Low cost multi-fiber optical cable

Abstract

An optical cable includes an outer jacket formed of an extruded polymer. A strength member resides near a center of the optical cable. The extruded polymer forming the outer jacket also surrounds and contacts the strength member, so that stresses applied to the outer jacket are transferred directly to the strength member. A horseshoe-shaped chamber is formed within the extruded polymer. The chamber extends more than 180 eighty degrees, such as about 240 to about 300 degrees, around the strength member. A plurality of optical fibers, which may be loose or connected as a ribbon and / or contained within one or more buffer tubes, reside within the chamber. The plurality of optical fibers travel in an undulating path within the chamber, as the plurality of optical fibers traverse a length of the optical cable.

Description

[0001] Atty Docket No.: 4799 / 0741PW01

[0002] LOW COST MULTI-FIBER OPTICAL CABLE

[0003] BACKGROUND OF THE INVENTION

[0004] 1. Field of the Invention

[0005]

[0001] The present invention relates to a communications cable. More particularly, the present invention relates to a communications cable with plural optical fibers, which may be contained within one or more buffer tubes, wherein the loose optical fibers or buffer tube(s) reside in a horseshoe-shaped chamber, and wherein a central strength member is attached to an outer jacket by an extrusion, which extrusion also produces the horseshoe shaped channel.

[0006] 2. Description of the Background

[0007]

[0002] Figure 1A depicts a cable 20 in accordance with the prior art, shown in US Patent 8,165,439, which is herein incorporated by reference. The cable 20 includes six buffer tubes 21, each of which contains a plurality of optical fibers 22, e.g., up to six optical fibers 22. One or more of the buffer tubes 21 may be replaced by a filler, e.g., a solid rod formed of a dielectric material having a same diameter as a buffer tube 21, if a cable 20 with a lower fiber count is needed.

[0008]

[0003] The buffer tubes 21 are stranded about a central strength member 23, e.g., a glass reinforced plastic (GRP) rod, wherein fibers to enhance strength are distributed through a rigid plastic rod. The central strength member 23 provides mechanical strength to a length of the cable 20, e.g., in a drop cable deployment, and also provides a good anchoring point for a connector at a cable termination.

[0009]

[0004] Typically, the buffer tubes 21 and any filler rods are stranded about the central strength member 23 in a helical, or alternatively a S-Z, stranding pattern. As best seen in Figure IB, in a S-Z stranding pattern the buffer tubes 21 twist about the central strength member 23 for several revolutions in a clockwise direction, e.g., five to seven revolutions, then reverse direction at a first switchback 27 and twist about the central strength member 23 for several revolutions in a counter-clockwise direction, e.g., five to seven revolutions, to a second switchback 29. A patternAtty Docket No.: 4799 / 0741PW01

[0010] of clockwise rotations in zones A and counterclockwise rotations in zones B repeats along the length of the cable 20 between first, second, third, fourth, ... switchbacks 27, 29, 31, 33, etc.

[0011]

[0005] During manufacturing, the central strength member 23 is paid off a reel and fed into a position, which will become the center of a cable core and hence the center of the overall cable 20. The buffer tubes 21 are stranded about the central strength member 23, and one or two binders 35 and 37 are wrapped about the buffer tubes 21, and any filler rods, to keep the cable core intact as the cable core is further processed during manufacturing.

[0012]

[0006] Next, an additional layer 25, such as an armor layer, a shielding layer, a water blocking tape, and / or a layer of aramid, polyester, or flexible fiberglass yams is applied around the cable core. The additional layer 25 surrounds the cable core. Finally, the cable jacket 24 is extruded around the additional layer 25 to form the optical cable 20. Ripcords 26 may optionally be positioned within the cable 20 to facilitate opening of the cable jacket 24 and additional layer 25 to permit access to the cable core.

[0013]

[0007] Other configurations of optical cables with buffer tubes surrounding a central strength member are generally known in the prior art. For example, see US Patents 8,380,029; 10,191,237; 10,310,192; 10,649,163 and 11,095,103, and US Published Application 2004 / 0120664, each of which is herein incorporated by reference. In the prior art cables wherein buffer tubes are stranded about a central strength member, the jacket gains its push / pull strength by a frictional engagement to the central strength member. For example, in Figure 1A, the inner wall of the jacket 24 has a frictional engagement to the outer walls of the buffer tubes 21 via the additional layer 25. The outer walls of the buffer tubes 21 are also frictionally engaged to the outer wall of the central strength member 23.

[0014]

[0008] During installation, when the cable 20 is being pushed or pulled through a conduit, duct or spanned between holders, the cable jacket 24 gains its push / pull strength via its indirect frictional connection to the central strength member 23. The installation forces tend to distort the buffer tubes 21 and the stresses can be transferred to the optical fibers 22 within the buffer tubes 21. Also, because the elements (jacket 24, additional layer 25, buffer tubes 21 and central strength member 23) are formed of different materials with different thermal contraction / expansion constants, this leads to different material contractions and expansions as the materials undergoAtty Docket No.: 4799 / 0741PW01

[0015] temperature changes in a cable installation environment. The differences in contraction and expansion cause stresses to be placed upon the buffer tubes 21 , and these stresses can be transferred to the optical fibers 22 within the buffer tubes 21.

[0016]

[0009] Forces placed on the buffer tubes 21 during installation and during thermal cycles can transmit though the buffer tubes 21 and to the optical fibers 22 therein causing damage and / or micro bends. Therefore, there has been a trend to form the buffer tubes 21 of strong and more expensive materials, like PBT, so as to protect the optical fibers 22 within the buffer tubes 21. Further, there is always a desire to reduce the cost and size of the cable 20. One method to reduce the cost and size would be to eliminate elements of the cable, while maintaining the performance of the cable.

[0017]

[0010] One prior art cable method to add push / pull strength to the outer jacket includes embedding two strength members into the jacket wall, as shown in Figure 1C. Figure 1C is based on US Patent 9,116,322, which is herein incorporated by reference. In the prior art shown in Figure 1C, the cable 40 includes a jacket 44 having a direct connection to a GRP strength member 43, in that two GRP strength members 43 are embedded within the material forming the jacket 44. The inner core of the cable 40 may include traditional features like buffer tubes 41 containing loose optical fiber 42 or stacked optical fibers 42A, filler rods, water blocking threads or tapes, rip cords, etc.

[0018]

[0011] Another prior art method to add push / pull strength to the outer jacket includes attaching a central strength member 12 to the jacket 15 during an extrusion of the jacket 15, as shown in the Figure ID. Figure ID is based on US Patent 4,707,074, which is herein incorporated by reference. In US Patent 4,707,074, the cable 10 includes an outer jacket 15 formed by an extrusion. The extrusion includes ribs 13 which lead to a first portion 11 surrounding a central strength member 12. The extrusion also includes four channels 16. The channels 16 house loose optical fibers 17. Each channel 16 extends less than forty-five degrees around the central strength member 12. The channels 16 are oscillated around the central strength member 12. Other US Patents, which illustrate similar configurations, are shown in US Patents 4,038,489; 5,097,870; 5,218,659; 5,285,008; 6,477,304; 8,559,778 and 8,818,156, each of which is herein incorporated by reference.Atty Docket No.: 4799 / 0741PW01

[0019] SUMMARY OF THE INVENTION

[0020]

[0012] The applicant has appreciated drawbacks with the designs of the optical cables of the prior art, which add strength to the outer jacket.

[0021]

[0013] In the case of adding two embedded strength members 43 to the jacket 44 material, this solution adds costs, makes the cable 40 less likely to pass a bum test, and adds weight / size to the cable 40. Two strength members 43 are needed instead of a single central strength member, which adds material to burn, weight and cost. Further, thejacket wall thickness is increased, which adds material to bum, weight and cost to the cable 40. Also, the two strength members 43 cause a bend preference in the cable 40. For example, in Figure 1C, where the two strength members 43 are located at the nine and three o’clock positions, the cable 40 would prefer to bend in the up and down directions, i.e., the twelve and six o’clock directions. The cable 40 would resist bending in the nine and three o’clock directions. This bend preference can complicate cable installation, especially within a conduit. A single, centrally located strength member does not impose a bend preference on a cable.

[0022]

[0014] In the case of a central strength member 12 bonded to the jacket 15 during an extrusion of thejacket 15, as shown in Figure ID, the cable 10 will not exhibit a bend preference. However, the channels 16 must be made to oscillate about the central strength member 12. Oscillation of the channels 16 accomplishes two functions. First, the optical fibers 17 within the channels 16 will have compensating slack to allow the cable 10 to be routed around bends during an installation. When the cable 10 is bent in one direction, the optical fibers 17 on the inside track of the bend become loose within the channel 16 moving toward thejacket 15 of the cable 10, while the optical fibers 17 on the outside track of the bend become tight within the channel 16 moving toward the middle of the cable 10. Because the channels 16 are spirally, about the central strength member 12, there is an offsetting or compensating effect as the inside track becomes the outside track and visa versus to alleviate the looseness and tightness of the optical fibers 17, as the cable 10 is installed.Atty Docket No.: 4799 / 0741PW01

[0023]

[0015] Further, the oscillating nature of the movement of the channels 16 about the central strength member 12 allows for a mid-span access of the optical fibers 17. In a mid-span access, a mid-section of the jacket 15 is removed, and the optical fibers 17 int eh channels 16 are access for a splicing operation. By accessing the optical fibers 17 at a switch-back, the optical fibers 17 may be partially unwound and distanced from the central strength member 12 and each other to assist with the splicing operation. However, the solution of Figure ID has a major drawback. It is very difficult and slow to extrude the channels 16 in an oscillating manner about the central strength member 12, as the optical fibers 17 are fed into the channels 16.

[0024]

[0016] Therefore, it is an object of the present invention to provide a cable, which eliminates elements as shown in Figures 1A and IB, and improves the jacket’s support by the central strength member, without resorting to any frictional connection to the central strength member via the buffer tubes.

[0025]

[0017] It is also an object of the present invention to provide a cable, which does not need two strength members embedded within a wall of the jacket.

[0026]

[0018] It is also an obj ect of the present invention to provide a cable, wherein the j acket is attached to the central strength member by an extrusion process, and a channel is formed therein to hold a plurality of optical fibers, wherein the channel can be formed by a straight extrusion process. The channel need not oscillate about the central strength member, yet the optical fibers have sufficient movement within the channel, so as to not be stresses by the bends of the cable during installation and can be easily spliced during a mid-span access.

[0027]

[0019] These and other objectives are accomplished by an optical cable which includes an outer jacket formed of an extruded polymer. A strength member resides near a center of the optical cable. The extruded polymer forming the outer jacket also surrounds and contacts the strength member, so that stresses applied to the outer jacket are transferred directly to the strength member. A horseshoe-shaped chamber is formed within the extruded polymer. The chamber extends more than 180 eighty degrees, such as about 240 to about 300 degrees, around the strength member. A plurality of optical fibers, which may be loose or connected as a ribbon and / or contained within one or more buffer tubes, reside within the chamber. The plurality of optical fibers travel in anAtty Docket No.: 4799 / 0741PW01

[0028] undulating path within the chamber, as the plurality of optical fibers traverse a length of the optical cable.

[0029]

[0020] Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

[0030] BRIEF DESCRIPTION OF THE DRAWINGS

[0031]

[0021] For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:

[0032]

[0022] Figure 1A is an end view of a first optical cable, in accordance with the prior art;

[0033]

[0023] Figure IB is a perspective, side view of the optical cable of Figure 1 A with a middle section of a jacket removed to show a cable core;

[0034]

[0024] Figure 1C is an end view of a second optical cable, in accordance with the prior art;

[0035]

[0025] Figure ID is a perspective, end view of a third optical cable, in accordance with the prior art;

[0036]

[0026] Figure 2 is a perspective view of an optical cable, in accordance with a first embodiment of the present invention;

[0037]

[0027] Figure 3 is an end view of the optical cable of Figure 2;

[0038]

[0028] Figure 4 is a perspective view of an optical cable, in accordance with a second embodiment of the present invention;

[0039]

[0029] Figure 5 is a perspective view of an optical cable, in accordance with a third embodiment of the present invention;

[0040]

[0030] Figure 6 is an end view of the optical cable of Figure 5;

[0041]

[0031] Figure 7 is an end view of an extruded polymer j acket without any optical fibers within the chamber;Atty Docket No.: 4799 / 0741PW01

[0042]

[0032] Figure 8 is an exploded perspective view of extrusion tooling, which includes a tip, a die and a die holder, for forming the jacket of the optical cable;

[0043]

[0033] Figure 9 is a close-up, perspective view of the tip; and

[0044]

[0034] Figure 10 is a close-up, perspective view of the die.

[0045] DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0046]

[0035] The present invention now is described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0047]

[0036] Like numbers refer to like elements throughout. In the figures, the thickness of certain lines, layers, components, elements or features may be exaggerated for clarity. Broken lines illustrate optional features or operations unless specified otherwise.

[0048]

[0037] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and relevant art and should not be interpreted in an idealized or overly formal sense unless expressly so defined herein. Well-known functions or constructions may not be described in detail for brevity and / or clarity.

[0049]

[0038] As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations,Atty Docket No.: 4799 / 0741PW01

[0050] elements, components, and / or groups thereof. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items. As used herein, phrases such as "between X and Y" and "between about X and Y" should be interpreted to include X and Y. As used herein, phrases such as "between about X and Y" mean "between about X and about Y." As used herein, phrases such as "from about X to Y" mean "from about X to about Y."

[0051]

[0039] It will be understood that when an element is referred to as being "on", "attached" to, "connected" to, "coupled" with, "contacting", etc., another element, it can be directly on, attached to, connected to, coupled with or contacting the other element or intervening elements may also be present. In contrast, when an element is referred to as being, for example, "directly on", "directly attached" to, "directly connected" to, "directly coupled" with or "directly contacting" another element, there are no intervening elements present. It will also be appreciated by those of skill in the art that references to a structure or feature that is disposed "adjacent" another feature may have portions that overlap or underlie the adjacent feature.

[0052]

[0040] Spatially relative terms, such as “under”, “below”, “lower”, “over”, “upper”, “lateral”, “left”, “right” and the like, may be used herein for ease of description to describe one element or feature’s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is inverted, elements described as “under” or “beneath” other elements or features would then be oriented “over” the other elements or features. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the descriptors of relative spatial relationships used herein interpreted accordingly.

[0053]

[0041] Figure 2 is a perspective view of an optical cable 101A, in accordance with a first embodiment of the present invention. Figure 3 is an end view of the optical cable 101 A of Figure 2. The optical cable 101 A includes a jacket 103 formed of an extruded polymer 105. Any known extruded polymer 105 for a cable jacket 103 may be used, such as PVC, FEP, PVDF, polypropylene, polyolefin, polyurethane, fluoropolymer, polyethylene, etc. An outer surface 107 of the jacket 103 defines a substantially circular outer perimeter of the optical cable 101 A and a diameter of the optical cable 101. In the illustrated embodiments, the outer surface 107 of theAtty Docket No.: 4799 / 0741PW01

[0054] jacket 103 has a diameter of less than 0.6 inches, more preferably less than 0.5 inches, such as less than 0.45 inches. However, the concepts of the present invention can be applied to larger diameter cables.

[0055]

[0042] A strength member 109 resides proximate a center of the optical cable 101 A. The strength member 109 is formed of a dielectric material with embedded reinforcement materials, e.g., short lengths of fiber, throughout the length of the strength member. The generic acronym FRP stands for “fiber reinforced polymer,” and can include a glass reinforced polymer (GRP), such as a fiber glass reinforced polymer. However, other types and lengths of fibers or reinforcement materials may be embedded within the dielectric material, e g., polymer. For example, the embedded fibers or reinforcement materials may be formed of aramid fibers (sold under the trademark Kevlar®), bamboo fibers or shavings, nano tubes, animal hair, metal / alloy strands, etc. It may also be possible for the strength member to include or be formed of metal, such as stranded steel wires or a solid steel wire. A typical diameter of the strength member 109 would be about 2 mm to 10 mm, although the diameter may be different, e.g., smaller or larger depending upon the size of cable and / or the strength needed.

[0056]

[0043] A first portion 111 of the extruded polymer 105 forming the jacket 103 also at least partially surrounds and contacts the strength member 109. In Figures 2 and 3, the first portion 111 completely surrounds the strength member 109 and the strength member 109 has a circular cross sectional shape and is placed directly into the center of the optical cable 101 A. These configurations represent preferred embodiments. All of the embodiments of the present invention may depart to some degree. For example, the first portion 111 need not completely surround the strength member 109, as a gap may be present to expose a portion of the strength member 109. The important aspect is that the strength member 109 is captured, e.g., held, by the first portion 111 , so that the jacket 103 is attached to the strength member 109. Also, the strength member 109 need not be circular in cross section, e.g., it may be oval or even triangular. Also, the strength member 109 need not be exactly centered within the optical cable 101 A. Such variations, although not preferred, would still provide some or all of the benefits of the present invention to different degrees.Atty Docket No.: 4799 / 0741PW01

[0057]

[0044] The optical cable 101A also includes a horseshoe-shaped chamber 113, e.g., an Omega-shaped chamber, C-shaped chamber. The chamber 113 is formed within the extruded polymer 105. The chamber 113 extends more than one hundred eighty degrees around the strength member 109 from a first sidewall end 115 of the chamber 113 to a second sidewall end 117 of the chamber 113. In a preferred embodiment, the chamber 113 extends at least two hundred forty degrees around the strength member 109 from the first sidewall end 115 to the second sidewall end 117 of the chamber 113, such as at least two hundred seventy degrees. The chamber 113 extends linearly along an entire length of the optical cable 101 A.

[0058]

[0045] As best seen in Figure 3, a first angular arc Al extends between the first sidewall end 115 of the chamber 113 and the second sidewall end 117 of the chamber 113. The first angular arc Al is about three hundred degrees, leaving a second angular arc A2 of about sixty degrees. The second angular arc A2 is filled with the extruded polymer 105 to serve as a connecting portion between the jacket 103 and the first portion 111 surrounding the strength member 109. Although the first and second angular portions are illustrated as three hundred degrees and sixty degrees, these are mere examples, and other combinations are possible, such as three hundred ten degrees and fifty degrees, two hundred ninety degrees and seventy degrees, etc.

[0059]

[0046] A first plurality of optical fibers 119 reside within the chamber 113. A first buffer tube 121 surrounds the first plurality of optical fibers 119. Figures 2 and 3 show at least twelve optical fibers 119 in the first buffer tube 121, e.g., exactly twelve optic fibers 119. However, it should be noted that more or fewer optical fibers 119 may be surrounded by the first buffer tube 121, such as six, eight, sixteen or twenty-four. The optical fibers 119 may be attached to each other to form a foldable, rollable or collapsible ribbon. Alternatively, the optical fibers 119 may be loosely held in the first buffer tube 121.

[0060]

[0047] The first buffer tube 121 undulates within the chamber 11 , which causes the first plurality of optical fibers 119 to travel in a first undulating path within the chamber 113, as the plurality of optical fibers 119 traverse the length of the optical cable 101A. An undulating path means a wavy path, wherein the wave pattern may be of uniform frequency and of uniform amplitude, although uniformity is not critical. The undulating path extends along a first direction along the length of said optical cable 101 A and toward the first sidewall end 115 of the chamberAtty Docket No.: 4799 / 0741PW01

[0061] 113, and then veers to a second direction along the length of the optical cable 101A and toward the second sidewall end 117 of the chamber 113, and then veers back to the first direction and so on, along the entire length of the optical cable 101 A.

[0062]

[0048] As best seen in Figure 3, the first undulating path may consume a third angular arc A3 about the strength member 109. The third angular arc A3 is shown as about eighty degrees in Figure 3. However, the third angular arc A3 may be greater or less than eighty degrees. For example, when the first buffer tuber 121 is the only buffer tube present in the chamber 113, the third angular arc A3 may occupy the entire sweep of the first angular arc Al of the chamber 113 from the first sidewall end 115 to the second sidewall end 117. The first undulating path serves at least two benefits. A first benefit is that the cable can be installed, e.g., curved, about conduit comers and installation pully wheels, without stressing the optical fibers 119, as the undulations can slightly straighten out when the optical fibers 119 are on the outside of a curve in the cable 101 A during installation. A second benefit is that the optical fibers 119 can be spaced apart from the strength member 109 and each other during a mid-span access.

[0063]

[0049] Figure 4 is a perspective view of an optical cable 10 IB, in accordance with a second embodiment of the present invention. All elements, which are the same as the optical cable 101 A of Figures 2 and 3 have been labeled with the same reference numerals. The primary difference is that the chamber 113 now includes a plurality of buffer tubes. For example, a second plurality of optical fibers 119 is surrounded by a second buffer tube 123. The second buffer tube 123 lies directly beside and abuts the first buffer tube 121. The first and second buffer tubes 121 and 123 undulate side-by-side along the length of the optical cable 101B within the chamber 113.

[0064]

[0050] Another distinction in Figure 4 is that the first and second buffer tubes 121 and 123 each contain twenty-four optical fibers 119. In one embodiment, each buffer tube 121 and 123 is a 2.5 mm buffer tube and each optical fiber 119 is a 200 micron optical fiber 119. However, other sizes of first and second buffer tubes 121 and 123 and optical fibers 119 are possible. Figure 4 shows twelve total buffer tubes, with each having twenty-four optical fibers. With twelve buffer tubes, the third angular arc A3 would be less than the eighty degrees shown in Figure 3, e.g., about twenty to thirty degrees. However, with perhaps a total of eight or nine buffer tubes, it would be possible to preserve the third angular arc in the seventy to eighty degree range. The greater theAtty Docket No.: 4799 / 0741PW01

[0065] undulation the more optical fiber 119 length is available to permit a sharper curvature of the cable 10 IB during installation and more separation between the optical fibers 119 and the strength member 109 during a mid-span access operation.

[0066]

[0051] Figure 5 is a perspective view of an optical cable 101C, in accordance with a third embodiment of the present invention. Figure 6 is an end view of the optical cable 101C of Figure 5. All elements, which are the same as the optical cable 101 A of Figures 2 and 3 have been labeled with the same reference numerals. The primary difference is the chamber 113 now includes a plurality of individual, buffered optical fibers 125. For example, Figure 5 shows twelve individual, buffered optical fibers 125 of a 900 micron size. However, other sizes and types of individual optical fibers may be employed. The buffered optical fibers 125 abut each other within the chamber 113. The buffered optical fibers 125 undulate side-by-side along the length of the optical cable 101C within the chamber 113.

[0067]

[0052] Another distinction in Figures 5 and 6 is that with twelve abutting, buffered optical fibers 125, the third angular arc A3 is shown as sixty degrees. However, with a total of eleven buffered optical fibers 125, it would be possible to preserve the third angular arc A3 at eighty degrees, as shown in Figure 3. Alternatively, the diameter of the cable can be enlarged so that twelve buffered optical fibers 125 have a third angular arc A3 of eighty degrees. Again, the greater the undulation, provided by the third angular arc A3, the greater the length of buffered optical fiber 125 is available to permit a sharper curvature of the cable 101C during installation and the more separation is permitted between the buffered optical fibers 125 relative to each other and relative to the strength member 109 during a mid-span access operation.

[0068]

[0053] Figure 7 is an end view of an extruded polymer 105A without any optical fibers within the chamber 113. The extruded polymer 105 A can be used with any of the previous embodiments of the optical cable 101 A, 101B and 101C, collectively labelled as 101 in Figure 7. All elements, which are the same as the optical cable 101 A of Figures 2 and 3 have been labeled with the same reference numerals. Figure 7 illustrates that the extruded polymer 105 A may include first and second notches 127 and 129 as rip features to facilitate accessing the optical fibers 119 or 125 during an end termination to a connector or a mid-span access.Atty Docket No.: 4799 / 0741PW01

[0069]

[0054] The first and second notches 127 and 129 reduce a wall thickness in the extruded polymer 105 A forming the jacket 103. The first and second notches 127 and 129 cause first and second weakened sections 131 and 133 in the jacket 103, which can be manually tom open to gain access to the chamber 113. In a illustrated embodiment, the first and second notches 127 and 129 are formed about one hundred and eighty degrees apart on an inner surface 135 of the jacket 103, which faces the chamber 113. However, is should be appreciated that the first and second notches 127 and 129 could alternatively be formed on the outer surface 107 of the jacket 103.

[0070]

[0055] Alternatively or in addition, the rip feature may be provided in the form of one or more ripcords provided within the chamber 113, such as two ripcords 137 and 129 positioned about one hundred eighty degrees apart beside or between the buffer tubes, as shown in Figure 4. Alternatively, the ripcords 137 and 139 may be embedded within the jacket 103, show by the small circles within the jacket 103 in Figure 7 representing ends of the ripcords 137 and 139. The ripcords 137 and 139 may be formed of stranded aramid fibers. For example, each ripcord 137 and 139 may be formed of plural stranded aramid fibers, each aramid fiber having a diameter of about 1 / 1000 of an inch, such that an overall diameter of the stranded bundle of aramid fibers is about 20 to 40 thousandths of an inch, more preferably about 25 to 35 thousandth of an inch. Larger or smaller diameter ripcords 137 and 139 may be possible and may be dependent upon the material being used to form the ripcords 137 and 139. For example, ripcords 137 and 139 may have a larger diameter when being formed of polyester.

[0071]

[0056] To form the first and second notches 127 and 129, extrusion tooling 141 is needed. Figure 8 is an exploded perspective view of the extrusion tooling 141, which includes a tip 143, a die 145 and a die holder 161. Figure 9 is a perspective view of the tip 143, which includes first and second projections 147 and 149 to form the first and second notches 127 and 129. Void 151, where no extruded polymer 105 flows, forms the chamber 113. The buffer tubes 121, 123 and / or buffered fibers 125 are passed through the void 151. Extruded polymer 105 flowing along inner surface 153 of the tip 143 forms an outer surface of the first portion 111, while extruded polymer 105 flowing along outer surface 155 of the tip 143 forms the inner surface 135 of the jacket 103. Figure 10 is an perspective view of the die 145. The central void 157, where no extruded polymerAtty Docket No.: 4799 / 0741PW01

[0072] 105 flows, receives the strength member 109, while the inner surface 159 of the die holder 161 (Figure 8) forms the outer surface 107 of the jacket 103.

[0073]

[0057] The chamber 113 may also include at least one water blocking element in the form of a water blocking thread, yarn or tape 163. The water blocking element may be a coated element, with a coating product, such as those sold under the trademark SWELLCOAT(TM), manufactured by FIBER-LINE®. A water blocking element may optionally be included to block water flow in the buffer tubes 121 and 123. Such threads, yards or tapes are capable of absorbing a water weight up to lOOx the weight of the dry coating of the thread, yam or tape. For example, threads, yams or tapes with water swellable powder may be provided within each buffer tube, e.g., the first and second buffer tubes 121 and 123, and / or within the chamber 113 placed alongside the buffer tubes or alongside the loose buffered optical fibers 125 to prevent water migration.

[0074]

[0058] In additional to the advantages listed in the Summary of the Invention section, the present invention provides the benefits of an SZ stranded cable, but does not require binders 35 and / or 37, as shown in Figure IB. Such binders 35 and / or 37 add costs, increase the size, slow the manufacturing speed, and may also lead to damage of the buffer tube(s) and the optical fibers therein if the cable is subjected to a lateral crushing force. The present invention also allows the buffer tubes to be formed of a weaker and cheaper material as compared to PBT.

[0075]

[0059] In Figures 2 and 3, the buffer tubes are of a loose tube design for accommodating twelve optical fibers, which are disconnected, i.e., loose. Alternatively, the optical fibers may be ribbonized, e g., connected to each other by a rolled, foldable or collapsible ribbon. More or fewer optical fibers may be included in each buffer tube as well, such as two bundles of twelve loose fibers each in each buffer tube, or two ribbons of twelve fibers each in each buffer tube.

[0076]

[0060] In the various embodiments of the present invention, the optical fibers may all be of a single mode type, may all be of a multimode type, or may be a mixture of the two types. The optical fibers may all be a same diameter or may be of different diameters such as 200um, 250um, or other diameters.

[0077]

[0061] The invention being thus described, it will be obvious that the same may be varied in many ways.

Claims

Atty Docket No.: 4799 / 0741PW01Claims:

1. An optical cable comprising:a jacket formed of an extruded polymer, wherein an outer surface of said jacket defines an outer perimeter of said optical cable;a strength member residing proximate a center of said optical cable, wherein a first portion of said extruded polymer forming said jacket also at least partially surrounds and contacts said strength member;a horseshoe-shaped chamber formed within said extruded polymer, wherein said chamber extends more than one hundred eighty degrees around said strength member from a first sidewall end of said chamber to a second sidewall end of said chamber; anda plurality of optical fibers residing within said chamber, wherein said plurality of optical fibers travel in an undulating path within said chamber as said plurality of optical fibers traverse a length of said optical cable.

2. The optical cable according to claim 1, wherein said plurality of optical fibers is a first plurality of optical fibers and said undulating path is a first undulating path, and further comprising:a first buffer tube surrounding said first plurality of optical fibers, wherein said first buffer tube undulates within said chamber to cause said first plurality of optical fibers to travel in said first undulating path within said chamber.

3. The optical cable according to claim 2, further comprising:a second plurality of optical fibers; anda second buffer tube surrounding said second plurality of optical fibers, wherein said second buffer tube undulates within said chamber to cause said second plurality of optical fibers to travel in a second undulating path within said chamber.Atty Docket No.: 4799 / 0741PW014. The optical cable according to claim 1, wherein said undulating path lies along a first direction along the length of said optical cable and toward said first sidewall end of said chamber, and then veers to a second direction along the length of said optical cable and toward said second sidewall end of said chamber, and then veers back to said first direction and so on along the length of said optical cable.

5. The optical cable according to claim 1, wherein said strength member is a central strength member and is formed as a dielectric strength member having embedded reinforcement material therein.

6. The optical cable according to claim 1, wherein said strength member is formed as a glass reinforced plastic (GRP) rod.

7. The optical cable according to claim 1, wherein said first portion of said extruded polymer completely surrounds said strength member.

8. The optical cable according to claim 1, wherein said outer surface of said jacket presents a substantially circular outer perimeter, which defines a diameter of said optical cable.

9. The optical cable according to claim 8, wherein said outer surface of said jacket has a diameter of less than 0.45 inches.

10. The optical cable according to claim 8, wherein said chamber extends at least two hundred forty degrees around said strength member from said first sidewall end of said chamber to said second sidewall end of said chamber.

11. The optical cable according to claim 8, wherein said chamber extends at least two hundred seventy degrees around said strength member from said first sidewall end of said chamber to said second sidewall end of said chamber.Atty Docket No.: 4799 / 0741PW0112. The optical cable according to claim 8, wherein said first portion of said extruded polymer forming said jacket completely surrounds and contacts said strength member.

13. The optical cable according to claim 1, further comprising:a first notch formed as a reduced wall thickness in said extruded polymer forming said jacket, which causes a first weakened section in said jacket which forms a first rip feature which can be tom open to gain access to said chamber.

14. The optical cable according to claim 13, further comprising:a second notch formed as a reduced thickness in said extruded polymer forming said jacket, which causes a second weakened section in said jacket which forms a second rip feature which can be tom open to gain access to said chamber, wherein said first and second notches are formed about one hundred and eighty degrees apart.

15. The optical cable according to claim 14, wherein said first and second notches are formed on an inner surface of said jacket which faces said chamber, and wherein said outer surface of said jacket presents a substantially circular cross-sectional shape.

16. The optical cable according claim 1, further comprising:at least one rip feature in the form of a ripcord within chamber.

17. The optical cable according claim 1, further comprising:at least one water blocking element in the form of a water blocking thread, yarn or tape within said chamber.

18. The optical cable according to claim 1, wherein said plurality of optical fibers includes at least twelve optical fibers.Atty Docket No.: 4799 / 0741PW0119. The optical cable according to claim 1, wherein said plurality of optical fibers are attached to each other to form a foldable, rollable or collapsible ribbon.

20. An optical cable consisting essentially of:a jacket formed of an extruded polymer, wherein an outer surface of said jacket defines an outer perimeter of said optical cable;a strength member residing proximate a center of said optical cable, wherein a first portion of said extruded polymer forming said jacket also at least partially surrounds and contacts said strength member;a horseshoe-shaped chamber formed within said extruded polymer, wherein said chamber extends more than one hundred eighty degrees around said strength member from a first sidewall end of said chamber to a second sidewall end of said chamber;a plurality of optical fibers residing within said chamber, wherein said plurality of optical fibers travel in an undulating path within said chamber as said plurality of optical fibers traverse a length of said optical cable;at least one water blocking element located within said chamber; andat least one rip feature to assist opening said jacket to access said chamber, said at least one rip feature being in the form of one or more ripcords within said chamber or jacket and / or one or more weakened wall sections within said jacket.

21. The optical cable according to claim 20, wherein said strength member is a central strength member and is formed as a glass reinforced plastic (GRP) rod.

22. The optical cable according to claim 20, wherein said first portion of said extruded polymer completely surrounds said strength member.

23. The optical cable according to claim 20, wherein said outer surface of said jacket presents a substantially circular outer perimeter, which defines a diameter of less than 0.45 inches.Atty Docket No.: 4799 / 0741PW0124. The optical cable according to claim 20, wherein said chamber extends at least two hundred forty degrees around said strength member from said first sidewall end of said chamber to said second sidewall end of said chamber.

25. The optical cable according to claim 20, wherein said chamber extends at least two hundred seventy degrees around said strength member from said first sidewall end of said chamber to said second sidewall end of said chamber.

26. The optical cable according to claim 20, wherein said at least one rip feature is formed as first and second weakened wall sections within said jacket formed about one hundred and eighty degrees apart.

27. The optical cable according to claim 20, wherein said at least one rip feature is formed as first and second ripcords disposed within said chamber.

28. The optical cable according claim 20, wherein said at least one water blocking element takes the form of one or more water blocking threads, yams or tapes within said chamber.

29. The optical cable according to claim 20, wherein at least some of said plurality of optical fibers are attached to each other to form a foldable, rollable or collapsible ribbon.

30. An optical cable consisting essentially of:a jacket formed of an extruded polymer, wherein an outer surface of said jacket defines an outer perimeter of said optical cable;a strength member residing proximate a center of said optical cable, wherein a first portion of said extruded polymer forming said jacket also at least partially surrounds and contacts said strength member;Atty Docket No.: 4799 / 0741PW01a horseshoe-shaped chamber formed within said extruded polymer, wherein said chamber extends more than one hundred eighty degrees around said strength member from a first sidewall end of said chamber to a second sidewall end of said chamber;at least one buffer tube holding a plurality of optical fibers, wherein said at least one buffer tube resides within said chamber, and wherein said at least one buffer tube travels in an undulating path within said chamber as said at least one buffer tube traverses a length of said optical cable;at least one water blocking element located within said chamber and / or said at least one buffer tube; andat least one rip feature to assist opening said jacket to access said chamber, said at least one rip feature being in the form of one or more ripcords within said chamber and / or one or more weakened wall sections within said jacket.

31. The optical cable according to claim 30, wherein said strength member is a central strength member and is formed as a glass reinforced plastic (GRP) rod.

32. The optical cable according to claim 30, wherein said first portion of said extruded polymer completely surrounds said strength member.

33. The optical cable according to claim 30, wherein said outer surface of said jacket presents a substantially circular outer perimeter, which defines a diameter of less than 0.45 inches.

34. The optical cable according to claim 30, wherein said chamber extends at least two hundred forty degrees around said strength member from said first sidewall end of said chamber to said second sidewall end of said chamber.Atty Docket No.: 4799 / 0741PW0135. The optical cable according to claim 30, wherein said chamber extends at least two hundred seventy degrees around said strength member from said first sidewall end of said chamber to said second sidewall end of said chamber.

36. The optical cable according to claim 30, wherein said at least one rip feature is formed as first and second weakened wall sections within said jacket formed about one hundred and eighty degrees apart.

37. The optical cable according to claim 30, wherein said at least one rip feature is formed as first and second ripcords disposed within said chamber.

38. The optical cable according claim 30, wherein said at least one water blocking element takes the form of one or more water blocking threads, yams or tapes within said chamber.

39. The optical cable according to claim 30, wherein at least some of said plurality of optical fibers within said at one buffer tube are attached to each other to form a foldable, rollable or collapsible ribbon.

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