Patent Publication Number: US-9835808-B2

Title: Cylindrical optical ferrule alignment apparatus

Description:
This application is a continuation of application Ser. No. 14/161,792, filed Jan. 23, 2014, which claims the benefit of U.S. Provisional Application No. 61/755,721, filed Jan. 23, 2013, with the entire contents of the two prior applications being herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an adapter for communicating a first fiber optic connector to a second fiber optic connector. More particularly, the present invention relates to an alignment feature of an adapter, which enables precise alignment of the cores of a multi-core fiber end of the first connector with the corresponding cores of a multi-core fiber end of the second connector. 
     2. Description of the Related Art 
       FIG. 1  shows an exploded view of a simplex connector, in the form of an LC connector  30 , in accordance with the prior art. The LC connector  30  comprises the following components, from left to right: plug housing  31 ; ferrule subassembly  32 ; spring  33 ; extender  34 ; and buffer boot  35 . For the purposes of the present discussion, the adjectives “front” and “lead” refer to the plug end of a connector (i.e., the left side of  FIG. 1 ). The adjectives “rear” and “tail” refer to the boot end of a connector (i.e., the right side of  FIG. 1 ). Components  31 - 35  share a common longitudinal axis  36 . 
     In the assembled connector  30 , the ferrule subassembly  32  with the cable end mounted thereto, “floats” along longitudinal axis  36  within an enclosure comprising plug housing  31 , extender  34 , and buffer boot  35 . Spring  33  provides spring-loading of the ferrule subassembly  32  within the enclosure, such that the ferrule subassembly  32  is biased toward the front end of plug housing  31 . Boot  35  relieves mechanical strain on the optical fiber cable  44 . 
     Ferrule subassembly  32  includes a ferrule  40 , a ferrule holder  41  (sometimes referred to as a ferrule barrel), and tubing  42 . The ferrule  40  has a precision hole extending down its length, along axis  36 . The hole is shaped to closely receive a bare optical fiber from a stripped end of an optical fiber cable  44 . The bare fiber is trimmed at the ferrule tip  45  and polished, resulting in an exposed fiber end face  43 . Ferrule holder  41  includes a hexagonal flange  46  and a front cone portion  49  having a pair of slots  47 ,  47 ′ in its perimeter. The details of the slots  47 ,  47 ′ and exposed fiber end face  43  are best seen in the close-up perspective view of the ferrule subassembly  32  shown in  FIG. 2 . 
     When connector  30  is fully assembled, the ferrule tip  45  is accessible through an opening  21  at the front of the plug housing  31 . The plug housing  31  includes a latch arm  22  that is used to releasably attach the connector  30  into a corresponding socket or jack (not shown). 
     As best seen in  FIG. 3 , when connector  30  is fully assembled, the hexagonal flange  46  is seated in a corresponding hexagonal cavity  23  within plug housing  31 , thereby limiting rotation of the flange/ferrule assembly  32  around axis  36 . 
       FIG. 4  shows a perspective view of a tuning wrench  50  that can be used to rotate the ferrule subassembly  32  around its longitudinal axis  36  in an assembled connector  30 . The ferrule subassembly  32  can be rotated in order to improve core alignment, as will be discussed in relation to  FIG. 5 . As shown in  FIG. 4 , the tuning wrench  50  includes a hollow shaft  51  having an opening  52  therein that fits through the plug housing opening  21  and around the ferrule  40 . Teeth  53 ,  53 ′ engage the pair of slots  47 ,  47 ′ in the front cone portion  49  of the ferrule holder  41 . 
     In use, the tuning wrench  50  pushes the ferrule subassembly  32  along its longitudinal axis  36  toward the tail end of the assembled connector  30 , such that spring  33  is compressed, and such that hexagonal flange  46  is unseated from its receiving cavity  23  in plug housing  31 . Once the hexagonal flange  46  is unseated, the ferrule subassembly  32  can then be freely rotated clockwise or counter-clockwise around its longitudinal axis  36 . Releasing the tuning wrench  50  causes the hexagonal flange  46  to be reseated in its receiving cavity  23 . It will be appreciated that the ferrule subassembly  32  can only be rotated to one of six orientations (i.e., sixty degree positional tuning) relative to the plug housing  31 , corresponding to the six possible engagement locations of the hexagonal flange  46  within the corresponding hexagonal cavity  23  of the plug housing  31 . 
       FIG. 5  illustrates the six potential placements  43 A- 43 F of the exposed fiber end face  43 . The reason the exposed fiber end face is not always dead center is due to manufacturing tolerances in getting the fiber core  12  centered in the cladding layer  14 , and/or an off-center or canted hole extending down the length of the ferrule  40 , and/or the hole in the ferrule  40  is oversized to allow for the epoxy adhering the optical fiber into the hole, and the epoxy is not forming an even layer around the optical fiber within the hole. 
     Therefore, it is commonly known to view and/or detect the end face  43  of the optical fiber and use the turning wrench  50  to select the one position, shown in bold with reference numeral  43 E, out of the six potential positions  43 A- 43 F, which best places the fiber core  12  of the exposed fiber end face  43  in the center of the opening  21  of the plug housing  31 . Alternatively the fiber core can be positioned closest to a preferred location, for example 12 o&#39;clock, to maximize transmission between two coupled connectors. The best positioning of the end face  43 , e.g., the position which best minimizes the eccentric error, may also be determined with resort to a light measuring detector, which measures the intensity of light being received from the center of the connector end. More details concerning the correction of the eccentric error can be found in US Published Application 2002/0085815, which is herein incorporated by reference. 
     As can be seen in  FIG. 3 , the fit between the hexagonal flange  46  and the corresponding hexagonal cavity  23  of the plug housing  31  has significant play  60 ,  61 . A typical hexagon flange  46  has a width dimension of X, e.g., 2.8000 mm, while a typical hexagonal cavity  23  within the plug housing  31  has a width dimension Y, e.g., 3.0700 mm. Based upon these measurements, Applicants have evaluated the play and found that the hexagonal flange  46  may rotated up to +/− twelve degrees within the hexagonal cavity  23  of the plug housing  31 . The +/− play is represented by the double headed arrows  60  and  61  in  FIG. 3 . Such play has been acceptable in the art, wherein the optic fiber  43  presented a single core  12  transmitting light. As one could typically select one of the potential six positions, e.g., a sixty degree optimization, and minimize the eccentric error to a level producing acceptable dB loss across a mated pair of connectors, and the +/− additional twelve degrees of play did not greatly deteriorate the dB loss across the mated pair of connectors. 
     A current development in the fiber arts is the multi-core optical fiber  43 ′. As shown in  FIG. 6 , the multi-core optical fiber  43 ′ presents multiple cores  12   a - 12   g  within a single cladding layer  14 . The depiction of  FIG. 6  shows a center core  12   a  and six satellite cores  12   b - 12   g.    
     When a first multi-core optical fiber connector  30  mates with a second multi-core optical fiber connector  30 A, it is important that each core  12   a - 12   g  of the first connector  30  comes into alignment with each core  12   a - 12   g  of the second connector  30 A. Therefore, the play  60  and  61  depicted in  FIG. 3  is not acceptable. A plus or minus twelve degree shift could allow the satellite cores  12   b - 12   g  to be completely offset and out of communication when a first multi-core optical fiber connector  30  is mated to a second multi-core optical fiber connector  30 A via a pass through adapter. 
     To address this concern, the prior art of US Published Application 2011/0229085, which is herein incorporated by reference, has reduced the allowable tolerances between the hexagonal flange  46  of the ferrule holder  41  and the hexagonal cavity  23  of the plug housing  31 . In US Published Application 2011/0229085, “a tightly toleranced internal hexagonal cavity” is employed, as it is important that the shape geometry employed on the collar of the ferrule holder “match” the shape geometry employed in the internal plug housing. Excessive play, e.g., +/− twelve degrees, would not be acceptable. 
     In US Published Application 2011/0229085, the external geometry of the ferrule holder, e.g., the hexagonal flange  46 , is tightly seated without play into the internal geometry of the plug housing, e.g., the hexagonal cavity  23 , relatively rotatable parts of the connector which could affect the angular placement of the satellite cores  12   b - 12   g  are preferably locked down in place with epoxy. 
     SUMMARY OF THE INVENTION 
     The Applicant has appreciated drawbacks in the multi-core fiber optic connectors of the prior art. It is an object of the present invention to address one or more of the drawbacks and other perceived needs in the art. 
     It is appreciated that precision molding of the internal cavity of the plug housing is difficult and increases the costs. Plug housings with out of tolerance internal cavities would need to be recycled. Further, the plastic portions of the housing can be subject to abrasion and may over time expand to develop play in the nesting between the external geometry of the ferrule holder and the internal geometry of the plug housing, which could lead to degraded communication performance in one or more cores. Also, the entire plug housing may slightly rotate about its central axis within a port of an adapter because of a clearance fit between the plug&#39;s housing and the walls of the port. 
     It is an object of the present invention to provide a low cost dependable fiber optic adapter, suitable for multi-core optical fibers. 
     It is an object of the present invention to provide an alignment sleeve which is robust and does not require a boss within the adapter housing, which may be snap attached into an adapter housing, and/or which may potentially obviate the need for a two piece adapter housing. 
     It is an object of the present invention to provide an alignment sleeve with security keying which may prevent an unauthorized fiber connector from achieving communication mating within an adapter. 
     These and other objects are accomplished by a device including a ferrule alignment sleeve, wherein said sleeve extends in a longitudinal direction and forms a generally tubular inner area; a first rim formed around a first opening at one end of said tubular area to receive an end of a first circular ferrule; a second rim formed around a second opening at an opposite end of said tubular area to receive an end of a second ferrule; and a first tab adjacent said first rim and projecting away from said tubular area. 
     Further, these and other objects are accomplished by a device including an adapter housing having a wall; a through hole formed in said wall of said adapter housing; and a latch projecting from said wall toward said through hole, wherein an end edge of said latch forms an edge of said through hole, and wherein said latch is deflectable so as to deflect without breakage when engaged by an object larger in size than said through hole being pressed into said through hole, and wherein said latch is resilient so as to snap back to an original position after the oversized object disengages said end edge of said latch. 
     Moreover, these and other objects are accomplished by a device including a ferrule alignment sleeve, wherein said sleeve extends in a longitudinal direction and forms a generally tubular inner area, and wherein a mid-section of said sleeve includes a recessed area extending into an outer surface of said sleeve toward said tubular inner area; a first rim formed around a first opening at one end of said tubular area to receive an end of a first circular ferrule; a second rim formed around a second opening at an opposite end of said tubular area to receive an end of a second ferrule; a first tab adjacent said first rim and projecting away from said tubular area; a second tab adjacent said second rim and projecting away from said tubular area; an adapter housing having a wall; a through hole formed in said wall of said adapter housing; and a latch projecting from said wall toward said through hole, wherein an end edge of said latch forms an edge of said through hole, and wherein said latch is deflectable so as to deflect without breakage when engaged by an object larger in size than said through hole being pressed into said through hole, wherein said latch is resilient so as to snap back to an original position after the oversized object disengages said end edge of said latch, and wherein said at least one resilient latch snaps into said recessed area of said sleeve as said sleeve passes through said through hole and acts to attach said sleeve within said adapter housing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given by way of illustration only, and thus, are not limits of the present invention. 
         FIG. 1  is an exploded, perspective view of an LC connector for an optical fiber, in accordance with the prior art; 
         FIG. 2  is a close-up, perspective view of a ferrule subassembly in  FIG. 1 ; 
         FIG. 3  is a diagram depicting play in the fitting of a hexagonal flange of a ferrule holder within a hexagonal cavity of a plug housing, in accordance with the prior art; 
         FIG. 4  is a perspective view of a turning wrench, in accordance with the prior art; 
         FIG. 5  is a diagram depicting six potential locations of a fiber end presented by a fiber optical connector due to an eccentric error in the fiber placement, in accordance with the prior art; 
         FIG. 6  is an end view of a multi-core optical fiber, in accordance with the prior art; 
         FIG. 7  is a perspective view of an alignment sleeve, in accordance with a first embodiment of the present invention; 
         FIG. 8  is a top view of the alignment sleeve of  FIG. 7 ; 
         FIG. 9  is a side view of the alignment sleeve of  FIG. 7 ; 
         FIG. 10  is a perspective view of a fiber optic adapter, in accordance with a first embodiment of the present invention; 
         FIG. 11  is an end view looking into the adapter in the direction of line XI-XI of  FIG. 10 ; 
         FIG. 12  is a cross-sectional view taken along line XII-XII in  FIG. 11 , and also illustrating the partial insertion of a fiber connector; 
         FIG. 13  is a perspective view of first and second mated fiber connectors within the adapter of  FIG. 10 , with all of the structure except the alignment sleeve removed from the adapter, and all of the structure except the ferrules, ferrule holders, and tubes removed from the first and second fiber connectors; 
         FIG. 14  is a side view of the arrangement of  FIG. 13 ; 
         FIG. 15  is a perspective view of a modified alignment sleeve with security keying features; 
         FIG. 16  is a perspective view of an alignment sleeve, in accordance with a second embodiment of the present invention; 
         FIG. 17  is a top view of the alignment sleeve of  FIG. 16 ; 
         FIG. 18  is a side view of the alignment sleeve of  FIG. 16 ; 
         FIG. 19  is an end view looking into the ports of a fiber optic adapter, in accordance with a second embodiment of the present invention; 
         FIG. 20  is an end view similar to  FIG. 19 , but showing alignment sleeves of  FIG. 16  being mounted within the ports; and 
         FIG. 21  is a perspective view of a cross-section taken along line XXI-XXI in  FIG. 20 , with first and second fiber connectors mated into the adapter. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     The present invention now is described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
     Like numbers refer to like elements throughout. In the figures, the thickness of certain lines, layers, components, elements or features may be exaggerated for clarity. Broken lines illustrate optional features or operations unless specified otherwise. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and relevant art and should not be interpreted in an idealized or overly formal sense unless expressly so defined herein. Well-known functions or constructions may not be described in detail for brevity and/or clarity. 
     As used herein, the singular forms “a”, an and the are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. As used herein, phrases such as “between X and Y” and “between about X and Y” should be interpreted to include X and Y. As used herein, phrases such as “between about X and Y” mean “between about X and about Y.” As used herein, phrases such as “from about X to Y” mean “from about X to about Y.” 
     It will be understood that when an element is referred to as being “on”, “attached” to, “connected” to, “coupled” with, “contacting”, etc., another element, it can be directly on, attached to, connected to, coupled with or contacting the other element or intervening elements may also be present. In contrast, when an element is referred to as being, for example, “directly on”, “directly attached” to, “directly connected” to, “directly coupled” with or “directly contacting” another element, there are no intervening elements present. It will also be appreciated by those of skill in the art that references to a structure or feature that is disposed “adjacent” another feature may have portions that overlap or underlie the adjacent feature. 
     Spatially relative terms, such as “under”, “below”, “lower”, “over”, “upper”, “lateral”, “left”, “right” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is inverted, elements described as “under” or “beneath” other elements or features would then be oriented “over” the other elements or features. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the descriptors of relative spatial relationships used herein interpreted accordingly. 
       FIGS. 7-9  show various views of a ferrule alignment sleeve  101 , in accordance with a first embodiment of the present invention. The sleeve  101  extends in a longitudinal direction  102  and forms an inner, generally tubular area  103 . A first rim  105  is formed around a first opening at one end of the tubular area  103  to receive an end of a first circular ferrule  40  (see  FIG. 12 ). A second rim  107  is formed around a second opening at an opposite end of the tubular area  103  to receive an end of a second ferrule  40 A. 
     A first tab  109  is located adjacent to the first rim  105  and projects away from the tubular area  103 . A second tab  111  is located adjacent to the second rim  107  and projects away from the tubular area  103 . In a preferred embodiment, the first tab  109  has a generally radiused or triangular tip at its distal end  113 , and the second tab  111  also has a generally radiused or triangular tip at its distal end  115 . 
     In one embodiment, the sleeve  101  is split in a direction parallel to its longitudinal line of extension  102  by an opening  117 . Hence, the sleeve  101  presents a C-shaped appearance in a cross-sectional view, taken through the tubular area  103  in a direction perpendicular to its longitudinal line of extension  102 . The sleeve  101  may be formed of zirconia, alumina, phosphor bronze, stainless steel, a filled polymer or unfilled polymer, a metal, an alloy, glass, ceramic, or similar material. Also, the sleeve  101  may be coated with a hard material, like diamond-grade materials or titanium nitride, to reduce wear due to abrasion. In the embodiment depicted in  FIGS. 7-9 , the outer surface  119  of the sleeve  101  presents a generally smooth, cylindrical surface. 
       FIG. 10  is a perspective view of a fiber optic adapter  201 , in accordance with a first embodiment of the present invention.  FIG. 11  is an end view looking into the adapter  201  in the direction of line XI-XI in  FIG. 10 .  FIG. 12  is a cross-sectional view taken along line XII-XII in  FIG. 11 , and also illustrating the partial insertion of a fiber connector. 
     The depicted adapter  201  is a duplex adapter having first and second ports  250  and  250 A on one lateral side, with each port  250  or  250 A sized to receive one of a mating pair of connectors, e.g., connectors  30  of  FIG. 1 . Third and fourth ports  251  and  251 A are located on the opposite lateral side of the adapter  201 . A connector  30  in first port  250  will have its single core or multi-core optical fiber mated to the optical fiber of a connector  30  in the second port  250 A. Likewise, a connector  30  in third port  251  will have its single core or multi-core optical fiber mated to the optical fiber of a connector  30  in the fourth port  251 A. Since the structure concerning the first and second ports  250 ,  250 A is the same as the structure concerning the third and fourth ports  251 ,  251 A, the following description will focus on the first and second ports  250  and  250 A only. 
     The adapter  201  is formed by a housing including by a first part  203  with a first wall  205  and a second part  207  with a second wall  209 . A first through hole  211  is formed in the first wall  205  of the first part  203 . A second through hole  213  is formed in said second wall  209  of the second part  207 . 
     A first cylindrical boss  215  has a proximate end attached to the first wall  205  and encircles the first hole  211 . The first cylindrical boss  215  extends away from the first wall  205  and terminates at a distal end with a first turned edge  217  protruding toward a center of the first cylindrical boss  215 . The first turned edge  217  has a first gap  219 . 
     A second cylindrical boss  221  has a proximate end attached to the second wall  209  and encircles the second hole  213 . The second cylindrical boss  221  extends away from the second wall  209  and terminates at a distal end with a second turned edge  223  protruding toward a center of the second cylindrical boss  221 . The second turned edge  223  has a second gap  225 . 
     The first wall  205  abuts, and is retained in abutment, with the second wall  209  while the first and second holes  211  and  213  are aligned, as illustrated in  FIG. 12 . The first and second walls  205  and  209  can be retained in the abutment position by adhesion, e.g., epoxy, by a fixing device, e.g., a clip, by molded features, e.g., snap engaging components, by ultrasonic welding, or by other known methods. Prior to attachment, the sleeve  101  of  FIGS. 7-9  is inserted into the aligned holes  211  and  213 . In particular, the sleeve  101  resides inside of the first boss  215  and the second boss  221 .  FIG. 11  depicts a sleeve  101  installed in the first port  250 , but no sleeve installed in the third port  251 . 
     The first rim  105  of the sleeve  101  cannot pass by the first turned edge  217  of the first boss  215  and the second rim  107  of the sleeve  101  cannot pass by the second turned edge  223  of the second boss  221 . By this arrangement, the sleeve  101  is attached within the first and second bosses  215  and  221 , and hence within the housing of the adapter  201 . The first tab  109  of the sleeve  101  passes through the first gap  219  in the first turned edge  217 . The second tab  111  of the sleeve  101  passes through the second gap  225  in the second turned edge  223 . 
     The first port  250  resides on a side of the first wall  205  possessing the first boss  215 . The second port  250 A resides on a side of said second wall  209  possessing the second boss  221 . A first fiber optic connector  30  would be seated into the first port  250 . The first fiber optic connector  30  would include a first ferrule holder  41  holding a first ferrule  40  and a first optical fiber end  43  residing within a central bore of the first ferrule  40 .  FIG. 12  depicts the first connector  30  being partially inserted into the first port  250 . As the first connector  30  is fully seated into the first port  250 , the first connector&#39;s latch arm  22  will enter into a latch track  252  and snap lock in place. As the first connector  30  begins to fully seat, the first tab  109  of the sleeve  101  extends into the first slot  47  formed in the first ferrule holder  41 . The generally radiused or triangular tip at the distal end  113  of the first tab  109  assists in the insertion of the first tab  109  into the first slot  47 . 
     A second fiber optic connector  30 A would be seated into the second port  250 A. The second fiber optic connector  30 A would include a second ferrule holder  41 A holding a second ferrule  40 A and a second optical fiber end  43 A residing within a central bore of the second ferrule  40 A. As the second connector  30 A is fully seated into the second port  250 A, the second latch arm  22 A will enter into a second latch track  252 A and snap lock in place. As the second connector  30 A begins to fully seat, the second tab  111  of the sleeve  101  extends into the second slot  47 A formed in the second ferrule holder  41 A. The generally radiused or triangular tip at the distal end  115  of the second tab  111  assists in the insertion of the second tab  111  into the second slot  47 A. 
       FIG. 13  is a perspective view of the first and second mated fiber connectors  30  and  30 A within the adapter  201  of  FIG. 10 , with all of the structure except the alignment sleeve  101  removed from the adapter  201 , and all of the structure except the ferrules  40  and  40 A, ferrule holders  41  and  41 A, and tubes  42  and  42 A removed from the first and second fiber connectors  30  and  30 A.  FIG. 14  is a side view of the arrangement of  FIG. 13 . 
     As seen in  FIGS. 13-14 , when the first and second tabs  109  and  111  engage into the first and second slots  47  and  47 A, the first and second slots  47  and  47 A become quite precisely aligned. The alignment can be very advantageous when the first optical fiber  43  is a first multi-core optical fiber, e.g.,  FIG. 6 , and the second optical fiber  43 A is a second multi-core optical fiber. By clocking the position of the satellite cores  12   b - 12   g  relative to the lower slot  47  of the ferrule holder  41  prior to attaching the fiber  43  to the ferrule  40 , e.g., by epoxy, it will be known that the first and second multi-core optical fibers  43  and  43 A are aligned with each other, such that all of the cores  12   a - 12   g  are in communication when the first and second tabs  109  and  111  of the sleeve  101  create an alignment between the lower slots  47  and  47 A and the ends  45  and  45 A of the ferrules  40  and  40 A abut. 
     If only the inner cavity  23  of the connector housing were used to align the multi-core fibers, the alignment could be off by up to plus or minus twelve degrees, as shown in  FIG. 3 . However, by the present invention&#39;s use of the “existing” slot  47  in the ferrule holder  41 , previously used to rotate the ferrule to improve upon the eccentric error of a single core fiber, the alignment error can be reduce to plus or minus one and a half degrees or less. Such a small angular variation allows the satellite cores  12   b - 12   g  to stay in alignment for effective communication across a pass-through adapter  201 . 
     Instead of using “existing” ferrule holders  41  with “existing” slots  47  and  47 ′, it is within the purview of the present invention, to machine a ferrule holder with a slot or plural slots design for the optimization of the function of the present invention. To that end, the slot could be wider at its opening and narrow down to a precise size. The wider opening could assist in the initial “finding” of the slot by the tabs  109  or  111 , and could operate in conjunction with the radius or triangular shape at the ends  113  and  115  of the tabs  109  and  111 . Further, the previous slots  47  and  47 ′ were designed only to engage with the teeth  53  and  53 ′ of the wrench  50  of  FIG. 4 , so as to permit a large course rotation of the ferrule holder, e.g., sixty degree. The dimensional tolerances of the prior art slots  47  and  47 ′ are not of great concern. In accordance with the present invention, the dimensional tolerances can be more precise and monitored during fabrication of the ferrule holder  41 . A close tolerance for the slots  47  or  47 ′ can further reduce the potential plus or minus error of the rotational alignment of the satellite cores  12   b - 12   g.    
     It is also a feature of the present invention that slots  47  could be closely spaced at precise distances from each other, have different and precise widths and or depths. The slots  47  could then be used as a keying feature. For example,  FIG. 15  is a perspective view of a modified alignment sleeve  161  with security keying features to engage in such a ferrule holder with multiple keying slots. 
     The sleeve  161  includes a first tab  163  located adjacent to the first rim  105  and projecting away from the tubular area  103 , and a second tab  165  located adjacent to the second rim  107  and projecting away from the tubular area  103 . The sleeve  161  further includes a third tab  167  adjacent the first rim  105  and projecting away from the tubular area  103  and a fourth tab  169  adjacent the second rim  107  and projecting away from the tubular area  103 . The third tab  167  is spaced a predetermined distance away from the first tab  163 . The fourth tab  169  is spaced a predetermined distance away from the second tab  165 . The predetermined spacing is a first keying aspect, such that a ferrule holder  41 , which does not possess two slots spaced by the predetermined distance, will not be able to fully seat into first port  250  of the adapter  201  and will therefore not be allowed to communicate with another connector seated into the second port  250 A of the adapter  201 . 
     As also seen in  FIG. 15 , the width dimension of the third tab  167  is different, e.g., narrower, than the width dimension of the first tab  163 , and the width dimension of the fourth tab  169  is different, e.g., narrower, than the width dimension of the second tab  165 . The width dimensions are a second keying aspect, such that a ferrule holder  41 , which does not possess two slots with the matching widths, will not be able to fully seat into the first port  250  of the adapter  201  and will therefore not be allowed to communicate with another connector seated in the second port  250 A of the adapter  201 . 
     As also seen in  FIG. 15 , the length dimension of the third tab  167  is different, e.g., longer, than the length dimension of the first tab  163 , and the length dimension of the fourth tab  169  is different, e.g., longer, than the length dimension of the second tab  165 . The length dimensions are a third keying aspect, such that a ferrule holder  41 , which does not possess two slots with the correct depths, will not be able to fully seat into the first port  250  of the adapter  201  and will therefore not be allowed to communicate with another connector seated in the second port  250 A of the adapter  201 . 
     Such keying features may be used to enhance network security by preventing unauthorized network access to individuals not in possession of a fiber connector with a ferrule holder  41  having the proper keying features, e.g., slot arrangement. 
       FIGS. 16-18  show various views of a ferrule alignment sleeve  301 , in accordance with a second embodiment of the present invention. The sleeve  301  extends in a longitudinal direction  302  and forms an inner, generally tubular area  303 . A first rim  305  is formed around a first opening at one end of the tubular area  303  to receive an end of a first circular ferrule  40  (see  FIG. 21 ). A second rim  307  is formed around a second opening at an opposite end of the tubular area  303  to receive an end of a second ferrule  40 A. 
     A first tab  309  is located adjacent to the first rim  305  and projects away from the tubular area  303 . A second tab  311  is located adjacent to the second rim  307  and projects away from the tubular area  303 . In a preferred embodiment, the first tab  309  has a generally radiused or triangular tip at its distal end  313 , and the second tab  311  also has a generally radiused or triangular tip at its distal end  315 . 
     In one embodiment, the sleeve  301  is split in a direction parallel to its longitudinal line of extension  302  by an opening  317 . Hence, the sleeve  301  presents a C-shaped appearance in a cross-sectional view, taken through some portions of the tubular area  303  in a direction perpendicular to its longitudinal line of extension  302 . The sleeve  301  may be formed of zirconia, alumina, phosphor bronze, stainless steel, a filled polymer or unfilled polymer, a metal, an alloy, glass, ceramic, or similar material. Also, the sleeve  301  may be coated with a hard material, like diamond-grade materials or titanium nitride, to reduce wear due to abrasion. 
     In the embodiment depicted in  FIGS. 16-18 , the majority of the outer surface  319  of the sleeve  301  presents a generally smooth, cylindrical surface. However, the sleeve  301  of  FIGS. 16-18  is thicker and much more robust that the sleeve  101  of  FIGS. 7-9 . A mid-section of the sleeve  301  includes a recessed area  321  extending into the outer surface  319  of the sleeve  301  toward the tubular inner area  303 . In a preferred embodiment, the recessed area  321  includes a plurality of flat surfaces, such as first, second, third and fourth flat surfaces  323 ,  325 ,  327  and  329 . 
       FIGS. 19-20  are end views of a fiber optic adapter  401 , in accordance with a second embodiment of the present invention. The exterior of the adapter  401 , in perspective view, is the same as depicted in  FIG. 10 . Also, the adapter  401  would include four ports for making optical connections, as described in connection with  FIG. 10 . 
     In the end view of  FIG. 19 , the adapter  401  has a housing including a wall  405 . A through hole  411  is formed in the wall  405 . A first latch  413  projects from the wall  405  toward the through hole  411 . Likewise, second, third and fourth latches  415 ,  417  and  419  project from the wall  405  toward different perimeter portions of the through hole  411 . 
     In a preferred embodiment, the first resilient latch  413  is a portion of the wall  405  defined between a first void channel  421  and a second void channel  423 . The second resilient latch  415  is a portion of the wall  405  defined between the second void channel  423  and a third void channel  425 . The third resilient latch  417  is a portion of the wall  405  defined between the third void channel  425  and a fourth void channel  427 . Finally, the fourth resilient latch  419  is a portion of the wall  405  defined between the fourth void channel  427  and the first void channel  421 . 
     Also in the preferred embodiment, end edges of said latches  413 ,  415 ,  417  and  419  form an edge of the through hole  411 . Each latch  413 ,  415 ,  417  and  419  is deflectable so as to deflect without breakage when engaged by an object slightly larger in size than the through hole  411  being pressed into the through hole  411 . Also, each latch  413 ,  415 ,  417  and  419  is resilient so as to snap back to an original position after the oversized object disengages the end edges of the latches  413 ,  415 ,  417  and  419 . 
       FIG. 20  depicts the insertion of the sleeve  301  of  FIGS. 16-18  into the adapter  401 . In  FIG. 20 , a sleeve  301  has been inserted into the through holes  411  of both ports  450  and  451  of the adapter  401 . During insertion of the sleeve  301 , the latches  413 ,  415 ,  417  and  419  deflect as the large cylindrical outer surface  319  enters the through hole  411 . Once the leading edge of the recessed area  321  reaches the latches  413 ,  415 ,  417  and  419 , the latches  413 ,  415 ,  417  and  419  snap into the recessed area  321  of said sleeve  301 . 
     The latches  413 ,  415 ,  417  and  419  act to attach the sleeve  301  to the wall  405  within the housing of the adapter  401 . In particular, the first, second, third and fourth flat surfaces  323 ,  325 ,  327  and  329  are engaged by the end edges of the first, second, third and fourth latches  413 ,  415 ,  417  and  419 , respectively. 
       FIG. 21  is a perspective view of a cross-section taken along line XXI-XXI in  FIG. 20  with first and second fiber connectors  30  and  30 A mated into the adapter  401 . 
     The adapter  401  has a housing including a first port  450  on a first side of the wall  405  and a second port  450 A on a second side of the wall  405 . A first fiber optic connector  30  is seated into the first port  450 . The first fiber optic connector  30  includes a first ferrule holder  41  holding a first ferrule  40  and a first optical fiber end  43  residing within a central bore of the first ferrule  40   
     A second fiber optic connector  30 A is seated into the second port  450 A. The second fiber optic connector  30 A includes a second ferrule holder  41 A holding a second ferrule  40 A and a second optical fiber end  43 A residing within a central bore of the second ferrule  40 A. 
     The first tab  309  of the sleeve  301  extends into a first slot  47  formed in the first ferrule holder  41  when the first fiber optic connector  30  is seated into the first port  450 . The said second tab  311  of the sleeve  301  extends into a second slot  47 A formed in the second ferrule holder  41 A when the second fiber optic connector  30 A is seated into the second port  450 A. The engagements made by the sleeve  301  align the first and second slots  47  and  47 A of the first and second ferrule holders  41  and  41 A, in a same or similar manner as described in conjunction with  FIGS. 12-14 . Again, the arrangement of  FIG. 21  is particularly advantageous when the first optical fiber end  43  presents a first multi-core optical fiber, and the second optical fiber end  43 A presents a second multi-core optical fiber, as the alignment of the said first and second slots  47  and  47 A aligns the cores of the first and second multi-core optical fiber ends  43  and  43 A during connector mating via the adapter  401 . 
     The embodiment of  FIGS. 16-21  has advantages over the embodiment of  FIGS. 7-15 . For example, the recessed area  321 , e.g., squared section, prevents a twisting force from being transferred through the sleeve  301  to the ferrule holder  41  or  41 A of the other connector  30  or  30 A. Any twisting force applied by a ferrule holder  41  or  41 A to the sleeve  301  will be absorbed by the latches  413 ,  415 ,  417  and  419 , rather that transmitted through the adapter  310  to impart a twisting force on the other connector&#39;s ferrule holder. 
     Another advantage is that the adapter  401  need not be formed in two pieces as illustrated in  FIG. 21 . Rather, the wall  405  may be a shared wall between the first and second ports  450  and  450 A. In the embodiment of  FIGS. 7-15 , it was convenient to separate the adapter  201  into halves  203  and  207 , so as to insert the sleeve  101  into the bosses  215  and  221  for retention. In the embodiment of  FIGS. 16-21 , the sleeve  301  is combined with the function of the bosses, and snaps into place within the adapter  401 , rendering the two piece construction unnecessary for retention of the sleeve  301 . 
     Instead of sleeve  301  snapping into the wall  405  of the adapter  401 , the sleeve  301  could also be adhered, e.g., by epoxy, or clipped or fastened into the adapter  401  by an attachment device, e.g., a clip, or molded directly into the wall  405  of the adapter  401 . 
     The security keying features, as described in conjunction with the embodiment of  FIG. 15 , may also used in the embodiments of  FIGS. 16-21  in a same or similar manner. 
     Although the figures have depicted LC type connectors with a hexagon flange  46  on the ferrule holder  41 , it should be appreciated that the hexagonal shape of the flange  46  is not necessary in an LC connector  30 , as the flange  46  could be square, conical, round with tabs or any combination of geometries known to one in the art. Also, the present invention is not limited to LC type connectors  30 . For example, simplex and duplex connector schemes using other type connectors such as SC, FC, ST, MU or 38999/29504 connector types may be substituted into the teachings of the present invention. Also, the mating of bare ferrule barrel assemblies could be accomplished (as shown in  FIGS. 13-14 ), whereby no connector envelope is employed. 
     Although the figures have depicted a split sleeve  101 ,  161  or  301 , it should be apparent that a solid sleeve may be used in the embodiments of the invention. 
     Although the specification has described, and  FIG. 6  has illustrated, a multi-core optical fiber end  43 ′ with a central core  12   a  and six, equally-spaced, satellite cores  12   b - 12   g , more or fewer satellites cores could be used. Further, the spacing between cores need not be equal or even symmetrical. Further, a central core  12   a  is not required. The benefits of the present invention in aligning a first layout pattern of cores in a multi-core optical fiber end  43 ′ to a same layout pattern of cores in another multi-core optical fiber end  43 A′ will exist regardless of any specific core pattern, so long as the pattern at the first optical fiber end  43 ′ is the same as the pattern at the second optical fiber end  43 A′. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.