10. As can be seen, the drop cables14are substantially evenly spaced around the circumference of central cable unit12. In the embodiment depicted, there are thirteen drop cables14. In embodiments, as few as a single drop cable14can be provided around the central cable unit12. In other embodiments, as many as twenty-four drop cables14can be provided around the central cable unit12. Additionally, the drop cables can include electrical transmission elements, such as wires.

In general, the number of drop cables14that can be provided around the central cable unit12depends on size of drop cables14, size of the central cable unit12, and any external limiting factors for overall size (e.g., a 2″ duct which houses the bundled optical fiber cable10). In an exemplary embodiment, the central cable unit12has an outer diameter of 20 mm, and the drop cables14each have an outer diameter d of 4.8 mm. In this exemplary embodiment, fifteen drop cables14are able to fit around the central cable unit12. The outer diameter D of the bundled optical fiber cable10according to this exemplary embodiment is approximately 30 mm.

As used herein, the diameter D referenced with respect to the embodiment ofFIG. 2refers to the diameter of a hypothetical circle defined by the outermost extents of the drop cables14. As viewed from the cross-section ofFIG. 2, the bundled optical fiber cable10is defined by a larger, central circle surrounded by smaller, outer circles. Thus, the actual outermost surface of the bundled optical fiber cable10undulates moving from drop cable14to drop cable14around the circumference. Accordingly, the actual cross-sectional width of the bundled optical fiber cable10varies at different positions measured around the circle.

Referring now to the structure of the bundled optical fiber cable10as shown inFIG. 2, the central cable unit12includes a cable jacket16having an inner surface17and an outer surface18. The inner surface17defines a cable bore19within which a plurality of optical fibers20are disposed. The optical fibers20can be arranged in a variety of suitable ways within the central cable unit12. In the embodiment depicted, the optical fibers20are arranged in a stack21of multiple ribbons22. In particular, the optical fibers20are arranged into a stack21of sixteen ribbons22having a plus-shaped cross-section. The sixteen ribbons22include an upper stack section23, a middle stack section24, and a lower stack section25. In embodiments, the upper stack section23and the lower stack section25contain the same number of optical fibers20and/or ribbons22. Also, in embodiments, the middle stack section24includes at least twice the number of optical fibers20per ribbon22as compared to the upper stack section23and/or the lower stack section25. Further, in embodiments, the middle stack section includes as least twice as many ribbons22as compared to the upper stack section23and/or the lower stack section25. In an exemplary embodiment shown inFIG. 2, the upper stack section23and the lower stack section25each have four ribbons22of twelve optical fibers20. The middle stack section24in the embodiment depicted has eight ribbons22of twenty-four optical fibers20. Thus, in the embodiment depicted, the total number of optical fiber20is 288. In embodiments, a single stack can contain up to 864 optical fibers20. As shown inFIG. 2, the stack21is surrounded by a stack jacket27, which, in embodiments, may provide color coding for multiple-stack configurations and/or water-blocking properties.

In an alternate embodiment, the central core of the bundled optical fiber cable does not include any optical fibers20. Instead the central core comprises a jacket and optionally also comprises one or more strength members.

In embodiments, multiple stacks21can be provided in the cable bore19. In an exemplary embodiment, the cable bore19contains six stacks21of 288 optical fibers20for a total of 1728 optical fibers20. In another embodiment, the cable bore19contains twelve stacks21of 288 optical fibers20for a total of 3456 optical fibers20. In embodiments having multiple stacks21, the stacks21may be wound around a central strengthening member, such as a glass-reinforced plastic member. As will be understood, the number of optical fibers20provided in the central cable unit12has a bearing on the overall size of the bundled optical fiber cable10. Thus, the number of optical fibers20that can be included in the central cable unit12may be dictated by the particular installation parameters. Central core of the type described are available from Corning Incorporated, Corning, N.Y., such as those marketed under the trademark RocketRibbon™.

Moreover, whileFIG. 2depicts the optical fibers20arranged in ribbons22that are further arranged into stacks21, the cable bore19could instead include a plurality of loose optical fibers20or a plurality of optical fibers20grouped into multiple buffer tubes. In the latter embodiment, the optical fibers20in the buffer tubes can, for example, be arranged in ribbons22, or the optical fibers20can, for example, be in a loose tube configuration. Further, each buffer tube can contain the same or a different number of optical fibers20. Central cable unit12of the type described in this paragraph are available from Corning Incorporated, Corning, N.Y., such as those marketed under the trademarks ALTOS®, SST-Ribbon™, and SST-UltraRibbon™. Additionally, in embodiments, the central cable unit12is configured to have a small diameter D for installation in small ducts (e.g., 2″ or less). Such central cable units12of this type are available from Corning Incorporated, Corning, N.Y. under the trademark MiniXtend®.

As can also be seen in the embodiment ofFIG. 2, the cable jacket16includes two strength members26. In embodiments, each strength member26is made of glass-reinforced plastic or metal. Further, while two strength members26are depicted, embodiments of the central cable unit12can include no strength members26or up to four strength members26. In embodiments, an additional toning member may be embedded in the cable jacket16along with the strength members26. The toning member is selected to be metal to allow for cable location via toning, which is a technique where a signal is sent over the toning member of a buried optical fiber cable such that the signal can be detected above ground for the purpose of locating the optical fiber cable.

FIG. 3depicts an embodiment of a subunit cable14. In the embodiment depicted inFIG. 3, the drop cable14is a loose tube cable in which the optical fibers20are contained in a buffer tube28. The buffer tube28has an interior surface29defining a bore30in which the optical fibers20are contained, and the buffer tube28has an exterior surface31around which strengthening yarns32may optionally be wound. The drop cable14also includes a jacket34around the buffer tube28. In embodiments, a ripcord36is embedded in the jacket34to provide access to the interior of the subunit cable14.

In the embodiment shown inFIG. 3, the drop cable14includes twenty-four optical fibers20. However, the drop cable14can include, e.g., from one optical fiber20up to thirty-six optical fibers20in embodiments depending on the particular needs of the installation. Further, the drop cable14depicted inFIG. 3is a loose tube cable. In other embodiments, the optical fibers20are arranged in one or more ribbons within the buffer tube28.

Referring toFIGS. 4 and 5, various aspects of drop cable14and filler rod48are shown. Filler rod48is coupled to drop cable14via elongate structures, shown as strands, or more particularly shown as yarn strands50. In one embodiment yarn strands50are elongate strands formed from aramid fibers. In one embodiment two yarn strands50are helically wrapped around outer surface42of drop cable14. In one embodiment, yarn strands50are wrapped in opposing helical directions around outer surface42of drop cable14. In one embodiment yarn strands50are affixed to outer surface42via a connector, shown as tape44.

Yarn strands50exert a tensile force on filler rod48and drop cable14when filler rod48and drop cable14are wound around central cable unit12. In one embodiment yarn strands50communicate a tensile force between drop cable14and filler rod48. The tensile force communicated between filler rod48and drop cable14facilitates forming bundled optical fiber cable10by causing funnel82to bias connector66away from central cable unit12as drop cable14and filler rod48are being wound around central cable unit12(as shown inFIGS. 9 and 10). Additionally, the tensile force communicated between filler rod48and drop cable14biases filler rod48and drop cable14towards remaining wound around central cable unit12.

Connection leg38of drop cable14extends away from central cable unit12until first end76of drop cable14is coupled to connector66. Connector66is communicatively coupled to optical fiber20within drop cable14(e.g., in optical communication with) to facilitate communicatively coupling drop cable14to another cable, such as another optical fiber cable. In one embodiment connector66has a diameter of 12 mm.

In one embodiment, connection leg38is 10 feet for aerial connections, 15 feet for duct connections, and 20 feet for other situations. In another embodiment connection leg38is lengthened by severing filler rod48from drop cable14(e.g., by severing yarn strands50), and then unwinding drop cable14from central cable unit12until connection leg38is the desired length. In a specific embodiment a band is coupled around the one or more drop cables14to prevent the one or more drop cables14from unwinding further from central cable unit12. In various embodiments when connectors66coupled to various drop cable14are proximate each other, connectors66are arranged tip to boot, which is to say that the front of a first connector66is proximate the back of the next connector66.

Turning toFIG. 5, tapered end75of jacket52of filler rod48is angled to facilitate coupling filler rod48to drop cable14. Tapered end75defines a surface77that is angled relative to the longitudinal axis79of filler rod48, and surface77interfaces against outer surface42of drop cable14. In one embodiment, two or more yarn strands50extend from a central portion of filler rod48.

Turning toFIG. 6, in another embodiment filler rod49has a flat end74. Filler rod49is substantially the same as filler rod48except for end74being perpendicular and/or mostly perpendicular to longitudinal axis79of filler rod49. In various embodiments, a filler, shown as foamed polyethylene54, is within the central portion of filler rod49and filler rod48. One or more yarn strands50are coupled to foamed polyethylene54and extend outwardly from end74.

Turning toFIG. 7, filler rod49is coupled to drop cable14via a connector, shown as swivel62. Swivel62permits axial rotation of filler rod49and drop cable14with respect to each other. In one embodiment swivel62permits unlimited axial rotation of filler rod49and drop cable14with respect to each other.

Turning toFIG. 8, various aspects of cable10are shown. Drop cable14terminate at various locations along cable10, whereas central cable unit12extends through cable10. In one embodiment anywhere from one to all of drop cables14terminate before the end of cable10.

Turning toFIGS. 9 and 10, various aspects of forming cable10are shown. One or more drop cables14are spooled around central cable unit12. In one embodiment, drop cables14are helically spooled around central cable unit12such that drop cables14maintain a constant circumferential position with respect to each other around central core.

Drop cable14is fed through funnel82in direction88. Sidewalls98of funnel82define a channel96through which drop cable14passes. The tensile force within drop cable14forces drop cable14towards the bottom of funnel82, as shown fromFIG. 9, towards channel96. Channel96is sized to be smaller than connector66. As a result, funnel82generally and channel96in particular biases connector66away from central cable unit12, thereby reducing the likelihood that connector66will interfere with drop cable14being spooled against central cable unit12. In a specific embodiment, sidewalls98of funnel82extend into sidewalls of channel96so that no angle is formed between the primary body of funnel82and channel96.

After drop cable14is spooled against central core, connector66passes through second opening86of funnel82. Filler rod48now spools against central cable unit12while connector66extends outwardly from central cable unit12. In one embodiment connector66is coupled to filler rod48via a connection, shown as stretchable fabric80.

Turning toFIG. 11, depicted is a schematic view of an apparatus and process for forming a cable according to this disclosure. Initially, central cable unit12is spooled around spool104, and one or more drop cables14are spooled around spools102. Drop cables14and central cable unit12are spooled towards closing point106where drop cables14are wound around central cable unit12. Central cable unit12and the one or more drop cables14are moved towards and wound around spool124.

In one embodiment spool104is axially rotated so that central cable unit12rotates as it approaches closing point106, whereas drop cables14are kept stationary. As a result, drop cables14are helically wound around central cable unit12. In another embodiment spools102for drop cables14are rotated around central cable unit12.

At closing point106, funnel82is held in place near central cable unit12to permit drop cable14to transit into first opening84and out of second opening86. In one embodiment funnel82is restrained by a donut that is affixed around sidewalls98, permitting funnel82to axially rotate while drop cable14transits funnel82towards central cable unit12. Permitting funnel82to rotate allows the tensile force on drop cable14to bias funnel82so that channel96extends towards central cable unit12. As described above, this positioning of channel96helps protect connector66from interfering with the placement of drop cable14on central cable unit12.