Abstract:
A plug type connector is adapted to be latched to a backplane wall in a fixed position and has a tapered front, nose or connector end for insertion into an adapter which plugs into the backplane wall. The adapter may be misaligned in any or all of the X, Y, Z axes. The tapered nose cams the X or Y misaligned adapter into axial alignment as the adapter and its mount are being inserted. A shortened front or connector end of the connector causes the ferrule of the connector to project beyond the optical plane of the connection so that it reaches a ferrule in a Z aligned adapter to complete the connection. A coil spring within the housing of the connector is tuned to allow counter movement of the ferrule where the ferrule in the adapter is too long, thereby shifting the position of the optical plane. The connector has a ferrule-barrel assembly within a housing and an insert member which has an enlarged diameter portion which is contained by openings in the housing to prevent rotation of the ferrule-barrel assembly.

Description:
RELATED APPLICATIONS 
     This application is related to U.S. patent application Ser. No. 09/515,976, filed on Feb. 29, 2000, entitled “Panel Mounting Assembly for Optical Fiber Connectors,” and U.S. patent application Ser. No. 09/515,998, filed Feb. 29, 2000, and entitled “Interconnection System for Optical Circuit Boards,” both filed concurrently with the present application. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to an optical fiber connector and, more particularly to a plug type optical fiber connector particularly for backplane connections. 
     BACKGROUND OF THE INVENTION 
     In optical fiber communications, connectors for joining fiber segments at their ends, or for connecting optical fiber cables to active or passive devices, are an essential component of virtually any optical fiber system. The connector or connectors, in joining fiber ends, for example, has, as its primary function, the maintenance of the ends in a butting relationship such that the core of one of the fibers is axially aligned with the core of the other fiber so as to maximize light transmissions from one fiber to the other. Another goal is to minimize back reflections. Such alignment is extremely difficult to achieve, which is understandable when it is recognized that the mode field diameter of, for example, a singlemode fiber is approximately nine (9) microns (0.009 mm). Good alignment (low insertion loss) of the fiber ends is a function of the alignment, the width of the gap (if any) between the fiber ends, and the surface condition of the fiber ends, all of which, in turn, are inherent in the particular connector design. The connector must also provide stability and junction protection and thus it must minimize thermal and mechanical movement effects. These same considerations apply to arrangements where the fiber, terminated in a plug connector, is to be used with active or passive devices, such as, for example, computers or transceivers and the like. 
     In the present day state of the art, there are numerous, different, connector designs in use for achieving low insertion loss and stability. In most of these designs, a pair of ferrules (one in each connector or one in the connector and one in the apparatus or device), each containing an optical fiber end, are butted together end to end and light travels across the junction. Zero insertion loss requires that the fibers in the ferrules be exactly aligned, a condition that, given the necessity of manufacturing tolerances and cost considerations, is virtually impossible to achieve, except by fortuitous accident. As a consequence, most connectors are designed to achieve a useful, preferably predictable, degree of alignment, some misalignment being acceptable. Alternatively, a device meant to accept a connector with the ferrule aligned in a bore and which comes to rest at a stop in the optical plane is acceptable. 
     Alignment variations between a pair of connectors can be the result of the offset of the fiber core centerline from the ferrule centerline. This offset, which generally varies from connector to connector, is known as “eccentricity”, and is defined as the distance between the longitudinal centroidal axis of the ferrule at the end face thereof and the centroidal axis of the optical fiber core held within the ferrule passage. The resultant eccentricity vector has two components, magnitude and direction. Where two connectors are interconnected, rotation of one of them will, where eccentricity is present, change the relative position of the fibers, with a consequent increase or decrease in the insertion loss of the connections. Where the magnitude of the eccentricities are approximately equal the direction component is governing, and relative rotation of the connectors until alignment is achieved will produce maximum coupling. 
     In U.S. patent application Ser. No. 09/363,908, of Andrews et al., filed Jul. 28, 1999, now pending there is shown an arrangement for “tuning” a connector to achieve optimum direction of its eccentricity. 
     Unfortunately, there are a number of other problems affecting insertion loss of the plug connection, particularly where the connector plug, which terminates, for example, a jumper cable, is used to connect through a backplane to, generally, a piece of equipment having a connector adapter or connector receiving means mounted thereon. By “backplane” is meant, generally, a wall which separates internal apparatus from external apparatus, and through which a connection or connections are made. Thus the interior apparatus may comprise printed wiring boards (PWBs) having connector adapters mounted thereon (a circuit pack) which mate with plug connectors, such as LC type connectors which are mounted in the backplane. The backplane may also comprise a mounting panel as in a switch box, with the apparatus on one side thereof and the plug connectors insertable from the other side. In general use, the floating connector is affixed to the backplane, and the circuit pack is plugged into the backplane as needed to mate with the backplane connector plug. 
     In all such arrangements, manufacturing tolerances can add up to serious misalignments in any of the X, Y, or Z axes. Thus when a coupling adapter or device receptacle with a circuit pack is mounted on a PWB, the PWB mount, the adapter mount, the adapter itself and the latching mechanism of the circuit pack, which have all been made to be within certain tolerance limits, could, for example, all be at the extreme tolerance limits, thus presenting a particular misalignment of the adapter connector ferrule receptacle along one or more of the X, Y, Z axes. When an adapter is inserted into the wall of the backplane, it may be seriously misaligned with the ferrule which is latched to a receptacle on the backplane. In many instances the insertion of the adapter into the plug is blind, i.e., the operator cannot see one or the other coupling components, and the operator cannot easily feel for the correct position. This results in damage to the ferrule of the plug. As a consequence, insertion loss may be increased to an undesirable level. In extreme cases, connection might not be possible. In addition, severe improper Z axis travel of the ferrule can result in twisting of the ferrule barrel of the connector, resulting in de-tuning of the plug connector when it has been tuned. 
     In addition, in a backplane wall in the Z axis, a standard LC plug connector may not be long enough to insure that the spacing between the optical plane, where the backplane plug ferrule abuts the device stop or ferrule assembly in the abut, and a reference face in the front of the backplane remains the same regardless of the backplane thickness. If it does not, proper abutment of the two ferrules may not occur, thereby causing a material increase in insertion loss. 
     SUMMARY OF THE INVENTION 
     The present invention is a modified plug connector designed to be usable in a connection regardless of tolerance discrepancies, and which insures the desired insertion loss regardless thereof. 
     As discussed hereinafter, the principles of the invention are incorporated in an LC type connector, but it is to be understood that these principles are applicable to other types of connectors as well. 
     In greater detail, the basic components of the connector comprise a ferrule-barrel assembly for holding the end of an optical fiber extending axially there through and a plug housing member which contains the ferrule-barrel assembly. A coil spring member contained within the housing surrounds the barrel and bears against an interior portion of the housing and an enlarged barrel member, thereby supplying forward bias to the ferrule assembly relative to the housing. In accordance with one aspect of the invention, the housing has a length extending from a cable entrance end to a connection end which terminates in a nose portion, that is great enough to enable insertion into the adapter regardless of the backplane thickness. The housing has a latching arm thereon, an insert member, a crimp member, and a rear yoke member having a trigger thereon for actuating the latching arm, and the overall length is such that the trigger member remains accessible regardless of the backplane thickness. The coil spring is likewise of increased length and affords to the ferrule a greater amount of travel on the axis to accommodate some Z direction misalignment of the adapter to which connection is to be made. This greater than normal travel insures that the ferrule will reach, and butt with the adapter ferrule despite, for example, the adapter being mounted too great or too little a distance in the Z direction from a reference plane defined by the front surface of the backplane. 
     In accordance with another aspect of the invention, the insert member, which functions as a strength member, has an enlarged diameter portion having locating flats thereon forming a truncated cylindrical portion that keeps with openings in the sidewalls of the housing to seat the insert firmly in place axially to resist axial pull. The insert member is affixed to the barrel-ferrule assembly which, consequently, is prevented from rotating within the housing. The ferrule-barrel assembly has a hex-shaped barrel that sits in a hex-shaped opening or recess in the housing bore. The barrel can be unseated and rotated to any of six positions to tune the connector to achieve optimum optical loss. Mounted on the rear portion of the insert member is a crimping member which is surrounded by a clip or yoke member having a trigger or activating arm mounted thereon. The crimping member is used to affix the strength members, e.g. aramid fibers, to the rear of the insert member to attach the cable to the connector. 
     In accordance with another aspect of the invention, the latching arm on the connector is positioned to latch to a backplane receptacle at a point approximately in the reference plane, or in a fixed position relative thereto, of the backplane. This has the beneficial effect of latching the connector to the backplane in the same place relative thereto regardless of the thickness of the backplane, while leaving the trigger accessible for un-latching the connector when necessary. 
     Because, as pointed out hereinbefore the adapter may be misaligned in the X and Y axes as a result of conflicting manufacturing tolerances, the nose portion of the connector housing is chamfered. The sloping surfaces of the chamfer serve as lead-ins for the adapters and function to cam the adapter or device receptacle into alignment with the ferrule of the backplane plug connector. 
     These and other principles and features of the present invention will be more readily understood from the following detailed description, read in conjunction with the accompanying drawings. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view of the basic elements of the plug connector of the present invention; 
     FIG.  2 ( a ) is a perspective view of the connector of FIG. 1 as partially assembled; 
     FIG.  2 ( b ) is a cross-sectional view of the connector of FIG. 1; 
     FIG.  2 ( c ) is a front elevation view of the connector of FIG. 1; 
     FIG. 3 is an exploded perspective view of a jumper cable as terminated by the connector of FIG. 1; 
     FIG. 4 is a perspective view of the assembled termination of the jumper cable; 
     FIG. 5 is a sectional arrangement of FIG. 4 as used as a backplane connector for a thin walled backplane; 
     FIG. 6 is a sectional elevation view of the connector arrangement of FIG. 4 as used as a backplane connector for a thick walled backplane; and 
     FIG. 7 is a top plan view of the backplane connector of the invention as used in a duplex connector arrangement. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is an exploded perspective view of the plug connector  11  of the present invention which, as depicted, is an LC type connector having a unitary housing  12  which, as pointed out hereinbefore has a length from the cable entrance end  13  to the connector or ferrule end  14  that is sufficient to make the connector  11  usable over a wide range of backplane thicknesses. As such, the connector  11  is considerably longer than the standard LC connector. A latching arm  16 , having first and second latching lugs  17  and  18  extends from housing  12 , for latching the connector  11  in place. As will be discussed more fully hereinafter, the axial location of the latching lugs  17  and  18  is important to the proper functioning of connector  11 . Housing  12  and latching arm  16  are preferably made of a suitable plastic material and, preferably are molded therefrom in a one piece structure. The plastic material should have sufficient resilience to allow the latching arm  16  to be depressed and to spring back to its non-depressed (latching) position, thereby forming a “living” hinge. Housing  12  has an axial bore  19  extending therethrough which accommodates a ferrule-barrel assembly  20 . Assembly  20  comprises a flexible hollow tubular member  22  attached to a metal or hard plastic barrel member  21  with an enlarged flange  23  from which extends a ferrule  24  which may be of a suitably hard and wear resistant material such as, preferably, ceramic, glass, or metal and which functions to contain an optical fiber therein. A coil spring  26  surrounds tubular member  22  and seats against the rear of flange  23  at its forward end, and against an insert  27  at its rear end. Insert  27  is tubular and accommodates tubular member  22 . 
     Insert  27  has an enlarged diameter section  28  having first and second flats  29  (only one of which is shown) thereon which enable insertion of insert  27  into the end of bore  19  at the cable entrance end  13  of housing  12 , which has a generally square configuration as is shown, for example, in U.S. patent application Ser. No. 09/413,431 of Driscoll et al. filed Oct. 6, 1999. Insert  27  also has a flange  31  thereon which functions as a stop to prevent insert  27  from being inserted too far into housing  12 , as best seen in FIG.  2 ( b ). FIGS.  2 ( a ),  2 ( b ), and  2 ( c ) are a perspective view, a cross-sectional elevation view, and a front elevation view, respectively, of the connector  11  of FIG.  1 . 
     At the cable receiving end of insert  27  is a groove  32  which is designed to receive the strength members, usually aramid fibers  33 , which are affixed thereto by means of a crimping member  34  as best seen in FIG. 3, thereby anchoring the incoming fiber cable  36  to connector  11 . As best seen in FIG. 1, each of the sidewalls of housing  12 , has an opening  37 , only one of which is shown, therein for receiving the enlarged diameter portion  28  of insert  27  and which functions to affix the insert  27  longitudinally, i.e., the Z direction, within housing  12 . The flats  24 — 24  of insert  27  are received within the walls at the cable entrance end  13  to prevent rotation thereof. 
     The front end of flange  23  has a polygonal shape, preferably hexagonal, with a slope  38  which is adapted to seat in a sloped recess portion  39  of bore  19 , as best seen in FIG.  2 ( b ). Recess portion  39  likewise has a polygonal shape adapted to receive flange  23  in any of, in the case of a hexagonal shape, six positions for tuning the connector. The tuning process is fully shown and explained in U.S. patent application Ser. No. 06/363,908 of Anderson et al., filed Jul. 28, 1999, the disclosure of which is incorporated herein by reference. 
     FIGS. 3 and 4 are perspective views of, respectively, the disassembled and assembled connector  11  as a termination of, for example, a jumper cable  36  which comprises, as shown in FIG. 5, a fiber  45 , a buffer layer  50  and an insulating protective layer  55  having strength members  33  therein. In addition to the parts discussed hereinbefore, connector  11  also includes a clip member  40  having a trigger arm  41  thereon. Clip member  40  has a rectangular or square bore  42  and is designed to be a slip fit on the cable receiving end of housing  12  as shown in FIG.  4 . Stop members  43 , only one of which is shown, function to locate clip member  40  longitudinally, and its latches to housing  12  by means of internal latches, not shown, which mate with latch openings  44 , only one of which is shown, in housing member  12 . A protective boot  46  extends from the rear of clip  44 , and prevents the yoke  40  from moving reward after assembly. The boot  46  has a bore  47  which surrounds and grips the crimping member  34 . A protective dust cap  48 , insertable in the ferrule or connection end  14  of the housing  12  protects the ferrule  24  when the connector is assembled, inasmuch as ferrule  24  projects beyond the end of housing  12 , as best seen in FIG.  2 ( b ) a distance β which may be, for example, approximately 0.10 (α 2.41 mm) inches, which is in a standard LC connector, approximately 0.07 inches (1.78 mm). 
     In accordance with the invention, the ferrule or connector end  14  of housing  12  has a tapered nose portion  49  having a front tip end  50  which surrounds the ferrule  24 , as best seen in FIG.  2 ( b ). As will be discussed more fully hereinafter, the tapered portion functions to align the connector  11  with an adapter or other device to which connector  11  is to be mated. The tapered portion is formed by removal of at least 30% of the material of the housing at the front tip  50  of the nose. In practice, it has been found that 70% removal yields excellent results. The nose portion results in a connector end  14  of the housing in the area of bore  19  that is somewhat shorter than in a standard LC connector housing, and, as a consequence, ferrule  24  projects farther outward from the housing which, as will be made clear hereinafter, makes proper alignment in the Z direction possible. 
     In use, the connector  11  is mounted in, and latched to a receptacle in the backplane wall from one side thereof, and a PWB or other device, preferably having an adapter or similar connector receiving device thereon is, usually subsequently, mounted to a circuit pack (not shown) on the other side of the backplane wall and makes connection with the plug connector  11 . This connection arrangement is shown in FIG. 5 for a thin backplane wall  51  and in FIG. 6 for a relatively thick backplane wall  52 . In either instance, the front surface  53  of the backplane wall  51  or  52  is a reference surface which, under normal usage is a fixed distance α from the optical plane  54  which is the plane in which ferrule  24  abuts with the device ferrule (not shown) within an adapter  56 . This distance may be, for example, 0.640 inches (16.26 mm). The adapter  56  is shown mounted on a spacer block  57  which is affixed to a PWB  58  so that, when PWB  58  is part of a circuit pack and latching arrangement (not shown) on the left hand side as viewed in FIGS. 5 and 6, the centerline of adapter  56  is coincident with the centerline of plug connector  11 , which is mounted in a suitable receptacle  59  of the type, for example, shown in copending U.S. patent application Ser. No. 09/515,998, filed Feb. 29, 2000, and entitled “Interconnection System for Optical Circuit Boards.” As can be seen in the figures, receptacle  59  is adjustable for different widths of backplane walls  51 ,  52 , and plug connector  11  is always latched therein in a fixed position relative to reference plane  53 . In addition, the length of housing  12  is such that trigger  41  is accessible, regardless of the width of wall  51 ,  52  by pushing forward on trigger  41  which will interact with latch arm  16  to unlatch lugs  17  and  18 . Receptacle  59  resides within a bore  62  in backplanes  51 ,  52  which, as can be seen, is slightly larger than the transverse dimension of the receptacle  59  therein. Thus, although connector  11  is held fixed in the Z direction in the back direction, receptacle  59  and hence plug  11  can be moved slightly in the forward Z direction for unlatching and in the X and Y directions. As will be explained hereinafter, such slight movement is important to the goal of achieving proper alignment of adapter  56  and plug connector  11 . 
     The added length of housing  12  makes possible somewhat better calibration of spring member  26  as to the force necessary to compress it slightly and also as to its restoring force, both of which involve movement of the ferrule-barrel assembly  21  against the barrel or flange  23  thereof spring  26  bears. As seen in FIGS. 5 and 6, the end of ferrule  24  is shown as lying in the optical plane  54 . This is for illustrative purposes only, inasmuch as, initially, the end of ferrule  24  will protrude beyond the optical plane  54  to its full extension β. This can be seen by the fact that the sloping surface  38  on flange or barrel  23  is not seated on the recessed portion  39  of bore  19 . When fully seated by the pressure of spring  26 , ferrule  24  extends beyond the optical plane  54  for the distance β. 
     When PWB is then plugged into its socket or mounting, not shown, assuming, for purposes of illustration, that adapter  56 , which has a connector equipped with a ferrule, not shown, therein, is misaligned in all three axes X, Y, and Z. If the ferrule therein, not shown, extends beyond the optical plane  54 , it will, when it butts against the end of ferrule  24 , push ferrule  24  toward the backplane against the pressure of spring  26 . Spring  26  is calibrated to allow such retrograde movement of ferrule  24  a distance of approximately 0.06 inches, altering the projection distance α from 0.100 inches (2.41mm) for example to 0.040 (1.14 mm) inches. In a standard plug connector, the range of movement is approximately 0.05 to 0.07 inches, which is insufficient for backplane connections in cases of misalignment especially in the Z direction. Thus, connector  11  compensates for such misalignment on the Z axis. On the other hand, if the ferrule in adapter  56  is too short to reach the optical plane  54 , the added length of ferrule  24  from the shortening of connector  11  in the connection end  14 , the end of which extends beyond the optical plane, can compensate therefor. In any case, the optical plane is moved from the α position relative to the reference surface  53 . 
     If the adapter  56  is misaligned in the X and/or Y directions, the end of the adapter  63  encounters the sloped nose  49  and is cammed into alignment thereby. In an extreme case, the misalignment may be so great as to force the connector  11  to move. Inasmuch as the receptacle  59  holds the connector  11  in a fixed position, the receptacle itself moves within its bore in the X and Y directions to accommodate the misalignment. Such flexibility of the plug connector  11  of the invention in adapting to misalignments of the devices with which it is connected results in drastic improvements in the insertion loss over what would normally be the case. 
     FIG. 7 is a plan view of the connector  11  as mounted in a duplex receptacle  64  for use with a duplex adapter  56 . 
     The plug connector of the invention as described in the foregoing, is rotation controlled in part at least because of the fit of the flats  29 — 29  in cooperation with the enlarged diameter portion  28  in sidewall openings  37 , which also increase the pull-out strength as a guard against accidental pull-out, and produces far better insertion loss performance than prior art connectors in backplane applications, as well as affording rotation control. 
     It is to be understood that the various features of the present invention might readily be incorporated into other types of connectors, and that other modifications or adaptations might occur to those skilled in the art. All such variations and/or modifications are intended to be included herein as being within the scope of the present invention as set forth hereinbefore. Further, in the claims hereafter, the corresponding structures, materials, or acts and equivalents of all means or step-plug-function elements are intended to include any structure, material, or acts for performing the functions in combination with other elements as specifically claimed.