WO2000048032A1

WO2000048032A1 - Support unit for optical fibers joints

Info

Publication number: WO2000048032A1
Application number: PCT/US2000/003423
Authority: WO
Inventors: Costantino Tagliaferri; Saverio Ciciriello
Original assignee: Minnesota Mining and Manufacturing Co
Current assignee: 3M Co
Priority date: 1999-02-11
Filing date: 2000-02-10
Publication date: 2000-08-17
Anticipated expiration: 2001-08-11
Also published as: IT1308599B1; AU3227100A; ITMI990266A1

Abstract

A support unit is provided for the joints in optical-fiber ribbons of the type commonly employed in optical fiber cables for the telecommunication industry. The unit comprises a bottom plane, at least one joint housing seat, ribbon inlet and outlet openings into and from the unit, and ribbon housing means for end portions of ribbons ending up in the unit. The joint housing seat, the inlet and outlet openings and the ribbon housing means are formed on either side of the bottom plane, so to form two sub-units, one on the front side and the other on the rear side, respectively.

Description

SUPPORT UNIT FOR OPTICAL FIBERS JOINTS

Field of the Invention The present invention relates to support units for optical fiber ribbons of the type employed in the telecommunications industry.

Background of the Invention A typical telecommunications network is made up of optical cables, each comprising a number of optical fibers (typically 100, 200, 400 or even more) . The optical fibers are arranged in ribbons of generally four fibers each, with each ribbon grouping together fibers that are directed to two specific end users.

In such a network, it is often necessary to provide joints in the optical fiber cables. Examples of such joints include "pothead" joints, "patch" joints, and "extraction" joints. Pothead joints are commonly used to join together a line cable and a main cable. These cables differ in that the main cable must be provided with well defined flame- retardant properties. Patch joints are used for joining together two cables when the available cable length is shorter than the length required for the application at hand. Extraction joints are used for joining a single user (or groups thereof) to a ring line.

Since, as noted above, each cable comprises a high number of optical fibers, a joint for an optical fiber cable must actually consist of an assembly of a great number of single junctions between individual ribbons of optical fibers. These junctions may be attained by butt welding the fibers (thereby forming fused fiber joints) or by bringing the fibers into abuttment mechanically, as through the use of mechanical joints. Theoretically, the fused fiber joints should allow for reduced attenuation of the signal traveling through the optical fibers, and would be preferable for this reason. As a practical matter, however, fused joints require a high degree of accuracy that is not always possible to achieve under normal field conditions.

Therefore, mechanical joints are still widely used, since they achieve good results while being relatively simple to implement. Some mechanical joints are known that allow for the simultaneous junction of all of the fibers in a ribbon. Both mechanical and fused joints may be housed in boxes, such as sealed junction boxes. Inside the box, drawers or trays are provided onto which several units are mounted. Each unit houses a single joint between two optical fiber ribbons, including the end portions of the optical-fiber ribbons that are joined together, although units are also available that house more than one joint. Typically, the units are mounted pivotally on the corresponding support, be it a drawer or tray. Each unit may be readily accessed by unfolding the assembly of all of the units.

In order to make connection and/or maintenance of the single users easier, the company managing the communications network usually requires that a specific unit corresponds to a particular user. Accordingly, junctions relating to different users are typically housed in different units.

This ensures that any work being done on a single user line will not affect the lines of other users. Practically speaking, this means that a one-to-one correspondence must exist between a single junction and a single unit. In the case of pothead or patch joints, each unit houses a butt joint between two fiber ribbons. Two optical fiber ribbons exit from this unit in opposite directions from the line ring structure. 00/48032

In the case of extraction joints, two optical fiber ribbons (relating to the so-called main line and to the so- called stand-by line, which are the upstream and downstream branches, respectively, of the ring structure) must be connected to the optical fibers of the user line, or to an outlet line of the ring structure (e.g., directed to a further ring structure or to a star structure) . To this end, specific mixer junctions are used that connect together (1) a first half of the fibers of the user line ribbon with the corresponding fibers of the main line, (2) the other half of the fibers of the user line ribbon with the corresponding fibers of the stand-by line, and (3) the remaining fibers of the main and stand-by lines with a virtual user. With a dedicated joint, the fibers are interconnected, restoring the continuity of the ring. Such arrangement is necessary in view of the aforementioned constraint of having only one user per unit.

A unit called a mixer unit carries the mixer and the loop joint. Therefore, three ribbons come out of the mixer unit, each of which in turn requires a butt joint in order to be welded onto the two ring branches and to the user branch. Accordingly, at least two additional units will be required in order to house the related joints. Therefore, in order to effect the mixer function, at least three units must be employed for each individual user.

Typically, single units with butt joints and groups of units which perform the mixer function are both housed on the same tray or drawer. Generally, the mechanical structure of the unit is the same (usually obtained through plastic material molding) , irregardless of the destination of the unit. The drawer or tray is equipped with means for correctly guiding and housing the portions of optical fiber ribbons going to and from each unit. Given the inherent fragility of the optical fibers within the ribbons, which are adversely affected by the application of mechanical stresses, particular care is needed during installation and maintenance to prevent the optical fibers from being damaged. There is thus a need in the art for a unit that provides a simpler, more functional, and less cumbersome arrangement of the optical fiber ribbon. These and other needs are met by the present invention, as hereinafter described.

Summary of the Invention In accordance with the present invention, a support unit is provided for the joints in optical fiber ribbons of the type commonly employed in fiber optic cables within the telecommunication industry. The support units of the present invention comprise a bottom plane, at least one joint housing seat, inlet and outlet openings for the ribbons coming into and going out of the unit, and a ribbon housing means for housing the end portions of those ribbons which terminate in the unit. In the support units of the present invention, the joint housing seat, the inlet and outlet openings, and the ribbon housing means are formed on the same front side of the bottom plane. The units are further equipped with at least one further joint housing seat, additional inlet and outlet openings for the ribbon going into and coming out from the unit, and an additional housing means, all disposed on the rear side of the bottom plane opposite to the front side.

As a result of its configuration, the support unit of the present invention is actually comprised of two sub- units, one formed on the front side and the other formed on the rear side of the unit. Each sub-unit may be readily accessed according to the usual procedure by turning the unit over. If the unit is required to house common butt joints, each sub-unit may house the joint corresponding to a user line, thus respecting at sub-unit level the correspondence constraint set by the network manager. The overall dimensions are reduced, since a unit according to the invention, though slightly larger than a conventional unit, performs the same function as two such units. Of course, the joints housing seats may house a butt, mixer, or loop joint.

Preferably, the unit of the present invention comprises at least a second and a third joint housing seat and at least a further second and third joint housing seat, formed on the respective front and rear sides of the bottom plane. In this way, each sub-unit may house three elements, which can be either a joint or a mixer. It is therefore possible to gather into only one unit all the components necessary for the mixer function for the two users, even bypassing the requirement of the virtual user. In fact, it is possible to house on one side of the unit (i.e., in any one of the two sub-units) the butt joint relative to a user, and on the other side (i.e. in the other sub-unit) the butt joint relative to the other user, the two remaining joints (butt joint towards the main line and butt joint towards the stand-by line) and the mixer, distributing them in the four available joint housings at will. In such a set-up, the constraint of correspondence between user and sub-unit is again respected. Moreover, a substantial savings in room is realized pursuant to the invention, since only one unit in accordance with the invention performs the function of a series of conventional units, even though the units of the present invention are only slightly larger than a conventional unit.

The joint housings may be preferably sized according to the specific joints and/or mixers that need to be housed. In this way, each housing is destined to a specific component. Preferably, the unit comprises a passage opening in the bottom plane for the optical fibers, which is advantageous if the unit functions as a mixer. By having two sub-units formed on a same body with a passage opening between the two sub-units, the fibers, which must pass from one sub-unit to the other, are not allowed to pass through the tray or drawer, thereby reducing the risk of damages. The ribbon housing means are preferably shaped such that the optical fibers of the housed ribbon do not undergo changes of direction with bending radiuses greater than a predetermined minimum value, both under static conditions and under pull conditions caused by the handling of the ribbons. This improves the protection of the optical fibers of the ribbons from possible folding during the installation and maintenance. In order to achieve this end, the ribbon housing means preferably comprises guiding walls protruding perpendicularly from the bottom plane and having a bending radius greater than the predetermined minimum value. The guiding walls are set one after the other, from the inlet opening to the joint housing seat and to the outlet opening, in such a way that each wall starts in a direction substantially tangent to the preceding wall (either to the inlet opening or to the joint housing seat) and ends up in a direction substantially tangent to the next one (either to the joint housing seat or to the outlet opening) . The minimum bending radius is thus ensured even in case of pull conditions on the ribbons. The minimum predetermined value of the bending radius is preferably not lower than 30 mm, a value which is normally tolerated by the optical fibers. The unit of the present invention advantageously comprises holding tabs which protrude perpendicularly from the guiding walls, and which are parallel to, and spaced from, the bottom plane. Such tabs are used to ensure that the portions of ribbon are effectively held on the unit. Further features and advantages of the unit according to the invention will appear more clearly from the following description of a preferred embodiment thereof, which is made with reference to the attached drawings.

Brief description of the Drawings FIG. 1 is a front perspective view of a unit according to the invention; and

FIG. 2 is a rear perspective view of the unit of FIG. 1.

Detailed Description of the Invention With reference to FIG. 1, a supporting unit 1 is provided for mechanical joints between optical fiber ribbons of the type commonly used in the telecommunications industry. The unit comprises a bottom plane 2 and a peripheral frame 3 which is integral with the bottom plane and which extends perpendicularly therefrom. The peripheral frame is positioned symmetrically on both the front 10 and rear side 20 of the unit. Preferably, the bottom plane and the frame are constructed as a unitary piece. Such a structure may be obtained, for example, by molding a suitable plastic material.

On the front side 10, the unit is provided with three joint housing seats, indicated as 11a, lib, lie. For ease of description, the elements which are equivalent to each other will be indicated herein by reference to the same number followed by a different letter (such as the above mentioned joint housing seats), and such elements will be indicated in their whole by the number only.

Each seat 11a and lib is adapted to receive a mechanical joint, whereas the seat lie is adapted to receive a mixer. For clarity of illustration, the mechanical joint and the mixer are not depicted in the drawings. By the term "mechanical joint", it is meant any mechanical joint element between optical fiber ribbons belonging to a fiber optic cable for telecommunications, such as a butt joint or a loop joint. However, for the purposes of their housing inside the unit, such elements are essentially equivalent.

On the front side 10, the unit is provided with two ribbon inlet and outlet openings 12a, 12b which are formed in the frame 3. The unit is also provided on this side with a ribbon housing means for receiving the end portions of the optical fiber ribbons which terminate in the mechanical joints housed in the joint housing seats 11. Such housing means comprises curved guiding walls 13a, 13r and 14a, 14o which protrude perpendicularly from the bottom plane in various arrangements. The walls 13 are grouped in islands of contiguous walls which are directly interlinked, though not necessarily tangent. In each island, the edges between contiguous walls are rounded. The walls 14 are insulated. Specifically, the various walls 13, 14 each have a bending radius which is greater than a predetermined minimum value set according to the maximum bending stress bearable by the optical fibers, preferably 30 mm. As noted in FIGS. 1 and 2, the walls 13, 14 are set consecutively, from the inlet/outlet openings 12 to the joint housing seats 11 and vice versa, so that each wall starts according to a direction substantially tangent to the preceding walls (either to the inlet/outlet openings, or to the joint housing seat) and ends up in a direction substantially tangent to the following one (either to joint housing seat or to the inlet/outlet opening) . It should be noted that, as used herein, the term "tangent" has a much broader meaning that extends beyond the strict geometric definition, and includes directions that diverge the one from the other by relatively small angles (e.g., smaller than 40°). Thus, as depicted in the drawings, the following pairs of walls are considered reciprocally tangent in accordance with the above mentioned meaning: 13a, 13b; 13c, 13d; 13d, 13e; 13e, 13f; 13g, 13 ; 13g, 14b; 131, 13m; 131, 14a; 14a, 13k; 14b, 13n; 13o, 13p; 13p, 13q; 13q, 13r; 14c, 14d; 14h, 141; 13a, 13c; and 13a, 13f. Further on, the openings 12a, 12b and the wall 13 are tangent, as are the seats 11a and lie and the walls 14d, 14g and 141, 14o. As with the frame 3, all the walls 13 are also preferably constructed as an integral unit with the bottom plane 1.

The unit is equipped on the front side 10 with holding tabs 15. The tabs are integral with the guiding walls 13 and 14, the openings 12 and the frame 3 perpendicularly protruding therefrom, and all are coplanar to each other, parallel to the bottom plane 2, and spaced therefrom.

On the rear side 20, the unit is provided with elements which are alike and corresponding to the elements provided on the front side 10, i.e., three joint housing seats 21a, 21c, two inlet/outlet openings 22a, 22b, guiding walls 23a, 23r and 24a, 24o and holding tabs 25. Such elements from 21 to 25 will not be described in detail as they are alike to the corresponding elements 11 and 15 on both the front and rear side of the unit, which elements have already been defined. Two sub-units are thus defined. The unit comprises passage openings 4a-4m, formed in the bottom plane and in the pivoting means 5. In use, the unit 1 is mounted on a tray or drawer (not illustrated) , by means of the pivoting means 5, according to a in se conventional way. The unit may house on each side one or two joints in the dedicated housings lla-llb or 21a-21b, according to the specific application, as will soon be explained, and a mixer in the dedicated housing lie or 21c. Each joint or mixer connects one or more end portions of optical-fiber ribbon housed in the ribbon housing means 11, 13 or 23, 24.

In case of simple butt junctions, each unit has a butt joint and two end portions of ribbon on a respective side 10 or 20. Therefore, each side 10 or 20 performs the function of a unit according to the prior art, by housing the components required for a single user.

In the case of extraction junctions, wherein the mixer function for a user needs to be performed, all the components required for the user are housed in the unit. In fact, the mixer, the loop joint and the three butt joints towards the user and towards the main and stand-by branches of the line are housed in five out of the six available housing seats 11-21. It should be noted that, in contrast to prior art devices, only the three ribbons come out of the unit, which ribbons are directed externally, i.e., to the two line branches and to the user, whereas the connections towards the loop joint remain inside the unit (by advantageously using the opening 4) . This feature affords greater protection to the ribbons, since the passage from unit to the tray is commonly a source of vulnerability for the ribbon.

Several variations of the unit 1 are possible. In one such variation, which is especially advantageous where the size of the unit is a consideration, the loop joint is removed and replaced with the butt joint for a second user, thus making it possible to place the mixing function for two users on a single unit, while observing the correspondence constraint set by the network manager. The two joints may be arranged towards the users on opposite sides of the unit, housing the other elements (a mixer and two butt joints towards the two line branches) in three of the four available seats 11 and 21. In this way, each side 10 or 20 of the unit 1 relates to a single user, and carries the connecting joint towards that user. As a result, the mixer function for two users requires only one unit, as compared to the four or six units required by the prior art.

Claims

What is claimed is:

1. A support unit for a joint between two optical fiber ribbons, comprising: a bottom plane; a joint housing seat; and inlet and outlet openings for the ribbon in and from the unit ribbon housing means for end portions of ribbons terminating in the unit; wherein said joint housing seat, said inlet and outlet openings and said ribbon housing means are formed on the same front side of the bottom plane, and wherein the unit further comprises on rear side of the bottom plane opposite to the front side (a) a further joint housing seat, (b) further inlet and outlet openings for the ribbon into and from the unit, and (c) further housing means.

2. The support unit of claim 1, wherein said unit further comprises a second joint housing seat and a second joint further housing seat, formed on the respective front and rear side of the bottom plane.

3. The support unit of claim 1, further comprising a passage opening for the optical fibers in said bottom plane.

4. The support unit of claim 1, further comprising a pivoting mount, extending along an axis substantially coplanar to the bottom plane, adapted to mounting the unit onto a tray.

5. The support unit of claim 1, wherein the ribbon housing means are shaped so that the optical fibers of the housed ribbons may not undergo changes of direction with bending radiuses greater than a predetermined minimum value, both under static conditions and under pull conditions caused by the handling of the ribbons.

6. The support unit of claim 5, wherein the ribbon housing means comprises guiding walls protruding perpendicularly from the bottom plane, and wherein the guiding walls have a bending radius greater that the predetermined minimum value and are set one after the other, from the inlet opening to the joint housing seat and to the outlet opening, in such a way that each wall starts in a direction substantially tangent to the preceding wall (either to the inlet opening or to the joint housing seat) and ends up in a direction substantially tangent to the next one (either to the joint housing seat or to the outlet opening) .

7. The support unit of claim 5, wherein the minimum predetermined value of the bending radius is not lower than 30 mm.

8. The support unit of claim 1, further comprising holding tabs protruding perpendicularly from the guiding walls, parallel to and spaced from the bottom plane.