WO2001084195A2

WO2001084195A2 - Fiber optic cable with strength member

Info

Publication number: WO2001084195A2
Application number: PCT/US2001/012716
Authority: WO
Inventors: Jason C. Lail; Jody L. Greenwood
Original assignee: Corning Cable Systems Llc
Priority date: 2000-04-28
Filing date: 2001-04-17
Publication date: 2001-11-08
Also published as: AU2001259097A1; WO2001084195A3

Abstract

A fiber optic cable (10) having a tube assembly (20) therein. Tube assembly (20) includes an optical fiber group (22) in a tube (21). A strength member (40) is aligned with and disposed between optical fiber ribbon sub-groups of group (22).

Description

Fiber Optic Cable With Strength Member

The present invention relates to fiber optic cables, and, more particularly, to fiber optic cables including at least one strength member.

Related Applications

This application is a continuation in part of United States Patent Application Serial No. 09/283,080.

Background of the Invention

Conventional fiber optic cables include optical fibers that conduct light which is used to transmit voice, video, and data information. Where the fiber optic cable is subjected to forces, the optical fibers may be stressed and attenuation of the transmitted light may occur. It is therefore important for fiber optic cables to be constructed in a robust manner whereby stress- induced attenuation can be avoided or minimized. In addition, although it is generally desirable for a fiber optic cable to have a high optical fiber count, it is also desirable for the cable to be as compact as possible, thereby maximizing optical fiber density.

High Fiber Count Cables in General

High fiber count cables can be classified into three general design categories, namely: single tube, stranded tube, and slotted core. Each category may include optical fiber ribbons and/or bundled optical fibers. The physical characteristics and/or optical performance of high fiber count cable designs can include, for example: general properties such as packing density, cable diameter, weight and flexibility; cable performance attributes such as environmental performance, mechanical performance, and polarization mode dispersion attributes; and field characteristics such as installation methods, cable stripping, and mid-span access.

Known cable designs that include optical fiber ribbons, and are classifiable into one of the three general categories, can define a backdrop for the present invention. For example, US-A-5608832 which is incorporated by reference herein, includes a central member. More specifically, the design includes stacks of optical fiber ribbons formed by three optical fiber ribbons disposed in respective three-sided chamber elements of approximately a U-shaped cross section. The chamber elements are stranded around the central member which includes a tensile element and an extruded plastic layer. US-A-5249249 and US-A-5293443 which are respectively incorporated by reference herein, also disclose designs employing central members . The respective disclosures describe a compartment holding at least two side-by-side stacks of optical fiber ribbons. US-A-5177809 which is incorporated by reference herein, includes a slotted rod. Disclosed therein is an optical cable having a plurality of light waveguides in a group of bands that are arranged in longitudinally extending chambers of a slotted rod. Each of the chambers in the slotted rod can have an increasing width as the radial distance from the center of the slotted rod increases.

The bands can be arranged in sub-stacks having increasing widths corresponding to the increased width of the chamber. In another embodiment, each of the bands in the stack has an increasing width in the radial direction to fill the chamber. Alternatively, each of the chambers has a rectangular cross section, with the cross section increasing in a step-like manner due to steps formed in partitions separating the chambers. The bands that are arranged in the chambers are arranged in sub-stacks to fill each portion of the chamber. The background of the present invention can include single tube cable designs having optical fiber ribbons. For example, US-A-5369720 which is incorporated by reference herein, discloses a stack of optical ribbons secured within a metal tube by an adhesive. The adhesive has a peel strength sufficiently low to permit separation of individual optical ribbons from the stack. One embodiment includes a stack of optical ribbons having a number of ribbons arranged generally parallel to each other, and a further pair of ribbons arranged perpendicular to the generally parallel ribbons and in abutment with edges thereof. In addition, US-A-5878180 discloses a single tube cable including a number of superimposed and adjacent stacks of optical fiber ribbons. The stacks of optical fiber ribbons are arranged over and/or adjacent to each other and in parallel. Another single tube variation, is disclosed in EP-A2-0495241 wherein optical fiber ribbons are tightly received in a zigzagged waterblocking tape. The ribbons are apparently pressed into slots in the zigzagged waterblocking tape. The zigzagged waterblocking tape disadvantageously consumes valuable space inside the tube, increases production costs, requires specialized manufacturing procedures, restricts relative movement of the ribbons during cable bending, increases friction between cable components, and/or adds size and stiffness to the cable.

In addition to attaining a desired fiber count, fiber optic cables should be able to withstand longitudinal compression and tension, and they typically include strength members for these purposes. However, the strength members may disadvantageously affect cable bending performance during installation, and may hinder optical, fiber access. A fiber optic cable having strength members located in a single plane generally will experience a preferential bending action favoring bending of the cable out of the plane defined by the strength members. On the other hand, a fiber optic cable having strength members at spaced locations encircling the center of the cable will not have a preferential bend, but the strength members typically include a helical lay so that the cable can be bent. Even taking into account the helical lay of the strength members, when bent in generally any axis, cables of the non-preferential bend type may be very stiff, a characteristic which may be highly undesirable depending upon installation requirements. Thus a cable of the preferential bend type will typically experience ease of cable bending in a preferred plane, and, as there are less strength members to deal with, may present a less time consuming optical fiber access procedure. A cable designer may therefore balance the need to have sufficient cable components for resisting crush, compression, and tension loads, against the size and stiffness contributions of the cable components that may render the cable difficult to install in a cable passageway.

Aspects of the Invention

The present inventive concepts are applicable to fiber optic cables having wide fiber count ranges, and can be used in fiber optic cables with or without a preferential bend characteristic. One aspect of the present invention is a fiber optic cable having a tube assembly, said tube assembly comprising: a tube surrounding a group of optical fiber ribbons and a strength member; said strength member being generally aligned with and between at least some of said optical fiber ribbons. Another aspect of the present invention is a tube surrounding at least one strength member, said strength member comprising bending characteristic features, whereby mechanical characteristics of said strength member are non-uniform along the length of the strength member. Another aspect of the invention involves a tube surrounding at least one strength member, said strength member being generally planar and at least some optical fibers being disposed on opposing sides of said strength member.

Brief Description of the Drawing Figures Figure 1 is an isometric view of a fiber optic cable according to an embodiment of the present invention. Figure 2 is a cross sectional view of the embodiment of Figure 1 taken at line 2-2.

Figure 2A is a schematic view of a strength member according to the present invention.

Figure 3 is cross sectional view of a fiber optic cable according to an embodiment of the present invention.

Figure 4 is an embodiment of a strength member for use in fiber optic cables according to the present invention. Figure 5 is an embodiment of a strength member for use in fiber optic cables according to the present invention .

Figure 6 is an embodiment of a strength member for use in fiber optic cables according to the present invention.

Figure 7 is an embodiment of a strength member for use in fiber optic cables according to the present invention.

Detailed Description of the Invention Referring to Figures 1-2, a first embodiment of the present invention comprises a tube assembly 20 that includes a tube 21 having at least one optical fiber group 22 therein. Optical fiber group 22 comprises optical fiber subgroups having respective sets of optical fibers, in a preferred embodiment, a set of optical fibers comprises at least one optical fiber ribbon. In the preferred embodiment of the present invention, tube 21 can include an optical fiber ribbon group 22 comprising at least one strength member 40 integrated with the optical fiber group 22.

In a preferred embodiment, strength member 40 is medially disposed between subgroups of optical fiber ribbons within group 22. In an exemplary embodiment, group 22 preferably comprises sets of lateral subgroups 23,24,25,26 including sub-groups 23a, 23b, on opposing sides of strength member 40 (Figure 2) . Lateral subgroups 23a, 23b can be immediately flanked by lateral subgroups 24a, 24b, and lateral subgroups 24a, 24b can be immediately flanked by lateral subgroups 25a, 25b, and so on with subgroups 26a, 26b. The subgroups preferably comprise optical fiber ribbons, but can include bundled or loose optical fibers. The lateral subgroups may have respective generally equal fiber counts respectively. The optical fiber count in medial subgroup 23 can be in the range of about 120 to about 240 fibers. A total fiber count for tube assembly 20 is preferably in the range of about 12 to about 864 fibers. In a preferred embodiment, the subgroups contain at least one respective layer having at least one optical fiber ribbon. A layer in a subgroup can comprise one continuous ribbon or one or more separate ribbons in general edge-to-edge alignment, touching or with gaps between the edges . Each subgroup can be progressively smaller, for example, starting at the medial subgroup and moving to the lateral subgroups. Optical fiber ribbon group 22 can therefore define a step-like profile that can be generally symmetrical about medial subgroup 23. The step-like profile can define a high fiber packing density by substantially filling up the volume of tube 21 with, for example, sets of optical fiber ribbons. In other words, and as disclosed in Co-pending United States Patent Application Ser . No. 09/283,080, incorporated by reference herein in its entirety, the fiber packing density of tube assembly 20 can be enhanced by the steplike profile.

In a preferred embodiment, at least some of the optical fiber ribbons and/or subgroups of optical fiber group 22 have low frictional characteristics for sliding contact therebetween. 'For example, certain optical fiber ribbons and/or each ribbon in an entire subgroup can be separated from adjacent ribbons by a film thickness of a lubricant 27 shown schematically in Figure 2. Lubricant 27 can be a viscous substance, for example a gel, a liquid, or a grease-like substance any of which permit sliding contact between optical ribbons within a subgroup and/or subgroups. A suitable pre-wet method for applying a lubricant between optical ribbons is disclosed in U.S. Patent No. 5,348,586 which is incorporated by reference herein. In addition, the optical fiber ribbons or subgroups can be separated by a lubricant comprising a superabsorbent substance dispersed therein. Alternatively, the outer common matrix of one or more optical ribbons can include a non-compatible material, e.g., a silicone containing material, that migrates to the surface thereof for low frictional characteristics. Moreover, low frictional characteristics can be attained without the use of a lubricant or non-compatible substance. For example, one or more subgroups can contain one or more optical fiber ribbons having an advantageously low coefficient of friction matrix material as described in U.S. Patent No. 5,561,730 which is incorporated by reference herein.

For maintaining stack integrity, the optical fiber ribbon groups can be held together by binders (not shown) . Extrusion of tube 21 about optical fiber group 22 can be accomplished in a buffering line, for example, as disclosed in US-A-5312499 which is incorporated by reference herein. More specifically, optical fiber ribbon group 22, including at least one strength member 40, can be fed through a device that extrudes tube 21 and applies a waterblocking grease therearound. As this occurs, ribbon group 22 can be helically twisted as a unit in a lay length in the range of about 200 mm to about 1000 mm along its longitudinal axis. The buffering line can be constructed so that a clearance is defined between optical fiber ribbon group 22 and the wall of tube 21.

Exemplary Embodiment

Tube assembly 20, including at least one strength member 40, can be used as a component in various fiber optic cable applications. For example, at least one tube assembly 20 can be stranded about a central member of the kind disclosed in US-A-5621841 which is incorporated by reference herein. Alternatively, at least one tube assembly 20 can be disposed in a slot of a slotted rod of the kind disclosed in U.S. Ser. No. 08/935,173 which is incorporated by reference herein. Moreover, in the preferred embodiment, a tube assembly 20 can be used to define a core in a mono-tube application.

To illustrate, an exemplary and preferred application of tube assembly 20, including at least one strength member 40, is one of a core of a mono-tube type fiber optic cable 10 (Figures 1-2). Fiber optic cable 10 includes tube assembly 20 as the core thereof. In the preferred embodiment, strength member 40 is a smooth, resiliently flexible member that resists bend, crush, and longitudinal compression and tension forces and provides anti-buckling . Strength member 40 can comprise unimodal or multi-modal materials, and can be a composite of several distinct components. Preferably, strength member 40 is coated with a thin layer of grease. Strength member 40 is preferably a generally planar strength member that is aligned with at least some of the optical fiber ribbons (Figures 1, 2, and 2A) . The lateral side of the strength member can be shaped to conform to the inner surface of tube 21. Strength member 40 is preferably formed of thermoplastic, e.g., polypropylene or polyvinyl chloride. Alternatively, strength member 40 can be formed of a non-woven material, e.g., glass, impregnated with thermoplastic or a thermosetting material. Strength member 40 is preferably essentially de-coupled from tube 21 (Figures 1-2).

However, the invention can be practiced in the form of a fiber optic cable 11 (Figure 3) having a strength member 40 loosely or tightly coupled to tube 21 by connecting edges of strength member 40 to tube 21. The edges can be connected to tube 21, for example, during extrusion of the tube. A fiber optic cable according to the present invention can include more than one strength member 40 defining chambers with optical fiber ribbon groups disposed in the chambers between and/or adjacent to the strength members, for example, as shown in Figure 3. Strength member 40 can include at least one aperture 41 therethrough for the purpose of, for example, permitting an optical fiber ribbon to pass through the aperture (Figure 4) and/or modifying mechanical characteristics of strength member 40.

In the preferred embodiment strength member 40 has generally uniform mechanical characteristics along its length, however, the mechanical characteristics thereof, e.g., bending behavior, can be non-uniform along its length. For example, strength member 40 can have bending characteristic features, e.g., at least one notch or narrowed section 42 (Figure 5) along its length. The narrowed section can be a reduced thickness and/or a reduced width of strength member 40. In other words, the bending characteristic of strength member 40 can be changed along its length. Desired mechanical properties can be also be attained by two layers of materials 43,44, for example, laminated together having desired mechanical properties together (Figure 6). Strength member 40 can include other features for obtaining desired characteristics, including slits, holes, dimples, hollows, and/or friction reducing coatings. The strength member can be used to support optical components, for example, connectors, optical switches, repeaters, and/or optical isolators.

In addition to or in lieu of the foregoing, a composite strength member 40 can include an anti-buckling member, e.g., in the form of a GRP 46, and/or at least one but preferably two tensile strength members 45 (Figure 7), e.g., aramid fibers.

In an exemplary embodiment, tube assembly 20 is surrounded by a first jacket 35, a corrugated or flat armor tape 38 of the metallic or plastic type, and a second jacket 39. A thin waterblocking layer 36, for example a conventional waterblocking tape, can be disposed between first and second jackets 35,39. However, where an armor layer and a second jacket are not required, jacket 35 may comprise the exterior surface of the cable. Ripcords 34 and 37 may be placed along strength members 32 and adjacent tape 36, respectively (Figures 1-2 ) .

Fiber optic cables 10,11 are preferably constructed for outdoor applications. During bending of cable 10 for example, optical fiber ribbon group 22 can readily bend about plane X-X (Figure 2), and the respective subgroups and/or the optical fiber ribbons therein may slide relative to each other and relative to strength member 40 for relieving stress in the optical ribbons. Rod-like strength members exteriorly of tube 21 need not be included in cables of the present invention. Additionally, the clearance between tube 21, strength member 40, and optical fiber ribbon group 22 allows for some adjustment in the lay length of group 22 during cable bending. Having four subgroups can allow group 22 to adjust during bending and facilitate termination and/or separation procedures.

The present invention has thus been described with reference to the exemplary embodiments, which embodiments are intended to be illustrative of the present inventive concepts rather than limiting. Persons of ordinary skill in the art will appreciate that variations and modifications of the foregoing embodiments may be made without departing from the scope of the appended claims. Strength members according to the present invention can be used in optical fiber cables having optical ribbons with each ribbon containing the same number of fibers per ribbon. Strength members 40 can be formed of various unimodal or multi-modal thermoplastic materials, e.g. polyethylene, and/or polystyrene, that is chemically suitable for use with any lubricant, superabsorbent, and/or grease-like waterblocking substance therein. A strength member can include at least one optical fiber or electrical conductor.

Claims

Accordingly, what is claimed is:

1. A fiber optic cable having a tube assembly, said tube assembly comprising: a tube surrounding a group of optical fiber ribbons and a strength member; said strength member being generally aligned with and between at least some of said optical fiber ribbons .

2. The fiber optic cable of claim 1, at least some of said optical fiber ribbons being part of respective optical fiber ribbon sub-groups .

3. The fiber optic cable of claim 1, said strength member being generally de-coupled from said tube.

4. The fiber optic cable of claim 1, said strength member being generally coupled to said tube.

5. The fiber optic cable of claim 1, said strength member being formed of a single material.

6. The fiber optic cable of claim 1, said single material being a unimodal or multi-modal thermoplastic material.

7. The fiber optic cable of claim 1, said strength member being a composite of at least two components.

8. The fiber optic cable of claim 1, said strength member comprising generally uniform mechanical characteristics along its length.

9. The fiber optic cable of claim 1, said strength member comprising generally non-uniform mechanical characteristics along its length.

10. The fiber optic cable of claim 1, said strength member comprising at least one narrowed portion along its length.

11. The fiber optic cable of claim 1, said strength member comprising at least two layers of material.

12. The fiber optic cable of claim 1, said strength member comprising at least one aperture.

13. The fiber optic cable of claim 1, said strength member comprising at least one anti-buckling member.

14. The fiber optic cable of claim 1, said strength member comprising at least one tensile strength member.

15. The fiber optic cable of claim 1, said cable including no rod-like strength members exteriorly of said tube .

16. A fiber optic cable comprising:

A tube having optical fiber ribbon sub-groups therein; strength members coupled to said tube at ends thereof defining chambers between said strength members with at least some of said optical fiber ribbon subgroups disposed between said strength members and said tube.

17. A fiber optic cable comprising: a tube surrounding at least one strength member, said strength member being generally planar and at least some optical fibers being disposed on opposing sides of said strength member.

18. A fiber optic cable comprising:

A tube surrounding at least one strength member, said strength member comprising bending characteristic features, whereby mechanical characteristics of said strength member are non-uniform along the length of the strength member.

19. The fiber optic cable of claim al, said strength member comprising at least one narrowed section.

20. The fiber optic cable of claims al, said strength member comprising a laminated structure.