Patent Publication Number: US-2023152534-A1

Title: Optical connector, ferrule, and method for manufacturing optical connector

Description:
TECHNICAL FIELD 
     The present disclosure relates to an optical connector, a ferrule, and a method for manufacturing an optical connector. 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2020-070809 filed on Apr. 10, 2020, and the entire contents of which are incorporated herein by reference. 
     BACKGROUND ART 
     Patent Literature 1 discloses an optical connector for connecting a plurality of optical fibers to a plurality of optical fibers of a connection counterpart. The optical connector includes the plurality of optical fibers and a ferrule holding the plurality of optical fibers. The ferrule has a ferrule main body where a plurality of fiber holes respectively holding the plurality of optical fibers are formed and a lens plate disposed on the front end surface of the ferrule main body. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: Japanese Unexamined Patent Publication No. 2019-90974 
       
    
     SUMMARY OF INVENTION 
     An optical connector according to one embodiment of the present disclosure includes: a plurality of optical fibers each having a coating removal portion where a predetermined length of coating is removed from a tip; and a ferrule having a main body portion holding the coating removal portion of each of the optical fibers and a lens portion facing the tip in a first direction in which an optical axis of each of the optical fibers extends. The main body portion has a base portion including a plurality of fiber grooves respectively supporting the coating removal portions of the optical fibers. The fiber grooves extend along the first direction and are arranged along a second direction intersecting the first direction. The base portion has a recess portion between the fiber grooves and the lens portion in the first direction. 
     A ferrule according to one embodiment of the present disclosure includes: a main body portion for holding a plurality of optical fibers; and a lens portion provided at a tip side of each of the optical fibers held in the main body portion. The main body portion has a base portion including a plurality of fiber grooves for respectively supporting the optical fibers. The fiber grooves extend along a first direction and are arranged along a second direction intersecting the first direction. The base portion has a recess portion between the fiber grooves and the lens portion in the first direction. 
     An optical connector manufacturing method according to one embodiment of the present disclosure includes: a step of preparing a plurality of optical fibers each having a coating removal portion where a predetermined length of coating is removed from a tip and the ferrule described above; a step of forming a tip surface on the coating removal portion by laser-cutting the coating removal portion; and a step of placing each of the optical fibers in each of the fiber grooves of the ferrule. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a top view illustrating an optical connector according to an embodiment. 
         FIG.  2    is a top view of the optical connector in which a part of the optical connector of  FIG.  1    is illustrated in a cross-sectional manner. 
         FIG.  3    is a cross-sectional view of the optical connector along the III-III line of  FIG.  1   . 
         FIG.  4    is an enlarged cross-sectional view of a part of a coating removal portion of  FIG.  3   . 
         FIG.  5 A  is a front view of a ferrule. 
         FIG.  5 B  is a rear view of the ferrule in which a part of the ferrule is illustrated in a cross-sectional manner. 
         FIG.  6 A  is a cross-sectional view illustrating an optical connector manufacturing method according to an embodiment. 
         FIG.  6 B  is a schematic cross-sectional view illustrating the step subsequent to  FIG.  6 A . 
         FIG.  7 A  is a schematic cross-sectional view illustrating the step subsequent to  FIG.  6 B . 
         FIG.  7 B  is a schematic cross-sectional view illustrating the step subsequent to  FIG.  7 A . 
         FIG.  7 C  is a schematic cross-sectional view illustrating the step subsequent to  FIG.  7 B . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Problems to be Solved by Present Disclosure 
     In the optical connector described in Patent Literature 1, in a case where, for example, the ferrule main body and the lens plate are integrally configured, the tip of the optical fiber is not exposed from the ferrule, and thus a desired tip surface cannot be formed on the optical fiber by polishing. Conceivable in this case is a method of forming a tip surface by laser-cutting the optical fiber before inserting the optical fiber into the ferrule. 
     However, when an optical fiber is laser-cut, the cut part of the optical fiber (that is, the tip part near the tip surface of the optical fiber) tends to become thicker than the other part of the optical fiber due to the heat of the laser. With the tip part thick as described above, it may be difficult to insert the optical fiber into a fiber hole. Meanwhile, although it is also conceivable to make the inner diameter of the fiber hole larger than the outer diameter of the tip part, in this case, the clearance between the fiber hole and the optical fiber is likely to expand and the position of the optical fiber is likely to deviate. 
     Effect of Present Disclosure 
     According to the optical connector, the ferrule, and the method for manufacturing an optical connector according to the present disclosure, it is possible to easily mount an optical fiber while suppressing the occurrence of a positional deviation of the optical fiber. 
     Description of Embodiment of Present Disclosure 
     First, the content of an embodiment of the present disclosure will be listed and described. An optical connector according to one embodiment of the present disclosure includes: a plurality of optical fibers each having a coating removal portion where a predetermined length of coating is removed from a tip; and a ferrule having a main body portion holding the coating removal portion of each of the optical fibers and a lens portion facing the tip in a first direction in which an optical axis of each of the optical fibers extends. The main body portion has a base portion including a plurality of fiber grooves respectively supporting the coating removal portions of the optical fibers. The fiber grooves extend along the first direction and are arranged along a second direction intersecting the first direction. The base portion has a recess portion between the fiber grooves and the lens portion in the first direction. 
     In this optical connector, the base portion of the ferrule has the recess portion between the fiber grooves and the lens portion. By the recess portion being provided between the fiber grooves and the lens portion, it is possible to ensure a space that allows the coating removal portion to become thick in the base portion. Accordingly, even in a case where the coating removal portion is thick, in mounting each optical fiber on the ferrule, on condition that each optical fiber is placed in each fiber groove such that the thickness of the coating removal portion is accommodated in the recess portion, each optical fiber can be easily mounted on the ferrule without being hindered by the thickness of the coating removal portion. Further, in this configuration, only the thickness of the coating removal portion can be released to the recess portion, and thus it is not necessary to increase the width of each fiber groove more than necessary in accordance with the thickness of the coating removal portion. As a result, a situation in which the clearance between each optical fiber and each fiber groove expands can be suppressed and a positional deviation of each optical fiber can be suppressed. 
     The coating removal portion may include a tip surface positioned at the tip. The tip surface may be inclined with respect to a plane perpendicular to the first direction. In this case, it is possible to suppress return light incidence on the optical fiber on the tip surface of the optical fiber. 
     The coating removal portion may include: a tip surface positioned at the tip; a first part separated from the tip surface in the first direction; and a second part positioned between the tip surface and the first part in the first direction and larger in maximum outer diameter than the first part. The fiber grooves may respectively support the first parts of the optical fibers. The recess portion may accommodate the second parts of the optical fibers. In a case where the tip surface of the coating removal portion is formed by, for example, laser cutting, the second part near the tip surface is likely to become thick. Therefore, when the optical fibers are mounted on the ferrule, the above effect is suitably achieved by placing each optical fiber in each fiber groove such that the thickened second part is accommodated in the recess portion. 
     A width of the recess portion in the first direction may be larger than a length of the second part in the first direction. In this case, a configuration in which the recess portion accommodates the second part of each optical fiber can be realized more reliably. 
     A bottom portion of the recess portion may be separated from the coating removal portion in a third direction intersecting the first direction and the second direction. In this case, it is possible to more reliably ensure a space that allows the coating removal portion to become thick in the base portion. 
     The main body portion may further have a lid portion facing the base portion with the optical fibers interposed therebetween in a third direction intersecting the first direction and the second direction. The lid portion may be disposed in a region facing the base portion, excluding a region facing the recess portion, and facing the fiber grooves. In this case, a positional deviation of each optical fiber can be effectively suppressed by pressing each optical fiber into each fiber groove with the lid portion. Further, in this configuration, the lid portion is not disposed in the region facing the recess portion. As a result, a situation in which the thickness of the coating removal portion in the recess portion hinders pressing each optical fiber into each fiber groove with the lid portion can be suppressed. 
     An adhesive for fixing the optical fibers to the main body portion may be provided in the recess portion. In this case, a positional deviation of each optical fiber can be effectively suppressed by fixing each optical fiber to the main body portion with the adhesive. 
     The base portion may further have a step portion on a side opposite to the recess portion with the fibers interposed therebetween in the first direction. Each of the optical fibers may further have a coating portion where the coating remains. A step surface formed between the coating portion and the coating removal portion by the coating may abut against the step portion in the first direction. In this case, the first-direction position of the tip surface of the coating removal portion in the recess portion can be adjusted by causing the step surface between the coating portion and the coating removal portion to abut against the step portion in the first direction. Accordingly, the position of the tip surface can be defined at a position that does not abut against the lens portion, and thus it is possible to suppress the occurrence of problems such as tilting of each fiber attributable to the tip surface abutting against the lens portion. As a result, the occurrence of a positional deviation of each optical fiber can be effectively suppressed. 
     The lens portion may include a front end surface facing a side opposite to the base portion in the first direction and a plurality of lenses provided so as to respectively correspond to the plurality of optical fibers and protruding from the front end surface. An outer surface of the ferrule may have a groove as a reference for measuring positions of the lenses and positions of the fiber grooves viewed from the first direction. The groove may continuously extend along the first direction over the main body portion from the lens portion. In this case, the deviation between the positions of the lens and the positions of the fiber grooves can be measured by measuring the positions of the lens with respect to the position of the groove at the time of viewing from one side in the first direction and the positions of the fiber grooves with respect to the position of the groove at the time of viewing from the other side in the first direction. 
     A ferrule according to one embodiment of the present disclosure includes: a main body portion for holding a plurality of optical fibers; and a lens portion provided at a tip side of each of the optical fibers held in the main body portion. The main body portion has a base portion including a plurality of fiber grooves for respectively supporting the optical fibers. The fiber grooves extend along a first direction and are arranged along a second direction intersecting the first direction. The base portion has a recess portion between the fiber grooves and the lens portion in the first direction. 
     In this ferrule, the base portion has the recess portion between the fiber grooves and the lens portion. Accordingly, even in a case where the optical fiber is thick, by the recess portion being provided between the fiber grooves and the lens portion, it is possible to ensure a space that allows the thickness in the base portion. Accordingly, in mounting each optical fiber on the ferrule, on condition that each optical fiber is placed in each fiber groove such that the thick part in each optical fiber is accommodated in the recess portion, each optical fiber can be easily mounted on the ferrule without being hindered by the thickness. Further, in this configuration, only the thickness can be released to the recess portion, and thus it is not necessary to increase the width of each fiber groove more than necessary in accordance with the thickness of each optical fiber. As a result, a situation in which the clearance between each optical fiber and each fiber groove expands can be suppressed and a positional deviation of each optical fiber can be suppressed. 
     An optical connector manufacturing method according to one embodiment of the present disclosure includes: a step of preparing a plurality of optical fibers each having a coating removal portion where a predetermined length of coating is removed from a tip and the ferrule described above; a step of forming a tip surface on the coating removal portion by laser-cutting the coating removal portion; and a step of placing each of the optical fibers in each of the fiber grooves of the ferrule described above. 
     In this optical connector manufacturing method, each optical fiber is placed in each fiber groove after forming the tip surface of the coating removal portion of each optical fiber by laser cutting. When the tip surface is formed on the coating removal portion by laser cutting, thickening may occur near the tip surface of the coating removal portion. Here, the base portion of the ferrule has the recess portion between the fiber grooves and the lens portion. By the recess portion being provided between the plurality of fiber grooves and the lens portion, it is possible to ensure a space that allows the coating removal portion to become thick in the base portion. Accordingly, even in a case where the coating removal portion is thick, in mounting each optical fiber on the ferrule, by each optical fiber being placed in each fiber groove such that the thickness of the coating removal portion is accommodated in the recess portion, each optical fiber can be easily mounted on the ferrule without being hindered by the thickness of the coating removal portion. Further, in this manufacturing method, only the thickness of the coating removal portion can be released to the recess portion, and thus it is not necessary to increase the width of each fiber groove more than necessary in accordance with the thickness of the coating removal portion. As a result, a situation in which the clearance between each optical fiber and each fiber groove expands can be suppressed and a positional deviation of each optical fiber can be suppressed. 
     In the step of forming the tip surface, the tip surface may be inclined with respect to a plane perpendicular to the first direction. In this case, it is possible to suppress return light incidence on the optical fiber on the tip surface of the optical fiber. 
     The optical connector manufacturing method described above may further include: a step of injecting an adhesive for fixing the optical fibers to the main body portion into the recess portion after the step of placing each of the optical fibers; and a step of disposing a lid portion so as to face the base portion with the optical fibers interposed therebetween in a third direction intersecting the first direction and the second direction after the step of injecting the adhesive into the recess portion. In the step of disposing the lid portion, the lid portion may be disposed in a region excluding a region facing the recess portion. By disposing the lid portion on the plurality of fiber grooves after injecting the adhesive into the recess portion in this manner, the adhesive can be spread not only in the recess portion but also to the region between the lid portion and the plurality of optical fibers. As a result, a positional deviation of each optical fiber with respect to the ferrule can be effectively suppressed. Further, a positional deviation of each optical fiber can be effectively suppressed by pressing each optical fiber into each fiber groove with the lid portion. Further, since the lid portion is not disposed in the region facing the recess portion, a situation in which the thickness of the coating removal portion hinders pressing each optical fiber into each fiber groove with the lid portion can be suppressed. 
     Details of Embodiment of Present Disclosure 
     Hereinafter, one embodiment of the present disclosure will be described in detail with reference to the drawings. In the following description, the same reference numerals will be used for the same or functionally identical elements with redundant description omitted. 
       FIG.  1    is a top view illustrating an optical connector  1  according to the present embodiment.  FIG.  2    is a top view of the optical connector  1  in which a part of the optical connector  1  of  FIG.  1    is illustrated in a cross-sectional manner.  FIG.  3    is a cross-sectional view of the optical connector  1  along the III-III line of  FIG.  1   . An XYZ orthogonal coordinate system for ease of understanding is illustrated in each of the drawings. An adhesive A is not illustrated in  FIGS.  1  and  2   . In the present embodiment, the X direction is a first direction and the direction of connection between the optical connector  1  and the optical connector of a connection counterpart, the Y direction is a second direction and is orthogonal to the X direction, and the Z direction is a third direction and is orthogonal to the X direction and the Y direction. The following description may be given with the directions of “front” and “rear” determined. In the X direction, the optical connector side of the connection counterpart with respect to the optical connector  1  is the front and the opposite side is the rear. 
     As illustrated in  FIGS.  1 ,  2 , and  3   , the optical connector  1  includes a tape fiber T including a plurality of optical fibers  10  and a ferrule  20  where the front end portion of the tape fiber T is inserted. The ferrule  20  has a main body portion  21  holding each optical fiber  10  of the tape fiber T and a lens portion  22  provided on a front end surface  21   a  of the main body portion  21 . 
     The main body portion  21  has a substantially rectangular parallelepiped appearance. The main body portion  21  has a base portion  23  and a lid portion  24  facing each other in the Z direction. The base portion  23  is a part supporting each optical fiber  10 . The base portion  23  is configured integrally with the lens portion  22 . The base portion  23  is configured by, for example, a light-transmitting resin such as polyetherimide (PEI), polycarbonate (PC), polymethylmethacrylate (PMMA), and polyethersulfone (PES). The base portion  23  includes a plurality of fiber grooves  26  respectively supporting the optical fibers  10 , a recess portion  27  formed in front of the fiber grooves  26 , and a step portion  28  formed behind the fiber grooves  26 . 
     As illustrated in  FIG.  2   , the plurality of fiber grooves  26  extend along the X direction and are arranged along the Y direction. In  FIG.  2   , the base portion  23  of the main body portion  21  is illustrated as an XY cross section, and each optical fiber  10  supported by each fiber groove  26  is illustrated in a visible state. The fiber grooves  26  are, for example, arranged in parallel and at equal intervals along the Y direction. The YZ cross section of each fiber groove  26  has, for example, a V shape opening toward the lid portion  24  in the Z direction (see  FIG.  5 B  to be described later). The fiber grooves  26  respectively support the optical fibers  10 . When viewed from the Z direction, bottom portions  26   a  of the fiber grooves  26  respectively coincide with, for example, the centers of the optical fibers  10 . 
     As illustrated in  FIGS.  2  and  3   , the recess portion  27  is recessed in the Z direction between, for example, each fiber groove  26  and the lens portion  22  in the X direction. The recess portion  27  is, for example, a linear groove extending along the Y direction. The recess portion  27  extends along the Y direction so as to, for example, connect the region between each fiber groove  26  and the lens portion  22  in the X direction. As illustrated in  FIG.  3   , the XZ cross section of the recess portion  27  has, for example, a rectangular shape. A bottom surface  27   a  of the recess portion  27  is, for example, a flat surface along the XY plane. The YZ cross section of the recess portion  27  also has, for example, a rectangular shape as in the case of the XZ cross section of the recess portion  27 . 
     The depth of the bottom surface  27   a  of the recess portion  27  is, for example, the same as the depth of the bottom portion  26   a  of the fiber groove  26 . In other words, the position of the bottom surface  27   a  in the Z direction coincides with the position of the bottom portion  26   a  in the Z direction. The depth of the bottom surface  27   a  of the recess portion  27  may be deeper than the depth of the bottom portion  26   a  of the fiber groove  26 . In other words, the bottom surface  27   a  may be positioned below the bottom portion  26   a . Here, “below” means the direction from the top portion of the fiber groove  26  toward the bottom portion  26   a  in the Z direction. The adhesive A for fixing each optical fiber  10  to the base portion  23  is injected and embedded in the recess portion  27 . The adhesive A is configured by, for example, a light-transmitting material. The adhesive A may enter the gap between the lid portion  24  and the base portion  23 . For example, the adhesive A may enter the inside of each fiber groove  26  (that is, the gap between each optical fiber  10  and each fiber groove  26 ). 
     The lid portion  24  is, for example, a plate-shaped member extending along the XY plane. The lid portion  24  is configured separately from the base portion  23 . The lid portion  24  is configured by, for example, a resin such as polyphenylene sulfide (PPS) or glass. The lid portion  24  may be configured by the same light-transmitting resin as the base portion  23  and the lens portion  22  such as polyetherimide (PEI), polycarbonate (PC), polymethylmethacrylate (PMMA), and polyethersulfone (PES). The lid portion  24  is disposed in the region that faces the base portion  23  in the Z direction, excludes the region facing the recess portion  27  in the Z direction, and faces each fiber groove  26  in the Z direction. In the present embodiment, as illustrated in  FIGS.  1  and  3   , an opening  23   b  is formed at the part of an upper surface  23   a  of the base portion  23  that faces the fiber grooves  26  and the recess portion  27 . Further, the lid portion  24  is disposed only in the region facing the fiber grooves  26  in the opening  23   b . In other words, the lid portion  24  is disposed in the region facing the fiber grooves  26  in the opening  23   b  and is not disposed in the region facing the recess portion  27  in the opening  23   b.    
     As illustrated in  FIG.  3   , the lid portion  24  includes an upper surface  24   b  and a lower surface  24   c  facing each other in the Z direction. The upper surface  24   b  and the lower surface  24   c  are, for example, flat surfaces extending along the XY plane. In one example, the upper surface  24   b  and the lower surface  24   c  are disposed parallel to each other along the Z direction. The upper surface  24   b  faces the side opposite to the base portion  23  in the Z direction. The lower surface  24   c  faces the base portion  23  (specifically, the fiber grooves  26 ) in the Z direction. The upper surface  24   b  of the lid portion  24  is flush with, for example, the upper surface  23   a  of the base portion  23 . The upper surface  24   b  of the lid portion  24  and the upper surface  23   a  of the base portion  23  configure an upper surface  20   a  of the ferrule  20  (see  FIG.  1   ). The upper surface  20   a  configures a part of the outer surface of the ferrule  20 . The lower surface  24   c  is in contact with each optical fiber  10 . The lower surface  24   c  presses each optical fiber  10  to each fiber groove  26  in the Z direction. As illustrated in  FIG.  3   , it is preferable that the lower surface  24   c  is configured to be in contact with a coating removal portion  13  of the optical fiber  10  and not to be in contact with a coating portion  12  of the optical fiber  10 . As a result, the coating removal portion  13  of each optical fiber  10  can be more reliably brought into contact with each fiber groove  26 . As a result, each optical fiber  10  can be positioned more reliably. 
     The lens portion  22  has, for example, a plate shape extending along the XZ plane. The lens portion  22  is configured integrally with the base portion  23 . Accordingly, the lens portion  22  is configured by the same material as the base portion  23 . As illustrated in  FIGS.  1 ,  2   , and  3 , the lens portion  22  includes a front end surface  22   a  and a rear end surface  22   b  facing each other in the X direction, an upper surface  22   d  connecting the front end surface  22   a  and the rear end surface  22   b  in the X direction, and a plurality of lenses  22   c  provided on the front end surface  22   a . The front end surface  22   a  and the rear end surface  22   b  are, for example, flat surfaces extending along the XY plane. In one example, the front end surface  22   a  and the rear end surface  22   b  are disposed parallel to each other along the X direction. The upper surface  22   d  is, for example, a flat surface extending along the XY plane. The upper surface  22   d  is disposed side by side with the upper surface  23   a  of the base portion  23  and the upper surface  24   b  of the lid portion  24  in the X direction. The upper surface  22   d  is, for example, disposed at the same position as the upper surfaces  23   a  and  24   b  in the Z direction and extends in parallel with the upper surfaces  23   a  and  24   b . The upper surface  22   d  configures the upper surface  20   a  of the ferrule  20  together with the upper surfaces  23   a  and  24   b . The front end surface  22   a  may be inclined with respect to the rear end surface  22   b.    
     Each lens  22   c  is a convex lens protruding forward from the front end surface  22   a . The lenses  22   c  are disposed side by side along the Y direction so as to respectively correspond to the positions of the optical fibers  10  (that is, the positions of the fiber grooves  26 ). Each lens  22   c  faces each optical fiber  10  in the X direction. Each lens  22   c  is optically coupled to each optical fiber  10 . When viewed from the X direction, the optical axis of each lens  22   c  coincides with, for example, the optical axis of each optical fiber  10 . The light emitted from each optical fiber  10  is converted into parallel light (that is, collimated light) by each lens  22   c  and then incident on the optical connector of the connection counterpart. The optical axis of each lens  22   c  and the optical axis of each optical fiber  10  may be deviated from each other. 
     Each optical fiber  10  is supported by each fiber groove  26 . As illustrated in  FIG.  2   , each optical fiber  10  is disposed so as to correspond to each fiber groove  26 . In other words, each optical fiber  10  extends along the X direction and is arranged along the Y direction. The optical axis direction of each optical fiber  10  coincides with the X direction. As illustrated in  FIG.  3   , each optical fiber  10  includes a tip surface  11 , the coating removal portion  13  including the tip surface  11 , and the coating portion  12  disposed on the side opposite to the tip surface  11  with the coating removal portion  13  interposed therebetween in the X direction. 
     The tip surface  11  is positioned at the tip of each optical fiber  10  closer to the lens portion  22  in the X direction. The tip surface  11  is, for example, slightly inclined (for example, approximately 8°) with respect to the YZ plane perpendicular to the X direction. The core of each optical fiber  10  is exposed from the tip surface  11 . The coating removal portion  13  is the part of each optical fiber  10  where a predetermined length of coating is removed from the tip surface  11 . In the coating removal portion  13 , the cladding of each optical fiber  10  is exposed. The coating portion  12  is a coating-remaining part. The diameter of the coating portion  12  is larger than the diameter of the coating removal portion  13  and is, for example, 250 μm. 
     The coating removal portion  13  has a tip part  13   a  including the tip surface  11  and an intermediate part  13   b  positioned between the tip part  13   a  and the coating portion  12  in the X direction. The tip part  13   a  is thicker than the intermediate part  13   b . In other words, a maximum outer diameter d 1  of the tip part  13   a  is larger than a maximum outer diameter d 2  of the intermediate part  13   b  (see  FIG.  4    to be described later). The maximum outer diameter d 1  of the tip part  13   a  is, for example, 0.2 μm to 10 μm larger than the maximum outer diameter d 2  of the intermediate part  13   b . The tip surface  11  is formed by laser cutting as will be described later. At the time of this laser cutting, the tip part  13   a  including the tip surface  11  becomes thick by the heat of the laser being applied to the tip part  13   a . As a result, the tip part  13   a  becomes thicker than the intermediate part  13   b.    
     As illustrated in  FIG.  3   , the tip part  13   a  of the coating removal portion  13  is disposed in the recess portion  27 . The intermediate part  13   b  of the coating removal portion  13  is disposed on the fiber groove  26 . The coating portion  12  is disposed on the step portion  28 . The step portion  28  is disposed at a position that does not interfere with the coating portion  12  in a state where the intermediate part  13   b  is disposed on the fiber groove  26 . In the example illustrated in  FIG.  3   , the step portion  28  is disposed at a position separated from the coating portion  12  in the Z direction. The depth of the step portion  28  in the Z direction may be deeper than the depth of the bottom portion  26   a  of the fiber groove  26  such that the step portion  28  does not interfere with the coating portion  12 . The step portion  28  may be disposed at a position in contact with the coating portion  12  in the Z direction. 
     A coating thickness-attributable step surface S is formed between the coating removal portion  13  and the coating portion  12  due to the thickness of the coating. The step surface S faces the step portion  28  in the X direction. In the example illustrated in  FIG.  3   , the step surface S abuts against the step portion  28  in the X direction. When each optical fiber  10  is placed on the base portion  23 , the position of the tip surface  11  of each optical fiber  10  with respect to the base portion  23  can be defined by the step surface S between the coating removal portion  13  and the coating portion  12  abutting against the step portion  28  in the X direction. The intermediate part  13   b  of the coating removal portion  13  is supported by the fiber groove  26 . The intermediate part  13   b  is, for example, in contact with each of the pair of surfaces configuring the fiber groove  26  and is separated from the bottom portion  26   a  of the fiber groove  26  in the Z direction. In other words, in the YZ cross section of the fiber groove  26  illustrated in  FIG.  5 B , the intermediate part  13   b  indicated by an inscribed circle C 3  is in two-point contact with the pair of surfaces configuring the fiber groove  26 . Further, in a state where the lid portion  24  is disposed on the intermediate part  13   b , in the YZ cross section of the fiber groove  26  illustrated in  FIG.  5 B , the intermediate part  13   b  indicated by the inscribed circle C 3  is in three-point contact with the pair of surfaces and the lid portion  24 . The intermediate part  13   b  is held by the pair of surfaces and the lid portion  24 . The inscribed circle C 3  illustrated in  FIG.  5 B  is a virtual circle inscribed in the pair of surfaces configuring the fiber groove  26  and coincides with the outline of the intermediate part  13   b . Accordingly, in  FIG.  5 B , the position of the intermediate part  13   b  can be indicated by the inscribed circle C 3 . 
       FIG.  4    is an enlarged cross-sectional view of the vicinity of the tip part  13   a  of  FIG.  3   . As illustrated in  FIG.  4   , the tip part  13   a  is accommodated in the recess portion  27 . The tip part  13   a  being accommodated in the recess portion  27  means a state where at least a part of the tip part  13   a  is disposed in the recess portion  27 . The shape of the recess portion  27  is set in view of the thickness of the tip part  13   a . The bottom surface  27   a  of the recess portion  27  is disposed at a position that does not interfere with the tip part  13   a  in a state where the intermediate part  13   b  is placed on the fiber groove  26 . As illustrated in  FIG.  4   , the bottom surface  27   a  of the recess portion  27  is, for example, disposed at a position separated from the tip part  13   a  in the Z direction. 
     The bottom surface  27   a  of the recess portion  27  may be disposed at a position in contact with the tip part  13   a . A width L 2  of the recess portion  27  in the X direction is set to be larger than a length L 1  of the tip part  13   a . The length L 1  of the tip part  13   a  is, for example, 200 μm or more and 300 μm or less. The width L 2  of the recess portion  27  is, for example, 400 μm or more and 500 μm or less. 
     In the recess portion  27 , the tip surface  11  of each optical fiber  10  is, for example, separated from the rear end surface  22   b  of the lens portion  22  in the X direction. The position of the tip surface  11  in the recess portion  27  can be adjusted by adjusting the length of the coating removal portion  13  in the X direction, that is, the distance between the step surface S and the tip surface  11  in the X direction with the step surface S between the coating portion  12  and the coating removal portion  13  abutting against the step portion  28 . The length of the coating removal portion  13  in the X direction can be accurately adjusted by adjusting the cutting position at the time of the laser cutting. By adjusting the length of the coating removal portion  13  in the X direction, the position of the tip surface  11  in the recess portion  27  can be set to be separated from the rear end surface  22   b  of the lens portion  22 . The tip surface  11  does not necessarily have to be separated from the rear end surface  22   b  and may be in contact with the rear end surface  22   b.    
     Referring back to  FIG.  1   , the upper surface  20   a  of the ferrule  20  includes a pair of grooves  31  serving as references for measuring the positions of the lens  22   c  and the positions of the fiber grooves  26  that are viewed from the X direction. The grooves  31  extend along the X direction in the upper surface  20   a  and are disposed side by side along the Y direction. The YZ cross section of each groove  31  has, for example, a V shape opening upward (that is, on the side opposite to the base portion  23  with respect to the lid portion  24  in the Z direction) in the Z direction (see  FIGS.  5 A and  5 B ). The tip part of this V shape (that is, the bottom portion of the V groove) may be rounded. 
     Each groove  31  extends over the X direction so as to connect both ends of the upper surface  20   a  in the X direction. In other words, each groove  31  continuously extends along the X direction over the rear end of the upper surface  23   a  of the base portion  23  from the front end of the upper surface  22   d  of the lens portion  22  in the upper surface  20   a . The grooves  31  are, for example, disposed side by side in both end portions of the upper surface  20   a  in the Y direction. Each groove  31  is, for example, disposed at a position where the fiber grooves  26  are interposed in the Y direction when viewed from the Z direction. 
       FIG.  5 A  is a front view illustrating the ferrule  20  that is viewed from the front side in the X direction.  FIG.  5 B  is a rear view illustrating the ferrule  20  that is viewed from the rear side in the X direction.  FIG.  5 B  illustrates the ferrule  20  in which each optical fiber  10  is yet to be placed in each fiber groove  26 , in which the base portion  23  and the lid portion  24  in the vicinity of each fiber groove  26  are illustrated as YZ cross sections. As described above, each groove  31  extends over the X direction in the upper surface  20   a . Accordingly, as illustrated in  FIG.  5 A , when the ferrule  20  is viewed from the front side in the X direction, the front end of each groove  31  can be visually recognized in the upper surface  22   d  of the lens portion  22 . Meanwhile, as illustrated in  FIG.  5 B , when the ferrule  20  is viewed from the rear side in the X direction, the rear end of each groove  31  can be visually recognized in the upper surface  23   a  of the base portion  23 . Accordingly, the position of the rear end of each fiber groove  26  and the position of each lens  22   c  can be measured with reference to the position of each groove  31  viewed from the X direction. 
     In measuring the positions of lens  22   c  with reference to the position of each groove  31 , the front end surface  22   a  of the lens portion  22  is imaged from the front side. In the captured image, the line connecting a center position P 1  of the inscribed circle inscribed in the pair of surfaces configuring one groove  31  and the center position P 1  of the inscribed circle inscribed in the pair of surfaces configuring the other groove  31  is defined as the Y axis, and the line orthogonal to the Y axis and starting from the midpoint of the line connecting the two center positions P 1  and P 1  is defined as the Z axis (see  FIG.  5 A ). Then, in the YZ plane indicated by the YZ axes, a center position (that is, an optical axis position) P 2  of the lens  22   c  with respect to the center position P 1  of each groove  31  is measured. 
     The main body portion  21  is imaged from the rear side in measuring the position of the rear end of each fiber groove  26  with reference to the position of each groove  31 . In the captured image, as in the above, the line connecting the center position P 1  of one groove  31  and the center position P 1  of the other groove  31  is defined as the Y axis, and the line orthogonal to the Y axis and starting from the midpoint of the line connecting the two center positions P 1  and P 1  is defined as the Z axis (see  FIG.  5 B ). Then, in the YZ plane indicated by the YZ axes, a center position P 3  of the inscribed circle C 3  inscribed in the pair of surfaces configuring the fiber groove  26  is measured with respect to the center position P 1  of each groove  31 . In this manner, by comparing the center position P 2  of each lens  22   c  with the center position P 3  of each fiber groove  26  with reference to the center position P 1  of each groove  31 , the amount of eccentricity between the center position P 2  of each lens  22   c  and the center position P 3  of each fiber groove  26  can be obtained. 
     In the present embodiment, each fiber groove  26  can be visually recognized from the rear side of the main body portion  21  since the base portion  23  is configured by a light-transmitting resin (that is, a transparent resin). Accordingly, the center position P 3  of each fiber groove  26  can be measured in an image in which the main body portion  21  is imaged from the rear side. On the other hand, in a case where the main body portion  21  is configured by an opaque resin, the center position P 3  of each fiber groove  26  can be measured by, for example, cutting the main body portion  21  in the YZ cross section at the position of the tip of each fiber groove  26 . Each groove  31  does not have to connect both ends of the upper surface  20   a  in the X direction. In other words, each groove  31  may extend in the X direction to a position on the upper surface  20   a  that does not reach both ends in the X direction. Even in such a case, regardless of whether the base portion  23  is configured by a transparent resin or an opaque resin, the center position P 1  of each groove  31  can be measured in the same manner as the measurement of the center position P 3  of each fiber groove  26 . 
     In measuring the center position of the front end of each fiber groove  26  with reference to the center position P 1  of each groove  31 , the center position of the front end of each fiber groove  26  can be measured with respect to the center position P 1  of each groove  31  by measuring the height profiles of each fiber groove  26  and each groove  31  from the upper surface  20   a  of the ferrule  20  using, for example, a contact meter or a laser displacement meter. Accordingly, by comparing the center position P 2  of each lens  22   c  with the center position of the front end of each fiber groove  26  with reference to the center position P 1  of each groove  31 , the amount of eccentricity between the center position P 2  of each lens  22   c  and the center position of the front end of each fiber groove  26  can be obtained. 
     A method for manufacturing the optical connector  1  described above will be described below with reference to  FIGS.  6 A,  6 B,  7 A,  7 B , and  7 C.  FIG.  6 A  is a cross-sectional view illustrating the method for manufacturing the optical connector  1  according to the present embodiment.  FIG.  6 B  is a cross-sectional view illustrating the step subsequent to  FIG.  6 A .  FIG.  7 A  is a cross-sectional view illustrating the step subsequent to  FIG.  6 B .  FIG.  7 B  is a cross-sectional view illustrating the step subsequent to  FIG.  7 A .  FIG.  7 C  is a cross-sectional view illustrating the step subsequent to  FIG.  7 B . 
     First, as illustrated in  FIG.  6 A , each optical fiber  10  having the coating portion  12  and the coating removal portion  13  is prepared. Further, the ferrule  20  having the base portion  23  integrated with the lens portion  22  and the lid portion  24  separate from the base portion  23  is prepared. The coating removal portion  13  can be formed by, for example, a method by which a coating is peeled off using a blade of metal or the like. Alternatively, the coating removal portion  13  may be formed by a chemical method such as decomposing and removing a coating with hot concentrated sulfuric acid. 
     Next, as illustrated in  FIG.  6 B , the tip surface  11  is formed by laser-cutting the coating removal portion  13 . Here, the coating removal portion  13  is laser-cut such that the tip surface  11  is slightly inclined (for example, approximately 8°) with respect to the YZ plane. At this time, as described above, the tip part  13   a  becomes thick by the heat of the laser being applied to the tip part  13   a  including the tip surface  11 . As a result, the tip part  13   a  becomes thicker than the intermediate part  13   b  of the coating removal portion  13 . 
     Next, as illustrated in  FIG.  7 A , each optical fiber  10  is disposed on the base portion  23  of the ferrule  20 . Here, the coating portion  12  is disposed on the step portion  28 , the intermediate part  13   b  of the coating removal portion  13  is disposed on the fiber groove  26 , and the tip part  13   a  of the coating removal portion  13  is disposed in the recess portion  27 . Then, the step surface S between the coating portion  12  and the coating removal portion  13  is caused to abut against the step portion  28  of the base portion  23  in the X direction. As a result, the X-direction position of the tip surface  11  in the recess portion  27  is defined. In the present embodiment, the position of the tip surface  11  in the X direction is set to a position separated in the X direction from the rear end surface  22   b  of the lens  22   c.    
     Next, as illustrated in  FIG.  7 B , the adhesive A is injected into the recess portion  27 . As a result, the inside of the recess portion  27  is embedded by the adhesive A. Next, as illustrated in  FIG.  7 C , the lid portion  24  of the ferrule  20  is disposed on each optical fiber  10 . Specifically, the lid portion  24  is disposed only in the region facing the fiber groove  26  via each optical fiber  10  in the opening  23   b  of the base portion  23 . At this time, the adhesive A injected in the recess portion  27  also spreads to the gap between the lid portion  24  and each optical fiber  10 . By curing the adhesive A in this state, each optical fiber  10  is fixed to the base portion  23  and the lid portion  24 . The optical connector  1  is obtained through the above process. 
     In the optical connector  1 , the ferrule  20 , and the method for manufacturing the optical connector  1  according to the present embodiment described above, the base portion  23  of the ferrule  20  includes the recess portion  27  between the fiber grooves  26  and the lens portion  22 . By the recess portion  27  being provided between the fiber grooves  26  and the lens portion  22  as described above, it is possible to ensure a space that allows the tip part  13   a  to become thick in the base portion  23 . Accordingly, in mounting each optical fiber  10  on the ferrule  20 , on condition that the intermediate part  13   b  is placed in each fiber groove  26  such that the thickened tip part  13   a  is accommodated in the recess portion  27 , each optical fiber  10  can be easily mounted on the ferrule  20  without being hindered by the thickness of the tip part  13   a . Further, in the present embodiment, only the thickness of the tip part  13   a  can be released to the recess portion  27 , and thus it is not necessary to increase the width of each fiber groove  26  more than necessary in accordance with the thickness of the tip part  13   a . As a result, a situation in which the clearance between each optical fiber  10  and each fiber groove  26  expands can be suppressed and a positional deviation of each optical fiber  10  can be suppressed. 
     In the present embodiment, the tip surface  11  is inclined with respect to a plane perpendicular to the X direction. As a result, it is possible to suppress return light incidence on each optical fiber  10  on the tip surface  11  of each optical fiber  10 . 
     In the present embodiment, each fiber groove  26  supports the intermediate part  13   b  of each optical fiber  10 . The recess portion  27  accommodates the tip part  13   a  of each optical fiber  10 . When the tip surface  11  of the coating removal portion  13  is formed by laser cutting, the tip part  13   a  near the tip surface  11  is likely to become thick. Therefore, when optical fibers  10  are mounted on the ferrule  20 , the above effect is suitably achieved by placing each optical fiber  10  in each fiber groove  26  such that the thickened tip part  13   a  is accommodated in the recess portion  27 . 
     In the present embodiment, the width L 2  of the recess portion  27  in the X direction is larger than the length L 1  of the tip part  13   a  in the X direction. As a result, a configuration in which the recess portion  27  accommodates the tip part  13   a  of each optical fiber  10  can be realized more reliably. 
     In the present embodiment, the recess portion  27  is a linear groove extending along the Y direction so as to connect the region between each fiber groove  26  and the lens portion  22  in the X direction. As a result, the shape of the recess portion  27  is simplified as compared with a case where the recess portion  27  is formed for each fiber groove  26 , and thus the ferrule  20  can be manufactured with ease. 
     In the present embodiment, the bottom surface  27   a  of the recess portion  27  is separated from the tip part  13   a  in the Z direction. As a result, it is possible to more reliably ensure the space that allows the tip part  13   a  to become thick in the base portion  23 . 
     In the present embodiment, the lid portion  24  is disposed in the region that faces the base portion  23 , excludes the region facing the recess portion  27 , and faces each fiber groove  26 . In this configuration, a positional deviation of each optical fiber  10  can be effectively suppressed by pressing each optical fiber  10  into each fiber groove  26  with the lid portion  24 . Further, since the lid portion  24  is not disposed in the region facing the recess portion  27 , a situation in which the thickness of the tip part  13   a  in the recess portion  27  hinders pressing each optical fiber  10  into each fiber groove  26  with the lid portion  24  can be suppressed. 
     In the present embodiment, the adhesive A for fixing the optical fibers  10  to the base portion  23  is provided in the recess portion  27 . A positional deviation of each optical fiber  10  can be effectively suppressed by fixing each optical fiber  10  to the base portion  23  with the adhesive A. 
     In the present embodiment, the step surface S formed between the coating portion  12  and the coating removal portion  13  abuts against the step portion  28  in the X direction. By causing the step surface S between the coating portion  12  and the coating removal portion  13  to abut against the step portion  28  in the X direction, the position of the tip surface  11  in the recess portion  27  can be adjusted. As a result, the position of the tip surface  11  can be defined at a position that does not abut against the lens portion  22 , and thus it is possible to suppress the occurrence of problems such as tilting, warping, and breakage of each optical fiber  10  attributable to the tip surface  11  abutting against the lens portion  22 . As a result, the occurrence of a positional deviation of each optical fiber  10  can be effectively suppressed. 
     In the present embodiment, the upper surface  20   a  of the ferrule  20  includes the pair of grooves  31  serving as references for measuring the center position P 2  of each lens  22   c  and the center position P 3  of each fiber groove  26  that are viewed from the X direction. As a result, the amount of eccentricity between the center position P 2  of the lens  22   c  and the center position P 3  of the fiber groove  26  can be measured by measuring the center position P 2  of each lens  22   c  with respect to the center position P 1  of each groove  31  at the time of viewing from the front side and the center position P 3  of each fiber groove  26  with respect to the center position P 1  of each groove  31  at the time of viewing from the rear side. 
     In the present embodiment, the adhesive A is injected into the recess portion  27 , and then the lid portion  24  is disposed so as to face the base portion  23  with each optical fiber  10  interposed therebetween. By disposing the lid portion  24  on the plurality of fiber grooves  26  after injecting the adhesive A into the recess portion  27  in this manner, the adhesive A can be spread not only in the recess portion  27  but also to the region between the lid portion  24  and the plurality of optical fibers  10 . As a result, a positional deviation of each optical fiber  10  with respect to the ferrule  20  can be effectively suppressed. 
     The optical connector, the ferrule, and the optical connector manufacturing method of the present disclosure are not limited to the embodiment described above, and various other modifications are possible. For example, in the embodiment described above, the configuration of the ferrule can be changed as appropriate. For example, in the embodiment described above, the recess portion is provided so as to extend along the Y direction such that connection is provided between each fiber groove and the lens portion. However, the recess portion may also be provided for each fiber groove. The XZ cross section and the YZ cross section of the recess portion are not limited to a rectangular shape and may have another shape such as a semicircular shape and a trapezoidal shape. The YZ cross section of each fiber groove is not limited to a V shape and may have another shape such as a semicircular shape and a rectangular shape. The YZ cross section of each groove serving as a reference for measuring the position of each lens and the position of each fiber groove is not limited to a V shape and may have another shape such as a semicircular shape and a rectangular shape. 
     The ferrule may be formed with a pair of guide pin insertion holes into which a pair of guide pins are respectively inserted. In this case, the pair of guide pin insertion holes may extend rearward along the X direction from the position where each lens on the front end surface of the lens portion is sandwiched in the Y direction. With end portions of the pair of guide pins respectively inserted in the pair of guide pin insertion holes, the ferrule and a connection counterpart ferrule can be aligned by the other end portions of the pair of guide pins being respectively inserted into a pair of guide pin insertion holes formed in the connection counterpart ferrule. 
     REFERENCE SIGNS LIST 
       1 : optical connector,  10 : optical fiber,  11 : tip surface,  12 : coating portion,  13 : coating removal portion,  13   a : tip part,  13   b : intermediate part,  20 : ferrule,  20   a : upper surface,  21 : main body portion,  21   a : front end surface,  22 : lens portion,  22   a : front end surface,  22   b : rear end surface,  22   c : lens,  22   d : upper surface,  23 : base portion,  23   a : upper surface,  23   b : opening,  24 : lid portion,  24   b : upper surface,  24   c : lower surface,  26 : fiber groove,  26   a : bottom portion,  27 : recess portion,  27   a : bottom surface,  28 : step portion,  31 : groove, A: adhesive, C 3 : inscribed circle, d 1 , d 2 : maximum outer diameter, L 1 : length, L 2 : width, P 1 , P 2 , P 3 : center position, S: step surface, T: tape fiber.