Fibre storage

Abstract: An optical fibre storage system comprising a container in which turns of fibre (4) are wound in a substantially helical formation, the diameter of the turns and container being such the turns of fibre are maintained in position by their natural resilience pressing them outwardly against the inside of the container (5). The inside of the container may be coated to aid location of the turns. In another embodiment an inflatable member located within the turns is inflated to press against them to aid positional stability. A source of gas may be connected to the container to enable propulsion of the fibre out of the container in a duct, or the container itself may be pressurised.

Description: This invention relates to storage of optical fibre and especially to storage of delicate fibres without extensive external sheathing. European patent 108590 describes a technique known as fibre blowing in which an optical fibre package is advanced through a duct by viscous drag of a fluid, usually gaseous, medium. The fibre package may be fed into the duct by wheels or other means from a reel or freely paid out from a coil. The fibre package installed by the fibre blowing technique may have a low density foam coating that provides a high surface area to weight ratio for the package, but in some instances it is possible to blow optical fibres that do not have additional foam or other sheathing, for example a 'bare' fibre consisting of a core, cladding and primary acrylic coatings may be installed by fibre blowing. Such bare fibres are delicate and therefore mechanical feeding techniques such as wheels to pull the fibre off a reel are preferably avoided. Also due to the fine nature of such fibres, loose laid coils tend to become entangled by virtue of adjacent turns sticking to each other so that rapid paying out from a loose coil is not satisfactory. The present invention is directed towards a storage technique for bare fibre that overcomes or alleviates the above problems. In Belgian patent 660121, published in 1965, there is described a bobbin system for the storage of metallic wires. The wire is wound within the bobbin, the springiness of the wire holding it against the inner surface of the bobbin. The wire is stored with one turn of twist for each loop of wire, which means that the wire can be unwound from the bobbin without rotation of the bobbin and without introducing twist into the unwound wire. In Japanese patent application 63 -199307 there is described a technique for installing optical fibres into drummed tubes. The fibre is housed in a closed container which is sealed to the tube into which the fibre is to be introduced. A supply of pressurised gas is applied to the container and hence to the tube . The fibre is thereby blown into the tube. The fibre is shown as simply coiled on the bottom of the container. The drummed tubes are preferabbly vibrated to facilitate the introduction of the fibre. There is no suggestion to use the technique with pre-installed ducts. The present invention provides a method of installing an optical fibre member into a previously installed duct, the method comprising the steps of : connecting a closed, gas-tight container of optical fibre member to the previously-installed duct, the container having turns of optical fibre member wound within it in a substantially helical formation, the turns and the container having a diameter such that turns of the fibre member are maintained in position by their natural resilience pressing them outwardly against the inside of the container; providing a supply of propellant gas at a pressure greater than atmospheric; initiating advance of the optical fibre member within the duct by viscous drag effects caused by the flow of propellant gas over the fibre member ; and continuing the advancement of the optical fibre member within the duct by means of viscous drag acting on the increasing length of the optical fibre member within the duct. The invention also provides a container of bare optical fibre suitable for use in the method according to the first aspect, the container being substantially gas-tight and having turns of bare optical fibre wound within it in a substantially helical formation, the diameters of the turns and the container being such that the turns of optical fibre are maintained in position by their natural resilience pressing them outwardly against the inside of the container. The invention is now described by way of example with reference to the accompanying drawings in which: Figure 1 is a cross section through a typical bare fibre; Figure 2 is a schematic diagram of an apparatus for coiling fibre within a container in accordance with the invention, and Figure 2a is an embodiment of a container having wound fibre within it; Figure 3 is a plan view of the apparatus of Figure 2; Figures 4 and 5 are schematic diagrams of a preferred embodiment of the invention for automatic release of fibre, shown respectively with fibre release inhibited and permitted; Figures 6a, 6b and 6c and Figures 7a, 7b and 7c are further embodiments of the inhibiting/release mechanism respectively permitting and inhibiting fibre propulsion; Figure 8 is a further embodiment of fibre release inhibitor; Figure 9 shows details of friction enhancing means; and Figure 10 is a schematic diagram of a fibre blowing system according to the invention. In Figure 1 a typical bare optical fibre 4 is shown which comprises a core 41 and cladding 42 (both of which are glass in normal optical fibres), which may together comprise a single or multi-mode fibre, and an outer acrylic coating 43 which may be coloured for identification purposes. This structure is typical of present bare optical fibres, but the present invention would also be applicable to other structures. The fibre, generally referenced 4, is stored in accordance with the present invention in a container 5 after production until such time as it is desired to use the fibre, and may be installed in the container directly from the fibre production line or from an intermediate storage stage. The container is of generally cylindrical shape having a diameter of 9 to 15cm for fibre of diameter .25mm, and the fibre is introduced into the container 5 by the apparatus shown in Figure 2. The apparatus comprises a tube 6 which has an upright (as viewed) portion 7 and a downwardly curved portion 8 which together define a J shape, and the end of the curved portion 8 has an additional curved lip 9 which extends laterally out of the plane of the J so that the opening of the lip is directed obliquely towards the side of the container 5, as illustrated in plan in Figure 3. Fibre 4 is threaded through the tube 6 and advanced therethrough by a flow of compressed gas introduced to the end of the upright portion 7 of the tube in the manner described in our European published patent applications 287225 and 345043, for example via a branch 10. A seal 11 prevents the gas from escaping in the direction of the incoming fibre. Other arrangements for fibre feed and gas entry may be employed. As the fibre 4 is advanced through the tube 6 by the gas flow the fibre passing out of the end of the lip 9 is directed on to the side wall of the container, and simultaneously the tube 6 is rotated about an axis passing along the upright portion 7 in the direction of arrow 12 so that the fibre is progressively directed in an annulus around the inside of the container 5. After each turn the tube 6 is moved incrementally upwardly so that the next turn lies adjacent the previous turn in a closely wound helix; instead of a stepwise movement the tube may be moved upwardly continuously so that the lip 9 moves on a helical path. Once the lip 9 reaches the top of the container 5 (or as close to the top as it is desired to wind fibre) the upward movement is reversed. On the downward travel the tube may be moved at the same rate as it is advanced upwardly so that a full sequence of turns of fibre is laid over the turns laid on the upward travel, but it is found preferably to move the tube downwardly more rapidly so that only one, a few or even a part turn is deposited on the inside of the container on the downward travel and then the upward travel is resumed as previously. The reason for this preference is that when the fibre 4 is uncoiled from the container 5 it is removed in the reverse direction so that the fibre turns are removed from the uppermost end of the turn sequence that is laid during upward travel of the ,tube and therefore it does not have to cross over the next turn. Conversely the fibre unwinds from the bottom of a sequence of turns that is laid during downward travel and thus there is a greater risk of interference with the adjacent turns. Instead of moving the J tube up and down it is possible to move the container. The speed with which the tube 6 is rotated and advanced vertically and the rate at which the fibre 4 is advanced through the tube 6 are controlled so that for each 360 o rotation of the tube a fibre length slightly exceeding that required to lay around the inner circumference of the container is advanced into the container. This both allows for the slightly helical path and enables the fibre to be pressed outwardly by virtue of its own natural resilience. In order to achieve this the fibre needs to be ejected from the end of the J tube to hit the side of the container. Containers suitable for use in the present invention include bottles of the type employed for bottling beers and carbonated soft-drinks. Such bottles are generally formed of oriented polyethylene terephthalate (PET) and have burst pressures of about 150psi (10 Bar) or more, despite their very thin walls. Safe working pressures as high as 4 Bar can thus be used, although in general lower pressures will be used. Alternative sources of the same bottle type may well enable operating pressures as high as 5 to 6 Bar to be used, despite the very low cost of the bottles. In a prototype experiment it was discovered that subsequent layers of turns of fibre had less tendency to drop than the first layer of turns, most probably due to the slightly greater friction between adjacent layers than between the first fibre layer and the smooth surface of the container. It is therefore preferable to have an inner surface on the container that provides some frictional resistance. This may be achieved by having a roughened surface or by a coating, especially a fibrous coating enabling the fibre 4 to stick between hairs that whilst aiding adherence of the turns of fibre are sufficiently weak to provide insignificant resistance to unwinding, thereby minimising risk of damage to the fibre. One means that we have found to be particularly useful in helping to prevent the coiled fibre from dropping to the bottom of the bottle is to provide pins or fingers, preferably resilient, on the interior surface of the bottle. Suitable pins or fingers may conveniently be provided by means of an insert or inserts, for example as shown in Figure 9. Four separate strips 50 of resilient material, in this case polyurethane rubber extend up the inside of the bottle. Each strip is provided, on the surface which faces inwardly of the bottle wall, with a plurality of thin flexible fingers 51, individual fingers, ribs or multiples of fingers or ribs are provided at intervals, preferably regularly spaced up the height of the bottle. Typically the installed vertical distance between adjacent projections or sets of projections is of the order of 10mm. For ease of manufacture, a single sheet of material provided with projections may be installed in a rolled form via the neck or opening of the bottle, the sheet unfurling once inside the bottle to provide the desired array of projections on the bottle's inside wall. Preferably such a sheet is fixed in place by means of an adhesive. Where several separate components are used spaced around the interior periphery of the bottle to provide the (partially) supporting pins, the components may be disposed vertically in the bottle - that is disposed parallel to the longitudinal axis of the bottle, or may be tilted or disposed in a helical path. If an inflatable balloon or membrane is to be used in the bottle, the distal ends of the fingers or ribs may be enlarged to reduce the risk of the balloon or membrane being perforated thereby. Typically the fingers will be 0.5 to 2mm in diameter. Typically the fingers or ribs will be 5 to 15mm in length, preferably about 10mm. It will be noted that each turn of fibre laid as described above has 360 degrees of stored torsion, and therefore when the fibre is pulled out from the turn this torsion is removed. Conveniently the container may be pressurised and provided with a fibre release and inhibitor assembly, generally referenced 15, shown in Figures 4 to 8. The container, after installation of turns of fibre as described above, is pressurised, sealed and maintained under pressure. When release of fibre is required a valve is opened and the fibre is progressively blown out of the container by release of the pressure until a sufficient length of fibre has been released whereupon the valve is closed and the release of pressure and fibre is inhibited. A simple valve that presses on to the fibre would cause damage, and likewise a sudden halt of the fibre may cause damage. The release/inhibitor mechanism therefore includes a brake. The release and inhibitor assembly comprises a passageway extending from the container and through which the fibre is threaded. This passageway divides into a double passageway with a dividing wall 16. As shown in Figures 4 and 5 the fibre is diverted into one of the passageways, referenced 17, and the other passageway 18 is provided with the valve 13. A separate port 22 for pressurising the container may be provided or the container may be pressurised through the assembly 15 with the valve 13 open, and then the valve 13 closed before the pressurising source is disconnected. During the pressurising process and for transportation the free end of the fibre 4 may be taped or clipped to the outermost end of the braking section to prevent unthreading. The end portion would generally be cleaved prior to connection after installation along a duct and so any damage caused due to securing or exposure is eliminated. An installation duct 19 is connected to the outermost end of the assembly 15, and after connection in order to commence installation the valve, referenced 13, is opened to the configuration shown in Figure 4. Pressurised gas then commences escaping from the container along the passageways 17 and 18 and into the duct 19 and propels the fibre package 4 along the duct. Various techniques may be employed to aid insertion of the first part of the fibre package into the duct 19 including manual insertion of a length of the fibre released from the container prior to connection of the duct, or venting the duct (or a connection tube) a short distance away from the container in order to create a high local flow. When it is desired to cease the installation process the valve 13 is closed. At this point there is still a passageway for propellant along the passageway 17, although this passageway in fact should be small and insufficient to provide a substantive alternative route for the air. A part of the wall between the passageways 17 and 18 is made of a membrane 20 of flexible, elastic material such as a soft grade of rubber and as pressure builds up in the now closed off passageway 18 the membrane 20 balloons outwardly into the passageway 17 and commences pressing against the fibre package 4 and the walls of passageway 17. The sizes of the membrane and passageways are such that at the operating pressures of the container the membrane 20 is able to completely close off the passageway 17. It should be noted that the passageway 17 is drawn in enlarged scale for clarity: in fact it should only be sufficiently wide for the passage of fibre and thus very little air flow to enable closure by the flexible membrane. Passage 18 is much larger for a high flow, with little pressure differential. Since the expansion of the membrane into the passageway 17 takes a finite time there is a period after closure of the valve 13 when the membrane bears against the fibre package and wall of the passageway 17 but not sufficiently firmly to stop all flow through the passageways. during this period the fibre package 13 is retarded both by friction and reduced flow, which has the advantage of preventing sudden tensioning of the fibre package when it is finally stopped. In a similar way successively opening and closing of valve 13 may be used to slow down installation when the pressure in the container is comparatively high (for example during the initial stages of discharge) without wasting propellant. After closure of valve 13 installation can be recommenced by opening the valve. Alternatively the installed length of fibre may be cut free and the remaining unused fibre used in another location. The structure of the passageways as shown in Figure 4 and 5 may comprise two side by side tubes with a common wall portion, the common wall portion having three ports, the end ports for diversion of the fibre and the central port for the provision of the flexible membrane. The fibre diversion tube (passageway 17) may be made smaller than passageway 18. An equivalent arrangement may be made with a partition down a single tube (as shown in Figure 6a) by a branched structure (Figure 6b) or a diversion path for the propellant (Figure 6c) leaving a straight through path for the fibre package. This latter arrangement with a straight fibre path is particularly preferable. In each case the general principle is the same, two passageways with communicating entry and exit ports and an intermediate port blocked by a membrane. The fibre package passes along one route and the alternative route can be blocked by a valve. Figures 7a, b and c show the same embodiments with the fibre braked. Another alternative to the embodiments shown in Figures 4 to 7 is to eliminate the port with the flexible membrane and locate a pressure sensitive seal around the entry port to the fibre passageway 17. Under flow conditions the seal 21 (shown in Figure 8) lightly rests against the fibre package, but as soon as pressure builds up above a predetermined level in the propellant passageway 18 the seal is urged tightly around the fibre preventing further movement or escape of propellant into passageway 18. With this latter embodiment the restriction caused by the seal 21 means that the main flow of propellant is along the passageway 18 and the section of fibre within the fibre passageway 17 is not subjected to viscous drag. However the length of fibre within the passageway 17 is not sufficient to significantly influence the installation. In a further embodiment, instead of relying solely upon pressure within the container to propel the fibre along duct 19, the container is fed with air (or other gas) through port 22 from a suitable source (not shown) and at sufficient pressure to advance the fibre 4 along the duct. The container remains pressurised at a substantially constant pressure during the fibre withdrawal procedure, the flow for the propulsion being provided by the source. Once sufficient installation along duct 19 has been achieved the source is removed and the pressure in the container permitted to fall to atmospheric pressure. With this arrangement it is not necessary to have a fibre brake because removal of the source inhibits further fibre advancement and it is not necessary to seal the container to retain propellant pressure. In a further modification of the invention shown in Figure 2a the container 5 is provided with an inflatable membrane or balloon 24. Air is introduced to inflate the balloon 24 via a valve 23 so that is presses against coils of fibre 4 wound in the container as previously described. This arrangement is particularly useful for aiding storage, especially for example for long term storage, or when the fibre coils are many layers deep, when the wound coils may become liable to mispositioning due to the container being knocked or roughly handled. To release the fibre it is possible either to deflate the balloon or membrane or, more preferably, by the pressure in the balloon or membrane being such that the pressure to which the interior of the container is raised in order to blow the fibre along duct 19 is sufficient to partially collapse the balloon or membrane out of holding contact with the turns. It will be realised that at least some of the balloon or membrane could remain gently touching the fibre, but insufficiently to cause significant retardation. It is also envisaged that in a situation where a fibre brake is not provided, such as when the propellant gas comes from an external source rather than an internal source, adjustment of pressure within the container and/or within the balloon or membrane will also provide a means to control fibre advancement by virtue of greater or lesser contact pressure between the turns of fibre and the balloon or membrane. Figure 10 shows a fibre blowing system which uses containerised fibre according to the present invention. The system facilitates easy and efficient installation of optical fibre, in particular primary coated fibre either one fibre at a time or several fibres at a time. The system uses only a minimal amount of air for the duct size and blowing rate used, because during fibre blowing all the compressed air which is supplied to the system is fed into the pre-installed duct 100. The operation of the system is as follows. If the bottles of fibre which are to be used are substantially unpressurised, that is they are nominally at atmospheric pressure, the fibre from each bottle 99 is manually or otherwise fed through a respective feed tube 98, through the tapered manifold 97, through the blowing head 96 and into the mouth of the pre-installed duct 100. Normally it should not be necessary to introduce the fibre(s) more than 1 or 2 metres into the pre-installed duct before blowing commences. Where the fibre blowing system provides only low friction against the passage of the fibre(s), less than 1 metre of fibre may be sufficient to enable quick initiation of blowing. This operation is facilitated if the one or more of the blowing head, the tapered manifold and the feed tubes is or are split in a suitable manner. After feeding the fibre through the blowing apparatus and sealing any split portions thereof, exhaust valve 95 is closed (if previously open) and inlet valve 94 opened. Low pressure compressed air, typically at 60psi (4.5 Bar) or less, for example 3-4 Bar, is fed in, pressurising the bottles 99 and the blowing apparatus. Continued supply of compressed air causes air to vent through the duct 100. Depending on how much fibre has already been fed into duct 100, care should be taken during the initial pressurisation of the system to avoid blowing the fibre back towards the bottles. Use of a low pressure, for example 1 Bar or 1 to 2 Bar, which is gradually increased, is beneficial. Once the system starts to be pressurised, air starts to escape via the pre-installed duct 100. The effect of this air flow is to cause the fibre or fibres to start advancing further into the pre-installed duct 100 under the influence of distributed viscous drag forces. As the length of fibre in the pre-installed duct grows, so the strength of the viscous drag force increases. At the initiation of the fibre blowing process it may be necessary to pulse the air supply fairly rapidly between 0.3 and 1 second between pulses, possibly by providing short pulses (less than 1 second duration) of higher pressure air, in order to initiate fibre advancement. Blowing pressures up to 150psi (10 Bar) may be used, depending upon the burst strength of the bottles 99 and the integrity of the system. Typically, however, pressures in the range 40 to 100psi (3 to 7 Bar) will be used, for example in the range 40 to 60psi (3 to 4 Bar). When it is desired to stop or to interrupt blowing, the air inlet valve 94 is closed. Bottles of the type used for carbonated soft drinks, such as those made of PET, typically have burst pressures of 10 Bar, so can safely be operated at 3 to 4 Bar. If pressurised bottles of fibre are available, the pressurised gas inside the bottles may be used in the initial fibre feeding stage. Valves 95 and 94 are closed, and clamp 93 is opened. The bottles are sealed to their respective feed tubes after the introduction of the fibre ends into the tubes. The valves on the bottles are then opened to blow the fibres through the feed tubes, tapered manifold and blowing head and into the duct 100. Blowing then proceeds as before, with compressed air fed via inlet valve 94. When it is desired to stop or interrupt fibre blowing, clamping means 93 which comprises a portion of soft resilient tubing, typically of silicone rubber, through which the fibres pass, and an external clamp arrangement, is closed non-abruptly. If fibre blowing is to be terminated, the valves on the bottles are then closed and the exhaust valve 95 opened. When transparent bottles having fibre support means such as those shown in Figure 9 are used, it is advantageous when loading the bottles to coil the fibre so that each level of supports carries a predetermined length of fibre, for example 100, 200 or 250 metres. The fibre will also normally be wound so that the top coil is fed out first, the next lower coil next and so on down to the bottom of the bottle. With such an arrangement it then becomes easy for the operator of the blowing equipment to monitor how much fibre has been fed out. Where a pre-installed duct is intended only ever to cary one or two fibres or fibre bundles, the internal bore of the duct can be as small as 2mm across. More usually a bore 3.5mm across, normally 3.5mm diameter, is suitable as it offers the possibility of many fibres or fibre bundles being installed, either simultaneously or sequentially. Fibres or fibre bundles may of course be installed many months or years after the duct is installed in a building. The present invention in all its aspects is particularly suitable for use in the installation of optical fibres in buildings or in 'campus' type applications. The low cost of the preferred containers for the fibres, and the simplicity, efficiency and quickness of the blowing system all contribute to making the system very attractive for in-building use. While the present invention has been particularly described with reference to 'bare optical fibre', such as that shown in Figure 1, it is similarly applicable to other fibre packages provided that they are reasonably set resistant. Thicker fibre members, such as those provided with additional resin coatings and those comprising more than 1 fibre, will in general require the use of larger diameter containers. Because there is, during fibre blowing, no flow of air through the tapered manifold, changes of section, which might otherwise give rise to venturi effects or pressure gradients, are not generally significant. It is of course important to minimise the friction between the running fibre and the blowing apparatus, including the manifold, but the fact that a venturi effect is not required for successful blowing generally eases the design constraints so that friction effects can be tackled practically independent of other considerations. For the avoidance of doubt, it is emphasised that the blowing system described with reference to Figure 10 does not need or rely on any venturi or other pressure drop effects in the blowing apparatus, but that the presence of any such effects, should they arise, will not in general detract from the utility of the system. The fact that no 'venting' - that is the passage of propellant gas to waste other than through the pre-installed duct, is needed during the fibre blowing process, means that the process can use very low pressures, for example 1-2 Bar or 3-4 Bar, be very quiet and efficient.

Claims: A method of installing an optical fibre member (4) into a previously-installed duct (19), the method comprising the steps of: connecting a closed, gas-tight container (1) of optical fibre member (4) to the previously-installed duct (19), the container (1) having turns of optical fibre member wound within it in a substantially helical formation , the diameters of the turns and the container being such that the turns of the fibre member are maintained in position by their natural resilience pressing them outwardly against the inside of the container; providing a supply of propellant gas at a pressure greater than atmospheric; initiating advance of the optical fibre member within the duct by viscous drag effects caused by the flow of propellant gas over the fibre member ; and continuing the advancement of the optical fibre member within the duct by means of viscous drag acting on the increasing length of the optical fibre member within the duct. A method as claimed in claim 1, wherein pressurised gas is fed in at a point (22) between the main volume of the container and the duct (19). A method as claimed in claim 1 , wherein the container is pressurised and is not connected to a further supply of compressed gas. A method as claimed in any one of the preceding claims wherein the fibre member (4) comprises not more than one optical fibre. A container (1) of bare optical fibre (4) suitable for use in the method of any one of claims 1 to 4, the container (1) being substantially gas-tight and having turns of bare optical fibre (4) wound within it in a substantially helical formation, the diameters of the turns and the container being such that the turns of optical fibre are maintained in position by their natural resilience pressing them outwardly against the inside of the container. A container as claimed in claim 5, wherein the inside wall of the container has a fibrous coating. A container as claimed in claim 5, wherein means (50,51) are provided within the container , and adjacent to the wall or walls thereof , to provide additional support at a plurality of points throughout the height of the container. A container as claimed in claim 7, wherein said means comprise a plurality of resilient elongate members (51). A container as claimed in any one of claims 5 to 8, in which an inflatable member is located inside the turns of fibre such that upon inflation it presses outwardly to support the turns. A container as claimed in any one of claims 5 to 9, wherein the container is pressurised. A container as claimed in any one of claims 5 to 10, wherein the optical fibre consists of a core , a cladding and an outer acrylic coating. A container as claimed in any one of claims 5 to 11, wherein the container is formed of plastics material. A container as claimed in claim 12, wherein the material is polyethylene terephthalate. A container as claimed in any one of claims 5 to 13, wherein the container has a burst pressure of at least 10 bar. A container as claimed in any one of claims 5 to 14, when connected to a duct.

Inventors: JENKINS PETER DAVID, JENKINS, PETER DAVID
Applicants: BRITISH TELECOMM, BRITISH TELECOMMUNICATIONS PUBLIC LIMITED COMPANY
Application year: 1990
Main classification: G02B6
IPC codes: G02B6, B65H49, B65H54