US20070230880A1 - Telecommunications cable jacket adapted for post-extrusion insertion of optical fiber and methods for manufacturing the same - Google Patents

Abstract

The present disclosure relates to a telecommunications cable having a jacket including a feature for allowing post-extrusion insertion of an optical fiber or other signal-transmitting member. The present disclosure also relates to a method for making a telecommunications cable having a jacket including a feature for allowing post-extrusion insertion of an optical fiber or other signal-transmitting member.

Description

TECHNICAL FIELD
• The present disclosure relates generally telecommunications cable for transmitting data and to methods for manufacturing telecommunications cable.
BACKGROUND
• A fiber optic cable typically includes: (1) a fiber or fibers; (2) a buffer or buffers that surrounds the fiber or fibers; (3) a strength layer that surrounds the buffer or buffers; 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 covered by a coating. Buffers typically function to surround and protect coated optical fibers. Strength layers add mechanical strength to fiber optic cables to protect the internal optical fibers against stresses applied to the cables during installation and thereafter. Example strength layers include aramid yarn, steel and epoxy reinforced glass roving. Outer jackets provide protection against damage caused by crushing, abrasions, and other physical damage. Outer jackets also provide protection against chemical damage (e.g., ozone, alkali, acids).
• It is well known that micro-bending of an optical fiber within a cable will negatively affect optical performance. Shrinkage of the outer jacket of a fiber optic cable can cause axial stress to be applied to the optical fiber, which causes micro-bending of the optical fiber. One cause of jacket shrinkage is thermal contraction caused by decreases in temperature. For example, fiber optic cables are typically manufactured using an extrusion process. After a given cable has been extruded, the cable is passed through a cooling bath. As the cable cools, the jacket can contract more than the internal optical fiber or fibers causing micro-bending of the fiber or fibers.
SUMMARY
• One aspect of the present disclosure relates to a telecommunications cable having a jacket including a feature for allowing post-extrusion insertion of an optical fiber or other signal-transmitting member.
• Another aspect of the present disclosure relates to a method for making a telecommunications cable having a jacket including a feature for allowing post-extrusion insertion of an optical fiber or other signal-transmitting member.
• A variety of other aspects are set forth in the description that follows. The aspects relate to individual features as well as to combinations of features. It is to be understood that both the foregoing general description and the following detailed descriptions are exemplary and explanatory only and are not restrictive of the invention as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a cross-sectional view of an example fiber optic cable in accordance with the principles of the present disclosure, the cross-section is taken along section line1-1 ofFIG. 12;
• FIG. 2 illustrates an example system for extruding the fiber optic cable ofFIG. 1;
• FIG. 3 is a cross-sectional view taken along section line3-3 ofFIG. 2;
• FIG. 4 is a cross-sectional view taken along section line4-4 ofFIG. 2;
• FIG. 5 shows an example crosshead that can be used with the system ofFIG. 6;
• FIG. 6 is a side view of a die used with the crosshead ofFIG. 5;
• FIG. 7 is a top view of the die ofFIG. 6;
• FIG. 8 is an end view of the die ofFIG. 6;
• FIG. 9 is a side view of a tip used with the crosshead ofFIG. 5;
• FIG. 10 is an end view of the tip ofFIG. 9;
• FIG. 11 is a top view of the tip ofFIG. 9;
• FIG. 12 shows an example system for inserting optical fiber into the cable extruded at the system ofFIG. 2;
• FIG. 13 is a cross-sectional view taken along section line13-13 ofFIG. 12;
• FIG. 14 is a cross-sectional view taken along section line14-14 ofFIG. 12;
• FIG. 15 is a cross-sectional view of another example fiber optic cable in accordance with the principles of the present disclosure;
• FIG. 16 is a cross-sectional view of an example crosshead used to extrude the fiber optic cable ofFIG. 15;
• FIG. 17 is a cross-sectional view taken along section line17-17 ofFIG. 16; and
• FIG. 18 is a cross-sectional view taken along section line18-18 ofFIG. 16.
DETAILED DESCRIPTION
• The present disclosure relates generally to telecommunication cable jackets having features that facilitate the post-extrusion insertion of optical fibers into the jackets. Example features that facilitate the post-extrusion insertion of optical fibers include slits, predefined slit locations (e.g., perforations, partial slits, weakened regions, etc.). In certain embodiments, a ripcord can be pulled from a jacket to create a feature that facilitates the post extrusion insertion of optical fiber into the jacket. The present disclosure also relates to methods for manufacturing jackets having features for facilitating the post extrusion insertion of optical fibers, and also relates to methods for inserting optical fibers into jackets. While the various aspect of the present disclosure are particularly useful for fiber optic cables, the aspects are also applicable to other types of telecommunications cables (e.g., copper cables).
• FIG. 1 illustrates an example fiberoptic cable20 in accordance with the principles of the present disclosure. The fiberoptic cable20 includes anoptical fiber22, a strength structure26 (e.g., one or more reinforcing members or layers), anoptional filler27 and ajacket28. Thejacket28 includes an interior passage31 (e.g., a hole) that runs along the length of thejacket28. Theoptical fiber22 is positioned within theinterior passage31. Thejacket28 also includes aslit29 that runs along the length of the jacket for allowing the post-extrusion insertion of theoptical fiber22 into theinterior passage31 of thejacket28. Thejacket28 further includes aninterior passage33 that runs parallel to thepassage31 for holding thestrength structure26.
• It will be appreciated that theoptical fiber22 can have any number of conventional configurations. For example, theoptical fiber22 may include a silica-based core surrounded by a silica-based cladding having a lower index of refraction than the core. One or more protective polymeric coatings (e.g., ultraviolet curable acrylate) may surround the cladding. Theoptical fiber22 may be a single-mode fiber or a multi-mode fiber. Example optical fibers are commercially available from Corning Inc. of Corning, N.Y. While only onefiber22 is shown within thejacket28, in other embodiments multiple fibers can be mounted within thejacket28.
• Thefiber22 is preferably an unbuffered fiber. However, buffered fibers could also be used. For example, the buffers can 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.
• Thestrength structure26 is adapted to inhibit axial tensile and/or compressive loading from being applied to theoptical fiber22. Thestrength structure26 preferably extends the entire length of the fiber optic cable. In certain embodiments, the strength structure can include one or more reinforcing members such as yarns (e.g., aramid yams), fibers, threads, tapes, films, epoxies, filaments, rods, or other structures. In a preferred embodiment, thestrength structure26 includes a reinforcing rod (e.g., a glass reinforced plastic rod having glass rovings in an epoxy base, a metal rod, a liquid crystal polymer rod, etc.) that extends lengthwise along the entire length of the cable.
• Thefiller27 is optional and functions to fill void areas within the jacket. Thefiller27 would typically be used for cables designed for environments where water intrusion is a concern. By filling the voids around and between the fibers, the filler prevents water from entering the voids. Example fillers include thixotropic gels, petrolatum compounds. In certain embodiments, the filler can have adhesive properties that assist in sealing the slit and in holding the slit closed after the fiber has been mounted within the jacket.
• Theslit29 allows thejacket28 to be spread-apart to allow thefiber22 to be inserted within theinterior passage31 of thejacket28. After insertion of thefiber22 into thepassage31, the slit can be held closed by the inherent mechanical properties of the jacket, which bias the slit to a closed position. Additional structure can also be used to assist in holding theslit29 closed after insertion of the fiber. For example, adhesives or other bonding agents can be used to bond together the opposing portions of the jacket that define theslit29. In other embodiments, a reinforcing sheath can be mounted over thejacket28 after insertion of the optical fiber to prevent the slit from opening.
• Thejacket28 is preferable manufactured from an extrudable base material such as an extrudable plastic material. Example base materials for the jacket include conventional thermoplastic polymers such as Alcryn® Melt-Processible Rubber sold by Advanced Polymer Alloys (a division of Ferro Corporation), polyethylene, polypropylene, ethylene-propylene, copolymers, polystyrene, and styrene copolymers, polyvinyl chloride, polyamide (nylon), polyesters such as polyethylene terephthalate, polyetheretherketone, polyphenylene sulfide, polyetherimide, polybutylene terephthalate, low smoke zero halogens polyolefins and polycarbonate, as well as other thermoplastic materials. Additives may also be added to the base material. Example additives include pigments, fillers, coupling agents, flame retardants, lubricants, plasticizers, ultraviolet stabilizers or other additives. The base material can also include combinations of the above materials as well as combinations of other materials.
• FIG. 2 illustrates asystem100 for extruding thefiber optic cable20 ofFIG. 1. Thesystem100 includes acrosshead102 that receives thermoplastic material from anextruder104. Ahopper106 is used to feed materials into theextruder104. Aconveyor108 conveys the material for thejacket28 to thehopper106. Theextruder104 is heated by aheating system112 that may include one or more heating elements for heating zones of the extruder as well as the crosshead to desired processing temperatures. A rip member115 (seeFIGS. 2 and 3) is fed into thecrosshead102 from afeed roll114. Therip member115 is preferably a cord, strip, string, fiber or other elongated structure constructed of one or more component parts. Example materials for manufacturing therip member115 include aramid yam, metal wire, polypropylene, extruded glass rod or other materials. A strength structure26 (seeFIGS. 2 and 3) is also fed into the crosshead from one or more feed rolls116. Awater trough118 is located downstream from thecrosshead102 for cooling the extruded product (seeFIG. 4) that exits thecrosshead102. The cooled final product is stored on a take-up roll120 rotated by adrive mechanism122. Acontroller124 coordinates the operation of the various components of thesystem100.
• Referring toFIG. 5, theextruder104 is depicted as including anextruder barrel140 and an auger/style extruder screw142 positioned within thebarrel140. An extruder screen can be provided at the exit end of theextruder104. The screen prevents pieces too large for extrusion from passing from the extruder into thecrosshead102.
• Referring still toFIG. 5, thecrosshead102 includes a jacketmaterial input location200 that receives thermoplastic material from theextruder104. A tip202 (shown atFIGS. 5 and 9-11) and a die204 (shown atFIGS. 5-8) are mounted at thecrosshead102. Thetip202 defines a firstinner passageway206 through which therip member115 is fed. Thetip202 also defines a secondinner passageway207 through which thestrength structure26 is fed. The second inner passageway is spaced below and generally parallel to the first inner passageway. Thedie204 defines anannular extrusion passage208 that surrounds the exterior of thetip202. Thecrosshead102 defines anannular passageway209 for feeding the thermoplastic jacket material from theextruder104 to theannular extrusion passage208. Within the crosshead, the flow direction of the thermoplastic material turns 90 degrees relative to the flow direction of theextruder104 to align with the direction of travel of thestrength structure26 and therip member115.
• Referring toFIGS. 6-8, aslitting blade mount220 is coupled to thedie204. Theslitting blade mount220 includes a pair of mountingplates221 separated by a space222 for receiving a slitting blade223 (shown atFIG. 5). Fasteners such as screws or bolts can be inserted through openings225 in theplates221 to secure theblade223 between theplates221.
• As shown atFIG. 5, theslitting blade223 is mounted directly at the exit of theannular extrusion passage208. As depicted, theblade223 extends to the exterior surface of therip member115 so as to cut a slit that extends completely from the exterior of the jacket to therip member115. However, in other embodiments, the blade may extend only a partial distance between the exterior of the jacket and the exterior of therip member115.
• In use of thesystem100, the base material for the jacket and any additives are delivered to thehopper106 by theconveyor108. From thehopper106, the material moves by gravity into theextruder104. In theextruder104, the material is mixed, masticated, and heated. Theextruder104 also functions to convey the material to thecrosshead102, and to provide pressure for forcing the material through thecrosshead102. As the material exits thecrosshead102, the material is forced between the tip and the die causing the material to be formed to a desired cross-sectional shape. For example, the material is formed with thepassages31,33 (seeFIG. 4) in which the strength structure and the rip member are positioned. After passing between the tip and the die, the material is cut/slit by theslitting blade223. Because the material is still relatively molten when cut, the surfaces defining the slit may adhere slightly back together after being slit. However, at the very least, the slitting blade provides a weakened region (i.e., a pre-defined slit location) corresponding to the slit.
• The extrusion process can be a pressure or semi-pressure extrusion process where product leaves the crosshead at the desired shape, or an annular extrusion process where the product is drawn down after extrusion. After cooling, the product is collected on the take-uproller120.
• FIG. 12 shows anexample system320 for inserting optical fiber (or other type of signal conveying member) into the cable extruded at the system of FIG.2. Thesystem320 includes a ripmember removal station322 and afiber insertion station324. Before the cable from the system ofFIG. 2 is processed at the system ofFIG. 3, it can be cycled through temperature variations to remove internal stress from the jacket material.
• Referring toFIGS. 12 and 13, thesystem320 includes two sets ofpinch rollers326 that assist in moving the cable through the opticalfiber insertion station324. The cable is pinched between therollers326 and the rollers are driven to control the position of the cable. Feed and take-uprollers328,329 also assist in controlling the position of the cable.
• The ripmember removal station322 includes a drivenroller330 that pulls the rip member315 from the cable as the cable is moved through thesystem320. As the rip member315 is removed from the cable, the jacket of the cable tears/rips along the pre-defined slit location thereby breaking any bonds between the opposing walls of the slit that may have occurred after the slitting process. In alternative embodiments, the removal of the rip member315 may be a manual process.
• The opticalfiber insertion station324 includes a spreading shoe340 (seeFIG. 14) having a spreader342 (e.g., a v-shaped plow or other structure having angled surfaces/ramps) that spreads apart the slit in the cable as shown atFIG. 14. Theinsertion station324 also includes aninsertion tool344 that receives optical fiber from an opticalfiber feed roll346. Theinsertion tool344 includes an angled receivingportion348 and abent tip350. Thebent tip350 fits through theslit29 and into thepassage31 of the cable. Thetip350 preferably co-axially aligns with thepassage31 of the cable jacket. A pair ofpinch rollers360,362 pushes the optical fiber into theinsertion tool344. The optical fiber is frictionally pinched between therollers360,362. Therollers360,362 are driven by adrive roller363 that engages the cable being processed by the system. Movement of the cable causes rotation of thedrive roller363 that, in turn, causes rotation ofrollers360,362. This feed configuration ensures that the optical fiber and the cable are fed though the system at the same linear speed.
• The opticalfiber insertion station324 also includes an optionalfiller injection tool366 for injecting filler into thepassage31. As shown atFIG. 12, thetool366 includes a syringe having a needle that extends into thepassage31 through theslit31. In other embodiments, an adhesive application station could be placed downstream of thefiller injection tool366 to apply adhesive to the jacket for the purpose of sealing and bonding the slit closed. In still other embodiments, a sheathing station can be placed downstream of the insertion station for applying an outer sheath about the jacket for protecting the jacket and for holding the slit closed.
• In use, the cable is fed fromfeed roller328 and moved through the system in a controlled manner byrollers326. At the ripmember removal station322, the rip member315 is torn from the jacket to ensure that the slit is fully open. Thereafter, at thefiber insertion station324, the slit is spread open and the optical fiber is fed into theinterior passage31 of the jacket through theslit29. Filler is then injected into the slit. The slit is then allowed to self-close, and the cable is collected atroller329.
• FIG. 15 illustrates an examplefiber optic cable420 in accordance with the principles of the present disclosure. Thefiber optic cable420 includes a plurality of bufferedoptical fibers422, a plurality ofstrength structures426 and ajacket428. Thejacket428 includes a relatively largecentral passage431 that runs along the length of thejacket428. Theoptical fibers422 as well as optional fillers are positioned within thecentral passage431. Thejacket428 also includes aslit429 that runs along the length of the jacket for allowing the post-extrusion insertion of theoptical fibers422 into thepassage431 of thejacket428. Thejacket428 further includesinterior passages433 that run parallel to thepassage431 for holding thestrength structure426. The components of thecable420 can be constructed of the same or similar types of material described with respect to the embodiment ofFIG. 1.
• Theslit429 is depicted having a V-shaped cross-section that provides a nested interlock for mechanically holding the opposing surface of the slit in alignment with one another. In other embodiments, different types of interlock configurations (e.g., hooks, latches, etc.) can be used. In certain embodiments, thefibers422 occupy less than half the volume of thepassage431 to facilitate movement between the fibers during bending. In certain embodiments, the fibers are not in contact with the surface of the jacket defining thepassage431. In certain embodiments, the fibers are not stranded. The passage is preferably adjacent the center of the cable.
• In one embodiment, thecable420 can be manufactured by a process similar the process use to make the embodiment ofFIG. 1. For example, the cable can initially be extruded through a crosshead, and then a bundle of optical fibers can subsequently be inserted into the cable after extrusion using an insertion system of the type shown atFIG. 12.
• FIG. 16 shows anexample crosshead502 suitable for extruding thecable420 ofFIG. 15. Thecrosshead502 includes a jacketmaterial input location500 that receives thermoplastic material from anextruder504. Atip602 and adie604 are mounted at thecrosshead502. Thetip602 defines a firstinner passageway606 through which a rip member615 (seeFIGS. 16 and 17) is fed. Thetip602 also defines second and thirdinner passageways607,611 through which thestrength structures426 are fed. Thedie604 defines anannular extrusion passage608 that surrounds the exterior of thetip602. Thecrosshead502 defines anannular passageway609 for feeding the thermoplastic jacket material from theextruder504 to theannular extrusion passage608. Within the crosshead, the flow direction of the thermoplastic material turns 90 degrees relative to the flow direction of theextruder504 to align with the direction of travel of thestrength structures426 and therip member615.
• Referring toFIG. 17, aslitting blade mount620 is coupled to thedie604. Ablade623 having a v-shaped cross-section is mounted to theblade mount620 at a location adjacent the exit of thecrosshead502. Theblade623 functions to cut the predefined slit location for theslit429 into the jacket of thecable420 as the cable exits thecrosshead502. After extrusion of thecable420, therip member615 is pulled from the jacket to ensure that that the pre-defined slit location is opened to form the slit. Thereafter, the slit is spread apart to allow the bundle of optical fibers to be inserted into the central passage of the jacket.
• Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended and the broad inventive aspects underlying the specific embodiments disclosed herein.

Claims (11)

1-16. (canceled)

17. A fiber optic cable comprising:

a jacket defining a first interior passage along a length of the jacket and a slit along the length of the jacket extending from the first interior passage through an exterior of the jacket; and

an optical fiber disposed in the first interior passage, wherein the slit is held in a closed position with the optical fiber in the first interior passage.

18. A fiber optic cable as claimed in claim1, wherein the slit is held in the closed position by an adhesive applied to at least one side of the slit.

19. A fiber optic cable as claimed in claim1, further comprising a reinforcing sheath mounted over the jacket, wherein the reinforcing sheath holds the slit in the closed position.

20. A fiber optic cable as claimed in claim1, wherein the jacket defines a second interior passage along the length of the jacket that is about parallel to the first interior passage.

21. A fiber optic cable as claimed in claim4, further comprising a strength structure disposed in the second interior passage.

22. A fiber optic cable as claimed in claim5, wherein the strength structure extends the entire length of the second interior passage.

23. A fiber optic cable as claimed in claim5, wherein the strength structure is a reinforcing member selected from the group consisting of yarns, fibers, threads, tapes, films, epoxies, filaments, and rods.

24. A fiber optic cable as claimed in claim1, wherein the jacket is of a material selected from the group consisting of polyethylene, polypropylene, ethylene-propylene, copolymers, polystyrene, styrene copolymers, polyvinyl chloride, polyamide, polyesters, polyethylene terephthalate, polyetheretherketon, polyphenylene sulfide, polyetherimide, polybutylene terephthalate, low smoke zero halogens polyolefins, and polycarbonate.

25. A fiber optic cable as claimed in claim1, wherein the optical fiber includes a buffer layer.

26. A fiber optic cable as claimed in claim9, wherein the buffer layer is a material selected from the group consisting of polyvinyl chloride, polyethylenes, polyurethanes, polypropylenes, polyvinylidene fluorides, ethylene vinyl acetate, nylon, and polyester.

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