Optical waveguides – Optical transmission cable – Loose tube type
Reexamination Certificate
1998-12-10
2001-06-19
Kim, Robert H. (Department: 2877)
Optical waveguides
Optical transmission cable
Loose tube type
C385S111000, C385S112000, C385S109000, C385S103000, C385S101000
Reexamination Certificate
active
06249629
ABSTRACT:
The present invention relates to fiber optic cables and, more particularly, to fiber optic cables having at least one strength component.
Conventional fiber optic cables include optical fibers that conduct light and are used to transmit voice, video, and data information. A fiber optic cable may be subjected to bend, crush, tensile, and/or impact forces. For optimal end use functionality, it is therefore important for a fiber optic cable to exhibit suitable mechanical performance characteristics whereby undue changes in optical attenuation can be avoided. Additionally, although it is desirable for a fiber optic cable to have a suitable optical fiber count, it is also desirable for the cable to be as compact as possible.
For mechanical robustness, conventional fiber optic cables typically include strength members. 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 cable installation requirements. A cable designer may therefore balance the need to have sufficient strength members for mechanical robustness, against the size and stiffness contributions of the cable components that may render the cable difficult to install in a cable passageway. Moreover, the cost of the strength members can be an important factor.
Several representative conventional fiber optic cable designs are illustrative of the foregoing concerns. For example, U.S. Pat. No. 4,143,942 discloses a fiber optic cable having fiber optic elements carried along the length of elongate strength members. A tape is applied over the fiber optic elements and elongate strength member to establish a cable core, and a protective jacket is disposed over the cable core. The tape maintains the fiber optic elements and elongate strength member in assembled relation, provides a heat barrier, and facilitates stripping of the jacket without disturbing the cable core. A filler material may be interposed between the jacket and the taped cable core. The strength members and heat barrier tape, however, can raise concerns about the cost, size, weight, and stiffness of the fiber optic cable.
Conventional strength members may include a composite of aramid fibers and a resin. For example, U.S. Pat. No. 4,269,024 discloses a continuous elongate strength member for reinforcing an optical fiber cable consisting of a composite of aromatic polyamide filaments impregnated with a synthetic resin. The filaments are individually coated with the resin, and the filaments of at least an outer layer of the assembly are helically stranded. The impregnation is carried out by separating the filaments and immersing them in a low viscosity dispersion of the resin in a liquid medium. The filaments are then stranded, and the resin is cured. The aramid fiber/resin composite type strength members can disadvantageously contribute to the cost, size, weight, and stiffness of the fiber optic cable and raise an additional concern regarding ease of manufacturability.
Conventional strength members need not be formed into unitary components. For example, U.S. Pat. No. 5,345,525 discloses a fiber optic cable including a core having bundles of optical fibers and a yarn-like strength member system that is wrapped with an oscillated or unidirectional lay about the optical fibers. The strength member system provides impact resistance for the optical fibers. The yarn-like strength member system can disadvantageously contribute to the cost, size, weight, and stiffness of the fiber optic cable. Moreover, the optical fiber bundles are not protected by buffer tubes which can result in undue attenuation increases when the cable experiences operating conditions in the field.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide a fiber optic cable having a plurality of tubes each having at least one optical fiber therein and at least one strength component. The strength component can be generally offset from a center-zone of the fiber optic cable. The cable may include a center-zone interstice, the center-zone interstice spanning generally the center of the fiber optic cable between the tubes and the at least one strength component. The cable may include a water swellable substance, the water swellable substance being generally located in the center-zone interstice for blocking the flow of water therein.
It is another object of the present invention to provide a fiber optic cable having a plurality of buffer tubes each having at least one optical fiber therein and at least one strength component, a center of the strength component being generally offset from a center of the fiber optic cable, the fiber optic cable having a compact size defining a center-to-center spacing between the center-zone of the cable and a center of each of the buffer tubes, the center-to-center spacing being about 2.0 mm or less for permitting a bend radius that minimizes undue attenuation in the optical fibers during cable bending, and providing a compact size for the cable that facilitates installation thereof in a cable passageway.
It is an object of the present invention to provide a fiber optic cable having tubes including at least one optical fiber therein and a strength component adjacent the tubes, the tubes and the strength component define a trilateral configuration, whereby upon bending of the fiber optic cable, the strength component is operative to resist bending forces and thereby prevent an undue change in attenuation in the optical fibers.
It is another object of the present invention to provide a fiber optic cable with tubes having at least one optical fiber therein and strength components adjacent the tubes. The tubes and the strength components define a quadrilateral configuration, whereby upon bending of the fiber optic cable, the strength components are operative to resist bending forces and thereby prevent an undue change in attenuation in the optical fibers.
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Aberle Timothy J.
Kim Robert H.
Siecor Operations LLC
Stafira Michael P.
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