Optical waveguides – Optical transmission cable
Reexamination Certificate
1999-05-25
2001-08-21
Ullah, Akm E. (Department: 2874)
Optical waveguides
Optical transmission cable
Reexamination Certificate
active
06278824
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical fibre cable comprising a filling material and to the composition of said filling material.
2. Related Art
The task of the filling material in an optical fibre cable is to protect the fibres throughout their lifetime. To carry out this function, the filling material is generally introduced into the structures containing the optical fibres in such a way that the optical fibres are embedded in it.
The composition of known fillers typically comprises a base oil, for example of the silicone, mineral (naphthenic or paraffin) or synthetic type. This base oil typically requires the addition of a “viscosity improver” such as an elastomeric polymer with a low glass transition point, which by imparting viscosity to the solution improves its performance as a filling material. The filler composition may also contain an antioxidant and a thickening/thixotropic agent, consisting of more or less silanized pyrogenic silica.
There are various known types of cable which have suitable housings for the optical fibres, filled with a filling material.
For example, the patent EP 632301 describes an optical fibre cable comprising, in a suitable housing, the optical fibres embedded in a composition capable of protecting the fibres from phenomena of attenuation, in which the said composition comprises a hydrocarbon compound, a catalyst and a thixotropic thickener such as silica.
Another example of a filler composition is disclosed in patent application EP 811864, which describes a composition for fillers comprising a mineral oil or a polyalphaolefin, a block copolymer, an anti-oxidant and if necessary a stabilizer of the “metal deactivator” type.
Other examples of optical cables with known fillers are disclosed in U.S. Pat. Nos. 5,285,513 and 5,187,763 and in the patent EP 541007.
Optical fibre cables, when installed underground, for example in leads or inside underground conduits, are subject to damage affecting their coatings, caused by mechanical abuse of various kinds, for example accidental impact by sharp tools such as spades or pickaxes, which have a cutting action on the cable. The said conditions may lead to the ingress of water, with the worst possibility that it will run longitudinally inside the cable and consequently in the proximity of the optical fibres. One of the tasks of the filler is therefore to limit or impede this passage of water inside the cable structure. Less disastrous faults, such as breaks in the outer sheaths only, may also lead to permeation of water in the liquid or vapor state, with consequent harmful effects on the optical fibres, and the development of a number of problems (for example, the delamination of the layer of plastic coating of the optical fibres), the final outcome of which is manifested in optical attenuation of the transmitted signals.
SUMMARY OF THE INVENTION
The applicant has observed that, in order to limit the possibility of the coating of the optical fibre coming into contact with water, it would be desirable to use a filling material with a good wetting capacity by comparison with this coating, in such a way as to make it more difficult for water to enter the interface between the fibre coating and the filling composition.
In relation to the mechanical stresses to which the optical fibres may be subjected, it should also be observed that, even if the cable does not undergo movement once it has been laid, it is inevitably subject to thermal variations which cause differential dimensional deformations in the components of the cable structure, according to the different materials from which these components are formed. The applicant has observed that these deformations may cause movements of the optical fibre inside the structure in which it is housed, by acting through the filling material. If this filling material is not sufficiently deformable during the passage of the optical fibre, the structure of the latter may be subject to excessively high localized pressures; this may cause the well-known phenomena of “micro-bending” in the fibre, which are one of the causes of attenuation of the optical signal.
The applicant has now discovered a new composition which can be used advantageously as a filling material for optical cables.
The filling composition according to the present invention not only maintains the desired characteristics of the known fillers, but also has a number of characteristics which make it possible to improve the compatibility of the fibres with the filling material and the intrinsic properties of this filler, both in terms of ease of processing and in terms of performance when the cable is in use.
REFERENCES:
patent: 4167534 (1979-09-01), Vincenzo et al.
patent: 4434308 (1984-02-01), Larkin et al.
patent: 4941729 (1990-07-01), Hardin et al.
patent: 5001304 (1991-03-01), Hardin et al.
patent: 5187763 (1993-02-01), Tu
patent: 5285513 (1994-02-01), Kaufman et al.
patent: 5378856 (1995-01-01), Allen
patent: 5455881 (1995-10-01), Bosisio et al.
patent: 5748823 (1998-05-01), Nave
patent: 5911023 (1999-06-01), Risch et al.
patent: 6085009 (2000-07-01), Risch et al.
patent: 0 541 007 A1 (1993-05-01), None
patent: 0 612 345 B1 (1994-08-01), None
patent: 0 811 864 A1 (1997-12-01), None
T.S. Coolbaugh et al., “Polydecene-based Systems for Use in Fiber Optic Cable Floods: District Enhanced Stability Regimes for Low and High Molecular Weight Base Fluids”, Polymer Preprints, 37 (1):473-474, (1996) XP-002081007.
D.W. Van Krevelen, “Properties of Polymers”, Elsevier Science Publishing Company Inc., 3rdedition, pp. 230-231, (1990).
Bosisio Claudio
Locatelli Emilio
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Pirelli Cavi E Sistemi S.p.A.
Ullah Akm E.
LandOfFree
Optical cable with filling material comprising an internal... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical cable with filling material comprising an internal..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical cable with filling material comprising an internal... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2468318