Abstract:
The optical fiber connector includes a connector housing ( 21 ), having a splice assembly ( 13 ) therein, and an end cap ( 5 ) attached to one end of the connector housing ( 21 ), from which leads out a primary coating portion ( 3 ). A boundary ( 4   c ) between a portion of the primary coating portion ( 3 ), obtained by removing an outer coating ( 4   b ) of the inner cover ( 4 ) while leaving an inner coating ( 4   a ), and a portion obtained by leaving the outer coating ( 4   b ) of the inner cover ( 4 ), is located in the interior of the connector housing ( 21 ). The end cap ( 5 ) is provided in the interior thereof with a tubular portion and an extension extending from an end of the tubular portion, the tubular portion including an insert hole for an insertion of the primary coating portion ( 3 ) approximately coaxially with a guiding hole formed in the splice assembly accommodated in the connector housing ( 21 ) for guiding the primary coating portion ( 3 ) leading out from the splice assembly. The extension includes a strain-control hole, communicating with the insert hole, for receiving said boundary ( 4   c ) of the primary coating portion ( 3 ), and for controlling stress at the boundary ( 4   c ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an optical fiber connector, having a splice assembly therein, for optically connecting together end surfaces of plain fiber portions, from each of which has been removed a cover of the optical fiber cable, while abutting the end surfaces to each other. 
       BACKGROUND 
       [0002]    In general, an optical fiber connector having a splice assembly therein for optically connecting end surfaces of plain fiber portions, from each of which has been removed a cover of the optical fiber cable, while abutting the end surfaces to each other, has been conveniently used at a work-site for easily connecting optical fiber cables to each other, as disclosed in Japanese Patent No. 3445479. 
         [0003]    Japanese Patent No. 3445479 discloses a so-called mechanical-splice-type optical fiber connector comprising a splice assembly for holding a ferrule having a primary coating portion and an extension of the primary coating portion leading out from a rear end surface of the ferrule, wherein a primary coating portion of an optical fiber cable is guided into the splice assembly from an end thereof so that end surfaces of the plain fiber portions are abutted to each other and optically connected to each other. 
         [0004]    Such an optical fiber connector is used, for example, when a domestic data communication service is provided through optical fibers, and is stored in an optical communication junction box of a predetermined size provided on a telephone pole or in a residence. The optical communication junction box also has optical fiber cables and optical devices other than the optical fiber connector. On a side of the optical fiber connector from which the optical fiber is led out, the optical fiber cable may be guided via a boot member for avoiding abrupt bending of the optical fiber cable. 
         [0005]    As optical fiber data communication services have become popular, the number of optical devices used therefor has increased, whereby the vacant space within the optical communication junction box has been reduced. Accordingly, it is desired to miniaturize the optical fiber connector to be accommodated in the optical communication junction box. When the boot member is mounted to a wall of the optical fiber connector, however, there is a problem in that a side of the optical fiber connector from which the optical fiber leads out is protruded to substantially enlarge the size of the optical fiber connector, which again reduces vacant space available within the box. To solve such a problem, a countermeasure has been demanded wherein the optical fiber can be bent within the connector and without using the boot member. 
         [0006]    On the other hand, a proposal has been made wherein the primary coating portion is covered solely with a thin inner coating to increase the vacant space within the box because it would be unnecessary to cover the outer circumference of the primary coating portion with a thick coating of, for example, polyethylene, within the optical communication junction box. In this case, the primary coating portion with, for example, a diameter of 0.25 mm suitably has a multi-layered structure covered with a thin coating for the purpose of facilitating handling and/or visibility. 
         [0007]      FIG. 5  illustrates one example of the prior arts cited as a comparison with the present invention. In the drawing, when a splice assembly  33  stored within an optical fiber connector  30  corresponds to a primary coating portion of 0.25 mm diameter, an outer coating of the primary coating portion  31  having a diameter larger than 0.25 mm is removed by using a skin peeling tool, or another tool, until the diameter becomes 0.25 mm. A boundary  32 , at which the diameter of the primary coating portion  31  changes, is protected within the interior of the optical fiber connector  30 . 
         [0008]    However, as the boundary  32  of the optical fiber core  31  has a step at which the diameter changes, there is a risk in that stress is concentrated at the boundary  32  if the primary coating portion  31  is bent within the interior of the connector  30 , resulting in a bending loss of optical signal or breakage of the primary coating portion. 
       SUMMARY 
       [0009]    Accordingly, the present invention is aimed to provide, when a boundary corresponding to a stepped portion of an inner cover of a primary coating portion is located inside of an optical fiber connector, an optical fiber connector capable of avoiding stress concentration at the boundary to prevent breakage of the primary coating portion. 
       Means for Solving the Problems 
       [0010]    To solve the above-mentioned problem, according to claim  1  of the present invention, an optical fiber connector, comprising a connector housing having a splice assembly therein, for abutting an end surface of a plain fiber portion, obtained by removing an outer cover and a multi-layered inner cover from an optical fiber cable, to an end surface of a mating plain fiber portion and optically connecting plain fiber portions to each other, and an end cap, attached to one end of said connector housing, from which a primary coating portion, obtained by removing the outer cover of said optical fiber cable while leaving the inner cover thereof, is led out, wherein a boundary formed on said primary coating portion, between a portion of said primary coating portion, obtained by removing an outer coating while leaving an inner coating of the inner cover, and a portion leaving the outer coating of the inner cover, is located in an interior of said connector housing, characterized in that said end cap is provided in the interior thereof with a tubular portion and an extension extending from an end of said tubular portion, said tubular portion including an insert hole for an insertion of said primary coating portion approximately coaxially with a guiding hole formed in said splice assembly accommodated in said connector housing for guiding said primary coating portion leading out from said splice assembly, said extension including a strain-control hole, communicating with said insert hole, for receiving said boundary of said primary coating portion, and for controlling stress at said boundary. 
         [0011]    According to claim  2  of the present invention, an optical fiber connector as defined by claim  1  is characterized in that said extension is located in said guiding hole. 
         [0012]    According to claim  3  of the present invention, an optical fiber connector as defined by claim  1  or  2  is characterized in that said strain-control hole is a straight hole. 
         [0013]    According to claim  4  of the present invention, an optical fiber connector as defined by any one of claims  1  to  3  is characterized in that a tapered portion is formed on primary coating portion leading out side of said insert hole; said tapered portion having a diameter gradually increasing toward an open end. 
       EFFECTS OF THE INVENTION 
       [0014]    According to the invention defined by claim  1 , as the strain-control hole communicating with the insert hole is provided in the extension of the tubular portion, even if the primary coating portion is bent at a position outside the end cap, the influence of the bending upon the boundary is mitigated to minimize the strain at the boundary. Thus, the concentration of stress at the boundary is avoided to prevent the primary coating portion from breaking, whereby the reliability of the optical connection is enhanced. 
         [0015]    According to the invention defined by claim  2 , as the extension is located within the guiding hole, it is possible to assuredly protect the boundary of the primary coating portion in a wide range. 
         [0016]    According to the invention defined by claim  3 , as the strain-control hole is a straight hole, the strain of the primary coating portion in the vicinity of the boundary is restricted to assuredly avoid the influence of the bending upon the boundary. 
         [0017]    According to the invention defined by claim  4 , as the tapered portion is formed in the insert hole but closer to the primary coating portion, the primary coating portion being bent outside the optical fiber connector is brought into contact with the tapered portion whereby the bending thereof is mitigated. Thus, it is possible to prevent the optical fiber from breaking due to bending. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is an exploded perspective view of one embodiment of an optical fiber connector according to the present invention. 
           [0019]      FIG. 2  is an exploded perspective view of a splice assembly shown in  FIG. 1 . 
           [0020]      FIG. 3  is a perspective view of an end cap shown in  FIG. 1  as seen from an opening side. 
           [0021]      FIG. 4  is a sectional view of part of the inventive optical fiber connector wherein a primary coating portion is bent on a side introducing the same. 
           [0022]      FIG. 5  is a sectional view of part of a prior art optical fiber connector wherein a primary coating portion is bent on a side introducing the same. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    The preferred embodiments of the present invention will be described in detail below with reference to the attached drawings.  FIG. 1  is an exploded perspective view of one embodiment of the inventive optical fiber connector. The optical fiber connector  1  according to this embodiment includes a primary coating portion  3  formed by covering an outer circumference of a plain fiber portion  2  with an inner coat  4  of a layered structure, an end cap  5  having an insert hole  10   a  for inserting the primary coating portion  3  therethrough, a splice assembly  13  for abutting end surfaces of the plain fiber portions  2  and optically connecting them, and a connector housing  21  for accommodating the splice assembly  13  therein and engaging with a female type connector housing, not shown, in a mating connector. 
         [0024]    The primary coating portion  3  is formed from an optical fiber cable by removing a thick outer cover of a covering layer thereof, and consists of a plain fiber portion (optical glass fiber) and an inner cover  4  of a multi-layered structure covering the optical fiber. The inner cover  4  of a multi-layered structure is formed by repeating a resin coating process on the optical fiber. The plain fiber portion is of a circular cross-section, and has a transparent core at a center thereof for transmitting an optical signal and a transparent clad, on the outside thereof, having a refractive index smaller than that of the core. 
         [0025]    The inner cover  4  is formed of two layers of acrylic resin. The covering layer of the inner cover  4  is stripped off from an end thereof to have a boundary  4   c  in which the thickness of the covering layer changes. The terminal treatment of the primary coating portion  3  is carried out by using a terminal treatment tool, not shown, so that a predetermined length of an outer coating peels off. The primary coating portion  3  abuts an end surface of a mating primary coating portion, in a component  16  of the splice assembly  13 , with a predetermined pressure, whereby both the end surfaces are optically connected to each other. In this text, the optical glass fiber is defined as a plain fiber portion  2 , and a structure wherein the optical glass fiber is covered with a multi-layered inner cover  4  is defined as a primary coating portion  3 . 
         [0026]    The end cap  5  of the optical fiber connector is a resin-molded member attached to a rear end of the connector housing  21  so that the splice assembly  13  does not come off from the connector housing  21 . One end of the end cap  5  is open and the other end thereof forms a rear wall having an insert hole  10   a . The insert hole  10   a  is gradually enlarged in diameter toward the outer extremity from which the primary coating portion  3  is inserted. 
         [0027]    A tubular portion  10  having the insert hole  10   a  for inserting the primary coating portion  3  is projected from the inner surface of the rear wall  6  while approximately axially communicating with a guiding hole  18   a  for guiding the primary coating portion  3  from a base member  18 . An extension  12  of the tubular portion  10  having a straight hole (strain-restricting portion)  12   a  is provided at an end of the tubular portion while communicating to the insert hole  10   a . The extension  12  is projected into the guiding hole  18   a  of the base member  18  in the splice assembly  13 . 
         [0028]    The rear wall  6  has upper and lower wall portions  7 ,  8  and left and right wall portions  9 ,  9 . A recess  7   a  engageable with an end of a cap member  17  in the splice assembly  13  is formed in the upper wall portion  7 . An engagement groove  9   a  engageable with a projection  23   a  provided on the outer surface of a side wall  23  of the connector housing  21  is formed on the inner surface of the respective side wall portion  9 . By the engagement of the projection  23   a  with the engagement groove  9   a , the end cap  5  is detachably mounted to the rear end of the connector housing  21 . Holes  6   a  for providing the engagement grooves  9   a  are formed in the rear wall  6  of the end cap  5 . 
         [0029]    Terms “front and rear” and “upper and lower” used in this text are defined as follows. A front direction means the direction in which the optical fiber connector  1  moves when it is connected to the mating optical fiber connector. A rear direction means the direction opposite to the above-mentioned connector-engagement direction; i.e., toward the primary coating portion  3  in  FIG. 1 . A lower direction means the direction toward the base member  18  in the splice assembly  13 , and an upper direction means the direction toward the cap member  17  in the splice assembly  13  in the drawings. 
         [0030]    The splice assembly  13  of the optical fiber connector  1  includes a ferrule  15  for holding one end of a plain fiber portion  14  while the other end the plain fiber portion  14  projects out therefrom, a component  16  which is an openable/closable element fixing member for connecting the plain fiber portion  14  projected from the other end of the ferrule  15  to the plain fiber portion  2 , the cap member  17  for closing a pair of opened bending pieces  16   a ,  16   a  in the component  16  to fix the plain fiber portions  2  and  14  between the pair of bending pieces  16   a ,  16   a , and the base member  18  for holding the ferrule  15  and the component  16 . 
         [0031]    The ferrule  15  in the splice assembly  13  is a tubular member made of resin or ceramic and having a through-hole  15   a  along a center axis thereof for passing the plain fiber portion  2  therethrough, and the outer circumference of the ferrule  15  is defined as a centering surface for positioning the ferrule  15  on the axis of the mating ferrule. An end surface of the ferrule  15 , abutting to that of the mating end surface, is a flat plane vertical to the center axis. 
         [0032]    A predetermined length of the connecting plain fiber portion  14  is inserted into the through-hole  15   a  formed from one end to the other end of the ferrule  15  and fixed by an adhesive. The connecting plain fiber portion  14  is disposed so that the axis thereof coincides with that of the ferrule  15 . 
         [0033]    Generally speaking, after the connecting plain fiber portion  14  has been inserted into the through-hole  15   a  of the ferrule  15  and fixed thereto, the end surface of the ferrule  15  is mirror-polished so that the end surface of the connecting plain fiber portion  14  is in the same plane as the end surface of the ferrule  15 . The plain fiber portion  2  extended from the other end surface of the ferrule  15  is cut at an optional position by a cutter. The cut surface is a flat plane vertical to the center axis of the ferrule  15 . 
         [0034]    The other end of the ferrule  15  from which the plain fiber portion  2  extends is press-fit into a hole (not shown) formed at one end of the base member  18 , and fixed to be integral with the base member  18  while one end of the ferrule  15  projects out from the base member  18 . A divided sleeve not shown is mounted to one end of the ferrule  15  to be positioned on a ferrule in the mating connector. 
         [0035]    The component  16  of the splice assembly  13  may be formed by die-cutting an aluminum sheet and folding the same along a center axis. Accordingly, the component  16  has a pair of bent pieces  16   a ,  16   a  opposed to each other. One of the pair of bent pieces  16   a ,  16   a  has a groove not shown disposed on the same axis as the center axis of the ferrule  15 . The pair of bent pieces  16   a ,  16   a  are openable/closable about a bent line thereof. By pivoting the pair of bending pieces  16   a ,  16   a  in the closing direction against the elastic recovery thereof while positioning the plain fiber portions  2  and  14  so that the end surfaces thereof abut to each other, the plain fiber portions  2  and  14  are fixed together by the grip of the pair of bending pieces  16   a ,  16   a.    
         [0036]    The cap member  17  of the splice assembly  13  is made, for example, of resin to have a pair of clipping walls  17   a ,  17   a  defining a space for receiving the pair of bent pieces  16   a ,  16   a  in the component  16 . The pair of clipping walls  17   a ,  17   a  are opposed and approximately parallel to each other with a predetermined gap therebetween. On the inner surfaces of the clipping walls  17   a ,  17   a , there are steps, not shown, and a distance between the steps which becomes smaller toward the inner part. Thereby, a force is applied to the pair of bending pieces  16   a ,  16   a  of the component  16  in the closing direction to bring the opposed surfaces of the pair of bending pieces  16   a ,  16   a  into tight contact with each other. Thus, the closed state of the component  16  is maintained unless the cap member  17  is detached from the component  16 . 
         [0037]    In the base member  18  of the splice assembly  13 , a hole is provided at an end for press-fitting the ferrule  15  thereinto, and a guiding hole  18   a  is provided at a rear end for inserting the plain fiber portion  2  thereinto. On the outer circumference of the base member  18 , an opening  18   c  is provided for receiving the component  16  and the cap member  17 . An end of the guiding hole  18   a  forms a tapered portion  18   b , a diameter of which increases as going to the open end, so that the plain fiber portion  2  can be smoothly inserted therealong without resistance. The extension  12  of the tubular portion  10  projected from the inner surface of the rear wall  6  of the end cap  5  is inserted into the tapered portion  18   b  so that the tapered portion  18   b  is overlapped with the extension  12 . Thereby, a strain of the boundary  4   c  having a step in the primary coating portion  3  introduced from the splice assembly  13  is controlled by the restraint due to the straight hole  12   a  in the extension  12 . Accordingly, even if the primary coating portion  3  introduced out from the optical fiber connector  1  is bent, no stress is concentrated to the boundary  3   c , whereby the breakage of the plain fiber portion  2  is avoidable. 
         [0038]    The connector housing  21  of the optical fiber connector  1  is molded with resin to have an inner space  22  in the interior thereof for accommodating the splice assembly  13 . A front half of the inner space  22  is covered with a tubular portion and a rear half is open in an upper wall  26  of the tubular portion. The ferrule  15  is disposed at a center of the tubular portion in a floating state. In a bottom wall  24  opposed to the upper wall  26  in the rear half, a guide groove  24   a  is formed to be in slide engagement with a rib  19  of the base member  18 . 
         [0039]    On the outer surface of each the side walls  23  vertically intersecting the upper wall  26  in the rear half, the projection  23   a  engageable with the engagement groove  9   a  on the inner surface of the side wall  9  of the end cap  5  is provided. By the engagement of the groove  9   a  with the projection  23   a , the connector housing  21  becomes one-piece with the end cap  5 . 
         [0040]    On the outer surface of the side wall  23  in the front half, an elastic arm  25  is provided contiguous to the end of the connector housing  21 . The elastic arm  25  is pivotally flexible in the left and right directions about a base thereof. On the outer surface of the elastic arm  25 , a projection  25   a  engageable with the engagement section of the mating connector is provided outward. When the optical fiber connector (a male type connector)  1  is engaged with the mating connector (a female type connector), the elastic arm  25  is flexed in the direction toward the inner surface of the side wall  23 , and if the optical fiber connector  1  is further deeply engaged, the elastic arm  25  returns to the original shape due to the elastic recovery of the elastic arm  25 , whereby the projection  25   a  of the elastic arm  25  is engaged with the engagement section of the mating connector to complete the connection of both the connectors. 
         [0041]    The present invention should not be limited to the above-mentioned embodiment, but includes other embodiments. For example, while the extension  12  of the tubular portion  10  projected from the inner surface of the rear wall  6  in the end cap  5  is inserted into the guiding hole  18   a  in the base member  18  in this embodiment, a structure wherein the extension  12  is disposed in the vicinity of the base member  18  may be adopted if the boundary  4   c  of the primary coating portion  3  is positioned on the outside of the base member  18  and a taper angle of the tapered portion  18   b  is too small to allow the insert of the extension  12  of the tubular portion  10 .