Winding – tensioning – or guiding – Wound storage package – Particular winding
Reexamination Certificate
1999-12-22
2002-04-16
Mansen, Michael R. (Department: 3653)
Winding, tensioning, or guiding
Wound storage package
Particular winding
C065S381000, C065S382000, C065S479000, C065S486000, C065S491000, C242S480800, C242S920000
Reexamination Certificate
active
06371394
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for winding a fibre element having different longitudinal portions. In particular, the present invention relates to a method for winding an optical fibre having different longitudinal portions onto a reel at the end of a process for drawing the said fibre.
For the purposes of the present invention, “fibre element” is understood as meaning an optical fibre, where appropriate provided with a surface coating and with other coatings.
As is known in the art, optical fibres are produced in special drawing towers from preforms which have been prepared beforehand. In practice, a preform is supplied, along a vertical direction, to a furnace so as to obtain a casting of molten material. The molten material is then drawn and cooled so as to obtain an optical fibre with the desired characteristics. These characteristics are obtained by suitably setting the parameters of the drawing process, namely the furnace temperature, the fibre drawing speed, and all the other parameters (described in detail below) which define the process conditions. At the end of the drawing process, the optical fibre is wound onto a storage reel, from where it is later unwound at the time of use, either for carrying out tests or so as to rewind it onto other reels.
Generally, the drawing process is carried out for its entire duration under the same process conditions, i.e. without any variation in the process parameters. In such a case, a fibre is drawn from a single preform such that it is substantially homogeneous and uniform along its whole length. At the end of the production process, this fibre is wound onto the storage reel in a cylindrical helix, without interruption and with a constant pitch. For the purposes of the present invention, “winding pitch” is understood as meaning the distance between two consecutive intersections of the helix with the same generatrix of the cylinder on which the said helix lies. Helical winding with a constant pitch is usually obtained by moving the reel axially so that it performs an alternating movement at a constant speed or by moving a member which supplies the fibre to the reel so that it performs a similar movement.
Drawing towers of the known type, owing to recent progress in technology, allow optical fibres which are up to several hundred kilometers long to be obtained from a single preform. In the future, technological improvements will probably result in even longer fibres being obtained from a single preform. In view of the high yields which can already be obtained nowadays in drawing processes, it may be necessary or advantageous to form, from a single preform, a fibre comprising longitudinal portions which have different chemical/physical characteristics, for example longitudinal portions with different core and/or cladding diameters, different internal tensions, etc. These physical variations may be obtained by changing, during the fibre drawing process, one or more characteristic process parameters.
For example, it may be advantageous to form a fibre comprising two or more longitudinal portions having substantially the same basic characteristics, but with one or more differences of an optical, geometric or mechanical nature. A first example is provided by M. Ohashi et al. in “Dispersion-Modified Single Mode Fiber by VAD Method”, NTT, Japan, The Transaction of the IEICE, Vol. E 73, No. 4, April 1990. In this article, in order to study the sensitivity of single mode optical fibres with a low dispersion of about 1.5-1.6 &mgr;m to micro-bendings, fibre portions which are several kilometers long are used, said fibres being made from a single preform and being different from one another solely in terms of the zero-chromatic-dispersion wavelength.
A further example relates to the study of the phenomenon of modal dispersion due to polarization (“Polarization Mode Dispersion”or PMD). As is known, this phenomenon is influenced by the photoelastic effect which occurs in the fibre, this being dependent upon structural characteristics associated with the tension to which the said fibre is subjected during the drawing process. For this type of study it is therefore advantageous to have fibre portions available that have the same physical/chemical characteristics and different internal tensions. U.S. Pat. No. 5,400,422 proposes a technique for forming, in an optical fibre, a sequence of Bragg gratings of varying pitch, during the actual fibre drawing process. The gratings are formed by exposing the fibre, using optical techniques of the interferometric type, to ultraviolet radiation pulses. The gratings are formed at predefined distance from each other along the fibre. In this case also, therefore, fibre portions with different characteristics are formed by varying, during the drawing process, the operating conditions of the process.
In other instances it may be necessary to produce local variations in the characteristics of the drawn fibre, i.e. variations affecting only small sections of the said fibre. A situation of this type is described in U.S. Pat. No. 4,163,370, in which a short section of fibre with a larger diameter is formed in order to improve the performance of the fibre in terms of modal dispersion.
The Applicant has noticed that, in cases where it is required to form a fibre comprising longitudinal portions which are different from one another, winding onto the reel without interruptions and with a constant pitch is not very advantageous since the different portions of wound fibre cannot subsequently be distinguished from one another. One way of solving this problem is to interrupt the winding process and, therefore, the drawing process, whenever a given fibre portion has been completely wound so as to be able to cut the fibre at the end of this portion and replace the reel onto which this portion has been wound with an empty reel. At this point, the winding process (and the drawing process) can be started again and the next fibre portion is wound onto a new reel. The need to interrupt the drawing process every time, however, gives rise to certain drawbacks, including loss of time, wastage of molten material from the preform and a possible variation in the drawing conditions, for example due to temporal variations in the characteristic parameters of the process.
Alternatively, if the fibre must be completely wound onto the same reel, it is possible, instead of cutting the fibre at the end of each wound portion, apply a marker to a predefined point on each portion, which can be subsequently identified. This operation may even be performed without interrupting the drawing process, as described in the already cited U.S. Pat. No. 5,400,422. However, the use of markers to identify the different fibre portions is unreliable since, at the normal fibre unwinding speeds, one or more of these markers could be accidentally overlooked. Moreover, this technique generally requires the presence of an operator during unwinding of the fibre, who is responsible for identification of the markers.
BRIEF SUMMARY OF THE INVENTION
The Applicant has found that, in the case of a fibre comprising longitudinal portions which are different from one another, if the fibre is wound by associating with each portion a respective winding pitch different from the winding pitches of the adjacent portions, subsequent identification of these portions during unwinding of the fibre can be performed rapidly, automatically and with very small probability of error. The Applicant proposes, inter alia, a winding method which can be performed without interruptions, thus avoiding the abovementioned drawbacks.
The Applicant has also found that, in order to reduce to a minimum the probability of error in identifying the various fibre portions during unwinding of the said fibre, it is preferable to modulate the winding pitch with periodic functions. This variation in the winding pitch is preferably performed by modulating, with the same law, the speed of axial translation of the reel during winding. If the fibre has been wound in this way, sub
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Mansen Michael R.
Pirelli Cavi e Sistemi S.p.A.
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