Sheathed optical fiber cable
First Claim
1. A method of making an optical fiber cable by steps comprising applying a sheath of polymeric material to surround one or more optical fibers so as to couple at least one of said fibers to said sheath, characterized in that said applying of said sheath is accomplished at an elevated temperature, followed by cooling said sheath to ambient temperature, wherein said polymeric material has a creep compliance sufficiently high so that thermal contraction of said sheath is offset by creep produced by a longitudinal tension that is applied to said sheath during at least a portion of said cooling, whereby substantially zero buckling of said fibers results from said cooling of said sheath.
3 Assignments
0 Petitions
Accused Products
Abstract
Optical fiber cables have an inner sheath extruded or otherwise applied to surround optical fibers. If the fibers are coupled to the sheath, substantial shrinkage of the sheath during manufacturing induces microbending losses in the optical fibers. The inventive technique involves choosing a sheath material having a low viscoelastic modulus, typically PVC, and the application of tension thereto during or after extrusion that prevents such shrinkage. This approach typically avoids the necessity of including longitudinal compressive strength members in the cable. A filled optical fiber cable having a flexible gel to prevent water entry advantageously uses the present technique.
20 Citations
12 Claims
- 1. A method of making an optical fiber cable by steps comprising applying a sheath of polymeric material to surround one or more optical fibers so as to couple at least one of said fibers to said sheath, characterized in that said applying of said sheath is accomplished at an elevated temperature, followed by cooling said sheath to ambient temperature, wherein said polymeric material has a creep compliance sufficiently high so that thermal contraction of said sheath is offset by creep produced by a longitudinal tension that is applied to said sheath during at least a portion of said cooling, whereby substantially zero buckling of said fibers results from said cooling of said sheath.
- 10. An optical fiber cable comprising an inner sheath of polymeric material surrounding one or more optical fibers and having a coefficient of coupling to at least one of said fibers of at least 0.01, characterized in that said polymeric material is chosen to have a sufficiently high creep compliance so that said sheath, in the absence of longitudinal compressive reinforcing elements within, or embedded in, said sheath, transmits to said fibers a longitudinal compressive stress small enough to result in substantially zero buckling of said fibers.
Specification