Patent Publication Number: US-2019196117-A1

Title: Optical connector ferrule and optical connector

Description:
TECHNICAL FIELD 
     The present invention relates to an optical connector ferrule and an optical connector. This application claims the benefit of priority of Japanese Patent Application No. 2016-185400, filed on Sep. 23, 2016, the content of which is incorporated herein by reference in its entirety. 
     BACKGROUND ART 
     Patent Literature 1 discloses a manufacturing method of optical fibers with an optical connector ferrule. In the manufacturing method of optical fibers with an optical connector ferrule, a plurality of optical fiber ribbons, from each of which a coating is removed, are inserted into the optical connector ferrule. The optical connector ferrule is provided with a window to be filled with an adhesive. By adjusting a shape and a position of the window, there is shown, in the window, a reference range in which a removal edge of the optical fiber ribbon is to be disposed. An operator can see a position of the removal edge of the optical fiber ribbon from the window. The operator performs insertion operation of the optical fiber ribbon while confirming that the position of the removal edge of the optical fiber ribbon is within the reference range. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Unexamined Patent Publication No. 2011-107633 
     SUMMARY OF INVENTION 
     The optical connector ferrule of this disclosure comprises: a first end and a second end provided to face each other in a first direction; an outer surface extending in the first direction between the first end and the second end; an opening provided in the second end; an introducing hole which extends from the opening toward the first end, and into which a plurality of optical fibers can be inserted as a bundle; a plurality of optical fiber holes which pass through from a tip portion of the introducing hole closer to the first end in the first direction to the first end, and into which the plurality of optical fibers are respectively inserted; and a window which opens to the outer surface and is connected to the introducing hole, and into which an adhesive is injected. A first opening of the window closer to the outer surface is larger than a second opening of the window closer to the introducing hole. An inner wall of the window includes a first surface provided in the peripheral direction of the inner wall, and the first surface is positioned closer to the introducing hole with respect to the outer surface in a second direction orthogonal to the outer surface, and faces toward the outer surface. 
     An optical connector of this disclosure comprises the above-described optical connector ferrule and the plurality of optical fibers inserted from the opening into the introducing hole and the plurality of optical fiber holes and fixed to the introducing hole and the plurality of optical fiber holes by the adhesive injected from the window. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a top view of an optical connector ferrule according to an embodiment. 
         FIG. 2  is a cross-sectional view of the optical connector ferrule shown in  FIG. 1  along the II-II line. 
         FIG. 3A  is a top view enlarging and showing a window of the optical connector ferrule shown in  FIG. 1 . 
         FIG. 3B  is a cross-sectional view of the window of the optical connector ferrule shown in  FIG. 3A  along the line. 
         FIG. 4  is a side cross-sectional view showing a configuration of an optical connector according to an embodiment. 
         FIG. 5A  is a top view enlarging and showing a window of the optical connector ferrule according to an embodiment when an adhesive is injected into the ferrule. 
         FIG. 5B  is a cross-sectional view of the window of the ferrule shown in  FIG. 5A  along the V-V line. 
         FIG. 6A  is a top view enlarging and showing a window of an optical connector ferrule according to a first modified example. 
         FIG. 6B  is a cross-sectional view of the window of the optical connector ferrule shown in  FIG. 6A  along the VI-VI line. 
         FIG. 7A  is a top view enlarging and showing a window of an optical connector ferrule according to a second modified example. 
         FIG. 7B  is a cross-sectional view of the window of the optical connector ferrule shown in  FIG. 7A  along the VII-VII line. 
         FIG. 8A  is a top view enlarging and showing a window of an optical connector ferrule according to a third modified example. 
         FIG. 8B  is a cross-sectional view of the window of the optical connector ferrule shown in  FIG. 8A  along the VIII-VIII line. 
         FIG. 9A  is a top view enlarging and showing a window of an optical connector ferrule according to a fourth modified example. 
         FIG. 9B  is a cross-sectional view of the window of the optical connector ferrule shown in  FIG. 9A  along the IX-IX line. 
         FIG. 10A  shows an example of a shape of a window of an optical connector ferrule according to an embodiment. 
         FIG. 10B  shows an example of a shape of a window of an optical connector ferrule according to an embodiment. 
         FIG. 10C  shows an example of a shape of a window of an optical connector ferrule according to an embodiment. 
         FIG. 10D  shows an example of a shape of a window of an optical connector ferrule according to an embodiment. 
         FIG. 11A  is a top view enlarging and showing a window of a conventional optical connector ferrule when an adhesive is injected into the optical connector ferrule. 
         FIG. 11B  is a cross-sectional view of the window of the optical connector ferrule shown in  FIG. 11A  along the XI-XI line. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Technical Problem Solved by Disclosure 
     When an optical connector comprising a configuration containing a plurality of optical fibers in an optical connector ferrule is manufactured, it is necessary that the plurality of optical fibers are fixed to the optical connector ferrule after the plurality of optical fibers are inserted into the optical connector ferrule. Therefore, a window for injecting an adhesive into the optical connector ferrule (ferrule window) is opened on an outer surface of the optical connector ferrule. For example, by injecting the adhesive from the window into the optical connector ferrule by a syringe, the plurality of optical fibers are fixed to the optical connector ferrule. At this time, when the adhesive has spilled out of the window onto the outer surface of the optical connector ferrule, it becomes necessary to perform a process of removing the spilled adhesive from the outer surface. When the spilled adhesive remains on the outer surface of the optical connector ferrule, there is a possibility that, when the optical connector ferrule is held to be floating in a housing, the floating function is impaired by interference from the adhesive to the housing. In this case, there is a possibility that connection performance of the optical connector comprising the optical connector ferrule is deteriorated. Further, since the outer surface of the optical connector ferrule does not meet a reference surface of a polishing table with high accuracy, it becomes difficult to polish a connecting end face of the optical connector ferrule with high accuracy. Consequently, it is desirable that an amount of adhesive to be injected into the optical connector ferrule is adjusted (controlled) so that the adhesive does not spill out of the window onto the outer surface of the optical connector ferrule. 
     However, since the size of the window is extremely small and the adhesive to be injected into the optical connector ferrule is in minute quantity, it is extremely difficult to adjust the amount of adhesive. Moreover, if the size of the window is enlarged, there is a possibility that, after a molding process of the optical connector ferrule, warpage occurs in the optical connector ferrule. This is because, since an opening portion, such as a window, cannot be provided on a surface facing the outer surface of the optical connector ferrule, thermal shrinkage greatly differs between the surface and the outer surface. The manufacturing method of optical fibers with an optical connector ferrule described in Patent Literature 1 adjusts the shape and the position of the window for injecting the adhesive to dispose the optical fiber ribbons at proper positions; therefore, the method does not solve the problem as described above. 
     An object of this disclosure is to provide an optical connector ferrule and an optical connector capable of preventing an adhesive from reaching an outer surface from a window for injecting the adhesive. 
     Advantageous Effects of Disclosure 
     According to an optical connector ferrule and an optical connector according to this disclosure, it is possible to prevent an adhesive from reaching an outer surface from a window for injecting the adhesive. 
     DESCRIPTION OF EMBODIMENTS OF INVENTION 
     First, details of an embodiment according to the present invention will be listed and described. An optical connector ferrule according to an embodiment of the present invention comprises: a first end and a second end provided to face each other in a first direction; an outer surface extending in the first direction between the first end and the second end; an opening provided in the second end; an introducing hole which extend from the opening toward the first end, and into which a plurality of optical fibers can be inserted as a bundle; a plurality of optical fiber holes which pass through from a tip portion of the introducing hole closer to the first end in the first direction to the first end, and into which the plurality of optical fibers are respectively inserted; and a window which opens to the outer surface and is connected to the introducing hole, and into which an adhesive is injected, wherein a first opening of the window closer to the outer surface is larger than a second opening of the window closer to the introducing hole, and an inner wall of the window includes a first surface provided in the peripheral direction of the inner wall, and the first surface is positioned closer to the introducing hole with respect to the outer surface in a second direction orthogonal to the outer surface, and faces toward the outer surface. 
     When an optical connector is manufactured by use of the above-described optical connector ferrule, after the plurality of optical fibers are inserted from the opening into the introducing hole and the plurality of optical fiber holes, the adhesive is injected from the window. By the adhesive, the plurality of optical fibers are fixed to the introducing hole and the plurality of optical fiber holes. Here, since the first opening is larger than the second opening and the first surface facing toward the outer surface is positioned closer to the introducing hole with respect to the outer surface, space for containing the adhesive having reached the first surface is reserved on the first surface. Consequently, it is possible to prevent the adhesive spilled from the introducing hole from reaching the outer surface. Accordingly, the time needed for the process of removing the adhesive from the outer surface can be reduced. Moreover, by adjusting the amount of adhesive using the position of the first surface (for example, the position of one side, of the sides constituting the first surface, closer to the introducing hole than the other sides) as a guide, the amount of adhesive can be suppressed. Consequently, since a stress due to volume changes (contraction stress) of the adhesive when being cured can be kept small, it is possible to keep deformation of the optical connector ferrule small. 
     In the above-described optical connector ferrule, the inner wall of the window may further include a second surface that connects the outer surface and the first surface, and an angle formed by the outer surface and the first surface may be smaller than an angle formed by the outer surface and the second surface. By providing the second surface like this between the outer surface and the first surface, the adhesive having reached the first surface becomes less likely to reach the outer surface. Consequently, it is possible to further prevent the adhesive from reaching the outer surface. 
     In the above-described optical connector ferrule, the first surface may be in parallel with the outer surface, or the first surface may be inclined with respect to the outer surface. Consequently, it is possible to suitably realize the above-described window of the optical connector ferrule. Moreover, when the first surface is inclined with respect to the outer surface, an inclination angle of the first surface with respect to the outer surface may be in a range of more than 0 degrees and equal to or less than 45 degrees. The smaller the angle is set, the larger a contact angle between the first surface and the surface of the adhesive becomes. Consequently, wettability between the first surface and the adhesive is reduced, and a surface tension of the adhesive is increased. This causes the adhesive having reached the first surface to be less likely to reach the outer surface; therefore, it is possible to further prevent the adhesive from reaching the outer surface. 
     In the above-described optical connector ferrule, a total area of the first surface may be equal to or more than 20% of a total area of the first opening, or, the total area of the first surface may be equal to or more than 50% of the total area of the first opening. By providing the first surface having such a total area, the adhesive having reached the first surface is sufficiently contained, and therefore, the adhesive becomes less likely to reach the outer surface. Consequently, it is possible to further prevent the adhesive from reaching the outer surface. 
     In the above-described optical connector ferrule, the first surface further includes a third surface and a fourth surface, and the third surface may be positioned closer to the center of the window with respect to the fourth surface and may be positioned closer to the introducing hole in the second direction with respect to the fourth surface. Consequently, even when the adhesive has spilled out of the third surface, it is possible to keep the spilled adhesive on the fourth surface. Consequently, it is possible to further prevent the adhesive from reaching the outer surface. 
     In the above-described optical connector ferrule, the first surface further includes a third surface and a fourth surface, and the third surface may be positioned close to the center of the window with respect to the fourth surface and may be positioned closer to the outer surface in the second direction with respect to the fourth surface. Consequently, even when the adhesive spills out of the third surface, it is possible to keep the spilled adhesive on the fourth surface. Consequently, it is possible to further prevent the adhesive from reaching the outer surface. 
     The above-described optical connector ferrule further comprises a step provided to the outer surface, and the step may protrude outwardly in the second direction from the outer surface closer to the first end with respect to the step. Moreover, in this case, the window may be separated from the step toward a front end in the first direction, and the first surface may be provided to, except for one portion, the other portions in the peripheral direction of the inner wall of the window, and the one portion may be closer to the step than the other portions. When the adhesive has reached the outer surface, there is a possibility that the adhesive adheres not only to the outer surface but also to the step. Further, it is difficult to remove the adhesive adhered to a corner portion formed by the step and the outer surface. Accordingly, there is a possibility that the time needed for the process of removing the adhesive is increased. Therefore, by providing the first surface at the other portions, except for one portion at the position closer to the step, in the inner wall of the window, the adhesive having reached the first surface can be separated from the step. This causes the adhesive to rarely reach the step, to thereby make it possible to prevent the time needed for the process of removing the adhesive from increasing. 
     In the above-described optical connector ferrule, the window may have a rectangular shape, a polygonal shape, a circular shape, an elliptical shape or a partially rounded shape. 
     An optical connector according to an embodiment of the present invention may comprise any one of the above-described optical connector ferrules and the plurality of optical fibers inserted from the opening into the introducing hole and the plurality of optical fiber holes and fixed to the introducing hole and the plurality of optical fiber holes by the adhesive injected from the window. As described above, according to the above-described optical connector ferrule, it is possible to keep deformation by the contraction stress of the adhesive small; therefore, according to the above-described optical connector comprising the above-described optical connector ferrule, it is possible to obtain good optical properties. Moreover, in this case, the adhesive may remain inside the window, not on the outer surface, in the second direction. 
     DETAILS OF EMBODIMENTS OF INVENTION 
     Hereinafter, specific examples of an optical connector ferrule and an optical connector according to an embodiment of the present invention will be described with reference to drawings. It is intended that the present invention is not limited to these examples, but defined by the claims, and all changes equivalent to meaning of the claims and within the scope of the claims are included in the present invention. In the following description, in description of the drawings, common components are assigned with the same reference sign, and redundant description is omitted. 
       FIG. 1  is a top view of an optical connector ferrule  10  according to the embodiment.  FIG. 2  is a cross-sectional view of the optical connector ferrule  10  shown in  FIG. 1  along the II-II line. The optical connector ferrule  10  according to the embodiment (hereinafter, simply referred to as “ferrule  10 ”) is, for example, an MT optical connector ferrule. The ferrule  10  has an outer appearance substantially in a shape of rectangular parallelepiped with a first direction A 1  as the longitudinal direction. As shown in  FIGS. 1 and 2 , the ferrule  10  comprises a front end surface  20   a  (a first end), a rear end surface  20   b  (a second end), a top surface  20   c  (an outer surface), a step  21 , an opening  40 , an introducing hole  50 , a plurality of optical fiber holes  51 , and a window  30 . The front end surface  20   a  and the rear end surface  20   b  are provided to face each other in the first direction A 1 . The top surface  20   c  connects the front end surface  20   a  and the rear end surface  20   b  via the step  21 . The top surface  20   c  is formed in the first direction A 1 . The step  21  is formed at a rear end of the top surface  20   c  closer to the rear end surface  20   b  in the first direction A 1 . The step  21  protrudes outwardly in a second direction A 2  orthogonal to the top surface  20   c  (in an example, the second direction A 2  is also orthogonal to the first direction A 1 ) from the top surface  20   c  closer to the front end surface  20   a  with respect to the step  21 . In an example, the step  21  consists of a flange-shaped portion formed at a rear end portion of the ferrule  10  closer to the rear end surface  20   b  in the first direction A 1 . 
     The opening  40  opens on the rear end surface  20   b  and receives a plurality of optical fibers. The introducing hole  50  extends from the opening  40  toward the front end surface  20   a . The plurality of optical fibers are inserted into the introducing hole  50  as a bundle. Fiber grooves  52  are provided at the tip portion of the introducing hole  50  closer to the front end surface  20   a  in the first direction A 1 . The fiber grooves  52  are provided at positions that can be visually recognized from the window  30 . A plurality of optical fiber holes  51  extend in the first direction A 1  to penetrate from the tip portion of the introducing hole  50  to the front end surface  20   a . The plurality of optical fiber holes  51  are arranged one-dimensionally or two-dimensionally on a cross section perpendicular to the first direction A 1 . The plurality of optical fibers guided by the fiber grooves  52  is respectively inserted into the plurality of optical fiber holes  51 . 
     The window  30  opens on the top surface  20   c  and is connected to the introducing hole  50 . The window  30  is provided to a position separated from the step  21  toward the front end surface  20   a  in the first direction A 1 . The window  30  is provided to inject the adhesive into the introducing hole  50  and the plurality of optical fiber holes  51 . In an example, the window  30  has a rectangular shape with the first direction A 1  as the short direction, and includes four sides constituting an inner wall of the window  30 . Of these four sides, two sides in the longitudinal direction extend in a direction orthogonal to the first direction A 1  and the second direction A 2 . Of the two sides in the longitudinal direction, one side is provided at a position closer to the step  21  than the other three sides. Of the four sides, two sides in the short direction are perpendicular to the two sides in the longitudinal direction.  FIG. 3A  is a top view enlarging and showing the window  30  of the ferrule  10  shown in  FIG. 1 .  FIG. 3B  is a cross-sectional view of the window  30  shown in  FIG. 3A  along the line. As shown in  FIG. 3B , in the second direction A 2 , a first opening S 1  of the window  30  closer to the top surface  20   c  is larger than a second opening S 2  of the window  30  closer to the introducing hole  50 . Here, the first opening S 1  being larger than the second opening S 2  means that, for example, an area of the first opening S 1  is larger than an area of the second opening S 2 . The inner wall of the window  30  includes a first surface  30   a , a second surface  30   b  and a surface  31 . The first surface  30   a , the second surface  30   b  and the surface  31  are provided at least at one portion of the inner wall of the window  30  in the peripheral direction. In this embodiment, the first surface  30   a , the second surface  30   b  and the surface  31  are provided over whole circumference of the inner wall of the window  30 . In an example, a ratio of the area of the first surface  30   a  to the area of the first opening S 1  is equal to or more than 20%, and more preferably, equal to or more than 50%. The first surface  30   a  faces toward the top surface  20   c , and is positioned closer to the introducing hole  50  with respect to the top surface  20   c  in the second direction A 2 . Here, facing toward the top surface  20   c  means that a normal vector of the first surface  30   a  contains a component of the second direction A 2  and the component faces toward the top surface  20   c . In an example, the first surface  30   a  is positioned equal to or more than 0.1 mm, and more preferably, equal to or more than 0.3 mm away from the top surface  20   c  toward the introducing hole  50 . Moreover, an angle formed by the top surface  20   c  and the first surface  30   a  is smaller than an angle formed by the top surface  20   c  and the second surface  30   b . In an example, the first surface  30   a  is in parallel with the top surface  20   c  and the second surface  30   b  is perpendicular to the top surface  20   c . The surface  31  connects the first surface  30   a  and the introducing hole  50 , and in an example, the surface  31  is perpendicular to the top surface  20   c.    
     An optical connector  1  of the embodiment is configured with the ferrule  10  and a plurality of optical fibers.  FIG. 4  is a side cross-sectional view showing a configuration of the optical connector  1  according to the embodiment. With reference to  FIG. 4 , a plurality of optical fibers  60  are inserted from the opening  40  into the introducing hole  50 , and, while being guided by the fiber grooves  52 , respectively inserted into the plurality of optical fiber holes  51 . At this time, an operator can visually recognize the plurality of optical fibers  60  from the window  30 . When the adhesive is injected from the window  30  in this state, the plurality of optical fibers  60  are fixed to the introducing hole  50  and the plurality of optical fiber holes  51  by the adhesive together. 
     Description will be given of effects obtained by the ferrule  10  and optical connector  1  according to the embodiment as described above. As described above, when the adhesive is injected from the window  30  of the ferrule  10 , the plurality of optical fibers  60  are fixed to the introducing hole  50  and the plurality of optical fiber holes  51 . At this time, it is desirable that the adhesive injected into the ferrule  10  does not spill out of the window  30  onto the top surface  20   c . However, in a window of a conventional ferrule (for example, refer to Patent Literature 1), there is a problem that an adhesive is likely to reach a top surface of the ferrule from the window.  FIG. 11A  is a top view enlarging and showing a window  101  of such a ferrule  110  when an adhesive  70  is injected into an optical connector comprising the ferrule  110 .  FIG. 11B  is a cross-sectional view of the window  101  shown in  FIG. 11A  along the XI-XI line. With reference to  FIGS. 11A and 11B , an inner wall  101   a  of the window  101  is perpendicular to a top surface  100   a . When the adhesive  70  is injected from the window  101  in this state, as shown in  FIGS. 11A and 11B , the adhesive  70  is likely to reach the top surface  100   a.    
       FIG. 5A  is a top view enlarging and showing an example of the window  30  of the ferrule  10  when the adhesive  70  is injected into the optical connector  1  of the embodiment.  FIG. 5B  is a cross-sectional view of the window  30  shown in  FIG. 5A  along the V-V line. As shown in  FIGS. 5A and 5B , in the embodiment, the first opening S 1  is larger than the second opening S 2 , and the first surface  30   a  facing toward the top surface  20   c  is positioned closer to the introducing hole  50 . Consequently, space for containing the adhesive  70  having reached the first surface  30   a  is reserved on the first surface  30   a . Therefore, since the adhesive  70  spilled from the introducing hole  50  remains in the space on the first surface  30   a , it is possible to prevent the adhesive  70  from reaching the top surface  20   c . Accordingly, it is possible to reduce the time needed for the process of removing the adhesive  70  from the top surface  20   c . Moreover, the amount of adhesive  70  can be suppressed by adjusting the amount of adhesive  70  using the position of the first surface  30   a  in the second direction A 2  as a guide. Consequently, since this can keep a contraction stress of adhesive  70  when being cured small, it is possible to keep deformation of the ferrule  10  small. 
     As in the embodiment, the inner wall of the window  30  includes the second surface  30   b  that connects the top surface  20   c  and the first surface  30   a , and the angle formed by the top surface  20   c  and the first surface  30   a  may be smaller than the angle formed by the top surface  20   c  and the second surface  30   b . The adhesive  70  having reached the first surface  30   a  becomes less likely to reach the top surface  20   c  by providing the second surface  30   b  between the top surface  20   c  and the first surface  30   a , as shown in  FIGS. 3A and 3B . This can further prevent the adhesive  70  from reaching the top surface  20   c.    
     The optical connector  1  according to the embodiment may comprise, as shown in  FIG. 4 , the ferrule  10  and the plurality of optical fibers  60  inserted from the opening  40  into the introducing hole  50  and the plurality of optical fiber holes  51  along the first direction A 1  and fixed to the introducing hole  50  and the plurality of optical fiber holes  51  by the adhesive  70  injected from the window  30 . As described above, it is possible to keep deformation due to the contraction stress of the adhesive  70  small by the ferrule  10 ; therefore, the optical connector  1  comprising the ferrule  10  can obtain good optical properties. 
     (First modified example)  FIG. 6A  is a top view enlarging and showing a window  30 A of a ferrule  10 A according to a first modified example of the above-described embodiment.  FIG. 6B  is a cross-sectional view of the window  30 A of the ferrule  10 A shown in  FIG. 6A  along the VI-VI line. A difference between the modified example and the above-described embodiment is inclination of the first surface. That is, the first surface  30   c  of the window  30 A in the ferrule  10 A of the modified example is, as shown in  FIG. 6B , inclined with respect to the top surface  20   c . In other words, the normal vector of the first surface  30   c  is inclined toward inside of the window  30 . Even when the first surface  30   c  is inclined in this manner, it is possible to suitably realize the configuration in which a first opening S 3  of the window  30 A closer to the top surface  20   c  is larger than a second opening S 4  of the window  30 A closer to the introducing hole  50  and the first surface  30   c  facing toward the top surface  20   c  is positioned closer to the introducing hole  50 . Further, the inclination angle of the first surface  30   c  with respect to the top surface  20   c  may be set within a range that is more than 0 degrees and equal to or less than 45 degrees. The smaller the inclination angle is set, the larger a contact angle between the first surface  30   c  and the surface of the adhesive  70  becomes. Consequently, wettability between the first surface  30   c  and the adhesive  70  is reduced, and a surface tension of the adhesive  70  is increased. This causes the adhesive  70  having reached the first surface  30   c  to be less likely to reach the top surface  20   c ; therefore, it is possible to further prevent the adhesive  70  from reaching the top surface  20   c . Moreover, for example, the amount of adhesive  70  can be suppressed by adjusting the amount of adhesive  70  using the position of, of the sides constituting the first surface  30   c , one side closer to the introducing hole  50  than the other sides as a guide. 
     Second Modified Example 
       FIG. 7A  is a top view enlarging and showing a window  30 B of a ferrule  10 B according to a second modified example of the above-described embodiment.  FIG. 7B  is a cross-sectional view of the window  30 B of the ferrule  10 B shown in  FIG. 7A  along the VII-VII line. A difference between the modified example and the above-described embodiment is the number of surfaces constituting the first surface. That is, the first surface  30   a  of the above-described embodiment is configured with one surface; however, a first surface  30   r  of the inner wall of the window  30 B in the modified example is divided into two surfaces (a third surface  30   d  and a fourth surface  30   e ). As shown in  FIGS. 7A and 7B , the inner wall of the window  30 B includes the third surface  30   d , the fourth surface  30   e , a fifth surface  30   f  and a sixth surface  30   g . The third surface  30   d  is positioned closer to the center of the window  30 B with respect to the fourth surface  30   e . Further, the fourth surface  30   e  is positioned closer to the top surface  20   c  of the ferrule  10 B in the second direction A 2  with respect to the third surface  30   d . In an example, the third surface  30   d  and the fourth surface  30   e  are in parallel with the top surface  20   c . The fifth surface  30   f  connects the third surface  30   d  and the fourth surface  30   e , and the sixth surface  30   g  connects the fourth surface  30   e  and the top surface  20   c . In an example, the fifth surface  30   f  and the sixth surface  30   g  are perpendicular to the top surface  20   c . By providing the third surface  30   d  and the fourth surface  30   e  in this manner, even when the adhesive  70  has spilled out of the third surface  30   d , it is possible to keep the spilled adhesive  70  on the fourth surface  30   e . This can further prevent the adhesive  70  from reaching the top surface  20   c . At least one of the third surface  30   d  and the fourth surface  30   e  may be inclined as the first surface  30   c  in the first modified example. 
     Third Modified Example 
       FIG. 8A  is a top view enlarging and showing a window  30 C of a ferrule  10 C according to a third modified example of the above-described embodiment.  FIG. 8B  is a cross-sectional view of the window  30  of the ferrule  10 C shown in  FIG. 8A  along the VIII-VIII line. A difference between the modified example and the above-described embodiment is the number of surfaces constituting the first surface. That is, the first surface  30   a  of the above-described embodiment is configured with one surface; however, a first surface  30   s  of the inner wall of the window  30 C in the modified example is divided into two surfaces (a third surface  30   h  and a fourth surface  30   i ). As shown in  FIGS. 8A and 88 , the inner wall of the window  30 C includes the third surface  30   h , the fourth surface  30   i , a fifth surface  30   j  and a sixth surface  30   k . The third surface  30   h  is positioned closer to the center of the window  30 C with respect to the fourth surface  30   i . Further, the third surface  30   h  is positioned closer to the top surface  20   c  of the ferrule  10 C in the second direction A 2  with respect to the fourth surface  30   i . In an example, the third surface  30   h  and the fourth surface  30   i  are in parallel with the top surface  20   c . The fifth surface  30   j  connects the third surface  30   h  and the fourth surface  30   i , and the sixth surface  30   k  connects the fourth surface  30   i  and the top surface  20   c . In an example, the fifth surface  30   j  and the sixth surface  30   k  are perpendicular to the top surface  20   c . By providing the third surface  30   h  and the fourth surface  30   i , even when the adhesive  70  spills out of the third surface  30   h , it is possible to keep the spilled adhesive  70  on the fourth surface  30   i . This can further prevent the adhesive  70  from reaching the top surface  20   c . Note that at least one of the third surface  30   h  and the fourth surface  30   i  may be inclined as the first surface  30   c  in the first modified example. 
     Fourth Modified Example 
       FIG. 9A  is a top view enlarging and showing a window  30 D of a ferrule  10 D according to a fourth modified example of the above-described embodiment.  FIG. 9B  is a cross-sectional view of the window  30 D of the ferrule  10 D shown in  FIG. 9A  along the IX-IX line. A difference between the modified example and the above-described embodiment is arrangement of the first surface. That is, the first surface  30   a  of the above-described embodiment was provided over whole circumference in the peripheral direction of the inner wall of the window  30 ; however, a first surface  30   m  of the modified example is provided to a portion along the peripheral direction of the inner wall of the window  30 D except for one portion S 5 . As shown in  FIGS. 9A and 9B , the inner wall of the window  30 D includes the first surface  30   m  and a second surface  30   p . The shape of the first surface  30   m  and the second surface  30   p  is similar to the first surface  30   a  and the second surface  30   b  of the above-described embodiment except for the point of not being provided at the one portion S 5  in the inner wall of the window  30 D. The one portion S 5  in the inner wall of the window  30 D is positioned closer to the step  21  than the other portions of the inner wall. Specifically, the one portion S 5  corresponds to, of the four sides constituting the window  30 D in the rectangular shape, a side closest to the step  21 . The other configuration except for the first surface  30   m  and the second surface  30   p  is the same as the configuration of the ferrule  10  of the above-described embodiment. 
     Here, when the adhesive  70  reaches the top surface  20   c , if the adhesive  70  reaches the step  21 , the adhesive adheres not only to the top surface  20   c , but also to the step  21 . Further, since the step  21  rises up from the top surface  20   c , the step  21  and the top surface  20   c  form a corner portion; it is difficult to remove the adhesive  70  adhered to such a corner portion. Accordingly, there is a possibility that the time needed for the process of removing the adhesive  70  is increased. Therefore, by providing the first surface  30   m  at the other portions except for the one portion at the position closer to the step  21  in the inner wall of the window  30 D, the adhesive having reached the first surface  30   m  can be separated from the step  21 . This makes it possible for the adhesive  70  to rarely reach the step  21 , to thereby make it possible to prevent the time needed for the process of removing the adhesive  70  from increasing. 
     The optical connector ferrule and the optical connector according to the present invention are not limited to the above-described embodiment, and various other modifications are available. For example, the above-described embodiment and each modified example may be combined with one another according to required purposes and effects. Moreover, in the above-described embodiment and each modified example, the shape of the window was rectangle; however, the shape of the window may be other than the rectangle.  FIGS. 10A to 10D  are top views showing other examples of the shape of the window of the ferrule. The shape of the window may be those shown in  FIGS. 10A to 10D . For example, the window may be a window  30 E having an octagonal shape (a polygonal shape) obtained by cutting all corners of the rectangular shape as shown in  FIG. 10A , a window  30 F having a hexagonal shape obtained by cutting corners on one side (the left side in the figure) of the rectangular shape as shown in  FIG. 10B , or a window  30 G having a hexagonal shape obtained by cutting corners on the other side (the right side in the figure) of the rectangular shape as shown in  FIG. 10C . Moreover, as shown in  FIG. 10D , by forming a window  30 H into a rounded shape, a circular shape or an elliptical shape, the adhesive may be made to hardly spill from the window  30 H. 
     Moreover, in the above-described embodiment, the front end surface and the rear end surface facing each other were parallel; however, these surfaces may not be parallel. 
     REFERENCE SIGNS LIST 
       1  . . . optical connector;  10 ,  10 A to  10 D,  110  . . . ferrule;  20   a  . . . front end surface (first end);  20   b  . . . rear end surface (second end);  20   c . . .  top surface (outer surface);  21  . . . step;  30 ,  30 A to  30 D,  101  . . . window;  30   a ,  30   c ,  30   m ,  30   r ,  30   s  . . . first surface;  30   b ,  30   p  . . . second surface;  30   d ,  30   h  . . . third surface;  30   e ,  30   i  . . . fourth surface;  30   f ,  30   j  . . . fifth surface;  30   g ,  30   k  . . . sixth surface;  40  . . . opening;  50  . . . introducing hole;  51  . . . optical fiber hole;  52  . . . fiber groove;  60  . . . optical fiber;  70  . . . adhesive;  101   a  . . . inner wall; A 1  . . . first direction; A 2  . . . second direction.