Abstract:
An optical connector consists of a ferrule unit including an optical fiber, a ferrule rigidly fitted to one end of the optical fiber, and a spring placed around the optical fiber which abuts at one end against the ferrule, a plug housing which receives the ferrule unit, and a spring cap having a rear wall and a fiber letting-out portion formed in the rear wall through which the optical fiber is let out. The spring cap is fittable, with the spring abutting at the other end thereagainst, to the plug housing. The plug housing has a resilient protecting means which, when the spring cap is fitted to the plug housing, overhangs a part of the optical fiber let out through the fiber letting-out portion of the spring cap. The optical fiber is protected at that port let out of the spring cap if bent.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an optical connector having an optical plug of a structure in which a spring cap is fitted to a plug housing. 
     2. Description of the Related Art 
     An optical connector is used in connecting, for example, an optical fiber (or optical fiber cable) which constitutes a multiple transmission circuit in a vehicle such as an automobile to a transmitter, receiver or another cable. 
     Such an optical connector, as shown in FIG. 9, consists of an optical plug  1  and a not-shown mating receptacle, the optical plug  1  including ferrule units  2 ,  2 , a plug housing  3 , and a spring cap  4 . The ferrule units  2 ,  2 , each having an optical fiber  5 , are assembled to the spring cap  4  and then inserted into the corresponding receiving cavities  6 ,  6  of the plug housing  3  until the spring cap  4  fits to the plug housing  3 . 
     More specifically, each ferrule unit  2  consists of the optical fiber  5 , a spring  7  and a ferrule  8 . To the optical fibers  5 ,  5 , the spring cap  4  and the springs  7 ,  7  are in this order assembled, and then the ferrules  8 ,  8  so as to be located at the ends of the optical fibers  5 ,  5 . Each spring  7  abuts at one end against the rear end surface of the related ferrule 
     The plug housing  3 , which is of box-like rectangular shape, has the receiving cavities  6 ,  6  formed to extend longitudinally therethrough. On its upper wall at the center, the plug housing  3  has a locking arm  9  used in coupling with the not-shown receptacle. 
     The spring cap  4  is designed to fit over the rear end of the plug housing  3  and has at the rear wall a support  10  with throughholes  11 ,  11  formed therein through which the optical fibers  5 ,  5  are let out. Each spring  7  abuts at the other (rear) end against the spring cap rear wall at the inner side. 
     With the spring cap  4  of the above conventional optical connector, however, because as shown in FIG. 10 each optical fiber letting-out throughhole  11  of the support  10  is formed merely cylindrical, if the optical fiber  5  is excessively bent, for example, by accident as shown by the imaginary line, stresses tend to focus on the optical fiber  5  at the throughhole  11 , resulting in breakage of the optical fiber  5  and a malfunction in the transmission circuit. 
     SUMMARY OF THE INVENTION 
     This invention has been accomplished to overcome the above drawback and an object of this invention is to provide an optical connector which protects the optical fiber at its optical-fiber letting-out portion. 
     In order to attain the object, according to this invention, there is provided an optical connector which comprises: a ferrule unit including an optical fiber, a ferrule rigidly fitted to one end of the optical fiber, and a spring placed around the optical fiber which abuts at one end against the ferrule; a plug housing which receives therein the ferrule unit; and a spring cap having a rear wall and a fiber letting-out portion formed in the rear wall through which the optical fiber is let out, the spring cap being fittable, with the spring abutting at an opposite end thereagainst, to the plug housing, wherein the plug housing has a resilient protecting means which, when the spring cap is fitted to the plug housing, overhangs a part of the optical fiber let out through the fiber letting-out portion of the spring cap. 
     Preferably, the resilient protecting means comprises a cantilever plate extending in a fitting direction of the spring cap and the plug housing. 
     Preferably, the resilient protecting means overhangs the part of the optical fiber let out through the fiber letting-out portion, at a side toward which the part of the optical fiber is assumed to be bent. 
     Preferably, the fiber letting-out portion comprises a slit formed in the rear wall of the spring cap through which the optical fiber and the resilient protecting means extend outside the spring cap. 
     Advantageously, the spring cap has an optical-fiber support of U-shaped cross section provided on the rear wall of he spring cap to surround, along with the resilient protecting means, the part of the optical fiber let out through the fiber letting-out portion. 
     Preferably, the spring cap has a plurality of resilient cantilever protecting plates provided on the rear wall of the spring cap to surround, along with the resilient protecting means, the part of the optical fiber let out through the fiber letting-out portion. 
     Preferably, three of the resilient cantilever protecting plates are provided to be located on left and right sides and a lower side of the fiber letting-out portion to surround, along with the resilient protecting means, the part of the optical fiber on a total of four sides around the part of the optical fiber. 
    
    
     The above and other objects, features and advantages of this invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an optical connector according to one embodiment of this invention, with its receptacle and optical plug shown separated; 
     FIG. 2 is an exploded perspective view of the optical plug of FIG. 1; 
     FIG. 3 is an enlarged perspective view of a plug housing in FIG. 2; 
     FIG. 4 is an enlarged perspective view of a spring cap in FIG. 2; 
     FIG. 5 is an enlarged perspective view of the spring cap in FIG. 2, seen from the plug housing side; 
     FIG. 6 is a front view of the spring cap in FIG. 2; 
     FIG. 7 is a rear view of the optical plug of FIG. 1; 
     FIG. 8 is a rear view of an optical plug according to this invention, with another embodiment of a spring cap; 
     FIG. 9 is a disassembled perspective view of a conventional optical plug; and 
     FIG. 10 is a sectional view of an optical fiber support of the optical plug of FIG.  9 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of this invention will now be described with reference to the attached drawings. 
     In FIG. 1, denoted  31  is an optical connector for use in a multiple transmission circuit in a vehicle such as an automobile, the optical connector  31  consisting of a receptacle  32  and an optical plug  33 . As will be apparent from the following description, the optical plug  33 , if a later-described optical fiber  42  is bent to an excessive degree, alleviates concentration of stress and protects the optical fiber  42  at its letting-out portion from such stress. 
     The receptacle  32  has a connector housing  34  which opens at the front and rear. The optical plug  33  is fitted through the front opening  35  in the connector housing  34 . Denoted  36  is a fitting chamber for the optical plug  33 , and inside the fitting chamber  36  is formed a locking groove  37  for a later-described locking arm  52 . Sleeves and then optical element modules (either not shown), which constitute the receptacle  32 , are placed through the rear opening (not shown) in the connector housing  34 , followed by closing the rear opening with a rectangular plate-like cap (not shown). Denoted  38  are receiving cylinders to each of which are fitted at the opposite ends the sleeve and a later-described ferrule  43 . 
     The optical plug  33 , as shown in FIG. 2, consists of ferrule units  39 ,  39 , a plug housing  40  which receives the ferrule units  39 ,  39 , and a spring cap  41  fitted over the rear end of the plug housing  40 . 
     Each ferrule unit  39  consists of an optical fiber  42 , the ferrule  43  fitted at the front end of the optical fiber, and a spring  44  placed around the optical fiber  42 , between the ferrule  43  and the spring cap  41 . 
     The optical fiber  42  consists of a core  45  of a transparent resin such as PMMA (polymethyl methacrylate (methacrylate resin)), a synthetic-resin made first sheath  46  around the core, and a synthetic-resin made second sheath  47  around the first sheath. The optical fiber  42  is peeled at the front end to be inserted into the related ferrule  43 . 
     The ferrule  43  is made of synthetic resin and has a cylindrical small diameter portion  48  and a large diameter portion  49 . The core  45  of the optical fiber  42  is received in the small diameter portion  48 , and the first sheath  46  in the large diameter portion  49 . The ferrule  43  and the related optical fiber  42  are firmly fixed together with an adhesive or the like. 
     The large diameter portion  49  of each ferrule  43  is circumferentially provided with two flanges  50 ,  50 , and the spring  44  around the optical fiber  42  is interposed between the rearward flange  50  and the spring cap  41 . 
     The plug housing  40 , as shown in FIGS. 2 and 3, has a box-like rectangular shape and has hollow receiving cavities  51 ,  51  formed therein which receive the ferrule units  39 ,  39 . On its upper wall, the plug housing  40  has a locking arm  52  lockingly engageable in the locking groove  37  of the receptacle  32  (FIG.  1 ), a pair of guide plates  53 ,  53  for the spring cap  41 , and protecting projections  54 ,  54  for the respective optical fibers  42 ,  42 . On its side walls at an intermediate length thereof, the plug housing  40  has locking projections  55 ,  55  (only one is shown) for locking engagement with the spring cap  41 . Each guide plate  53 , which is integral with and in the same vertical plane as the related side wall of the plug housing  40 , extends in a fitting direction of the plug housing  40  with the spring cap  41 , from the rear end of the side wall to an intermediate length thereof. 
     The protecting projections  54 ,  54  are cantilever projections (plate-like cantilever projections in the present embodiment) provided at the rear end of the plug housing  40 , have resiliency and, when the spring cap  41  and the plug housing  40  are fitted together, project outside the spring cap  41  to prevent harsh bending of the optical fibers  42 ,  42  let out of the spring cap  41  at the rear end. 
     In other words, in the present embodiment, on the assumption that the optical fibers  42 ,  42  would be excessively bent upwardly (FIG.  1 ), the protecting projections  54 ,  54  overhang (extend from the upper wall of the plug housing  40 ) at the upper edges of the openings of the receiving cavities  51 ,  51  formed at the rear end of the plug housing  40 . Due to this arrangement, the protecting projections  54 ,  54 , if the optical fibers  42 ,  42  are harshly bent, resiliently contact with and act on the optical fibers  42 ,  42  in the direction of restricting their bending and pushing them back. The concentration of stress on the optical fibers  42 ,  42  at the letting-out portion is thus alleviated to protect the optical fibers  42 ,  42 . 
     Because the protecting projections  54 ,  54 , as indicated above, are provided to overhang the optical fibers  42 ,  42  at a side toward which the optical fibers are assumed to be bent, the protecting projections  54 ,  54  reliably make resilient contact with the optical fibers  42 ,  42  bent in the thus assumed direction. 
     The protecting projections  54 ,  54  may be provided to have a thickness that becomes smaller toward their tip ends. 
     The spring cap  41  is provided in one piece and, as shown in FIGS. 4 to  6 , consists of a base wall  56 , a pair of opposite side walls  57 ,  57  and a rear wall  58  and is fittable, as mentioned above, over the rear end of the plug housing  40 . 
     Each side wall  57 , as shown in FIG. 5, has two sections D 1 , D 2  adjoining each other in the longitudinal direction thereof, the section D 1  having a longitudinal slit  61  formed therein and a locking portion  59  located at the front end of the slit  61  (the end toward the plug housing  40 ) for locking engagement with the related locking projection  55  of the plug housing  40  (FIG.  3 ), and the section D 2  having at the inner side a guide groove  60  for sliding therein of the related guide plate  53  (FIG.  3 ). Because the locking portion  59  is located on a side toward the plug housing  40  as compared with a line connecting the points A and B on the spring cap  41  (FIGS.  4  and  5 ), the locking portion  59  easily comes into engagement with the related locking projection  55  if, during fitting the spring cap  41  to the plug housing  40 , the side wall  57  rides on the locking projection  55 , bends outwardly at the front upper portion C, and rides over the locking projection  55 . The slit  61  formed in each side wall  57  reduces the rigidity of the side wall  57  and makes its front upper portion C bendable more easily. 
     Each guide groove  60  is provided in an inverted U shape and extends in the fitting direction of the plug housing  40  with the spring cap  41 . The guide groove  60  receives from the front end the related guide plate  53  (FIG. 3) and is closed at the rear end by the rear wall  58  of the spring cap  41 . 
     The rear wall  58  is formed with fiber letting-out portions  63 ,  63  for passage therethrough of the optical fibers  42 ,  42  (FIG.  2 ). Each spring  44  abuts at the rear end against the rear wall  58  around the respective fiber letting-out portion  63 . In the present embodiment, each letting-out portion  63  is provided in a substantially U-shaped slit extending from the upper edge of the rear wall  58 . The optical fiber  42  and the protecting projection  54 , when the spring cap  41  and the plug housing  40  are fitted together, extend through this slit to the outside of the spring cap  41 . 
     The rear wall  58  has supports  64 ,  64  projecting rearwardly therefrom. The supports  64 ,  64  have substantially U-shaped cross section and support the optical fibers  42 ,  42  let out through the letting-out portions  63 ,  63 . Each support  63  is provided to substantially enclose a lower half of the related letting-out portion (slit)  63  and is upwardly closed, when the spring cap  41  and the plug housing  40  are fitted together, by the related protecting projection  54  (FIG.  1 ). 
     With the construction as mentioned above, if the optical plug  33  fits in the receptacle  32 , the receiving cylinders  38 ,  38  of the latter advance into the plug housing  40 , while at the same time the small diameter portions  48 ,  48  of the ferrule units  39 ,  39  advance into the receiving cylinders  38 ,  38 , at which time the large diameter portions  49 ,  49  of the ferrule units  39 ,  39  abut against the front ends of the receiving cylinders  38 ,  38  with an appropriate pressure resulting from the springs  44 ,  44 . In this condition, the front ends of the ferrule units  39 ,  39  and the sleeves, and the optical element modules and the sleeves are located relative to each other with a minimum space (not shown) therebetween. 
     Another embodiment of a spring cap according to this invention will now be described with reference to FIG.  8 . An optical plug  65  as shown in FIG. 8, like the optical plug  33  (FIG.  2 ), is assembled from the ferrule units  39 ,  39 , the plug housing  40  and a spring cap  66 . 
     The spring cap  66  has the same structure as the spring cap  41  in the preceding embodiment (FIG.  4 ), except that each support  64  is replaced by three protecting projections  67 . 
     The three protecting projections  67 , like the protecting projection  54  (FIG.  3 ), are resilient plate-like cantilever projections provided at the related letting-out portion of the spring cap  66  through which the related optical fiber  42  is let out. 
     The three protecting projections  67 , as shown in FIG. 8, project rearwardly on the left and right and lower sides of the fiber letting-out portion and, along with the protecting projection  54  extending from the plug housing  40 , surround the optical fiber  42  let out through the fiber letting-out portion at the four sides, so as to protect the related optical fiber  42  if the optical fiber is excessively bent at any of the angles of 360 degrees. It is to be noted, however, that the number and arrangement of the protecting projections  54 ,  67  are not limited to those as shown in FIG. 8, and five or more protecting projections may be provided in another arrangement insofar as capable of serving the mentioned effect as protecting projections. 
     The optical plug  65  with the spring cap  66  employed therein serves the same effect as the optical plug  33  in the preceding embodiment. 
     Having now fully described the invention, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without departing from the spirit and scope of the invention as set forth herein. For example, this invention is also applicable to an optical connector for use in a one-core type optical fiber bidirectional communication system.