SPLICELESS ACCESS ENCLOSURES FOR FIBRE OPTIC CABLES

This invention relates to access enclosures for fibre optic cables and methods of forming the enclosures.

In fibre optic cable networks, it is customary to provide at spaced locations on the network, access enclosures which enable connections or splices to be made to "lead-in" cables which extend to customer locations. Normally, the access enclosures have provision for storage of slack lengths of optic fibre which can be temporarily withdrawn from the enclosure housing to enable fibre splicing equipment to be used to splice the slack lengths of fibre to fibres in the lead-in cables.

Typically, an access enclosure includes a housing within which is mounted a support structure which has a plurality of trays thereon. The slack lengths of fibres are wound onto the trays so that the slack lengths can be selectively removed and rewound thereon. The housing can be domed shape in' which case the optic cables pass through cable ports in an end cap of the housing. Alternatively, an in-line enclosure can be provided in which case the housing is cylindrical in shape and the cables pass through cable ports in respective end caps.

US Patent Nos. 6,434,313; 6,359,228; 6,496,640; and 6,944,389 disclose various aspects of access enclosures and the content of those specifications is incorporated herein by cross-reference.

In some fibre optic network architectures, a distribution cable is provided with distribution splice enclosures located at various locations on the network. Typically the distribution cable forms a ring. Tie cables can extend from the distribution splice enclosures to enable other optic fibre connections to be made. The tie cables typically extend to access enclosures or access splice enclosures and the present invention is concerned with improvements in the way in which the access splice enclosures are provided.

Typically, the tie cable for an access splice enclosure may have say 144 optic fibres located within a sheath. Further, groups of say 12 optic fibres are located within tubes within the sheath. When the access enclosure is being installed, the technician removes an end part of the sheath of the tie cable and end parts of the tubes so as to expose lengths of optic fibre, say about 2 to 3 metres in length. The technician feeds the sheathed end of the cable through a cable port in an end cap of the housing and then splices together typically by fusion, ends of selected pairs of fibres. The joined fibres are wound onto storage trays located within the housing. Normally the technician winds an unspliced portion of the joint fibres on the trays in a bank on one side of the enclosure, the remainder of the fibre which includes splice is then wound on a tray on the opposite bank. This provides for compact and neat storage of the slack lengths of optic fibres within the access enclosure. Whilst this arrangement is reasonably satisfactory, it does have drawbacks. First, each of the splices needs to be carried out in the field which is time consuming. Second, each of the splices introduces some loss into the connection.

US Patent No. 6,504,987 discloses a fibre organiser which has a plurality of storage trays for storing slack lengths of fibre thereon. The trays are hingedly connected to a support structure. Some of the trays- are arranged to store uncut fibres. The arrangement, however, is such that the fibres enter the trays from the rear parts of them, that is to say generally perpendicularly to the hinge axes. Accordingly, when the trays are rotated, some stress can be caused to the fibres. The specification discloses the concept of having uncut optic fibres on the trays but the arrangement is such that the uncut fibres would need to be confined to a single bank of trays. This is because the arrangement is such that the fibres would need to cross over to the other bank of trays through the centre of the support structure, that is to say generally transversely to the pivot axis of the trays. This is not possible with uncut fibres.. Consequently, the uncut fibres would need to be confined to separate banks of trays.

An object of the present invention is to provide a novel access enclosure and method of forming same which can have uncut fibres which extend between the trays in both banks of trays.

According to the present invention there is provided a method of holding uncut optic fibres in an access enclosure having a support structure, a plurality of first storage trays pivotally connected to the support structure to form a first bank of support trays on one side of the support structure and a plurality of second storage trays pivotally connected to the support structure to form a second bank of support trays on the opposite side of the support structure, the method including the steps of: separating a loop of uncut optic fibre from a fibre optic cable; storing a first portion of the loop on one of said first storage trays; routing a second portion of the loop about the support structure to the opposite side of the support structure; and storing a third portion of the loop on one of said second storage trays.

The invention also provides an access enclosure for holding at least one loop of uncut optic fibre, the access enclosure including: a support structure; a plurality of first storage trays pivotally connected to the support structure to form a first bank of support trays on one side of the support structure; a plurality of second storage trays pivotally connected to the support structure to form a second bank of support trays on the opposite side of the support structure; a first portion of the loop being stored on one of said first storage trays; guide means for guiding a second portion of the loop about the support structure to the opposite side of the support structure; and a third portion of the loop being stored on one of said second storage trays.

It will be appreciated that in the method of the invention, loops or slack lengths of fibres located on the trays are unbroken (i.e. are spliceless) and hence losses associated with splices are avoided. Further, the entire assembly process can be carried out in a laboratory or factory whereby the assembly process can be effected under ideal conditions. The assembly is therefore more reliable, less expensive to produce and less lossy. The access enclosure assembly with parts of the cable extending therefrom can be supplied to a customer as a completed unit ready for connection to a distribution splice enclosure, which

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gives further cost savings.

Frequently the fibres are located in buffer tubes which extend longitudinally within the sheath of the cable. In the method and enclosure assembly of the invention, the buffer tubing can also be removed so that the slack lengths of fibre are directly wound onto the trays. Alternatively, the buffer tubing can remain intact and the buffer tubes with the optic fibres therein are wound onto the trays.

The invention will now be further described with reference to the accompanying drawings, in which:

FIGURE 1 is a schematic diagram showing part of a known fibre optic network;

FIGURE 2 is a schematic diagram showing the internal structure of a known access splice enclosure;

FIGURE 3 shows schematically a typical layout for slack fibres in the known access splice enclosure;

FIGURE 4 is a fragmentary view partly in section of a typical fibre optic cable;

FIGURE 5 is a schematic view showing an access splice enclosure of the invention;

FIGURE 6 is a schematic view showing the internal structure of the access splice enclosure of the invention; FIGURE 7 is a diagrammatic view showing the typical path of a fibre within the access splice enclosure;

FIGURES 8, 9 and 10 diagrammatically illustrate some steps in the method of the invention;

FIGURE 11 is a fragmentary view of part of the support structure showing the path of a fibre;

FIGURE 12 shows an end cap of the enclosure;

FIGURE 13 is a schematic plan view of one of the trays of the enclosure;

FIGURE 14 is a fragmentary cross-sectional view along the line 14-14;

FIGURE 15 is a plan view showing the path of a fibre wound on a tray; FIGURE 16 shows the path of a fibre which has been spliced;

FIGURE 17 is a fragmentary view showing more details of the side of the support

structure and trays; and

FIGURE 18 is a frontal view which shows in more detail the lower part of the support structure.

Figure 1 diagrammatically illustrates part of a fibre optic network 2. The network 2 includes a distribution cable 4 which typically may have 312 optic fibres such as single mode optic fibres therein. The network includes a number of distribution splice enclosures 6 (one of which is shown in Figure 1) spaced along the cable 4 which is normally configured as a ring. In this architecture, the network includes access splice enclosures 8, one of which is shown in Figure 1. The access splice enclosures 8 are connected to the distribution splice enclosures 6 by means of tie cables 10. The enclosures 8 enable connections to be made to lead-in cables 12, one of which is shown in Figure 1. The number of lead-in cables 12 can vary in accordance with the number of customers which need to be serviced and their communication demands. In the illustrated arrangement each of the tie cables 10 have 144 optic fibres therein.

The access splice enclosure 8 can be of known type, such as a Corning UCNCP 9-20 MAX. Enclosures of this type are well known and need not be described in detail. As diagrammatically shown in Figures 2, 11 and 12, the enclosure 8 includes an end cap 13, support structure 16 and a domed housing 17 having an open end 19. The end cap 13 is, in use, clamped into the open end 19 of the housing and is retained therein by a clamping ring (not shown). The enclosure 8 includes a first bank 18 of trays 22 on one side of the support structure 16 and a second bank 20 of trays 23 on the other side of the support structure 16. In the illustrated arrangement there are twelve trays 22 (Trayl— Trayl 2) in the bank 18 and twelve trays 23 {Tray 13-Tr ay 24) in the bank 20. The trays 22 and 23 are hinged to the support structure 16 and are also selectively removable therefrom.

When the access splice enclosure 8 is being installed, the end of the tie cable 10 is stripped of sheathing by the technician at the installation site and slack lengths of the exposed fibre optic cables are spliced together and wound on the trays 22 and 23, as will be described in more detail below. Figure 4 illustrates a typical structure for the tie cable

10. It includes an outer sheath 24 which encloses a bundle of say twelve buffer tubes 26, within each of which is a group of say twelve optic fibres 28, thus making up the 144 fibres (identified as Fibrel to Fibrel44) in the cable. The optic fibres 28 can be single mode optic fibres, each of which has a core, cladding and coating, in the usual way. The technician usually strips say two to three metres of the sheath 24 from the end of the tie cable 10 so as to expose the buffer tubes 26. The buffer tubes 26 are then removed except for terminal tube portions 29 which would normally be about 200mm in length. The coated optic fibres 28 project from the exposed terminal tube portions 29 of the buffer tubes 26. The technician then makes a splice between the free ends of pairs of the fibres 28. In the arrangement shown in Figure 2, the fibres designated Fibrel to Fibreό are spliced to the fibres designated Fibre73 to Fibre78; the fibres designated Fibre7 to Fibrel 2 are spliced to the fibres designated Fibre79 to Fibre84; and so on until the fibres designated Fibre67 to Fibre72 are spliced to the fibres designated Fibrel 39 to Fibrel 44. Normally a heat shrinkable sleeve (not shown) is applied to the optic fibres for protecting the splices 30.

Figure 3 diagrammatically shows Fibrel connected by means of a splice 30 to the end of Fibre73. About three or four loops of Fibrel are wound about the lowermost tray 22 (Trayl) and then joined Fibre73 is crossed over the support structure 16 to the adjacent lowermost tray 23 (Trayl 3) and about three or four loops of the Fibre73 are wound onto lowermost tray 23 (Tray 13). Total length of Fibrel and Fibre73 wound on Trayl and Trayl 3 is about 4 to 5 metres and this provides a sufficient slack length of fibre for future splicing which may be necessary. After splicing and winding Fibrel and Fibre73, the five fibres designated Fibre2 to Fibreό are spliced to the fibres designated Fibre74 to Fibre78 and these are also wound onto the lowermost pair of trays 22 and 23 (Trayl and Trayl 3). This results in unspliced loops of fibres being stored on the trays 23 in the bank 20 and all of the spliced fibres being stored on the trays 22 in bank 18. Each of the trays 22 and 23 is the same and is in the form of an injection moulded generally planar body having a base plate 80 which is formed with an upstanding peripheral flange 82. The tray includes first and second aligned hinges 84 and 86 which cooperate with complementary hinge sockets 88 and 90 which form part of tray retainer structures which in turn form part of the support

structure 16, as shown in Figure 18. The hinges 84, 86 and sockets 88, 90 permit the trays 22 and 23 to pivot about hinge axes 92, one of which is shown in Figure 13. One of the trays 22 from the first bank 18 is shown but the trays 23 in the other bank are identical. The hinges 84 and 86 are in the form of hollow cylindrical bodies, as diagrammatically shown in Figure 14. Each of the hinges includes a slot 94 which permits optic fibres to pass generally concentrically through the hinges, as will be described in more detail below. The sockets have complementary slots (not shown) which are aligned when the trays are rotated upwardly so as to permit lateral entry or exit of fibres from the interior of the hinges. When, however, the trays are rotated downwardly to their assembled positions the slots are no longer aligned and the fibres are captive in the hinges. The tray 22 includes inward guide walls 96 and 98 and central guide walls 100 and 102. The inward guide walls 96 and 98 with the peripheral flange 82 define an outer storage area 104 for the slack optic fibre. An inner storage area 106 is defined between the guide walls 96, 98 and 100, 102. The tray includes projecting fingers 108 which support splices in the optic fibres when they are made to form a connection to a tie end cable. The peripheral flange 82 and the guide walls 96, 98, 100 and 102 are provided with various projecting tabs 110 which serve to retain the fibres on the tray. Because the fibres are located within the first and second hinges 84 and 86, they are generally coaxially oriented with the hinge axis 92 of the tray upon which the fibres are stored. Accordingly, the trays can be rotated without laterally displacing the fibres at the points where they enter and exit the trays.

Figures 5, 6 and 7 illustrate a fibre optic network 40 which is formed using the techniques of the invention. Essentially the same hardware can be used and therefore the same reference numerals have been used to denote parts which are the same as or correspond to those of the earlier network. The access enclosure assembly 41 of the invention has an access splice enclosure 9 and two tie end cables 42 and 44 extending therefrom. In this arrangement, the tie cable is formed from a single length of fibre optic cable which is looped so as to form the two tie end cables 42 and 44. In use the tie end cables 42 and 44 extend from the access splice enclosure 9 to the distribution splice enclosure 6. Assuming the network 40 has the same capacity as the network 2, in which the tie cable 10 has 144 fibres therein, the single tie cable 10 is replaced by two tie end

cables 42 and 44, each having 72 fibres therein (designated Fibre 1 to Fibre72). As will be described in more detail below, a single length of fibre cable is used to form the tie end cables 42 and 44 and, significantly, the optic fibres therein are uncut within the access splice enclosure 9. That is to say, the optic fibres do not include any splices 30 within the splice enclosure 9.

Figure 6 shows schematically the interior of the enclosure 9 of the network 40. The enclosure 9 is the same as the enclosure 8, except that the optic fibres therein are uncut and do not include any splices 30. In this arrangement, the fibres designated Fibre 1 to Fibreό of cable 42 are wound onto the lowermost tray 22 (Trayl) of the bank of trays 18 and are then crossed over so as to then be wound on the lowermost tray 23 (Trayl 3) of the bank 20 where they are designated Fibrel to Fibreό of the tie end cable 44. It is understood, however, that the fibres are unbroken, as diagrammatically illustrated in Figure 7, which shows Fibrel wound on Trayl, then crossing laterally about the support structure 16 so as to become Fibrel wound on Trayl 3. The winding of Fibre2 to Fibreό onto Trayl is continued and these fibres are crossed over to become fibres designated Fibre2 to Fibreό on Trayl 3. The winding of all of the remaining fibres, Fibre? to Fibrel 2 continues, as described above.

Figures 8, 9 and 10 diagrammatically illustrate ringbarking of a length of fibre optic cable 25 so as to form the tie end cables 42 and 44. Initially the cable 25 may be say 30 metres long and the sheath 24 is cut at cut line 50 and then cut again at cut line 52 which is say 5 metres along the cable 25. The sheath 24 between the cut lines 50 and 52 is removed so as to expose the buffer tubes 26, as shown in Figure 9, the cut lines 50 and 52 thereby defining the inner ends of the remaining segments of the sheath 24. Each of the buffer tubes 26 is then cut along cut lines 54 and 56 and the tubes 26 between the cut lines 54 and 56 are removed so as to expose the 72 individual optic fibres 28, as shown in Figure 10. The exposed parts of the buffer tubes 26 thus become tube terminal portions 58 and 60 which are preferably about 200mm in length. In this way, the tie end cables 42 and 44 are defined with the exposed fibres 28 therebetween remaining uncut. Preferably, the tie end cables 42 and 44 are the same length and are about 10 to 20 metres in length. In an

altemative arrangement, the buffer tubes 26, or at least some of them, can remain intact so that the buffer tubes 26 can be wound onto the trays with the optic fibres 28 intact therein.

The exposed fibres 28 can then be formed into a loop so that the adjacent parts of the tie end cables 42 and 44 can be placed through port recesses 62 and 64 formed in an end cap half 66 as shown in Figure 12. The housing includes a second end cap half 68 which is formed with port recesses 70 and 72 which are complementary to the recesses 62 and 64 respectively. The tie end cables 42 and 44 are located so that the ends of the sheath 24 are located adjacent to the inner face of the end cap half 66 whereby the terminal portions 58 and 60 of the tubes will be located within the housing of the enclosure. The two end cap halves 66 and 68 can then be screwed together to form the end cap 13 and the exposed fibres 28 can be wound onto the trays 22 and 23 in substantially the same sequence as described above. It will be appreciated that other forms of end cap can be used such as a heat shrink end cap which is available to be used with the Corning UCNCP 9-20 MAX enclosure.

The manner in which the fibres are wound onto the trays 22 and 23 will now be described in somewhat more detail with reference to Figure 11 and Figures 13 to 18. As diagrammatically illustrated in Figures 11 and 12, the buffer tube terminal portions 58 and 60 emerge from the end cap 13 and are retained' in buffer tube support means 74 and 76 which form part of the support structure 16. The buffer tubes are omitted from Figure 11 for clarity of illustration but are shown in Figure 12. Normally the buffer tube terminal portions 58 and 60 would end at the support means 74 and 76 and thereafter the fibres pass through guide channels 75, 77, 79 and 81 located at either side of the support structure, as best seen in Figures 11 and 17. In the illustrated arrangement, the channels 79 and 81 hold the fibres which pass to the trays in the first bank 18 whereas the guide channels 75 and 77 hold the fibres which pass to the trays in the second bank 20. The guide channels 75, 77, 79 and 81 are defined by various tabs so that the fibres can be wound about the tabs into the guide channels without being cut.

The winding of fibre designated Fibre 1 will now be described in more detail, it being understood that the winding of the other fibres is generally similar. Fibre 1, denoted by the reference numeral 101, is initially routed upwardly in the guide channel 79 and moved up to the point Tray I is hinged to the support structure 16. Trayl is rotated to a position where the slot 94 is exposed and Fibrel is threaded through the hinges 84 and 86 and is then wound in an anti-clockwise direction initially in the outer storage area 104 and then to the inner storage area 106, as diagrammatically illustrated in Figure 15. As best seen in Figure 18, the support structure 16 includes two routing disc formations, 112 and 114 which can be used for changing the direction of the fibres at a large radius. In this arrangement, Fibrel changes direction by curving about the routing, formations 112 and 114 so that it can then pass through a cross-over passage 130, as shown in Figure 17, so that it can then be threaded into the guide channel 75 which is associated with the trays of the second bank 20. The cross-over passage 130 is defined between tabs 132 and 134 and sidewall portions 136 and 138 which form part of the support structure 16. The cross-over passage 130 is open so that the fibres can enter the passage without being cut. A similar cross-over passage (not shown) is located on the other side of the support structure but this is not shown in Figure 17. The fibre can be threaded into the guide channel 75 up to the level of Tray 13 which is on the same level as Trayl. Fibrel then is threaded through the hinges 84 and 86 of the Trayl 3 and is then wound in an anti-clockwise direction in the storage areas 104 and 106. It then travels down the guide channel 77 to the buffer tube terminal portion 58 where it exits. In the illustrated arrangement, fibres are located on corresponding trays in the two banks. This is for ease of identification and location of the fibres. It is, however, possible to locate fibres on different trays in the opposite bank.

It will be appreciated that the method and device of the invention enable a preassembled access enclosure which has unspliced fibres wound on both banks of trays.

For fibres on other trays their winding paths are generally similar except that the fibres extend for greater distances up and down the guide channels 75, 77, 79 and 81 so as to reach the level of the higher trays. Normally all of the fibres cross over the same crossover passage 130 in a bundle, although this is not strictly necessary.

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lt will be appreciated that the path of the fibre is such that it is not subjected to any sharp turning radii nor is it placed under strain when the trays are rotated since the fibres enter and exit both trays through the hinges 84 and 86 since the fibres are generally parallel to the hinge axes 92 and/or are concentric therewith.

Figure 16 diagrammatically illustrates the path of a fibre 105 which has been spliced to a customer fibre (from the lead-in cable 12) by means of a splice 113. As can be seen, the splice 113 is retained between the projecting fingers 108, as seen in Figure 16. •

It will be appreciated that, in accordance with the invention, it is possible to assemble under factory or laboratory conditions, an access enclosure assembly which includes the enclosure 9 and the two tie end cables 42 and 44 extending therefrom. When the access enclosure assembly of the invention is to be deployed, the optic fibres at the free ends of the tie end cables 42 and 44 can be spliced into appropriate fibres of the distribution cable 4 in the enclosure 6. Also, any lead-in cables can be connected as required. This normally would involve selecting a length of a slack fibre stored on one of the trays, removing it from the tray and cutting it. It can then be spliced to fibres in the lead-in cable 12, in accordance with known techniques. It will be appreciated that initially there are no splices in the enclosure 9 and the only splices made thereafter are for the purpose of making connections in lead-in cables 12.

The access enclosure assembly 41 of the invention offers a number of advantages, including: (i) significant reductions in field labour at the site where the access enclosure is to be located;

(ϋ) less interruption of the network because of quicker installation of the assembly;

(iii) improved quality and consistency of workmanship as the enclosure is assembled in optimum conditions in a laboratory or factory as opposed to field assembly; (iv) cost savings in inventory control;

(v) improved product delivery because only a single assembly needs to be delivered instead of a multiplicity of components which need to be selected for assembly on site; and

(vi) minimum stress on fibres attributable to rotation of the trays because the fibres enter and exit the trays through the tray hinges.

Many further modifications will be apparent to those skilled in the art without departing from the spirit and scope of the invention.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia.