Abstract:
A ferrule includes a recess formed on an obliquely polished surface to house a protrusion formed on an obliquely polished surface of another ferrule, so as to avoid an angular change at an interface between end surfaces of the pair of obliquely polished end surfaces of the ferrules facing each other.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a ferrule for an optical connector for connecting multiple optical fibers in a lump, and more specifically to a ferrule for an optical connector including a ferrule end surface which is obliquely polished. 
     2. Description of the Related Art 
     Mechanically transferrable (MT) connectors and multifiber push-on (MPO) connectors have been known as examples of optical connectors each including a multicore optical fiber and used to connect optical fiber ribbons and the like. 
     MT connectors are disclosed in Japanese Patent Application Publication No. Hei 9-178980 and in Japanese Patent Application Publication No. Hei 9-184942. In these MT connectors, optical fibers respectively fixed to ferrules are disposed so as to face each other and these fibers are precisely positioned by way of two guide pins. Moreover, a certain pressure is applied to both of the ferrules through a clamp spring or the like and a stable connection state is retained by maintaining this pressure. 
     An MPO connector has been disclosed in Japanese Patent Application Publication No. Hei 10-170764. This MPO connector does not require any matching agents or tools which are necessary for the MT connectors and thus is easily attachable or detachable by a single touch. 
     Each of the MT connectors and the MPO connector includes ferrules as main constituents for fixing leading-edge portions at ends of respective optical fibers. A pair of ferrules are disposed so as to face each other, and each of the ferrules is pressurized from its rear end toward its front end surface by use of either an external clamp spring which is mounted thereon or a spring previously contained in a connector housing. 
     A front end surface of each of the ferrules is obliquely polished at an angle of approximately 8 degrees. When the ferrules are aligned so that each two adjacent obliquely polished surfaces abut on each other, the center lines of the ferrules are arranged in a straight line. 
     When the optical fibers are thus brought into contact in a manner that each adjacent two obliquely polished surfaces abut on each other, physical contact (PC) connection that suppresses an increase of a connection loss due to Fresnel reflection is established without using a refractive index matching agent. 
     The ferrules are formed of polyphenylene sulfide (PPS) resin or epoxy resin. 
     SUMMARY OF THE INVENTION 
       FIGS. 1 and 2  show a state of the above-described conventional ferrules  1  and  1  in the PC connection. When obliquely polished end surfaces la of the ferrules  1  and  1  facing each other are pressurized in axial directions F with springs (not shown) for pressurization, the ferrules  1  and  1  facing each other mutually slide in directions indicated with arrows S along the oblique surfaces due to a clearance between a guide pin P and a guide-pin guide hole  2 , thereby causing axial misalignment. Accordingly, a shear stress occurs between the guide pin P and an edge of the guide-pin guide hole  2 . If this stress occurs repeatedly, a bump Q protruded by plastic deformation of the edge of the guide hole  2  is formed as a consequence. 
     This bump Q pressurizes the end surface of the facing ferrule, whereby a minute clearance is formed between the obliquely polished surfaces that had been closely attached to each other. As a result, the physical contact (PC) connection will be obstructed. 
     An aspect of the present invention provides a ferrule for an optical connector which includes an obliquely polished front end surface, a guide-pin guide hole formed in a longitudinal direction from the front end surface, and a recess formed at an edge of the guide-pin guide hole on the front end surface. Here, the front end surface establishes close contact with an obliquely polished front end surface of another ferrule and the contact is retained by pressurization. 
     According to the present invention, when a bump protruded in a space between the guide pin and the edge of the guide-pin guide hole, the bump is housed inside the recess. Therefore, this bump will not obstruct PC connection. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a vertical cross-sectional view showing a state of application of conventional ferrules for optical fibers. 
         FIG. 2  is another vertical cross-sectional view showing the state of application of the conventional ferrules for optical fibers. 
         FIG. 3  is a perspective view showing a first embodiment of the present invention. 
         FIG. 4  is a perspective view showing a second embodiment of the present invention. 
         FIG. 5  is a vertical cross-sectional view showing a state of application of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
       FIG. 3  shows a first embodiment of the present invention. 
     A ferrule  1  includes guide-pin guide holes  2  formed so as to penetrate a side edge of the ferrule from the front end surface of the side edge, an adhesive filling hole  3  formed in an upper surface of the ferrule  1 , multiple insertion holes  4  being communicated with this adhesive filling hole  3  and allowing insertion of front ends of optical fibers, and an obliquely polished surface  5  as well as a non-obliquely polished surface  6  both of which are formed on the front end surface of the ferrule  1 . 
     Specifically, near an entrance of each guide-pin guide hole  2 , a recess  7  communicated with this entrance is formed. The recess  7  is formed into a groove shape along the obliquely polished surface  5 , and this groove-shaped recess  7  is formed to reach an upper surface  8  of the ferrule  1 . 
     To be more specific, the groove-shaped recess  7  is formed so as to extend toward the non-obliquely polished surface  6  and reach the upper surface  8  of the ferrule  1 . Comparing with a case where the groove-shaped recess is formed toward an obliquely polished surface side (a side opposite to the side where non-obliquely polished surface  6  is formed), this structure prevents a depth of the recess  7  from being shallow because of the inclination. 
     Moreover, the groove-shaped recess  7  preferably has a width equal to or greater than a diameter of each of the guide-pin guide holes  2 . 
     Operations and effects of this invention will now be described with reference to  FIG. 5 . A pair of ferrules  1  and  1  are held by pressurization toward each other by use of pressurizing means (not shown) such as a clamp spring or the like. When the ferrules  1  and  1  are held by pressurization, the obliquely polished surfaces  5  slide relatively to each other along the oblique surfaces. As a result, a shear stress occurs in the vicinity of an edge of the guide-pin guide hole  2 , which is in contact with a guide pin P. If this stress occurs repeatedly, a bump Q may be formed due to plastic deformation. In this case, the recess  7  formed at the edge of the guide-pin guide hole  2  on the obliquely polished surface  5  on the opponent side will house this bump Q. Therefore, the bump Q will not pressurize the obliquely polished surface  5  on the opponent side and change a position thereof. 
     In other words, since the recess  7  houses the bump Q, a minute clearance will not be formed between the ferrules  1  and  1  by pressurizing the obliquely polished surface  5  of the opponent ferrule. Therefore, PC contact will not be obstructed. 
     Second Embodiment 
     In the first embodiment, an end of each of the recesses  7  itself is simply extended to the upper surface  8  of the ferrule  1 . Alternatively, in a second embodiment, a taper portion  9  is first formed around each of the guide-pin guide holes  2  as shown in  FIG. 4 , and another groove can be formed continuously to this taper portion  9 . By forming the recess into a taper, it is possible to prevent a cracked resin formed at the time of connecting or disconnecting a joint pin from protruding toward a contact edge surface and thereby adversely affecting optical connection. 
     Each of the groove-shaped recesses  7  illustrated in  FIG. 3  and  FIG. 4  is extended until reaching the upper surface  8  of the ferrule. Instead, the recess may be extended halfway before reaching the upper surface  8  of the ferrule. 
     INDUSTRIAL APPLICABILITY 
     The present invention is applicable to a ferrule for an MT connector and to a ferrule for a MPO connector. Moreover, an array of the insertion holes  4  for optical fibers formed on the front end surface is not limited only to a single row. The invention is also applicable to a structure including multiple rows of the insertion holes.