Abstract:
A fiber tray is provided for installing fiber optic cable and other types of cable that are vulnerable to performance losses if a certain minimum bend radius is not maintained. The fiber tray allows a user to create a subassembly that maintains bend radius control while easing assembly. The construction of the fiber tray also minimizes the depth of the tray and gives freedom to the user to vary the routing patterns of the cable so that a component that is attached to the end of the cable can be located at a predetermined spot on the tray.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Fiber optic cables and other cables such as CAT5 cable require that users do not bend them pass a certain amount, otherwise performance losses will be induced. This characteristic of a cable is referred to as the minimum bend radius. For example, the minimum bend radius for CAT5 cable is one inch and it is 50 mm for SMF-28 fiber optic cable when light waves having a wavelength of 1550 nm are passing through it. Any network or test instrument using these types of cable needs to maintain these minimum bend radii, otherwise the performance of the network or test instrument will be compromised. Maintaining bend radius control can be difficult, especially when fiber optic cable is routed within the interior of a small housing for a fiber optic test instrument. None of the previous methods for routing fiber optic cable in a test instrument have been successful for a number of reasons. 
         [0002]    One previous method of routing fiber optic cable in a test instrument has been to wind the fiber into the bottom of one half of the housing of the test instrument and try to maintain bend radius control by hand. The cable is then taped into place. This method has several disadvantages. First, some assemblers are not knowledgeable about fiber optics and fail to understand the importance of maintaining bend radius control. Second, even knowledgeable and experienced assemblers will occasionally violate minimum bend radius because of the considerable amount of dexterity necessary to maintain bend radius control. Third, repeatedly taping the cable leads to microbends that reduce the optical power transmitted in the fiber to any bulkhead or connector. Finally, this method requires that the optical components be mounted to a circuit board. Minimum bend radius is often exceeded due to the transition from the bottom of the housing of the test instrument to the printed circuit board that is necessary during the process of connection of the fiber to the optical components. All of these problems lead to undesirable performance losses in the fiber and test instrument. 
         [0003]    Another method that has been used to route fiber optic cable in a test instrument is to use fiber clips or routing channels. The disadvantage that these components have is that they typically only allow for one path for which the cable to follow. Given the variance in the length of cable used, this meant that optical components and splices would not be found in the desired location. This caused the assembler to bend the fiber in an effort to make the components fit into the available space. Another drawback is that these commercially available components were too tall to fit into a small housing, which limited their use. 
         [0004]    Accordingly, there exists a need to provide bend radius control for cabling in a test instrument that allows the user to easily assemble the test instrument, locate optical components in the desired location, and minimize the space that the management of the cabling takes up in the test instrument. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention satisfies the aforementioned needs by supplying a tray that comprises a sheet of material that has a plurality of holes that define a routing path for the cable to follow. A fixture with jig pins is placed under the tray such that the jig pins extend through the holes of the tray, allowing the user to route the cable around the jig pins helping to maintain minimum bend radius control. Once the cable is in its proper place, the user fastens the cable to the tray so that the cable cannot move substantially. Then, the user removes the jig pins, creating a tray and cable subassembly that is ready to be placed within a housing. Once the tray has been placed into one half of the housing, a padded member may be placed on top of the cable that is on the exposed side of the tray, protecting the cable from damage. Finally, the other half of the housing is fastened onto the first half of the housing, sealing the tray, cable, and padded member within the housing. 
         [0006]    Alternatively, a routing channel and a second series of holes may be part of the tray such that the routing channel, second series of holes, and first series of holes define multiple routing paths, allowing the user to compensate for varying lengths of cable such that a component that is attached to the end of the cable can be located at a predetermined location should the user wish to do so. Furthermore, a clip may also be provided proximate to one of the routing paths to help hold the cable in place. This version of the tray can then be assembled into a housing with a padded member in a similar fashion as discussed above. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is an exploded view of the tray of the preferred embodiment and a padded member being assembled into the housing of a test instrument; 
           [0008]      FIG. 2  is perspective view of the tray of  FIG. 1  with a fixture having jig pins extending through the holes of the tray and a mounting bolt that holds the tray onto the fixture; 
           [0009]      FIG. 3  is a top plan view of the tray, fixture and mounting bolt of  FIG. 2  with routing paths shown prior to the routing of fiber optic cable; 
           [0010]      FIG. 4  is a top plan view of the tray, fixture and mounting bolt of  FIG. 3  with fiber optic cable routed and taped into place; 
           [0011]      FIG. 5  is a top plan view of the tray of  FIG. 4  with the fixture and mounting bolt removed; 
           [0012]      FIG. 6  is a perspective view of a routing channel; and 
           [0013]      FIG. 7  is a perspective view of a fiber clip. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0014]    Looking at  FIG. 1 , there is shown the preferred embodiment of the present invention. This embodiment includes a tray  10  that is made from sheet metal that is bent into the proper shape by a die. The tray  10  also has features on it which allow fiber optic cable  12  to be routed in paths having different lengths without creating any kinks in the cable  12  which would violate the minimum bend radius of the cable  12 . Attached to the end of the fiber optic cable  12  is an optical component  14 , such as a laser or detector, that can be located at a predetermined place so that it can be easily attached to the printed circuit board (not shown) via electrical cables (not shown) prior to the assembly of the test instrument. 
         [0015]    As can be seen, the tray  10  and fiber optic cable  12  form a subassembly that can be located within one half of the housing  16  of the test instrument and which can be tested prior to the assembly of the test instrument, finding performance losses and preventing needless rework. After the tray  10  has been placed into the first half of the housing  16  of the test instrument, then a piece of compressed foam  18  is placed onto the exposed side of the tray  10  on top of the cable  12 , protecting it from damage. Finally, the second half of the housing  20  of the test instrument is mated with the first half of the housing  16  and is fastened thereto by screws (not shown). The resulting test instrument is one free of performance losses and that can be taken apart easily for rework if desired. 
         [0016]      FIG. 2  more clearly shows that the construction of the tray  10  includes a main body  22  that has four mounting flanges  24  that extend from its sides vertically above the main body  22 , an outside routing channel  26 , an inside routing channel  28 , an inside series of holes  30 , an outside series of holes  32 , a left fiber clip  34 , and a right fiber clip  36 . The mounting flanges  24  have holes  38  on their top surface and are located such that holes  38  will align with the screw bosses (not shown) and counterbores (not shown) of the first and second halves of the housings  16 ,  20  so that when the test instrument is screwed together, the mounting flanges  24  will be secured and the tray  10  will not move thereafter. The main body  22  also has a transition ramp  40  that reduces the distance vertically from the main body  22  to the top surfaces of the mounting flanges  24 . This shape is complimentary to the inside surface of the first half of the housing  16  of the test instrument, which in turn is complimentary to the outside surface of the first half of the housing  16  of the test instrument. This allows the tray  10  to fit nicely within the first and second halves of the housing  16 ,  20  without taking up too much room. However, this also means that there is not a great deal of room to fit the fiber optic cable  12  either. 
         [0017]    Consequently, as shown in  FIG. 2 , the inside series of holes  28  and outside series of holes  32  are found on the portion of the main body  22  located after the transition ramp  40  where any permanent structures for providing bend radius control are impractical. Instead, a fixture  42  is provided with jig pins  44  that are configured to extend through the inside series of holes  30  and outside series of holes  32  temporarily so that the fiber optic cable  12  can be routed around these pins  44 . Once the cable  12  and any component  14  that is attached to its end have been positioned as desired, a piece of tape  46  near the first and second series of holes  30 , 32  and another piece of tape  46  located near the optical component  14  can be used to prevent the cable  12  from moving significantly. It should also be noted that the pins  44  are angled away from the center of the tray  10  so that any memory that is in the cable  12  will not cause the cable  12  to ride up the pins  44  and away from the main body  22  of the tray  10 , making routing of the cable  12  and its attachment to the tray  10  cumbersome. It is also preferable for the tray  10  to have a mounting hole  48  that allows the user to screw the tray  10  using a mounting bolt  50  to the top of the fixture  42 , ensuring that the tray  10  does not ride up on the jig pins  44  when the user is routing or attaching the cable  12 . Once the fiber optic cable  12  has been routed and attached to the tray  10 , the mounting bolt  50  holding the tray  10  and fixture  42  together can be removed and the fixture  42  can be separated from the tray  10 . The cable  12  will then relax slightly but not enough to cause a violation of its minimum bend radius or any performance losses associated therewith. 
         [0018]      FIG. 3  illustrates that the inside series of holes  30  and jig pins  44  form a first routing pattern  52  and that the inside routing channel  28  provides a pathway to continue the same routing pattern  52 . Similarly, the outside series of holes  32  and jig pins  44  form a second routing pattern  54  and the outside routing channel  26  provides a pathway to continue the same routing pattern  54 . Both the first and second routing patterns  52 , 54  consist of two different generally elliptical paths that are offset from each other with the inside and outside routing channels  28 , 26  being positioned opposite of the inside and outside series of holes  30 , 32 . A third routing pattern can be achieved by winding the cable  12  around the inside series of holes  30  with jig pins  44  and the outside routing channel  26 . Likewise, a fourth routing pattern can be realized by winding the cable  12  around the outside series of holes  26  with jig pins  44  and the inside routing channel  28 . 
         [0019]    Hence, the user has four different routes with three different route lengths from which to choose when routing the cable  12  and the component  14  that is attached to its end. So the user can compensate for long and short fiber lengths and tape the cable  12  and the component  14  that is found on its end in a predetermined spot as best seen in  FIG. 4 . Then the fixture  42  can be removed from the tray  10  after the mounting bolt  48  has been unscrewed (see  FIG. 5 ). 
         [0020]    Looking now at  FIG. 6 , the inside and outside routing channels  28 ,  26  are identical in construction and are attached to the main body  22  of the tray  10  using double sided tape (not shown). The channels  28 ,  26  have a C-shaped cross section that follows an arcuate path, ensuring that any cable  12  that is placed within the interior of the channels  28 ,  26  will not be bent to a radius that is less than its minimum bend radius. The channels  28 ,  26  have openings  56  near both ends and in the middle of the outside wall  58 . A ledge  60  also extends from the top of the inside wall  62  directly above these openings  56 . In use, a fiber optic cable  12  is slid between each ledge  60  and opening  56  consecutively until the cable  12  is continuously bound within the interior of the channels  28 ,  26 . The ledges  60  then serve to keep the cable  12  from inadvertently falling out of the channels  28 ,  26  provided that the cable  12  is kept taut. 
         [0021]    Finally, turning to  FIG. 7 , the left and right fiber clips  64 ,  66  are also identical in construction and are also attached to the main body  22  of the tray  10  next to two of the mounting flanges  24  by way of double sided tape (not shown) near the middle of the tray  10 . Thus, the left and right fiber clips  64 ,  66  help to define the elliptical routing paths  52 ,  54  discussed previously by being placed in the gaps found between the routing channels  28 ,  26  and the inside and outside series of holes  30 ,  32 . Each fiber clip  64 ,  66  comprises a tall L-shaped member  68  and a short L-shaped member  70  that face each other. The difference in height between the L-shaped members  68 ,  70  creates a gap  72  through which the cable  12  can slide to enter the clip  64 ,  66 . Then the user pushes down on the cable  12  until it is seated underneath the short L-shaped member  70 . The fiber optic cable  12  will not fall out of the clip  64 ,  66  at this point provided that the cable  12  is kept taut. 
         [0022]    Both clips  64 ,  66  are oriented such that the gap  72  is only accessible from the inside of the tray  10 . This helps to make sure that the cable  12  cannot fall out of the clip  64 ,  66  and ride up the mounting flanges  24  where the cable  12  could be pinched between the mounting flanges  24  and the second half of the housing  20 . This would cause damage to the cable  12  and require rework. Once the cable  12  has been properly routed using the inside and outside series of holes  30 ,  32  with jig pins  44 , the inside and outside routing channels  28 , 26 , and the left and right fiber clips  64 ,  66 , and after the cable  12  has been attached by tape  46  near the inside and outside series of holes  28 ,  30  with jig pins  44  and near the optical component  14  that is proximate to the center of the tray  10 , the fixture  42  can be removed and the test instrument assembled as mentioned earlier. 
         [0023]    As can be seen, this embodiment provides a tray  10  that can ease the assembly of a fiber optic test instrument, that can prevent any performance losses caused by kinked cable  12 , that allows the user to control the location of an optical component  14  that is attached to the end of the cable  12  without kinking the cable  12 , and that can minimize the space utilized within a test instrument for cable management. Of course the present invention is not limited to fiber optic cabling and could be achieved with more or fewer routing channels and clips than has been discussed. Therefore, the spirit and scope of this invention should be interpreted in view of the attached claims.