Loose fill fiber optic cable with steel jacket

Abstract

Fiber density and installation length are improved by enclosing optical fibers in a very small diameter metal jacket, resulting in increased cable stiffness and durability. The metal jacket consists of a small diameter, thin sidewall laser-welded steel tube that is loosely filled with optical fiber strands and a gel waterproofing material that provides a longitudinal water-barrier. The fibers are free to “float” within the steel jacket, and thus are decoupled from external mechanical forces and stresses that act on the cable during installation. When bundles of the steel-jacketed fiber optic cables are installed with pushing and blowing, about twice the installation length is reached as compared with pure blowing. Also, the number of cables and fiber density in each guide tube can be increased, thus increasing the fiber capacity of the feeding ducts and branch ducts of a fiber optic communications network.

We claim:  
     
         1 . A fiber optic cable comprising a core of one or more optical fiber strands loosely enclosed within a tubular metal jacket.  
     
     
         2 . A fiber optic cable according to  claim 1 , wherein the tubular metal jacket comprises a longitudinally sealed steel tube.  
     
     
         3 . A fiber optic cable according to  claim 1 , wherein the tubular metal jacket comprises a small diameter, thin sidewall laser-welded steel tube.  
     
     
         4 . A fiber optic cable according to  claim 1 , further comprising water-proofing gel surrounding the optical fiber strands and filling the tubular metal jacket.  
     
     
         5 . A fiber optic cable according to  claim 1 , wherein the number of fibers contained and the outside diameter/inside diameter of the tubular metal jacket are selected as follows: containing 4 fibers: 1.42/1.12 mm; containing 12 fibers: 2.0/1.8 mm; containing 48 fibers: 3.5/3.2 mm; containing 60 fibers: 3.9/3.6 mm.  
     
     
         6 . A fiber optic cable according to  claim 1 , further comprising a polymer jacket disposed about the tubular metal jacket, wherein the number of fibers contained, the outside diameter of the tubular metal jacket and the outside diameter of the polymer jacket are selected as follows: containing 4 fibers: metal jacket—1.42 mm, polymer jacket—3.9 mm; containing 12 fibers: steel tube—2.0 mm, polymer jacket—3.9 mm; containing 48 fibers: metal jacket—3.5 mm, polymer jacket—5.0 mm; containing 60 fibers: metal jacket—3.9 mm, polymer jacket—5.0 mm.