Strain relief unit for fiber shuffling device

[0001] The present invention relates to a device for providing strain relief to optical fibers routed through a fiber shuffling device.

[0002] Bundles of four, eight or twelve optical fibers are often fused or otherwise bound together in a ribbon. Multi-fiber connectors, such as MT-type connectors, are used to effect a connection between two bundles of fibers or between a bundle of fibers and a device. In the construction of optical fiber circuits using multiple ribbons, it is often necessary to reorganize the fibers such that a fiber bundled as part of one ribbon in one part of the circuit becomes bundled as part of another ribbon in another part of the circuit.

[0003] FIG. 1 shows an example of a portion of such an optical fiber circuit 10 having four input signal ribbons 14, 16, 18 and 20 each having four optical fibers 14a–14d, 16a–16d, 18a–18d and 20a–20d, respectively. The circuit portion 10 also has four output signal ribbons 22, 24, 26 and 28, each having four optical fibers 22a–22d, 24a–24d, 26a–26d and 28a–28d, respectively. In this exemplary circuit portion, it is desired to rearrange the optical fibers such that each input optical fiber of a ribbon becomes a fiber in a different output ribbon according to the pattern shown in FIG. 1 and described in detail in Table 1 below.

[0004]

TABLE 1
Optical Fiber Reorganization Pattern
Input Fiber	Becomes	Output Fiber
14a		22a
14b		24a
14c		26a
14d		28a
16a		22b
16b		24b
16c		26b
16d		28b
18a		22c
18b		24c
18c		26c
18d		28c
20a		22d
20b		24d
20c		26d
20d		28d

Other patterns of optical fiber reorganization are, of course, feasible and the pattern will generally be determined by the requirements of the system of which the particular circuit portion is a part.

[0005] Various fiber shuffling devices are known for effecting such complex patterns of reorganization between optical fibers of various ribbons. One such fiber shuffling device is the Schott Optical Shuffle™ device manufactured and/or distributed by Schott Fiber Optics, Inc. of Southbridge, Mass., U.S.A., and disclosed in U.S. Pat. No. 6,464,404 B1 to Robinson et al., the entire disclosure of which is hereby incorporated herein by reference. Another exemplary fiber optic shuffling device is the Concours NP™ Optical Circuit device manufactured and/or distributed by US Conec Ltd. of Hickory, N.C. An exemplary Schott Optical Shuffle™ device 40 is shown in FIG. 2. Such a device 40 is typical of fiber shuffling devices in that a plurality of fibers are arranged in a given bundled orientation at a first side 40a of the device 40, are arranged within the device 40, and are rearranged in a different bundled orientation at a second side 40b of the device 40 such that at least one bundle on the second side 40b of the device 40 includes fibers from at least two different bundles on the first side 40a of the device 40. While it should be understood that light may propagate in either of opposite longitudinal directions along a given fiber, an example is provided below with reference to FIG. 1, wherein the first side and second sides are discussed in the context of “input” and “output” sides for illustrative purposes, without regard to the direction of light propagation along the fibers.

[0006] Referring now to FIGS. 1 and 2, the exemplary device 40 receives multiple input ribbons 14, 16, 18, 20, each comprising multiple optical fibers as described above. Multiple output ribbons 22, 24, 26, 28 extend out from the device 40, each having selected optical fibers from the input ribbons. The output optical fibers are the input optical fibers reorganized into different output ribbons to effect the desired connectivity required for a particular circuit, for example, the connectivity of Table 1. A significant advantage is realized when such reorganization is accomplished without the use of optical interfaces, since such optical interfaces cause losses in the signal transmission.

[0007] A fiber shuffling device, such as the Schott Optical Shuffle™ device 40 of FIG. 2, works with “bare” ribbon, i.e., ribbon having no external covering or jacket over the optical fibers. While bare ribbon is acceptable for use within a cabinet or other form of shielding, it is preferred that ribbon exposed to ambient conditions have a protective outer jacket that shields the optical fibers from physical damage. Typical jackets are made of an extruded plastic material, preferably PVC, and may include additional protective layers, such as a woven inner sleeve of aramid fibers for improved tensile strength.

[0008] Applicant has recognized, however, a problem with jacketed ribbons exiting fiber shuffling devices such as the Schott Optical Shuffle™ device. Specifically, there is no direct connection between the jackets and the device, and any load imposed on the jacketed ribbons is borne by the length of ribbon between the end of the fiber shuffling device and the beginning of the jackets. This is problematic since the optical fibers of the ribbons are not designed to bear significant tensile loads and are therefore more prone to damage and impaired optical performance. Furthermore, Applicant has recognized the presence of the jacket significantly increases the bending stiffness of the ribbon, and, when bending loads are imposed on the jacketed ribbons, most of the bending occurs over the un-jacketed, bare portion of the ribbon. Bending of the optical fibers should also be avoided because it can degrade the optical performance of the fibers.

[0009] Accordingly, Applicant has identified a need for strain relief for fiber shuffling devices so that jacketed ribbon may be used in conjunction with such devices while protecting the optical fibers from excessive bending or tensile loads and thus avoid or mitigate adverse effects on optical performance.

[0010] The present invention provides a strain relief unit for use in conjunction with a fiber shuffling device. The strain relief unit includes a first attachment member adapted for attaching to the fiber shuffling device and a second attachment member connected to said first attachment member, e.g. by a support member, and adapted for attaching to a portion of a jacket of an optical fiber. In this manner, the strain relief unit provides a direct connection between the jacket(s) of the optical fiber(s) and the fiber shuffling device. Any load imposed on the jacketed fiber/ribbon is borne by the strain relief unit, rather than the length of ribbon between the end of the fiber shuffling device and the beginning of the fiber's jacket.

[0011] The strain relief unit may also include internal channels extending from the fiber shuffling device to an opening for receiving the jacketed fiber. In this manner, the strain relief unit manages the optical fiber bend radiuses to prevent signal propagation losses.

[0016] FIG. 3 is a perspective view of an exemplary strain relief unit 50 in accordance with the present invention for connecting a jacketed bundle or ribbon of optical fibers to a fiber shuffling device 40. For illustrative purposes, the exemplary strain relief unit 50 of FIG. 3 is configured for use with the Schott Optical Shuffle™ device 40 of FIG. 2, although it should be understood that it can be used with any fiber shuffling device. The example of FIG. 3 is consistent with the example of FIG. 1 in that there are four bundles of input signal fibers 14, 16, 18, 20, and that each of these bundles is an unjacketed, ribbonized bundle of four optical fibers. However, it will be understood that the present invention is equally applicable to any number of input signal fibers and fiber bundles, whether ribbonized or unribbonized, and whether jacketed or unjacketed.

[0017] In the example of FIGS. 3 and 4, the individual input signal optical fibers 14a–20d are rearranged (“shuffled”) according to the example of FIG. 1 to provide output signal optical fibers 22a–28d regrouped into four bundles of four fibers each. In this example, each output signal bundle is formed into a ribbon 22, 24, 26, 28 and provided with an outer jacket 30, 32, 34, 36. By way of example, each outer jacket 30, 32, 34, 36 includes an inner sleeve, such as a sleeve of woven Kevlar or other aramid yarn, surrounding the optical fiber ribbon and an outer sleeve, such as a PVC sleeve, positioned coaxially around the inner sleeve. However, it will be understood that the present invention is equally applicable to any number of output signal fibers and fiber bundles, whether ribbonized or unribbonized, provided that they are jacketed.

[0018] As shown in FIGS. 3 and 4, the strain relief unit 50 includes a first attachment member 52 adapted for attaching to the shuffling device 40, and a second attachment member 54 connected to the first attachment member and adapted for attaching to a portion of the jacket(s). In the examplary embodiment shown, a support member 56 supportively connects the first and said second attachment members 52, 54.

[0019] In the embodiment shown in FIGS. 3 and 4, the first attachment member 52 is configured to engage and retain the fiber shuffling device 40. The exemplary strain relief unit 50 of FIGS. 3 and 4 has a first attachment member 52 configured to include a tube 52a extending from support member 56 to engage the fiber shuffling device 40. The tube 52 has an inner surface 52b adapted to receive the fiber shuffling device 40 in frictional or other engagement for attaching the fiber shuffling device 40 to the support member 56. As shown in FIGS. 3 and 4, the fiber shuffling device 40 is connected by frictional engagement to the first attachment member 52.

[0020] The first and second attachment members 52, 54 and connected so that a tensile load applied to one attachment member is at least partially transferred to the other attachment member. For example, the attachment members 52, 54 may be connected by an elastically resilient, deformable or rigid member, such as a substrate, housing, etc. In the exemplary embodiment shown the first and second attachment members 52, 54 are connected by a support member 56 that includes a housing 56 having an opening 56b adapted to receive a portion 30a, 30b, 30c, 30d of the output signal optical fiber jacket 30, 32, 34, 36. More specifically, the support member 56 is integrally formed with the first and second attachment members 52, 54 as a unit. In the embodiment of FIGS. 3 and 4, there are a plurality of openings 56b, one for each respective output signal optical fiber ribbon 22, 24, 26, 28. Optionally, as shown in FIGS. 3 and 4, the housing 56a includes first and second portions 50a, 50b engagable with one another to enclose a portion of the fiber shuffling device 40 and a portion of the optical fiber ribbons extending therefrom. The first and second portions 50a, 50b are shown engaged in FIG. 3.

[0021] The housing 56a defines an internal channel 56c positioned to extend from the tube 52a to a position at opening 56b between the first and second contact surfaces 54a, 54b. The channel 56c is adapted to receive and guide a segment of optical fiber ribbon 22, 24, 26, 28 from the fiber shuffling device 40 to a corresponding opening 56b in a manner limiting bending of the ribbons to acceptable levels. In the embodiment shown, there are a plurality of discrete channels 56c, separated by housing walls 56d, for accommodating the plurality of output signal optical fiber ribbons 22, 24, 26, 28.

[0022] The second attachment member 54 includes first and second contact surfaces 54a, 54b positioned adjacent to one another in spaced relation within said opening 56b, said contact surfaces being spaced apart so as to be frictionally engagable with a portion 30a, 32a, 34a, 36a of each corresponding jacket 30, 32, 34, 36 for attaching the corresponding optical fiber ribbon to the housing 56a. As mentioned above, each jacket defines an inner sleeve surrounding said optical fiber ribbon and an outer sleeve positioned coaxially around the inner sleeve. The inner sleeve has interlaced high strength fibers engagable with the contact surfaces 54a, 54b by means of friction, adhesion, mechanical interengagement, etc.

[0023] In use, a subassembly including the input signal fibers/ribbons, fiber shuffling device and output signal fibers/ribbons may be assembled as known in the art. Application of a jacket to ribbonized or unribbonized bundles of optical fibers is well known in the art.

[0024] The strain relief unit 50 may then be provided on the subassembly by manually laying out the subassembly on a portion 50b of the strain relief unit 50, effectively using this portion 50b as a backplane for routing and arrangement of optical fibers/ribbons. Specifically, the fiber shuffling device 40 is positioned within the tube 52a of portion 50b, with the output signal optical fiber ribbons 22, 24, 26, 28 positioned in respective channels 56c of the housing 56, between corresponding housing walls 56d. The channels 56c guide the output signal optical fibers/ribbons 22, 24, 26, 28 and support them in a manner preventing sharp bends or kinks that would tend to damage the individual optical fibers or disrupt signal propagation therealong. Jackets 30, 32, 34, 36 of the output signal optical fiber ribbons 22, 24, 26, 28 are then pressed into position with corresponding contact surfaces 54a, 54b of the openings 56b of the housing 56 such that corresponding portions 30a, 32a, 34a, 36a of the jackets are engaged by the contact surfaces 54a, 54b. Preferably, this engagement is effected through a friction fit. The other portion 50a of the strain relief unit 50 may then be mated to portion 50b. Portions 50a and 50b may be joined in any suitable manner, such as by adhesive, welding, or by interlocking or non-interlocking mechanical fastening devices, as generally known in the art. In this manner, the strain relief unit 50 rigidly attaches the fiber shuffling device 40 to the jackets 30, 32, 34, 36 of the output signal optical fiber ribbons 20, 22, 24, 26. Accordingly, the strain relief unit 50 provides a direct connection between the jackets and the shuffling device, and any load imposed on the jacketed fiber/ribbon is borne by the strain relief unit 50, rather than by the length of fiber/ribbon between the end of the shuffling device and the beginning of the jacket.

[0025] Similarly, the input signal optical fibers/ribbons may be similarly fitted with a strain relief unit 50, provided that the input signal optical fibers/ribbons are jacketed.

[0026] It should be noted that such fibers/ribbons have traditionally been routed through a shuffling device before terminating the individual fibers or ribbons to suitable connectors. Because there are often problems in properly terminating the fibers/ribbons to connectors, the yield of connectorized fibers is less than 100%. Accordingly, many subassemblies of connectorized fibers/ribbons and shuffling devices are regularly found defective and discarded. For example, if the yield for terminating a ribbon to a connector is 95% (5% terminated incorrectly), for a device having four input ribbons and four output ribbons, the yield of connectorized subassemblies is approximately 66% (that is, 0.95⁸).

[0027] Applicant has found that the yield for connectorized subassemblies can be improved by connectorizing ribbons, e.g. the input signal ribbons, before routing the fibers of such ribbons through the shuffling device. In other words, only pigtails of connectorized non-defective fibers/ribbons are routed through a shuffling device. In this manner, the subassemblies are formed with half of the ribbons, e.g. the input ribbons, having terminations known to be non-defective (effectively, a 100% yield). This leaves only the output ribbons to be connectorized after forming a subassembly including the shuffling device. Accordingly, in the example above, the yield of connectorized subassemblies increases from approximately 66% to approximately 81% (that is, 0.95⁴). Accordingly, fewer shuffling devices, optical fibers/ribbons and connectors need be discarded.

[0028] Having thus described particular embodiments of the invention, various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications and improvements as are made obvious by this disclosure are intended to be part of this description though not expressly stated herein, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description is by way of example only, and not limiting. The invention is limited only as defined in the following claims and equivalents thereto.