Fiber optic cable

Details Fiber optic cable Fiber optic cable

1998-01-23

2001-01-09

Davie, James W. (Department: 2881)

Optical waveguides

Optical transmission cable

Ribbon cable

C385S115000, C385S121000

Reexamination Certificate

active

06173101

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns a fiber optic cable. Its applications include, but are not exclusive to, the field of fiber optic cable jointing boxes, also known as splice organizers.
2. Description of the Prior Art
Jointing boxes generally include a pluralility of substantially rectangular cassettes that can be stowed side by side in racks or stacked in the form of drawers. The cassettes accommodate fiber optic cable connectors and spare lengths of fiber optic cable, these spare lengths being provided to enable subsequent resplicing operations.
Ribbon or flat cable type fiber optic cables in which the optical fibers are disposed parallel to each other and are embedded in an extruded insulative sheath forming a ribbon are known in themselves. It is advantageous to use a flat cable of this kind in a jointing cassette because mass jointing is simpler than jointing independent fibers.
The inventors have found that coiling a flat cable in a jointing cassette leads to curvature problems, the radius of curvature being limited by the stiffness of the flat cable, the effect of which is to cause difficulties in passing the flat cable into certain parts of the cassette and a problem caused by a spring effect of the flat cable which tends naturally to open out when it is coiled up on itself.
An aim of the present invention is to overcome the drawbacks of the prior art.
SUMMARY OF THE INVENTION
To this end, the invention consists in a fiber optic cable including a plurality of optical fibers and a protective sheath, said cable having an end section in the form of a ribbon and a central section wherein said protective sheath is of substantially tubular form.
This structure enables easy connection by virtue of the end section in ribbon form whilst avoiding the spring effect observed with ribbons coiled up on themselves.
The advantage of the structure of the invention over prior art ribbons increases in proportion to the number of optical fibers in the ribbon. The width of the ribbon being proportional to the number of optical fibers, the ribbons used in the prior art can fairly rapidly spill out of the coiling cassette. In contrast to this, the diameter of the tubular sheath of the invention does not increase in proportion to the number of optical fibers. Moreover, the greater the number of optical fibers constituting the ribbon, the greater the preferential inertia of the ribbon, in other words the ribbon has a single axis of curvature; this can constitute an obstacle to placing the ribbon in the splicing boxes. This drawback disappears with the structure of the invention.
In one particular embodiment each end section of the cable is in the form of a ribbon.
The cable preferably includes at least three optical fibers. Each optical fiber preferably has a primary protection cladding and a non-stick layer. The non-stick layer facilitates deformation of the cable to obtain a tubular section from a ribbon section.
The optical fibers are advantageously mechanically free relative to the sheath in the part of the cable where the sheath is of tubular form. In this case, the principal function of the sheath is to prevent the optical fibers spilling out of their coiling path.
The invention also consists in a method of fabricating a fiber optic cable in accordance with the invention which consists in choosing a fiber optic ribbon and modifying the shape of the insulative sheath by thermal and/or mechanical stressing.
In particular, the stressing can include a heating step to flexibilize the insulative sheath and a step in which mechanical pressure is applied to each edge of the ribbon to impart a substantially tubular shape to the sheath.
The features and advantages of the invention will emerge more clearly from the following description of embodiments of the invention given by way of non-limiting illustrative example with reference to the accompanying drawings.


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