Abstract:
An optical fiber adapter for coupling first and second dissimilar optical fiber connectors together without signal or coupling degradation has a body portion having a transverse wall. First and second latch gates form chambers for containing an alignment sleeve and one of the chambers has a spring member seated in a recess in the wall at one end of the chamber. The spring member exerts a spring force on the sleeve in opposition to the spring force of one of the connectors, so that the sum of the spring forces on the ferrules of the connectors is substantially zero, thereby insuring proper alignment and positioning of the ferrules..

Description:
RELATED APPLICATIONS  
       [0001]    This application is related to U.S. patent application Ser. No. 09/438,311 of Sheldon et al, filed Nov. 10, 1999 and assigned to Lucent Technologies, Inc., the disclosure of which is incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention disclosed herein relates to optical fiber adapters for coupling a first plug terminated optical fiber cable to a second plug terminated optical fiber cable. In particular, it relates to such an adapter for coupling terminating plugs having dissimilar size ferrules.  
         BACKGROUND OF THE INVENTION  
         [0003]    In the present state of the optical fiber art, optical fibers or cables are generally terminated in plug type connectors, and coupling two fibers together is usually accomplished by use of an adapter which receives the connector and aligns them in abutting relationship for the low-loss transmission of signals across the junction. An early type of adapter is formed as a tubular body sized and shaped to allow an alignment sleeve to pass therethrough in which the ferrules of the couplers are held in aligned, abutting relationship. An example of such an early type of coupling is disclosed in U.S. Pat. No. 5,082,345 of Cammons et al., which is adapted to couple two of the same type of optical fiber connectors together. In the Cammons patent, the ferrule of one of the connectors is introduced into one end of the alignment sleeve and the combination thus formed is passed into the adapter body. The second connector is then inserted into the adapter and its ferrule inserted into the other end of the alignment sleeve. Later developments have produced adapters wherein the alignment sleeve is contained within the adapter into which both connectors are inserted, such as is shown in U.S. Pat. No. 5,212,752 of Stephenson et al.  
           [0004]    There have been developed a large number of fiber (or cable) terminating connectors, some serving certain specific operational purposes, others by way of improved economy of manufacture, and others for simplicity of construction and/or use. Thus, there are differing connectors bearing the designations SC, ST®), FC, LC, and MU, all of which are widely used, giving rise to the situation where, quite often, a cable having a terminating connector of one type is to be connected to a cable having a termination of a different type. An early solution to this problem is disclosed in U.S. Pat. No. 5,067,783 of Lampert et al., which discloses an optical fiber adapter or build-out system comprising first and second pieces, each for receiving a particular connector differing from the other and which, when joined together, permitted coupling of FC to ST®, as well as FC to FC and ST® to ST®E. Although the Lampert et al. invention represents an advance in the art, the problem remains that new connector developments, such as the LC and the SC connectors, must be accommodated, and thus a more universal coupling apparatus is needed. U.S. Pat. No. 5,274,729 of King et al. discloses a universal build-out system which solves the ongoing problem of coupling the plethora of differing types of connectors together, and allows for the connection of SC, ST®, and FC connectors to one another, in any combination as desired. More recently, in U.S. patent application ser. No. 09/282,926; filed Apr. 1, 1999, and entitled “Universal Modular Fiber Build-Out”, there is disclosed a system for coupling not only the large 2.5 mm diameter ferrules of SC, ST®, and FC connectors to one another, but also implementing, for the first time, the coupling of the small 1.25 mm diameter ferrules of the LC connector to the large diameter ferrule of the SC, ST®, and FC connectors. The alignment sleeve can take the form of a stepped sleeve of the two differing diameters. The aforementioned Sheldon et al. application Ser. No. 09/438,311 discloses similar arrangements wherein the adapter or build-out is of one piece instead of the more common two piece arrangement, thereby resulting in a less costly device.  
           [0005]    It is standard in all of the commonly used connectors that the ferrule is movable in translation and is biased toward the coupling end of the connector generally by means of a coil spring. In a standard adapter each ferrule is biased beyond the plane of contact until the connectors are seated within the adapter, at which position the ferrules abut each other with substantially equal force and retreat from their forward position to where the plane of contact is substantially centered within the adapter, and the forces on the ferrules being equalized, the ferrules are able to move or float together in the axial direction, thereby maintaining proper alignment. However, if one of the springs has substantially greater force than the other, or if one connector has no spring, that ferrule will advance forward within the adapter until it encounters a surface that stops further movement and, as a consequence, proper alignment is degraded, the ferrules being no longer “floating”. Thus, even though the stepped sleeve accommodates the different diameter ferrules, the sleeve itself will be moved out of position due to the force of the stronger spring. When, for example, the adapter is designed to couple the large diameter (2.5 mn) ferrule of an SC type connector to the smaller diameter (1.25 mn) ferrule of the LC or MU type connector, the spring of the SC connector provides approximately two and two-tenths (2.2) pounds of force, which easily overcomes the one and two tenths (1.2) pounds of force provided by the spring of the LC or MU type connector thereby pushing the smaller ferrule out of the plane of contact, with consequent degraded alignment.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention is an adapter, comprising either a one piece or a two piece body, that contains a stepped alignment sleeve for receiving, at one end, a large diameter ferrule and, at the other end, a small diameter ferrule which sleeve is contained within the adapter by means of latch gates which allow some translational movement of the sleeve. The adapter itself is sized and shaped at one end to receive a first optical fiber connector, having, for example, a large diameter ferrule, and sized and shaped at the other end to receive a second optical fiber connector having a small diameter ferrule, as taught in the aforementioned Sheldon et al. application, and the stepped alignment sleeve is adapted to receive the ferrules thereof. A transverse wall portion within the adapter from either side of which axially extend the latch gates has a circular recess on the wall side from which extends the latch gate which contains the enlarged portion of the stepped alignment sleeve. Within the recess is mounted or positioned a spring member such as a Belleville spring or, alternatively, a coil spring, or an elastomeric spring such as an O-ring, which is adapted to bear against the shoulder formed in the stepped alignment sleeve at the junction of the two differing diameters thereof. Where, for example, the large diameter portion of the sleeve is to receive the large ferrule of an SC connector, whose spring exerts approximately two and two-tenths (2.2.) pounds of force, and the small diameter portion of the sleeve receives the ferrule of an LC type connector, whose spring exerts approximately one and two-tenths (1.2) pounds of force, the adapter spring in the recess exerts approximately one pound of force against the enlarged portion of the alignment sleeve. This one pound force works against the two and two-tenths pounds of the SC connector spring so that it is, in effect, reduced to the one and two-tenths pounds of force of the LC connector spring and the alignment sleeve floats within the chamber formed by the latch gates, thereby preventing degradation of alignment.  
           [0007]    The invention is applicable to any of a number of combinations of connectors having dissimilar spring biasing forces with the principles and features thereof being applicable thereto, including the situation, where one of the connectors has no biasing force. A further understanding of these principles and features may be had from the following detailed description, read in conjunction with the accompanying drawings. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 a  is an elevation view, partially in cross-section, of an SC type of optical fiber connector;  
         [0009]    [0009]FIG. 1 b  is an elevation view, partially cross-section, of an LC type of optical fiber connector;  
         [0010]    [0010]FIG. 2 is an elevation view in cross-section of a coupling adapter in a preferred embodiment of the invention;  
         [0011]    [0011]FIG. 3 is a front elevation view of a detail of the adapter of FIG. 2;  
         [0012]    [0012]FIG. 4 a  is a perspective view of a detail of the adapter of FIG. 2;  
         [0013]    [0013]FIG. 4 b  is an elevation view of the detail of FIG. 4 a;  and  
         [0014]    [0014]FIG. 5 is an elevation view of a different embodiment of the detail of FIG. 4 a.    
     
    
     DETAILED DESCRIPTION  
       [0015]    The principles and features of the present invention are applicable for use with virtually all optical fiber connectors and adapters. However, for simplicity, they are illustrated hereinafter as used in an adapter for coupling an SC type connector having a large diameter ferrule (2.5 mm) to an LC type connector having a small diameter ferrule (1.25 mm). It will be understood that the features of the invention are also applicable to those situations wherein the ferrule diameters of the connectors may be substantially the same, but the spring forces on the ferrules are sufficiently different to cause misalignment.  
         [0016]    In FIG. 1 there is shown an SC type connector  11  in cross-section terminating a buffered optical fiber  12 . As can be seen, connector  11  comprises a housing  13  having a bore  14  therein which contains a barrel assembly  16  having a ferrule  17  at the connector end  18  of the connector. A coil spring  19  supplies a forward bias to ferrule  17 , as discussed hereinbefore, and the ferrule  17  is movable in translation or axially over a limited range, as indicated by the arrow. FIG. 1 b  depicts, partially in cross-section, the connector end  21  of an LC type connector  22  which comprises a housing  23  having a bore  24  therein which contains a barrel assembly  26  having a ferrule  27  which projects out of the connector end  21 . A coil spring  28  applies a bias to the barrel assembly  26 , as discussed previously, and hence ferrule  27  is axially movable over a limited distance as indicated by the arrow. The ferrule  17  of the SC connector  11  is housed in an enlarged bore  29  and the ferrule  27  of the LC connector  22  is housed in an enlarged bore  31 , as shown. The connectors  11  and  22  are standard connectors in wide use, and, as discussed previously, have different spring forces acting on their ferrules which can lead to degradation of the coupling, with resultant signal degradation when they are coupled together.  
         [0017]    [0017]FIG. 2 depicts the adapter  32  of the present invention comprising a first receptacle (jack)  33  for receiving the LC type connector  22  therein and a second receptacle  34  for receiving the SC type connector  11  therein. Receptacle or jack  33  is a standard LC type jack as is shown and described in U.S. Pat. No. 5,638,474, the disclosure of which is incorporated herein by reference, as will be explained hereinafter, and has a flange  36  and front wall  35 . Flange  36  and latches  37  function to secure the receptacle or jack  33  to a panel, for example, not shown. Receptacle  34  is a standard type SC jack such as is shown in U.S. Pat. No. 5,212,752 of Stephenson et al., the disclosure of which is incorporated herein by reference, and is attached to jack  33  by suitable means, shown in FIG. 2, as press fit pin  38 . Other means for jointing receptacle  33  and  34  such as ultrasonic bonding or incorporating as a unitary adapter housing may be used. Together, receptacles  33  and  34  form an elongated adapter body.  
         [0018]    In accordance with the present invention, wall  35  has a latch gate  40  extending therefrom into jack  34 , at the interior base of which is a circular recess  39  which contains a spring member  41 . Extending from the opposite side of wall  35  is a second latch gate  42 . The exterior dimension (diameter) of gate  40  is less than the interior diameter of enlarged bore  29  of the SC connector  11  and the diameter of gate  42  is less than the inside diameter of enlarged bore  31  of LC connector  22 . It can be seen that latch gate  40  forms a chamber  43  which contains the large diameter portion  44  of a stepped ferrule alignment sleeve  46  and latch gate  42  similarly defines a chamber  47  which contains the small diameter portion  48  of the stepped alignment sleeve  46 . Alignment sleeve  46  is preferably made of metal or, for instance, plastic or ceramic material. Latch gates  40  and  42  are preferably made of the same plastic material as the jacks  33  and  34 . Preferably the latch gate  40  has to be sufficiently resilient to allow alignment sleeve  46  to be forced into the containment chambers  43  and  47  and, when the sleeve  46  is within the chambers, they snap into the position shown to hold sleeve  46  within the chambers  43  and  47  while allowing some movement thereof. To this end, as is characteristic of latch gates, such as are shown in the aforementioned Sheldon et al. patent application Ser. No. 09/438,311, the distal ends of the gates  40  and  42  have enlarged ridges  49  thereon. FIG. 3 is an end view of the latch gate  40 , showing splits  51  which allow the gate  40  to flex as stepped alignment sleeve  46  is being inserted through the gate into the chambers  43  and  47 . An end view of gate  42  would be similar, but the splits  51  are not required.  
         [0019]    In operation, connector  11  is inserted into jack  34  and its ferrule  17  into the large diameter portion  44  of alignment sleeve  46 , and connector  22  is inserted into jack  33  and its ferrule  27  into the small diameter portion  48  of sleeve  46 . Coil spring  19  of the SC connector  11 , being stronger than spring  28  of LC connector  22 , in the absence of spring member  41 , spring  19  would tend to overcome spring  28  until sleeve  46  bottomed in recess  39 , thereby shifting the plane of abutment of the two ferrule  17  and  27 . However, spring member  41  bears against the shoulder  52 , best seen in FIG. 4 b , and supplies a bearing force to sleeve  46  in opposition to that supplied by spring  19 . As pointed out hereinbefore, the force of spring member  41  is substantially equal to the force difference between springs  19  and  28 , so that the stepped sleeve  46  is prevented from bottoming in recess  39 , and the plane of abutment of the ferrules does not shift, and the junction is not mis-aligned.  
         [0020]    [0020]FIG. 4 is a perspective view of the alignment sleeve  46  and the spring member  41 , shown as a Belleville spring having a central hole  52  to allow passage of the small diameter portion  48  of sleeve  46  therethrough. FIG. 4 b  is a side elevation view of the arrangement of FIG. 4 a . It can be seen that the junction of portions  44  and  48  of sleeve  46  forms a shoulder  52  against which spring member  41  bears. For easier insertion of sleeve  46  into latch gates  40  and  42 , the junction end of large diameter portion  44  at the shoulder  52  has a rounded edge. FIG. 5 is a view similar to that of FIG. 4 b  in which the spring member is a coil spring  56 . The operation is the same as that with the Belleville spring, with the coil spring being seated in recess  39  and bearing against shoulder  52 .  
         [0021]    The features of the present invention have been illustrated herein in an embodiment for coupling SC and LC connectors together. It is to be understood that the same principles can be used for coupling other types of connectors together where there is a difference in the bias forces applied to the ferrules thereof. In addition, the apparatus of the preferred embodiment is a coupling adapter having two parts. It is to be understood that the principles and features of the present invention are equally applicable to a unitary or once piece adapter similar to those disclosed in the aforementioned Sheldon et al. application. It is further to be understood that the introduction of combinations of different diameter ferrules with a fiber stub and with either one or two cylindrical alignment sleeves will also require force balancing. Using two sleeves, the adapter serves the same purpose but obviates the requirement of a precision stepped sleeve.  
         [0022]    It is further to be understood that the various features of the present invention, in being incorporated into other types of coupling arrangements might be subject to various modifications or adaptations to achieve force balancing in accordance with the present invention which might occur to workers in the art. All such variations, adaptations, or modifications are intended to be included herein as being within the scope of the invention as set forth herein. Further, in the claims hereinafter, the corresponding structures, materials, acts and equivalents of all means or step-plus-function elements are intended to include any structure, materials, or acts for performing the functions in combination with other elements as specifically claimed.