REMOTE-SPLITTER FIBER OPTIC CABLE
Technical Field
The present invention generally relates to data transmission media. More particularly, the present invention relates to factory-spliced fiber optic cables having distribution fibers accessible over substantially the entire length of the fiber cable.
Background of the Invention
Recent advances in technology and the loosening of federal regulations have blurred the once-distinct lines between cable television (CATV) and telephony service. Currently, there is a great demand for a distribution infrastructure that will support the demanding throughput requirements of an integrated CATV and telephony network. The explosion of the Internet and the growing desire for individuals to enjoy interactive television are creating communication throughput demands that the existing copper-cable infrastructure simply cannot satisfy.
Fiber optics as a transmission medium promises a significant increase in information throughput to meet the needs of the telecommunications industries. Existing "fiber deep" distribution systems typically provide optical fiber to the serving area, with coaxial cable or twisted pair copper lines from the serving area to the subscriber's home. The information-transmitting capacity of fiber optics is 10 to 100 times higher than that of conventional copper-conductor communications cable. Consequently, there is a strong desire in both the CATV and the telephony industries to push optical fiber as deeply as possible into subscriber communities and neighborhoods.
Unfortunately, the cost of using fiber optics is typically much greater than copper-conductor cable. The high manufacturing, installation, and maintenance costs of fiber cable have created an economic barrier to
providing fiber cable to a subscriber's home. For instance, with existing fiber cable, splice cases are located at discrete locations, called "splice points," along the length of the fiber cable. A drop fiber must be pulled from a splice case and spliced to a main fiber with an optical splitter. The drop fiber cannot be pulled from the cable at any other point along the length of the fiber cable. Currently, the drop fiber must typically be spliced to the main fiber in the field by a field technician. The field technician is likely to encounter environmental hazards, such as weather or debris, which can result in poor-quality splices. Moreover, preparing the main fiber to be spliced, and actually performing the splice, are very time- consuming and difficult tasks to perform in the field.
Field splicing the fiber cable is a difficult task which increases the cost of installing the fiber cable. Also, having a large number of drop fibers emanate from a single location on the fiber cable makes maintaining the fiber drops difficult for a field technician. There is a strong desire to decrease the costs of using fiber cable to make a Fiber-To-The-Home (FTTH) distribution system realizable. A cost-effective fiber optic cable to enable FTTH service has eluded those skilled in the art. Therefore, a need exists for a remote-splitter fiber optic cable that alleviates the problems identified above.
Summary of the Invention
Generally stated, a fiber optic cable according to the present invention has, within the fiber cable outer sheath, distribution fibers spliced to an optical splitter fed by a main fiber. The distribution fibers lie within a distribution buffer tube and are accessible at substantially any point along a length of the fiber cable. In particular, a subset of the distribution fibers extend downstream from the optical splitter, while the remaining distribution fibers extend in the upstream direction from the optical splitter. More particularly, a fiber optic cable according to the present invention has a plurality of buffer tubes, including at least a main buffer tube and a distribution buffer tube, within the cable outer sheath. Within the main buffer tube are multiple main fibers. A main fiber is terminated at an optical splitter, and distribution fibers are spliced to the outputs of the optical splitter. A subset of the distribution fibers extends in the downstream direction of the fiber cable in one distribution buffer tube, and another subset of the distribution fibers from the optical splitter extends in the upstream direction of the fiber cable in another distribution buffer tube.
The foregoing configuration, i.e. an optical splitter having distribution fibers extending in both the upstream and downstream directions, is repeated throughout the fiber cable at a predetermined spacing. At each point along the entire length of the resulting fiber optic cable, rather than only at discrete splice points as with existing cables, at least one distribution fiber is accessible. In one embodiment, at a point along the fiber cable, two groups of distribution fibers are accessible. A first group of the accessible distribution fibers is fed by a first main fiber spliced to a first optical splitter. The other group of accessible distribution fibers is fed from a second main fiber spliced to a second optical splitter. Accordingly, at any point along the fiber cable, a service technician can connect a subscriber to one of at least two available transmitters.
In one embodiment, the optical splitters are factory-installed, which results in a splice of improved quality relative to field-spliced splitters, and significantly reduces the installation time and effort. These benefits, as well as other benefits derived from the present invention, result in a fiber optic cable which reduces the overall cost of providing a fiber optic telecommunications network. By reducing the installation and maintenance costs associated with installing fiber optic cable, the present invention makes a cost effective FTTH distribution infrastructure more easily realizable.
Accordingly, it is an object of the present invention to provide an improved fiber optic cable.
It is another object of the present invention to provide a cost effective fiber optic cable which can make a FTTH telecommunications distribution medium realizable.
It is a further object of the present invention to provide a fiber optic cable having factory-installed optical splitters within the cable sheath, pre-spliced to a feeder portion and a distribution portion of the fiber cable.
The various aspects of the present invention may be more clearly understood and appreciated from a review of the following detailed description of the disclosed embodiments, with reference to the appended drawings and claims.
Brief Description of the Drawings
Fig. 1 is a cut-away illustration of a length of a fiber optic cable according to a preferred embodiment of the present invention.
Fig. 2 is a cut-away somewhat schematic illustration of the fiber optic cable of Fig. 1, detailing an optical splitter location.
Figs. 3A-3D illustrate an exemplary manufacturing process to achieve a fiber cable in accordance with the present invention. Fig. 4 is an illustration of a length of fiber optic cable in accordance with an alternative embodiment of the present invention.
Detailed Description of Preferred Embodiments
Fig. 1 and Fig. 2 illustrate a fiber optic cable 100 constructed according to a preferred embodiment of the present invention. Fig. 1 is a cut-away view of a length of the fiber cable 100, and Fig. 2 is a cut-away view of the fiber cable 100 at optical splitter location 102, detailing optical splitter 110a. For this discussion, the "upstream end" is the end of the fiber cable 100 to be connected to a service provider or other optical signal transmitter. The "downstream end" is the terrriinal end of the fiber cable 100. The "upstream direction" is the direction along the length of cable from the subscriber area back toward the service provider, i.e. a CATV head-end. The "downstream direction" is the opposite direction, or from the service provider to the subscriber area. Fig. 1 depicts main fibers 107a, 107b beginning at the upstream end of the fiber cable 100 and extending the length of the fiber cable 100 until terminated at an optical splitter, such as optical splitters 110a, 110b, respectively. The outer sheath 101 of the cable 100 provides the support necessary for fiber optic cabling. Within the outer sheath 101 and extending the length of the fiber cable 100 is a main buffer tube 105 (Fig. 2). The main fibers 107a, 107b reside within the main buffer tube 105 (Fig. 2). Those skilled in the art will appreciate that as many main fibers as are necessary to service a subscriber area may reside within the main buffer tube 105. Existing fiber cables often have multiple buffer tubes, each carrying a group of main fibers. The buffer tubes may be individually color-coded to enable identifying each group of main fibers. Being able to identify the main fibers is necessary to isolate a particular transmission path from the service provider or CATV head-end to a subscriber. However, for the purpose of clarity only, this discussion of a preferred embodiment is limited to a single main buffer tube 105 housing main fibers 107a, 107b. The main buffer tube 105 and the main fibers 107a, 107b within may be referred to as a "feeder portion."
Also within the cable outer sheath 101 are multiple distribution buffer tubes 109a-109d (Fig. 2). Each distribution buffer tube extends the length of the fiber cable 100 between two adjacent optical splitters, such as between optical splitter 110a and optical splitter 110b (Fig. 1). There may be two or more distribution buffer tubes extending between a pair of adjacent optical splitters. For instance, distribution buffer tube 109c (Fig. 2) and distribution buffer tube 109d both span the length of fiber cable 100 between optical splitter 110a and optical splitter 110b. Likewise, distribution buffer tube 109a and distribution buffer tube 109b both span the length of fiber cable 100 between optical splitter 110a and the next adjacent upstream optical splitter (not shown).
Main fiber 107a is terminated at the optical splitter 110a, one of multiple optical splitters 110a, 110b, . . . spaced apart along the length of the fiber cable 100, at splitter location 102. The optical splitter 110a may be spliced to the main fiber 107a during manufacturing. Any industry-standard method of terminating the main fiber 107a at the optical splitter 110a is acceptable, such as fusion splicing. The remaining main fibers, such as main fiber 107b, continue downstream within the main buffer tube 105 (Fig. 2). The outputs of optical splitter 110a are spliced to a number of distribution fibers, such as distribution fibers 120a, 120b. The distribution fibers reside within and are coextensive with the distribution buffer tubes. Because a 1x16 optical splitter is used in the disclosed embodiment, 16 distribution fibers are spliced to the individual outputs of optical splitter 110a. In the disclosed embodiment, eight of the distribution fibers spliced to the outputs of optical sp Utter 110a extend in the upstream direction within distribution buffer tube 109b (Fig. 2). The remaining eight distribution fibers spliced to the outputs of optical splitter 110a extend in the downstream direction within distribution buffer tube 109c (Fig. 2). Distribution buffer tube 109d, which spans the length of fiber cable 100 between optical splitter 110a and optical splitter 110b, contains upstream distribution fibers, such as distribution fiber 121, associated with optical splitter 110b, which is the next adjacent downstream optical splitter. Those skilled in the art will appreciate that all the distribution fibers spliced to optical splitter 110a can also reside within the same buffer tube without departing from the spirit of the present invention. The upstream distribution buffer tube 109b, the downstream distribution buffer tube 109c, and the distribution fibers within those buffer tubes are collectively
referred to as a "distribution portion" corresponding to optical splitter 110a.
The distance between each optical splitter 110a- 110b depends on the size of the optical splitters, and the number of subscribers that will be serviced by each optical splitter. The number of subscribers serviced by an optical splitter may be equal to the number of distribution fibers fed by the optical splitter. For instance, a 1x16 splitter could service sixteen subscribers, so the distance between optical splitters would correspond to the approximate distance spanned by sixteen subscribers. If sixteen subscribers span approximately 1000 linear feet of fiber cable 100 in a typical populated area, then a 1x16 optical splitter 110a would be sufficient to service the sixteen subscribers and allow approximately 1000 linear feet between optical splitters 110a- 110b. Accordingly, the distance between the optical splitters 1 lOa-HOb can be increased if 1x32 splitters are employed. Although the exemplary embodiment makes use of a 1x16 optical splitter 110a, the size of the optical splitter 110a is dependent on the particular application. It is envisioned that fiber cables of varying configurations will be manufactured based on the needs of particular service providers.
The resultant fiber cable 100 of the disclosed embodiment provides access to sixteen distribution fibers at any location along the length of the fiber cable 100. For instance, at a location 115 along the length of the fiber cable 100, there are eight distribution fibers, such as distribution fiber 120c emanating from optical splitter 110b, within the upstream distribution tube 109d (Fig. 2). There are also eight distribution fibers, such as distribution fiber 120b emanating from optical splitter 110a, in the downstream distribution tube 109c (Fig. 2). It will be appreciated that the fiber cable 100 provides access to distribution fibers from at least two separate main fibers along the length. Consequently, the fiber cable 100 creates the ability to service a particular subscriber from at least two separate interface splice locations.
To connect a subscriber, a field technician penetrates the outer sheath 101 and one of the available distribution buffer tubes, such as distribution buffer tube 109d, at a convenient location, such as location 115. Once the outer sheath 101 and the distribution buffer tube 109d are penetrated, the field technician extracts a selected distribution fiber, such as distribution fiber 120c, from the distribution buffer tube 109d. As noted, the selected distribution fiber 120c emanates from optical splitter 110b. Once the distribution fiber 120c has been withdrawn from the cable outer
sheath 101, the field technician seals the penetration to prevent the cable 100 from being damaged by water infiltration and the like. The method of sealing the cable outer sheath 101 can be any industry-acceptable method, as will be obvious to those skilled in the art. The selected distribution fiber 120c is then spliced to a drop fiber 130, which is in turn placed to the subscriber's location and connected to the subscriber's premises equipment. Those skilled in the art will appreciate that the drop fiber 130 can be connected to the subscriber's premises equipment using any industry-acceptable method, including connectors or splices. The field technician can also access any of the other distribution fibers available at location 115. For instance, if a particular subscriber serviced by the distribution fiber 120c creates an excessive burden on the bandwidth associated with optical splitter 110b, the field service technician can reallocate that subscriber to one of the distribution fibers in the downstream distribution buffer tube 109c (Fig. 2), such as distribution fiber 120b emanating from optical splitter 110a. To do so, the field service technician may disconnect the drop fiber 130 from the distribution fiber 120c and reconnect the drop fiber 130 to a distribution fiber within distribution buffer tube 109c, such as distribution fiber 120b. In this way, the burden of the subscriber is shifted to optical splitter 110a fed by main fiber 107a. As a result, the exemplary embodiment makes available an FTTH distribution medium with the ability to redistribute resources in accordance with subscribers' needs.
The "remote-splitter" fiber cable 100 of the present invention can be more cost-effectively fabricated than the current practice of field- splicing optical splitters into an existing fiber cable. A manufacturer can pre-assemble the fiber cable 100 with a main buffer tube 105, and as many distribution buffer tubes as desired for a particular application. The number of distribution fibers resident in each distribution buffer tube is dependent on the size of the optical splitter employed.
Figs. 3A-3D illustrate an example of a procedure for manufacturing a fiber cable 100 (Fig. 1) in accordance with the present invention. While the disclosed procedure produces a fiber cable constructed in accordance with the present invention, those skilled in the art will understand that there may be other methods for producing such cables. In Fig. 3A, the procedure begins with a substantially conventional fiber optic cable 300 having an outer sheath 305 and a plurality of buffer tubes within the outer sheath 305. The length of the fiber cable 300 is
predetermined based on the number of optical splitters which will be installed, the size of the optical splitters, and the number of drops which will emanate from the fiber cable 300.
In the disclosed embodiment, there are a main buffer tube 310, a first distribution buffer tube 315a, and a second distribution buffer tube 315b. The buffer tubes extend longitudinally within the outer sheath 305 for the length of the cable 300. Within the main buffer tube 310 is at least one main fiber 325 extending the length of the fiber cable 300. Within the distribution buffer tubes 315a, 315b are distribution fibers 330. The number of distribution fibers in each distribution buffer tube 315a, 315b depends on the size of the optical splitters 340 (Fig. 3B) used.
Turning to Fig. 3B, at predetermined locations along the length of the fiber cable 300, the outer sheath 305 is penetrated for access to the buffer tubes within. A longitudinal slot 312 is cut in the main buffer tube 310 for access to the main fibers 325 (Fig. 3A) within. A single main fiber 325a is withdrawn from the main buffer tube 310 and severed. A severed end of the main fiber 325a is fusion spliced to the input of an optical splitter 340. In the disclosed embodiment, a 1x16 optical splitter 340 is used. Those skilled in the art will understand that optical splitters of other sizes may be used to perform the same function, and are equivalent to the 1x16 splitter. The remaining main fibers 325 in the main buffer tube 310 pass on through to the next splitter location.
In the next step of the disclosed embodiment, the distribution buffer tubes 315a, 315b, as well as the distribution fibers 330 within, are completely severed. In the disclosed procedure, two distribution buffer tubes 315a, 315b are severed, corresponding to an upstream buffer tube 315a and a downstream buffer tube 315b. The selection of two distribution buffer tubes is not a critical aspect of the disclosed embodiment, and a different number of buffer tubes can be accessed if desired. For instance, if all the distribution fibers 330 for each optical splitter 340 reside in the same distribution buffer tube 315a, then only one distribution tube 315a may be severed. Severing the distribution fibers 330 results in four sets of fiber ends proximate to the spliced optical splitter 340: upstream fiber ends 350a, 350b and downstream fiber ends 355a, 355b. Turning now to Fig. 3C, the appropriate fiber ends are fusion spliced to the outputs of the optical splitter 340. In the exemplary embodiment, eight upstream fiber ends 350a and eight downstream fiber ends 355a are spliced to the 1x16 optical splitter 340. The unspliced
upstream fiber ends 350b are the terminal ends of the upstream distribution fibers spliced to the next adjacent downstream optical splitter. Likewise, the downstream fiber ends 355b are the terminal ends of the downstream distribution fibers spliced to the next adjacent upstream optical splitter.
Turning finally to Fig. 3D, once the main fiber 325a (Fig. 3C) and the distribution fiber ends 350a, 355a (Fig. 3C) have been spliced to the optical splitter 340 (Fig. 3C), the outer sheath 305 is resealed. Those skilled in the art will understand that the outer sheath 305 may be resealed in any conventional manner, such as placing a splice case and weatherproof cable connectors. In this manner, a fiber cable having remote splitters is fabricated which provides the ability to penetrate the fiber cable 100 outer sheath 305 at substantially any location along its length, and extract a distribution fiber 330. That distribution fiber 330 can then be spliced to a drop fiber to service a subscriber.
Fig. 4 illustrates an alternative embodiment of a fiber optic cable 400 according to the present invention. The fiber cable 400 contains main buffer tube 405, distribution buffer tube 410, and distribution buffer tube 411. An access slot 412 provides access to the main fibers resident within the main buffer tube 405. A main fiber 415 protrudes from access slot 412 and is fusion spliced, in a conventional manner, to a 1x32 optical splitter 420.
Distribution fibers 430 are resident within distribution buffer tube 410. The outputs 425 of the optical splitter 420 are fusion sphced to the ends of the distribution fibers 430 protruding from distribution buffer tube 410. The distribution fibers 430 extend in the downstream direction within the distribution buffer tube 410. In this alternative embodiment, the fiber cable 400 provides a length of fiber cable having 32 distribution fibers 430 accessible from substantially any location along the length of the cable 400. However, each accessible distribution fiber 430 corresponds to a single optical splitter 420. The distribution fibers 435 protruding from distribution buffer tube 411 all emanate from the next upstream optical splitter.
While embodying most advantages discussed above, fiber cable 400 does not allow the field technician to reallocate a particular subscriber to another transmitter as in the previous embodiment. All the distribution fibers 430 are routed in the downstream direction. However, fiber cable 400 does provide access to the entire complement of
distribution fibers 430 along substantially the entire length of the fiber cable 400. Moreover, the fiber cable 400 may be constructed in the factory, which enables higher quality splices, and greatly reduces the time and cost associated with installing and mamtaimng fiber cable, thereby making realizable a more cost efficient FTTH distribution infrastructure.
The disclosed embodiments illustrate only the buffer tubes necessary to enable one of ordinary skill in the art to practice the present invention. Those skilled in the art will appreciate that typical fiber cable consists of multiple buffer tubes carrying a plurality of groups of main fibers. Although the disclosed embodiments are discussed with reference to a single feeder portion and a single distribution portion, it is within the purview of the present invention that a fiber cable can comprise a plurality of feeder portions and a plurality of corresponding distribution portions. Moreover, the discussion of the disclosed embodiments is in no way intended to limit the present invention to a more narrow scope than that defined by the appended claims.
In summary, the present invention provides a cost effective fiber cable which will allow the telecommunications industry to more easily realize a FTTH network. Advantageously, the present invention provides a remote-splitter fiber optic cable with pre-fabricated optical splitters, the distribution fibers of each optical splitter being displaced within distribution buffer tubes in such a manner as to provide access to a plurality of distribution fibers at any location along the length of the fiber cable. Therefore, from the foregoing description of an exemplary embodiment, other embodiments of the present invention will suggest themselves to those skilled in the art and the scope of the present invention is limited only by the claims below and equivalents thereof.