Source: http://www.google.com/patents/US8041168?dq=5179747
Timestamp: 2018-01-19 18:18:24
Document Index: 285213763

Matched Legal Cases: ['Application No. 61', 'Application No. 61', 'Application No. 61', 'Application No. 61', 'Application No. 61', 'Application No. 61', 'Application No. 61', 'Application No. 61', 'Application No. 61', 'Application No. 61']

Patent US8041168 - Reduced-diameter ribbon cables with high-performance optical fiber - Google Patents
Disclosed is an improved optical fiber that employs a novel coating system. When combined with a bend-insensitive glass fiber, the novel coating system according to the present invention yields an optical fiber having exceptionally low losses. The coating system features (i) a softer primary coating...http://www.google.com/patents/US8041168?utm_source=gb-gplus-sharePatent US8041168 - Reduced-diameter ribbon cables with high-performance optical fiber
Publication number US8041168 B2
Application number US 12/615,698
Also published as US20100135625
Publication number 12615698, 615698, US 8041168 B2, US 8041168B2, US-B2-8041168, US8041168 B2, US8041168B2
Patent Citations (162), Non-Patent Citations (38), Referenced by (26), Classifications (17), Legal Events (2)
Reduced-diameter ribbon cables with high-performance optical fiber
US 8041168 B2
Disclosed is an improved optical fiber that employs a novel coating system. When combined with a bend-insensitive glass fiber, the novel coating system according to the present invention yields an optical fiber having exceptionally low losses. The coating system features (i) a softer primary coating with excellent low-temperature characteristics to protect against microbending in any environment and in the toughest physical situations and, optionally, (ii) a colored secondary coating possessing enhanced color strength and vividness. The secondary coating provides improved ribbon characteristics for structures that are robust, yet easily entered (i.e., separated and stripped). The optional dual coating is specifically balanced for superior heat stripping in fiber ribbons, with virtually no residue left behind on the glass. This facilitates fast splicing and terminations. The improved coating system provides optical fibers that offer significant advantages for deployment in most, if not all, fiber-to-the-premises (FTTx) systems.
1. A buffer tube, comprising:
one or more optical-fiber ribbons, each of said optical-fiber ribbons comprising a plurality of optical fibers, wherein at least one of said optical-fiber ribbons includes at least one optical fiber comprising a glass fiber and a low-modulus primary coating surrounding said glass fiber, said low-modulus primary coating possessing (i) an in situ modulus of less than 0.50 MPa and (ii) a glass transition temperature of less than −55° C.; and
a tube surrounding said optical-fiber ribbons;
wherein the buffer tube has a buffer-tube filling coefficient of at least about 0.3.
2. A buffer tube according to claim 1, wherein at least one of said optical fibers is a single-mode optical fiber.
3. A buffer tube according to claim 1, wherein at least one of said optical fibers meets the ITU-T G.657.A standard and/or the ITU-T G.657.B standard.
4. A buffer tube according to claim 1, wherein at least one of said optical fibers is a multimode optical fiber.
5. A buffer tube according to claim 1, wherein said low-modulus primary coating possesses an in situ modulus of between 0.2 MPa and 0.5 MPa.
6. A buffer tube according to claim 1, wherein said low-modulus primary coating possesses a glass transition temperature of less than about −60° C.
7. A buffer tube according to claim 1, wherein:
said optical-fiber ribbons are arranged in a rectangular ribbon stack; and
the buffer tube has a buffer-tube filling coefficient of between about 0.32 and 0.38.
8. A buffer tube according to claim 1, wherein:
the buffer tube has a buffer-tube filling coefficient of at least 0.35.
9. A buffer tube according to claim 1, wherein:
said optical-fiber ribbons are arranged in a ribbon stack; and
the buffer tube has an optimal minimum clearance of less than about 0.32 millimeter.
10. A buffer tube according to claim 9, wherein the buffer tube has an optimal minimum clearance of between about 0.1 millimeter and 0.2 millimeter.
11. A buffer tube according to claim 9, wherein the buffer tube has an optimal minimum clearance of less than about 0.1 millimeter.
12. An optical-fiber ribbon cable, comprising:
one or more buffer tubes positioned within said cable jacket, wherein one or more of said buffer tubes enclose one or more optical-fiber ribbons, each of said optical-fiber ribbons comprising a plurality of optical fibers;
wherein at least one of said optical-fiber ribbons includes at least one optical fiber comprising a glass fiber and a primary coating surrounding said glass fiber, said primary coating possessing (i) an in situ modulus of less than 0.50 MPa and (ii) a glass transition temperature of less than −55° C.;
wherein one or more of said buffer tubes possess a buffer-tube filling coefficient of at least about 0.3.
13. An optical-fiber ribbon cable according to claim 12, wherein the optical-fiber ribbon cable has a cumulative buffer-tube filling coefficient of at least about 0.35.
14. An optical-fiber ribbon cable according to claim 12, wherein at least one of said buffer tubes has a buffer tube filling coefficient of at least about 0.4.
15. An optical-fiber ribbon cable according to claim 12, wherein at least one of said buffer tubes comprises optical-fiber ribbons arranged as a ribbon stack.
16. An optical-fiber ribbon cable according to claim 12, wherein:
one or more said buffer tubes comprise optical-fiber ribbons arranged as a ribbon stack; and
for each said buffer tube comprising optical-fiber ribbons arranged as a ribbon stack, said buffer tube has an optimal minimum clearance of less than about 0.25 millimeter.
17. An optical-fiber ribbon cable according to claim 12, wherein:
for each said buffer tube comprising optical-fiber ribbons arranged as a ribbon stack, said buffer tube has an optimal minimum clearance of between about 0.15 millimeter and 0.3 millimeter.
18. An optical-fiber ribbon cable according to claim 12, wherein:
for each said buffer tube comprising optical-fiber ribbons arranged as a ribbon stack, said buffer tube has an optimal minimum clearance of about 0 millimeter.
19. An optical-fiber cable according to claim 12, wherein at least one of said optical fibers meets the ITU-T G.657.A standard and/or the ITU-T G.657.B standard.
20. An optical-fiber cable according to claim 12, wherein said primary coating possesses an in situ modulus of less than about 0.4 MPa.
This application further claims the benefit of U.S. Provisional Application No. 61/112,965 for Reduced-Diameter Ribbon Cables with High-Performance Optical Fiber (filed Nov. 10, 2008), U.S. Provisional Application No. 61/177,996 for a Reduced-Diameter Optical Fiber (filed May 13, 2009) and U.S. Provisional Application No. 61/248,319 for a Reduced-Diameter Optical Fiber (filed Oct. 2, 2009).
The present invention embraces optical fibers possessing an improved coating system that reduces stress-induced microbending. The present invention further embraces the use of such optical fibers in ribbon cables having relatively high filling coefficients and fiber counts, and thus reduced cable dimensions.
FIG. 13 schematically depicts a cross-sectional view of an optical-fiber ribbon cable employing bend-insensitive optical fibers according to the present invention.
In one aspect, the present invention embraces optical fibers possessing an improved coating system that reduces stress-induced microbending, even in exceptionally cold environments required for FTTx deployments. The coating system according to the present invention includes a primary coating that combines low in situ modulus (e.g., less than about 0.5 MPa as measured on the fiber) and low glass transition temperature (Tg) (e.g., less than about −50° C.) to reduce stresses caused by external force and temperature. In addition, the coating system can be processed at high production speeds (e.g., 15-20 msec or more).
The present invention achieves a microbend-resistant optical fiber, particularly a single-mode optical fiber, by employing as its primary coating a UV-curable, urethane acrylate composition. In this regard, the primary coating includes between about 40 and 80 weight percent of polyether-urethane acrylate oligomer as well as photoinitiator, such as LUCERIN TPO, which is commercially available from BASF. In addition, the primary coating includes one or more oligomers and one or more monomer diluents (e.g., isobornyl acrylate), which may be included, for instance, to reduce viscosity and thereby promote processing. A suitable composition for the primary coating according to the present invention is a UV-curable urethane acrylate product provided by DSM Desotech (Elgin, Ill.) under the trade name DeSolite® DP 1011.
Example 1 Comparison of Mechanical Properties
The glass transition temperature of the conventional primary coating is estimated by the peak in tan δ to be approximately −30° C. Thus, the conventional primary coating (and similar formulations) will behave like a glassy polymer at extremely low temperatures (e.g., less than −40° C., particularly less than −50° C.). (Although stress induced by strain is time dependent at low temperatures, estimated glass transition temperature is a useful comparative property.)
The glass transition temperature of the exemplary primary coating according to the present invention is estimated by the peak in tan δ at less than about −50° C. (e.g., about −60° C.). This is at least about 20° C. below the glass transition temperature of the comparative, conventional primary coating. Accordingly, primary coatings according to the present invention provide much more rapid stress relaxation during temperature excursions.
Those having ordinary skill in the art will appreciate that, at room temperature, such fiber crossovers can sometimes cause added loss (i.e., if the optical fiber is very sensitive) but that typically little or no added loss is observed. Consequently, the drum (with wound fiber) was temperature cycled twice from about room temperature through (i) −40° C., (ii) −60° C., (iii)+70° C., and (iv)+23° C. (i.e., near room temperature) while making loss measurements at 1550 nanometers. In both temperature cycles, fiber attenuation was measured after one hour at each test temperature.
Using matched fiber samples (as with the basket weave/temperature cycling test of Example 2) fiber attenuation was measured after winding at room temperature (i.e., 23° C.) for each test condition. Then, the drum (with 400 meters of wound fiber) was temperature cycled from about room temperature through (i) −40° C., (ii) −60° C., and (iii)+23° C. (i.e., near room temperature) while making loss measurements at 1550 nanometers using an optical time domain reflectometer (OTDR).
Optical Fiber (dB/km)/ −40° C. −60° C.
(Coating Color) (N/mm) (dB/km)/(N/mm) (dB/km)/(N/mm)
As in Example 3, using matched fiber samples, fiber attenuation was measured after winding at room temperature (i.e., 23° C.). Then, the drum (with about 400 meters of wound fiber) was temperature cycled from about room temperature through (i) −40° C., (ii) −60° C., and (iii)+23° C. (i.e., near room temperature) while making loss measurements at 1550 nanometers using an optical time domain reflectometer (OTDR).
The respective microbend sensitivities were further measured for exemplary optical fibers, including (i) an enhanced single-mode glass fiber (ESMF) with a low-modulus coating, (ii) various bend-insensitive glass fibers (e.g., Draka Comteq's single-mode glass fibers available under the trade names BendBrightXS®) with conventional primary coatings, and (iii) various bend-insensitive glass fibers and macrobend-resistant glass fibers (e.g., Draka Comteq's single-mode glass fibers available under the trade names BendBrightXS® and BendBright®) with low-modulus primary coatings.
glass fiber w/ primary coating 23° C. −40° C. −60° C.
A BendBrightXS ® w/ DP1014XS 1.114 1.019 1.002
B BendBrightXS ® w/ DP1014XS 1.786 1.612 1.542
C BendBrightXS ® w/ DP1016 1.488 1.367 1.536
D BendBrightXS ® w/ DSM 950-076 2.726 3.215 3.595
E BendBrightXS ® w/ DSM 950-076 4.288 4.766 5.150
200-micron macrobend-resistant SMFs with low-modulus primary
F BendBright ® w/ DP1014XS 4.683 4.348 4.878
G BendBright ® w/ DP1016 5.985 5.800 6.399
H ESMF w/ DP1014 0.705 0.663 0.648
A BendBrightXS ® w/ DP1014XS 0.954 0.869 0.758
B BendBrightXS ® w/ DP1014XS 1.574 1.426 1.478
C BendBrightXS ® w/ DP1016 1.496 1.381 1.509
D BendBrightXS ® w/ DSM 950-076 2.238 2.683 3.015
E BendBrightXS ® w/ DSM 950-076 4.020 4.363 4.671
F BendBright ® w/ DP1014XS 2.670 2.447 2.761
G BendBright ® w/ DP1016 3.725 3.550 3.927
Moreover, Tables 2 and 3 (above) indicate that, all things being equal, Draka Comteq's single-mode glass fibers available under the trade name BendBrightXS®, which employ a trench-assisted design, provide better microbending performance than do single-mode fibers that do not employ trench-assisted and/or void-assisted design (e.g., Draka Comteq's single-mode glass fibers available under the trade name BendBright®). This is somewhat unexpected—trench-assisted and other bend-insensitive glass designs are generally understood to have more pronounced effects upon macrobending rather than microbending.
glass fiber w/ primary coating 23° C.
nominal 200-micron bend-insensitive SMFs with low-modulus primary
A BendBrightXS ® w/ DP1014XS 0.97
B BendBrightXS ® w/ DP1014XS 0.98
C BendBrightXS ® w/ DP1014XS 1.05
D BendBrightXS ® w/ DP1014XS 0.74
E BendBrightXS ® w/ DP1014XS 0.70
F ESMF w/ DP1007 2.004
G ESMF w/ DP1007 1.661
H ESMF w/ DP1007 1.542
I ESMF w/ DP1007 1.568
J ESMF w/ DP1007 1.973
In this regard, this application incorporates by reference product specifications for the following Draka Comteq single-mode optical fibers: (i) Enhanced Single Mode Fiber (ESMF); (ii) BendBright® single-mode optical fiber; (iii) BendBrightXS® single-mode optical fiber; and (iv) BendBright-Elite™ single-mode optical fiber. This technical information is provided as Appendices 1-4, respectively, in priority U.S. Provisional Application No. 61/248,319 for a Reduced-Diameter Optical Fiber (filed Oct. 2, 2009), which, as noted, is incorporated by reference in its entirety.
The 200-micron optical fibers that are formed from Draka Comteq's 125-micron BendBrightXS® bend-insensitive single-mode glass fiber and Draka Comteq's ColorLockXS brand coating system were tested for tensile strength and dynamic fatigue in accordance with the FOTP-28 standard, which is hereby incorporated by reference in its entirety. Representative mechanical reliability for these 200-micron optical fibers, which possessed differently colored secondary coatings, is provided (below) in Table 5.
Tensile Strength Tensile Strength Dynamic
50% failure 15% failure Fatigue
ColorLockXS color (kpsi) (kpsi) (n-value)
Accordingly, the optical fiber (e.g., bend-insensitive optical fiber) as herein disclosed may be included in optical-fiber ribbon cables having relatively high filling coefficients and fiber counts, and thus reduced cable dimensions.
Those having ordinary skill in the art will know that to reduce optical attenuation in optical-fiber ribbon cables, optical-fiber ribbons have typically been placed inside buffer tubes.
Such buffer tubes are typically reinforced and protected by additional layers of plastic, metal, and/or fiberglass. In such designs, the optical-fiber ribbons are allowed to “float” in an unstressed state inside the buffer tube as the tube itself and/or the surrounding cable components expand and contract (e.g., during installation and use).
The dimensions of the hollow space (i.e., cavity) inside the buffer tube and of all of the surrounding cable components are typically selected to prohibit the application of undue mechanical forces on the optical-fiber ribbon. The boundaries of optical-fiber ribbon-cable design have been limited by how much stress (e.g., tensile stress) can be applied to an optical fiber (both short term and long term) and by how much attenuation the optical fiber experiences as a result of microbending and macrobending during cable expansion and contraction (e.g., thermal contraction and/or post-extrusion shrinkage). In other words, the density of optical fibers within buffer tube cables has been limited by a need for a clearance (e.g., empty space) between optical-fiber ribbons and the interior surface of the buffer tubes. Ribbon-stack clearances in conventional buffer tubes range between about 0.35 millimeter and 2.8 millimeters. Accordingly, such buffer tubes typically have a filling coefficient of less than about 0.26.
Buffer tubes may also employ additional elements such as water-swellable tapes or compressible elements for blocking the longitudinal flow of water or to couple the ribbon or ribbon stack to the buffer tube. Such elements may also help to reduce the risk of microbending and macrobending. Despite the need to limit the risk of attenuation, it is desirable to design cables and buffer tubes with high optical-fiber density to reduce cable diameter and cost.
As a result of cost and performance trade-offs, the fiber-optic-cable industry has effectively standardized most cable designs and dimensions. This standardization is possible because most manufacturers use optical fibers with similar bend sensitivities.
Existing fiber optic ribbon cables provide adequate performance, but there remains a desire to produce fiber optic ribbon cables with smaller diameters that provide improved handling and that can function well in harsh environments. In addition, smaller fiber optic ribbon cables use less material and, as such, can be produced at a reduced cost.
The bend-insensitive optical fibers according to the present invention facilitate the manufacture of optical-fiber ribbon cables and buffer tubes that possess high fiber densities and that are capable of withstanding harsh environments. In general, it is desirable to increase the density of transmission elements (e.g., optical-fiber ribbons) in buffer tubes or cables while maintaining acceptable attenuation during installation and use (e.g., during mid-span storage).
Multiple optical fibers as disclosed herein may be sandwiched, encapsulated, and/or edge bonded to form an optical-fiber ribbon. In general, optical-fiber ribbons can be divisible into subunits (e.g., a twelve-fiber ribbon that is splittable into six-fiber subunits).
Moreover, a plurality of such optical-fiber ribbons may be aggregated to form a ribbon stack, which can have various sizes and shapes. For example, it is possible to form a rectangular ribbon stack. Alternatively, a non-rectangular ribbon stack in which the uppermost and lowermost optical-fiber ribbons have fewer optical fibers than those toward the center of the stack may be employed. Such ribbon stacks may utilize, for example, 12-fiber, 24-fiber, and/or 36-fiber ribbons. This construction may be useful to increase the density of optical-fiber elements (e.g., optical fibers) within the buffer tube and/or cable.
In this regard, various ribbon stack configurations are disclosed in the following patents, each of which is hereby incorporated by reference: U.S. Pat. No. 6,778,745 for an Optical Fiber Cable Apparatus Having Encased Ribbon Stack; U.S. Pat. No. 6,744,955 for a Buffer Tube Having a High Fiber Count Ribbon Stack Packaging Configuration and Corner Stack; U.S. Pat. No. 6,621,966 for a Fiber Optic Cable with Profiled Group of Optical Fibers; U.S. Pat. No. 6,519,399 for a Fiber Optic Cable with Profiled Group of Optical Fibers; U.S. Pat. No. 6,487,348 for a Variable Fiber Count Optical Fiber Cable Core; U.S. Pat. No. 6,192,178 for a Fiber Optic Cable with Profiled Group of Optical Fibers; U.S. Pat. No. 5,878,180 for an Optical Fiber Cable with Stacks of Optical Fiber Ribbons; U.S. Pat. No. 5,293,443 for a Cable Utilizing Multiple Light Waveguide Stacks; and U.S. Pat. No. 5,249,249 for a Cable Utilizing Multiple Light Waveguide Stacks.
An optical-fiber ribbon or ribbon stack defines a maximum cross-sectional width. As used herein, the term “maximum cross-sectional width” is meant to characterize the largest cross-sectional dimension of an optical-fiber element (e.g., an optical-fiber ribbon or ribbon stack).
For example, the maximum cross-sectional width of a rectangular optical-fiber ribbon stack is defined by its diagonal. More specifically, a ribbon stack containing 144 optical fibers may be arranged as a rectangular stack of twelve (12) 12-fiber ribbons. Assuming the optical fibers have an outer diameter of about 242 microns, each 12-fiber ribbon may be about 0.3 millimeter thick and about 3.0 millimeters wide, and thus the ribbon stack would be about 3.6 millimeters thick and about 3.0 millimeters wide. The rectangular stack's diagonal, and thus its maximum cross-sectional width, is equal to: (3.62+3.02)1/2=4.68 millimeters.
In an alternative embodiment reduced-diameter optical fibers may be employed. In this regard, assuming the optical fibers have an outer diameter of about 200 microns, each 12-fiber ribbon may be about 0.26 millimeter thick and about 2.6 millimeters wide. Therefore, the ribbon stack would be about 3.12 millimeters thick and about 2.6 millimeters wide. The rectangular stack's diagonal, and thus its maximum cross-sectional width, is equal to: (3.122+2.62)1/2=4.06 millimeters.
In a typical embodiment, a buffer tube may loosely enclose one or more optical-fiber ribbons (e.g., a ribbon stack) formed from several bend-insensitive fibers of the present invention to thereby achieve a ribbon tube. A single buffer tube enclosing a ribbon stack (i.e., a ribbon tube) may be centrally positioned within a cable sheath to form a central ribbon-tube cable. In this regard, FIG. 13 depicts an exemplary central ribbon-tube cable 20. The central ribbon-tube cable 20 includes a buffer tube 21, enclosing a 12×12 ribbon stack 22. A cable jacket 23 surrounds the buffer tube 21.
In an alternative embodiment, two or more ribbon tubes may be enclosed (e.g., stranded or unstranded) within an outer protective sheath to form a ribbon cable. For example, six buffer tubes, each containing a 12×12 ribbon stack, may be stranded about a central strength member and enclosed by a cable jacket.
The ribbon cables in accordance with the present invention may include one or more radial strength members (e.g., formed from glass-reinforced plastic (GRP)), which may be embedded in the cable jacket. The radial strength members may be positioned within the cable to as to give the cable a preferential bend.
Optical-fiber ribbons (e.g., a ribbon stack) formed from several bend-insensitive fibers of the present invention may be variously positioned within buffer tubes. For example, such bend-insensitive optical-fiber ribbons can be deployed in optical-fiber buffer tubes and cables as disclosed in commonly assigned U.S. Pat. No. 7,515,795 for a Water-Swellable Tape, Adhesive-Backed for Coupling When Used Inside a Buffer Tube (Overton et al.); commonly assigned U.S. Pat. No. 7,599,589 for a Gel-Free Buffer Tube with Adhesively Coupled Optical Element (Overton et al.); commonly assigned U.S. Patent Application Publication No. 2009/0003781 and its related U.S. patent application Ser. No. 12/146,526 for an Optical Fiber Cable Having a Deformable Coupling Element (Parris et al.); commonly assigned U.S. Patent Application Publication No. 2009/0003779 and its related U.S. patent application Ser. No. 12/146,535 for an Optical Fiber Cable Having Raised Coupling Supports (Parris), and commonly assigned U.S. Patent Application Publication No. 2009/0003785 and its related U.S. patent application Ser. No. 12/146,588 for a Coupling Composition for Optical Fiber Cables (Parris et al.), each of which is hereby incorporated by reference in its entirety.
The present optical-fiber ribbons may be deployed in buffer tubes having water-swellable elements. The buffer tubes may include filling greases or lubricants (e.g., thixotropic filling greases). The present invention also embraces dry cable structures (i.e., grease-free buffer tubes).
The present optical-fiber ribbons may be deployed within buffer-tube structures having annular free space, that is to say that there is free space between the optical-fiber element (e.g., a ribbon stack) and its surrounding structure (e.g., the inner surface of a buffer tube or the surface of a water-swellable tape or coupling element(s) positioned between the buffer tube and the ribbon stack).
Moreover, as used herein in this context, the term “annular free space” is intended to characterize unfilled space that can exist between the optical-fiber element and its surrounding structure around the entire perimeter of the optical-fiber element, regardless of the respective shapes of the optical-fiber cable and its components (e.g., a rectangular ribbon stack within a round buffer tube). In this regard, the term “annular free space” as used herein is not limited to the regular gap between two concentric tubes (or casings) having circular cross-sections (i.e., a perfect annulus).
The term “optimal minimum clearance” refers to the minimum distance between the optical-fiber element and its surrounding structure (e.g., the surrounding buffer tube or surrounding water-swellable tape) when the optical-fiber element is optimally positioned to maximize clearance. Those having ordinary skill in the art will appreciate that clearance is typically maximized when the optical-fiber element is centrally positioned within its surrounding structure. By way of illustration, the optimal minimum clearance for a rectangular ribbon stack is the distance between a corner optical fiber and its closest adjacent surrounding structure when the rectangular ribbon stack is centrally positioned (e.g., within the surrounding buffer tube).
When the closest adjacent surrounding structure to the centrally positioned optical-fiber element is the inner surface of the buffer tube, the optimal minimum clearance is equal to one-half of the difference between the buffer tube's inner diameter and the optical-fiber element's maximum cross-sectional width. Because of the improved bend insensitivity of the present bend-insensitive optical fibers, optical-fiber cables and buffer tubes containing the present optical fibers may have a relatively high optical-fiber density resulting from a relatively small clearance.
In particular, the buffer tube may have an optimal minimum clearance of less than about 0.32 millimeter, such as between about 0.15 millimeter and 0.3 millimeter. Typically, the present buffer tubes have an optimal minimum clearance of less than about 0.25 millimeter (e.g., between about 0.10 millimeter and 0.20 millimeter), more typically less than about 0.15 millimeter (e.g., between about 0.05 millimeter and 0.10 millimeter). Indeed, a zero-clearance buffer-tube configuration (i.e., about 0 millimeter) is within the scope of the present invention.
As noted, the present optical-fiber ribbons may be deployed within buffer-tube structures or cable cavities (i.e., cables not having buffer tubes such as a drop cable) having one or more compressible coupling elements and/or compressible water-swellable tapes, which may also serve to alleviate microbending and macrobending. Exemplary compressible coupling elements are disclosed in commonly assigned U.S. Patent Application Publication No. 2009/0003781 (Parris et al.).
Within such buffer tubes or cable cavities, the optical-fiber element may be in contact with one or more compressible coupling elements and/or water-swellable tapes so that there is no annular free space within the buffer tubes or cable cavities. For example, one or more compressible coupling elements may compressibly squeeze the optical-fiber element (e.g., at the corners of the ribbon stack). The compressible coupling elements and/or compressible water-swellable tapes used within such buffer tubes or cable cavities need not be as thick or as compressible as the compressible coupling elements and/or water-swellable tapes found in conventional buffer tubes or cable cavities. Consequently, the pertinent cable and buffer-tube diameters may be smaller than those of conventional ribbon cables without promoting undue microbending or macrobending.
As noted, the present buffer tubes may have relatively high optical-fiber densities and thus high filling coefficients.
As used herein, the term “buffer-tube filling coefficient” refers to the ratio of the total cross-sectional area of the optical fibers within a buffer tube versus the inner cross-sectional area of that buffer tube (i.e., defined by the inner boundary of the buffer tube). By way of clarification, the term “buffer-tube filling coefficient” excludes ribbon matrix materials (e.g., subunit and common ribbon matrices).
Additionally, as used herein, the term “cumulative buffer-tube filling coefficient” refers to the ratio of the total cross-sectional area of the optical fibers enclosed within buffer tubes versus the sum of the inner cross-sectional areas of the buffer tubes containing those optical fibers.
In this regard, the present buffer tubes typically possess a buffer-tube filling coefficient of at least about 0.3 (e.g., between about 0.32 and 0.38), more typically at least about 0.35, such as about 0.4 or more.
Moreover, as used herein, the term “ribbon-stack filling coefficient” refers to the ratio of the total cross-sectional area of a ribbon stack enclosed within a buffer tube versus the inner cross-sectional area of the buffer tube. In this regard, the term “ribbon-stack filling coefficient” specifically includes ribbon matrix materials (e.g., subunit and common ribbon matrices). Assuming a rectangular ribbon stack, the present buffer tubes typically have a ribbon-stack filling coefficient of at least about 0.35, more typically at least about 0.4 (e.g., between about 0.45 and 0.65). That said, even higher ribbon-stack filling coefficients might be achieved by employing non-rectangular ribbon stacks.
In an exemplary embodiment, a 12×12 ribbon stack having a width of about 3 millimeters and a thickness of about 3.6 millimeters may be placed in a buffer tube having an inner diameter of about 5 millimeters. The buffer tube may be filled with a thixotropic composition. In this embodiment, the optimal minimum clearance would be about 0.16 millimeters and the buffer-tube filling coefficient would be about 0.34. Furthermore, the ribbon-stack filling coefficient would be about 0.55.
Buffer tubes in accordance with the present invention typically have a thickness of between about 0.5 millimeter and 1.0 millimeter. Accordingly and by way of example, a buffer tube having an inner diameter of about 5 millimeters may have a outer diameter of between about 6 millimeters and 7 millimeters.
In an alternative embodiment, a 12×12 ribbon stack having a width of about 3 millimeters and a thickness of about 3.6 millimeters may be placed in a buffer tube having an inner diameter of about 5.2 millimeters. A layer of water-swellable tape having a thickness of about 0.2 millimeters may be placed in the interior of the buffer tube. In this alternative embodiment, the optimal minimum clearance would be about 0.06 millimeters and the buffer tube filling coefficient would be about 0.31. Furthermore, the ribbon-stack filling coefficient would be about 0.51.
Smaller cable structures, as described previously, have many benefits, including less material usage, which not only can reduce manufacturing costs but also can make such cables more suitable for deployments in tight enclosures. As compared with previous cables, these smaller cable structures typically weigh less and are easier to handle.
This application further incorporates entirely by reference the following commonly assigned patents, patent application publications, and patent applications: U.S. Pat. No. 5,574,816 for Polypropylene-Polyethylene Copolymer Buffer Tubes for Optical Fiber Cables and Method for Making the Same; U.S. Pat. No. 5,717,805 for Stress Concentrations in an Optical Fiber Ribbon to Facilitate Separation of Ribbon Matrix Material; U.S. Pat. No. 5,761,362 for Polypropylene-Polyethylene Copolymer Buffer Tubes for Optical Fiber Cables and Method for Making the Same; U.S. Pat. No. 5,911,023 for Polyolefin Materials Suitable for Optical Fiber Cable Components; U.S. Pat. No. 5,982,968 for Stress Concentrations in an Optical Fiber Ribbon to Facilitate Separation of Ribbon Matrix Material; U.S. Pat. No. 6,035,087 for an Optical Unit for Fiber Optic Cables; U.S. Pat. No. 6,066,397 for Polypropylene Filler Rods for Optical Fiber Communications Cables; U.S. Pat. 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No. 6,321,014 for a Method for Manufacturing Optical Fiber Ribbon; U.S. Pat. No. 6,210,802 for Polypropylene Filler Rods for Optical Fiber Communications Cables; U.S. Pat. No. 6,493,491 for an Optical Drop Cable for Aerial Installation; U.S. Pat. No. 7,346,244 for a Coated Central Strength Member for Fiber Optic Cables with Reduced Shrinkage; U.S. Pat. No. 6,658,184 for a Protective Skin for Optical Fibers; U.S. Pat. No. 6,603,908 for a Buffer Tube that Results in Easy Access to and Low Attenuation of Fibers Disposed Within Buffer Tube; U.S. Pat. No. 7,045,010 for an Applicator for High-Speed Gel Buffering of Flextube Optical Fiber Bundles; U.S. Pat. No. 6,749,446 for an Optical Fiber Cable with Cushion Members Protecting Optical Fiber Ribbon Stack; U.S. Pat. No. 6,922,515 for a Method and Apparatus to Reduce Variation of Excess Fiber Length in Buffer Tubes of Fiber Optic Cables; U.S. Pat. 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U.S. Classification 385/114, 385/109, 385/100, 385/113
Cooperative Classification G02B6/02395, G02B6/4482, C03C25/106, G02B1/048, G02B6/4411, G02B6/4429, G02B6/4494
European Classification G02B6/44C5A, G02B1/04D4, G02B6/44C7, C03C25/10P2D2, G02B6/02
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:OVERTON, BOB J.;REEL/FRAME:024267/0227