Optical waveguides – Optical transmission cable
Patent
1998-04-07
2000-04-25
Lee, John D.
Optical waveguides
Optical transmission cable
385107, 385136, G02B 654
Patent
active
060553502
DESCRIPTION:
BRIEF SUMMARY
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.
1. Background of the Invention
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.
2. Background of the Prior Art
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.sup.2, whereas EP-A-108590 stated that a pressure below about 5.6 kg/cm.sup.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 pre
REFERENCES:
patent: 4892442 (1990-01-01), Shoffner
patent: 5013125 (1991-05-01), Nilsson et al.
P. Lesueur et al., "A New Application of Air Pulled Cabled in Microduct For The Local Loop," International Wire Cable Symposium Proceedings 1995, p. 332-335 (No Month).
Brown George Henry Platt
Tansey John
BICC Public Limited Company
Corning Limited
Kim Ellen E.
Lee John D.
Mainetti Technology Limited
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