FIBER OPTIC COAXIAL CABLE AND ASSEMBLY WITH A CONNECTOR

FIELD OF THE INVENTION

The invention relates to coaxial signal communication cables which are composite optical fiber and electrically conductive signal cables and to connectors for their termination.

BACKGROUND OF THE INVENTION

It would be useful in the field of signal communication cables to have a composite electrical/optical signal cable which is not necessarily larger than a coaxial electrical signal cable, which can have the same electrical impedance qualities as a coaxial electrical cable, is small and symmetrical to provide better hydrodynamic, aerodynamic, and fluid dynamic properties, and allows even bending in all directions without damage to the cable. The cable of the invention provides such a cable and a connector for its termination.

SUMMARY OF THE INVENTION

The invention comprises a composite fiber optic/electrical coaxial signal cable which has a fiber optic core which comprises an optical fiber clad with a material having a higher refractive index than the optical fiber and a soft polymer buffer layer surrounding the fiber and cladding. A soft polymer buffer layer, preferably of porous expanded polytetrafluoroethylene (ePTFE), surrounds the clad core and optionally a tape wrap of metallized polymer tape, the metal facing outwardly to contact a layer of conductive metal strands spiralled around its periphery. A layer of insulation surrounds the conductive metal strands. The insulation is preferably a porous polymer, especially porous ePTFE. A conductive metal shield surrounds the layer of insulation and

optionally a protective polymer jacket surrounding the cable. An assembly of the cable of the invention is made with a connector which comprises a hollow conductive metal tube which is provided with means to terminate two levels of conductive metal, the spiralled metal strands and the shield. The metal strands and the shield separated by insulation in the center of the assembly form a precisely configured center passage to accommodate an optical fiber for accurate abutment with another like optical fiber. The fiber optic core may be of equal diameter to the spiralled conductive strands which are also of equal diameter. The optical fiber may be silicaceous, glass clad with silica or glass, silica clad with glass or silica of higher refractive index, or may be an organic polymer clad with a hard polymer. The cable of the invention may optionally have a strength member of strong organic fibers braided around it. Both the soft polymer buffer surrounding the clad optical fiber and the layer of insulation surrounding the spiralled conductive metal strands are preferably of porous ePTFE.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a perspective view of a cable of the invention with the layers cut away to show structure.

Figure 2 is a cross-sectional side view of a cable of the invention partially inserted into a connector.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the drawings, the invention is now described in detail to more fully and carefully delineate the structure of and materials used in the invention.

Figure 1 displays a perspective view of a cable of the invention with the various layers cut away so that the structure of the cable can be easily viewed and understood.

The core of the cable comprises layers i, 2, 3, 4, and 5. An optical fiber 1 is clad with a hard polymer layer 2 in the case of

an organic polymer fiber or a glass or silica layer 2 if fiber 1 comprises glass or silica. Layer 3 is a buffer layer, usually of a soft polymer, such as a foam, but preferably comprises porous ePTFE, which is soft and resilient to provide excellent buffering properties for the optical fiber 1. The preferred ePTFE is that disclosed in U.S. Patents 3,953,566, 3,962,153, 4,096,227,

4,187,390, 4,902,423, and 4,478,665, fully described as to composition, processes for making, and properties thereof, which are assigned to W. L. Gore & Associates, Inc. Buffer layer 3 may optionally be covered with a polymer tape layer 4 which may be metallized on its exterior to enhance conductivity of the layer 6 of electrical conductors. Metal coating 5 on tape 4 may be any conductive metal, but is usually aluminum. Polymer tape layer 4 may comprise any polymer customarily used to tape wrap an electrical conductor or optical fiber, but is preferably polyester, an example of which is Milene ^® polyester available from W. L. Gore & Associates, Inc.

The metallized tape layer is surrounded and in electrical contact with a layer 6 of electrical conductors which may be any of the metals and alloys customarily employed for electrical conductors in the wire and cable art. Copper, copper alloys, or silver plated copper or copper alloy are preferred.

A layer of insulation 7 is then placed over spiralled electrical conductor layer 6 usually by tape wrapping, such as in the case of porous ePTFE tape, the preferred insulation, but may be extruded over conductor layer 6 in the case of a thermoplastic insulation or foamed over layer 6. A foamed polyolefin polyester, or thermoplastic fluorocarbon resin may be used, for example.

Over insulation 7 is placed a conductive shield 8, which may be metal tape, braided wire or metal tape strips or strands, or metallized polymer tape. Those metals and alloys known to be useful for the purpose may be used here, such as copper, copper alloys, steel, aluminum, and silver plated strands of these metals, for example. It would be useful and beneficial for the objective of having a composite electrical/fiber optic signal cable of about the same size as a standard coaxial electrical cable to use ePTFE as the dielectric material. By utilizing ePTFE as a dielectric material

the overall diameter of the finished composite cable is essentially the same as a standard electrical coaxial cable having a center conductor of equivalent guage size and a dielectric of non-porous material . Over shield 8 may be optionally placed a strength member 9, which is usually of braided strong polymer fibers, such as polyester, polyamide-imide, polyimide, polyamide or aromatic polyamide, and liquid crystal polymer for example. Completing the cable, an outer protective jacket JJ) may be used, which is extruded or tape wrapped from polymers, such as polyvinyl chloride, polyethylene, polypropylene, polyurethane rubber, or rubber, for example.

Figure 2 shows a cross-sectional piece of a cable of the invention partially inserted into a connector, which provides electrical contact member 22 for contact with electrical conductor layers 6 and 7 of the cable and shield layer 8 of the cable by contact member 21.. Precisely contoured space is provided within the center of the connector for the fiber optic core of the cable (layers I, 2, and 3) so that the core will abut precisely a similar core affixed to the connector to provide optical signal connection and transmission through optical fiber 1.

The symmetrical construction of the cable of the invention advantageously provides resistance to outside pressure, even bending, saves space and material to provide a smaller cheaper cable, and provides a cable having both fiber optic and coaxial electrical signals in a small cable the same size as for coaxial electrical signals only. Since the cable can be made smaller than the usual composite electrical/fiber optic cable, the hydrodynamic, aerodynamic, and fluid dynamic properties are improved, since both size and shape are important for improvement in those properties. If greater pressure resistance is desired in a cable, a full density insulation can be used for insulation 7, where resulting lesser signal properties can be tolerated.

The cable of the invention is especially useful for ta per- resistant security cables, underwater cables, down-hole cables in petroleum or gas wells, hybrid signal and power cables, hybrid optical signal plus electrical signal cables, and hybrid optical power plus electrical signal or power cables.