Abstract:
A fiber tray for routing and packaging an optical fiber is disclosed. The fiber tray includes a generally round central section, a lead-in section, and a lead-out section. All three sections are integrally formed out of a thin sheet of a material and coated with a tacky adhesive material for fiber retention. The adhesive allows for fiber removal and rerouting if required. The tray includes guiding walls, which establish the path of the optical fiber on the tray. The optical fiber is routed in a single layer on the tacky surface of the fiber tray. The optical fiber is supported and immobilized essentially along its entire length, including the length of the optical fiber routed on the lead-in and the lead-out sections.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present invention claims priority from U.S. Patent Application No. 61/229,934 filed Jul. 30, 2009, entitled “Molded Fiber Tray with Adhesive Surface for Fiber Retention” which is incorporated herein by reference for all purposes. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to packaging of optical fiber, and in particular to fiber trays for routing and packaging optical fiber within optoelectronic devices. 
       BACKGROUND OF THE INVENTION 
       [0003]    Many modern electro-optical and optoelectronic devices include fiber-coupled components. Optical fibers of these components need to be routed within the devices. Optical fibers of different components or modules are coupled together by splicing. The splice locations need to be mechanically protected. 
         [0004]    Optical fiber has a number of unique packaging requirements that are different from those of an electrical wire, for example. One such requirement is that of a minimal fiber bending radius. The capability of an optical fiber to guide light is limited. When the optical fiber is bent at a radius less than a so-called minimum bending radius, the fiber begins to leak some light at the bend. Furthermore, the capability of the optical fiber to bend without structural damage is also limited. Most optical fibers are made of thin polymer-coated fused silica strands. When the optical fiber is bent beyond a minimal radius, the fused silica strand can develop microcracks, which can result in a fiber breakage. 
         [0005]    Another packaging requirement of optical fibers stems from somewhat random nature of an optical fiber splicing process. It is well known that no two splices are identical, and occasionally, a splicing operation will fail. When this occurs, an operator usually breaks the splice and splices the fibers again. To repeat the splicing, however, the operator needs to cut both optical fibers some length away (usually a few centimeters or more) from the splice break point, and prepare (strip and cleave) the fibers again. As a result of cutting the fibers, the total fiber length shortens and the optical fiber needs to be re-routed. To be able to reroute the fiber without an essential change of the fiber path within the device, the fiber is usually placed in loops within the device. For repeating the splicing operation, a length of the optical fiber, approximately equal to one loop length, is cut from both fibers being spliced, and the splicing operation is repeated. It is a good practice to loop the fibers at least three times on both sides of the splice point, to be able to repeat the splicing operation three times if so required. 
         [0006]    Yet another packaging requirement of optical fibers results from a well-known “springing” property of optical fibers. Even thin singlemode fibers have a tendency to straighten when left unattached to a tray or a mount. Although some “memory” of previous fiber coiling is present, the fiber usually does not simply stay bent as most electrical wires would. This calls for restraining the optical fiber within the device using clips and bobbins. 
         [0007]    Yet another packaging requirement of optical fibers results from sensitivity of optical performance of most optical fibers to a sharp mechanical stress, which is especially true for polarization-maintaining fibers. The optical fiber must be mechanically restrained in such a manner as to avoid sharp stress points on the fiber surface. In many cases, it is also preferable to prevent the optical fiber from randomly moving within the device. 
         [0008]    One of the simplest and most frequently used methods of routing an optical fiber within a device includes coiling the fiber on a flat surface such as a printed circuit board, using multiple clips or clamps attached to the flat surface along the fiber path for restraining the fiber. Although simple, this method does not prevent the fiber from moving because the clips usually allow for some leeway to prevent sharp stresses on the fiber, which are detrimental as noted above. Furthermore, the fiber can easily get entangled in the clips during routing, and different operators can use the same clip patterns to route the fiber slightly differently or even completely differently, which impacts reproducibility and reworkability of the devices. 
         [0009]    Another frequently used method is to use a fiber spool or bobbin for coiling the fiber. Referring to  FIG. 1 , a prior-art optoelectronic device  1  is shown including a printed circuit board  8  having mounted thereupon electrical connectors  12  and  14 , standoffs  11 , two electro-optical components  6 , a bobbin  16 , and two fiber connectors  2 . The electro-optical components  6  are fiber coupled with optical fiber  4  through stress-relieving elements  5 . The optical fiber  4  is wound on the bobbin  16 . The optical fiber  4  is held in place on the bobbin  16  using fasteners  38 . A detailed description of the optoelectronic device  1  is provided by Vanderhoof et al. in U.S. Pat. No. 6,208,797, which is incorporated herein by reference. 
         [0010]    Disadvantageously, the bobbin  16  cannot prevent the optical fiber  4  from moving at locations where the optical fiber  4  is not wound on the bobbin  16 . Furthermore, the bobbin  16  occupies valuable space on the printed circuit board  8 , as well as large overall volume over the printed circuit board  8 . In fact, a volume occupied by a prior-art bobbin, such as the bobbin  16 , can be at least an order of magnitude greater than the volume occupied by the optical fiber  4  wound on the bobbin  16 . Fiber bobbins disclosed by Grant et al. in U.S. Pat. No. 5,142,661 and by DeMeritt et al. in U.S. Pat. No. 5,659,641, incorporated herein by reference, have similar drawbacks. 
         [0011]    Rawlings in U.S. Pat. No. 5,469,526, incorporated herein by reference, discloses an optical fiber support in form of an oval “raceway” for guiding an optical fiber. Disadvantageously, the optical fiber support of Rawlings does not provide an adequate means for immobilizing the fiber within the raceway. Also, the raceway of Rawlings takes a large fraction of the overall volume within a package of the device. 
         [0012]    One method to immobilize an optical fiber without introducing an excessive mechanical stress is to use an adhesive surface with a tacky or a pressure-sensitive adhesive or simply using a single- or a double-sided sticky tape. Such an approach is disclosed, for example, by Parstorfer in U.S. Pat. No. 4,753,509, which is incorporated herein by reference, wherein an optical fiber is immobilized near fiber splice regions using “adhesive holding zones” placed near the fiber splices. Disadvantageously, the method of Parstorfer does little to immobilize the optical fiber in other regions of the device. 
         [0013]    The prior art is lacking a fiber tray that supports and immobilizes the optical fiber substantially along its entire length within the device while providing a repeatable routing of the optical fiber along a uniquely defined path, without having to occupy a considerable height or volume inside the package. Accordingly, it is a goal of the present invention to provide such a fiber tray. Furthermore, a fiber tray of the invention, while being thin, allows for easy fiber rerouting after the fiber length has changed due to re-splicing. 
       SUMMARY OF THE INVENTION 
       [0014]    A fiber tray of the invention is a thin, preferably monolithically formed, tray having narrow short walls uniquely defining a path of the optical fiber on a flat or nearly flat upper surface of the tray. The fiber tray has lead-in and lead-out sections, which may be disposed out of the plane of the upper surface, for supporting the fiber along most of its length inside the device, and an adhesive (tacky) layer on the upper surface for retaining the fiber after it has been routed. Due to the optical fiber being routed on a single even adhesive surface provided with lead-in and lead-out sections, the fiber tray of the invention occupies a much smaller overall volume than prior art fiber trays, while having enough rigidity to provide an adequate structural support for the optical fiber substantially along its entire length. 
         [0015]    In accordance with the invention there is provided a fiber tray comprising:
       a support member having a substantially flat top surface for supporting at least one loop of an optical fiber;   a lead-in member and a lead-out member, each having a top surface for guiding the optical fiber from an input location to the top surface of the support member to an output location, the top surface of the support member and the top surfaces of the lead-in and lead-out members together forming a continuous fiber carrying surface for supporting the optical fiber substantially along its entire length between the input and the output locations;   first and second walls extending generally upwardly from the fiber carrying surface, so as to define, on both sides, a continuous guiding path for the optical fiber in going from the input location to the output location;   and   a mounting member for mounting the fiber tray;   wherein the fiber carrying surface has an adhesive layer thereon, for affixing the optical fiber thereto.       
 
         [0022]    In one embodiment, the fiber tray is formed out of a thin sheet of material, of the order of thickness of the optical fiber it is supporting, or even less than the thickness of the optical fiber, to minimize the overall thickness of the fiber tray. Due to the presence of the adhesive layer, traditional fiber restraining elements such as clips, straps, or high walls are not required, which allows the entire fiber tray to be very thin as noted above. 
         [0023]    In accordance with another aspect of the invention there is further provided an optoelectronic assembly comprising the fiber tray and a printed circuit board, wherein the mounting member extends generally downwardly for mounting to the printed circuit board, such that the support member clears electronic components mounted on the printed circuit board. 
         [0024]    In accordance with another aspect of the invention there is further provided a method of routing an optical fiber using the fiber tray, including:
       (a) attaching the fiber tray to a device having first and second fiber coupled components having first and second optical fibers;   (b) routing the first optical fiber on the top surface of the lead-in member and coiling the first fiber on the flat top surface of the support member proximate to the first wall; and   (c) routing the second optical fiber on the top surface of the lead-out member and coiling the second fiber on the flat top surface of the support member proximate to the second wall, in a direction opposite to a direction of coiling of the first fiber.       
 
         [0028]    In accordance with yet another aspect of the invention there is further provided a method of building an optoelectronic device, including:
       (d) routing the optical fiber on the fiber tray;   (e) marking the first and the second optical fibers proximate to a splice mounting location on the support member;   (f) cutting the first and the second fibers at the marked locations;   (g) splicing the first and the second fibers; and   (h) re-routing the first and the second optical fibers so as to coil the first and the second optical fibers on the support member in opposite directions, and affixing the splice at the splice mounting location.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]    Exemplary embodiments will now be described in conjunction with the drawings in which: 
           [0035]      FIG. 1  is a three-dimensional view of a prior-art optoelectronic device having a bobbin for routing an optical fiber; 
           [0036]      FIG. 2A  is a three-dimensional view of a fiber tray of the present invention; 
           [0037]      FIG. 2B  is a side view of the fiber tray of  FIG. 2A ; 
           [0038]      FIG. 3  is a top view of a transponder device of the invention having the fiber tray of  FIGS. 2A and 2B  for fiber routing and support; 
           [0039]      FIGS. 4A to 4D  are top views of the transponder device of  FIG. 3  as the optical fiber is routed on the fiber tray of the transponder device; and 
           [0040]      FIGS. 5A and 5B  are views of devices having fiber trays of the invention mounted in a swing-out configuration along a side of the devices. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0041]    While the present teachings are described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments. On the contrary, the present teachings encompass various alternatives, modifications and equivalents, as will be appreciated by those of skill in the art. 
         [0042]    Referring to  FIGS. 2A and 2B , a fiber tray  200  of the invention includes a support member  202  having a substantially flat top surface  203  for supporting at least one loop of an optical fiber, not shown; a lead-in member  204  having a top surface  205 ; and a lead-out member  206  having a top surface  207  for guiding the optical fiber from an input location  208  to the top surface  203  of the support member  202  to an output location  210 . The top surfaces  205  and  207  of the lead-in and the lead-out members  204  and  206 , respectively, together with the top surface  203  of the support member  202  form a continuous fiber carrying surface for supporting the optical fiber substantially along its entire length between the input and the output locations  208  and  210 . The fiber carrying surface has an adhesive layer on top, not shown, for affixing the optical fiber to the surface. A “tacky” adhesive layer, allowing removal and repositioning of the optical fiber along a required path, is preferable. If the optical fiber needs to be moved, reworked, or repositioned, the adhesive layer provides an effective means of doing so without risking damaging the optical fiber. Other types of adhesive layers, such as curable epoxy layers, can also be used. The adhesive layer is preferably disposed over the entire fiber carrying surface. 
         [0043]    The adhesive material to be applied to the fiber carrying surface of the fiber tray  200  should provide enough adhesion for the optical fibers  310 A and  310 B to be permanently attachable to the fiber tray  200 . Yet, the adhesive should be yielding enough to allow the optical fibers  310 A and  310 B to be removable. Preferably, the adhesive should allow for fiber removal and re-routing for at least  30  days. If a rework is required after  30  days, the adhesive layer can be removed and re-applied to the tray  200 , or the tray  200  can be replaced. The latter is actually preferable from the economical standpoint, because the tray  200  is very inexpensive when produced in large quantities, 
         [0044]    The fiber tray  200  includes outer and inner walls  212  and  214 , respectively, extending upwardly from the fiber carrying surfaces  203 ,  205  and  207 , so as to define a continuous guiding path for the optical fiber in going from the input location  208  to the output location  210 . The walls  212  and  214  together define the guiding path on both sides of the path. 
         [0045]    The fiber tray  200  further includes mounting members  216 A to  216 E for mounting the fiber tray  200 . In the embodiment shown, five mounting members  216 A to  216 E are used, although any number, including only one suitably placed mounting member, can be used. The mounting members  216 A to  216 E extend generally downwardly from the support member  202 , lead-in member  204 , and the lead-out member  206 , for mounting to a base, not shown. The support member  202  includes a recessed splice mounting location  220  for mounting a fiber splice, not shown. 
         [0046]    The fiber tray  200  further includes optional rigidity bars  218 , for increasing rigidity of the support member  202 . The walls  212  and  214  function as “rigidity ribs”, thereby improving overall rigidity of the fiber tray  200 . As a result, the fiber tray  200  is thin but rigid enough to reliably support the optical fiber routed on its fiber carrying surface. The support member  202 , the lead-in and the lead-out members  204  and  206 , respectively, the walls  212  and  214 , and the mounting members  216 A to  216 E are preferably integrally formed using a suitable manufacturing process such as injection molding or vacuum forming. 
         [0047]    Referring now to  FIG. 3 , a transponder device assembly  300  has the fiber tray  200 , a printed circuit board  302  populated with electronic components  304 , a receiver photodiode  305 , a transmitter laser diode  306 , a modulator, not shown, for modulating light of the transmitter laser diode  306 , and an enclosure  308  supporting the printed circuit board  302 , the receiver photodiode  305 , the transmitter laser diode  306 , and the fiber tray  200 . The transmitter laser diode  306  (also called “Integrated Tunable Laser Assembly”, or ITLA) is mounted below a level of the printed circuit board  302 , and is disposed in an opening  303  in the printed circuit board  302 . 
         [0048]    The receiver photodiode  305  is coupled to an optical fiber  307  that is external to the enclosure  308 . The modulator is coupled to an optical fiber  310 A that is fed through a slot  309  in the printed circuit board  302  towards the input location  208 . The modulator is disposed under the printed circuit board  308  and not seen in  FIG. 3 . The optical fiber  310 A is supported by the lead-in member  204 , being routed proximate to the inner wall  214  of the support member  202  of the tray  200 . The optical fiber  310 A is looped three times on the top surface  203  of the support member  202  so as to form a flat spiral having a gradually increasing radius, without overlapping. The optical fiber  310 A ends at a splice  312  mounted at the splice mounting location  220 . The splice  312  couples the optical fiber  310 A with an optical fiber  310 B leading to the transmission laser diode  306 . The laser diode optical fiber  310 B is looped three times on the top surface  203  of the support member  202  proximate to the outer wall  212  thereof, so as to form a flat spiral having a gradually decreasing radius. The laser diode optical fiber  310 B is supported by the lead-out member  206 , down to the output location  210 . The laser diode optical fiber  310 B is fed through the same slot  309  in the printed circuit board  302  and toward the laser diode  306 . The top surface  203  of the support member  202  and the top surfaces  205  and  207  of the lead-in and lead-out members  204  and  206 , respectively, together form the continuous fiber carrying surface for supporting the optical fibers  310 A and  310 B substantially along the entire length between the input and the output locations  308  and  310 , except for a short length over the fiber splice mounting location  220 , and a lead-in location  311  wherein the modulator optical fiber  310 A enters the upper surface  203  of the support member  202 . The fiber carrying surface at the input and the output locations  308  and  310  is at a lower height than a height of the flat top surface  203  of the support member  202 . Thus, the lead in and lead out members  204  and  206 , respectively, provide a smooth and continuous fiber support as they ramp up and down to the top surface  203  of the support member  202 . 
         [0049]    One of the key advantages of the fiber tray  200  of the invention is that it can be made very thin, thus saving valuable space within the package  308 , allowing the package  308  to be thinner and/or providing more space for heat removal through air convection. The fiber tray  200  can me made out of a thin plastic sheet having a thickness smaller than a diameter of the optical fibers  310 A or  310 B. A practical range for the flat sheet thickness is between 0.04 mm to 1.0 mm. The flat sheet is preferably less than 0.6 mm thick. The inner and the outer walls  214  and  212  are preferably less than 1.5 mm high, but taller than a diameter of the optical fiber  310 A and  310 B, so that the walls  212  and  214  can protect the optical fiber  310 A and  310 B when the fiber tray  200  is placed upside down on a flat surface, or when it is covered with a flat sheet of material. For example, for a standard 0.9 mm diameter optical fiber, the walls  212  and  214  can be 0.9 mm to 1.0 mm high. The fiber tray  200  can be made so thin that it occupies a geometrical volume inside the enclosure  308 , comparable to the geometrical volume occupied by the optical fibers  310 A and  310 B themselves. By way of example, in the transponder device assembly  300 , the optical fibers  310 A and  310 B occupy a total volume of approximately 1000 mm 3 , and the fiber tray occupies a volume of approximately 2000 mm 3 . 
         [0050]    The mounting members  216 A to  216 E extend downwardly (away from the viewer in  FIG. 3 ) for mounting to the printed circuit board  302 . The height of the mounting members  216 A to  216 E is selected so that the support member  202  clears the electronic components  304  mounted on the printed circuit board  302 . The mounting members  216 A,  216 C, and  216 D are affixed to the printed circuit board  302  at locations wherein the printed circuit board  302  is attached to the enclosure  308  using common screws  322 , thus making more area on the printed circuit board  302  available for mounting the electronic components  304 . The mounting members  216 B and  216 E are support legs for supporting the fiber tray  200 . The mounting members  216 B and  216 E also serve as alignment features for aligning the fiber tray  200  to the printed circuit board  302 . 
         [0051]    Still referring to  FIG. 3 , the fiber tray  200  is dimensioned to support up to six loops of a standard 0.9 mm optical fiber arranged in a flat spiral. A total length of the optical fibers  310 A and  310 B is about 1700 mm. The dimensions and shape of the fiber tray  200  are such that a minimum bending radius of 25 mm is guaranteed along the entire fiber length. Unlike in prior-art spools and bobbins, the optical fibers  310 A and  310 B are supported in a single layer. 
         [0052]    Although the fiber tray  200  is shown as having only two lead-in/lead-out members  204  and  206  and only one fiber mounting location  220 , a fiber tray of the invention can have more lead-in or lead-out members and more splice mounting locations, as required. The top surfaces of these lead-in and lead-out members are preferably disposed at different heights for avoiding one segment of an optical fiber crossing another while resting thereupon, to avoid a sharp bending of the optical fiber. 
         [0053]    Turning now to  FIGS. 4A and 4B , the process of fiber routing in the transponder device  300  is illustrated. The modulator fiber  310 A is routed on the top surface  205  of the lead-in member  204  and is coiled on the flat top surface  203  of the support member  202  proximate to the inner wall  214 , as shown in  FIG. 4A . Three loops of the fiber  310 A are formed. The laser fiber  310 B is routed on the top surface  207  of the lead-out member  206 , with the end  402  of the laser fiber  310 B initially remaining free as shown at  402  in  FIG. 4A , wherein the laser fiber  310 B is called “ITLA fiber”. Then, the laser fiber  310 B is coiled on the flat top surface  203  of the support member  202  proximate to the outer wall  212  forming three loops. The laser fiber  310 B is coiled in a direction opposite to a direction of coiling of the modulator fiber  310 A, as shown in  FIG. 4B . It is also seen in  FIG. 4B  that the laser fiber  310 B is routed above the modulator fiber  310 A at a location  404 . The location  404  corresponds to the location  311  in  FIG. 3 . 
         [0054]    Once both fibers  310 A and  310 B are coiled, they are marked proximate to the splice mounting location  220  on the support member  202 . Then, the fiber coils are unwound, the fibers  310 A and  310 B are cut at a fixed offset from the marked locations, and the optical fibers  310 A and  310 B are spliced. Then, the optical fibers  310 A and  310 B are re-routed and re-coiled again, so as to coil the optical fibers  310 A and  310 B on the support member  202  in opposite directions. Then, the splice  312  is affixed to the support member  202  at the splice mounting location  220 . Because the top surfaces  205 ,  207 , and  203  of the fiber tray  200  are coated with an adhesive, the fibers  310 A and  310 B will remain coiled when the routing procedure is completed. 
         [0055]    Referring to  FIGS. 4C and 4D , the fiber routing procedure is illustrated again, but with the optical fibers  310 A and  310 B coiled not as tightly as is shown in  FIGS. 4A and 4B . When the optical fibers  310 A and  310 B are coiled not as tightly, more fiber length can be accommodated on the fiber tray  200 . This feature of the fiber tray  200  allows one to relax the fiber length tolerance. 
         [0056]    Turning to  FIG. 5A , an optoelectronic assembly  500 A is shown in a three-dimensional view. The fiber assembly  500 A has a base  502 , a printed circuit board  503  disposed in the base  502 , and a fiber tray  505  mounted to the base  502  in a swing-out configuration. The fiber tray  505  is an embodiment of the fiber tray  200  of  FIGS. 2A ,  2 B,  3 , and  4 A to  4 D, having mounting members  504  that are different from the mounting members  216 A to  216 E. The mounting members  504  include swing members or hinges, that allow the fiber tray  505  to rotate out at an acute angle from an upper surface of the base  502 , i.e. non-parallel to a plane of the upper surface of the base  502 , for ease of fiber routing and also to provide an easy access to the printed circuit board  503 . Ideally, the swing member  504  extends along a side of the base  502  and the printed circuit board  503  defining an axis of rotation for the fiber tray  505 . The input/output locations of the optical fibers  310 A and  310 B are preferably disposed near the hinges  504 , to allow the fiber tray  505  to be swing in and out of the plane of the base  502 , while having the optical fibers  310 A and  310 B mounted thereon. 
         [0057]    Since the fiber tray  505  is only about one millimeter thick, a “book” of a plurality of fiber trays  505  can be made. Referring to  FIG. 5B , an optoelectronic assembly  500 B is shown in a side view. A plurality of the mounting fiber trays  505  are included with all of the hinges  504  disposed along a same side  508  of the base  502 . After all the optical fibers are routed, the “book”  510  can be “closed”, as indicated at  506 .