Abstract:
The present invention provides a method of grinding an optical fiber connector such that the end faces of optical fibers to be held by the optical fiber connector extends externally from the end face of said optical fiber connector, comprising a step of grinding the end faces of the optical fibers while applying a grinding liquid containing a grinding material and alcohol onto a grinding sheet.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a method of grinding an optical fiber connector.  
           [0002]    In recent years, an integral resin-molded MT connector has been used as a multi-core connector. As shown in FIG. 4(A), the MT connector  1  has a plastic ferrule body  2  formed with an opening  2   a  at one end and a rubber boot portion  3  externally extending from the distal end of the ferrule body  2 .  
           [0003]    The distal end of the body  2  is also provided with a flange  2   b . The flange  2   b  includes an aperture  2   f  formed therethrough. The aperture  2   f  communicates with the opening  2   a . The opening  2   a  also communicates with a plurality of through-holes  2   c  which are formed through the body  2  and opened at the end face  2   e  thereof. The body  2  includes a pair of pin receiving apertures  2   d  formed therein at the opposite sides (see FIG. 4(B)).  
           [0004]    Where the MT connector  1  is used to hold optical fibers  4 , the tip end of an optical fiber tape  5  is first stripped off to expose the optical multi-core fibers  4  housed within the optical fiber tape  5 .  
           [0005]    The exposed tip ends of the optical fibers  4  are then inserted into the opening  2   a  through the aperture  2   f . After the exposed optical fibers  4  have been passed through the through-holes  2   c , their tip ends extend externally from the end face  2   e  of the body  2 .  
           [0006]    Subsequently, an adhesive  6  (e.g., thermosetting adhesive) is injected into the opening  2   a  to cover the optical fibers  4  extending externally from the end face  2   e  (see FIG. 4(C)).  
           [0007]    After the adhesive  6  has thermally been hardened, the end face  2   e  of the body  2  is ground to remove the externally extending optical fiber tips  4  and adhesive  6 . Thus, the optical fibers  4  can be held within the MT connector  1 .  
           [0008]    As shown in FIGS.  5 (A), (B) and FIG. 6(A), a pair of such MT connectors  1   a  and  1   b  respectively holding the optical fibers  4  are connected to each other through a pair of connection pins  7 . More particularly, the connection pins  7  are first inserted into the pin receiving apertures  2   d  in one of the MT connectors  1   a  and then inserted into the pin receiving apertures  2   d  in the other MT connector  1   b.    
           [0009]    Finally, as shown in FIG. 6(B), a fitting clip  8  is mounted around the pair of connected MT connectors  1   a  and  1   b  to hold them in the abutting relationship. This completes the connection of optical fibers. Alternatively, the MT connectors  1   a  and  1   b  may fixedly be mounted in housings which are in turn inserted into a connector adaptor to hold the MT connectors  1   a  and  1   b  in the abutting relationship.  
           [0010]    In the prior art, the end faces of the MT connector land optical fibers  4  have been ground flat. In such a case, however, an index matching agent (or matching oil) must additionally be applied onto the end face  2   e  to avoid any connection loss and to ensure a desired return loss.  
           [0011]    To avoid such an additional work, there has been proposed a technique known as PC (Physical Contact) connection in which the end face  2   e  of the body  2  is ground such that the end faces of the optical fibers  4  externally extend from the end face  2   e  of the body  2  by few microns. On connection, the optical fibers  4  in the MT connectors are brought into contact with one another. As a result, the connection property of low loss and reflection can be realized without use of any index matching agent. The grinding process herein was carried out while applying a mixture of alumina power and distilled water onto a grinding sheet.  
           [0012]    In such a prior art grinding process, the cores of the optical fibers  4  will be ground more than the clad portions to create recesses at the cores of the optical fibers  4 . When the optical connecters are connected to each other, the recesses create gaps between the cores. This may adversely affect the light transmission and return loss to reduce the reliability in the optical connectors.  
         SUMMARY OF THE INVENTION  
         [0013]    The present invention provides a method of grinding an optical fiber connector such that the end faces of optical fibers to be held by the optical fiber connector extends externally from the end face of said optical fiber connector, comprising a step of grinding the end faces of the optical fibers while applying a grinding liquid containing a grinding material and alcohol onto a grinding sheet. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    FIGS.  1 (A) to (C) are plan views illustrating a process of grinding an optical fiber connector according to one embodiment of the present invention.  
         [0015]    [0015]FIG. 2 is a side view showing a grinding sheet and grinding liquid which are used in the process of grinding an optical fiber connector according to one embodiment of the present invention.  
         [0016]    [0016]FIG. 3(A) is a view illustrating a recess created at an optical fiber core when it is ground according to the prior art grinding process while FIG. 3(B) a view illustrating a recess created at an optical fiber core when it is ground according to the present invention.  
         [0017]    [0017]FIG. 4(A) is a plan view of an MT connector; FIG. 4(B) is a front view of the same; and FIG. 4(C) is a plan view illustrating optical fibers externally extending from the end face of the connector body and covered with an adhesive.  
         [0018]    [0018]FIG. 5(A) is a plan view showing a pair of MT connectors prior to connection while FIG. 5(B) is a similar plan view showing the MT connectors after connected to each other.  
         [0019]    [0019]FIG. 6(A) is a side view showing the pair of MT connectors prior to connection while FIG. 6(B) is a similar side view showing the MT connector pair held by a fitting clip in the abutting state. 
     
    
     DETAILED DESCRIPTION  
       [0020]    The present invention will now be described by way of example with reference to the drawings. Parts similar to those of the prior art are denoted by similar reference numerals and will not further be described.  
         [0021]    In one embodiment of the present invention, the adhesive  6  (e.g., thermosetting adhesive) is injected into the opening  2   a  to cover the optical fibers  4  externally extending from the end face  2   e  of the body (see FIG. 4(C)). After the adhesive  6  has thermally been hardened, the adhesive  6  deposited on the end face  2   e  of the body  2  is ground off (see FIG. 1(A)). This adhesive removing step is continued for about 60 seconds.  
         [0022]    The flatting is carried out to improve the flatness and to reduce scratches on the end face  2   e  of the body (see FIG. 1(B)). This flatting step is continued for about 30 seconds. The grinding step is then performed such that the end faces of the optical fibers  4  extend externally from the end face  2   e  of the body  2  (see FIG. 1(C)). This grinding step is continued for about 90 seconds.  
         [0023]    Finally, the finishing step is made to remove small scratches on the end faces of the optical fibers  4 . This finishing step is continued for about 5 seconds.  
         [0024]    The aforementioned grinding step is carried out by mounting a grinding sheet  11  of about one mm thick on a grinder  9  of a grinding machine (not shown) as shown in FIG. 2 and rotating the grinder  9  to grind the end faces of the body and optical fibers while applying a grinding liquid  12  consisting of a mixture of grinding material and alcohol onto the grinding sheet  11 .  
         [0025]    The grinding sheet  11  may be in the form of diamond sheet, for example. The grinding liquid  12  may be a liquid prepared by mixing alumina power with monoethylene glycol in a ratio of 1:2. In the prior art, a grinding liquid prepared by mixing aluminum powder with distilled water was used. In such a case, the finished fiber faces were inferior. Thus, the prior art must grind the optical fibers by using a grinding liquid prepared by mixing ceric oxide with distilled water in the finishing step. Nevertheless, it could not avoided that the recesses  4   a  were created at the cores of the optical fibers  4  merely by performing the grinding step using that grinding liquid.  
         [0026]    On the contrary, the finished optical fiber end faces can be improved when the grinding liquid consisting of alumina powder and monoethylene glycol is used as in this embodiment. In the finishing step, the creation of recesses  4   a  in the optical fibers can be reduced without use of the grinding liquid prepared by mixing ceric oxide with distilled water.  
         [0027]    [0027]FIG. 3 shows experimental results which were obtained by the inventors. FIGS.  3 (A) and (B) show measurements obtained by using a surface roughness measuring machine when the later was used to measure the surface roughness in the ground MT connector  1 . FIG. 3(A) shows the result from the prior art while FIG. 3(B) shows the result from the grinding process according to this embodiment.  
         [0028]    Referring to FIG. 3(A), the prior art created a recess  4   a  having its depth of about 0.1 μm or less at the core of the optical fiber  4 .  
         [0029]    On the other hand, the grinding process according to this embodiment will create no recess at the core of the optical fiber  4 , as shown in FIG. 3(B).  
         [0030]    As a result, the Fresnel reflection of this embodiment created when the ground MT connectors are connected to each other in the abutting relationship as shown in FIG. 6 was smaller than that of the prior art.  
         [0031]    Experimental estimation of the grinding liquid carried out by the inventors will be described below.  
         [0032]    As shown in Table 1, the fiber end recess, fiber extension and operability were estimated relating to a grinding liquid (or grinding material) prepared by mixing one part of alumina powder with 1-3 parts of monoethylene glycol by weight and another grinding liquid (or grinding material) prepared by mixing one part of alumina powder with 1-3 parts of distilled water by weight.  
                                                                   TABLE 1                                       For One Part of Alumina Powder by Weight            Grinding   Monoethylene Glycol   Distilled Water            Material   1   2   3   1   2   3               Fiber   None   None   None   Yes   Yes   Yes       recess       Fiber   Good   Good   Bad   Good   Good   Bad       Extension           (None)           (None)       Operability   Slightly   Good   Good   Good   Good   Good           Bad                  
 
         [0033]    As will be apparent from Table 1, the grinding liquid prepared by mixing one part of alumina powder with 1-2 parts of monoethylene glycol by weight does not form any fiber recess and provides good fiber extension.  
         [0034]    The inventors also performed experiments relating to the concentration of the grinding liquid. Usually, the mixed liquid has been prepared by mixing one part of alumina powder with two parts of monoethylene glycol by weight. The experiments were carried out by using grinding liquids prepared by mixing monoethylene glycol with distilled water in various ratios shown in Table 2.  
                                                 TABLE 2                                       Monoethylene               Alumina Powder   Glycol   Distilled Water                                    Type 1   10 g   15 g    5 g       Type 2   10 g   10 g   10 g       Type 3   10 g    5 g   15 g       Normal   10 g   20 g    0 g                  
 
         [0035]    Table 3 shows the results from the above experiments. As will be apparent from Table 3, no core was formed and the finished end faces were good, even though the concentration was changed. However, it was found that as the concentration of the monoethylene glycol decreased, the fiber extension also decreased.  
                                                     TABLE 3                                   Extension   Core Recess   Finished End Face                                        Type 1   2.95 μm   None   Good           Type 2   2.83 μm   None   Good           Type 3    2.6 μm   None   Good                      
 
         [0036]    The present invention is not limited to the above embodiment, but may be modified or changed into various forms without departing from the scope of the invention as claimed in the appending claims. For example, the present invention may be applied to any connector other than the MT connector.  
         [0037]    According to this embodiment of the present invention, the creation of recess in the cores of the optical fibers can be reduced to provide good extension of the optical fibers from the end face of the ferrule body, since the optical fibers are ground by using the grinding sheet while applying the grounding liquid prepared by mixing a grinding material with alcohol. As a result, the return loss can be improved to increase the reliability in the optical fiber connector.