GB2289805A

GB2289805A - Blowing an optical fibre element

Info

Publication number: GB2289805A
Application number: GB9510529A
Authority: GB
Inventors: Stephen Polshaw
Original assignee: BICC PLC
Current assignee: Balfour Beatty PLC
Priority date: 1994-05-24
Filing date: 1995-05-24
Publication date: 1995-11-29
Anticipated expiration: 2015-05-24
Also published as: GB9410340D0; GB2289805B; GB9510529D0

Abstract

A method of providing a building or other location with an optical fibre element (1) comprises introducing a leading end of the optical fibre element into the bore of a previously installed duct (3) and propelling it along the duct by fluid drag of a gaseous medium, e.g. air. The element (1) is terminated with an optical connector (2) at its leading end before it is introduced into the duct so that the element and connector are propelled along the duct together.

Description

BLOWING AN OPTICAL FIBRE ELEMENT This invention relates to the provision of buildings and other locations with optical fibre elements.

A method for providing a building or other location with an optical fibre element by propelling the element along a previously installed duct using the fluid drag of a gaseous medium is described in European Patent Application No: 108,590. This method has a number of advantages over prior methods of installation of optical fibres such as pulling the fibre cables by means of a pulling rope. In particular, because the gaseous medium imparts a distributed motive force along the length of the optical fibre element, stresses on the optical fibre are reduced, especially where the route that the optical fibre is to take contains a number of bends. In such a case, pulling the optical fibre element along the route with a pulling cord would cause frictional drag on the fibre at the bends in the duct and, as stated in the application, only a few bends would be sufficient to cause locking of the optical fibre element.

Although this method of installing optical fibres is very successful, it has the disadvantage that the optical fibres must be terminated with connectors on site with the result that the quality of the termination may be poor and in any case is not under the control of the cable or connector manufacturer.

Accordingly, the present invention provides a method of providing a building or other location with an optical fibre element, in which a leading end of the optical fibre element is introduced into the bore of a previously installed duct and the element is propelled along the duct by fluid drag of a gaseous medium, wherein the element is terminated with an optical connector at least its leading end before it is introduced into the duct and the optical connector is propelled along the duct together with the element.

Although it is only necessary according to the invention to terminate the leading end of the optical fibre element before it is blown along the duct it is preferred to terminate both ends of the optical fibre element before it is introduced into the duct. The or each optical connector is preferably provided on the optical fibre element in a production facility before the element is transported to the building or other location. The ability to terminate the optical fibre elements under factory conditions and to test the termination enables a significantly higher level of quality to be guaranteed in respect of the termination.

The method according to the invention may employ any optical fibre elements that are installed by "blowing-in" methods, for example single jacketed fibres (single buffered fibres), or optical fibre cables. Preferably, the element is an optical ribbon cable that comprises a plurality of fibres. The ribbon cable may have any number of fibres provided that it can be installed by blowing, although it preferably comprises not more than 12 fibres and especially from four to eight fibres. The ribbon cable may be in the form described in US Patent No: 4,930,860 in which the individual fibres forming the cable arejacketed with a jacket to assist their blowing or the fibres may be assembled together to form a ribbon cable and the cable as a whole may be provided with single jacket to assist blowing of the cable.

The jacket that may be provided on the optical fibre element may be formed to any of a number of designs in order to assist blowing of the element. Ideally it should have a relatively low density and have an irregular surface an d may also include a lubricant and/or antistatic agent in order to prevent sticking of the element to the duct walls. One jacket that may be employed is described in European Patent Application No: 345,968 and includes a filler, e.g. particulate PTFE, or microspheres in a radiation cured polymer.

As will be appreciated, the lateral dimensions ofthe optical connector will be considerably greater than the lateral dimensions of the optical fibre element, and will normally be almost as large as the bore ofthe duct in order to include elements for ensuring correct alignment and mechanical coupling with a corresponding connectors We have found that even when the lateral dimensions of the connector are almost the same as the bore of the duct, the terminated element may still be satisfactorily blown into the duct. In particular, we have found that such connectors are able to negotiate bends in the duct during blowing-in without becoming jammed therein. At the same time, even when the connector is nearly the same size as the duct bore, it allows sufficient flow of the gaseous medium past it to cause the optical fibre element to be entrained by the medium and for the motive force on the fibre element to be distributed over the length of the element as indicated in European Application No: 108,590. Although in principle the connector may have any transverse shape, it may for this reason be preferred for it to have a transverse cross-sectional shape that differs from that of the bore, for example to have a rectangular shape. The maximum lateral dimension of the connector (i.e. diagonal dimension in the case of a connector having a rectangular cross-section) is preferably not more than 90% of the bore (the internal diameter) of the duct.

It will normally have a maximum lateral dimension of at least 50% of the bore of the duct, and especially at least 75% of the bore.

The invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a schematic side plan and front end plan view of one form of electrical connector and optical fibre ribbon in a duct, and Figure 2 & 3 are schematic views of further forms of connector for use in the present invention.

Referring to the accompanying drawings, figure 1 shows in plan view and in end view a length of optical fibre ribbon 1 which has four optical fibres 1' and is terminated with a rectangular optical connector 2 and is being blown along a duct 3 by a flow of dry air or nitrogen. The connector 2 is of the same general shape as that of the optical connectors shown in European Patent Application No: 505,197 but the width of the connector may be reduced in order to assist insertion into, and passage along, the duct 3. The connector has a clip 2' for retaining it in a mass termination connector and a pair of pins or cylindircal recesses 4 for ensuring correct alignment with a corresponding connector. The connector has a width of 4.2mm and a thickness of 3mm so that its maximum transverse dimension is 5.2mm. The duct 3 has a bore of 6.0mm so that the maximum transverse dimension is 86% of the bore. The optical ribbon has ajacket formed from a radiation polymerised urethane/acrylate polymer containing PTFE particles as described in European Patent application No: 345,968 to assist blowing in. The terminated ribbon may satisfactorily be blown into the duct at a rate of 50 to 100 metres per minute. In contrast, if an optical element is similarly terminated but has no such jacket, the speed at which it can be blown in is reduced to about 10% of that ofthejacketed ribbon, indicating that the presence of the connector does not affect the mechanism by which the ribbon is blown to any significant extent. Also, the ability of the ribbon to twist about its longitudinal axis will assist the ribbon and the connector being blown past bends occurring in different orthogonal directions in the duct.

Figures 2 and 3 show alternative schematic designs of connector that may be employed in the method according to the invention. In these connectors guide pins 4 and associated recesses for receiving pins 4 are not in the same plane as the fibres 1' of the ribbon 1 but have been placed on either side ofthe major surfaces ofthe ribbon, thereby allowing the width of the connector to be reduced at the expense of its thickness and enabling the connector to have an elliptical or circular cross-section.

Claims

1. A method of providing a building or other location with an optical fibre element, in which a leading end of the optical fibre element is introduced into the bore of a previously installed duct and the element is propelled along the duct by fluid drag of a gaseous medium, wherein the element is terminated with an optical connector at at least its leading end before it is introduced into the duct and the optical connector is propelled along the duct together with the element.

2. A method as claimed in claim 1, wherein the optical fibre element is terminated with an optical connector at each end thereof before it is introduced into the duct.

3. A method as claimed in claim 1 or claim 2, wherein the or each optical connector is provided on the optical fibre element in a production facility before the element is transported to the building or other location.

4. A method as claimed in any one of claims 1 to 3, wherein the optical fibre element is an optical ribbon cable that comprises a plurality of optical fibres.

5. A method as claimed in any one of claims 1 to 4, wherein the optical connector at the leading end of the element has a maximum lateral dimension that is not more than 90% of the bore of the duct.

6. A method as claimed in any one of claims 1 to 5, wherein the optical connector at the leading end of the element has a maximum lateral dimension that is at least 50% of the bore of the duct.

7. A method as claimed in any one of claims 1 to 6, wherein the optical fibre element is provided with ajacket containing a filler or microspheres and which has an irregular surface for assisting propulsion of the element.