Patent Description:
The present invention relates generally to fiber optic cables, and particularly to such cables that may be routed through ducts.

Fiber optic cables are often pulled through ducts to enter a building or other structure at a far end of the duct, in order to connect the cable fibers with other fibers at the far end. Cables used in duct applications typically have a high fiber count and a relatively small form factor so as to have enough flexibility for tight bending or coiling. For example, a fiber optic cable suited for duct applications is available from OFS Fitel, LLC, under the registered trademark DuctSaver (R). The cable is capable of connecting very large fiber distribution hubs, and of use in data centers, FTTx applications, and access networks.

<FIG> shows a cross-section or profile of the mentioned DuctSaver fiber optic cable <NUM>, and <FIG> is a side view of an end length of the cable <NUM> after a HDPE outer jacket <NUM> is stripped away to expose other elements of the cable <NUM>. In the illustrated embodiment, optical fibers of the cable <NUM> are in the form of rollable ribbons <NUM> that are wrapped by a water blocking tape <NUM>. The wrapped ribbons <NUM> are protectively surrounded by a crush resistant central core or tube <NUM>. The cable <NUM> also has helically applied fiberglass strength members <NUM>, and diametrically opposed ripcords <NUM> are embedded in the outer jacket <NUM>.

An optical fiber ribbon may include, for example, from <NUM> to <NUM> fibers that are bonded alongside one another. The fibers of a rollable ribbon, in particular, are bonded periodically to one another in a way that allows the ribbon to fold and unfold easily about its long axis, a feature not possible without impairing the fibers when bonded continuously to one another as in traditional flat ribbons. Multiple rollable ribbons can therefore be folded and contained inside a cable of a given outside diameter, and the cable will have greater flexibility than that of a cable of the same diameter but which contains the same number of ribbons in flat form. Also, when removed from a cable and unfolded on a flat surface, the fibers of a rollable ribbon can be prepared the same way as the fibers of traditional flat ribbons. See generally, <CIT>) and <CIT>); <NPL>); and <NPL>).

Before a cable is pulled through a duct, a grip or sock is usually fixed over a leading end of the cable. The grip is configured to protect the fibers and other elements at the leading end from being damaged while the cable is being pulled through the duct by a cord that is attached at one end to the g rip. See, e.g., <CIT>), <CIT>), <CIT>), and <CIT>). After the leading end of the cable is pulled out of the far end of the duct, and in addition to removing the grip, an installer must strip away a length of the outer jacket, remove all cable elements other than the fibers, and then prepare the fibers for splicing to corresponding fibers of one or more other cables at the far end of the duct.

For example and referring to <FIG>, after removing the cable jacket <NUM> and strength members <NUM> at the leading end of the cable <NUM>, the installer must cut away a length of the central core <NUM> and remove the water blocking tape <NUM> in order to expose the fiber ribbons <NUM>. Next, he or she must flatten each of the ribbons <NUM>, strip away coatings on the fibers of each ribbon, and then cleave the ends of the fibers using a special tool to enable the fibers to be spliced to other fibers at the far end of the duct. Thus, the installation procedure at the far end of the duct is time consuming and there is an ongoing desire by customers to shorten it.

A known approach toward reducing the installation time involves terminating the fibers at the leading end of the cable in fiber optic connectors, before the cable is pulled through a duct. The approach is not optimal in many cases, however. For example, when connectors are bundled together at the leading end of a cable and are covered by a pulling grip or sock, the overall size of the bundled connectors is likely to preclude a smooth passage of the leading end over the full length of the duct. Moreover, it may be difficult if not impossible to fix a pulling grip or sock firmly and safely over the leading end of the cable up to and including the cable jacket, and the cost and/or need to interface the terminated cable fibers with the fibers of another, non-terminated cable at the far end of the duct could limit the usefulness of this approach for all applications.

<CIT> discloses a fiber optic cable assembly including a fiber optic cable and a cable pulling assembly. The fiber optic cable includes a first end, an oppositely disposed second end, an outer jacket and a strength member disposed in the outer jacket. The cable pulling assembly is engaged to the second end of the fiber optic cable. The cable pulling assembly includes an enclosure defining a cavity. The second end of the fiber optic cable is disposed in the cavity. An adhesive is disposed in the cavity. The adhesive secures the strength member of the fiber optic cable to the enclosure.

<CIT> teaches a cable comprising a cable outer sheath surrounding a cable core and at least a ring surrounding partly said cable outer sheath so that said ring presses said cable outer sheath on said cable core in a way adapted to increase a transfer, on said cable core, of a pulling effort exerted on said cable outer sheath.

<CIT> discloses a device for connecting an optical cable and a protective tube fitted onto a bare optical fiber protruding from the optical cable. The device comprises two end portions and a central portion. One end portion comprises a channel for housing a cut end of the cable external sheath, from which the bare fiber exits. This channel is longitudinally opened. The opposite end portion receives the protective tube. The central portion comprises a second channel with a tapered guiding wall aligning the bare optical fiber with the protective tube. It is also disclosed an optical fiber protection assembly comprising the device and a protective tube arranged in the device.

<CIT> A discloses a method for providing a building or other location with an optical fibre element, for example fibres or a ribbon cable, that is terminated by a connector. A leading end of the optical fibre element is introduced into the bore of a duct and the element is propelled along the duct by fluid drag of a gaseous medium. The element is terminated at at least its leading end by an insert for the connector and after the element has been propelled along the duct, a housing is located about the insert to form the connector.

<CIT> discloses several methods of pulling a fiber optic cable through a duct.

According to the invention, a method of pulling a fiber optic cable through a duct is defined according to claim <NUM>.

According to another aspect of the invention, a fiber optic cable arrangement is defined according to claim <NUM>.

The present invention reduces installation time in the field by preparing the fibers at a leading end of a fiber optic cable for splicing to other fibers at a far end of a duct, before the cable is pulled through the duct. The time required by an installer at the far end of the duct to splice the fibers at the leading end of the cable to the other fibers is therefore substantially reduced.

The invention can be used advantageously with fiber optic cables like the earlier mentioned DuctSaver and others that contain optical fiber ribbons capable of being fusion spliced to other fibers, when the ribbons are laid flat and the fibers are separated from one another. See <CIT>); <CIT>); and <CIT>).

According to the invention, prior to pulling a fiber optic cable such as, e.g., the cable <NUM> through a duct, the cable jacket <NUM>, central core or tube <NUM>, streng th elements <NUM>, and any water-blocking material <NUM> or armor in a leading end of the cable are removed. The fibers of the ribbons <NUM> are exposed over a determined length so as to fit, for example, into fusion splice trays arranged at the far end of a duct through which the leading end of the cable is pulled. Coatings on the fibers are removed, and the fibers are precision cut using, e.g., a conventional optical fiber cleaver tool. As a result, an installer at the far end of the duct no longer needs to spend time preparing the leading end of the cable further by removing the cable jacket and other elements that surround the cable fibers, exposing the fibers, and cleaving the fibers before splicing them to other fibers at the far end of the duct.

<FIG> illustrates a fiber optic cable arrangement <NUM> according to the invention. The cable arrangement <NUM> includes a fiber optic cable <NUM> which, like the cable <NUM> in <FIG>, has an outer jacket <NUM>, and optical fibers in the form of ribbons <NUM> about which a water blocking tape <NUM> is wrapped. The wrapped ribbons <NUM> are protectively surrounded by a crush resistant central core or tube <NUM>. In the illustrated embodiment, the cable <NUM> also has helically applied fiberglass strength members <NUM>, and diametrically opposed ripcords <NUM> embedded in the outer jacket <NUM>.

A leading end <NUM> of the cable <NUM> is configured so that determined lengths of the outer jacket <NUM>, the strength members <NUM>, the central core <NUM>, and the water blocking tape <NUM> are removed, thereby exposing end lengths of the optical fiber ribbons <NUM>. One of the exposed ribbons, ribbon 114a, is shown enlarged and in flat or unfolded form in the right half of <FIG>.

Optical fibers of the exposed ribbon 114a are prepared so that (a) previously applied coatings on the end lengths of the fibers are removed, (b) the end lengths of the fibers are cleaved, and (c) the cleaved end lengths of the fibers are placed inside one or more protective covers <NUM>. The covers <NUM> are formed and dimensioned to prevent the cleaved fibers from getting dirty or damaged, and to keep the covered fibers isolated inside a pulling grip or sock to be applied afterward (see <FIG>).

<FIG> shows one embodiment of a protective cover 132a for the cleaved fibers. The cover 132a has a base <NUM> with, for example, a number of parallel grooves <NUM> each of which is sized to seat a corresponding one of the fibers of ribbon 114a. The cover 132a also has a lid <NUM> constructed and arranged to snap closed over the base <NUM>. Cover 132a can made from, e.g., a plastics or polymeric material. A second embodiment of a protective cover 132b for the cleaved fibers is shown in <FIG>. The cover 132b has an open passage140 that is dimensioned and formed to receive the cleaved fibers of the ribbon 114a, and to hold the fibers tightly in place until withdrawn later by an installer. Overall dimensions of the covers 132a or 132b should be sufficient to protect the cleaved fibers when closed, for example, approximately <NUM> in. wide by <NUM> in. Alternatively, and instead of using one of the rigid covers 132a or 132b in <FIG>, the area of the cleaved fibers may be covered and protected by applying a tape, foam, or gel to the area.

As a further alternative, and instead of using either of the rigid covers 132a or 132b, or applying a tape, foam, or gel to the area of the cleaved fibers before pulling the cable <NUM> through a duct, the ends of the fibers of each ribbon <NUM> may be protected by inserting the fibers into a holder <NUM> such as, e.g., a <NUM> micron coating fiber holder such as shown in <FIG> and available from OFS Fitel, LLC, part no. S710S-<NUM>. In such an arrangement, end lengths of un-prepared fibers are placed firmly into corresponding holders <NUM> before the cable <NUM> is covered by a grip and pulled through a duct. The fibers could then be easily prepared for splicing by an installer at the far end of a duct, including (<NUM>) coating removal, (<NUM>) fiber cleaving, and (<NUM>) fusion splicing the fibers to other fibers at the far end.

<FIG> is a side view of the leading end <NUM> of the cable <NUM> as in <FIG>, depicting a mesh pulling grip or sock <NUM> placed over the leading end. The sock <NUM> is dimensioned and formed to envelop the leading end <NUM> of the cable including the protective covers <NUM>, up to and including the cable outer jacket <NUM> to which the sock <NUM> is fixed by tape or otherwise.

A distal end <NUM> of the sock <NUM> is capped with an eyelet <NUM>. The sock <NUM> together with the leading end <NUM> of the cable <NUM> can then be pulled through a duct <NUM> by way of a cord <NUM> attached to the eyelet <NUM> at the distal end <NUM> of the sock. The pulling force applied by the cord <NUM> is distributed over the sock <NUM> and down to the cable <NUM> so that the force does not act directly on the cable fibers <NUM>. When the grip <NUM> is pulled to exit at the far end on the duct <NUM> and the protective covers <NUM> are removed, the exposed fibers of the cable will be ready for splicing to other fibers at the far end.

Splicing of the cable fibers <NUM> to the other fibers at the far end of the duct <NUM> may be achieved by traditional fusion methods using plasma arc, or by alternative methods such as, e.g., placing the fibers into trays and fusing them by a liquid chemical bonding process wherein the trays house clad alignment devices to aid in the bonding process, or by mechanical splicing using aligned v-grooves in separate splice trays. A mechanical splice mechanism may also be provided within the mesh sock <NUM> before the leading end <NUM> of the cable <NUM> is pulled through the duct <NUM>.

The exposed fibers may, for example, be fusion spliced to unprepared or factory prepared fibers of a second cable whose fibers are disposed within a frame management system, similar to a known Multi-Access Modular Unit (MAMU) system at the far end of the duct <NUM>. The system may comprise pre-terminated or connectorized optical fanouts wherein the connector ends are mounted into an optical distribution frame, and the second cable end is a bare ribbon. In this scenario, the second cable end may also be factory-prepared and ready for placement into a fusion splice machine.

Claim 1:
A method of pulling a fiber optic cable (<NUM>) through a duct (<NUM>) so that fibers (<NUM>) of the cable (<NUM>) are ready for splicing to other fibers at a far end of the duct (<NUM>), comprising:
providing a fiber optic cable (<NUM>) having an outer jacket (<NUM>) and containing a number of fibers (<NUM>);
prior to pulling a leading end of the cable (<NUM>) through a given duct (<NUM>), removing a determined length of the outer jacket (<NUM>) at the leading end, thereby exposing a number of cable elements including at least one of strength members (<NUM>), ripcords (<NUM>), blocking tape (<NUM>), and a central core (<NUM>) that surround the fibers (<NUM>);
followed by removing the exposed cable elements to expose the fibers (<NUM>), and preparing the exposed fibers (<NUM>) by (a) removing coatings on the ends of the fibers, (b) cleaving each of the ends of the fibers, and (c) placing the cleaved ends of the fibers into one or more protective covers (<NUM>);
fixing a grip or sock (<NUM>) over the leading end of the cable (<NUM>) including the protective covers (<NUM>), up to and including the outer jacket (<NUM>) of the cable (<NUM>);
pulling the grip (<NUM>) together with the cable (<NUM>) through the duct (<NUM>) to exit at the far end of the duct (<NUM>); and
removing the grip (<NUM>) and the protective covers (<NUM>) at the far end of the duct (<NUM>), thereby exposing the cleaved ends of the cable fibers (<NUM>) for splicing to other fibers at the far end of the duct (<NUM>).