Optical fiber cable

Details Optical fiber cable Optical fiber cable

1999-06-29

2001-05-01

Spyrou, Cassandra (Department: 2874)

Optical waveguides

Optical transmission cable

Ribbon cable

C385S109000, C385S110000, C385S112000

Reexamination Certificate

active

06226431

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an optical fiber cable having an improved capability for isolating the fibers from external stresses which can result in optical transmission losses or stress corrosion leading to fiber fracture.
Optical fibers are composed of very thin strands of pure silica or glass, and they can be characterized as perfectly elastic-brittle in their mechanical behavior. In order to provide the fibers with protection from external stresses which might cause them to fracture, it has been conventional to coat the fibers with a protective material, such as a thick layer of a rapidly curing polymeric material. As noted in U.S. Pat. No. 5,675,686 such protective material protects the bare fibers from the stresses incurred during shipping and processing. Also, the coated optical fibers may be surrounded with a buffer material, such as expanded PTFE which may be bonded to the coated optical fiber.
It is an object of the present invention to provide an improved optical fiber cable in which the novel compliant unitizing structures minimize both the loads transferred to the fibers and the displacements enforced upon the fibers during the processes and loadings of production, handling, and installation of the cable, so as to enable the design of dry core, high fiber count (HFC) cables with minimum optical transmission loss induced by microbending and/or macrobending of the fibers.
It is also an object to increase fiber packing density for HFC designs by permitting more fibers to be enclosed within a given cable diameter.
SUMMARY OF THE INVENTION
The above and other objects and advantages of the present invention are achieved by the provision of an optical fiber cable which comprises one or more compliant core units enclosed within a supporting outer sheath. Each of the compliant core units comprises at least one optical fiber enclosed in and supported by a compliant unitizing structure. Such a structure may be constructed from a highly expanded polymeric foam, or a material having an elastic response substantially the same as that of a highly expanded polymeric foam. The core units are retained in the outer sheath under a compressive deformation, but so as to permit relative movement therebetween.
The elastic response of the foam as employed with the present invention is characterized by a nearly constant, relatively low stress for compressive strains up to about 60%.
In a preferred embodiment, each of the compliant core units comprises a bundle of parallel optical fibers, such as a ribbon or linear array of multiple fibers.


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