Abstract:
A conductive tubular member surrounding an optical fiber and its connector termination. When the fiber connector termination engages a complementary connector extending through an opening in a conductive faceplate of an electronics system, the tubular member engages the securement nut holding the connector to the faceplate to function as a waveguide which attenuates radiation leaking from non-conductive gaps in the faceplate and connector. In addition, the tubular member functions as a ground path for electrostatic discharges.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to the provision of an electromagnetic compliance and electrostatic discharge shield assembly for an optical fiber connector extending through an opening in a conductive faceplate. 
     Modern electronic systems equipment, such as for telecommunications purposes, often includes various subassemblies packed closely together and interconnected by cabling. Such systems operate at relatively high frequencies and therefore electromagnetic radiation and interference is often a problem. To obviate this problem, the cables often include a conductive outer jacket which provides shielding and grounding for the cable. In addition, the subassemblies are often encased within a conductive housing. While such a housing is somewhat effective, electromagnetic radiation can still pass through gaps in the housing. At the increasingly high frequencies utilized in today&#39;s equipment, even a small gap permits unwanted electromagnetic radiation to pass therethrough. In addition, an electrostatic discharge from a person approaching the housing can jump through the gap and damage sensitive electronic components within the housing. One source of such a small gap is an optical fiber connector extending through an opening in a faceplate. The optical fiber itself is non-conductive, as are portions of the connector. Accordingly, there exists a need to provide an effective shielding and grounding assembly to eliminate the effects of such gaps. 
     SUMMARY OF THE INVENTION 
     According to the present invention, there is provided an electromagnetic compliance and electrostatic discharge shield assembly for an optical fiber connector extending through an opening in the faceplate. The assembly comprises a conductive nut adapted to secure the connector to the faceplate. A conductive elongated tubular member is provided which is adapted to surround an optical fiber connected to the connector and to engage the exterior of the nut at one end of the tubular member. 
     In accordance with an aspect of this invention, the tubular member tapers inwardly toward its end remote from the one end. 
     In accordance with another aspect of this invention, the nut has an engagement feature on its exterior circumferential surface and the tubular member has at the one end an interior engagement feature complemental to the exterior engagement feature of the nut. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing will be more readily apparent upon reading the following description in conjunction with the drawings in which like elements in different figures thereof are identified by the same reference numeral and wherein: 
     FIG. 1 is an exploded perspective view of a first embodiment of an assembly constructed in accordance with the present invention; 
     FIG. 2 is a partially cut away side view of the assembled embodiment of FIG. 1; 
     FIG. 3 is a perspective view of a second embodiment of a tubular member according to the present invention; 
     FIG. 4 is a perspective view of a third embodiment of a tubular member according to the present invention; 
     FIG. 5A shows sheet metal for forming a fourth embodiment of the tubular member according to the present invention prior to its final assembly and FIG. 5B is a perspective view, partially cut away, of the fourth embodiment of the tubular member according to the present invention; and 
     FIG. 6 is an exploded perspective view of a fifth embodiment of a nut and complementary tubular member according to the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, an optical fiber connector  10  is adapted to have an end extending through an opening  12  in a conductive faceplate  14  of an electronics system. As is conventional, the connector  10  includes a flange  16  and external threads  18 . The threads  18  are adapted to be engaged by a nut on the other side of the faceplate  14  from the flange  16  so as to securely hold the connector  10  to the faceplate  14 . An optical fiber  20  is terminated by a connector  22  which is adapted to engage the connector  10 . The foregoing is conventional and well understood by one skilled in the art. 
     It is known that the amount of leakage through a gap is a function of the size of the gap and the length of a conductive waveguide in communication with the gap. The longer the length, the less radiation from a gap of fixed size. It is also known that the ratio of length to width of a waveguide in a range from about 6:1 to 10:1 provides 180 dB of effective loss. Accordingly, the present invention increases the “length” of the gap. 
     According to the present invention, a conductive nut  24  is provided to secure the connector  10  to the faceplate  14 . The nut  24  has internal threads for engaging the threads  18  of the connector  10  and is provided with a pair of diametrically opposed slots  26  so that it can be tightened on the threads  18  by using a screwdriver. The interior dimension of the nut  24  is sufficiently large that the connector  22  can fit inside the nut  24  after the nut  24  is used to secure the connector  10  to the faceplate  14 , as shown in FIG.  2 . The nut  24  is preferably provided with an engagement feature on its exterior circumferential surface. Illustratively, the engagement feature is a circumferential exterior groove  28 . 
     To increase the gap length, there is provided a conductive elongated tubular member  30 . In the embodiment shown in FIGS. 1 and 2, the tubular member  30  is formed of an electrically conductive elastomer. The tubular member  30  has at one end an interior engagement feature complemental to the exterior engagement feature of the nut  24 . As best seen in FIG. 2, this engagement feature is an inwardly directed protrusion, illustratively a circumferential interior rib  32 , which snaps into the groove  28 . Illustratively, the tubular member  30  is tapered inwardly toward its other end so as to closely surround the fiber  20 . This further serves to decrease the effective gap. In addition to providing shielding against radiation, the aforedescribed assembly also provides shielding for electrostatic discharge by providing a conductive path from the tubular member  30  through the nut  24  to the faceplate  14 . 
     In use, the tubular member  30  is placed on the fiber  20  prior to the fiber  20  being terminated by the connector  22 . After the connector  22  terminates the fiber  20 , the connector  22  is attached to the connector  10  within the interior of the nut  24  and the tubular member  30  is moved along the fiber  20  until the rib  32  engages the groove  28 . 
     FIG. 3 illustrates an embodiment of a tubular member  34  which is formed of drawn sheet metal. In this embodiment, the end  36  of the tubular member  34  is designed to snugly fit over the nut  24  and the end  36  is formed with longitudinal slits  38  which provide resiliency. To engage the groove  28 , the tubular member  34  is illustratively formed with a plurality of inwardly directed bumps  39  located along a circle lying in a plane orthogonal to the longitudinal axis of the tubular member  34 . 
     FIG. 4 illustrates an embodiment of the tubular member  40  which is a straight sheet metal tube. Like the embodiment shown in FIG. 3, the end  42  fits snugly over the nut  24 , is formed with longitudinal slits  44  which provide resiliency, and includes inwardly directed bumps  45 . 
     As an alternative to the bumps described above, the tubular members  34 ,  40  can have their ends  36 ,  42 , respectively, folded inwardly to form an interior rib which engages the groove  28 . 
     FIGS. 5A and 5B illustrate an embodiment of a tubular member  46  formed from an annular segment of sheet metal which is then formed into a frusto-conical shape. The sheet making up the tubular member  46  may be folded inwardly at its larger radial periphery  47  to form a rib which engages the groove  28  of the nut  24 . The tubular member  46  further has a plurality of radial slits  49  originating at its larger radial periphery  47  to provide resiliency. 
     FIG. 6 shows a shielding assembly having a nut  48  and a conductive tubular member  50 . The nut  48  has interior threads  52  for engaging the threads  18  of the connector  10 . The nut  48  further has exterior threads  54  and has at least two diametrically opposed exterior flatted portions  56  which are grippable by a wrench for installation on the connector  10 . The tubular member  50  has interior threads  58  for engaging the threads  54  of the nut  48 . The other end of the tubular member  50  is hexagonally shaped so that it may be gripped by a wrench for installation. 
     For each of the tubular members  30 ,  34 ,  40 ,  46 ,  50 , the ratio of its length to its internal diameter at the end adjacent the faceplate  14  is preferably in the range from about 6:1 to about 10:1. 
     Accordingly, there have been disclosed embodiments an improved electromagnetic compliance and electrostatic discharge shield assembly for an optical fiber connector. While various illustrative embodiments of the present invention have been disclosed herein, it is understood that various adaptations and modifications to the disclosed embodiments are possible and it is intended that this invention be limited only by the scope of the appended claims.