Abstract:
In an optical connector of the invention, the rotation in a conventional angle polish connector can be prevented, while external force acting on the connector can be prevented from affecting a ferrule. The optical connector includes a ferrule  15,  which has an angle-polished front portion and is accommodated in a housing  19  in a state where pressing force is applied in a coupling-forward direction by an elastic means so as to enable the ferrule  15  to move in the axial direction. A key groove  21  and a key  23  which are provided between the housing  19  and the ferrule  15  are engaged so as to make their relative movement possible in the movement direction. The clearance C between the groove width W of the key groove  21  and the key  23  increases along the direction in which the ferrule  15  retreats.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an optical connector having a ferrule whose front portion is angle polished. 
       BACKGROUND ART 
       [0002]    Japanese Patent Application Publication No. H10-221568 and Japanese Patent Application Publication No. 2002-6174 describe an optical connector containing a ferrule having a key groove for regulating a rotation around the axis. In  FIG. 9 , area (a) shows a partially cut away side view of a conventional optical connector  500 , area (b) shows a perspective view of a ferrule  503  included in the optical connector  500 , and area (c) shows a sectional view of a plug frame (housing)  501  contained in the optical connector  500 . In the optical connector  500 , the ferrule  503  of cylindrical form contained in the plug frame  501  has a flange  505  around an outside circumferential part. The plug frame  501  is capable of sliding in the axial direction, while the rotational movement around the axis is regulated by engaging keys  509 , which are formed inside the plug frame  501  (area (c)), and key grooves  507 , which are formed in the flange  505  (area (b)). 
         [0003]    The ferrule  503  is designed to be pushed toward a coupling end face  503   a  by a spring  511  provided in the plug frame  501 . The ferrule  503  is prevented from moving forward in the coupling direction beyond that when the flange  505  butts against the stopper wall  515  which protrudes in a ferrule storage hole  513  formed inside the plug frame  501 . 
         [0004]    The ferrule  503  is connected with a ferrule of another optical connector by butting the coupling end face  503   a  against the counterpart, and consequently an optical fiber  517 , which is terminated to be capable of being detachably connector-coupled, is connected with an optical fiber of such optical connector. The ferrule  503  can slightly be pushed backward in the coupling direction within an elastic limit of the spring  511  at the time of butting with the ferrule of a counterpart optical connector. This enables preventing the coupling end face  503   a  being damaged by excessive stress concentration, and the pushing force of the spring  511  functions as a force for mutual butting of the ferrules, so that a target coupling loss can stably be attained. 
         [0005]    A conventional optical connectors in which low reflection is realized adopts a technique for reducing reflection at a physical contact surface by means of angled physical contact (APC) polish. It is known that in order to stably achieve physical contact (PC) of angle polished coupling surfaces, it is important to suppress the rotational angle of a ferrule to 2 degrees or less. It might be conceivable to make such rotational angle to be zero in order to achieve more stable characteristic; however, if the rotation of the ferrule is completely restrained, PC coupling might be decoupled when an external force is applied to the connector main body, and consequently the characteristic might become unstable. 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0006]    The object of the present invention is to provide an optical connector in which the rotation of a ferrule in an angle polish optical connector can be prevented and with which decoupling can be prevented when an external force acts on the connector. 
       Solution to Problem 
       [0007]    To this end, an optical connector of the invention comprises: a ferrule having an angle-polished end face; a housing for accommodating and holding the ferrule, allowing the ferrule to move in the axial direction; an elastic means for pushing the ferrule forward in the coupling direction; and further comprises a key and a key groove which are provided between the housing and the ferrule and are engaged with each other, allowing their relative movement along the axial direction, wherein the clearance between the key and the key groove increases along the direction of the ferrule&#39;s retreat. It is preferable that the maximum allowance for relative rotational movement as defined by the key and the key groove about their axis be equal before and after the retreat of the ferrule. 
       Advantageous Effects of Invention 
       [0008]    With the optical connector according to the present invention, it is possible to prevent rotation of a ferrule in an angle polish optical connector, as well as decoupling of the optical connector when external force acts on the connector. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0009]      FIG. 1  is an outside perspective view of an optical connector according to an embodiment of the present invention. 
           [0010]      FIG. 2  is a cross-sectional view of a main part of the optical connector shown in  FIG. 1 . 
           [0011]      FIG. 3  is a perspective view of a mechanical splice contained in the optical connector shown in  FIG. 1 . 
           [0012]      FIG. 4  is a perspective view of a housing contained in the optical connector shown in  FIG. 1 . 
           [0013]    IN  FIG. 5 , area (a) is a partially cut away perspective view of the housing shown in  FIG. 4 ; area (b) is an enlarged partial view of area (a) of  FIG. 5 . 
           [0014]    In  FIG. 6 , areas (a) and (b) are schematic diagrams of main part of a conventional optical connector as seen before and after the retreat of a ferrule in the connector. 
           [0015]    In  FIG. 7 , areas (a) and (b) show schematic diagrams of main part of the optical connector shown in  FIG. 1 , as seen before and after the retreat of the ferrule, respectively; area (c) is a schematic diagram of main part of the optical connector of  FIG. 1 , as seen at a headshake of the ferrule. 
           [0016]      FIG. 8  is a schematic diagram of a main part of a modified example of an optical connector according to the present invention. 
           [0017]    In  FIG. 9 , area (a) is a partially cut away side view of a conventional optical connector; area (b) is a perspective view of a ferrule contained in the conventional optical connector; and area (c) is a sectional view of a plug frame contained in the conventional optical connector. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0018]    Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. The drawings are provided for the purpose of explanation and are not intended to limit the scope of the invention. In the drawings, an identical mark represents the same element and the repetition of explanation is omitted. The ratio of dimensions in the drawings is not necessarily exact. 
         [0019]      FIG. 1  is a perspective outside view of an optical connector  17  according to an embodiment of the present invention.  FIG. 2  is a cross-sectional view of a main part of the optical connector  17 , and  FIG. 3  is a perspective view of a mechanical splice  33  contained in the optical connector  17 . The optical connector  17  mainly comprises a mechanical splice  33 , a housing  19  for accommodating and holding the mechanical splice  33 , and a grip  35  provided on the outside of the housing  19  and used as a holding part at the time of coupling with a connector. 
         [0020]    The mechanical splice  33  comprises a ferrule  15 , a base member  37 , a fixing part  39 , and a damper  41  for fixing an optical fiber (not shown) by pushing a cover against the base member  37 . The ferrule  15 , which has a minute hole  43  for inserting an optical fiber, is put in a ferrule housing hole  45  inside the housing  19 , the central axis of the ferrule  15  being substantially coincident with that of the hole  45 . The ferrule  15  is made of zirconia or glass. 
         [0021]    The front portion  11 , which has an opening of the minute hole  43 , of the ferrule  15  is processed by angle polish. The ferrule  15  in the housing  19  is capable of moving in a direction along an axis  31 , with pressing force being afforded toward the front portion  11  by an elastic means (e.g., spring) (not shown) contained in the housing  19 . A flange  47  is formed at a substantially central section in terms of the axial direction of the ferrule  15 . When the flange  47  butts against the stopper wall  51  protruding in the ferrule housing hole  45  ( FIG. 5 ), the flange  47  prevents the ferrule  15  from excessively moving further in the coupling direction. 
         [0022]    The ferrule  15  enables an optical fiber, which is processed for termination, to be connected with an optical fiber line of a counterpart optical connector when the front portion  11  of the ferrule  15  butts against the ferrule of the counterpart optical connector. When the ferrule  15  butts against the ferrule of the counterpart optical connector, it is pushed back in the coupling direction within the deformation range of the elastic means. This enables preventing the coupling end face from being damaged by excessive stress concentration, and the pressing force of the elastic means functions as a butting force for the ferrules so that the target coupling loss can stably be obtained. 
         [0023]      FIG. 4  is a perspective view of a housing  19  contained in the optical connector  17 . In  FIG. 5 , area (a) is a perspective view of the housing  19  as seen by partially cutting away at a plane including the axis; area (b) is an enlarged partial view of area (a). The optical connector  17  has, between the housing  19  and the ferrule  15 , a key groove  21  and a key  23  which are engaged so that their relative movement may be possible in the movement direction. The key groove  21  and the key  23  may be formed on either side of the housing  19  and the ferrule  15 , and in the case of the optical connector  17 , the key  23  is formed on the inner side of the housing  19  and the key groove  21  is formed on the outer side of the ferrule  15 . In the optical connector  17 , two pairs of the key groove  21  and the key  23  are provided at both sides in terms of diametrical direction; however, the key groove  21  and the key  23  may be provided with one pair, or more than two pairs with respect to the circumferential direction. 
         [0024]    The optical connector  17  is an angle PC connector in which back-reflected light is extremely decreased and low coupling loss is realized. That is, in the optical connector  17 , the coupling end face is angled and has a convex spherical shape so that back-reflected light may be led outside of the fiber. The back-reflected light, which is due to discontinuity of refractive index in an optical line, is caused by existence of an air layer at a coupling point or a machining-damage layer generated by processing the end face of an optical fiber, or the like. If such back-reflected light returns to a semiconductor laser which is a light source, it will cause mode interference and variation in luminescence power or oscillation frequency. 
         [0025]    In the APC optical connector  17 , in order to reduce back-reflected light, a sufficiently large tilt angle is chosen so that insertion loss will not be increased. The larger the slant angle of fiber end face, the smaller the back-reflected light will become; on the other hand, the less the connector coupling reliability will become. Therefore, the oblique angle is determined at the minimum value within the allowable limit in terms of back-reflected light. It is said that the optimal tilt angle for stably achieving return loss is about 8 degrees. (“The recent trend of ultra-low reflection angled PC connector” The Institute of Electronics, Information and Communication Engineers: IEICE technical report EMD 96-95 (1997-01)) 
         [0026]    An inherent problem of APC is a rotation about the axis  31  of the ferrule  15 . If disparity in the rotation angle occurs, the center of curvature will shift. It is important to suppress the rotational angle of the ferrule  15  to 2 degrees or less in order to achieve stable PC coupling of APC faces. In order to stabilize the characteristic more, it would be sufficient if such rotation is eliminated. 
         [0027]    In  FIG. 6 , areas (a) and (b) are schematic diagrams of main part of a conventional optical connector  500  as seen before and after the retreat of a ferrule in the conventional optical connector, respectively. In the conventional optical connector  500 , the ferrule  503  is positioned inside the housing  501  so that the ferrule  503  may not rotate. If the clearance C of the key  509  and the key groove  507  is made smaller, control of the rotation can be made more strictly. However, when coupling of the connector  500  with another connector is done by butting, variation in the relative angle between the key  509  and the key groove  507  is also regulated according to the clearance C even if the ferrule  503  retreats by given distance B. Consequently, if external force is added to the housing  501 , the force will be directly added to the PC coupling face of the connector, and accordingly the PC coupling will become unstable, which will tend to increase coupling loss. 
         [0028]    In  FIG. 7 , areas (a) and (b) show schematic diagrams of main part of the optical connector  17 , as seen before and after the retreat of the ferrule, respectively; area (c) is a schematic diagram of main part of the optical connector  17 , as seen at a headshake of the ferrule. In the optical connector  17 , the clearance C between the key  23  and the groove width W in the key groove  21  increases along the direction in which the ferrule  15  retreats. The key groove  21  is formed in parallel with the axis  31  in the flange  47  ( FIG. 3 ) of the ferrule  15 . On the other hand, the key  23  is formed on the stopper wall  51  ( FIG. 5 ) so as to extend along the axis  31  toward the rear side of the housing  19 , and the key width gradually decreases along the axis  31  toward the tip. More specifically, the key  23  is formed in a shape including base portion  23   a,  which has a width d 1  substantially corresponding with the groove width W of the key groove  21 , front portion  23   b,  whose width d 2  is narrower than the base portion  23   a  and which is connected with the base portion  23   a  via taper portion T, and front chamfered portion  53  ( FIG. 5 ). 
         [0029]    In the optical connector  17 , the rotation and headshake of the ferrule  15  are controlled with high precision by engagement of the key groove  21  with the base portion  23   a  of the key  23  until the ferrule  15  accomplish PC coupling with a counterpart connector. When the ferrule  15  retreats by a given distance B because of contraction of the elastic means upon PC coupling, the rotation of the ferrule  15  is regulated by the clearance between the base portion  23   a  and the key groove  21  (area (b)). As to the head-shake (variation in the relative angle between the key and the key groove), since the clearance between the groove width of the key groove  21  and the key  23  increases along the direction in which the ferrule retreats, the maximum allowance for the variation in the relative angle between the key and the key groove becomes larger; that is, the head-shake of the ferrule becomes possible (area (c)), and consequently even if an external force is added to the housing  19 , it would have little effect on the PC coupling. 
         [0030]    The key  23  and the key groove  21  are structured such that the maximum allowance for relative rotational movement about their axis  31  is equal before and after the retreat of the ferrule. That is, the engagement between the base portion  23   a  and the key groove  21  is maintained before and after the retreat of the ferrule ( FIG. 7 , area (b)). The effect of rotational control, however, decreases when the interval between the key  23  and the key groove  21  becomes larger according to the retreat of the ferrule. The structure thus obtained is such that the control of the rotation is maintained by keeping the small clearance even if the longitudinal overlapping length is short and the maximum allowance for variation in the relative angle between the key and the key groove is increased, resulting in ease of the head-shake of the ferrule  15 ; and an external force, even if added to the housing  19 , will have less effect. 
         [0031]      FIG. 8  is a schematic diagram of a main part of a modified example of an optical connector according to the present invention. In the optical connector  17 , the key groove  21  is a parallel groove and the key  23  has a width which gradually decreases toward the front tip; conversely, in the modified example, the key  23  is modified to a parallel key  23 A, while the key groove  21  is modified to a key groove  21 A whose width gradually increases toward the longitudinally inner side. In the modified example also, the rotation and the head-shake are controlled with high precision until the ferrule  15  accomplish PC coupling, and when the ferrule  15  retreats by a given distance  13 , the clearance between the groove width of the key groove  21 A and the key  23 A increases along the direction in which the ferrule retreats; thus, even if the restraint is eased (i.e., the head-shake is allowed, while the rotation is regulated), it is made possible that an external force which is added to the housing  19  can hardly have effect on PC coupling. 
       INDUSTRIAL APPLICABILITY 
       [0032]    The invention is suitable for an optical connector used in an optical fiber communications system. 
       CITATION LIST 
     Patent Literature 
       [0033]    Patent document 1: Japanese Patent Application Publication No. H10-221568 
         [0034]    Patent document 2: Japanese Patent Application Publication No. 2002-6174