Optical waveguides – Optical transmission cable – Loose tube type
Reexamination Certificate
2002-02-21
2004-04-06
Zarroli, Michael C. (Department: 2839)
Optical waveguides
Optical transmission cable
Loose tube type
C385S111000
Reexamination Certificate
active
06718101
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an optical cable (also called an optical fiber cable) with continuous accessibility, particularly suitable for local subscriber loops and for internal cabling, providing very simple accessibility at any location and thus providing a very low cost branch-off without having to use a branch connection box.
BACKGROUND OF THE INVENTION
Many types of optical cables are known, making it possible to supply local networks or the cabling of buildings. In the majority of cases, these cables have a very dense structure. They comprise a relatively large number of fibers, and they are branched off using a branch connection box. It is by virtue of this branch connection box that after an often lengthy and tricky operation of removing the sheath from the cable over relatively great lengths, then of distributing the fibers, that it is possible to branch off one or more fibers. However, this operation is expensive and tricky. In addition, it is not without risk for the unbranched-off fibers which, in the majority of cases, are moreover high datarate carriers, that is to say ones having a large number of links transmitting voice, data or images. In addition, because of their architecture, these techniques are very often synonymous with distributed systems (for the cabling of buildings in particular), requiring the placement of numerous elementary cables, not to mention the presence of optoelectronic end devices. These distributed systems thus have the major drawback of leading to extremely high laying costs, which, for optical systems, generates a negative end result compared with the known copper systems.
To compensate for this major drawback, and to reduce the cost of installation, the majority of optical cable solutions developed to date tend toward cables which are as dense as possible, based on either stacks of ribbons, or on cylindrical modules of very small dimensions. Each ribbon or each cylindrical module may, for example, contain from 4 to 12 fibers, or even more. All of these ribbons or of these cylindrical modules are packed as closely as possible in a protective sheath possibly provided with reinforcements, according to the functional specifications of the cable. The sought-after aim is to obtain maximum density while retaining the appropriate mechanical and thermal properties for the optical cable.
The density thus obtained in the highest performance cables of the prior art allows them to be laid in microconduits, for example by blowing or pushing or pulling. However, these cables have the drawback of being quite difficult to access thereby making the tap-off operation, that is to say the branching-off of one module among n or of one fiber among n, expensive and tricky. They are therefore better suited to distributed techniques where the breakout made necessary takes place in a box designed to this end. In addition, the dense and cylindrical structure of the jacket of such cables requires an internal “cabling” of the optical elements (modules or optical fibers). This internal cabling is an assembly of optical elements with a given pitch either in a continuous helix (helical cabling), or in SZ (SZ cabling), so as to guarantee the integrity of the fibers when winding the cables.
Thus, in these known techniques, in order to operate correctly from the mechanical and thermal point of view and in order to comply with the radii of curvature, the relatively dense cable structures require “cabling” of this sort, which only increases the difficulty of access to the fibers and in particular makes it necessary for all the sheath to be removed over considerable lengths so as to allow the operator to handle the bundles with enough flexibility to access the sought-after module and, even more difficult, the sought-after fiber. In addition, cabling of this sort decreases the speed of cablemaking, and increases the costs. It can therefore be seen that, whatever their shape, oval, cylindrical, or other, none of these structures has been designed for continuous and easy accessibility of the fibers.
There is therefore a need for a cable designed to allow continuous and easy accessibility, therefore allowing easy branching, while remaining a very economical solution and installation system. Solving this problem is all the more significant since placing several cables in parallel, for example in order to supply several workstations inside a building, remains an expensive operation which places optical systems at a disadvantage with regard to copper.
A branchable optical cable is known, the principle of which is to place cable elements in a sheath or profile in the shape of a U open on one side, which may then be opened out right along the cable, at any location on the cable, and thus allow access to the cable elements. This cable was the subject matter of patent application FR 99 13271 filed by the applicant. However, a cable of this sort involves the special manufacture of cable elements and the use of a profile which may prove heavy and bulky and quite difficult to utilize, especially in terms of its storage on a cable drum, its laying and its accessibility.
OBJECTS AND DESCRIPTION OF THE INVENTION
The applicant has therefore developed an optical cable with continuous and easy accessibility, therefore making it possible to extract very easily from it, at any location, an optical element protecting one or more optical fibers, intended to supply a room or a region comprising several workstations. The cable developed by the applicant offers tensile strength and crush resistance properties which enable easy installation, for example in a conduit or in cable trays, in the latter case with an increased ability to follow localized curves and with a density which remains reasonable. Because of its structure, the cable which is subject of the invention also has excellent thermal behavior and can be wound with no problem on cable drums, without requiring cabling of the elementary optical elements inside the sheath.
The subject of the invention is therefore an optical cable with continuous accessibility, comprising a closed protective sheath surrounding a cavity having in cross section two substantially perpendicular axes intersecting at the center of the cavity, and at least two optical fibers arranged such that they occupy the greater part of the cavity along one axis but that they allow a sizeable clearance along the other axis of the cavity. The optical fibers can be organized into at least two optical elements (also called optical modules). The optical fibers, or optical modules, therefore form a sort of sheet, which is relatively loose or not depending on the number of fibers or modules. This arrangement of the cable according to the invention does not exclude some superposition of the fibers or of the modules within the sheet. Preferably, one of the axes is longer than the other axis. The optical elements are preferably positioned along this long axis, and therefore the clearance is left in the short axis. The clearance left in one of the axes is considerable with respect to the usual clearance of a dense optical cable structure, which is generally reduced to the strict minimum. This clearance therefore allows variations, called overlength, of the order of one percent or of a few percent (overlengths considered in per thousand in dense structures). Moreover, the sheet of fibers or of modules may move by translation in the cavity while remaining on the same axis (on the long axis in the case of an ovalized cavity).
The cavity has any shape, for example circular or oval or ovalized (that is to say between an oval and a rectangle), preferably ovalized. The sheath has any external shape, for example circular or oval or ovalized, preferably ovalized. In a particularly preferred embodiment, sheath and cavity are of ovalized shape, and their long axes are coincident.
In some embodiments, the sheath may comprise one or more mechanical reinforcing members, preferably positioned on either side of the cavity, again preferably along the long axis. These reinforc
Brault Dominique
Filliatre Daniel
Lagreve Christian
Le Noane Georges
Acome (Societe Cooperative de Travailleurs)
Piper Rudnick LLP
Zarroli Michael C.
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