Optical waveguides – Optical transmission cable – Tightly confined
Reexamination Certificate
2000-01-07
2001-11-13
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
Optical transmission cable
Tightly confined
C385S112000, C385S101000, C385S114000
Reexamination Certificate
active
06317541
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
This invention relates to a new and improved low thermal skew optic cable covered with successive layers of materials in such manner that heat or cold from a localized source is distributed relatively uniformly throughout the fiber optic cable.
2. Description of Related Art
The use of fiber optic cables as carriers for electronic signals is well known Frequently such fiber optic cables are coated with a plastic jacket which not only provides thermal insulation but functions as a slick surface to make it easier to pull a cable through a conduits, etc. The use of metallic braid and the use of a metallized polymer film under the braid are likewise well known in industry, for example, in coaxial cables.
SUMMARY OF THE INVENTION
Fiber optic cables may comprise several fibers either as filaments or ribbons within a single cable. One of the fibers may provide a clock signal used to recover data at the receiving end. Frequently, such cables are positioned in proximity to a source of heat or cold such as a hot water pipe or air conditioning duct, whereupon one of the fibers or ribbons is at a different temperature than another located farther from the source of heat or cold. This results in different travel times of data over the different fibers, a phenomenon known as “thermal skew”. The present invention reduces thermal skew.
Temperature gradients which may result in differential delay times through different fibers in a multi-fiber cable may be a performance limiter because of temperature differentials between fibers on opposite sides when the cable is positioned so that one side is close to a source of heat or cold. A principal object of the present invention is to reduce temperature gradients in such structures. Temperature gradients may result in change in length of the fibers and also a change in the index of refraction.
In accordance with this invention, a thermal shield is formed around the core of the cable. In one preferred form of the invention a layer of foam plastic surrounds the fiber optic core or bundle. A metallic braid such as tinned copper surrounds the foam plastic. To block radiative heat transfer through gaps in the braid, a layer of metallized plastic film may be positioned underneath the braid. As further heat insulation and also to make the cables slick, a plastic jacket may be placed over the metallic braid.
In a modified form of the invention a second layer of foam plastic is positioned around the aforementioned metallic braid and the second layer of foam plastic is covered with a second metallized plastic film with a second metallic braid around the outside of the film. Again, a plastic jacket may go over the second or outer metallic braid.
In addition to enhancing radiant reduction, the use of two metallic braids also makes it possible to use one braid for power and the other for return to operate electronics at the far end of the cable.
Still another feature of the invention is that the use of metallic braids increases the tensile strength of the cable and thus may eliminate the need for Keviar strength members which are often incorporated into fiber optic cables in order to pull the cable.
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Conley Rose & Tayon PC
Kivlin B. Noäl
Palmer Phan T. H.
Sun Microsystems Inc.
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