Optical waveguides – Optical transmission cable – Tightly confined
Reexamination Certificate
1999-02-11
2001-05-15
Kim, Robert H. (Department: 2877)
Optical waveguides
Optical transmission cable
Tightly confined
C385S101000, C385S102000, C385S103000
Reexamination Certificate
active
06233384
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to fiber optic cables and, more particularly, to a fiber optic cable that is ruggedized to be resistant to crushing, torquing, and excessive bending of the internal optic fiber.
BACKGROUND OF THE INVENTION
Fiber optic cables are used for a variety of applications. A fundamental problem associated with the use of fiber optic cables is the inherent fragility of glass fibers. This fragility renders it difficult to form a flexible cable that can withstand bending, twisting, impact, vibration, and other types of stress.
Failures in glass fiber elements typically result from surface flaws or imperfections in the fiber elements. The stress concentration at such surface flaws may be many times greater than the nominal stress at the same point. Because there is no axial yielding in glass fibers, stress at surface flaws cannot be relieved. If a high tensile stress is applied to a glass fiber, surface flaws may propagate with eventual failure of the fibers. Thus, it is necessary that the fiber optic elements be protected from crushing forces or other forces which might nick the surfaces of the fiber optic elements to create points of high stress concentration, while at the same time providing a flexible fiber optic cable. The various types of damage (denting, crushing, kinking, twisting, etc.) often occur during installation and use due to the cable being bent over sharp objects, clamped too tightly, struck by another object, twisted, or bent beyond its minimum bend radius.
U.S. Pat. No. 4,147,406 to Anderson provides one approach for solving this problem. In Anderson, a fiber optic cable is provided wherein a spiral-cut, nonmetallic tube is applied over a glass fiber optic core comprised of one or more fiber optic element bundles cabled along an axial strength member having greater tensile strength and lower elongation per unit length than the fiber optic elements. Using this construction, the axial loading to which the cable may be subjected is taken by the axial strength member rather than subjecting the fiber optic bundles to undesirably high tensile forces. A thin-walled, nonmetallic jacket over the spiral-cut, nonmetallic tube and, optionally, a textile braid or serve layer between the cabled fiber optic bundles and the spiral-cut tubing are also provided in Anderson for improved abrasion resistance. Although this device provides some protection for the fiber optic cable, a more crush resistant fiber optic cable than that produced according to Anderson is desirable.
U.S. Pat. No. 5,061,823 to Carroll describes a crush-resistant coaxial transmission line. This patent describes a spiraled, rigid, metal wire layer between the outer conductor of the coaxial transmission line and the outer jacket of the cable. A ruggedized fiber optic cable would be desirable.
SUMMARY OF THE INVENTION
This invention provides a ruggedized fiber optic cable having greatly increased resistance to crushing, kinking, and torquing. Specifically, the invention provides a ruggedized fiber optic cable having an optic fiber core; a layer of rigid metal wire spiraled around the core at a minimum angle of 45° to the axis of the cable; and at least one layer of mechanical braid surrounding the layer of rigid metal wire. The inventive cable has a crush resistance of greater than 150 pounds per linear inch, preferably greater than 200 pounds per linear inch, more preferably greater than 250 pounds per linear inch, more preferably still greater than 350 pounds per linear inch, and most preferably at least 450 pounds per linear inch.
In another embodiment, the invention provides a ruggedized fiber optic cable having an optic fiber core; a fluoropolymer first jacketing material surrounding the fiber; braided aromatic polyamide plastic fibers surrounding the first jacketing material; a fluoropolymer second jacketing material surrounding the aromatic polyamide plastic fibers; an expanded PTFE buffering layer surrounding the second jacketing material; a PTFE first jacket surrounding the buffering layers; a layer of rigid metal wire spiraled around the first jacket at a minimum angle of 45 degrees to the axis of the cable; at least one layer of mechanical braid surrounding the rigid metal wire; a PTFE second jacket disposed around the mechanical braid; and wherein the cable has a crush resistance of at least 450 pounds per linear inch.
REFERENCES:
patent: 4147406 (1979-04-01), Anderson
patent: 4374608 (1983-02-01), Anderson
patent: 4375313 (1983-03-01), Anderson et al.
patent: 4505541 (1985-03-01), Considine et al.
patent: 4645298 (1987-02-01), Gartside, III
patent: 5061823 (1991-10-01), Carroll
patent: 5212755 (1993-05-01), Holmberg
patent: 5274725 (1993-12-01), Bottoms, Jr.
patent: 5325457 (1994-06-01), Bottoms, Jr. et al.
patent: 5345525 (1994-09-01), Holman et al.
patent: 5371825 (1994-12-01), Traut
patent: 5557698 (1996-09-01), Gareis et al.
patent: 5841072 (1998-11-01), Gagnon
Maniyatte Varghese J.
Schuett Donald M.
Sowell, III Robert L.
von Kleeck Mark T.
Gore Enterprise Holdings Inc.
Kim Robert H.
Nguyen Sang H.
Sheets Eric J.
Wheatcraft Allan M.
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