Abstract:
An object of the present invention is to provide an optical connector capable of preventing impairment of PC connections by a hard sleeve during PC connection of optical connectors having a hard sleeve installed in engaging pin holes thereof. The optical connector has a ferrule formed with integrally molded plastic and having engaging pin holes, and a hard sleeve installed in the engaging pin holes and having a hardness that is higher than the plastic of the ferrule. The hard sleeve and the plastic of the ferrule surrounding this hard sleeve are polished so as to be lower than the coupling end surface, and the end of the hard sleeve does not protrude beyond the coupling end surface.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an optical connector. 
   2. Background Art 
   Conventional mechanically transferable (MT) optical connectors (such as those defined in IEC 60874-16 or JIS C 5981) are known to be optical connectors in which connection is made by inserting and engaging an engaging pin in an engaging hole and positioning to make an end-to-end connection. In addition, multifiber push-on (MPO) optical connectors (such as those defined in IEC 61754-7 or JIS C 5982) are known to be optical connectors composed by using the MT optical connector as a ferrule and incorporating in a housing formed from plastic and so forth. 
   However, since the MT optical connectors typically employ a constitution in which a metal engaging pin is inserted and engaged in an engaging pin hole formed in a plastic ferrule, the engaging pin hole becomes worn due to retraction and insertion of the engaging pin, thereby resulting in the problem of this wear causing a decrease in positioning accuracy. Consequently, there is a need to prevent wear of the engaging pin hole so as to effectively prevent a decrease in positioning accuracy caused by wear of the engaging pin hole as well as the resulting problems such as an increase in connection loss. 
   In response to this need, a technique is known for suppressing wear of the engaging pin hole accompanying extraction and insertion of the engaging pin in which a hard sleeve comprised of a material having high hardness such as zirconia-based ceramics is installed in the engaging pin hole to serve as a lining. 
   In the case of installing a hard sleeve in the engaging pin hole, if the end of the hard sleeve protrudes from the connecting end surface of the optical connector, the ends of the hard sleeves collide with each other during end-to-end connection of two optical connectors, thereby resulting in the risk of impairment of the physical contact (PC) connection of the optical connectors. 
   Consequently, in Japanese Unexamined Patent Application, First Publication No. 8-278426, a method is disclosed for polishing the end surface of the hard sleeve using a diamond grinder having a diameter similar to that of the hard sleeve so as to regress the end surface of the hard sleeve farther back than the connecting end surfaces of the optical connectors. However, in the case of this method, since it is necessary to accurately align the diamond grinder at the location of the hard sleeve during polishing, this work is extremely difficult, thereby resulting in the risk of decreased yield. Moreover, since the hard sleeve has high hardness, considerable time is required for its polishing, thereby resulting in the problem of poor productivity. 
   In consideration of the problems, an object of the present invention is to provide an optical connector capable of preventing impairment of PC connection by the end of a hard sleeve during PC connection of optical connectors having a hard sleeve installed in their engaging pin holes. 
   SUMMARY OF THE INVENTION 
   In order to solve the problems, the optical connector of the present invention is provided with a ferrule formed with integrally molded plastic and having engaging pin holes, and a hard sleeve installed in the engaging pin holes and having a hardness that is higher than that of the plastic of the ferrule. The hard sleeve and the plastic of the ferrule surrounding this hard sleeve are polished so as to be lower than the coupling end surface, and the end of the hard sleeve does not protrude beyond the coupling end surface. 
   In addition, the optical connector of the present invention is provided with a ferrule formed with integrally molded plastic and having engaging pin holes, and a hard sleeve installed in the engaging pin holes and having a hardness that is higher than that of the plastic of the ferrule. The hard sleeve and the plastic of the ferrule that surrounds this hard sleeve are polished on an incline with respect to the coupling end surface so as to be lower than the coupling end surface, and the end of the hard sleeve does not protrude beyond the coupling end surface. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side view showing the appearance of one embodiment of the optical connector of the present invention. 
       FIG. 2  is a front view showing the optical connector shown in FIG.  1 . 
       FIG. 3  is a bottom view showing the optical connector shown in FIG.  1 . 
       FIG. 4  is a partially enlarged view showing the periphery of the end of a hard sleeve in the optical connector shown in FIG.  1 . 
       FIG. 5  is a side view showing an optical connector prior to the formation of polished end surfaces on both sides of a coupling end surface in a manufacturing process for manufacturing the optical connector shown in FIG.  1 . 
       FIG. 6  is a front view showing the end surface of an optical connector prior to the formation of polished end surfaces on both sides of a coupling end surface in a manufacturing process for manufacturing the optical connector shown in FIG.  1 . 
       FIG. 7  is a front view showing the state of an optical connector during formation of polished end surfaces on both sides of a coupling end surface in a manufacturing process for manufacturing the optical connector shown in FIG.  1 . 
       FIG. 8  is a side view showing the state of an optical connector during formation of polished end surfaces on both sides of a coupling end surface in a manufacturing process for manufacturing the optical connector shown in FIG.  1 . 
       FIG. 9  is a partial overhead view showing another embodiment of the optical connector of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The following provides a detailed explanation of the optical connector of the present invention with reference to the drawings. 
     FIG. 1  is a slide view showing the appearance of one embodiment of the optical connector of the present invention. 
     FIG. 2  is a side view showing the optical connector shown in  FIG. 1 , while  FIG. 3  is a bottom view showing the optical connector shown in FIG.  1 .  FIG. 4  is a partially enlarged view showing the periphery of the end of a hard sleeve. Furthermore, the optical fiber holes are omitted from  FIG. 3  since there is not enough space in the coupling end surface to show them in the drawing. 
   In these drawings, a reference symbol  10  indicates an optical connector. This optical connector  10  can be preferably applied to, for example, a multifiber push-on (MPO) optical connector (such as that defined in IEC 61754-7 or JIS C 5982). 
   The optical connector  10  is provided with a ferrule  1  formed with an integrally molded plastic, and a hard sleeve  5  installed in engaging pin holes  4  provided in both sides of the coupling end surface  11  of this ferrule  1 . 
   The ferrule  1  is made of a plastic such as silica-filled epoxy resin, polyphenylene sulfide (PPS) or polybutylene terephthalate. As shown in  FIGS. 1 and 3 , the front end surface  1   a  of this ferrule  1  is polished to incline by a predetermined angle α (see  FIG. 5 ) to form the coupling end surface  11 . Optical fiber insertion holes  3  into which optical fibers  2  are inserted are opened in the coupling end surface  11 . 
   The number of the optical fiber insertion holes  3  can be set as is suitable. Although  12  holes are shown in  FIG. 2 , the number of these holes is not limited to  12 , for example, only a single optical fiber insertion hole  3  may be opened in the coupling end surface  11 . 
   A pair of engaging pin holes  4  are provided to the left and right of the optical fiber insertion holes  3 . The engaging pin holes  4  pass through ferrule  1  from its front end surface  1   a  to its rear end surface  1   b . A hard sleeve made of a material having high hardness is inserted into each engaging pin hole  4 . 
   A material that is at least harder than the plastic used to form the ferrule  1  is used for the material of the hard sleeves  5 . In addition, a material is used that has a degree of wear resistance that does not practically present a problem with respect to repeated insertion and extraction of the engaging pins inserted into hard sleeve  5 . Examples of such materials that can be used include ceramics such as zirconia or alumina, glass such as quartz glass and metal such as stainless steel. Ceramics are preferably used, and zirconia ceramics are used. 
   The end of the hard sleeve  5  and the plastic of the ferrule  1  that surrounds the engaging pin holes  4  are polished to form a polished end surfaces  12  which inclines by a predetermined angle α with respect to the coupling end surface  11 . 
   Preferably, the end of the hard sleeve  5  is made to protrude farther than the plastic of the ferrule  1 . As shown in  FIG. 4 , the protrusion of the end of the hard sleeve  5  farther than the plastic of the ferrule  1  does not only refer to the case in which the peripheral surface of the end of the hard sleeve  5  is completely exposed. It also includes the case in which the plastic of the ferrule  1  is pushed up towards the end of the hard sleeve  5 , and the amount of adhesion of the periphery of the hard sleeve  5  to the plastic of ferrule  1  gradually decreases from the base section towards the protruding end so that only a small amount of plastic remains near the end peripheral surface. 
   Next, an explanation is provided of an example of a manufacturing method of the-mentioned optical connector  10 . 
   First, optical fibers  2  are inserted into the optical fiber insertion holes  3 , and optical fibers  2  are adhered to the optical fiber insertion hole  3  using an adhesive. 
   Next, the front end surface  1   a  of the ferrule  1  is polished to incline by a predetermined angle α relative to the optical axis to form the coupling end surface  11  (FIGS.  5  and  6 ). A specific example of the angle α is defined as, for example, 8°±0.5° in IEC 61574-7. 
   An example of a specific polishing step for forming the coupling end surface  11  is a step in which adhesive protruding from the optical fiber insertion hole  3  is removed by rough polishing, and after the angled polishing of the front end surface  11   a  of the ferrule  1 , the final precision polishing is performed by buffing. 
   After forming the coupling end surface  11 , as shown in  FIGS. 4 ,  7 , and  8 , the ferrule  1  is inclined at an angle θ relative to the coupling end surface  11 , and the hard sleeve  5  and the plastic of the ferrule  1  that surrounds this hard sleeve  5  are polished. 
   Since the hard sleeve  5  is harder than the plastic of the ferrule  1 , when the hard sleeve  5  and the plastic of ferrule  1  that surrounds the hard sleeve  5  are polished, the hard sleeve  5  protrudes from the polished end surface  12  formed on the ferrule  1  after polishing. During manufacturing of the optical connector of the present invention, although the end  5   a  of the hard sleeve  5  may protrude from the polished end surface  12 , it should not protrude from the coupling end surface  11 . 
   Therefore, the following provides an explanation of an example of a method for determining the angle θ for ensuring that the end of the hard sleeve  5  does not protrude farther than the coupling end surface  11  of the optical connector  10  with reference to FIG.  4 . 
   In  FIG. 4 , double-dot chain line x indicates the center line of the ferrule  1  (line located in the middle of the center line of the engaging pin hole  4 ). In addition, double-dot chain line y indicates the center line of the engaging pin hole  4 . 
   Reference symbol  2   a  indicates an optical fiber  2  that is the closest to the engaging pin hole  4 , while reference symbol  2   b  indicates an optical fiber  2  that is adjacent to the optical fiber  2   a . Length P is the pitch of the optical fiber insertion hole  3 . 
   Diameter d is the diameter of the optical fiber  2 , while diameter D is the diameter of the engaging pin hole  4 . 
   Length Q is the interval between the center line x of the ferrule  1  and the center line y of the engaging pin hole  4 , and is equivalent to half the interval between the center lines y of two engaging pin holes  4 . 
   Length B is the interval between the outer surface of the optical fiber  2   a  and the hard sleeve  5  inserted into the engaging pin hole  4 . 
   Length Δ is the protruding height of the hard sleeve  5  from the polished end surface  12 . 
   Length A is the interval between optical fiber  2   a  and the center line x of the ferrule  1 . 
   The following relational expression (1) is valid with respect to the length A when the number of the optical fiber insertion holes  3  arranged in the direction of width of the coupling end surface  11  is taken to be n.
 
 A =(1/2)( n− 1) P   (1)
 
   In addition, the following relational expression (2) is valid as is clear from FIG.  4 . 
     B=Q−A−d /2 −D /2  (2) 
   Moreover, the following relational expression (3) is valid to ensure that the end  5   a  of the hard sleeve  5  does not protrude farther than the coupling end surface  11 .
 
tan θ≧Δ/B  (3)
 
   Solving the relational expressions (1) through (3) makes it easy to determine a suitable angle θ for the desired optical connector  10 . 
   For example, assuming that P=0.25 mm, Q=2.3 mm, d=0.125 mm and D=1.1 mm, and if a value of 0.004 mm is used as an example of a measured value of the length Δ, the results shown in Table 1 are obtained. In Table 1, θ min indicates the minimum value of the angle θ to ensure that the end  5   a  of the hard sleeve  5  does not protrude farther than the coupling end surface  11 . 
   
     
       
             
             
             
           
             
             
             
           
         
             
               TABLE 1 
             
             
                 
             
             
               n 
               A/mm 
               θ min/° 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               4 
               0.375 
               0.17 
             
             
               8 
               0.875 
               0.28 
             
             
               12 
               1.375 
               0.73 
             
             
                 
             
           
        
       
     
   
   In this manner, by determining the angle θ and polishing the hard sleeve  5  and the plastic of the ferrule  1  that surrounds the hard sleeve  5 , the protrusion of the end  5   a  of the hard sleeve  5  farther than the coupling end surface  11  is effectively prevented. Thus, when making a PC connection for the optical connector  10  in which the hard sleeve  5  is installed in the engaging pin holes  4 , impairment of the PC connection by end  5   a  of the hard sleeve  5  can be effectively prevented. 
   The number of steps required for polishing can be reduced as a result of the end  5   a  of the hard sleeve  5  protruding farther than the polished end surface  12 . In other words, the product resulting from polishing the hard sleeve  5  and the plastic of ferrule  1  that surrounds this hard sleeve  5  in a single step can be used as the optical connector  10 . There is no need to additionally polish the end  5   a  of the hard sleeve  5 . 
   Another embodiment of the present invention is shown in FIG.  9 . In this embodiment, the polished end surface  22  surrounding the hard sleeve  5  is lowered by a step  23  with respect to the coupling end surface  21 , and the hard sleeve  5  and the plastic of ferrule  1  that surrounds this hard sleeve  5  are polished so as to be lower than the coupling end surface  21 . In this type of optical connector  20 , since the end  5   a  of the hard sleeve  5  is not protruding farther than the coupling end surface  21 , impairment of a PC connection by end  5   a  of hard sleeve  5  can be effectively prevented when making a PC connection. 
   The present invention is not limited to the embodiments. Various modifications can be achieved, and such modifications are all included in the scope of the present invention.