Methods for forming fiber optic cables and fiber optic cables having helical buffer tubes

A method for forming a fiber optic cable includes paying off a buffer tube such that the buffer tube extends generally along a longitudinal axis. The method further includes binding the buffer tube with a strength member. The strength member has at least one of a tension or a stiffness that is greater than a respective tension or stiffness of the buffer tube. The resulting fiber optic cable includes the strength member extending along a longitudinal axis and the buffer tube wrapping helically about the strength member. A fiber optic cable includes a strength member extending generally along a longitudinal axis. The fiber optic cable further includes a buffer tube wrapping helically about the strength member. The strength member has at least one of a tension or a stiffness that is greater than a respective tension or stiffness of the buffer tube.

FIELD

The present disclosure relates generally to methods for forming fiber optic cables, as well as fiber optic cables, having helical buffer tubes.

BACKGROUND

Optical fiber is increasingly being used for a variety of applications, including broadband applications such as voice, video and data transmissions. As a result of this increasing demand, fiber optic networks typically include a large number of mid-span access locations at which one or more optical fibers are branched from a distribution cable. These mid-span access locations provide a branch point from the distribution cable and may lead to an end user, commonly referred to as a subscriber. Fiber optic networks which provide such access are commonly referred to as FTTX “fiber to the X” networks, with X indicating a delivery point such as a premises (i.e. FTTP).

Various cable types and sizes are utilized throughout the network. However, recently, demand has increased for fiber optic cables which can span longer distances, such as greater than 350 feet, while still meeting certain design requirements. For example, demand has increased for long-span fiber optic cables which are all-dielectric and have low sag, and which have reduced optical and mechanical issue potential, while remaining at relatively low costs and with relatively small diameters.

Accordingly, improved fiber optic cable designs and methods for forming such fiber optic cables are desired in the art. In particular, improved cable designs and forming methods which facilitate use over relatively long spans while meeting other design requirements would be advantageous.

BRIEF DESCRIPTION

In accordance with some embodiments, a method for forming a fiber optic cable is provided. The method includes paying off a buffer tube such that the buffer tube extends generally along a longitudinal axis. The method further includes binding the buffer tube with a strength member. The strength member has at least one of a tension or a stiffness that is greater than a respective tension or stiffness of the buffer tube. The resulting fiber optic cable includes the strength member extending along a longitudinal axis and the buffer tube wrapping helically about the strength member.

In accordance with other embodiments, a fiber optic cable is provided. The fiber optic cable includes a strength member extending generally along a longitudinal axis. The fiber optic cable further includes a buffer tube wrapping helically about the strength member. The strength member has at least one of a tension or a stiffness that is greater than a respective tension or stiffness of the buffer tube.

DETAILED DESCRIPTION

As used herein, terms of approximation such as “generally,” “about,” or “approximately” include values within ten percent greater or less than the stated value. When used in the context of an angle or direction, such terms include within ten degrees greater or less than the stated angle or direction, e.g., “generally vertical” includes forming an angle of up to ten degrees in any direction, e.g., clockwise or counterclockwise, with the vertical direction.

Referring now toFIGS. 1 and 2, the present disclosure relates generally to improved fiber optic cables10. Fiber optic cables10in accordance with the present disclosure can advantageously be utilized over relatively long spans, such as greater than 150 feet, greater than 250 feet, greater than 350 feet, and/or greater that or equal to 400 feet. In particular, such cables10can extend through such distances with less than one foot loaded sag, or less than 5% loaded sag, or less than 4% loaded sag, or less than 3% loaded sag. Loaded sag is calculated in accordance with NESC Heavy design criteria. Further, such cables10may advantageously be all-dielectric, have relatively small outer diameters, and advantageously be manufactured and deployed at relatively low costs.

Cables10in accordance with the present disclosure may further be capable of accommodating tensile loads of greater than 1000 pounds, such as greater than 1050 pounds, such as greater than or equal to 1100 pounds.

Cables10in accordance with the present disclosure may further be capable of accommodating cable strain of greater than 1.0%, such as greater than 1.05%, such as greater than or equal to 1.1%.

As shown, a cable10in accordance with the present disclosure may include a buffer tube20. The buffer tube20may, in exemplary embodiments, surround and be in contact with one or more optical fibers30. Buffer tube20may be formed from a suitable polymer material, such as a suitable thermoplastic. For example, buffer tube20may be formed from a polyester, such as in some embodiments, a polybutylene terephthalate. In some embodiments, buffer tube20may be formed from a polypropylene.

In some embodiments, buffer tube20may have a maximum outer diameter22of between 1.4 millimeters and 1.8 millimeters, such as between 1.5 millimeters and 1.7 millimeters, such as approximately 1.6 millimeters. Additionally or alternatively, buffer tube20may have a maximum thickness24of between 0.4 millimeters and 0.8 millimeters, such as between 0.5 millimeters and 0.7 millimeters, such as approximately 0.6 millimeters. However, it should be understood that the present disclosure is not limited to such ranges, and rather than suitable buffer tubes20having other suitable diameters and/or thicknesses are within the scope and spirit of the present disclosure.

One or more optical fibers30may be disposed within the buffer tube20. Each optical fiber30may generally include a core32and one or more cladding and coating layers34, as is generally understood. Any suitable optical fiber types may be utilized in accordance with the present disclosure, including for example single-mode or multi-mode optical fibers.

Cable10may further include a strength member40. In exemplary embodiments, the strength member40is a yarn, although in alternative embodiments the strength member40may be a cord or a composite component. Strength member40may, in exemplary embodiments, be formed from aramid fibers or from a fiber-reinforced polymer. For example, the fiber-reinforced polymer may be a glass-fiber reinforced polymer (i.e. fiberglass).

Strength member40may have a maximum outer diameter42. In exemplary embodiments, the maximum outer diameter42is less than the maximum outer diameter22, such that the maximum outer diameter22is greater than the maximum outer diameter42.

As shown, when formed into the cable10, the strength member40may extend generally along a longitudinal axis12, such as of the cable10. The strength member40may thus extend in a generally linear, non-helical manner. In embodiments wherein the cable10includes an outer jacket, as discussed herein, the strength member40may thus extend generally longitudinally along the longitudinal axis10within the outer jacket. Further, the buffer tube20may wrap helically about the strength member40. Buffer tube20may thus extend in a helical, non-linear fashion along, for example, longitudinal axis12. Buffer tube20may contact the strength member40, and the buffer tube20and strength member40may be bound together.

Further, in exemplary embodiments, the buffer tube20may have a stiffness and a tension. The strength member40may also have a stiffness and a tension. In exemplary embodiments, at least one of the stiffness or the tension of the strength member40is greater than the respective one of the stiffness or the tension of the buffer tube20. For example, in exemplary embodiments, the tension of the strength member40is greater than the tension of the buffer tube20. Additionally or alternatively, the stiffness of the strength member40is greater than the stiffness of the buffer tube20.

Cable10may further include an outer jacket50which surrounds the buffer tube20and strength member40. Outer jacket50may define an interior52in which buffer tube20and strength member40are disposed. In some embodiments, outer jacket50may contact the buffer tube20and/or strength member40, while in other embodiments the outer jacket40may be spaced from the buffer tube20and/or strength member40. Outer jacket50may include an outer surface54which is the outermost exterior surface of the cable10. In exemplary embodiments, a cross-sectional profile of the outer jacket50may be circular.

Outer jacket50may be formed from a suitable polymer, such as suitable thermoplastic. For example, in some embodiments, outer jacket50may be formed from a polyolefin, such as in exemplary embodiments a polyethylene. Alternatively, however, other suitable materials may be utilized.

Outer jacket50may have a maximum outer diameter56of less than or equal to 12 millimeters, such as less than or equal to 11 millimeters, such as less than or equal to 10 millimeters, such as between 8 millimeters and 12 millimeters, such as between 9 millimeters and 11 millimeters, such as approximately 10 millimeters.

In some embodiments, cable10may additionally include a plurality of strength elements60, such as for example aramid fibers. The strength elements60may surround the buffer tube20and/or strength member40, and may be disposed within the outer jacket50.

Referring still toFIGS. 1 and 2as well as toFIG. 3, the present disclosure is further directed to methods for forming fiber optic cables10. A method may include, for example, paying off a buffer tube20such that the buffer tube20extends generally along a longitudinal axis12. When the buffer tube20is paid off and extends generally along such longitudinal axis12, the buffer tube20is thus extending in a generally non-helical manner. The buffer tube20may, for example, be payed off from a reel110, or directly from an upstream step in the cable forming process. In exemplary embodiments, the one or more optical fibers30are disposed within the payed off buffer tube20.

A method may further include, for example, binding the buffer tube20(which is extending generally along the longitudinal axis12as discussed) with a strength member40. Such binding may occur, for example, via use of a binding head120. In this manner, the strength member40may be in contact with the buffer tube20and wrapped helically around the buffer tube20.

The strength member40which is bound to the buffer tube20may have at least one of a tension or a stiffness that is greater than a respective tension or stiffness of the buffer tube20, as discussed herein. The greater tension and/or stiffness may advantageously cause movement of the buffer tube20and strength member40after and due to such binding. The advantageous result of such movement is that the strength member40may extend generally along the longitudinal axis12, as discussed herein, while the buffer tube20wraps helically around the strength member40. Accordingly, when such method is utilized, the resulting cable10advantageously includes the strength member40extending generally along the longitudinal axis12and the buffer tube20wrapping helically around the strength member40.

Notably, in exemplary embodiments, the relative tensions are maintained in the resulting cable10.

A method may further include, for example, surrounding the buffer tube20and strength member40with a plurality of strength elements60. The strength elements60may, for example, be paid off from fiber reels130or other suitable supply locations. In exemplary embodiments, such step may occur after the binding step.

A method may, in some embodiments, further include jacketing the buffer tube20and the strength member40, as well as in exemplary embodiments the strength elements60, such that an outer jacket50surrounds the buffer tube and strength member40, as well as in exemplary embodiments the strength elements60. Such step may occur, for example, after the binding step as well as, in exemplary embodiments, after the surrounding step. A jacketing apparatus140, which may for example include an extruder and other suitable devices for facilitating jacketing, may be utilized.

In exemplary embodiments, the paying off, binding, surrounding, and/or jacketing steps are performed in a continuous in-line process, with no take-up of the cable components between steps. Alternatively, however, take-up may be utilized as necessary between certain steps, such after binding and before surrounding and/or jacketing.