Disclosed are hydrophobic compositions useful for filling the voids within jacketed optical fiber cables. The compositions include about 85 to 95 parts by weight of mineral oil, 5 to 15 parts by weight of a (styrene)-(ethylene/propylene) diblock copolymer having a styrene: (ethylene/propylene) ratio of 37.5:62.5 to 27.5:72.5 and a specific gravity of about 0.90 to 0.95, optional antioxidant, and optional metal deactivator.

A cable 20 of this invention includes at least one core 22 comprising a plurality of coated optical fibers 25 and a filling material 26 which is disposed about the fibers 25. Typically, the fibers 25 and the filling material 26 are disposed within a tubular member 28 which is disposed within a sheath system 27. The sheath system 27 may include longitudinally extending strength members 30 in addition to a plastic jacket 32. The filling material made in accordance with the preferred embodiment of the present invention is one which comprises at least two different hydrocarbons as an oil constituent and/or two different fumed silicas as part of a thickening agent. The hydrocarbon(s) may be a synthetic oil such as polyalphaolefin, for example, or a mineral oil, or a combination of synthetic oils and/or mineral oils. The combination of oils is used to help low temperatures properties as well as better incorporate a gelling system which may include a copolymer. A copolymer is used mainly to reduce oil separation. Additionally, a combination of gelling agents such as mixtures of two different fumed silicas is used to build a more stable and desirable network structure in the filling material. The novel combination of oils and fumed silicas produces a filling material capable of passing EIA/TIA Standard FOTP-81, Compound Flow (Drip) Test for Filled Optical Cable, Section 8 up to 80.degree. C. and has a critical-yield stress of less than about 0.002 psi.

A cable of this invention includes a core comprising a plurality of coated optical fibers and a filling composition of matter which is disposed about the fibers. Typically, the fibers and the filling material are diposed within a tubular member which is disposed within a sheath system. The sheath system include longitudinally extending strength members and a plastic jacket. The filling composition which fills interstices in the core is one which includes an oil constituent which is a relatively high molecular weight aliphatic hydrocarbon. The aliphatic hydrocarbon is a synthetic oil such as polyalphaolefin or mineral oil. A relatively large percent by weight of an antioxidant system is used to prevent thermal oxidative degradation of the filling material as well as of materials in contact with the filling material. Advantageously, for stabilization and metal deactivation, the composition includes zinc dialkyldithiophosphate or diaryldithiophosphate. A styreneethylene propylene copolymer is also included in order to reduce oil separation of the filling material. A fumed silica is used to impart gel properties to the material.

A hybrid strength member (300) for an optical cable (10) is made from dielectric materials, and provides excellent compressive and tensile properties within a single structure. The strength member includes two concentric layers of filamentary strands that are embedded in a thermoset material such as epoxy. The filamentary strands of the inner layer (310) primarily comprise aramid fibers, while the filamentary strands of the outer layer (320) primarily comprise glass fibers. A pair of strength members (300-1, 300-2) is embedded in a plastic jacket of the optical cable at diametrically opposite sides of a central core tube that contains a number of optical fibers. Each strength member includes a thin coating (330) of a relatively soft material (i.e., a hardness of less than 80D on the Shore durometer scale) to enhance its coupling to the plastic jacket. Moreover, each strength member has a compressive stiffness that is effective to inhibit substantial contraction of the cable, and a tensile stiffness that is effective to receive tensile loads without substantial transfer of such loads to the glass fibers.

A cable of this invention includes a core comprising a plurality of coated optical fibers and a filling composition of matter that is disposed about the fibers. Typically, the fibers and the filling material are disposed within a tubular member that is disposed within a sheath system. The sheath system includes longitudinally extending strength members and a plastic jacket. The filling composition that fills interstices in the core is one that includes an oil constituent that is a relatively high molecular weight aliphatic hydrocarbon. A relatively small percent by weight of a stereochemically hindered antioxidant system is used to prevent thermal oxidative degradation of the filling material as well as of materials in contact with the filling material. Such stereochemically hindered antioxidants will not migrate out of filling material into other cable and fiber materials, thereby increasing their effectiveness. As a result, a relatively low concentration of antioxidant is needed, as compared with the amount used in the prior art. A styrene ethylene propylene copolymer is also included in order to reduce oil separation of the filling material. A colloidal filler is used to impart gel properties to the material.