Abstract:
An optical connector includes a resin core pin guide member, a molded resin, and at least one optical fiber hole. The core pin guide member guides a distal end portion of an optical fiber. The molded resin molds the core pin guide member while exposing one end face thereof, thus constituting a ferrule main body attached to the distal end portion of the optical fiber. The one end face of the core pin guide member is flush with a distal end face of the ferrule main body. The optical fiber guide hole has an inner wall constituted by the core pin guide member and the molded resin. The distal end portion of the optical fiber is inserted in the optical fiber guide hole. A method of manufacturing an optical connector is also disclosed.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an optical connector and, more particularly, to a ferrule for an optical connector that connects optical fibers to each other. 
     FIG. 10A shows a ferrule for an optical connector disclosed in Japanese Patent Laid-Open No. 62-276513 (Reference 1), and FIG. 10A shows this ferrule from which its upper and lower molds are removed. 
     As shown in FIG. 10B, a press plate  74  made of a silicon material is adhered to a silicon support plate  73  having an upper surface formed with V-shaped optical fiber guide grooves and guide pin grooves, thereby forming optical fiber guide holes  81  and guide pin holes  82  each having a regular-triangular cross section. Optical fibers  75  are inserted in the optical fiber guide holes  81 , and closed with upper and lower molds  72  and  71 , as shown in FIG.  10 A. Molding with a resin  76  is performed including the optical fibers  75 , thereby fixing the optical fibers  75 . 
     Japanese Patent Laid-Open No. 62-276514 (Reference 2) also discloses a technique similar to that of FIGS. 10A and 10B. 
     FIG. 11A shows a ferrule for an optical connector disclosed in Japanese Patent Laid-Open No. 3-179406 (Reference 3), and FIG. 11B shows the main part of the same. 
     As shown in FIG. 11A, a ceramic support plate  90  having an upper surface formed with V-shaped optical fiber guide grooves and guide pin grooves is buried in a molded resin  93 . Optical fiber guide holes  91  and guide pin holes  92  each having a circular cross section are formed in the molded resin  93  with reference to these optical fiber guide grooves and guide pin grooves. 
     More specifically, the optical fiber guide holes  91  and guide pin holes  92  extend from the interior of the molded resin  93  and open in a side end face  94  of the molded resin  93  through the optical fiber guide grooves and guide pin grooves of the ceramic support plate  90 . As shown in FIG. 11B, the side end face  94  of the molded resin  93  is separate from a side surface  95  of the ceramic support plate  90  by a distance L. 
     Japanese Patent Laid-Open No. 3-179405 (Reference 4) also discloses a technique similar to that of FIGS. 11A and 11B. 
     In the prior art of FIGS. 10A and 10B or FIGS. 11A and 11B, the grooves are formed in the silicon support plate  73  or ceramic support plate  90 , and the optical fiber guide holes  81  or  91  and the guide pin holes  82  or  92  are formed at the predetermined portions of the silicon support plate  73  or ceramic support plate  90 . 
     In the prior art of FIGS. 10A and 10B, when optical connectors are to be connected to each other, the distal ends of the optical fibers  75  cannot be made to project by a small amount (e.g., 0.5 μm to 1 μm) from the side end face of the ferrule in order to bring the distal ends of the optical fibers  75  into direct contact with each other. 
     More specifically, the projecting shape of the optical fibers  75  can be obtained by subjecting the side end face of the ferrule to optical mirror surface finishing by means of buffing (buff polishing). The mirror surface finishing is also called PC (Physical Contact) polishing. According to mirror surface finishing, in order to decrease connection loss of propagation light by Fresnel reflection, the distal ends of the optical fibers  75  are made to project from the side end face of a ferrule by a small amount, and the end faces of opposing optical fibers  75  are brought into direct contact with these projecting distal ends, thereby realizing a low connection loss. 
     This buff polishing (PC polishing) uses a polishing medium, e.g., diamond abrasive grains. The distal ends of the optical fibers  75  cannot be made to project by a small amount unless the end face of the ferrule is formed of only a resin (plastic) softer than the optical fibers  75 . 
     This is due to the following reason. When the difference in hardness between the side end face of the ferrule and the optical fibers  75  is small, like the conventional ferrule shown in FIGS. 10A and 10B, or when a ceramic material or silicon harder than the optical fibers  75  exists, the finished surface including the optical fibers  75  may become flat, or inversely the distal ends of the optical fibers  75  may be recessed. 
     In the prior art shown in FIGS. 11A and 11B, the side end face of the ferrule is formed of only the molded resin  93  to be separate from the side surface  95  of the ceramic support plate  90  by the distance L. 
     Generally, a coefficient of linear expansion is large in a resin and small in a ceramic material or silicon. Hence, after a high-temperature molded resin is set, if it is cooled down to room temperature (temperature of the environment where the connector is to be used), a difference in size occurs between the resin and ceramic material. 
     For this reason, the optical fiber guide holes  91  and guide pin holes  92  appearing in the side end face of the ferrule cannot reflect the high-precision size of the ceramic support plate  90  serving as the core pin guide member. 
     More specifically, due to the difference in coefficient of linear expansion between the ceramic support plate  90  and molded resin  93 , the hole pitch error may occur at the resin portion corresponding to the distance L between the side surface of the ceramic support plate  90  and the side end face  94  of the molded resin  93 . 
     In the prior art shown in FIGS. 11A and 11B, when L=0 is set, i.e., when the side surface  95  of the ceramic support plate  90  is set to coincide with the side end face of the ferrule, the distal ends of the optical fibers cannot be made to project from the side end face of the ferrule by a small amount in accordance with buffing in the same manner as in the prior art of FIGS. 10A and 10B. Accordingly, it becomes impossible to realize a low connection loss by bringing the distal ends of opposing optical fibers into direct contact with each other. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an optical connector in which optical fiber guide holes and guide pin holes can be formed at high precision, and a method of manufacturing the same. 
     It is another object of the present invention to provide an optical connector in which the distal ends of optical fibers can be made to project by a small amount to realize a low connection loss, and a method of manufacturing the same. 
     In order to achieve the above objects, according to the present invention, there is provided an optical connector comprising a core pin guide member made of a resin to guide a distal end portion of an optical fiber, a molded resin for molding the core pin guide member while exposing one end face thereof, thus constituting a ferrule main body attached to the distal end portion of the optical fiber, the one end face of the core pin guide member being flush with a distal end face of the ferrule main body, and at least one optical fiber guide hole which has an inner wall constituted by the core pin guide member and the molded resin and into which the distal end portion of the optical fiber is inserted. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of an optical connector according to an embodiment of the present invention; 
     FIG. 2A is a perspective view showing the first manufacturing step of the optical connector shown in FIG. 1, and 
     FIG. 2B is a sectional view taken along the line I—I of FIG. 2A; 
     FIG. 3A is a perspective view showing the second manufacturing step of the optical connector shown in FIG. 1, and 
     FIG. 3B is a sectional view taken along the line II—II of FIG. 3A to which an upper mold is added; 
     FIG. 4A is a perspective view showing the third manufacturing step of the optical connector shown in FIG. 1, and 
     FIG. 4B is a sectional view taken along the line III—III of FIG. 4A; 
     FIG. 5A is a perspective view showing the fourth manufacturing step of the optical connector shown in FIG. 1, and 
     FIG. 5B is a sectional view taken along the line IV—IV of FIG. 5A; 
     FIG. 6A is an enlarged perspective view of FIG. 5A, and 
     FIG. 6B is a perspective view of FIG. 6A seen from the opposite side; 
     FIG. 7 is a sectional view showing the sixth manufacturing step of the optical connector shown in FIG. 1; 
     FIG. 8 shows how to connect the optical connectors each shown in FIG. 1 to each other; 
     FIG. 9A is a sectional view showing a state wherein the optical connectors shown in FIG. 8 are connected to each other, and 
     FIG. 9B is an enlarged sectional view of the main part of FIG. 9A; 
     FIG. 10A is a longitudinal sectional view showing a conventional optical connector manufacturing step, and 
     FIG. 10B is a sectional view taken along the line V—V of FIG. 10A from which the upper mold is removed; and 
     FIG. 11A is a perspective view showing another conventional optical connector manufacturing step, and 
     FIG. 11B is a sectional view taken along the line VI—VI of FIG. 11A from which the upper mold is removed. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention will be described in detail with reference to the accompanying drawings. 
     FIG. 1 shows an optical connector according to an embodiment of the present invention, which is an MPO (Multifiber Push On) connector. Referring to FIG. 1, a core pin guide member  10  made of a resin and a molded resin (ferrule main body)  40  constitute a resin ferrule. The molded resin  40  molds the core pin guide member  10  at the distal end of the ferrule. The core pin guide member  10  and molded resin  40  are made of the same thermosetting resin. It suffices if the core pin guide member  10  and molded resin  40  are made of thermosetting resins having the same heat characteristics. 
     Optical fiber guide holes  41  and guide pin holes are formed at the interface between the molded resin  40  and small and large V-groove surfaces formed on the upper surface of the core pin guide member  10 , as will be described later. Optical fibers  50  are inserted in the optical fiber guide holes  41  at the distal end of the ferrule, and a rubber boot  55  is pressed into the rear end portion of the ferrule. An adhesive (not shown) is introduced into the ferrule through an adhesive dropping hole  44  formed at the center of the ferrule, to fix the optical fibers  50 . 
     The side end face of the ferrule has a buffed vertical surface  46 A and a buffed tilt surface  46 B, and the distal ends of the optical fibers  50  are flush with the side end face of the ferrule. The distal ends of the optical fibers  50  project from the buffed tilt surface  46 B by a small amount (0.5 μm to 1 μm). The vertical surface  46 A of the ferrule is a flat surface perpendicularly intersecting the optical fibers  50 , and the tilt surface  46 B is a flat surface inclined from the vertical surface  46 A by an angle θ. 
     In this embodiment, the tilt surface  46 B is inclined from the vertical surface  46 A by an angle θ=8°. This tilt surface  46 B is formed to realize a high reflection attenuation amount by preventing the reflected light from being set in the waveguide mode. 
     The distal ends of the optical fibers  50  are made to project from the tilt surface  46 B by a small amount by mirror surface finishing of buff polishing. This enables direct contact, i.e., PC (Physical Contact), of the distal ends of the optical fibers  50  in connecting optical connectors, thereby realizing a low connection loss. 
     FIGS. 2A to  6 B show a method of manufacturing the optical connector shown in FIG. 1 in the order of manufacturing steps. 
     As shown in FIGS. 2A and 2B, first, the core pin guide member  10  made of a thermosetting resin, e.g., an epoxy resin, is prepared. Two large V-grooves are formed as guide pin grooves  12  in the upper surface of the core pin guide member  10  to be separated from each other by a predetermined distance, and four small V-grooves are formed as optical fiber guide grooves  11  between the two guide pin grooves  12  at a constant interval. 
     The core pin guide member  10  is fabricated in advance and selected in accordance with size measurement of the finished products after molding, so that only a nondefective core pin guide member is used in the manufacture of the ferrule. The core pin guide member  10  is placed on a core pin guide member setting surface  21  of a lower mold  20  corresponding to the distal end of the ferrule. 
     As shown in FIGS. 3A and 3B, two guide-hole core pins  32  of a core pin member  30  are placed on the guide pin grooves  12 , and four optical fiber hole core pins  31  are placed on the optical fiber guide grooves  11 . At this time, these pins  32  and  31  are supported by a core pin support  33  such that all of their centers are located linearly on a center line of the ferrule that extends horizontally along the side end face and are set at predetermined intervals. 
     An upper mold  25  is aligned with the lower mold  20 , and mold closing is performed. In FIG. 3A, the upper mold  25  is not illustrated. Thereafter, a thermosetting resin, e.g., an epoxy resin, is injected into a cavity formed by the upper and lower molds  25  and  20 , and is thermoset. 
     As shown in FIGS. 4A and 4B, the upper and lower molds  25  and  20  are opened to release the molds from the product. Hence, the core pin guide member  10  and core pin member  30  are molded with the thermosetting resin, e.g., the molded resin  40  made of an epoxy resin. 
     As shown in FIGS. 5A and 5B, the core pin member  30  is pulled out from the molded resin  40 , and its unnecessary portion such as the distal end portion is removed to obtain a ferrule constituted by the core pin guide member  10  and molded resin  40 . 
     As a result, in the ferrule, the optical fiber guide holes  41  and guide pin holes  42  are formed by the core pins  31  and  32 , respectively. Most of the inner wall of the optical fiber guide holes  41  is formed of the molded resin  40 , and part of the inner wall that corresponds to portions where the core pins  31  are in contact with the optical fiber guide grooves  11  is constituted by the optical fiber guide grooves  11  of the core pin guide member  10 . 
     Similarly, most of the inner wall of the guide pin holes  42  is formed of the molded resin  40 , and part of the inner wall that corresponds to portions where the core pins  32  are in contact with the guide pin grooves  12  is constituted by the guide pin grooves  12  of the core pin guide member  10 . 
     The side end face of the ferrule on the distal end side, which is constituted by the core pin guide member  10  and molded resin  40 , forms a vertical surface  46  perpendicularly intersecting the optical fiber guide holes  41 . 
     FIG. 6A shows the optical connector of FIG. 5A in enlargement, and FIG. 6B shows the same from the opposite side (lower side). 
     Referring to FIGS. 6A and 6B, the optical fiber guide holes  41  and guide pin holes  42 , the inner wall of which is constituted by the molded resin  40  and core pin guide member  10 , are arranged to be axially symmetrical, i.e., point symmetrical, vertically and horizontally in the side end face of the ferrule. 
     In this embodiment, the diameter of each of the two guide pin holes  42  is 0.701 μm, and the diameter of each of the four optical fiber guide holes  41  arranged between the guide pin holes  42  at a constant interval is 0.127 μm. Regarding the size of the molded resin  40 , A=7 mm, B=3 mm, and C=8 mm. 
     How to attach the ferrule fabricated in the above manner to the distal ends of the optical fibers will be described. 
     As shown in FIG. 7, the optical fibers  50  are inserted in the optical fiber guide holes  41  of the ferrule from the rear end side so as to reach the side end face  46 , and the rubber boot  55  is fitted in the distal end of the ferrule. Subsequently, an adhesive is dropped into the ferrule through the adhesive dropping hole  44  formed in the ferrule, to fix the optical fibers  50 . 
     When the diameter of each optical fiber guide hole  41  is 0.127 μm, the diameter of each optical fiber  50  is 0.125 μm. 
     Finally, the side end face of the ferrule is polished and buffed (PC polishing) to form the tilt surface  46 B having a tilt angle of 8°, thereby obtaining an optical connector shown in FIG.  1 . Polishing for forming the tilt surface  46 B is performed through flat finishing with a hone. 
     Buff polishing is performed by using a polishing medium, e.g., diamond abrasive grains. Since the side end face is entirely formed of a resin (plastic) having a lower hardness than that of the optical fibers  50 , the tilt surface  46 B from which the distal ends of the optical fibers  50  project slightly can be formed. Therefore, the end faces of the opposing optical fibers  50  can be connected to each other by bringing them into direct contact with each other. 
     FIG. 8 shows a state wherein 4-fiber optical connectors  1  and  2  having pins and pin holes of the type shown in FIG. 1 are connected to each other. As described above, when the diameter of each guide pin hole  42  is 0.701 μm, guide pins  49  each having a diameter of 0.699 μm are inserted in the guide pin holes  42  to connect the optical connectors  1  and  2  to each other. 
     FIG. 9A shows a state wherein the optical connectors shown in FIG. 8 are connected to each other, and FIG. 9B shows a PC portion of FIG. 9A in enlargement. 
     Even if the tilt surface  46 B is formed, since the centers of the optical fiber guide holes  41  and guide pin holes  42  are located point-symmetrical in the optical connectors  1  and  2 , respectively, the optical connectors  1  and  2  can be connected to each other by inverting one of the optical connectors  1  and  2  manufactured to have the same shape upside down. 
     As shown in FIG. 9B, since the distal ends of the optical fibers  50  project from the tilt surface  46 B, which is mirror-surface polished by buff polishing, by 0.5 μm to 1 μm, the distal ends of the optical fibers  50  can be brought into direct contact (PC) with each other. 
     As has been described above, according to the present invention, the core pin guide member is formed of a resin, and the resin core pin guide member and the molded resin constitute the side end face of the ferrule. Therefore, the distal ends of the optical fibers can be made to project by a small amount in order to prevent misalignment between the optical fiber holes and guide pin holes and to realize a low connection loss and a high reflection attenuation amount.