Optical waveguides – Optical transmission cable – Ribbon cable
Reexamination Certificate
2000-02-24
2001-02-06
Ullah, Akm E. (Department: 2874)
Optical waveguides
Optical transmission cable
Ribbon cable
Reexamination Certificate
active
06185352
ABSTRACT:
The present invention relates to optical fiber cables, and, more particularly, to optical fiber fan-out cables. Conventional fiber optic cables include optical fibers that conduct light in the transmission of voice, video, and data information. Optical cables have the advantages of large bandwidth and low power loss. Typical applications for optical cables include fiber-to-the-curb (FTTC), fiber-to-the-home (FTTH), fiber-to-the-desk (FTTD), plenum, riser, and local area networks (LANs). In a premises environment, optical ribbon cables can be used to interconnect operating equipment, for example, computers, modems, and telephones. Original Equipment Manufacturers (OEMs) may require low-cost, optical interconnect cables that are factory connectorized to multi-fiber connectors, for example, for transceiver applications.
Transceiver applications require sufficient space between fibers to avoid electrical crosstalk. Opto-electrical and electro-optical transducer components, for example, are used in such systems to interface between electrical and optical modes of signal transmission. Electrical systems, however, may experience crosstalk between the signal wires thereof. This type of electrical crosstalk occurs due to electromagnetic fields surrounding the transmitting wires. The electromagnetic fields of one circuit induce currents and electromotive forces in adjacent circuits. For example, electrical crosstalk affecting a telephone line may result in the undesired mixing of caller conversations. Spacing the electrical wires of different circuits tends to reduce electrical crosstalk. On the other hand, because optical-based systems use confined light as the information carrying medium rather than electricity, optical-based systems are not as susceptible to crosstalk and therefore do not require a significant crosstalk type spacing between the optical fibers.
Opto-electrical and electro-optical transducers generally require electrical components, for example, wires to be spaced apart sufficiently enough to avoid crosstalk. For convenience, respective ends of optical fibers in single fiber cables, or dual tight-buffered cables, are connected to such transducers by placing them in housings comprising spaced-apart, fiber receiving apertures. Another method is to connectorize a two-fiber optical ribbon with a 250 &mgr;m to 750 &mgr;m spacing between the fibers. Such conventional methods can be relatively expensive in respect of installation and material costs because two fibers must be individually connectorized. Another method is to connectorize a 2-fiber optical ribbon with a 750 &mgr;m spacing to a multi-fiber connector, as described in U.S. Pat. No. 5,966,489 which is incorporated by reference herein. Optical fibers bonded to or received within tapes, as disclosed in U.S. Pat. No. 4,272,155, can be unsuitable for use with such connectorization procedures.
Multi-fiber interconnect cables are typically used indoors. Indoor fiber optic cables have been developed for installation in plenums and risers, and/or ducts of buildings. In order for a fiber optic cable to be rated for riser or plenum use, the cable must meet flame retardance standards as determined by means of vertical or horizontal flame tests. Exemplary requirements for such tests have been established by Underwriters Laboratories (UL). Since riser cables are typically installed in vertical shafts, the relevant standard for riser rated fiber optic cables is embodied in UL 1666, a flame test in a vertical shaft without a forced air draft in the shaft. UL 1666 does not include a smoke evolution requirement. UL has promulgated the riser rating requirements in a document entitled “Test for Flame Propagation Height of Electrical and Optical-Fiber Cables Installed Vertically in Shafts”, wherein values for flame propagation height are set forth.
The relevant standard for plenum rated fiber optic cables is embodied in UL 910, a horizontal flame test setting forth flame propagation and smoke evolution requirements. In the construction of many buildings, a plenum can include, for example, a space between a drop ceiling and a structural floor above the drop ceiling. A plenum typically serves as a conduit for forced air in an air handling system, and the plenum is oftentimes a convenient location for the installation of fiber optic cables. If, in the event of a fire, the fire reaches the plenum area, flames that would otherwise rapidly propagate along non-plenum rated cables are retarded by plenum rated cables. Moreover, plenum rated cables are designed to evolve limited amounts of smoke. Riser rated cables tested to UL 1666 typically do not exhibit acceptable flame spread and smoke evolution results and are therefore unsuitable for plenum use.
The UL 910 test is promulgated by UL in a document entitled: “Test for Flame Propagation and Smoke-Density Values for Electrical and Optical-Fiber Cables Used in Spaces Transporting Environmental Air”. A key feature of the UL 910 test is the Steiner Tunnel (horizontal forced air draft) test as modified for communications cables. During the UL 910 test, flame spread values are observed for a predetermined time (20 minutes under the current standard), and smoke is measured by a photocell in an exhaust duct. Data from the photocell measurements are used to calculate peak and average optical density values. Specifically, according to UL 910, the measured flame spread must not exceed five feet, peak smoke (optical) density must not exceed 0.5, and average smoke (optical) density must not exceed 0.15. For example, the fiber optical cables disclosed in U.S. Pat. Nos. 4,895,427, 5,229,851, and 5,249,249 contain flammable filling, flooding, or thixotropic grease compounds that render the cables unsuitable for use as plenum cables.
SUMMARY OF THE INVENTION
One aspect of the present invention is a fiber optic fan-out cable having optical sub-units. The optical sub-units are disposed about a central member, at least some of the optical sub-units respectively comprise a sub-unit jacket, strength fibers, and at least one respective optical fiber ribbon therein, the optical fiber ribbon including a plurality of optical fibers, the strength fibers generally surrounding and contacting the optical fiber ribbon in the sub-unit jacket. A cable jacket surrounds the central member and defines an annular space wherein the optical fiber sub-units are disposed about the central member. The annular space preferably includes essentially no strength fibers therein outside of the sub-unit jackets, the strength fibers being essentially located within the optical sub-unit jacket. However, if additional cable strength is required, then strength elements may be added to the annular space as needed.
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Siecor Products Report, Non-Plenum Ribbon Interconnect Cables, Sep. 1998, pp. 1-2.
Siecor Products Report, Plenum Ribbon Interconnect Cables, Nov. 1998, pp. 1-2.
Aberle Timothy J.
Siecor Operations LLC
Ullah Akm E.
LandOfFree
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