Patent Publication Number: US-2019179087-A1

Title: Optical connector ferrule and optical connector

Description:
TECHNICAL FIELD 
     An aspect of the present invention relates to an optical connector ferrule and an optical connector. 
     This application claims the benefit of priority based on Japanese Patent Application No. 2016-205062 filed on Oct. 19, 2016, and the entire disclosure of the Japanese Patent Application is incorporated herein by reference. 
     BACKGROUND ART 
     Patent Literature 1 describes a technique regarding a method for producing an optical fiber with a ferrule. The ferrule used in this production method has an insertion opening into which an optical fiber ribbon is inserted, a plurality of optical fiber holes, and an adhesive filling window for filling the plurality of optical fiber holes with an adhesive to fix optical fibers of the optical fiber ribbon to the plurality of optical fiber holes. In this production method, when the optical fiber ribbon is seen from the adhesive filling window, the optical fiber ribbon is inserted from the insertion opening so that a covering peeled edge of the optical fiber ribbon is located in a predetermined position. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Unexamined Patent Publication No. 2011-107633 
     SUMMARY OF INVENTION 
     An optical connector ferrule according to an embodiment has a pair of end faces aligned in a first direction, a plurality of fiber holding holes extending in the first direction between the pair of end faces, and aligned in a second direction intersecting the first direction to hold a plurality of optical fibers individually, and a fiber introduction space having an opening at one end face, communicating with the plurality of fiber holding holes, and receiving the plurality of optical fibers collectively. An inner surface defining the fiber introduction space includes a fiber supporting surface having a plurality of guide grooves formed in such a way as to extend individually from ends of the plurality of fiber holding holes towards the one end face and a pair of first inner lateral surfaces extending individually from both ends of the fiber supporting surface in the second direction. A space between the pair of first inner lateral surfaces expands gradually as further away from the fiber supporting surface. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates a sectional view of an optical connector according to an embodiment, the sectional view illustrating a side section taken along a connecting direction. 
         FIG. 2  is a plan view illustrating a distal end portion of an optical fiber ribbon. 
         FIG. 3  is a sectional view taken along a line Ill-Ill in  FIG. 2 . 
         FIG. 4  is a sectional view illustrating a side section taken along a connecting connection of the optical connector ferrule. 
         FIG. 5  illustrates a sectional view taken along a line V-V in  FIG. 4 , the sectional view illustrating a section taken along an XY plane. 
         FIG. 6  illustrates a sectional view taken along a line VI-VI in  FIG. 4 , the sectional view illustrating a section taken along an XZ plane. 
         FIG. 7A  is a drawing schematically illustrating how a plurality of optical fibers are mounted in an optical connector ferrule as a comparison example, the drawing being a plan view of the plurality of optical fibers and a fiber supporting surface. 
         FIG. 7B  is a drawing schematically illustrating how the plurality of optical fibers are mounted in the optical connector ferrule as the comparison example, the drawing being a sectional view of the plurality of optical fibers and the fiber supporting surface. 
         FIG. 8A  is a drawing schematically illustrating how the plurality of optical fibers are mounted in the optical connector ferrule as the comparison example, the drawing being the plan view of the plurality of optical fibers and the fiber supporting surface. 
         FIG. 8B  is a drawing schematically illustrating how the plurality of optical fibers are mounted in the optical connector ferrule as the comparison example, the drawing being a sectional view of the plurality of optical fibers and the fiber supporting surface. 
         FIG. 9A  is a drawing schematically illustrating how a plurality of optical fibers are mounted in an optical connector ferrule of the embodiment, the drawing being a plan view of the plurality of optical fibers and the fiber supporting surface. 
         FIG. 9B  is a drawing schematically illustrating how the plurality of optical fibers are mounted in the optical connector ferrule of the embodiment, the drawing being a sectional view of the plurality of optical fibers and the fiber supporting surface. 
         FIG. 10  is a sectional view showing a first modified example, the sectional view illustrating a section taken along an XY plane of a fiber introduction space. 
         FIG. 11  is a sectional view showing a second modified example, the sectional view illustrating a section taken along an XY plane of a fiber introduction space. 
         FIG. 12  is a sectional view showing a third modified example, the sectional view illustrating a section taken along an XZ plane of a fiber introduction space. 
         FIG. 13  is a sectional view showing a fourth modified example, the sectional view illustrating a section taken along an YZ plane of a fiber introduction space. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Technical Problem 
     When producing an optical connector including a multiple-core optical connector ferrule such as an MT ferrule, firstly, a covering of a distal end portion of an optical fiber ribbon is removed, and a plurality of optical fibers are separated. Next, the plurality of optical fibers are inserted from an opening at a rear end of the ferrule while maintaining the state where the plurality of optical fibers separated from one another are aligned into the row. Then, the plurality of optical fibers are caused to move forwards gradually while the plurality of optical fibers are caused to follow individually a plurality of guide grooves formed in an interior of the multiple-core optical connector ferrule. By doing so, the plurality of optical fibers are inserted into a plurality of fiber holding holes each communicating with each of the plurality of guide grooves. Thereafter, the optical fiber ribbon and the plurality of optical fibers which are separated from one another are fixed to the multiple-core optical connector ferrule with an adhesive. 
     In the optical connector production process described above, it is necessary to cause the individual optical fibers to follow the corresponding guide grooves in an ensured manner. This is because when the positions of the individual optical fibers deviate from the guide grooves, distal ends of the optical fibers come to collide with a portion other than the fiber holding holes when the optical fibers are caused to move forwards, leading to fears that the optical fibers are damaged. However, a diameter of each optical fiber is extremely thin, such as 125 μm, and an inter-center interval (pitch) between the optical fibers is also extremely narrow. Thus, it is not easy to cause each optical fiber to follow the corresponding guide groove in an ensured manner visually by the operator, resulting in a problem in that skill is required to perform this operation properly. 
     This disclosure has been made in view of this problem, and an object thereof is to provide an optical connector ferrule and an optical connector which can enable each optical fiber to follow its corresponding guide groove easily. 
     Advantageous Effect of the Disclosure 
     According to the optical connector ferrule and the optical connector of this disclosure, each optical fiber is allowed to follow easily its corresponding guide groove. 
     Description of Embodiment 
     Firstly, the contents of an embodiment of this disclosure will be described. An optical connector ferrule according to an embodiment has a pair of end faces aligned in a first direction, a plurality of fiber holding holes extending in the first direction between the pair of end faces, and aligned in a second direction intersecting the first direction to hold a plurality of optical fibers individually, and a fiber introduction space having an opening at one end face, communicating with the plurality of fiber holding holes, and receiving the plurality of optical fibers collectively. An inner surface defining the fiber introduction space includes a fiber supporting surface having a plurality of guide grooves formed in such a way as to extend individually from ends of the plurality of fiber holding holes towards the one end face and a pair of first inner lateral surfaces extending individually from both ends of the fiber supporting surface in the second direction. A space between the pair of first inner lateral surfaces expands gradually as further away from the fiber supporting surface. 
     In this optical connector ferrule, the pair of first inner lateral surfaces that extend individually from both the ends of the surface (the fiber supporting surface) on which the plurality of guide grooves are formed are included in the inner surface that defines the fiber introduction space. Then, the space between the pair of first inner lateral surfaces expands gradually as further away from the fiber supporting surface. By adopting this configuration, when the plurality of optical fibers that are aligned in the second direction are moved towards the plurality of guide grooves from a position that faces the fiber supporting surface, the optical fibers that are positioned at both the lateral ends of the aligned optical fibers are guided by the pair of first inner lateral surfaces. As a result, the individual optical fibers can move on to their corresponding guide grooves with good positional accuracy. Thus, according to this optical connector ferrule, the individual optical fibers can be caused to follow their corresponding guide grooves easily. 
     In the optical connector ferrule described above, the pair of first inner lateral surfaces may be flat, and a normal of each of the pair of first inner lateral surfaces may be inclined relative to the second direction. This enables the pair of first inner lateral surfaces to be formed easily. 
     In the optical connector ferrule described above, in a section normal to the first direction, the pair of first inner lateral surfaces are curved. This can deflect a force applied to the optical fibers when the optical fibers come into contact with the pair of first inner lateral surfaces, and therefore, the damage to the optical fibers can be suppressed further. 
     In the optical connector ferrule described above, the inner surface defining the fiber introduction space may include further a pair of second inner lateral surfaces extending individually from ends of the pair of first inner lateral surfaces in the first direction towards the opening, and a space between the pair of second inner lateral surfaces may expand gradually as further away from the pair of first inner lateral surfaces. By adopting this configuration, when the plurality of optical fibers are caused to move towards the plurality of guide grooves along the first direction from the opening side, the optical fibers located at both the lateral ends are guided by the pair of second inner lateral surfaces. As a result, the individual optical fibers can move on to their corresponding guide grooves with good positional accuracy. Thus, according to this optical connector ferrule, the individual optical fibers can be caused to follow their corresponding guide grooves easily. 
     In the optical connector ferrule described above, the pair of second inner lateral surfaces are flat, and a normal of each of the pair of second inner lateral surfaces is inclined relative to the second direction. 
     This enables the pair of second inner lateral surfaces to be formed easily. 
     In the optical connector ferrule described above, in a section including the first direction and the second direction, the pair of second inner lateral surfaces may curved convexly towards the fiber introduction space. This can make boundary portions between the pair of first inner lateral surfaces and the pair of second inner lateral surfaces smoother, and therefore, the damage to the optical fibers can be suppressed further. 
     In the optical connector ferrule described above, the inner surface defining the fiber introduction space may include further a bottom surface extending from an end of the fiber supporting surface in the first direction towards the opening, and the bottom surface may extend away from an imaginary plane including the fiber supporting surface as further away from the fiber supporting surface. By adopting this configuration, when the plurality of optical fibers are caused to move from the opening side towards the plurality of guide grooves along the first direction, even though the position of the plurality of optical fibers is lower than the fiber supporting surface, the plurality of optical fibers are guided on to the fiber supporting surface by the bottom surface. Consequently, according to this optical connector ferrule, the individual optical fibers can be caused to follow their corresponding guide grooves easily. 
     In the optical connector ferrule described above, the bottom surface may be flat and be inclined relative to the first direction. This enables the bottom surface to be formed easily. 
     In the optical connector ferrule described above, in a section normal to the second direction, the bottom surface may be curved convexly towards the fiber introduction space. This can make a boundary portion between the fiber supporting surface and the bottom surface smoother, and therefore, the damage to the optical fibers can be suppressed further. 
     An optical connector according to the embodiment comprises the optical connector ferrule according to any one of the above aspects, and the plurality of optical fibers introduced into the fiber instruction space collectively from the opening and held individually in the plurality of fiber holding holes. According to this optical connector, by comprising any one of the optical connector ferrules, the individual optical fibers can be caused to follow their corresponding guide grooves easily. This can provide the optical connector in which the damage to the optical fibers is reduced and which has a high reliability. 
     Details of the Embodiment 
     A specific example of the optical connector ferrule and the optical connector according to the embodiment of this disclosure will be described as below by reference to drawings. The present invention is not limited to these specific examples and is intended to include all modifications that are defined by the scope of claims, have equivalent meanings to the scope of the claims and fall in the scope of the claims. In the following description, like reference numerals are given to like elements so as to omit the repetition of similar descriptions in descriptions made by reference to the drawings. 
       FIG. 1  is a sectional view of an optical connector  1 A according to an embodiment, the sectional view illustrating a side section taken along a connecting direction. For easy understanding, an XYZ orthogonal coordinate system is illustrated in  FIG. 1 , and a Z direction coincides with the connecting direction. In this embodiment, the Z direction is an example of a first direction, and an X direction is an example of a second direction. The optical connector  1 A of this embodiment is, for example, an MPO connector. As illustrated in  FIG. 1 , this optical connector  1 A includes an optical fiber ribbon  30 , and an optical connector ferrule  10  that is attached to a distal end portion of the optical fiber ribbon  30 . 
       FIG. 2  is a plan view illustrating the distal end portion of the optical fiber ribbon  30 .  FIG. 3  is a sectional view taken along a line in  FIG. 2 . As shown in  FIG. 3 , the optical fiber ribbon  30  is formed by fixing a plurality of (for example,  12 ) optical fibers  31  that are aligned into the row along the X direction to one another. Each optical fiber  31  has a glass portion  32  having a circular cross section and a first resin covering  33  configured to cover a circumference of the glass portion  32 . Then, these optical fibers  31  are covered collectively by a second resin covering  34 , whereby the optical fiber ribbon  30  is made up. A diameter of the glass portion  32  is, for example, 125 μm, an outside diameter of the first resin covering  33  is, for example, 250 μm. An inter-center interval between the optical fibers  31  is, for example, 250 μm. 
     As illustrated in  FIG. 2 , a plurality of bare fibers  36  are separated from one another at the distal end portion of the optical fiber ribbon  30 . Specifically, the second resin covering  34  and the first resin coverings  33  illustrated in  FIG. 3  are removed, and the individual optical fibers consist of the bare fibers  36  made up only of the glass portions  32  and are independent of one another. The bare fibers  36  are arranged in such a way as to be aligned in the X direction and extend in the Z direction which constitutes a longitudinal direction (an optical axis direction) of the bare fibers  36 . 
       FIG. 4  is a sectional view illustrating a side section taken along the connecting direction of the optical connector ferrule  10  (a section taken along a YZ plane).  FIG. 5  is a sectional view taken along a line V-V in  FIG. 4 , illustrating a section taken along an XY plane.  FIG. 6  is a sectional view taken along a line VI-VI in  FIG. 4 , illustrating a section taken along an XZ plane. 
     The optical connector ferrule  10  of this embodiment is, for example, an MT ferrule. The optical connector ferrule  10  has an external appearance of a substantially rectangular parallelepiped shape and has a pair of end faces of a front end face  10   a  and a rear end face  10   b  that are aligned (face each other) in the Z direction, a pair of lateral surfaces  10   c,    10   d  that are aligned (face each other) in the X direction, and an upper surface  10   e  and a lower surface  10   f  that are aligned (face each other) in the Y direction. The optical connector ferrule  10  is made of a resin (for example, a PPS resin) and is formed through molding or injection molding. 
     The optical connector ferrule  10  has a plurality of fiber holding holes  12 . The plurality of fiber holding holes  12  are formed between the front end face  10   a  and the rear end face  10   b  in an area lying closer to the front end face  10   a.  The plurality of fiber holding holes  12  are formed in such a manner that the fiber holding holes  12  extend in the Z direction and are aligned in the X direction. A shape of a section of each fiber holding hole  12  that is normal to the Z direction is circular. The individual optical fibers (the bare fibers  36  in this embodiment) are inserted into their corresponding fiber holding holes  12 , and the individual fiber holding holes  12  hold their corresponding optical fibers (the bare fibers  36 ). In this embodiment, one end of the individual fiber holding holes  12  is opened to the front end face  10   a.  The fiber holding holes  12  each have a front portion  12   a  configured to hold the bare fiber  36  and a rear portion  12   b  configured to facilitate the insertion of the bare fiber  36 . An inside diameter of the front portion  12   a  is smaller than an inside diameter of the rear portion  12   b  and is slightly greater than a diameter of the bare fiber  36  (that is, a diameter of the glass portion  32 ). The inside diameter of the rear portion  12   b  is in a range of 180 μm to 250 μm and is preferably 190 μm. Then, an adhesive is caused to flow into a gap between the fiber holding hole  12  and the bare fiber  36 , whereby the bare fiber  36  is fixed to the fiber holding hole  12 . 
     The optical connector ferrule  10  has a fiber introduction space  20 . The fiber introduction space  20  has an opening  14  in the rear end face  10   b  and extends forwards from the rear end face  10   b  along the Z direction. Then, a front end of the fiber introduction space  20  connects to the rear portions  12   b  of the plurality of fiber holding holes  12 . As illustrated in  FIG. 1 , the plurality of optical fibers (the bare fibers  36  in this embodiment) are introduced collectively into the fiber introduction space  20  from the opening  14 , and the fiber introduction space  20  receives these optical fibers collectively. A rectangular adhesive introduction window  15  is formed in the upper surface  10   e  of the optical connector ferrule  10 , and a front portion of the fiber introduction space  20  connects to the adhesive introduction window  15 . 
     Here, the fiber introduction space  20  will be described in detail. An inner surface of the optical connector ferrule  10  that defines the fiber introduction space  20  of this embodiment includes, as illustrated in  FIG. 5 , a fiber supporting surface  21 , and a pair of first inner lateral surfaces  22   a,    22   b.  The fiber supporting surface  21  is a surface extending from the front end of the fiber introduction space  20  towards the rear end face  10   b.  The fiber supporting surface  21  is located on a rear side of the lower surface  10   f  and follows the XZ plane. A position of the fiber supporting surface  21  in the Y direction is substantially equal to a position of the plurality of fiber holding holes  12  in the Y direction. A plurality of guide grooves  21   a  are formed on the fiber supporting surface  21 . The individual guide grooves  21   a  extend from ends of the individual fiber holding holes  12  towards the rear end face  10   b  along the Z direction. A section of each guide groove  21   a  that is normal to its longitudinal direction (the Z direction) is, for example, semi-circular. A radius of the semi-circle is, for example, equal to a radius of the rear portion  12   b  of the fiber holding hole  12 . The plurality of guide grooves  21   a  are formed in such a manner as to be aligned parallel to one another in the X direction. 
     One first inner lateral surface  22   a  is located on a rear side of one lateral surface  10   c  and extends from one end of the fiber supporting surface  21  in the X direction to an inner lateral surface  15   a  of the adhesive introduction window  15  in a direction that intersects the X direction. The other first inner lateral surface  22   b  is located on a rear side of the other lateral surface  10   d  and extends from the other end of the fiber supporting surface  21  in the X direction to an inner lateral surface  15   b  of the adhesive introduction window  15  in the direction that intersects the X direction. Edges of sides (sides at the upper surface  10   e ) of the first inner lateral surfaces  22   a,    22   b  which is situated opposite sides at the fiber supporting surface  21  may reach the upper surface  10   e  or may be located between the fiber supporting surface  21  and the inner lateral surfaces  15   a,    15   b  of the adhesive introduction window  15 . 
     A space between the first inner lateral surfaces  22   a,    22   b  gradually expands as further away from the fiber supporting surface  21 . In this embodiment, the first inner lateral surfaces  22   a,    22   b  are both flat, and respective normal vectors V 11 , V 12  of the first inner lateral surfaces  22   a,    22   b  are inclined towards the adhesive introduction window  15  relative to an axis Al extending in the X direction. In other words, the first inner lateral surfaces  22   a,    22   b  are both inclined outwards of the fiber introduction space  20  relative to a YZ plane from ends of the fiber supporting surface  21  as starting points. In one example, the first inner lateral surfaces  22   a,    22   b  are parallel to an axis (a center axis of the optical connector ferrule  10 ) that extends in the Z direction. 
     As illustrated in  FIG. 6 , the inner surface of the optical connector ferrule  10  that defines the fiber introduction space  20  of this embodiment further includes a pair of second inner lateral surfaces  23   a,    23   b.  One second inner lateral surface  23   a  is located on a rear side of one lateral surface  10   c  and extends from an end of the first inner lateral surface  22   a  in the Z direction towards the opening  14  of the fiber introduction space  20 . The other second inner lateral surface  23   b  is located on a rear side of the other lateral surface  10   d  and extends from an end of the other first inner lateral surface  22   b  in the Z direction towards the opening  14  of the fiber introduction space  20 . Rear end edges of the second inner lateral surfaces  23   a,    23   b  may reach the opening  14  or may be located between the first inner lateral surfaces  22   a,    22   b  and the opening  14 . 
     A space between the second inner lateral surfaces  23   a,    23   b  expands gradually as further away from the first inner lateral surfaces  22   a,    22   b,  respectively. In this embodiment, the second inner lateral surfaces  23   a,    23   b  are both flat, and respective normal vectors V 21 , V 22  of the second inner lateral surfaces  23   a,    23   b  are inclined towards the opening  14  relative to an axis A 2  extending in the X direction. In other words, the second inner lateral surfaces  23   a,    23   b  are both inclined outwards of the fiber introduction space  20  relative to the YZ plane from ends of the first inner lateral surfaces  22   a,    22   b  that faces the rear end face  10   b  as starting points. 
     As illustrated in  FIG. 4 , the inner surface of the optical connector ferrule  10  that defines the fiber introduction space  20  of the embodiment further includes a bottom surface  24 . The bottom surface  24  is located on a rear side of the lower surface  10   f  and extends from an end of the fiber supporting surface  21  in the Z direction towards the opening  14  of the fiber introduction space  20 . A rear end edge of the bottom surface  24  may reach the opening  14  or may be located between the fiber supporting surface  21  and the opening  14 . The bottom surface  24  is formed in such a manner as to gradually extend away from an imaginary plane P 1  including the fiber supporting surface  21  as further away from the fiber supporting surface  21 . In this embodiment, the bottom surface  24  is flat, and a normal vector V 3  of the bottom surface  24  is inclined towards the opening  14  relative to an axis A 3  extending in the Y direction. In other words, the bottom surface  24  is inclined outwards of the fiber introduction space  20  relative to the XZ plane from an end of the fiber supporting surface  21  which faces the opening  14  as a starting point. In one example, the bottom surface  24  is parallel to an axis extending in the X direction. 
     Advantageous effects will be described which are obtained by the optical connector IA and the optical connector ferrule  10  according to this embodiment which have been described heretofore.  FIGS. 7A, 7B, 8A, and 8B  are drawings illustrating schematically how a plurality of bare fibers  36  are attached to an optical connector ferrule as a comparison example.  FIGS. 9A and 9B  are drawings illustrating schematically how the plurality of bare fibers  36  are attached to the optical connector ferrule  10  of the embodiment.  FIGS. 7A, 8A and 9A  are plan views of the plurality of bare fibers  36  and the fiber supporting surface  21 .  FIGS. 7B, 8B and 9B  are sectional views of the plurality of bare fibers  36  and the fiber supporting surface  21 . 
     Normally, when a plurality of optical fibers are attached to an optical connector ferrule, a plurality of bare fibers  36  are moved on to a fiber supporting surface  21 , and the plurality of bare fibers  36  are disposed individually in a plurality of guide grooves  21   a.  Then, the plurality of bare fibers  36  are pushed out forwards in the Z direction while keeping the bare fibers  36  staying in the corresponding guide grooves  21   a,  whereby the plurality of bare fibers  36  are inserted individually into a plurality of fiber holding holes  12 . Here, as shown in  FIGS. 7A and 7B , when the positions of the plurality of bare fibers  36  deviate from the guide grooves  21   a  when the plurality of bare fibers  36  are moved on to the fiber supporting surface  21 , as shown in  FIGS. 8A and 8B , distal ends of the bare fibers  36  come to collide against portions other than the fiber holding holes  12  when the bare fibers  36  are caused to advance, leading to fears that the bare fibers  36  are damaged. Specifically, when the bare fibers  36  are pushed in excessively with the distal ends of the bare fibers  36  having come to collide against the portions other than the fiber holding holes  12 , the bare fibers  36  are disconnected, requiring a distal end portion of an optical fiber ribbon  30  to be worked again. Alternatively, advancing the bare fibers  36  again and again repeatedly damages surfaces of the bare fibers  36  due to the contact with the guide grooves  21   a,  leading to a possibility of disconnection of the optical fibers, and this changes the optical propagation properties of the optical fibers. However, the bare fibers  36  are extremely thin, and the inter-center interval (pitch) between the bare fibers  36  is also extremely narrow. Consequently, it is not easy to cause the individual bare fibers  36  to follow the corresponding guide grooves  21   a  in an ensured manner visually by the operator, leading to a problem in that skill is required. 
     To cope with the problem described above, with the optical connector ferrule  10  of this embodiment, as illustrated in  FIGS. 9A and 9B , when the plurality of bare fibers  36  are caused to move towards the plurality of guide grooves  21   a  from the position facing the fiber supporting surface  21 , the bare fibers  36  located at both the ends of the plurality of bare fibers  36  are guided by the pair of first inner lateral surfaces  22   a,    22   b.  As a result, the individual bare fibers  36  can move on to the corresponding guide grooves  21   a  with good positional accuracy. Consequently, according to the optical connector ferrule  10 , since the individual bare fibers  36  can easily be caused to follow the corresponding guide grooves  21   a,  a risk of the distal ends of the bare fibers  36  being brought into collision against portions other than the fiber holding holes  12  can be reduced. This can not only reduce a risk of disconnection of the bare fibers  36  to suppress an increase in production cost but also reduce the damage made to surfaces of the bare fibers  36 , and therefore, it is possible to provide the highly reliable optical connector  1 A. 
     As in this embodiment, the space between the pair of second inner lateral surfaces  23   a,    23   b  may gradually expand as further away from the pair of first inner lateral surfaces  22   a,    22   b,  respectively. By adopting this configuration, when the plurality of bare fibers  36  are caused to move towards the plurality of guide grooves  21   a  from the opening  14  side along the Z direction, the bare fibers  36  located at both the ends of the plurality of bare fibers  36  are guided by the second inner lateral surfaces  23   a,    23   b.  As a result, the individual bare fibers  36  can move onto the corresponding guide grooves  21   a  with good positional accuracy, and therefore, the individual bare fibers  36  can easily be caused to follow the corresponding guide grooves  21   a.    
     As in this embodiment, the bottom surface  24  may gradually extend away from the imaginary plane P 1  including the fiber supporting surface  21  as further away from the fiber supporting surface  21 . By adopting this configuration, when the plurality of bare fibers  36  are caused to move towards the plurality of guide grooves  21   a  from the opening  14  side along the Z direction, even though the positions of the plurality of bare fibers  36  are lower than the fiber supporting surface  21 , the plurality of bare fibers  36  are guided up to the fiber supporting surface  21  by the bottom surface  24 . Consequently, the individual bare fibers  36  can easily be caused to follow the corresponding guide grooves  21   a.    
     As in this embodiment, the first inner lateral surfaces  22   a,    22   b,  the second inner lateral surfaces  23   a,    23   b,  and the bottom surface  24  may be flat. By adopting this configuration, the shape of a mold for molding the optical connector ferrule  10  is simplified, whereby the first inner lateral surfaces  22   a,    22   b,  the second inner lateral surfaces  23   a,    23   b  and the bottom surface  24  can be formed easily. At least one of the first inner lateral surfaces  22   a,    22   b,  the second inner lateral surfaces  23   a,    23   b  and the bottom surface  24  may be a smooth surface that is not flat (for example, a curved surface). Even in such a case, the advantageous effects of the embodiment can be provided. 
     FIRST MODIFIED EXAMPLE 
       FIG. 10  is a sectional view illustrating a first modified example, the sectional view illustrating a section taken along an XY plane of an optical connector ferrule  10 A (a section corresponding to  FIG. 5  of the embodiment). The optical connector ferrule  10 A of this modified example has a fiber introduction space  20 A. An inner surface of the fiber introduction space  20 A includes first inner lateral surfaces  22   c,    22   d  in place of the first inner lateral surfaces  22   a,    22   b  of the embodiment. In the section, the first inner lateral surfaces  22   c,    22   d  are shaped so that a space between the first inner lateral surfaces  22   c,    22   d  gradually expand as further away from a fiber supporting surface  21  and are shaped into a convexly curved surface towards an inside of the fiber introduction space  20 A. By adopting this configuration, the individual bare fibers  36  can more easily be caused to follow corresponding guide grooves  21   a,  and a force applied to the bare fibers  36  when the bare fibers  36  come into contact with the first inner lateral surfaces  22   c,    22   d  can be deflected. Thus, the damage to the bare fibers  36  can be suppressed further, and hence, the reliability of the optical connector can be enhanced further. The other configurations of the fiber introduction space  20 A excluding the first inner lateral surfaces  22   c,    22   d  remain the same as those of the fiber introduction space  20  of the embodiment. 
     SECOND MODIFIED EXAMPLE 
       FIG. 11  is a sectional view illustrating a second modified example, illustrating a section taken along an XY plane of an optical connector ferrule  10 B (a section corresponding to  FIG. 5  of the embodiment). The optical connector ferrule  10 B of this modified example has a fiber introduction space  20 B. An inner surface of the fiber introduction space  20 B includes first inner lateral surfaces  22   e,    22   f  in place of the first inner lateral surfaces  22   a,    22   b  of the embodiment. In the section, the first inner lateral surfaces  22   e,    22   f  are shaped so that a space between the first inner lateral surfaces  22   e,    22   f  gradually expand as further away from a fiber supporting surface  21  and are shaped into a convexly curved surface towards an outside of the fiber introduction space  20 B. Even with this form, a force applied to the bare fibers  36  when the bare fibers  36  come into contact with the first inner lateral surfaces  22   e,    22   f  can be deflected, and therefore, the damage to the bare fibers  36  can be suppressed further, thereby making it possible to enhance further the reliability of the optical connector. The other configurations of the fiber introduction space  20 B excluding the first inner lateral surfaces  22   e,    22   f  remain the same as those of the fiber introduction space  20  of the embodiment. 
     THIRD MODIFIED EXAMPLE 
       FIG. 12  is a sectional view illustrating a third modified example, the sectional view illustrating a section taken along an XZ plane of an optical connector ferrule  10 C (a section corresponding to  FIG. 6  of the embodiment). The optical connector ferrule  10 C of this modified example has a fiber introduction space  20 C. An inner surface of the fiber introduction space  20 C includes second inner lateral surfaces  23   c,    23   d  in place of the second inner lateral surfaces  23   a,    23   b  of the embodiment. In the section, the second inner lateral surfaces  23   c,    23   d  are shaped so that a space between the second inner lateral surfaces  23   c,    23   d  gradually expand as further away from first inner lateral surfaces  22   a,    22   b  and are shaped into a convexly curved surface towards an inside of the fiber introduction space  20 C. By adopting this configuration, the individual bare fibers  36  can more easily be caused to follow corresponding guide grooves  21   a,  and boundary portions between the first inner lateral surfaces  22   a,    22   b  and the second inner lateral surfaces  23   c,    23   d  can be made smoother. Consequently, the damage to the bare fibers  36  can be suppressed further, thereby making it possible to enhance further the reliability of the optical connector. 
     FOURTH MODIFIED EXAMPLE 
       FIG. 13  is a sectional view illustrating a fourth modified example, the sectional view illustrating a section taken along a YZ plane of an optical connector ferrule  10 D (a section corresponding to  FIG. 4  of the embodiment). The optical connector ferrule  10 D of this modified example has a fiber introduction space  20 D. An inner surface of the fiber introduction space  20 D includes a bottom surface  24   a  in place of the bottom surface  24  of the embodiment. In the section, the bottom surface  24   a  is shaped so that the bottom surface  24   a  gradually extends away from an imaginary plane P 1  including a fiber supporting surface  21  as further away from the fiber supporting surface  21  and is shaped into a convexly curved surface towards an inside of the fiber introduction space  20 D. By adopting this configuration, the individual bare fibers  36  can more easily be caused to follow corresponding guide grooves  21   a,  and a boundary portion between the fiber supporting surface  21  and the bottom surface  24   a  can be made smoother. Consequently, the damage to the bare fibers  36  can be suppressed further, thereby making it possible to enhance further the reliability of the optical connector. 
     The optical connector ferrule and the optical connector according to the invention are not limited to the embodiment and the modified examples, and other modifications can be made thereto. For example, the embodiment and the individual modified examples may be combined together as required according to required objects and advantageous effects. In the embodiment and the modified examples, the first inner lateral surfaces, the second inner lateral surfaces and the bottom surface are described as being flat and being formed into the curved surface. However, in the present invention, the first inner lateral surfaces, the second inner lateral surfaces and the bottom surface may be formed into other smooth surfaces. 
     In the embodiment, the plurality of optical fibers are described as being aligned into the row. However, the present invention can also be applied to an optical connector and an optical connector ferrule (for example, a 24-core ferrule, a 48-core ferrule) in which optical fibers are aligned into a plurality of rows (in multiple stages). In the embodiment, the front end face and the rear end face, which face each other, are described as being parallel. However, the present invention can also be applied to an optical connector and an optical connector ferrule in which a front end face and a rear end face are not parallel. 
     REFERENCE SIGNS LIST 
       1 A: optical connector;  10 ,  10 A to  10 D: optical connector ferrule;  10   a:  front end face;  10   b:  rear end face;  10   c,    10   d:  lateral surface;  10   e:  upper surface;  10   f:  lower surface;  12 : fiber holding hole;  12   a:  front portion;  12   b:  rear portion;  14 : opening;  15 : adhesive introduction window;  15   a,    15   b:  inner lateral surface;  20 ,  20 A to  20 D: fiber introduction space;  21 : fiber supporting surface;  21   a:  guide groove;  22   a  to  22   f:  first inner lateral surface;  23   a  to  23   d:  second inner lateral surface;  24 ,  24   a:  bottom surface;  30 : optical fiber ribbon;  31 : optical fiber;  32 : glass portion;  33 : first resin covering;  34  second resin covering;  36 : bare fiber; P 1 : imaginary plane; V 11 , V 12 , V 21 , V 22 , V 3 : normal vector.