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LIGHTGUIDE FIBER CROSS CONNECTION_MODULE
Background of the Invention This invention relates to lightguide cable interconnection equipment; and it relates more particularly to eguipment for interconnectinq multifiber cables and individual fibers, as for example, in customer premises installations in a telecommunications system. The term "fiber" is employed herein to mean a lightguide, or optical, fiber, various types of which are now well known in the art.
Overall guiding criteria often applied to the development of lightguide cable interconnection equipment include, e.g., achieving a high degree of flexibility, a high connector density, an uncomplicated working vehicle ; or arrangement, and a minimum number of cabinet or enclosure designs. The main functions of such equipment include providing a convenient interface between dif~erent sections of fiber optic cabling in a telephone system, providing a central test access point to optical fibers, permitting rapid rearrangement among transmission equipment and optical fibers, providing transition hardware to fan out optical fibers from cabled fiber configurations, providing for organized optical fiber slack storage, and providing a fiber cable interconnection panel. Similar criteria and functions are outlined, along with some proposed lightguide cable interconnecting equipment embodiments, in a paper entitled, "Bell System Lightguide Cable Interconnection Equipment, Central Office to Customer Premises," by M. R. Gotthardt and appearing in Proceedings of the 32nd International Wire and Cable Symposium, November 15-17, 1983, Cherry Hill, New Jersey, pages 45-48.
It has been found, however, that, on a stand-alone basis, equipment of the type outlined in theforegoing paper is, at least for small numbers of fibers, bulky and relatively inconvenient for use in some cu ~ er :
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premises locations. In addition, such equipment is relatively expensive because, for example, fanout modules included there-in are mounted in an equipment box which is, in turn, mounted either in a typical type of e~uipment frame or on a wall.
Also, such equipment involves significant fiber rounting bends in addition to those used for coiling slack fiber for storage purposes. Factors such as the number and type of connectors e~ployed in a lightguide transmission system and the number of sharp bends in the lightguide dressing path are important. The reason is that each may represent a signal energy loss, and lightguide cable interconnecting equipment usually has only a fixed loss budget that cannot be exceeded without forcing the entire fiber transmission path to be redesigned in a signal level plan sense.
It is also observed, incidentally, that certain types of lightguide connectors such as the biconic connectors mentioned by Gotthardt are characterized by subjecting signals transmitted in connected fibers to increasing loss as the number of reconnections of an individual connector increases as when fiber interconnections are changed from time to time.
In some cases the entire connector must be discarded after, for example, 100 connector insertions. This represents a signiicant labor cost to replace the connector as well as certain accounting costs to keep track of the number of insertions when used for cross connect jumpers so that the connectors can be replaced as they begin to reach levels of numbers of insertions which could be expected to result in loss levels which would exceed the equipment loss budget.
Summary of the Invention In accordance with an aspect of the invention there is provided a lightguide fiber cross connection equipment unit comprising at least one set of front and back plate members connected by plural side members to form a box having fiber pass-through apertures in different sides thereof, means in one of said side members for interconnecting lightguide fibers inside said box to respective lightguide fibers out-side said box, means, adjacent to said one side, for retaining ~,.
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fiber slack in a looping configuration approximately parallel to said back plate member, and means, adjacent to said re-taining means, and including a plurality of said members, for comprising a channel between two of said apertures to accommodate fiber passage into, through, and out of said box.
Brief Description of the Drawinq A more complete understanding of the invention and the various fea-tures, objects, and advantages thereof may be obtained from a consideration of the following detailed description and the appended claims in connection with the attached drawings in which:
FIGS. 1, 2 and 3 are front, side, and bottom views, respectively, of a cross connection box in accordance with the invention;
FIG. 4 is a simplified frontal view of a first embodiment of a combination of boxes of the type in FIG. 1 to form a fiber distributing frame; and FIG. 5 is a simplified frontal view of a second embodiment of a plurality of the boxes of the type shown in FIG. 1 to form a fiber distributing frame.
Detailed Description FIGS. 1, 2 and 3 show frontal, side, and bottom views of a cross connection box, or module, 10 in accordance j with the invention. The box is, illustratively, a rectangular hexahedron having a hinged door 11 which is shown in an open position to illustrate the interior of the box. A portion of the door is broken away to conserve space in the drawing. Cards 12 are advantageously secured to the inside of the door 11 for entry of a list of fiber identifications and cross connections in the box. When the door 11 is closed against a latsh plate 13, as illustrated in FIGS. 2 and 3, it forms a front plate for the box. That front plate is connected to a back plate 16 by four side members 17 through 20, res~ectively, to form the box 10.
The removable sides 18 and 20 are the top and bottom of the box as shown in the orientation of FIG. 1. Side members 18 and 20 are advantageously removable, as schematically represented by, e.g., threaded fastening arrangements 24, A
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for a reason to be subsequently explained. Those two side members, together with the side member 17, define two apertures 21 and 22 as best illustrated in the FIG. 3 where the aperture 22, defined in part by the side members 17 and 20, is shown.
The interior region of the box 10 between apertures 21 and 22 is a pass-through region comprising a channel formed, as seen in the bottom view of FIG. 3, by the door 11, side member 17, and back plate 16. The purpose of that channel is to accommodate the extension of lightguide fibers into, through, and out of the box 10 either individually or as cables. The term "cable" is here used to indicate a bundle of fibers with a common protective coating which is analogous in a sense to an insulated multiwire cable.
Lightguide retaining rings 23, 26, and 27 further ; define the channel region. These rings are advantageously split rings made of a suitably springy material, either metallic or plastic, of a type now well known in the art.
The end view of one such ring, i.e., ring 27, is illustrated in FIG~ 3. These rings allow insertion of cable or fiber through the split in the ring without the need for threading it axially through the ring. Tie, or anchor, posts 28 and 29 are provided adjacent to the apertures 21 and 22, respectively, Eor tying cables and/or fibers for strain relief purposes.
Fasteners such as the screws 30 are provided for mounting the box 10 to a stable base such as a wall or an equipment frame, not shown.
Adjacent to the aforementioned pass-through channel region of box 10 is a slack loop region which advantageously overlaps somewhat the channel region. The loop retaining region is defined by more lightguide retaining rings~ such as the rings 31 through 36, which are arranged to guide, or retain, fibers in a basically circular looping path. That path is large enough to assure ~; at least the minimum fiber bending radius for the fibers .
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which are expected to be used in the box 10. It is known that optical fibers which are bent too sharply experience at least two problems. They subject signals transmitted along the bent portion of the fiber to distortion, and stresses at the bend make them more subject than usual to fracture if struck. Thus, the slack loop involves no significant signal distortion due to bending. This fiber looping region lies in the same plane as the aforementioned channel pass-through region defined by rings 23, 26, and 27 and is perpendicular to the plane of the side member 19 of the box wherein connectors are mounted.
Connectors, such as the connector 37, are mounted in a removable panel 38. A second panel 39 is also removable and is illustrated without connectors in place since it constitutes reserve for expansion. The panel 39 would be replaced by a panel similar to 38 and including connectors when required to accommodate a larger number of lightguide fibers. Connectors 37 implement the joining of lightguide fibers inside the box lO with respective lightguide fibers outside the box. Such connectors are advantageously of the flexible ferrule type shown in Canadian Patent Application Serial No. 449,123 which was filed in the name of J.M. Anderson on March 8, 1984. Such connectors con,prise a sleeve, which engages the panel 38, and receive an individual fiber connector plug in each end. Connectors of that type have been found to be reusable in hundreds of lightguide fiber insertions without significant change in the signal loss through the resulting connection.
Such connectors permit a fiber connector plug secured to its fiber to be insèrted or removed without removing the sleeve from the panel; so only one fiber of a connected pair need be moved when connection of that one is to be changed. Of course, any connectors that meet the user's insertion loss requirements can be mounted on a similar connector panel in the side member 19.
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~0~34 The coplanar orientation just outlined for the pass-through channel and the fiber slack loop regions of the interior of the box 10 assure a minimum number of fiber bends and also assure that such bends as are required are relatively sweeping with la,rge radii. For example, a cable, from which at least one fiber is to be separated for termination at a connector in the box, enters the box through the aperture 21 and is anchored at the right-hand side of post 28. After removal of cable coating, the fiber is extended through all of the slack loop rings 31 through 36, beginning at ring 36, in a counterclockwise directionO
It will thus be appreciated that the slack loop region defined by the latter six rings is spaced from the side member 19 and connectors 37 by an ade~uate distance to assure at least the minimum fiber bending radius. A
similar cable entering through aperture 22 to the right of post 29 has its separated fibers extended in a clockwise ~-~ direction through the slack loop rings 31 through 36, beginning at ring 35. Fibers which extend through the box 10 in the channel region as integral cables, without fiber separation, extend to the left of posts 28 and 29, through rings 23, 26, and 27 and exit with no change.
Another advantage of the coplanar arrangement is that it permits box 10 to be thin and thus useful for applications where space is limited. Box depth in a direction perpendicular to the plane of the slack loop retaining region need be only ade~uate to accommodate the largest of (a) the connectors for the maximum number of fibers to be terminated in the box, (b) the slack loop retaining region depth, in a direction perpendicular to the loop configuration plane, needed for that maximum number of fibers, or (c) the channel region in the latter direction needed for the maximum number of fibers, individually or in cablesr to be brought into or through the box.
Secured to the side member 19 of the box 10 is a removable cross connect jumper guide panel 40 which is a lateral extension of the back member 16 of the box. This : . , , , , :
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panel has secured thereto a retaining ring 41 of the split variety but of a substantially larger diameter and heavier construction than rings such as 36 because cross connect jumpers usually have larger-diameter protective coatings and more of them may need to be accommodated than inside a single box. Ring 41 has at its split a gap at an angle to the normal direction of run for a cross connect jumper to reduce the likelihood of a jumper coming out accidentally.
The ring 41 and the panel 40 provide a guiding arrangement for cross connect jumper lightguide fibers extending between connectors 37 either on the same box 10 illustrated in FIG. 1 or between such connectors and similar connectors on other boxes that may be mounted nearby as will be hereinafter descri~ed.
15In one application, boxes of the type illustrated in FIG. 1 were employed to accommodate in each, 12 lightguide fiber connectors 37 on two connector panels.
;~ The box in that application was 8 inches tall by 7.5 inches wide (excluding panel 40) by 2.3 inches deep. In addition, ` 20 many fibers, e.g., approximately 80 individual fibers with respective protective coatings can be accommodated on a pass-through basis in the pass-through channel region ` defined by retaining rings 23, 26, and 27. Even more can be accommodated if fibers manufactured in multifiber cables are involved.
FIG. 4 illustrates several boxes of the type shown in FIG. 1 combined into different types of side-to-side adjacency. In the case of the box pairs 42,43 and 44,45, the boxes of the pairs are arranged in side-to-side adjacency with their connector panel regions in reyistration. For this purpose one of the boxes of each pair, e.g., the boxes 43 and 45, are rotated 180 degrees in the plane of the drawing to realize the aforementioned registration so that the doors of all boxes open away at the extreme edges of the combination to leave a total box ~,' access region undivided by doors ~or the boxes. Similarly, mountings for the fiber connector panels such as 38 on the :- -.. : --, ,, , ~, -, ' , ,: . . ~ ' - ' ~7~13A
boxes are advantageously arranged in a symmetrical fashion on the side 19 of the respective boxes so that the aforementioned rotation can be accomplished with successful registration thereafter. One set (38,3g) of connector panels in either of the boxes is advantageously removed since only one set of connectors is required for the illustrated registration in the indicated pairs.
Similarly, the cross connect jumper guide panels 40 and their rings 41 of the boxes of the pairs are all removed to allow the boxes to be placed in sufficiently close proximity so that only one set of fiberguide connectors is required within any pair of boxes.
Similarly, different pairs of boxes such as the pairs 42,~4 and 43,45 are arranged in side-to-side adjacency with their closest pass-throu~h channel aperture regions in registration. Thus, the aperture 22 of the box 44 registers with the aperture 21 of the box 42; and similarly, the aperture 22 of rotated box 43 registers with the aperture 21 of the rotated box 45. When pairs of boxes are so arranged, internal side members 18 and 20 of the combination are advantageously removed. This makes it easier to fan out a portion of the fibers of a single cable ` in each of at least two boxes, e.g., 42 and 44, at different levels in a column.
The box combination of FIG. 4 is used to illustrate some of the possibilities for fiber interconnection and fanout that are possible with boxes of the type described. For example, a cable 46 enters the top of box 44 where it is tied off and the protective coating removed therefrom so that the two fibers in the cable may be conveniently fanned out. Those fibers are then passed through the fiber slack looping region of box 44 in a counterclockwise direction and ultimately terminated at connectors facing the box 45 where they are joined to similar fibers of a cable 47 which has been similarly treated in the box 45. This type of arrangement is particularly advantageous for interconnection of the fibers ,, ~. -. ,, , , :
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g of two cables where such interconnections are likely to remain the same for a long period of time; and the employment of cross connect jumpers, and corresponding extra connections per path, is not required.
In another example, a cable 48 enters the bottom of the box 42 where it is tied off for strain relief and its protective coating removed over a portion of the length of the fibers therein. Those exposed fibers are then inserted into the fiber slack looping region in the box 42 for passage through that region in a clockwise direction.
Two of the fibers of the cable 48 are terminated at connectors on the connector panel serving both of the boxes 42 and 43 while the remaining fibers of the cable 48 continue around the looping region and exit from the box 42 at the upper corner thereof. The cable is tied to the right of the post 28 in box 42 and passes to the left of post 29 in box 44. The cable then passes through rings 27, 26, and 23 in the box 44 and out of that box in the cable form with the protective coating still on the ` 20 bundle of fibers. The two fibers which were terminated in the box 42 are joined through respective connectors to fibers in the box 43 which, in turn, pass through the slack looping region thereof as part of a cable 49. That cable extends in box 43 in a path similar to that described for cable 48, before being tied off in box 43 and passing through the pass-through channel region of box 45 to exit therefrom in the illustrated upper right-hand corner of the box 45. It will be appreciated, of course, that more pairs of boxes can be added to form a larger columnar array in the fashion illustrated in the FIG. 4. Likewise, a box-pair column only one pair high can be employed if that is appropriate in a given installation.
FIG. 5 illustrates plural cross connection boxes of the type shown in FIG. 1 but with doors 11 closed. The boxes are arranged in aperture registration in the fashion illustrated in FIG. 4 with respect to, for example, the boxes 42 and 44. In FIG. 5, two columns o boxes 50 ' ;'., "'.~, ` , ~`.
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through 53 and 54 through 57 are illustrated. Fiber cables advantageously enter at the tops of the columns and pass through channel regions or have fibers separated out for termination within boxes as previously described. It should be appreciated that for the arrangement oE FIG. 5, as well as that of FIG. 4, the boxes are combined as shown with no special equipment frame required to achieve that result. Individual boxes are simply secured to a convenient wall or post member (not shown) in the desired configuration by means of the fasteners 30 previously mentioned in connection with FIG. 1. Horizontal or sloping surfaces could also be used for mounting. In addition, cards 61 are advantageously secured to the outside of the door 11 for entry of a list of fiber identifications.
This, plus the use of connectors of the Anderson type, allows jumpers to be changed without opening box doors.
Only two cross connect jumpers 58 and 59 are shown in FIG. 5 to illustrate the manner in which a fiber terminated within any box can be cross connected to a fiber terminated in any other, or in the same, box of the columns. Thus, boxes arranged in columns on a side-to-side basis with aperture registration are useful as a fiber distributing frame for applications where large numbers of fibers are involved. The cross connect fiber jumper 58 extends between a connector of the box 50 and a connector of the box 52 after passing across guide panels ~0 of the boxes 50, 51, and 52 and through guide retaining rings 41 of those boxes. Similarly, a jumper fiber 59 extends from a connector at the box 50 downwardly through the whole column of boxes 50 through 53, through a fiber tray or trough 60 which extends across the bottom of the two columns of boxes and up through the cross connect jumper guide arrangements of boxes 57, 56, and 55, to terminate in a connector on the box 55. More than two columns of boxes can, of course, be similarly combined.
Although the present invention has been described in connection with particular applications and embodiments - , ~
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thereof, it is to be understood that additional applications, embodiments, and modifications which are apparent to those skilled in the art are included ~ithin the spirit and scope of the invention.
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