Abstract:
A coupler to interconnect or couple optical fibers together and position ends of the optical fibers juxtaposed with each other, additionally includes a captive split tubular alignment sleeve to accept ferrules on ends of optical fibers to be aligned and coupled. The coupler may be incorporated into an opto-electronic module, captured, and then held against normal forces of connecting and disconnecting the optical fiber. A short optical fiber extends from the coupler through a wall of an enclosure and is terminated adjacent an opto-electronic device to carry optical signals for transmission or reception of optical signals. This coupler may be further used to splice or interconnect optical fibers, in temporary connections or splices, without fusing the glass of the fibers.

Description:
CROSS REFERENCE TO RELATED CO-PENDING UNITED STATES PATENT APPLICATIONS 
     The present application is related to the following commonly assigned and co-pending United States Patent Applications: 
     U.S. Ser. No. 09/809,699, entitled: COMPACT OPTICAL TRANSCEIVERS INCLUDING THERMAL DISTRIBUTING AND ELECTROMAGNETIC SHIELDING SYSTEMS AND METHODS THEREOF; 
     U.S. Ser. No. 09/809,531, entitled TECHNIQUE AND APPARATUS FOR COMPENSATING FOR VARIABLE LENGTHS OF TERMINATED OPTICAL FIBERS IN CONFINED SPACES; and 
     U.S. Ser. No. 09/809,127, entitled: HIGH FREQUENCY MATCHING METHOD AND SILICON OPTICAL BENCH EMPLOYING HIGH FREQUENCY MATCHING NETWORKS; all filed concurrently herewith and all incorporated herein as a part hereof. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to the field of optical signal transmission and reception over optical fibers and, more specifically, to the interconnection of optical fibers within a transceiver module with optical fibers and connectors of an optical fiber cable. 
     BACKGROUND OF THE INVENTION 
     In order to interconnect network optical fibers to opto-electronic devices, such as transmit optical sub-assemblies or receive optical sub-assemblies of a computer or server, a typical technique uses a relatively, long optical fiber or pigtail with an interfacing connector on one end thereof. The optical fiber and connector are typically assembled with the optical fiber routed to an opto-electronic device which either produces or receives an electronically generated and controlled optical signal. The assembled device is installed into a host device, and the interfacing connector then is positioned and fixed to the host device. 
     This handling and positioning of a relatively long pigtail of optical fiber seriously exposes the optical fiber pigtail to damage and breakage, because the optical fiber is very fragile and cannot be sharply bent. Any rough handling or sharp bending of an optical fiber, during manufacture and assembly will cause cracking or breakage of the optical fiber, thereby rendering the optical sub-assembly useless and necessitating replacement of the optical fiber. Replacement of the optical fiber is not always practical, resulting in the entire opto-electronic subassembly becoming useless. 
     Because the pigtail may be exposed to outside forces after assembly, the optical fiber continues to be subject to damage and must be shielded and protected as well as being provided with connection techniques that will not damage the optical fiber. 
     Consequently, it is desirable to prevent such possible damage by making the pigtail as short as possible to prevent excessive stresses on the optical fiber pigtail during assembly and handling. 
     OBJECTS OF THE INVENTION 
     It is an object of the invention to couple a pair of optical fibers together in a simple, reliable manner. 
     It is another object of the invention to couple a pair of optical fibers without the use of any special tools. 
     It is a further object of the invention to eliminate the use of long and easily damaged pigtails of optical fiber of opto-electronic devices and modules. 
     It is an additional object of the invention to reduce the incidence of breakage of optical fibers, which are attached to opto-electronic devices, during assembly and handling. 
     It is still another object of the invention to permit minor misalignment of an opto-electronic device of a transceiver module relative to a connector by utilizing a short pigtail of optical fiber, and which is entirely contained within the module and protected from damage. 
     Other Objects of the Invention will become apparent to one of skill in the art once the invention is fully understood. 
     SUMMARY OF THE INVENTION 
     In order to accomplish the objects of the invention and overcome the problems and shortcomings of the prior art approaches to fabricating and assembling opto-electronic modules with long optic fiber pigtails, any associated potential for pigtail damage must be considered during the critical periods of assembly and connection, where breakage or damage is most likely. Utilizing an optical fiber coupler to interconnect the optical fibers, an optical signal transmitter/receiver module which houses the opto-electronic devices and supports couplers for the optical fibers does not require long optical fiber pigtails. 
     This optical fiber coupler utilizes a pair of mating, snap-together, tubular shells or members in order to trap and contain a split tubular sleeve. The split tubular sleeve will admit the ends of optical fibers and ferrules attached to the optical fibers and position the optical fiber ends in an aligned, juxtaposed position, thus permitting maximum light transmission across the gap interface between end faces of the optical fibers. 
     The coupler structure is provided with exterior annular recesses and flanges which mate with a support cradle having complementary flanges and recesses. The support cradle is disposed in and retained in an extended portion of a transceiver module housing. Once assembled, the aligned notches in a cover of the transceiver module housing wall and one wall of a mating module housing cover form a port. An optical fiber may extend through the resulting port and extend between the opto-electronic devices within the module housing and the coupler in the extended housing. The extended housing forms a channel for each coupler and further guides the external cable connector as the ferrule of an external cable connector is inserted into the split coupling sleeve of the coupler. 
     The most fragile part of the entire opto-electronic transceiver module is the short pigtail of optical fiber extending through an opening in the wall and into the coupler. The coupler allows fixed mounting and retention of the exterior end of an optical fiber, minimizing the potential for damage to the optical fiber during both assembly of the transceiver module and later use of the module such as during connection or disconnection of external optical fiber ends. 
     This Summary of the Invention is provided as a brief summary description of the invention and is not intended to be used to limit the scope of the invention in any manner. 
     A more detailed and complete understanding of the invention may be acquired from the attached drawings and the Detailed Description of the Invention which follow. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric view of the optical fiber coupler of the invention in its assembled form, viewed from the exterior end thereof. 
     FIG. 2 is an isometric view of the optical fiber coupler of the invention in its assembled form, viewed from the interior connection end thereof. 
     FIG. 3 is an exploded isometric view of the optical fiber coupler of the invention viewed from the exterior connection end thereof. 
     FIG. 4 is a section view, taken along line  4 — 4  in FIG. 1 of the coupler of the invention, with a transceiver terminated optical fiber and associated ferrule disposed in connection with the coupler. 
     FIG. 5 is an exploded view of a transceiver module in which the coupler is installed in the preferred embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     OF 
     THE BEST MODE AS CONTEMPLATED BY THE INVENTORS FOR CARRYING OUT THE INVENTION 
     Referring initially to FIGS. 1 and 2, the coupler  8  of the invention is illustrated in elevated isometric views from each end thereof. 
     An optical fiber  10  is shown inserted into a ferrule  12 . The ferrule  12  is attached to the optical fiber  10  either by potting the optical fiber  10  within the ferrule  12  with an epoxy or other hard setting potting compound to fix the optical fiber  10  relative to ferrule  12 . If the optical fiber  10  is metal clad, the ferrule  12  and the clad optical fiber  10  may be soldered. Polished end face  11  of optical fiber  10  is preferably flush with the end face  26  of the ferrule  12  and the end face and the optical fiber are slightly rounded into a convex end face  26 . The ferrule  12  is shown inserted into a first coupler member  30 . 
     A plurality of latch retainers  18  are formed on one end  16  of the first coupler member  30 . Latch retainers  18  each have tapered surfaces  20  which converge and form camming surfaces  20  so they engage the enlarged portion  22  of ferrule  12 . Latch retainers  18  are forced to flex and permit the passage of enlarged portion  22  of ferrule  12  during connection of optical fibers  10 . After ferrule  12  is inserted fully into the coupler member  30 , the latch retainers  18  flex to their original form, and thus dispose latch faces  24  juxtaposed with the rear end face  26  of ferrule  12 . This latching action retains the ferrule  12  and its attached optical fiber  10  relative to the coupler member  30 . 
     In general, the key aspect of coupling two optical fibers  10  is that the end faces  11  of the fiber  10  must be placed very closely juxtaposed to each other and must be as precisely aligned as possible. Also, the end faces  11  of the optical fibers  10  should be perpendicular to the axis of the fiber  10 . This may be readily accomplished by potting the optical fiber  10  or soldering the optical fiber  10  to the ferrule  12 ,  13  and then polishing the fiber end  11  with a slight radius so as to physically contact the ends of both fibers upon insertion within sleeve  60 . 
     Refer now to FIG.  2 . The manufacturing of various surfaces on the coupling members  30 ,  40  ferrules  12 ,  13  and the interior passage  28  therethrough is virtually impossible to control to a degree necessary to insure precise alignment of the axis of optical fiber  10  and a ferrule  12  with a second coupled optical fiber  10  and a second ferrule  13 . 
     The structure of the first coupler member  30  is formed with openings  32  defined by surfaces  34 . The openings  32  and, more particularly, surface  34  which is most distant from the ferrule  12  provide latch surfaces to engage the second coupler member  40 . 
     Second coupler member  40  is inserted into the end  42  of the first coupler member  30  distal from the ferrule  12 . The second coupler member  40  latches to the first coupler member  30  as will be described below with reference to FIGS. 3 and 4. 
     Again referring to FIGS. 1 and 2, the second coupler member  40  has an extending tubular section  44  with an opening  46  in exterior end  48 , the end  48  distal from and projecting away from the mating end  42  thereof which mates with and latches to the first coupler member  30 . 
     The tubular section  44  provides an entrance port through opening  46  for insertion of a second ferrule  13 , similar to ferrule  12 . To assist in the insertion of a ferrule  13  into the coupler member  40 , a mating connector housing  45  may be disposed around ferrule  13 . Additionally, exterior surface  50  of section  44  provides a guide for a mating connector  47  which includes ferrule  13  to assist in the insertion of ferrule  13  into optical fiber alignment sleeve  60 . 
     Confined within the assembled coupler members  30 ,  40  is a split tubular optical fiber alignment sleeve  60 . Alignment sleeve  60  provides an aligning function for the ferrules  12 ,  13 . Aligning the ferrules  12 ,  13  and the optical fibers  10  with a moveable or floating split sleeve  60  allows additional freedom for movement of the ferrules  12 ,  13  in relation to coupler members  30 ,  40  and, therefore, reduces costs. The inside diameter of the split sleeve  60  is slightly smaller than the diameter of the mating ferrules  12 ,  13  and is forced open or spread at the split to admit the ferrules  12 ,  13  and the optical fiber cable ferrule  13  into each end of the sleeve  60 . The insertion of ferrules  12 ,  13  forces sleeve  60  to open and causes the ferrules  12 ,  13  to be frictionally retained within the coupler  8 ; the constricting spring force of the sleeve  60  centers ferrules  12 ,  13  and thereby centers and axially aligns the optical fibers  10  relative to the sleeve  60  and thus relative to each other. With proper dimensional control of the projecting ends  70 , the end faces  26  of ferrules  12 ,  13  are finally disposed closely juxtaposed with each other within the sleeve  60  and closely aligned for maximum coupling and transfer of the optical signals between the two optical fibers  10 . 
     Referring to FIG. 3, mating ferrules  12 ,  13  and the components of the coupler assembly  8  are illustrated in an exploded isometric view, along with the mating ferrules,  12 ,  13 . The first coupler member  30  is formed with longitudinal channels  52  formed and spaced around the interior periphery of the central channel  46  through member  30 . The grooves  52  are formed to accept and constrain against lateral or twisting movement of latching retainer arms  54  within first coupler member  30 . The channels  52  are aligned with the openings  32  through the sidewall  35  of the first coupler member  30 . The concave surface  58  of the first coupler member  30  restricts but does not eliminate the amount of lateral freedom of split sleeve  60 . 
     The end surface of lands  56  engage segmented annular surface  62  intermediate latching retainer arms  54  of the second coupler member  40  to prevent excessive insertion forces being transferred by the coupler member  40  onto the split sleeve  60 . While split sleeve  60  possesses sufficient resilience in a radial direction to firmly grip the projecting end  70  of the ferrules  12 ,  13 , the sleeve  60  does not possess sufficient columnar strength to withstand axial compression by the coupler members  30 ,  40 . Therefore, the sleeve  60  must spread or open at the split  64  to admit ferrules  12 ,  13  and withstand the insertion forces. 
     Latch fingers  54  of coupler member  40  are long enough to dispose latch portions  68  within opening  32 , positioning latch surface  66  juxtaposed with surface  34  once fully inserted to the point that lands  56  are engaged with segmented annular surface  62 . The internal channels  28  of coupler members  40  are dimensioned so that the diameters are larger than the outside diameter of sleeve  60  as expanded by the ferrules  12 ,  13 . 
     Referring now to FIG. 4, a sectional view of the assembled coupler members  30 ,  40  containing split sleeve  60  is illustrated. First coupler member  30  is formed during a molding operation to include at least a significant segment of an internal annular flange surface  84 . The annular flange surface  84  preferably is interrupted with gaps therein corresponding to and aligned with the arcuate spans of the openings  32  extending through the sidewalls  35  of the first coupler member  30 . The flange surface  84  or flange segment surfaces  84  define a barrier with an opening diameter smaller than the outside diameter of the undeflected or unexpanded sleeve  60 . 
     Similarly, the second coupler member  40  is formed to have a reduced diameter entry port  86  in the end  48  thereof, relative to the outside diameter of the unexpanded sleeve  60 . The entry port  86  is defined by an inwardly extending radial flange  88  forming an annular flange surface  90 . Flange surface  90  and flange surface  84  cooperate to trap and retain sleeve  60  within the assembled coupler  8 . Sleeve  60  is intentionally shorter than the axial distance between flange surfaces  84 ,  90  so as to prevent a columnar compression of the sleeve  60  during assembly of the coupler members  30 ,  40  into coupler  8 . 
     Flange  80  is formed extending radially from the exterior surface of coupler member  40  at a position which forms or leaves an annular recess  82  between surface  56  of coupler member  30  and flange  80 . The flange  80  provides a pair of surfaces  94  which may be accepted by cradle  112  or cradle member  112 . Cradle  112  has complementary inwardly extending partial or complete flanges  113  to hold the coupler member  40  against axial dislocation from the forces of insertion of the ferrule  13  into sleeve  60  and the forces encountered upon disconnection or withdrawal of ferrule  13  from sleeve  60 . 
     A transceiver module may be advantageously constructed using the coupler assembly  8 . 
     FIG. 5 illustrates an exploded isometric form of such a transceiver module  100 . The transceiver module  100  comprises a base  102 , an electronic circuit board  104  or circuit card  104 , a transmit optical subassembly  106  (TOSA), a receive optical subassembly  108  (ROSA), a cover  110 , a cradle  112 , a coupler  8 , and a coupler cradle cover  116 . 
     The base  102  is preferably fabricated from aluminum or other metal or alloy with high thermal conductivity properties. Base  102  is formed or otherwise provided with a port  120  or opening  120  that will accept a connector (not shown) for connecting the circuit board or card  104  to the electronics of a host device (not shown). Conventional connectors may be used to accomplish such connections; alternatively, electronic connections may be provided with a plurality of via connections through base  102  and may be attached by a solder ball array on the via connections to an electronic circuit board of the host (not shown). 
     An electronic circuit board  104  is disposed inside chamber  122  formed within and by the base  102  and supports conductors  124  and electronic components  126  mounted on the circuit board  104  to drive, control or convert and convey electronic signals to and from the TOSA  1060  and ROSA  108 , respectively. 
     The base  102  is formed or otherwise provided with pedestals  130  on the floor  132  of base  102 . The pedestals  130  support the ROSA  108  and the TOSA  106  and are generally aligned with holes or slots  134  formed in one of the walls  136  of enclosure  138  of base  102 . The slots  134  permit easy insertion into and passage of single optical fibers  10  through the wall  136 , and thus interconnect the opto-electronic subassemblies  106 ,  108  to couplers  8 . 
     Base  102  is further provided with an extension  140  for supporting optical fiber couplers  8  on a shelf-like member  140  which extends from the enclosure  138  and is formed to accept and retain a cradle  112 . The cradle  112  is formed to have a partial annular groove  114  in the interior thereof to accept and capture flange  80  of the coupler  8  and prevent longitudinal movement of the coupler  8  whenever ferrule  13  is being inserted into or removed from coupler  8  and sleeve  60 . 
     Cradle cover plate  116  mates with structure of shelf  140  both to retain coupler  8  within cradle  112  and trap cradle  112  in recesses  158  in shelf  140 . Cover plate  116  comprises channels  162  formed therein to guide connectors  47 , which incorporate the cable ferrule  13 , during insertion of the cable ferrule  13  into coupler  8  and sleeve  60 , removing the need to precisely align ferrule  13  with the second coupler member  40 . 
     Enclosure  138  of base  102  is mated with a cover plate  110 . Cover plate  110  is attached to the module base  102  by screws (not shown) or other conventional attachment techniques such as adhesives or sealants, if appropriate. The cover plate  110  may be further provided with a plurality of pins  150 , arranged extending outwardly therefrom, which act as cooling fins to dissipate heat generated by the opto-electronic devices  106 ,  108  and electronic components  126  within the chamber  122  of enclosure  138  to the surrounding air to prevent the possible overheating of the internal electrical components  126 . 
     A wall  152  of cover plate  110  which mates with wall  136  of base enclosure  138  has holes or slots  154 , which are aligned with holes or slots  134 , and which holes or slots  134 ,  154  together form a hole whenever the cover plate  110  is installed. These holes formed by slots  134 ,  154  provide for passage of the optical fibers  170 . Thus, the optical fibers  170  may be easily installed even if terminated by ferrules  12 . The unterminated ends  172  of optical fibers  170  then can be fixed proximate the opto-electronic sub assemblies  106 ,  108  and the ferrule  12  terminated ends of optical fibers  170  can be inserted into coupler  8 . 
     Module  100  may be advantageously fabricated by die casting using a zinc alloy. The die casting process is capable of producing closely dimensioned parts having complex shapes such as pedestals  130 , retention slots  158 , and slots  154 . The zinc alloy is highly heat conductive. Die casting also can provide economical structures which have shapes that permit elimination of separate parts such as cradle  112  by incorporating the flanges  113  and groove  114  into an interior surface of the shelf-like extension  140 . 
     The optical fiber coupler  8  may be used to connect any pair of compatible ferrule terminated optical fibers in a number of different environments. The coupler  8  along with a suitable support, forming a cradle cavity analogous to the above described cradle  112 , may be used in any situation where the coupling of optical fibers must be disconnectably joined or spliced, or may be used as an emergency splice pending actual fusing or permanently splicing of the optical fibers. 
     The foregoing Detailed Description of the Preferred Embodiment of the Invention is intended to disclose the invention in sufficient detail that one of skill in the art may practice the invention. The Detailed Description of the Preferred Embodiment of the Invention is not intended to limit the scope of the invention in any manner. 
     The foregoing references to a transceiver module are made for purposes of example and illustration and are not indicative that this invention can only be used in such manner. Clearly, it should be understood that this invention may be use either in conjunction with a modular unit or as a stand alone coupler for optical fibers. 
     One of skill in the art will recognize that minor changes may be made in the design details of the disclosed invention while not removing the resulting devices from the scope of the claims attached hereto, such claims being intended to define the scope of the invention.