Patent Application
20190219783
The invention relates to optical fiber cables. More particularly, the invention relates to optical fiber cables having optical fiber ribbons therein.
Conventionally, loose tube microcables typically are defined as cables that use buffer tubes and that have optical fiber densities of at least approximately 4.2 fibers/millimeter2. Such fiber density is based on the optical fiber count (e.g., 12 optical fibers) and the nominal buffer tube outer diameter (e.g., 1.9 millimeters (mm)) of a conventional microcable, such as a MiDia FX+ cable manufactured by OFS Fitel.
However, a more practical density metric is the ratio of optical fiber cross-sectional area to buffer tube cross-sectional area. This density metric becomes particularly useful when discussing various optical fiber sizes, e.g., 250 micron diameter fiber and the recently introduced 200 micron diameter fiber. The MiDia FX+ cable discussed above uses twelve 250 micron diameter fibers per 1.9 millimeter outer diameter buffer tube, and thus the ratio of optical fiber cross-sectional area to buffer tube cross-sectional area is approximately 0.21.
Microcables typically are intended to be used in air-blown applications, i.e., within ducts, and specifically within microducts. The locations in which these ducts are installed generally have space that is at a premium in terms of scarcity and/or cost. Resultantly, the space inside these ducts is also quite limited, thus placing a relatively major constraint on the size of the cables that can be installed therein. Because the cable size is constrained, a way to increase optical fiber density in a duct is to pack more optical fibers into the cables that meet this size constraint.
Recent examples of increasing optical fiber density in loose tube microcables include the progressive development of microcables with buffer tubes having an outer diameter of 1.7 mm and containing twelve 250 micron diameter optical fibers, microcables with buffer tubes having an outer diameter of 1.5 mm and containing twelve 250 micron diameter optical fibers, and microcables with buffer tubes having an outer diameter of 1.7 mm but with twice as many optical fibers per buffer tube, which is accomplished using optical fibers with an outer diameter of 200 microns. Through this development, one can observe the increased fiber density by either cable size reduction or increased fiber count per buffer tube (and subsequently per cable).
With regard to increasing optical fiber count per buffer tube, one limitation is the identification of optical fibers based on color. In North America, colors for identification of fibers are defined in ANSI/TIA-598-D-2014—“Optical Fiber Cable Color Coding.” This standard is referenced by industry cable standards, such as Telcordia GR-20, and notably the first edition of ICEA S-122-744 (U.S. national standard for microduct cable. There are 12 distinct optical fiber colors defined in TIA-598 that are commonly used in the industry (although there have been some proposals to extend that to 16 optical fiber colors). Presently, ANSI/TIA-598-D-2014 requires that any extension beyond 12 optical fibers within a tube identify fibers 1-12 using the 12 distinct colors, then use unique tracer identification for additional fibers beyond 12. This tracer identification typically takes the form of ring-marking of the optical fiber, where identification marks are applied with an ink-jet printer or other suitable means. In such cases, optical fibers 1-12 are the standard colors defined in ANSI/TIA-598-D-2014, optical fibers 13-24 are the same colors as fibers 1-12 but have a single repeating mark as a tracer, optical fibers 25-36 are the same colors as fibers 1-12 but have two repeating marks as a tracer, etc. However, adding these tracers is undesirable because adding the tracers adversely affect the manufacturability and the quality of the optical fiber itself. One manufacturability issue is that ring-marks are generally applied at relatively low line speeds compared to the standard optical fiber coloring process. One quality issue is that the printed ink marks can act as point defects on the optical fiber, which increase signal attenuation.
For higher fiber count optical fiber cables, a typical solution used to increase density is through use of flat optical fiber ribbons. Note that an advantage of flat optical ribbons over loose optical fibers is the ability to use mass fusion splicing, in which a plurality of fibers can be spliced at once, increasing worker efficiency during installation. However, with regard to use in microcable applications, stacked flat optical fiber ribbons disallow tight-packing of optical fibers in circular buffer tubes, because rectangular/square shapes are formed when stacking these flat optical fiber ribbons. It is possible to package flat optical ribbons in loose tube cable structures, such as the AccuTube cable manufactured by OFS Fitel, but the resulting cables are too large to be used for microduct applications. Therefore, the use of stacked, flat optical fiber ribbons is not a suitable approach for a loose tube microcable application. Central tube microcables can incorporate flat optical fiber ribbons, however, those designs have a drawback of having one or more relatively small, rigid strength member reinforcements on the outside of the cable, resulting in relatively poor installation performance. Loose tube cables, which typically use a relatively large, rigid strength member rod in the center of the cable, generally exhibit better installation performance, as their relatively high rigidity makes it easier to “push” these cables with air. An additional problem with conventional loose tube microcables with loose optical fiber is that they do not support mass fusion splicing unless the installer takes the time-consuming step of field-ribbonizing the optical fiber.
The invention is embodied in an optical fiber cable. The optical fiber cable includes at least one multi-fiber unit tube. The multi-fiber unit tube is substantially circular and dimensioned to receive a plurality of optical fibers. The optical fiber cable also includes at least one rollable optical fiber ribbon comprising a plurality of optical fibers positioned within the at least one multi-fiber unit tube. The plurality of optical fibers in the at least one rollable optical fiber ribbon are rolled in such a way that the at least one rollable optical fiber ribbon is formed in a variable shape. The optical fiber cable also includes a jacket surrounding the at least one multi-fiber unit tube.
In the following description like reference numerals indicate like components to enhance the understanding of the invention through the description of the drawings. Also, although specific features, configurations and arrangements are discussed hereinbelow, it should be understood that such is done for illustrative purposes only. A person skilled in the relevant art will recognize that other steps, configurations and arrangements are useful without departing from the spirit and scope of the invention.
Some existing optical fiber cable manufacturers have developed a partially bonded optical fiber ribbon, also referred to as a rollable ribbon or pliable ribbon, where the optical fibers forming the optical fiber ribbon are not bonded over their entire length. The optical fibers are bonded intermittently, thus allowing the optical fibers of the optical fiber ribbon the flexibility to be folded or rolled about an axis parallel to the fibers so that the optical fiber ribbon can take on a variable shape, e.g., an approximately round cylindrical shape or as a relatively compact bundle with an approximately cylindrical shape or other suitable shape. In this manner, the shape of the optical fiber ribbon conforms to the shape of adjacent optical fiber ribbons along its length thereby reducing any space between them. The ability of the optical fibers of the optical fiber ribbon to be folded or rolled allows for better filling of a circular cable within which the optical fiber ribbon is positioned, resulting in more optical fibers to be included in a given cable diameter compared to optical fiber cables with conventional fully bonded ribbon structures.
As discussed hereinabove, one limitation to increasing optical fiber count per buffer tube is the identification of optical fibers based on color. Any extension beyond the current 12 distinct optical fiber colors conventionally requires unique tracer identification, generally using ring-marking of the optical fiber, where identification marks are applied by conventional means. However, adding these tracers is undesirable, as the tracers may adversely affect the manufacturability and quality of the optical fiber itself. Also, as discussed hereinabove, the conventional use of flat optical fiber ribbons for increased optical fiber count per buffer tube prevents tight-packing of optical fibers in circular buffer tubes because rectangular/square shapes are formed when stacking these flat optical fiber ribbons.
According to embodiments of the invention, the use of rollable optical fiber ribbons, e.g., partially bonded rollable optical fiber ribbons, offers a hybrid solution to attain greater fiber count microcables. The use of rollable optical fiber ribbons allows for the identification of optical fibers beyond the twelve standard colors, without using the tracers as mentioned above. Accordingly, normal coloring processes can be applied to the rollable optical fiber ribbon fibers, thereby eliminating the adverse manufacturing effects and optical fiber quality issues associated with adding tracers directly on the surface of the colored optical fibers.
According to embodiments of the invention, one way to avoid the use of tracers is to vary the sequence of fiber colors for each rollable optical fiber ribbon. For example, if a first rollable optical fiber ribbon is blue-orange-green-brown, a second rollable optical fiber ribbon can be blue-green-brown-orange. In this manner, the first rollable optical fiber ribbon can be distinguished from the second rollable optical fiber ribbon because the optical fibers in each rollable optical fiber ribbon are joined together.
According to embodiments of the invention, another way to avoid the use of tracers is by printing on the rollable optical fiber ribbon, e.g., using an ink-jet printer, such as a VideoJet printer. Printing on the rollable optical fiber ribbon, e.g., using an ink-jet printer, allows a marking ink of any number of readable characters to be printed directly on the rollable optical fiber ribbon for identification. Printing on the rollable optical fiber ribbon, e.g., using an ink-jet printer, is extremely desirable because such printing on the rollable optical fiber ribbon can be performed during the ribbon manufacturing process without the need for a change in line speed or productivity.
By controlling the line pay-off and take-up to have a certain amount of tension, and by controlling the guide roller to have a certain amount of width, printing on the rollable optical fiber ribbon can be performed at a relatively high rate of speed with suitable legibility, even though the surface of the rollable optical fiber ribbon is not uniform like that of a flat optical fiber ribbon. Therefore, printing on the rollable optical fiber ribbon, e.g., using an ink-jet printer, eliminates the need for an additional process of applying wrapping binder thread around the rollable optical fiber ribbon (as well as the inconvenience of having to remove the binder thread during fiber installation).
Another advantage to printing on the rollable optical fiber ribbon instead of using tracers on 200 or 250 micron loose fiber is that printing allows a readable legend or markings to be printed on the rollable optical fiber ribbon, instead of one or more dashes when using tracers. For example, a readable legend, such as “1-AW-1” (e.g., for AllWave ribbon 1) can be printed on the rollable optical fiber ribbon. Also, because a readable legend can be printed on the rollable optical fiber ribbon, the distance between readable markings can be spaced out, which can help compensate for any attenuation effects of the printing. Also, printing a readable legend on the rollable optical fiber ribbon allows for fewer passes to achieve suitable identification for the rollable optical fiber ribbon. For example, if you have 24 optical fibers per tube, using tracer identification requires 12 ring-marking passes. However, for a 24-fiber tube using two 12-fiber rollable or flat optical fiber ribbons, printing on the ribbon only requires 2 ribboning passes. For 48 optical fibers per tube, using tracer identification requires 36 ring-marking passes, while printing for a 48-fiber tube using four 12-fiber rollable or flat optical fiber ribbons requires only 4 ribboning passes.
Another advantage of using rollable ribbons is that it simplifies tube manufacturing equipment. To manufacture a microcable buffer tube with 48 loose fibers, you need a large, relatively expensive payoff with 48 different spindles. In contrast, to make a 48-fiber buffer tube with 4-fiber ribbons, you only need 12 payoff spindles, which is common for the manufacture of 12-fiber tubes. In a preferred embodiment using 12-fiber rollable ribbons, only 4 payoff positions are needed in the loose-tube manufacturing process.
Also, the use of rollable optical fiber ribbons allows for a more circular cross-section of optical fibers than that offered by stacked, flat optical fiber ribbons. Consequently, buffer tubes can have a reduced cross-sectional area to better match that of the rollable optical fiber ribbons housed therein.
By comparison, the multi-fiber unit tube structure 62 includes a plurality of rollable optical fiber ribbons 64 that are rolled and/or folded into more densely configured unit shapes, e.g., generally circular shapes and other shapes. For example, each rollable optical fiber ribbon 64 is a 4-fiber (shown as optical fibers 66A-D) rollable optical fiber ribbon 64. As shown, each rollable optical fiber ribbon 64 (each having optical fibers 66A-D) is rolled and/or folded into a more densely configured unit shape. As a result, the rollable optical fiber ribbons 64 allows for a more circular cross-section of optical fibers than that offered by the stacked, flat optical fiber ribbons 54. As shown, for the same number of optical fibers (24), the multi-fiber unit tube structure 62 housing the rollable optical fiber ribbons 64 has a smaller diameter than the multi-fiber unit tube structure 52 housing the stacked, flat optical fiber ribbons 54. The difference in diameter between the multi-fiber unit tube structure 62 and the multi-fiber unit tube structure 52 is shown generally as a distance 72.
Also, in addition to increased optical fiber density, another advantage of using rollable optical fiber ribbons is the ability to use mass fusion splicing, which is the fusing of multiple optical fibers at a time, as opposed to fusing just one optical fiber at a time. The ability to use mass fusion splicing is a rather distinct feature of a cable product/family that employs the use of rollable optical fiber ribbons, because microcables largely employ loose fibers in their designs.
For example, when housing rollable optical fiber ribbons into a multi-fiber unit tube structure, the rollable optical fiber ribbons can be forced into roughly cylindrical shapes (and other suitable shapes). However, when rollable optical fiber ribbons are made, and when rollable optical fiber ribbons are taken out of their multi-fiber unit tube structure, each rollable optical fiber ribbon wants to lay flat, with the matrix material holding the individual optical fibers in sequential order. With the rollable optical fiber ribbon lying flat, the rollable optical fiber ribbon can be directly fusion spliced using the same methods used for fusion splicing conventional flat optical fiber ribbons.
The use of rollable optical fiber ribbons in microcables with 12, 24, 36, 48 or 72 optical fibers per multi-fiber unit tube provides at least the same packing density as conventional loose optical fiber or multi-fiber unit tube cables. However, even for cables with the same optical fiber packing density, the use of rollable optical fiber ribbons within multi-fiber unit tube microcables provides labor savings for installers by supporting mass fusion splicing.
For conventional flat optical fiber ribbon stack structures, such as the multi-fiber unit tube structure 52 shown in
By comparison, for rollable optical fiber ribbon structures according to embodiments of the invention, such as the multi-fiber unit tube structure 62 shown in
As shown by the comparisons discussed hereinabove, the use of rollable optical fiber ribbons offers an improved compactness compared to conventional flat optical fiber ribbons. Also, as discussed hereinabove, the use of rollable optical fiber ribbons offers an improved identification scheme compared to conventional optical fibers with tracers (i.e., ring-marked optical fibers).
Each multi-fiber unit tube structure 116 can be made of any suitable material. For example, each multi-fiber unit tube structure 116 can be made of polypropylene, polybutylene terephthalate (PBT), polyethylene, nylon, polycarbonate, thermoplastic polyurethane (TPU), poly(vinyl chloride) (PVC) or other suitable material or materials. Flame retardant additives may be incorporated into the multi-fiber unit tube structure 116 to help impart fire resistance, which may be desirable if some or all of the cable is deployed inside a building. Also, one or more dry water swellable materials may be incorporated into the multi-fiber unit tube structure 116 to block water penetration therein. The multi-fiber unit tube structure 116 can be a homogeneous tube. Alternatively, the multi-fiber unit tube structure 116 can be a multi-layer tube produced by coextrusion.
The outer sheath or jacket 112 can be made of any suitable material. For example, the jacket 112 can be made of polyethylene, thermoplastic polyurethane, nylon 12, or other suitable material. Flame-retardant additives may be incorporated into the jacket 112 to impart fire resistance to the cable. In one embodiment, the jacket 112 is made from high-density polyethylene (HDPE), with a nominal jacket thickness of approximately 0.5 mm or less. For microcable applications, it is desirable to use the thinnest possible jacket that can be fabricated without pinholes or other defects.
As discussed hereinabove, because of its specific structure, e.g., being a partially bonded optical fiber ribbon or an optical fiber ribbon having other suitable structure, each rollable optical fiber ribbon 118 can be rolled and/or folded into one or more densely configured unit shapes, as shown. For example, each rollable optical fiber ribbon 118 can be rolled into a circular or somewhat circular shape, so that the rollable optical fiber ribbons 118, either individually or collectively, more closely resemble the shape of their respective multi-fiber unit tube structure 116 compared to a conventional stack of flat optical fiber ribbons or other conventional optical fiber ribbons arrangements.
Both loose-tube cable structures 110, 120 have an outer diameter of approximately 10.2 mm. However, the loose-tube cable structure 110 in
Each multi-fiber unit tube structure 136 can be made of any suitable material. For example, each multi-fiber unit tube structure 136 can be made of polypropylene, polybutylene terephthalate (PBT), polyethylene, nylon, polycarbonate, thermoplastic polyurethane (TPU), poly(vinyl chloride) (PVC) or other suitable material or materials. One or more dry water swellable materials may be incorporated into the multi-fiber unit tube structure 136 to block water penetration therein. The multi-fiber unit tube structure 136 can be a homogeneous tube. Alternatively, the multi-fiber unit tube structure 136 can be a multi-layer tube produced by coextrusion. In one embodiment, in which the rollable ribbon 138 is made from 250 micron optical fiber, each multi-fiber unit tube structure 136 has a thickness of 0.25 mm, an outer diameter of 1.70 mm, and an inner diameter of 1.20 mm.
The outer sheath or jacket 132 can be made of any suitable material. For example, the jacket 132 can be made of polyethylene, thermoplastic polyurethane, nylon 12, or other suitable material. Flame-retardant additives may be incorporated into the jacket 132 to impart fire resistance to the cable. In one embodiment, the jacket 132 is made from high-density polyethylene (HDPE), with a nominal jacket thickness of approximately 0.50 mm or less, and an outer diameter of 6.40 mm.
Each multi-fiber unit tube structure 156 can be made of any suitable material. For example, each multi-fiber unit tube structure 156 can be made of polypropylene, polybutylene terephthalate (PBT), polyethylene, nylon, polycarbonate, thermoplastic polyurethane (TPU), poly(vinyl chloride) (PVC) or other suitable material or materials. One or more dry water swellable materials may be incorporated into the multi-fiber unit tube structure 156 to block water penetration therein. The multi-fiber unit tube structure 156 can be a homogeneous tube. Alternatively, the multi-fiber unit tube structure 156 can be a multi-layer tube produced by coextrusion. In one embodiment, each multi-fiber unit tube structure 156 has a thickness of 0.20 mm, an outer diameter of 1.50 mm, and an inner diameter of 1.10 mm.
The outer sheath or jacket 152 can be made of any suitable material. For example, the jacket 152 can be made of polyethylene, thermoplastic polyurethane, nylon 12, or other suitable material. Flame-retardant additives may be incorporated into the jacket 152 to impart fire resistance to the cable. In one embodiment, the jacket 152 is made from high-density polyethylene (HDPE), with a nominal jacket thickness of approximately 0.5 mm or less, and an outer diameter of 6.50 mm.
It will be apparent to those skilled in the art that many changes and substitutions can be made to the embodiments of the invention herein described without departing from the spirit and scope of the invention as defined by the appended claims and their full scope of equivalents.
