Abstract:
In an optical connector including an optical connector plug holding a first optical fiber and an optical connector plug holding a second optical fiber, the optical connector plugs cooperates with each other to obtain a connected state in which exposed longitudinal ends of the first and the second optical fibers are brought into contact with each other. The first optical fiber includes a long fiber portion and a short fiber portion higher in breakage resistance than the long fiber portion. One of the longitudinal ends of the short fiber is fused to one of longitudinal ends of the long fiber portion. Another of the longitudinal ends of the short fiber portion is exposed to serve as one of the exposed longitudinal ends.

Description:
[0001]    This invention claims priority to prior Japanese application JP 2003-75168, the disclosure of which is incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    This invention relates to an optical connector for connecting optical fibers by bringing longitudinal end faces of the optical fibers into contact with each other.  
           [0003]    An optical connector of the type is disclosed, for example, in U.S. Pat. No. 6,491,442 as an optical fiber connector. By the use of the optical fiber connector, it is possible to suitably connect an optical system.  
           [0004]    In the optical fiber connector, an outer member holds a portion of an optical fiber remote from its connecting end which is connectable to a connecting end of a counterpart optical fiber. An aligning member is held by the outer member so as to be movable along the optical fiber. The aligning member carries out positioning of the connecting end of the optical fiber. The aligning member is urged by a spring in a direction to project from the outer member.  
           [0005]    When connecting the optical fiber to the counterpart optical fiber, the aligning member is moved in a direction opposite to the foregoing direction against an urging force applied by the spring. So that, the connecting end of the optical fiber is projected from the aligning member and is brought in press contact with the connecting end of the counterpart optical fiber with bending of at least one of the optical fibers.  
           [0006]    In order to prevent breakage due to such bending, use is made of the optical fiber which is strengthened and is therefore expensive. This results in an increase in cost required for connection of the optical system.  
         SUMMARY OF THE INVENTION  
         [0007]    It is therefore an object of the present invention to provide a connection apparatus capable of connecting an optical system with high accuracy and at low cost.  
           [0008]    It is another object of the present invention to provide an optical connector which requires a reduced amount of an expensive optical fiber.  
           [0009]    Other objects of the present invention will become clear as the description proceeds.  
           [0010]    According to one aspect of the present invention, there is provided an optical connector comprising a first connector element holding a first optical fiber and a second connector element holding a second optical fiber, the first and the second connector elements cooperating with each other to obtain a connected state in which exposed longitudinal ends of the first and the second optical fibers are brought into contact with each other, wherein the first optical fiber comprising a long fiber portion having longitudinal ends, a short fiber portion higher in breakage resistance than the long fiber portion and having longitudinal ends, and a fusion connection portion where one of the longitudinal ends of the short fiber is fused to one of the longitudinal ends of the long fiber portion, another of the longitudinal ends of the short fiber portion being exposed to serve as the exposed longitudinal end of the first optical fiber.  
           [0011]    According to another aspect of the present invention, there is provided a connector element for connecting a connection object and comprising an optical fiber; and a clamp portion holding the optical fiber, the optical fiber including a long fiber portion having longitudinal ends, and a short fiber portion connected to one of the longitudinal ends of the long fiber portion and having high breakage resistance and flexibility, the short fiber portion having a connecting end protruding from the clamp portion to be brought into contact with said connection object. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0012]    [0012]FIG. 1 is a perspective view of an optical connector according to one embodiment of the present invention in an unconnected state, with a part removed so that the interior is seen;  
         [0013]    [0013]FIG. 2 is a vertical sectional view of the optical connector illustrated in FIG. 1 in the unconnected state;  
         [0014]    [0014]FIG. 3 is a perspective view of the optical connector illustrated in FIG. 1 in a connected state, with a part removed so that the interior is seen;  
         [0015]    [0015]FIG. 4 is a vertical sectional view of the optical connector illustrated in FIG. 1 in the connected state;  
         [0016]    [0016]FIG. 5 is an exploded perspective view of a connector element contained in the optical connector illustrated in FIG. 1;  
         [0017]    [0017]FIG. 6 is a vertical sectional view of a clamp portion contained in the connector element illustrated in FIG. 5;  
         [0018]    [0018]FIG. 7 is an enlarged front view of a characteristic part of an optical fiber held by the clamp portion illustrated in FIG. 5;  
         [0019]    [0019]FIG. 8A is a graph showing data related to the optical fiber illustrated in FIG. 7; and  
         [0020]    [0020]FIG. 8B is a graph showing data related to an ordinary optical fiber. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]    Referring to FIGS.  1  to  4 , description will be made of an optical connector according to one embodiment of the present invention.  
         [0022]    The optical connector illustrated in the figure is for use in connecting an optical system and comprises an optical connector plug  12  as a first connector element holding a first optical fiber group  11  and an optical connector plug  14  as a second connector element holding a second optical fiber group  13 . Each of the first and the second optical fiber groups  11  and  13  includes a number of optical fibers. Each of the optical fibers of the first optical fiber group  11  will be called a first optical fiber. Each of the optical fibers of the second optical fiber group  13  will be called a second optical fiber.  
         [0023]    The optical connector plugs  12  and  14  are connected to each other by an optical connector adapter  21 . The optical connector adapter  21  has a number of V grooves  21   a . Each optical fiber of the first optical fiber group  11 , i.e., the first optical fiber and each optical fiber of the second optical fiber group  13 , i.e., the second optical fiber are positioned to face to each other in each V groove  21   a.    
         [0024]    When the optical connector plugs  12  and  14  are moved towards each other, each optical fiber of the first optical fiber group  11  and each optical fiber of the second optical fiber group  13  are brought into contact with each other. When the optical connector plugs  12  and  14  are moved further towards each other, bending of each optical fiber of the first optical fiber group  11  occurs as clearly shown in FIG. 4. By restoring force produced by such bending, each optical fiber of the first optical fiber group  11  is brought into strong contact with each optical fiber of the second optical fiber group  11  so as to connect the optical system with high precision. At this time, each optical fiber of the second optical fiber group  13  is prevented from occurrence of bending by a structure which will later be described.  
         [0025]    Referring to FIG. 5 in addition to FIGS. 1 through 4, the optical connector plug  12  will be described in detail.  
         [0026]    The optical connector plug  12  comprises a frame-like main body  22  made of plastic and having a generally rectangular shape, a plastic cover  22  covering the main body  22 , four holding portions or clamp portions  25  made of plastic and clamping or holding the first optical fiber group  11 , and a fiber protector  26  made of metal and attached to an end of the main body  22  to protect an end of each optical fiber of the first optical fiber group  11 . The clamp portions  25  are arranged in parallel and adjacent to each other and inserted into a receiving portion  22   a  of the body  22 . The cover  23  serves to protect the first optical fiber group  11 .  
         [0027]    The optical connector plug  14  is similar in structure to the optical connector plug  12 . Corresponding parts are designated by like reference numerals with an apostrophe. An elastic member  19  is attached to a lower surface of a cover  23 ′. The elastic member  19  serves to press the second optical fiber group  13  to prevent occurrence of the above-mentioned bending. The elastic member  19  may be formed integral with the cover  23 ′. Alternatively, the elastic member  19  may be a separate component made of rubber or the like and attached to the cover  23 ′.  
         [0028]    Thus, a pair of the optical connector plugs to be connected to each other may have a first structure in which the optical fiber is bent and a second structure in which the optical fiber is not bent. In case of the second structure, the optical fiber is pressed by the elastic member attached to the lower surface of the cover.  
         [0029]    Next referring to FIGS. 6 and 7, description will be made of the clamp portion  25  and the optical fiber  31  held by the clamp portion  25 .  
         [0030]    The optical fiber  31  has a long fiber portion  33  positioned on the right side of a line  32  and a short fiber portion  34  positioned on the left side of the line  32 . The long fiber portion  33  and the short fiber portion  34  are connected at a fusion connection portion  35  by fusion connection.  
         [0031]    The long fiber portion  33  is an ordinary optical fiber and comprises a tape-covered part  33   a  covered with a tape and a tape-removed part  33   b  where the tape is removed. The length L 2  of the tape-removed part  33   b  is equal to 6 mm.  
         [0032]    The short fiber portion  34  comprises a special optical fiber having a polymer layer on its outer peripheral surface and is designed to have high breakage resistance as compared with the ordinary optical fiber. The short fiber portion  34  comprises a polymer-coated part  34   a  coated with the polymer layer and a polymer-removed part  34   b  where the polymer layer is removed. The length L 1  of the polymer-removed part L 1  is equal to 3 mm.  
         [0033]    The clamp portion  25  has an opening portion  25   a  formed on its upper side, an adhesive filling part  25   b  continued from the opening portion  25   a , and a narrow hole  25   c  through which the short fiber portion  34  is inserted. After the optical fiber  31  is set in the clamp portion  25 , an adhesive (for convenience of illustration, only a part of the adhesive is depicted by a reference numeral  37 ) is filled through the opening portion  25   a  into the inside of the clamp portion  25 . The adhesive is filled within a range depicted by L 3 .  
         [0034]    Although not shown in the figure, the optical connector plug  14  has a similar structure. On each V groove  21   a  of the optical connector adapter  21 , the special optical fiber of the optical connector plug  12  and the special optical fiber of the optical connector plug  14  are positioned with respect to each other and contacted with each other.  
         [0035]    Generally, the ordinary optical fiber is degraded in strength at a portion where coating is removed. However, since the tape-removed part  33   a , the fusion connection portion  35 , and the polymer-removed part  34   b  are protected by the adhesive within the clamp portion  25 , the optical fiber  31  as a whole is not deteriorated in mechanical characteristics and is hardly affected by the change in environment, such as temperature and humidity.  
         [0036]    [0036]FIG. 8A shows connection loss due to fusion bonding between the special optical fiber having the polymer layer and the ordinary optical fiber. FIG. 8B shows connection loss due to fusion bonding between the ordinary optical fibers. Herein, N represents the connection loss (dB).  
         [0037]    It has been found out that, In each of FIGS. 8A and 8B, the connection loss is within a practically allowable range. The polymer layer at an end of the short fiber portion  34  is peeled off due to discharge during fusion bonding and, therefore, the outer diameter of the polymer-removed part  34   b  is reduced (for example, 0.115 mm). However, as the connection loss due to fusion bonding, the value in case of connection between the special optical fiber and the ordinary optical fiber is comparable to that in case of connection between the ordinary optical fibers.  
         [0038]    In case of FIG. 8A, the average value of the connection loss N is equal to 0.028 and the standard deviation is equal to 0.015.In case of FIG. 8B, the average value of the connection loss N is equal to 0.025 and the standard deviation is equal to 0.017.  
         [0039]    Referring to FIGS. 5 through 7, description will be made of a method of assembling the optical connector plug  12 . After the short fiber portion  34  and the long fiber portion  33  are fusion bonded and connected to each other, the optical fiber  31  is fixed to each clamp portion  25 . After a predetermined number of the optical fibers  31  are fixed, the clamp portions  25  are fixed to the receiving portion  22   a  of the main body  22 . Each clamp portion  25  is a separate component independent of the main body  22 , assembling is easy. The optical connector plug  14  is assembled in the similar manner.  
         [0040]    When the optical connector plugs  12  and  14  are connected through the optical connector adapter  21  as illustrated in FIGS. 3 and 4, the end of each short fiber portion of the optical connector plug  12  and the end of each short fiber portion of the optical connector plug  14  are butted to each other on each V groove  22   a  of the optical connector adapter  21 . Therefore, the short fiber portion  34  protruding from each clamp portion  25  is bent. However, the short fiber portion is not broken because it is the special optical fiber having the polymer layer and has high breakage resistance.  
         [0041]    Although the present invention has been shown and described in conjunction with the several preferred embodiments thereof, it will readily be understood by those skilled in the art that the present invention is not limited to the foregoing description but may be changed and modified in various other manners without departing from the spirit and scope of the present invention as set forth in the appended claims.