Patent Publication Number: US-6985665-B2

Title: Strain relief unit for fiber shuffling device

Description:
FIELD OF THE INVENTION 
   The present invention relates to a device for providing strain relief to optical fibers routed through a fiber shuffling device. 
   DISCUSSION OF RELATED ART 
   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. 
     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  14   a – 14   d,    16   a – 16   d,    18   a – 18   d  and  20   a – 20   d,  respectively. The circuit portion  10  also has four output signal ribbons  22 ,  24 ,  26  and  28 , each having four optical fibers  22   a – 22   d,    24   a – 24   d,    26   a – 26   d  and  28   a – 28   d,  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. 
                   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.
 
   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  40   a  of the device  40 , are arranged within the device  40 , and are rearranged in a different bundled orientation at a second side  40   b  of the device  40  such that at least one bundle on the second side  40   b  of the device  40  includes fibers from at least two different bundles on the first side  40   a  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. 
   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. 
   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. 
   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. 
   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. 
   SUMMARY OF THE INVENTION 
   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&#39;s jacket. 
   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. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a symbolic diagram of an exemplary prior art optical shuffle regrouping bundles of input signal optical fibers into bundles of output signal optical fibers. 
       FIG. 2  is a diagram of an exemplary prior art fiber shuffling device for performing the optical shuffle of  FIG. 1 . 
       FIG. 3  is a perspective view of a strain relief unit in accordance with the present invention for use with the fiber shuffling device of  FIG. 2 . 
       FIG. 4  is a top view of the strain relief unit of  FIG. 3 , showing an internal portion thereof. 
   

   DETAILED DESCRIPTION 
     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. 
   In the example of  FIGS. 3 and 4 , the individual input signal optical fibers  14   a – 20   d  are rearranged (“shuffled”) according to the example of  FIG. 1  to provide output signal optical fibers  22   a – 28   d  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. 
   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 . 
   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  52   a  extending from support member  56  to engage the fiber shuffling device  40 . The tube  52  has an inner surface  52   b  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 . 
   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  56   b  adapted to receive a portion  30   a,    30   b,    30   c,    30   d  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  56   b,  one for each respective output signal optical fiber ribbon  22 ,  24 ,  26 ,  28 . Optionally, as shown in  FIGS. 3 and 4 , the housing  56   a  includes first and second portions  50   a,    50   b  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  50   a,    50   b  are shown engaged in  FIG. 3 . 
   The housing  56   a  defines an internal channel  56   c  positioned to extend from the tube  52   a  to a position at opening  56   b  between the first and second contact surfaces  54   a,    54   b.  The channel  56   c  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  56   b  in a manner limiting bending of the ribbons to acceptable levels. In the embodiment shown, there are a plurality of discrete channels  56   c,  separated by housing walls  56   d,  for accommodating the plurality of output signal optical fiber ribbons  22 ,  24 ,  26 ,  28 . 
   The second attachment member  54  includes first and second contact surfaces  54   a,    54   b  positioned adjacent to one another in spaced relation within said opening  56   b,  said contact surfaces being spaced apart so as to be frictionally engagable with a portion  30   a,    32   a,    34   a,    36   a  of each corresponding jacket  30 ,  32 ,  34 ,  36  for attaching the corresponding optical fiber ribbon to the housing  56   a.  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  54   a,    54   b  by means of friction, adhesion, mechanical interengagement, etc. 
   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. 
   The strain relief unit  50  may then be provided on the subassembly by manually laying out the subassembly on a portion  50   b  of the strain relief unit  50 , effectively using this portion  50   b  as a backplane for routing and arrangement of optical fibers/ribbons. Specifically, the fiber shuffling device  40  is positioned within the tube  52   a  of portion  50   b,  with the output signal optical fiber ribbons  22 ,  24 ,  26 ,  28  positioned in respective channels  56   c  of the housing  56 , between corresponding housing walls  56   d.  The channels  56   c  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  54   a,    54   b  of the openings  56   b  of the housing  56  such that corresponding portions  30   a,    32   a,    34   a,    36   a  of the jackets are engaged by the contact surfaces  54   a,    54   b.  Preferably, this engagement is effected through a friction fit. The other portion  50   a  of the strain relief unit  50  may then be mated to portion  50   b.  Portions  50   a  and  50   b  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. 
   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. 
   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, 0.95 8 ). 
   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, 0.95 4 ). Accordingly, fewer shuffling devices, optical fibers/ribbons and connectors need be discarded. 
   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.