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Optical fiber cables with a central strength member encircled by a jacket having ducts which are disposed around the strength member and which receive one or more optical fibers with jacket material between the ducts and the outer surface of the jacket. The optical fibers are free to move in the duc

Optical fiber cables with a central strength member encircled by a jacket having ducts which are disposed around the strength member and which receive one or more optical fibers with jacket material between the ducts and the outer surface of the jacket. The optical fibers are free to move in the ducts, and preferably, the optical fibers are tight buffered. Portions of the jacket intermediate the ducts connect to the strength member which resists longitudinal movement of the jacket relative to the core. However, the jacket can be separated from the core by manual pulling force after the jacket is axially and radially cut at a pair of diametrically opposite ducts. Preferably, the jacket has outer surface indicia showing the positions of the slots, and the cables can include water blocking materials.

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What is claimed is: 1. An optical fiber cable having a length and a longitudinal axis, said cable comprising: a longitudinal strength member disposed at said axis; a tubular plastic jacket encircling the strength member and having a circumferentially continuous outer portion, wherein the strength m

What is claimed is: 1. An optical fiber cable having a length and a longitudinal axis, said cable comprising: a longitudinal strength member disposed at said axis; a tubular plastic jacket encircling the strength member and having a circumferentially continuous outer portion, wherein the strength member and the jacket define at least one longitudinal duct between the jacket outer portion and the strength member, and wherein the jacket includes connecting portions only at circumferentially opposite sides of the duct which provide connections to the strength member; wherein said connecting portions provide connections to the strength member which resist longitudinal movement of the connecting portions with respect to the strength member when the cable is subjected to pulling forces directed parallel to the axis of the cable but which connections can be interrupted by manual forces applied to the jacket and directed radially of said axis; wherein there is at least one longitudinally extending optical fiber in the at least one duct; and wherein the optical fiber in the duct is exposed upon the interruption of the connection of the jacket to the strength member at either of the circumferentially opposite sides of the duct. 2. An optical fiber cable as set forth in claim 1 wherein the pulling forces are up to 600 pounds and the manual forces are not more than 100 pounds. 3. An optical fiber cable as set forth in claim 1 wherein the connections prevent longitudinal movement of the connecting portions with respect to the strength member when said pulling forces are up to 300 pounds and the connections can be interrupted by said manual forces of not more than 75 pounds. 4. An optical fiber cable as set forth in claim 1 wherein said manual forces are not more than 20 pounds. 5. An optical fiber cable as set forth in claim 1 wherein the strength member is a high tensile strength core and the connecting portions engage the core. 6. An optical fiber cable as set forth in claim 1 wherein the strength member has a core of high tensile material encircled by a layer of plastic material which is different from the plastic material of the connecting portions, and which is intermediate the core and the connecting portions. 7. An optical fiber cable as set forth in claim 1 wherein the strength member has a core encircled by a layer of plastic material which is different from the plastic material of the connecting portions and which is intermediate the core and the connecting portions and wherein the connecting portions have a circumferential length between the outer portion of the jacket and the layer of plastic which decreases the rupture strength of such portions to not more than 100 pounds. 8. An optical fiber cable as set forth in claim 7 wherein the circumferential length is at said layer and the rupture strength is not more than 75 pounds. 9. An optical fiber cable as set forth in claim 7 wherein the circumferential length is radially spaced from said layer and circumferentially adjacent the duct. 10. An optical fiber cable as set forth in claim 7 wherein the outer protective layer is a plastic. 11. An optical fiber cable as set forth in claim 1 wherein said strength member comprises a core of high tensile material encircled by a layer of material intermediate the core and said jacket. 12. An optical fiber cable as set forth in claim 11 wherein said core comprises a material selected from the group consisting of metal and glass fibers. 13. An optical fiber cable as set forth in claim 11 wherein said layer comprises a layer of plastic. 14. An optical fiber cable as set forth in claim 11 wherein said layer comprises a water blocking material. 15. An optical fiber cable as set forth in claim 1 further comprising a water blocking material in said duct. 16. An optical fiber cable as set forth in claim 1 wherein the optical fiber is a tight buffered optical fiber having an outer protective layer. 17. An optical fiber cable as set forth in claim 1 wherein the outer surface of the jacket has at least one indicium which provides a visible indication of the position of the duct along the cable length. 18. An optical fiber cable as set forth in claim 17 wherein the jacket has a longitudinal groove extending inwardly from the outer surface of the jacket and corresponding in position to the position of the duct in the jacket and wherein said groove is said indicium. 19. An optical fiber cable as set forth in claim 17 wherein said jacket comprises at least two ducts disposed on diametrically opposite sides of said axis and wherein the jacket has at least two longitudinal grooves, one groove for each slot, which extend inwardly from the outer surface of the jacket and which correspond in positions to the positions of the slots to provide said indicia. 20. An optical fiber cable as set forth in claim 19 wherein diametrically opposite grooves have visibly different characteristics so that one of the grooves can be distinguished from the other of the grooves. 21. An optical fiber cable as set forth in claim 1 wherein the ducts have an alternating lay with respect to said axis. 22. An optical fiber cable as set forth in claim 1 wherein there is a plurality of longitudinal ducts between the jacket outer portion and the strength member, the ducts being equally spaced circumferentially of the strength member, with each pair of ducts having a connecting portion therebetween and wherein there is at least one optical fiber in at least a plurality of the ducts. 23. An optical fiber cable as set forth in claim 22 wherein the strength member has a core encircled by a layer of plastic intermediate the core and the jacket. 24. An optical fiber cable as set forth in claim 23 wherein the plastic of said layer is different from the plastic of said jacket. 25. An optical fiber cable as set forth in claim 24 wherein the plastic of one of said layer and said jacket is a polar plastic and the plastic of the other of said layer and said jacket is non-polar. 26. An optical fiber cable as set forth in claim 24 wherein the plastic of said layer has a melt temperature higher than the melt temperature of the plastic of said jacket. 27. An optical fiber cable as set forth in claim 22 wherein a pair of the ducts are disposed at diametrically opposite sides of said axis and wherein the jacket has a pair of longitudinal grooves extending inwardly of the outer surface of the jacket, one of the grooves being disposed, along its length, radially outwardly of one of the pair of ducts and the other of the grooves being disposed, along its length, radially outwardly of the other of the pair of ducts. 28. An optical fiber cable as set forth in claim 27 wherein the jacket has at least one longitudinal rib adjacent one of said grooves and at the outer surface of the jacket. 29. An optical fiber cable as set forth in claim 1 wherein the cross-sectional dimension of the duct is selected in relation to the cross-sectional dimension of the fiber or fibers in the duct so that the fiber or fibers can move longitudinally with respect to the jacket. 30. An optical fiber cable as set forth in claim 1 wherein the at least one duct extends around the strength member. 31. An optical fiber cable as set forth in claim 1 wherein the at least one duct extends helically around the strength member. 32. An optical fiber cable as set forth in claim 1 wherein the at least one duct extends in an S-Z lay configuration about the strength member.