Abstract:
A fiber optic connector ferrule in which a coating-accommodating portion for mounting a coated portion of an optical fiber and maintaining the optical fiber such that the axis thereof becomes substantially straight from the mounted portion to the front end is formed behind a fiber-arranging hole by the steps of: disposing one or a plurality of mold pins each having a columnar portion formed on a distal end side thereof and a prismatic portion, disposed on a proximal end side thereof, having substantially a quadrangular cross section, with side faces of the prismatic portions being in contact with each other, within a mold such that each mold pin is slidable in an axial direction of the columnar and prismatic portions; and filling the mold with a resin, and axially pulling off each mold pin after the resin is cured, thereby causing the columnar portion to form the fiber-arranging hole and causing the prismatic portion to form the coating-accommodating portion for mounting the coated portion.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a fiber optic connector ferrule for arranging optical fibers, and a method of making the same. 
     2. Related Background Art 
     In general, when optical fiber ribbons are to be connected to each other, the coating is removed from an end portion of optical fiber ribbons so as to expose each optical fiber, and a fiber optic connector ferrule made of a synthetic resin for arranging the optical fibers is attached to this end portion, thereby establishing the connection. The connector ferrule is used for accurately arranging the optical fibers. FIG. 11 shows the configuration of a typical fiber optic connector ferrule manufactured to JIS C 5981. 
     The fiber optic connector ferrule  102  shown in FIG. 11 has a plurality of parallel fiber-arranging holes  120  for arranging the respective optical fibers therewithin. Disposed on the inside or the fiber insertion side of each fiber-arranging hole  120  is a tapered portion  121  whose inside diameter gradually increases so as to continue to a groove portion  122 . The connector ferrule  102  also has an open portion  123  used for receiving an adhesive for securing an optical fiber ribbon  103  (see FIGS.  13  and  14 ), a pin hole  124  into which a guide pin is inserted at the time of connecting with the other fiber optic connector ferrule to be paired. 
     While the connector ferrule  102  is being molded by transfer molding or injection molding, each fiber-arranging hole  120  is formed by an axially-slidable mold pin  101  (see FIG. 12) disposed within a mold (not shown) adapted to open vertically. For easier understanding of the structure, only two mold pins  101  are shown in FIG.  12 . Each mold pin  101  is a round pin having a circular cross section, and is constituted by a first columnar portion  101   a , a second columnar portion  101   c  having an outside diameter greater than that of the first columnar portion  101   a , and a tapered portion  101   b  connecting the first and second columnar portions  110   a ,  101   c , all of which are concentric. The mold pins  101  are held by holding members  113  on the proximal end side thereof. At this time, a plurality of mold pins  101  are accurately positioned by V-shaped grooves  114  of one of the holding members  113 . 
     SUMMARY OF THE INVENTION 
     When the connector ferrule  102  is molded by use of the mold pins  101 , a certain extent of thickness H is necessary in the holding member  113  on the V-shaped groove  114  side since the mold pins  101  are held by the V-shaped grooves  114 . Then, since the connector ferrule  102  is formed while the holding members  113  are being inserted into the mold, a step may be formed behind the groove portions  122 , i.e., further on the fiber insertion side, as shown in FIG.  13 . 
     Consequently, as shown in FIG. 13, when an optical fiber ribbon  103  is inserted into the connector ferrule  102 , coated portion  131  of the optical fiber ribbon  103  may not be supported from the lower side, whereby optical fibers  130  in the optical fiber ribbon  103  may bend. This case has been problematic in that transmission characteristics deteriorate due to a bending stress and, at worst, the optical fibers  130  may break while being used. Similar problems may also occur in the case where a fiber optic connector ferrule without the open portion  123  is manufactured. 
     Also, although not usually done, the coated portion  131  may be inserted to the inner end of the connector ferrule  102  in order to be supported from the lower side as shown in FIG.  14 . Though the coated portion  131  is positioned on the groove portion  122  in this case, the lower face of the coated portion  131  would align with the axis of the optical fiber  130  within the fiber-arranging hole  120 . As a consequence, the optical fibers  130  may also bend. For eliminating the above-mentioned problems and stably connecting optical fiber ribbons  103  to each other, there has been a demand for further improvements in making a fiber optic connector ferrule which can securely hold not only the optical fibers  130  but also the coated portion  131 . 
     Therefore, it is an object of the present invention to provide a fiber optic connector ferrule which prevents transmission characteristics of an optical fiber from deteriorating and has no danger of damaging the optical fiber, and a method of making the same. 
     For achieving the above-mentioned object, the method of making a fiber optic connector ferrule in accordance with the present invention is a method of making a fiber optic connector ferrule in which one or a plurality of fiber-arranging holes for arranging and securing respective optical fibers are provided, the method comprising the steps of: (1) disposing one or a plurality of mold pins each having a columnar portion formed on a distal end side thereof and a prismatic portion, disposed on a proximal end side thereof, having substantially a quadrangular cross section, with side faces of the prismatic portions being in contact with each other, within a mold such that each mold pin is slidable in an axial direction of the columnar and prismatic portions; and (2) filling the mold with a resin, and axially pulling off each mold pin after the resin is cured, thereby each of fiber-arranging holes being formed and a coating-accommodating portion for mounting a coated portion of the respective optical fibers being formed. 
     In the fiber optic connector ferrule made by this method, the coating-accommodating portion can maintain the axis of the optical fiber substantially straight to the front end in the respective fiber-arranging hole. This fiber optic connector ferrule securely holds the optical fibers at the portion that are likely to bend, i.e., the area ranging from the front end of the coated portion to the end of the optical fibers. 
     Also, since the proximal end side of the mold pin is formed as the prismatic portion, it is advantageous in that no burrs would occur on the insertion side of the coating-accommodating portion in the accomplished fiber optic connector ferrule, whereby the optical fiber can be prevented from being damaged by burrs, and that the positioning of the optical fibers in the optical axis direction can be achieved without being prevented by burrs. Conventionally, since the mold pin  101  (see FIG. 12) having a circular cross section has been used, there have been cases where a resin immerses into the V-shaped groove  114 . Such immersing resin forms burrs on the insertion side of the groove portion  122 . 
     At least one side edge of the prismatic portion may be chamfered along the lengthwise direction of the mold pin, and this chamfered portion is disposed, when the mold pins are arranged within the mold, at a part forming the coating-accommodating portion. As a consequence, in the molded fiber optic connector ferrule, the coating-accommodating portion is provided with a guiding projection for guiding the optical fiber to be inserted into the fiber-arranging hole. As a result, a workability of attaching the optical fiber ribbon to the fiber optic connector ferrule will be improved. 
     It is preferred that a tapered portion whose outside diameter gradually expands in a direction away from the columnar portion is disposed between the columnar portion and the prismatic portion. This tapered portion forms a fiber-guiding portion, at the insertion-side end portion of the fiber-arranging hole in the fiber optic connector ferrule, for guiding the optical fiber to be inserted into the fiber-arranging hole. As a result, when the optical fiber is to be attached to the fiber optic connector ferrule, the optical fiber can be smoothly inserted into the fiber-arranging hole without being damaged. When the tapered portion is used together with the above-mentioned chamfered portion forming the guiding projection, the operation of attaching the optical fiber to the fiber optic connector ferrule can further be smoothed. 
     The upper or lower side part of the prismatic portion may be provided with a predetermined notch, which is used for positioning and arranging each mold pin at a predetermined position within the mold, since all mold pins can accurately be arranged thereby. 
     The present invention will be more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given by way of illustration only and are not to be considered as limiting the present invention. 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will be apparent to those skilled in the art from this detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view showing the configuration of a first embodiment of the fiber optic connector ferrule in accordance with the present invention; 
     FIG. 2 is an exploded perspective view of a mold used for manufacturing the connector ferrule of FIG. 1; 
     FIGS. 3 and 4 are side and sectional views showing a mold pin used in the mold of FIG. 2, respectively; 
     FIG. 5 is a sectional view showing the state where an optical fiber ribbon is attached to the connector ferrule of FIG. 1; 
     FIG. 6 is a perspective view showing a second embodiment of the connector ferrule in accordance with the present invention; 
     FIGS. 7 and 8 are side and sectional views showing a mold pin used for preparing the connector ferrule of FIG. 6, respectively; 
     FIGS. 9 and 10 are side and sectional views showing another type mold pin; 
     FIg. 11 is a perspective view showing the configuration of a conventional fiber optic connector ferrule; 
     FIG. 12 is a perspective view showing a mold pin used for making the connector ferrule of FIG. 11; and 
     FIGS. 13 and 14 are sectional views showing respective states where an optical fiber ribbon is attached to the conventional fiber optic connector ferrule. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following, preferred embodiments of the present invention will be explained in detail with reference to the accompanying drawings. To facilitate the comprehension of the explanation, the same reference numerals denote the same parts, where possible, throughout the drawings, and a repeated explanation will be omitted. 
     FIG. 1 is a perspective view showing the configuration of a first embodiment of the fiber optic connector ferrule in accordance with the present invention. 
     The basic configuration of this fiber optic connector ferrule  2 A is identical to that of the conventional fiber optic connector ferrule shown in FIG. 11 except that a coating-accommodating portion  22  shaped like a flat groove having a flat floor face is formed further on the fiber insertion side of the fiber-guiding portion  23 . Also, an inlet  26  is formed behind the coating-accommodating portion  22 . 
     FIG. 2 shows a mold used for manufacturing the connector ferrule  2 A. FIGS. 3 and 4 show a detailed configuration of a mold pin  1 A. 
     As shown in FIG. 2, the mold for molding the connector ferrule  2 A comprises an upper mold  4 , a lower mold  5 , and mold pins  1 A and  6  slidably disposed between the upper and lower molds  4 ,  5 . In order for the configuration to be seen easily, only two mold pins  1 A and one of mold pins  6  are shown in FIG.  2 . 
     The inside of the lower mold  5  is shaped so as to match the outer form of the lower half of the connector ferrule  2 A, whereas the outside thereof is provided with V-shaped grooves  52  for holding the mold pins  6  and V-shaped grooves  53  for holding the mold pins  1 A. Further, a resin injection port  51  for injecting a resin into the mold is provided. 
     Though not shown, the inside of the upper mold  4  is shaped so as to match the outer form of the upper half of the connector ferrule  2 A, whereas the outside thereof is provided with rectangular grooves  41  for holding the mold pins  6 , and a rectangular groove  42  for holding the mold pins  1 A. 
     The mold pin  6  has a cylindrical form with a diameter slightly greater than that of the a guide pin, thereby forming the guide pin hole  24 . On the other hand, the mold pins  1 A function to form the fiber-arranging holes  20 , fiber-guiding portions  23 , and coating-accommodating portion  22  in the connector ferrule  2 A. As shown in FIGS. 2 to  4 , each mold pin  1 A is constituted by a front end portion  10 , a tapered portion  11  formed on the proximal end side of the front end portion  10 , and a prismatic portion  12  formed further on the proximal end side of the tapered portion  11 . 
     The front end portion  10  is adapted to form the fiber-arranging hole  20  in the connector ferrule  2 A and has a circular cross section. In view of shrinkage of the resin upon molding and the like, the front end portion  10  has an outside diameter substantially identical to or slightly greater than that of the optical fiber. Specifically, though variable depending on the molding condition and material, the outside diameter of the front end portion  10  is 0.1265 mm when the outside diameter of the optical fiber  30  (see FIG. 5) is 0.125 mm. Also, though variable depending on the dimensions of the connector ferrule  2 A, the length of the front end portion  10  is about 10 mm. 
     The tapered portion  11  is adapted to form the fiber-guiding portion  23  in the connector ferrule  2 A, and is formed between the front end portion  10  and the prismatic portion  12  so as to continuously link them, with its outside diameter gradually expanding. Namely, no step is formed at the boundary between the tapered portion  11  and the front end portion  10  and at the boundary between the tapered portion  11  and the prismatic portion  12 . 
     The prismatic portion  12  is adapted to form the coating-accommodating portion  22  in the connector ferrule  2 A and has a quadrangular cross section. Each side of the quadrangle in the cross section is greater than the diameter of the above-mentioned front end portion  10 . The center axis of the front end portion  10  and that of the prismatic portion  12  align with each other. Though the mold pin  1 A used in this embodiment is provided with the tapered portion  11 , the front end portion  10  would directly project from the end face of the prismatic portion  12  if no tapered portion  11  were formed. 
     Further, upper side face of the prismatic portion  12  is provided with a notch  15 . The width of the quadrangular cross section of the prismatic portion  12  in the arranging direction is identical to the arranging pitch of the optical fibers  30 , and is specifically 0.25 mm. As a consequence, when a plurality of mold pins  1 A are arranged with their prismatic portions  12  being in close contact with each other, the front end portions  10  are arranged with a pitch identical to the arranging pitch of the optical fibers  30 , whereby the optical fibers  30  can be inserted without bending into the fiber-arranging holes  20  formed by the front end portions  10 . 
     On the other hand, the height from the center axis of the prismatic portion  12  to the base in the quadrangular cross section is identical to the distance from the center axis of the optical fiber  30  to the outer surface of the coated portion  31  in an optical fiber ribbon  3 . Namely, when a plurality of mold pins  1 A are arranged, the positional relationship between the front end portion  10  and the prismatic portion  12  corresponds to the positional relationship between the optical fiber  30  and the coated portion  31  in the optical fiber ribbon  3  attached to the connector ferrule  2 A. 
     When a fiber optic connector ferrule without the open portion  21  is to be made, the height from the center axis of the prismatic portion  12  to the upper side in the quadrangular cross section is also made identical to the distance from the center axis of the optical fiber  30  to the outer surface of the coated portion  31  in the optical fiber ribbon  3 . 
     A plurality of the above-mentioned mold pins  1 A are held parallel to each other by the holding members  13  with the prismatic portions  12  being in close contact with each other, and are installed so as to be able to enter into and retract from a space between the molds  4 ,  5 . The holding members  13  have a holding groove  14 . The holding groove  14  is formed along the longitudinal direction of a plurality of the mold pins  1 A to be held, and holds them at predetermined positions therein. Provided within the holding groove  14  is a positioning protrusion  16  perpendicular to the longitudinal direction of the mold pins  1 A to be held. The positioning protrusion  16  engages the notch  15  of the mold pin  1 A being set, thereby positioning a plurality of mold pins  1 A in their longitudinal direction. 
     Also, when the mold pin  1 A is set within the mold, the front end of the mold pin  1 A is positioned as being held between the V-shaped groove  53  of the lower mold  5  and the rectangular groove  42  of the upper mold  4  from the lower and upper sides. On the other hand, the front end of the mold pin  6  is positioned as being held between the V-shaped groove  52  of the lower mold  5  and the rectangular groove  41  of the upper mold  4  from the lower and upper sides. When the mold pins  1 A,  6  are set between the molds  4 ,  5 , the inside of the molds  4 ,  5  is filled with a molten resin through the resin injection port  51 . After the resin is cooled and solidified, the mold pins  1 A,  6  are slid backward so as to be pulled out from the molds  4 ,  5 . Subsequently, the molds  4 ,  5  are vertically opened, and the connector ferrule  2 A is taken out therefrom. 
     When the optical fiber ribbon  3  is to be attached to the connector ferrule  2 A, the optical fibers  30  with the exposed front end are introduced into the connector ferrule  2 A from the inlet  26  side. The optical fibers  30  introduced into the connector ferrule  2 A reach the fiber-guiding portions  23  along the coating-accommodating portion  22 , and then are smoothly guided by the fiber-guiding portions  23  so as to be inserted into their corresponding fiber-arranging holes  20 . Thereafter, a boot is fitted into the inlet  26 , and the optical fiber ribbon  3  is fixed to the connector ferrule  2 A by means of an adhesive or clamp member. 
     When the optical fibers  30  are accommodated within the fiber-arranging holes  20 , then the coated portion  31  of the optical fiber ribbon  3  is accommodated within the coating-accommodating portion  22 . Here, since the geometries of the fiber-arranging holes  20  and coating-accommodating portion  22  are formed so as to correspond to those of the optical fibers  30  and coated portion  31  as shown in FIG. 5, the optical fiber ribbon  3  can be mounted so as to keep the optical fibers  30  in the optical fiber ribbon  3  straight without bending. 
     A second embodiment of the fiber optic connector ferrule in accordance with the present invention will now be explained. FIG. 6 is a perspective view showing the fiber optic connector ferrule  2 B of the second embodiment. 
     In this connector ferrule  2 B, a plurality of parallel guiding projections  25  each having a height of h 1  are formed on the surface of the coating-accommodating portion  22 . Each guiding projection  25  is formed on an extension of an edge of its corresponding fiber-guiding portion  23  along the inserting direction of the optical fiber  30 . Consequently, when the optical fiber ribbon  3  is to be attached to the connector ferrule  2 B, the guiding projection  25  functions as a guide for guiding the optical fiber  30  to the fiber-guiding portion  23 , thus allowing the optical fiber  30  to be inserted into the fiber-arranging hole  20  more smoothly. 
     Here, since the coated portion  31  of the optical fiber ribbon  3  will be lifted up and bend the optical fiber  30  if the height h 1  of the guiding projection  25  is too high, it is necessary for the height h 1  to be such that it can be absorbed by a deformation of the coated portion  31  itself, or such that it generates only a slight amount of bending which does not affect transmission characteristics of the optical fiber  30 . 
     The method of making the connector ferrule  2 B in accordance with the second embodiment differs from the method of making the connector ferrule  2 A in accordance with the first embodiment only in the geometries of mold pins  1 B used. 
     In each mold pin  1 B, as shown in FIGS. 7 and 8, both side edges of a certain face (the face provided with a notch  15  in this embodiment) are provided with their respective chamfered portions  17 B. Each chamfered portion  17 B is formed like a curved face having a predetermined radius of curvature h 1  in its cross section, so as to smoothly continue to the respective side face of the prismatic portion  12 . No chamfered portion  17 B is formed at the part to be gripped by the holding members  13 . 
     The mold pins  1 B are gripped by the holding members  13  such that all the chamfered portions  17 B are arranged in their arranging direction. Here, if the notch  15  is formed, then the positions of the chambered portions  17 B will align with each other as a matter of course. When the connector ferrule  2 B is being made, the chamfered portions  17 B would align on the lower side of the arranged mold pins  1 B. This notch may be formed on lower side face of each mold pin. 
     The chamfered portion  17 B may be formed not only as a curved chamfered portion  17 B such as the one shown in FIGS. 7 and 8, but also as a planar chambered portion  17 C such as the one shown in FIGS. 9 and 10. A mold pin  1 C having such chamfered portions  17 C can similarly form guiding projections. In this case, the height h 2  of the chamfered portion  17 C corresponds to the above-mentioned height (radius of curvature) h 1 . 
     The fiber optic connector ferrule and the method of making the same in accordance with the present invention should not be restricted to the above-mentioned embodiments. For example, though the fiber optic connector ferrule has the open portion  21  in the above-mentioned embodiments, the fiber optic connector ferrule may be free of the open portion  21 . In this case, the coating-accommodating portion  22  is not formed like a groove but a hole. 
     Also, when a chamfered portion is to be provided, it may be formed at one side edge in a face of the mold pin instead of both side edges thereof. Even in this configuration, if one chamfered portion is positioned at the mating faces of two mold pins when the mold pins are held by holding members, then a guiding projection for guiding each optical fiber to its corresponding fiber-arranging hole can be formed. 
     The present invention is not limited to the fiber optic connector ferrule for an optical fiber ribbon. Single optical fiber cables can be also secured to the fiber optic connector ferrule according to the present invention. 
     From the invention thus described, it will be obvious that the invention may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended for inclusion within the scope of the following claims.