Abstract:
The invention relates to an optical pin-and-socket connector for the detachable connection of a plurality of optical cores ( 115 ) having an insert ( 112, 112 ′), in which the cores ( 115 ) are inserted on a first side, the cores ( 115 ) ending in said connector with the optical fibers ( 119, 120 ) thereof, and said connector having an expansion device ( 117, 118 ) on a second side, on which the beams exit the fibers ( 119, 120 ) in an expanded manner. A simplification of the assembly and installation is achieved in that the insert ( 112, 112 ′) comprises two separate partial elements ( 113, 117, 118 ) that can be assembled, one of which is configured as an expansion device ( 117, 118 ) and the other is configured as a retaining block ( 113 ) for receiving the ends of the optical cores ( 115 ).

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the field of optical telecommunications. It relates in particular to an optical plug connector as claimed in the precharacterizing clause of claim  1 . 
     2. Discussion of Related Art 
     Because of their wide bandwidth and insensitivity to electromagnetic interference fields, optical fiber networks are being used increasingly in all fields for data transmission. In this case, plug connectors are used for detachable connection between different cables and their cores, which plug connectors are arranged at the cable ends or core ends and, in the mated state, reliably input the light signals which emerge from the fiber ends on one side of the connector into the fiber ends on the other side of the connector. 
     As the complexity of transmission networks increases and the appliances that are used are increasingly miniaturized, the packing density of the plug connections is becoming ever more important. With standardized individual plugs of the LC, SC, ST type or the like, the achievable densities are essentially governed and limited by the comparatively large plug housings. A certain amount of compression can be achieved by the combination of individual plugs in pairs to form duplex plugs (see for example EP-A1-1 341 015). Other plug connector systems of the MT type admittedly achieve higher densities by using a common ferrule for a plurality of fibers, but they are restricted to optical cables in the form of ribbons, and are not suitable for the common plug connection between individual cores (see for example EP-A2-0 997 757 or WO-A1-2006098734). 
     In particular, plug connector systems such as these require direct contact between the end surfaces of the individual fibers which are fixed in the ferrules, and this necessitates accurate processing of the fiber ends which are flush with the ferrules, by various types of grinding processes, and precise orientation of the fiber ends during installation into the plug connectors and during mutual alignment in the inserted state. 
     On the other hand, it is known for optical means such as lenses to be used at the fiber ends in plug connector systems, in order to widen the beam emerging from the fiber ends and to make it parallel, thus making the requirements for mutual alignment of the fibers to be connected less stringent. Plug connector systems such as these are known for individual fibers, for example, from U.S. Pat. No. 5,768,458 A1 or for a plurality of fibers from JP-A-2007041222. It is also possible to use specially shaped mirror elements (DE-A1-100 43 985) instead of lenses. 
     However, with plug connector systems such as these, the fabrication of the fiber ends, as well as their alignment and fixing with respect to the beam-widening optical means or elements, are complex and problematic. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is therefore to provide an optical plug connector and an optical plug connector system which allow high connector densities, are of simple design and are distinguished by simplified fabrication of the cable and core ends, and to specify a method for their production. 
     The object is achieved by the totality of features of claims  1 ,  12  and  14 . One essential feature for the optical plug connector according to the invention is an insert into which the cores of a cable to be connected are inserted on a first side, and in which the cores end with their optical fibers. This insert has a widening apparatus on a second side, on which the beams emerge widened from the fibers. The insert comprises two separate partial elements which can be joined together, one of which is in the form of a widening apparatus and the other is in the form of a holding block for holding the ends of the cores. This advantageously makes it possible to still process the fiber ends with comparatively few restrictions when the core ends are already held by the holding block. 
     The holding block and the widening apparatus are preferably designed and matched to one another such that, when the insert is joined together, the fibers of the core ends which are held by the holding block have a fiber section of predetermined length which projects out of the holding block and into the widening apparatus. The fiber ends are therefore freely accessible and can be processed precisely and quickly by means of a laser method. 
     The core ends can be held particularly easily if the holding block has a core hole for each of the core ends, which core hole extends into the holding block on the first side and merges via an adjacent insertion cone into a fiber hole which ends on the opposite side of the holding block. 
     In this case, it is advantageous for the connection density if the core holes or fiber holes are arranged parallel to one another and in a plurality of rows one above the other in the holding block. A checkerboard-like or very densely packed arrangement, or some other suitable arrangement of the holes, can be provided in this case. 
     Another refinement of the optical plug connector according to the invention is characterized in that the widening apparatus has first means for widening the beams which emerge from the cores, and has second means for holding and adjusting the fiber sections which project out of the holding block with respect to the first means, wherein either the first means comprise refractive optical elements, in particular in the form of lenses, spherical lenses or GRIN lenses, or comprise reflective optical elements, in particular in the form of mirrors or parabolic mirrors. 
     According to a further refinement of the invention, the second means comprise adjusting holes or V-grooves. 
     Another refinement is distinguished in that the end surfaces of the fiber sections which project out of the holding block are laser-processed, wherein a process which is known as laser cleaving is preferably used for this purpose. 
     The insert is preferably fitted into a housing. 
     In the method according to the invention, in a first step, the optical fibers are exposed over a predetermined length at the core ends which are associated with the plug connector, before, in a second step, the core ends with the exposed fibers are inserted into the holding block and are fixed there, such that a fiber section of each of the exposed fibers projects out of the holding block, in a third step, the projecting fiber sections are processed by a laser cleaving process, in a fourth step, the holding block with the core ends held in it is joined to a widening apparatus that is provided to form an insert, and finally the insert is fitted into a housing. 
     One preferred refinement of the method according to the invention is distinguished in that a widening apparatus is used which comprises optical means for widening the beams which emerge from the cores, and in that the exposed fiber sections are adjusted with respect to the optical means when the holding block and the widening apparatus are being joined together. 
     The optical plug connector system according to the invention comprises two optical plug connectors which are matched to one another and can be detachably connected to one another, wherein the two plug connectors are designed according to the invention. 
     The inserts of the two plug connectors are preferably of the same type. 
     It is also advantageous if the inserts of the two assembled plug connectors are aligned with one another with respect to the optical axes, and are at a distance from one another. 
     In particular, the plug connectors can be latched to one another by a screw connection, a bayonet fitting or a sprung quick-action catch, wherein the plug connectors can preferably be latched to one another forming a seal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be explained in more detail in the following text with reference to exemplary embodiments and in conjunction with the drawing, in which: 
         FIG. 1  shows a top view of one exemplary embodiment of an insert according to the invention; 
         FIG. 2  shows a side perspective view of one exemplary embodiment of an insert according to the invention; 
         FIG. 3  shows a front perspective view of one exemplary embodiment of an insert according to the invention; 
         FIG. 4  shows a side perspective view of one exemplary embodiment of an insert according to the invention; 
         FIG. 5  shows the arrangement of two inserts as shown in  FIGS. 1-4  within a plug connector system; 
         FIG. 6  shows a perspective exploded illustration of the various partial elements of the insert as shown in  FIGS. 1-4 ; 
         FIG. 7  shows the holding block for the insert from  FIGS. 1-4  with the projecting fiber sections which are accessible for processing; 
         FIG. 8   a  shows a widening apparatus, as an alternative to the exemplary embodiment shown in  FIG. 6 , with parabolic mirrors and V-grooves; 
         FIG. 8   b  shows a longitudinal section through an insert having the widening apparatus as shown in  FIG. 8   a;    
         FIG. 9   a  shows an exemplary embodiment, which is comparable to  FIG. 8 , with only one mirror per insert and plug connector; 
         FIG. 9   b  shows the optical coupling between the inserts of two plug connectors from  FIG. 9   a  in the mated state; 
         FIG. 10  shows a longitudinal section through an insert having an alternative widening apparatus to that in  FIG. 8  with spherical lenses; 
         FIG. 11  shows a highly schematic illustration of an example of the fitting of the insert as shown in  FIGS. 1-4  into a plug connector; 
         FIG. 12  shows a highly schematic illustration of a plug connector system having two mated plug connectors as shown in  FIG. 11 ; and 
         FIG. 13  shows various steps for the production of a plug connector according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 11  shows a highly schematic illustration of a plug connector  110  according to one exemplary embodiment of the invention. A plurality of optical cores  115  end in an insert  112  within the plug connector  110 , which insert  112  is fitted into a housing  111  and designed as shown in  FIGS. 1-7 . By way of example, two plug connectors  110  and  110 ′ of the same type are plugged together in the plug connector system  100  illustrated in  FIG. 12 , with their inserts  112 ,  112 ′ being aligned with one another on the optical axes  136  as shown in  FIG. 5 , and being at a distance a from one another, across which the two inserts  112 ,  112 ′ interchange beams. 
     As can be seen in particular from  FIG. 6 , the insert  112  in this exemplary embodiment comprises a plurality of partial elements, specifically a holding block  113 , an adjusting apparatus  117  and an optical widening block  118 . The adjusting apparatus  117  and the optical widening block  118  together form a widening apparatus  114  ( FIGS. 1-4 ) whose purpose is to widen the beams emerging from the core ends  115 , for inputting into the complementary plug connector. The holding block  113  holds the ends of the cores  115  with the fibers  119  exposed over a distance, and mechanically fixes them. For this purpose, preferably parallel arrangements in two rows one above the other in each case comprising a core hole  121 , an insertion cone  122  and a fiber hole  123  are provided in the holding block  113 , are arranged one behind the other in the insertion direction of the core  115 , and hold the cores  115  and the fibers  119  in the manner illustrated in  FIG. 5 . 
     In this exemplary embodiment, the adjusting apparatus  117  is a plate of constant thickness, which has adjusting holes  124  in the form of precise microholes at the points which correspond to the fiber holes  123 , in which adjusting holes  124  the fibers  119  whose fiber sections  120  project out of the holding block  113  (see  FIG. 7 ) are guided precisely by these fiber sections  120 . 
     In this example, the widening block  118  is an integral block composed of glass or some other transparent material, on whose outside beam-widening optical elements in the form of convex lenses  116  are formed, which form a two-row arrangement corresponding to the holes  121 ,  123  and  124  and, when the insert  113  has been joined together, correspond with the adjusting holes  124  with respect to the optical axis. However, the widening block  118  may also be joined to the adjusting apparatus  117  to form a micromechanically processed unit. 
     During the fabrication process, the fibers  119  are first of all exposed over a certain length on the individual cores  115 . The core ends  115  with the exposed fibers  119  are then inserted into the appropriate holes  121 ,  123  in the holding block  113 , until this results in the configuration illustrated in  FIG. 7 , in which the fiber sections  120  of the fibers  119  project freely out of the opposite side of the holding block  113 . In this case, the insertion cones  122  make it easier to insert the fibers  119  into the fiber holes  123 . The fiber sections  120 , which project out of the fiber holes  123 , are now freely accessible for processing, preferably laser processing (laser cleaving) by means of a laser beam  135  which originates from a laser  134 , during which process the length of the fiber section  120  and the end surface of the fiber are processed optically precisely. Details relating to the process of laser cleaving can be found in the following publication: Ammer, T.; Strasser, M. M.; Studer, H.; Zaina, P.; Compare, C., Novel small form factor optical ribbon fiber connector for singlemode applications, Fibres and Optical Passive Components, 2005. Proceedings of 2005 IEEE/LEOS Workshop on 22-24 Jun. 2005 page(s): 339-344. 
     The arrangement comprising the cores  115  and holding block  113  that has been processed in this way is now joined to the widening apparatus  114  that is provided, with the exposed fiber sections  120  entering the adjusting holes  124  in the adjusting apparatus  117  as shown in  FIG. 5  and with the end surface of said fiber sections abutting to a greater or lesser extent on the widening block  118 . During operation, the beams emerge from the fiber ends and enter the widening block  118 , which they leave—widened by the optical widening elements  116 —on the opposite side. They are focused again in the opposite manner in the mating plug of the same type, and are input into the fiber ends. This allows coupling between the plug connectors, requiring neither direct mechanical contact between the front faces of the plug connectors nor high-precision alignment of the optical axes. 
     Other exemplary embodiments of widening apparatuses for the purposes of the invention are shown in  FIGS. 8 to 10 .  FIG. 8   a  shows a widening apparatus  125  in which the beam coming from the fiber  119  is deflected twice via two reflective elements in the form of parabolic mirrors  129 ,  130 , and is widened in the process. The widening apparatus  125  is in this case composed of a separate upper part  126  and a separate lower part  127 , in each of which one of the parabolic mirrors  129 ,  130  is arranged. V-grooves  128  which match the mirror pairs  129 ,  130  are provided alongside one another in the lower part  127  and, interacting with the upper part  126  placed thereon, adjust the inserted fiber sections, clamping them, thus forming an integrated adjusting apparatus. Together with the holding block  113 , this therefore results in the insert  132  that is illustrated schematically in  FIG. 8   b.    
       FIG. 9  shows an exemplary embodiment which is comparable to  FIG. 8 , wherein the sub- figure 9   a  shows the arrangement in the unmated state, and the sub- figure 9   b  shows the arrangement in the mated state. The mutually complementary inserts  138 ,  138 ′ have a respective widening apparatus  139  and  139 ′, which have only one reflective element in the form of a respective mirror  137  or  137 ′. The optical coupling between the two inserts  138 ,  138 ′ in the mated state ( FIG. 9   b ) takes place at right angles to the optical axis of the two optical fibers  119 . The specific configuration of the widening apparatuses  139 ,  139 ′ makes it possible to manage with only one injection-molded part (for the widening apparatus  139 ,  139 ′), which can be fitted on both sides of the plug connection. 
       FIG. 10  shows a further exemplary embodiment of a widening apparatus  131  which, together with the holding block  113 , forms the insert  142 . In order to widen the beam, the widening apparatus  131  in each case contains a spherical lens  133 , the center point of whose sphere lies on the optical axis of the associated fiber  119 . However, other types of beam-widening elements are also feasible, for example cylindrical lenses with a gradient index (GRIN) or the like. 
     Overall, the invention results in an optical plug connector which is distinguished by the following advantages:
         No spacers are required in the plug connection.   No fiber block needs to be polished.   No precautions need be taken for index matching.   The precision requirements for the holding block are low.   All of the fibers can be processed in one process.   Mechanical contact is possible between the fiber ends and the widening apparatus.