Optical waveguides – Optical fiber waveguide with cladding
Reexamination Certificate
1999-12-07
2002-05-07
Kim, Ellen E. (Department: 2874)
Optical waveguides
Optical fiber waveguide with cladding
C385S100000, C385S107000, C385S136000
Reexamination Certificate
active
06385378
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of installing an optical fibre unit in a tube. The term “optical fibre unit” is used herein to describe an article which comprises a single optical fibre, or a plurality of optical fibres assembled to form a multi-fibre unit.
2. Description of Related Art
At the present time there are broadly two approaches to the in situ installation of optical fibre units in tubes. The first, and older, approach is to pull the fibre unit into the tube using an elongate pulling member. Fibre units which are to be installed in this way are heavyweight units/cables, and are provided with a substantial measure of reinforcement, for example by surrounding the fibre or fibre bundles with a rugged sheath, and/or using a steel, Kevlar, or similar strength member. (“Kevlar” is a Registered Trade Mark for a polyarylimide material). The philosophy behind this approach is that pulling exerts substantial forces on the optical fibre unit, and that such reinforcement is needed to withstand those forces. It must be borne in mind that the installation force within a fibre unit being installed by pulling increases progressively from the trailing end of the unit to the leading end. The theory has been that for the installation force at the trailing end to be sufficient, the force at the leading end must be so high that, in the absence of such reinforcement, the fibre will be damaged by it mechanically, or even if it survives mechanically, its optical properties will be adversely affected.
The second approach is to use a lightweight fibre unit and install it using a flow of fluid in a tube, preferably a flow of a gas, and more preferably, a flow of air. Such a method is described, for example, in EP-A-108590. Using a fluid has the effect that the propelling force exerted on the fibre unit is, at least in theory, substantially the same throughout its length, and this force is much less than the maximum force present in a fibre unit which is being installed by pulling. Accordingly, significant reinforcement of the fibre is not required, and indeed would be undesirable since it would increase the weight per unit length of the fibre and hence the fluid drag required to achieve installation.
However, although the blowing approach has attractions, and is being successfully used, it has a number of disadvantages. Thus, the distance over which, and speed with which, fibres can be installed is limited for any given tube diameter by the pressure drop and flow restrictions imposed thereby. Increasing the tube diameter to reduce these effects means that the tubes or bundles thereof occupy more space in the network and are thus more difficult to manage, particularly when a number of such bundles are present, for example at exchange buildings. Also, it arguably requires a more skilled installer than is needed when pulling is being used, and it requires more sophisticated installation equipment. Furthermore, this equipment is bulky and its use noisy, and it may be unacceptable to a customer to have this equipment brought on to his premises, should the end from which blowing is to take place be on those premises. Indeed, it may be physically impossible to locate the equipment there. Nevertheless, despite these disadvantages, blowing has been used increasingly, at least in the United Kingdom, for optical fibre unit installation.
JP-A-63-124005 (Sumitomo Electric Industries, Ltd.) describes a modification of the blowing method of EP-A-108590 for installing lightweight fibres. In this, in addition to exerting an installation force on the fibres by means of a flow of air, the fibres are also subjected to a pulling force. It is to be noted that the force exerted by the air is evidently substantial, since the air pressure quoted is 7 kg/cm
2
, whereas EP-A-108590 stated that a pressure below about 5.6 kg/cm
2
, usually below half that figure, had been found sufficient to install fibre members of up to 3.5 g/m over lengths of 200 m.
SUMMARY OF THE INVENTION
The present invention is based on the discovery that, provided the optical fibre unit is sufficiently lightweight, it can in fact be successfully installed substantially only by pulling, even in routes which are long and which include significant bends, because the low weight per unit length has the result that the required pulling force is below that at which the unit is likely to be damaged, or its optical properties impaired even at the leading end of the fibre. Accordingly, the fibre unit which is proposed herein to be installed by pulling should not include any reinforcement which would have the effect of substantially increasing the weight of the fibre, though, as explained below, it may have lightweight reinforcement.
Thus, according to one aspect of the invention there is provided a method of installing an optical fibre unit in a tube, in which the fibre unit is a lightweight fibre unit, and at least substantially all of the installation force is provided by attaching a pulling member to one end thereof and exerting a pulling force thereon.
The use of pulling not only avoids the disadvantages of blowing referred to above, but generally enables a much higher installation speed to be achieved than is achievable under corresponding conditions using blowing.
The fibre unit preferably has a weight of not more than 10 g/m, and more preferably less than 10 g/m, still more preferably not more than 5 g/m, and for a low fibre count of, say, 8 fibres, is preferably not more than 2 g/m. For a 4 fibre unit might be as little as 0.7 to 0.8 g/m.
The fibre unit may have a protective sheath thereon, for example of an acrylate curable by ultraviolet light, optionally containing particulate matter as described in EP-A-345968 (incorporated herein by reference), to which attention is directed for further details. The fibre unit described in EP-A-345968 is particularly advantageous for present purposes, as the surface thereof, which has protuberances therein as a result of the particulate matter, has been found to provide significantly less resilience to pulling than would otherwise be the case. Materials other than UV-curable acrylate may, however, be used, for example high density polyethylene. However, the thickness of the sheath need be no greater than is required to protect the surface of the optical fibre member and need not be chosen with a view to providing a high tensile strength for the fibre unit.
The fibre unit may have no significant reinforcement, but if it does then the reinforcement must be such as will not add greatly to the weight per unit length of the fibre unit. One form of reinforcement which may be used is a thread made of Kevlar (Registered Trade Mark). A suitable Kevlar thread will preferably not have a weight per unit length of greater than 0.15 g/m, and may have a weight per unit length of as little as 0.05 g/m whilst still providing significant reinforcement.
The tube should be one which exerts a low resistance to the fibre unit being pulled through it, and attention is directed to U.S. Pat. No. 4,892,442 for a description of tubes suitable for this purpose, such tubes having an inner layer which is impregnated with a highly lubricious material. U.S. Pat. No. 4,892,442 (which is incorporated herein by reference) describes, by way of example, the use for the inner layer of Teflon (Registered Trade Mark for polytetra-fluoroethylene) silicone impregnated polyethylene, and graphite impregnated polyethylene. Where an impregnated polyethylene is used this is preferably a high density polyethylene. It should be noted that rather than using a tube lined with a material impregnated with a lubricious agent, one could use a tube formed of such a material throughout its cross section.
In order to insert the lightweight fibre unit into a tube by pulling, it is necessary that the tube should first have a pulling member located therein, and extending along the length of the tube, and that there should be a suitable means for attaching the trailing end of the pulling member to the leading end o
Brown George Henry Platt
Tansey John
Darby & Darby
Emtelle (UK) Limited
Kim Ellen E.
LandOfFree
Method of installing an optical fibre unit in a tube does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of installing an optical fibre unit in a tube, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of installing an optical fibre unit in a tube will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2904621