Abstract:
An improved, lower cost, optical fiber interconnect device of the type known as a “perfect shuffle” and processes for the preparation thereof. The present invention relates to devices that are smaller in size than prior art devices and that exhibit superior optical properties including lower attenuation loss (lower insertion loss) and to processes which produce such devices.

Description:
FIELD OF THE INVENTION 
     The present invention relates to optical fiber interconnect devices of the type known as a “perfect shuffle” and to processes for preparing such interconnect devices. More particularly, the present invention relates to devices smaller in size than prior art devices and to devices that exhibit superior optical properties including lower attenuation loss (lower insertion loss) and to fabrication processes which produce such devices. 
     BACKGROUND OF THE INVENTION 
     In applications for the transmission of information via laser light energy through optical fibers, the optical fibers are typically arranged into groups and these groups are assembled as ribbons that contain multiple optical fibers. The groups may be arranged into supergroups by stacking multiple optical fiber ribbons to form an array structure. Such an array is typically comprised of rows and columns of fibers, each row comprising all the fibers contained within a particular ribbon and each column comprising one particular fiber from each ribbon. When it is necessary to distribute information from one optical fiber in a row group to an optical fiber in a column group an interconnect device known in the art as a “perfect shuffle” is typically used. Since interconnection devices typically introduce loss when inserted into a fiber optic transmission system, it is desirable that losses within the device be as low as possible. Single mode optical fiber systems are desirable when large amounts of information need to be transmitted but are particularly sensitive to transmission losses related to precise alignment of fibers. Prior art devices typically create a physical connection within the device, such as a splice or other optical junction, between an incoming fiber and an outgoing fiber and this physical connection creates an optical loss within the interconnection device. 
     Thus a need exists for an optical fiber perfect shuffle interconnection device that can be easily manufactured and which achieves lower optical losses than prior art devices. 
     The present invention overcomes many of the limitations of the prior art and provides some additional benefits at reduced cost of manufacture. 
     SUMMARY OF THE INVENTION 
     There is disclosed and claimed herein an optical fiber interconnect apparatus of the type known as a “perfect shuffle” and methods of making this optical fiber interconnect apparatus, useful for connecting two M by N arrays of optical fibers, each array comprising M rows and N columns or N rows and M columns of fibers, wherein each row is identified by a first subscript i and each column is identified by a second subscript j, wherein a fiber at a input position ij of the input array is routed to a corresponding fiber at an output position ji of the output array, the method comprising: (a) assembling a first input array of optical fibers, comprising M optical fiber ribbons, where each ribbon comprises a row-group of fibers and (b) assembling a second output array of optical fibers, comprising N optical fiber ribbons, where each ribbon comprises a column-group of fibers so that a fiber at a position ij of the input array is routed to a corresponding fiber at a position ji of the output array. 
     The first input array of optical fibers is assembled by assembling a first group of ribbons each comprising a row-group of fibers. In a first ribbon assembly method, each ribbon is assembled by laying down a plurality of N optical fibers onto a first adhesive-coated carrier tape. The tape has a predetermined width, a first and second end and a centerline. Each fiber has a first end corresponding to the input array and a second end corresponding to the output array. A first portion of each fiber is placed on the adhesive-coated surface of the tape parallel to the centerline. The first fiber portion is chosen to be adjacent the first end of each fiber, with the first end of each fiber extending substantially beyond the first end of the carrier tape and the second end of each fiber extending substantially beyond the second end of the carrier tape. After the fibers are laid down on the first tape a second adhesive-coated carrier tape is positioned atop the first tape with the adhesive coated surface facing the adhesive coated surface of the first tape so that the first fiber portions are sandwiched between the first and second tapes to form the first optical fiber ribbon. The ribbon assembling step is then repeated until M ribbons are assembled. The M ribbons are stacked atop one another to form the first input array of fibers. 
     The second output array of optical fibers is created by assembling a second group of ribbons, each comprising a column-group of fibers. A first ribbon of the second group is assembled by selecting a first optical fiber from each row-group (i.e., each ribbon) of the first array. A second portion of each selected fiber is laid down onto a third adhesive-coated carrier tape. This second fiber portion is chosen to be adjacent the second end of each fiber, with the second end of each fiber extending substantially beyond the second end of the carrier tape. 
     The third adhesive-coated carrier tape has first and second ends and a centerline. The first end of the third tape is adjacent to the second end of the first and second tapes. Each fiber is placed on the adhesive-coated surface of the tape parallel to the centerline with the second end of each fiber extending substantially beyond the second end of the third carrier tape. A fourth adhesive-coated carrier tape is then positioned atop the third tape so that the selected fibers are sandwiched between the third and fourth tapes to form a first column-group optical fiber ribbon. 
     A second ribbon of the second group is assembled by selecting a second optical fiber from each row-group (i.e., each ribbon) of the first array and sandwiching these second optical fibers between third and fourth tapes to form a second column-group optical fiber ribbon. Successive ribbons of the second group are assembled by selecting successive optical fibers from each row-group (i.e., each ribbon) of the first array until N ribbons are assembled. The N ribbons are then stacked atop one another to form the second output array of fibers. 
     In a second assembly method the ribbons are formed by positioning the fibers in a side-by-side arrangement and coating them with a liquid adhesive that is then cured to form the ribbons. 
     Thus a fiber at input position ij of the input array is routed to a corresponding output position ji of the output array, without any splices or optical junctions within the device. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a first step for assembling a first ribbon of a first group; 
     FIG. 2 is a perspective view of a second step for assembling the first ribbon; 
     FIG. 3 is a perspective view of a third step for assembling the first ribbon; 
     FIG. 4 is a perspective view of an arrangement for stacking the first group of ribbons; 
     FIG. 5 is a perspective view showing the stacked group of first ribbons with a second group of fiber clamps installed. 
     FIG. 6 is a perspective view of a first step for assembling a first ribbon of a second group; 
     FIG. 7 is a perspective view of a second step for assembling the first ribbon of the second group; 
     FIG. 8 is a perspective view of a third step for assembling the first ribbon of the second group; 
     FIG. 9 is a perspective view showing the assembled device; 
     FIG. 10 shows an optional step of twisting the second groups ribbons into alignment with the first group of ribbons; 
     FIG. 10A is a sectional view identifying the array positions of the fibers of the input array; 
     FIG. 10B is a sectional view identifying the array positions of the fibers of the output array; 
     FIG. 11 shows an assembled device with a support sleeve over at least part of the first ribbons and at least part of the second ribbons; 
     FIG. 12 shows a second assembly method wherein a liquid adhesive is used to form the ribbons; 
     FIG. 13 shows a first step of a third assembly method, wherein the ribbons of a first array are formed simultaneously; 
     FIG. 14 shows a second step of a third assembly method, wherein the ribbons of a second array are formed simultaneously; 
     FIG. 15 shows a quality control method to verify the position of a fiber within an array. 
     FIG. 15A shows a typical signal created by the photodetector imaging a ribbon within an array. 
    
    
     DESCRIPTION OF THE INVENTION 
     The following description provides detail particular to a first assembly method depicted in FIGS. 1-9, a resulting apparatus in FIGS. 10-11, a second assembly method depicted in FIG. 12, a third assembly method depicted in FIGS. 13-14, and a quality control method depicted in FIGS. 15-15A. It is to be appreciated that the invention encompasses other assembly methods. For clarity of illustration an 8 by 8 fiber array is depicted in FIGS. 1-12 and a 4 by 4 array is depicted in FIGS. 13 and 14. It should be appreciated that larger arrays, such as a 12 by 12 array, a 16 by 32 array, or even larger arrays, would typically be assembled for use in commercial optical fiber telecommunication systems. 
     Referring to FIG. 1, a series of eight spools  20  of commercial glass optical fiber, such as a single-mode fiber known as “SMF 28” available from Corning Glass Works, are provided. Each of the eight fibers  22  is threaded through a guide  24  and the end of each fiber is secured in a clamp  26 - 1 . A first adhesive-coated tape  32 , such as a transparent polyester tape, is secured to an assembly surface  36  at a suitable distance from the guide  24 . The tape  32  has a first end  32 E 1  and a second end  32 E 2  and a centerline  32 C. 
     As seen in FIG. 2 the fibers  22  are drawn through the guide  24  until a suitable length is unwound. The clamp  26 - 1  is then positioned so that a suitable length of fiber extends beyond the second end  32 E 2  of the first tape  32 . A first portion  22 P 1  of each fiber  22  lying above the tape  32  is pressed down, adhering the fibers to the tape  32  in a side by side arrangement. 
     As seen in FIG. 3 a second clamp  26 - 2  is secured to the fibers adjacent to the guide  24 . The fibers  22  are then cut off just beyond clamp  26 - 2  so that suitable length of fiber  22  extends beyond the first end  32 E 1  of the first tape  32 . A second tape  42  is then applied atop the fibers  22  and tape  32 , sandwiching the portion  22 P 1  of the fibers  22  between tapes  32  and  42  to form a first row-group ribbon  12 - 1 . 
     The steps of FIGS. 1-3 are then repeated until eight ribbons  12 - 1  through  12 - 8  have been formed. As seen in FIG. 4 the eight ribbons are stacked and secured together to form an input array  12 A of fibers. Clamps  26 - 1  through  26 - 8  secure the fiber ends of ribbons  12 - 1  through  12 - 8  respectively. 
     As seen in FIG. 5 a second set of clamps  28 - 1  through  28 - 8  is added to secure the column positions of the fibers  22 . Clamp  28 - 1  secures a first fiber from each ribbon  12 - 1  through  12 - 8  to form a first column group; clamp  28 - 2  secures a second fiber from each ribbon  12 - 1  through  12 - 8  to form a second column group; and successive clamps  28 -n secure successive fibers from each ribbon  12 - 1  through  12 - 8  to form successive column groups. 
     As seen in FIG. 6 the array  12 A of fibers has been rotated by ninety degrees from the position shown in FIG.  5  and the first set of clamps  26 - 1  through  26 - 8  have been removed. In FIG. 6 a third adhesive-coated tape  52  is secured to the assembly surface  36 . The tape  52  has a first end  52 E 1  and a second end  52 E 2  and a centerline  52 C. 
     The clamp  28 - 1  is then positioned so that a suitable length of fiber  22  of the first column group extends beyond the second end  52 E 2  of the third tape  52 . A second portion  22 P 2  of each fiber  22  lying above the tape  52  is pressed down, adhering the fibers to the tape  52  in a side by side arrangement. A fourth tape  62  is then applied atop the first column group of fibers  22  and tape  52 , sandwiching the portion  22 P 2  of the fibers  22  between tapes  52  and  62  to form a first column-group ribbon  14 - 1 . 
     The steps of FIG. 6-8 are then repeated until eight ribbons  14 - 1  through  14 - 8  have been formed. As seen in FIG. 9 the eight ribbons are stacked and secured together to form an output array  14 A of fibers. From this figure it may be appreciated that the first fiber portions  22 P 1  of the ribbons of the input array  12 A and the second fiber portions  22 P 2  of the ribbons of the output array  14 A are spaced apart to define an intermediate fiber portion  22 P 3 . This intermediate fiber portion  22 P 3  may be encapsulated in a suitable encapsulant  10 E (shown as a transparent material for clarity of illustration) or may be covered with a sleeve  10 S, as will be described in conjunction with FIG.  11 . 
     As seen in FIG. 10, an optional step of twisting the second output group of ribbons  14  into alignment with the first input group of ribbons  12  may be performed so that the input and output ribbons lie in parallel planes. 
     The sectional view FIG. 10A shows the row and column identification of the fibers of the input array  12 A. The input ends of the fibers are identified with the symbol “IN” and the subscripts “i” and “j” indicate the respective row and column identification of the fibers. For example fiber IN 1,1  indicates the fiber in row position  1  and column position  1 , fiber IN 1,4  indicates the fiber in row position  1  and column position  4  and fiber IN 8,8  indicates the fiber in row position  8  and column position  8 . The sectional view FIG. 10B shows the row and column identification of the fibers of the output array  14 A. The input ends of the fibers are identified with the symbol “OUT” and the subscripts “i” and “j” indicate the respective row and column identification of the fibers. For example, fiber OUT 1,1  indicates the fiber in row position  1  and column position  1 , fiber OUT 4,1  indicates the fiber in row position  4  and column position  1  and fiber OUT 8,8  indicates the fiber in row position  8  and column position  8 . 
     It may be appreciated from FIGS. 10,  10 A and  10 B that the fiber identified as IN 1,1  in the input array is identified as OUT 1,1  in the output array, the fiber identified as IN 1,4  in the input array is identified as OUT 4,1  in the output array, and the fiber identified as IN 1,8  in the input array is identified as OUT 8,1  in the output array, thus establishing that a fiber at a position ij of the input array is routed to a corresponding fiber at an output position ji of the output array. 
     An assembled device  1  having a support sleeve  10 S positioned over at least part of the first input group of ribbons  12  and at least part of the second output group of ribbons  14  may be seen in FIG.  11 . 
     In a second assembly method, seen in FIG. 12, the ribbons  12  or  14  are formed by positioning the fibers  22  in a side-by-side arrangement and coating them with a liquid adhesive  72  that is then cured to form the ribbons. The adhesive may be applied by any suitable coating method. As shown, a group of fibers  22  is positioned on an assembly surface  36  having suitable non-stick properties and then the adhesive is hand-applied with a dispensing tool  74 . The adhesive-coated fibers are then illuminated with a radiant energy source  76  to cure the adhesive  72 . A fast-curing adhesive, such as an ultraviolet (UV) cureable adhesive, available from DSM Desotech of Elgin, Ill., may be used and cured with an ultraviolet source  76 . Alternately, a thermosetting adhesive may be used in conjunction with an infrared heat source  76 . 
     In the first and second methods, the M by N array  12 A is created by forming the ribbons  12 - 1  through  12 -M in a sequential manner. In contrast, in a first step of a third assembly method, seen in FIG. 13, the M by N array  12 A is created by forming the ribbons  12 - 1  through  12 -M simultaneously. In a preferred alternative of the third method the ribbons  12 - 1  through  12 -M are formed as a single wide ribbon  12 W, which is then slit into the individual ribbons  12 - 1  through  12 -M. The individual ribbons  12 - 1  through  12 -M are then stacked to form the input array  12 A. Alternately, the ribbons  12 - 1  through  12 -M may be separately formed in a side by side arrangement and then stacked to form the input array  12 A. In the third assembly method the ribbons may be formed by joining the fibers in a side by side arrangement either using a tape-joining method similar to the first assembly method or by an adhesive-joining method similar to the second assembly method. 
     For clarity of illustration FIGS. 13 and 14 show a 4 by 4 array  12 A, although any size array  12 A may be assembled employing the present invention. In FIG. 13 a series of sixteen spools  20  of glass optical fiber  22  are provided. The fibers are passed through a guide  124  which has a 4 by 4 row and column matrix of openings corresponding to the row and column positions of the array  12 A. A clip guide  126  is employed to capture a first row group of fibers  22 R- 1  adjacent to guide  124  and to guide these fibers into a slot  128 S 1  in guide roll  128 . A pinch device, such as a pinch roll or pinch shoe,  130 R 1  is lowered into position to hold the row group of fibers in slot  128 S 1 . The clip guide  126  is then released from the first row group of fibers  22 R- 1 . 
     The clip guide  126  is then employed to capture a second row group of fibers  22 R- 2  and to guide these fibers into a slot  128 S 2  in guide roll  128 . A pinch device  130 R 2  is lowered into position to hold the second row group of fibers in slot  128 S 2 . In a similar manner each row group of fibers up through group  22 R-M is positioned in corresponding slots  128 M and held in place by pinch device  130 M. The side-by-side positioned row groups of fibers  22 R- 1  through  22 R-M are then advanced through the adhesive coating assembly  140  and the curing assembly  144  and thus form the wide ribbon  12 W. The coating assembly  140  may be a roll-coater as shown or any other suitable coater. The curing assembly  144  comprises a housing  144 H and an ultraviolet lamp  144 L (similar to the light source  76  of FIG. 12) or other source of actinic radiation. The wide ribbon  12 W is advanced through the slitting assembly  150 , where slitting blades  150 B slit the wide ribbon  12 W into individual ribbons  12 - 1  through  12 -M, which are then stacked to form fiber array  12 A. 
     After a desired length of fiber array  12 A is formed, advance of the fibers  22  and the resulting ribbons  12  is stopped, slitting blades  150 B are retracted, adhesive coating assembly  140  is opened, the ultraviolet lamp  144 L is turned off, the curing assembly  144  is opened, and the pinch rolls  130  are retracted, releasing the fibers from the slots  128 . 
     As may be seen in FIG. 14, an N by M array  14 A is created by forming the ribbons  14 - 1  through  14 -N in a manner similar to the formation of ribbons  12 - 1  through  12 -M. The clip guide  126  is employed to capture a first column group of fibers  22 C- 1  adjacent to guide  124  and to guide this group of fibers into the slot  128 S 1  in the guide roll  128 . A pinch device  130 R 1  is lowered into position to hold the column group of fibers  22 C- 1  in slot  128 S 1 . The clip guide  126  is then released from the first column group of fibers  22 C- 1 . The clip guide  126  is then employed to capture a second column group of fibers  22 C- 2  and to insert this group of fibers into a slot  128 S 2  in guide roll  128 . The pinch device  130 R 2  is lowered into position to hold the second column group of fibers  22 C- 2  in slot  128 S 2 . In a similar manner each column group of fibers up through group  22 C-N is positioned in corresponding slots up through  128 N and held in place by pinch device  130 N. The side-by-side positioned column groups of fibers  22 C- 1  through  22 C-N are passed through the adhesive coating assembly  140 , the curing assembly  144  and thus form a wide ribbon  14 W. The wide ribbon  14 W passes through the slitting assembly  150 , where slitting blades  150 B slit the wide ribbon  14 W into individual ribbons  14 - 1  through  14 -N, which are then stacked to form the fiber array  14 A. 
     After a desired length of fiber array  14 A is formed, advance of the fibers is stopped, slitting blades  150 B retracted, adhesive coating assembly  140  and the curing assembly  144  are opened, and the pinch rolls  130  are retracted, releasing the fibers from the slots  128 . 
     In a production environment, the step of forming array  12 A and the step of forming array  14 A may be then repeated sequentially to form as many optical interconnection devices as may be desired. 
     In assembling the devices of the present invention it is important to assure that the individual fibers  22  are positioned accurately within the arrays  12 A and  14 A. A quality control method, depicted schematically in FIG. 15, is employed which utilizes optical sources and optical detectors. An end of each fiber  22  at the core of each fiber spool  20  is coupled to an optical source  90  using a conventional ferrule coupler. The optical source  90  is typically mounted on an end face of the spool  20  and utilizes a conventional slip-ring device  92  to connect it to an electrical energy source  94 . The optical sources  90  are selectively energized to illuminate each fiber  22  in a sequential manner. An optical detector arrangement  96  is used to detect which fiber  22  within the array is transmitting optical energy. 
     In contrast to prior art quality control methods which require access to both ends of a fiber within an interconnect device, and thus require cutting the interconnect devices apart, the present quality control method eliminates the need to cut the devices apart. The present quality control method is particularly useful in conjunction with the third assembly method. Each ribbon  12  or  14  may be passed over a curved mandrel assembly  97 M, causing the bend radius of each of the fibers  22  to be such that light in the fiber core evanescently couples from the fiber, i.e., the bend radius is less than the minimum loss-free bend radius for the fiber  22 . Light that escapes the fiber  22  when so bent may be detected by any suitable optical detector  96 D, such as a charge-coupled-device (CCD) camera. A line-scan camera  96 C having a suitable lens  96 L has been found suitable to image the bent portion of the individual fibers  22  of a ribbon  12  or  14  onto the one or more rows of photodetectors  96 P within the camera. The camera output signal  96 S may then be transmitted to a suitable controller  200 , which is typically implemented as a general purpose personal computer. The controller (computer) may be used to selectively energize the optical sources  90  and verify the row and column address ij of the detected optical signal  96 S from the illuminated fiber with the address ij of the energized optical source  90 . 
     FIG. 15 illustrates a typical analog signal  96 S from the camera  96 C. The analog signal may be transmitted to the controller  200  through a conventional interface module which converts the analog signal to a binary signal for subsequent analysis and array address detection. A camera having a built-in comparator circuit that converts the analog signal to a digital representation may also be used. Any suitable commercially available camera such as those available from Dalsa, Inc. or EG&amp;G Reticon may be used. 
     In operation the controller  200  causes the mandrel assembly  97  to move to an asserted position  97 P, causing the fibers  22  of the ribbon  12  or  14  to bend around the mandrel  97 M. Controller  200  then energizes one of the optical sources  90 , causing optical energy to be transmitted through the core of the corresponding fiber  22 . The camera  96 C images the bent portions of the fibers  22  on the mandrel  97 M through lens  96 L onto the photodetectors  96 P, causing a signal  96 S to be transmitted to the controller  200 . The signal  96 S is analyzed and the array address of the fiber  22  that is emitting light is calculated and compared to the address of the energized optical source. 
     For those skilled in the art further modifications should come to mind with the benefit of this invention. It is to be understood that a wide variety of modifications can be made to the present invention without departing from the spirit and the scope thereof. Such variations are claimed as the property and privilege of the invention herein.