Patent Publication Number: US-9429717-B2

Title: Ferrule and ferrule with optical fiber

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application of Ser. No. 12/878,502, filed on Sep. 9, 2010, whose priority is claimed on Japanese Patent Application No. 2010-148288 filed on Jun. 29, 2010, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a ferrule mounted to a front end of an optical fiber in order to optically connect the optical fiber with an optical part, such as an optical element on a board or a module or an optical fiber mounted on another connector and to a ferrule with an optical fiber. 
     2. Description of the Related Art 
     In recent years, a scheme of fixing an optical fiber so that an optical element, such as a light emitting element (e.g., a semiconductor laser) or a light receiving element (e.g., a photo diode) mounted on a board is optically connected with the optical fiber wired along the board and having an optical connector assembled with a front end thereof has been widely used. 
     When the optical fiber is optically connected with an optical element or another optical fiber, deviation of an axial direction of the optical fiber increases connection loss. Accordingly, it is necessary to position an axis of the optical fiber in order to prevent the increase of the connection loss. 
     For example, an optical path changing member having an optical-fiber insertion hole into which an optical fiber is inserted, and a front-end arrangement space communicating with the optical fiber insertion hole is described in Japanese Unexamined Patent Application, First Publication No. 2009-104096. In the optical path changing member, a front end of the optical fiber is disposed in the front-end arrangement space, which is filled with adhesive to fix the optical fiber to a predetermined position. 
     Thus, as in the case that an intermediate portion of the optical fiber (an optical fiber portion disposed in the insertion hole) is positioned and the front end of the optical fiber is disposed in the front-end arrangement space to adhere and fix the optical fiber, the adhesive is shrunk when cured, and thus force is applied to the optical fiber in the front-end arrangement space in the lateral direction. As a result, the front end portion of the optical fiber moves and an output direction deviates. Even when a positioning mechanism for positioning the front end of the optical fiber is formed in a ferrule in order to avoid such a problem, it is necessary to precisely match positions of the positioning mechanism for positioning the front end portion and a positioning mechanism for positioning the intermediate portion, making it difficult to mold the ferrule. 
     The present invention has been achieved in view of the above circumstances, and it is an object of the present invention to provide a ferrule capable of being easily molded and reducing a deviation of an output direction. 
     SUMMARY OF THE INVENTION 
     A ferrule according to an embodiment of the present invention is mounted to a front end of an optical fiber for optically connecting the optical fiber to another optical part. The ferrule includes: a positioning mechanism for positioning an intermediate portion of the optical fiber; and a recess having at least a first inner wall for allowing the front end of the optical fiber portion positioned by the positioning mechanism to protrude, and a second inner wall opposite to the first inner wall. The distance between the first inner wall and the second inner wall is less than or equal to four times the outer diameter of the optical fiber. Adhesive is filled into the recess and cured in a state in which the optical fiber protrudes from the first inner wall and substantially contacts the second inner wall to fix the optical fiber. 
     The ferrule may be a resin that is transparent to a used wavelength. 
     The recess may have an adhesive application slot with an opening larger than the distance between the first inner wall and the second inner wall. 
     The adhesive application slot may have an inclined surface at least one of the first inner wall and the second inner wall. 
     The ferrule may further include a reflecting portion for changing an optical path between the front end of the optical fiber positioned by the positioning mechanism and the other optical part. 
     In a ferrule with an optical fiber according to an embodiment of the present invention, the optical fiber is fixed to the ferrule. 
     An optical connector according to an embodiment of the present invention includes the ferrule. 
     A ferrule according to an embodiment of the present invention is a ferrule for optically connecting an optical fiber to an optical part, and the ferrule includes a boot accommodating hole which is configured to accommodate a boot attached to the optical fiber and which is formed on a rear end surface of the ferrule, an optical fiber hole which is configured to position an intermediate portion of the optical fiber having a predetermined outer diameter and which extends forward from a front end of the boot accommodating hole, and a recess configured for an adhesive to be disposed therein and comprising a first inner wall from which a front end of the optical fiber positioned by the optical fiber hole is protrudable, and a second inner wall opposite to the first inner wall. The second inner wall is configured to be abutted by almost an entire area of a front end surface of the optical fiber, a bottom of the recess is positioned lower than a lower edge of the front end of the optical fiber that protruded from the first inner wall, the recess comprises an adhesive application slot with an opening larger than the distance between the first inner wall and the second inner wall, the first inner wall comprising a first inclined surface, and the second inner wall comprising a second inclined surface which does not reach a front face of the ferrule, and a distance between the first inner wall and the second inner wall is more than or equal to half of the outer diameter of the optical fiber and less than or equal to four times the outer diameter of the optical fiber. 
     In addition, the ferrule may be formed of a resin that is transparent to a wavelength of light transmitted through the optical fiber. 
     The ferrule may further comprises a reflecting portion reflecting light on an optical path between the front end of the optical fiber positioned by the optical fiber hole and the optical part. 
     Moreover, an optical connector for optically connecting an optical fiber to an optical part according to an embodiment of the present invention includes an optical fiber and a ferrule. The ferrule includes a boot accommodating hole which is configured to accommodate a boot attached to the optical fiber and which is formed on a rear end surface of the ferrule, an optical fiber hole which is configured to position at least an intermediate portion of the optical fiber and which extends forward from a front end of the boot accommodating hole, a recess comprising a first inner wall from which a front end of the optical fiber protrudes, and a second inner wall opposite to the first inner wall, and an adhesive disposed in the recess and a surrounding portion of the optical fiber protruding from the first inner wall. A bottom of the recess is positioned lower than a lower edge of the front end of the optical fiber that protruded from the first inner wall, the recess comprises an adhesive application slot with an opening larger than the distance between the first inner wall and the second inner wall, the first inner wall comprising a first inclined surface, and the second inner wall comprising a second inclined surface which does not reach a front face of the ferrule, a distance between the first inner wall and the second inner wall is more than or equal to half of the outer diameter of the optical fiber and less than or equal to four times the outer diameter of the optical fiber, and substantially an entire area of a front end surface of the optical fiber abuts the second inner wall. 
     In the ferrule, a plurality of the optical fibers may be fixed, and the reflecting portion may include a recessed reflecting surface and may be provided to each of the plurality of the optical fibers. 
     In the ferrule, a plurality of the reflecting portions may be arranged in an arrangement direction of the plurality of the optical fibers. 
     In addition, the ferrule may include a lens located on an extension line of the optical fiber. 
     Moreover, in the optical connector, the ferrule may include a lens located on an extension line of the optical fiber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a plan view showing a ferrule with an optical fiber according to an embodiment of the present invention. 
         FIG. 1B  is a cross-sectional view of the ferrule with an optical fiber taken along a line I-I of  FIG. 1A  according to the embodiment. 
         FIG. 2A  is a plan view showing an example of a ferrule with an optical fiber in a comparative example. 
         FIG. 2B  is a cross-sectional view of the ferrule with an optical fiber taken along a line II-II of  FIG. 2A  in the comparative example. 
         FIG. 3  is a diagram for explaining position deviation of an optical fiber due to shrinkage when adhesive is cured. 
         FIG. 4  is a plan view showing a ferrule according to another embodiment of the present invention. 
         FIG. 5A  is a cross-sectional view of a ferrule taken along a line IV-IV of  FIG. 4  in the embodiment. 
         FIG. 5B  is a cross-sectional view of a ferrule taken along a line V-V of  FIG. 5A  in the embodiment. 
         FIG. 6  is a cross-sectional view showing an example in which an optical fiber is optically connected with an optical element on a board using the ferrule shown in  FIG. 4 . 
         FIG. 7A  is a plan view showing a ferrule in which an adhesive application slot with an inclined surface is formed in an embodiment. 
         FIG. 7B  is a cross-sectional view of the ferrule taken along a line VII-VII of  FIG. 7A  in the embodiment. 
         FIG. 8A  is a plan view showing a ferrule with a convex lens in an embodiment. 
         FIG. 8B  is a cross-sectional view of the ferrule taken along a line VIII-VIII of  FIG. 8A  in the embodiment. 
         FIG. 9A  is a plan view showing a ferrule with a recessed reflecting surface in an embodiment. 
         FIG. 9B  is a cross-sectional view of the ferrule taken along a line IX-IX of  FIG. 9A  in the embodiment. 
         FIG. 10A  is a cross-sectional view showing an example of an optical fiber hole. 
         FIG. 10B  is a cross-sectional view showing an example of a V-shaped groove; 
         FIG. 10C  is a cross-sectional view showing an example of a U-shaped groove; 
         FIG. 11  is a cross-sectional view showing an example of a ferrule including a body with a V-shaped groove and a pressing lid. 
         FIG. 12A  is a cross-sectional view showing an example of a state of an optical connection using the ferrule in the example. 
         FIG. 12B  is a cross-sectional view showing an example of a state of an optical connection using the ferrule in the comparative example. 
         FIG. 13  is a graph showing an example of the result of measuring a standard deviation of a beam angle α according to the embodiment. 
         FIG. 14  is a perspective view showing a ferrule of a modified example. 
         FIG. 15  is a cross-sectional view partially showing the ferrule shown in  FIG. 14  into which the inserted optical fiber is inserted. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. 
     As shown in  FIGS. 1A and 1B , a ferrule  1  of the present embodiment is mounted to a front end of an optical fiber  2  and used to optically connect the optical fiber  2  with another optical part. This ferrule  1  has a positioning mechanism  7  for positioning an intermediate portion of the optical fiber  2 , and a recess  6 . This recess  6  has a first inner wall  6   b  for allowing a front end portion of the optical fiber  2  positioned by the positioning mechanism  7  to protrude, and a second inner wall  6   a  opposite to the first inner wall  6   b . In the ferrule  1 , adhesive  4  is filled into the recess  6  and cured to fix the optical fiber  2  in a state in which the optical fiber  2  protrudes from the first inner wall  6   b  and the front end of the optical fiber  2  substantially contacts the second inner wall  6   a.    
     This ferrule  1  may be used as a ferrule for an optical connector. The optical connector includes a ferrule  1 , and a structure (e.g., a housing, a latch, a screw, a spring, an arm, or an engagement pin) for mechanically connecting the ferrule  1  to another optical part, or a board or a module having the other optical part mounted thereon. 
     The optical fiber  2  is, for example, an optical fiber core wire, a single-core optical fiber core wire led at a front end of a multi-core optical fiber tape core wire, an optical fiber strand, or a bare optical fiber. In the example shown in  FIG. 1B , an optical fiber  2  has a coating  3  provided therearound. The coating  3  is removed (led) from the front end portion of the optical fiber  2  disposed in the positioning mechanism  7  and the recess  6 . In this disclosure, the optical fiber portion which is disposed in the positioning mechanism  7  and from which the coating  3  has been removed is referred to as an intermediate portion of the optical fiber  2 . It is preferable that a front end face  2   a  of the optical fiber  2  is formed perpendicular to a longitudinal direction of the optical fiber  2 . 
     The type of the optical fiber is not particularly limited, and may be any of a silica optical fiber, a plastic optical fiber, a multi-mode optical fiber, a single-mode optical fiber or the like. 
     Examples of the positioning mechanism  7  for positioning the intermediate portion of the optical fiber  2  include an optical fiber hole  22   a  shown in  FIG. 10A , a V-shaped groove  22   b  shown in  FIG. 10B , and a U-shaped groove  22   c  shown in  FIG. 10C .  FIGS. 10A to 10C  show cross-sectional surfaces perpendicular to the longitudinal directions of the positioning mechanism  7  and the optical fiber  12 . 
     The ferrule  1  may be a single-core ferrule to which one optical fiber is mounted or a multi-core ferrule to which two or more optical fibers are mounted. The positioning mechanism  7  has an opening at the first inner wall  6   b  so that the optical fiber  2  can protrude into the recess  6 . When the optical fiber  2  is inserted into the positioning mechanism  7 , gas such as air inside the positioning mechanism  7  is discharged into the recess  6 . This allows the optical fiber  2  to be smoothly inserted even when a difference between an inner diameter of the optical fiber hole  22   a  and an outer diameter of the optical fiber  2  is small. 
     In the present embodiment, the ferrule  1  includes a ferrule body  5  integrally molded using a transparent material. The ferrule body  5  may be formed of transparent resin, such as polycarbonate, modified polyolefin, epoxy resin, and polyetherimide (PEI). 
     The ferrule body  5  may be manufactured, for example, using resin molding such as injection molding. The shape of the ferrule body  5  is not particularly limited. For example, the shape may be a flat cuboid or the like. 
     To optically connect the optical fiber  2  disposed in the recess  6  to another optical part, the second inner wall  6   a  may be transparent to a used wavelength at least in an adjacent portion opposite to the front end face  2   a  of the optical fiber  2 . In this case, other portions of the ferrule body  5  may be formed of an opaque material. Further, light used for optical connection in the present invention is not limited to visible light. The light may be ultraviolet light or infrared light. The light may be any light having small connection loss allowed for actual use. 
     A reflective index of the material of the ferrule body  5  is not particularly limited. The reflective index of the material may be higher than, lower than, or equal to that of the optical fiber  2 . 
     The recess  6  has an adhesive application slot  6   d  with an upper opening. When the adhesive  4  is filled from the adhesive application slot  6  into the recess  6  and cured, the optical fiber  2  is fixed to the recess  6  by the adhesive  4 . The adhesive  4  may penetrate into the positioning mechanism  7 . Accordingly, even in the positioning mechanism  7 , the intermediate portion of the optical fiber  2  may be fixed to the ferrule  1 . 
     It is preferable that the adhesive  4  is transparent to light and, particularly, has the same reflective index as the core of the optical fiber  2 . It is preferable that the adhesive  4  has an excellent adhesion force with respect to the materials of the ferrule  1  and the optical fiber  2  which are the adherends. Specifically, the adhesive  4  includes thermoset epoxy adhesive, acrylic adhesive, or the like. 
     It is preferable that, prior to filling and curing of the adhesive  4 , the front end face  2   a  of the optical fiber  2  contact (abut) the second inner wall  6   a  of the recess  6  in a state in which the front end face  2   a  of the optical fiber  2  is pressed into the second inner wall  6   a  of the recess  6 , so that there is no clearance between the front end face  2   a  of the optical fiber  2  and the second inner wall  6   a  of the recess  6 . When pressure is applied between the front end face  2   a  of the optical fiber  2  and the second inner wall  6   a , the front end portion of the optical fiber  2  protruding from the first inner wall  6   b  is more stably held in the recess  6 . In this case, it is unnecessary for the optical fiber  2  to contact a bottom portion  6   c  of the recess  6 . When there is a clearance between the front end face  2   a  of the optical fiber  2  and the second inner wall  6   a  and the clearance is filled with the adhesive  4 , the adhesive  4  functions as a reflective-index matching agent. Accordingly, it is possible to suppress light loss. 
     Since the cured adhesive obstructs movement of the optical fiber  2  after the optical fiber  2  is adhered and fixed, it does not matter that the optical fiber  2  is adhered and fixed in a state in which the front end face  2   a  of the optical fiber  2  contacts the second inner wall  6   a  or is close to the second inner wall  6   a  with a clearance therebetween. That is, it is preferable that the direction of the front end of the optical fiber  2  protruding from the first inner wall  6   b  to the recess  6  can be maintained and unchanged between an adhesive filling process and an adhesive curing process. 
     In the present embodiment, a distance L between the first inner wall  6   b  and the second inner wall  6   a  is less than or equal to four times the outer diameter D of the optical fiber  2 . That is, the value of L/D is 4 or less (L/D≦4). 
     When the distance L between the first inner wall  6   b  and the second inner wall  6   a  in the recess  6 A of the ferrule  1 A is excessively greater than the outer diameter D of the optical fiber  2  as shown in  FIG. 2 , a shrinkage  4   a  of the adhesive  4  occurs when the adhesive  4  is cured, and the front end face  2   a  of the optical fiber  2  moves and deviates from a central axis C of the optical fiber  2  positioned by the positioning mechanism  7 , as shown in  FIG. 3 . In this case, a deviation occurs in an output direction of light from the front end of the optical fiber  2  (or an input direction of light to the front end of the optical fiber  2 ), and making it difficult to match positions of optical fiber  2  when the optical fiber  2  is optically connected to another optical part. In particular, when the ferrule includes a member (not shown) for connection with a board or a module having the other optical part mounted thereon, the deviation of the output or input direction of the optical fiber  2  makes it difficult to change and adjust the direction of the entire ferrule. 
     As shown in  FIG. 3 , the shrinkage  4   a  of the adhesive  4  is larger in a central portion of the recess  6 A in the longitudinal direction of the optical fiber  2  (a horizontal direction of the paper), and smaller at the inner walls  6   a  and  6   b  at both sides of the recess that are opposite to each other in the longitudinal direction. Such a phenomenon can be understood that the shrinkage  4   a  is suppressed by interaction between the adhesive  4  and the inner walls  6   a  and  6   b . However, when L/D is great, the movement of the adhesive  4  occurs even in the vicinity of the second inner wall  6   a  due to the shrinkage  4   a  of the central portion. Moreover, a length of the optical fiber  2  protruding as a cantilever from the positioning mechanism  7  increases. Therefore, the front end portion of the optical fiber  2  is bent with failure of resistance against the movement of the adhesive  4 . As a result, it is understood that the direction of the front end portion of the optical fiber  2  deviates. 
     On the other hand, as shown in  FIGS. 1A and 1B , when L/D is 4 or less, the length of the optical fiber protruding from the positioning mechanism  7  is small. Therefore, by the rigidity of the optical fiber  2  itself, the movement of the front end portion of the optical fiber  2  caused by the shrinkage of the adhesive  4  is suppressed to a negligible level. As a result, the direction of the front end of the optical fiber  2  cannot deviate. 
     The lower limit of L/D is not particularly limited, and it is preferable that the distance L between the first inner wall  6   b  and the second inner wall  6   a  is secured to the extent that the adhesive  4  is allowed to be applied into the recess  6 . For example, when the outer diameter D of the optical fiber  2  is 0.125 mm, it is preferable that L is about 0.06 mm or more and L/D is 0.5 or more. 
     When the shrinkage of the adhesive  4  increases, a movement amount of the front end portion of the optical fiber  2  increases. This tends to increase the deviation of the direction of the front end of the optical fiber  2 . Therefore, it is preferable to use the adhesive  4  with a small shrinkage ratio. For example, it is preferable to use adhesive with a shrinkage ratio of 3 to 5% rather than adhesive with a shrinkage ratio of 5 to 10%. When the adhesive applied into the recess  6  of the ferrule  1  has a depth of Z before curing and a depth of Z−ΔZ after curing, the shrinkage ratio of the adhesive can be obtained using the following equation:
 
(shrinkage ratio of adhesive)=(shrinkage amount Δ Z )/(filling depth  Z  before adhesive is cured)×100(%)
 
     According to the ferrule  1  of the present embodiment, the deviation in the output (or input) direction of each optical fiber  2  becomes small. Accordingly, the ferrule  1  of the present embodiment is particularly suitable as a multi-core ferrule in which a plurality of optical fibers  2  are adhered and fixed. 
     In the case of the multi-core ferrule, when connection loss exceeds an allowable range at one of a plurality of optical fibers adhered and fixed to the ferrule, the ferrule with optical fibers is treated as a defective product. Therefore, when distinctly manufacture a ferrule with optical fibers in which connection loss of all the optical fibers is in the allowable range, the effect of the present invention that reduces the directional deviation of the front end of the optical fiber when a plurality of optical fibers are adhered and fixed to the ferrule is more prominent. 
     The ferrule  1  of the present embodiment has advantageous effect about its miniaturization because of its simple structure. For example, the size of the ferrule  1  is not particularly limited, but the ferrule  1 , for example, may be 7 mm long or less and 7 mm wide or less. 
     (Modified Example of Ferrule) 
     Next, a ferrule  101  of a modified example will be described. The ferrule  101  of the modified example is different from the above-described ferrule  1  in that the ferrule  101  includes a lens  108 . Identical reference numerals are used for the elements which are identical to those of the first embodiment, and the explanations thereof are omitted or simplified here. 
       FIG. 14  is a perspective view showing the ferrule  101 .  FIG. 15  is a cross-sectional view partially showing the ferrule  101  into which the optical fiber  2  is to be inserted. 
     The ferrule  101  is formed of a ferrule body  105 . The ferrule body  105  is a single member made of a resin material. As a resin material used to form the ferrule body  105 , polyetherimide, polycarbonate, cyclic olefin copolymer, cyclic olefin polymer, or other transparent polymers may be adopted. Part of the ferrule body  105  which serves as an optical path from the optical fiber  2  to the lens  108  may be only formed of a transparent member. 
     As shown in  FIG. 14 , the ferrule  101  includes a front-end face (connection edge face)  118 , a rear-end face  118 , and a side surface  101   c . The front-end face  118  is to be butt-jointed to a ferrule of the other optical connector (not shown in the figure). The rear-end face  119  is located on the opposite side of the front-end face  118 . The front-end face  118  is located close to the front end face  2   a  of the optical fiber  2 . The side surface  101   c  is located between the front-end face  118  and the rear-end face  119  of the ferrule  101 . 
     As shown in  FIG. 15 , the ferrule  101  includes a positioning mechanism  7  which positions a center portion of the optical fiber  2 . In the positioning mechanism  7 , the optical fiber  2  is located. The optical fiber  2  is fixed to the positioning mechanism  7  by, for example, an adhesive. 
     A recess  106  is provided on the side surface  101   c  of the ferrule  101 . The recess  106  is opened on the side surface  101   c . The recess  106  is communicated with the positioning mechanism  7 . The recess  106  is formed in a rectangular shape in a plan view. The recess  106  has a first inner wall  106   b  for allowing a front end portion of the optical fiber  2  positioned by the positioning mechanism  7  to protrude, and a second inner wall  106   a  opposite to the first inner wall  106   b . The second inner wall  106   a  is positioned between the optical fiber  2  and the lens  108 . The front end face  2   a  of the optical fiber  2  is brought into contact with the second inner wall  106   a.    
     A distance L between the first inner wall  106   b  and the second inner wall  106   a  is less than or equal to four times the outer diameter D of the optical fiber  2 . That is, the value of L/D is 4 or less (L/D≦4). 
     As shown in  FIG. 15 , the recess  106  is filled with an adhesive (refractive index matching material)  4 . As a result, it is possible to prevent the front-end position of the optical fiber  2  from being displaced during use. 
     The ferrule  101  has inclined surfaces  125   a  and  125   b , with an adhesive application slot  106   d  having an opening size increasing toward the side surface  101   c , between inner walls  106   a  and  106   b  of a recess  106  and the side surface  101   c . Accordingly, even when a distance L between the first inner wall  106   b  and the second inner wall  106   a  is small, the adhesive application slot  106   d  can have an increasing opening area above the recess  106 . Accordingly, when the adhesive  4  is applied as drops from above the recess  106 , the adhesive  4  easily enters the recess  106  through the adhesive application slot  106   d.    
     A recess  109  is provided on the front-end face  118  of the ferrule  101 . The recess  109  is depressed with respect to the front-end face  118 . A plurality of lenses  108  are formed on the surface  109   a  that faces forward of the recess  109 . The lenses  108  are accommodated in the recess  109  and do not protrude forward from the front-end face  118 . The lenses  108  are located on the extension lines P of the inserted optical fibers  2 . The lenses  108  are arranged to be optically aligned with corresponding optical fiber insertion holes (optical alignment). 
     The plurality of lenses  108  are molded integrally in one body which serves as part of the ferrule  101 . The lenses  108  collimate light emitted from the front ends of the optical fibers  2 . The lense  108  condenses, on the front end of the optical fiber  2 , light emitted from the other ferrule that is butt-jointed to the ferrule  101 . It is preferable that the focal point of the lens  108  be located on the second inner wall  106   a.    
       FIGS. 4 to 6  shows an example of a ferrule  11  that is suitable for an optical connector used for optical connection with an optical element  17  mounted on a photoelectric conversion module  16 . 
     The ferrule  11  shown in  FIG. 4  includes a ferrule body  20  comprising a positioning mechanism  22  for positioning an intermediate portion of an optical fiber  12 , and a recess  21 . This recess  21  has a first inner wall  21   b  for allowing a front end portion of the optical fiber  12  positioned by the positioning mechanism  22  to protrude, and a second inner wall  6   a  opposite to the first inner wall  21   b.    
     As shown in  FIGS. 5A and 5B , in the ferrule body  20 , a lower surface  20   a  is a bonding surface opposite to the photoelectric conversion module  16 , and the recess  21  is formed at an upper surface  20   b  opposite to the lower surface  20   a . The optical fiber  12  protrudes from a first inner wall  21   b , and adhesive  14  is filled into the recess  21  and cured in a state in which the optical fiber  12  substantially contacts a second inner wall  21   a  to fix the optical fiber  12 . 
     In the present embodiment, a plurality of optical fibers  12  are collectively coated with one coating  13  to form a tape-shaped optical fiber core wire (fiber ribbon). The tape-shaped optical fiber core wire may be inserted into the ferrule  11  together with a boot  15 , as shown in  FIG. 4 . A boot accommodating hole  23  is formed on a rear end surface  20   d  of the ferrule body  20 , and when the optical fiber  12  is inserted into the positioning mechanism  22 , the boot  15  is accommodated in the boot accommodating hole  23 . 
     The boot  15  has a cross-sectional surface of a substantially rectangular cylindrical shape, and has a through hole  15   a  into which the optical fiber is inserted. The boot accommodating hole  23  has a greater cross-sectional area of an opening than the positioning mechanism  22 . The boot accommodating hole  23  has substantially the same width and thickness as the boot  15 . The boot  15  is engaged with the boot accommodating hole  23  by the elastic force thereof. The boot  15  may be securely fixed to the boot accommodating hole  23  by an adhesive (not shown). 
     When a plurality of optical fibers  12  are mounted to the ferrule  11 , the recess  21  communicates with the positioning mechanism  22  for each optical fiber  12  and is formed over an entire arrangement range of the plurality of optical fibers  12  in an arrangement direction of the optical fibers  12  (a vertical direction in  FIG. 4 ). In this case, only if the adhesive  14  is applied into the single recess  21 , all the optical fibers  12  can be adhered and fixed. 
     The recess  21  has inner walls  21   a  and  21   b , a bottom portion  21   c , and an adhesive application slot  21   d , like the recess  6  of the above-described ferrule  1 . Since the structure of the recess  21  and the adhesive  14 , adhering and fixing of the optical fiber  12  in the recess  21  or the like, may be the same as those of the recess  6  and the adhesive  4  of the above-described ferrule  1 , a description thereof will be omitted. 
     As shown in  FIG. 6 , the photoelectric conversion module  16  has an optical element  17  mounted thereon or embedded therein. Examples of the optical element  17  include a light emitting element such as a semiconductor laser (e.g., a laser diode; LD) or a light receiving element such as a photo diode (PD). The photoelectric conversion module  16  is provided on a circuit board (not shown) and has a function for driving the light emitting element based on a control signal from a driving circuit on the circuit board, and a function of delivering an electrical signal output from the light receiving element to a processing circuit on the circuit board. 
     The photoelectric conversion module  16  includes a holder member (not shown) for holding the ferrule  11  having the optical fiber  12  fixed thereto (a ferrule with an optical fiber  10 ). The structure of the holder member is not particularly limited thereto, but may be an arm supported by a spring, latch, pin engagement, magnet or the like. When the ferrule with an optical fiber  10  is held on the photoelectric conversion module  16 , the lower surface  20   a  of the ferrule body  20  is opposite to the optical element  17 . In this case, the optical fiber  12  positioned by the positioning mechanism  22  is disposed in parallel with the circuit board and so on. The positioning mechanism  22  may be in parallel with or inclined with respect to the lower surface  20   a  of the ferrule body  20 . 
     The front face  20   c  of the ferrule body  20  is located on an extended line of an optical path  12   b  to which the front end face  12   a  of the optical fiber  12  disposed in the recess  21  is directed. A reflecting portion  24  for changing optical paths  12   b  and  17   a  between the front end of the optical fiber  12  and the optical element  17  is provided on the front face  20   c . The reflecting portion  24  reflects, from its inner surface, light propagating in the ferrule body  20  based on a difference in reflective index between the ferrule body  20  and an external medium (e.g., air). A metal layer or a resin layer may be provided on the front face  20   c  to improve reflectance. It is preferable that the reflecting portion  24  has high reflectance. 
     The reflecting portion  24  may be, for example, a surface inclined with respect to a longitudinal direction of the optical fiber  12  positioned by the positioning mechanism  22  and to a direction perpendicular to the longitudinal direction. An inclination angle of the reflecting portion  24  is not particularly limited, and when the optical path  12   b  of optical fiber  12  is substantially perpendicular to the optical path  17   a  of the optical element  17  as shown in  FIG. 6 , the inclination angle may be about 45°. 
     In the embodiment shown in  FIG. 6 , the front face  20   c  of the ferrule body  20  is an inclined face formed close to the recess  21  from the lower surface  20   a  to the upper surface  20   b  to be coincident with the inclination angle of reflecting portion  24 . When a plurality of optical fibers  12  are mounted to the ferrule  11 , it is advantageous from a manufacturing viewpoint, e.g., a mold manufacturing cost, to make the reflecting portions  24  corresponding to the respective optical fibers  12  coplanar at the front face  20   c . In the present embodiment, the front face  20   c  formed as the reflecting portion  24  is coplanar over an entire arrangement range of the plurality of optical fibers  12  in an arrangement direction of the optical fibers  12  (a vertical direction in  FIG. 4 ). 
     When the optical element  17  is a light emitting element, the reflecting portion  24  reflects light incident from the lower surface  20   a  toward the front end face  12   a  of the optical fiber  12 . On the other hand, when the optical element  17  is a light receiving element, the reflecting portion  24  reflects light output from the front end face  12   a  of the optical fiber  12  toward the optical element  17  through the lower surface  20   a . When the optical element  17  is a composite element having a light-emitting unit and a light-receiving unit, optical connection may be performed through the reflecting portion  24  in a direction from the optical element  17  to the front end of the optical fiber  12  and a direction from the front end of the optical fiber  12  to the optical element  17 . 
     A ferrule with an optical fiber  10 A shown in  FIGS. 7A and 7B  has inclined surfaces  25   a  and  25   b , with an adhesive application slot  21   d  having an opening size increasing toward an upper surface  20   b , between inner walls  21   a  and  21   b  of a recess  21  and the upper surface  20   b . Accordingly, even when a distance L between the first inner wall  21   b  and the second inner wall  21   a  is small, the adhesive application slot  21   d  can have an increasing opening area above the recess  21 . Accordingly, when the adhesive  14  is applied as drops from above the recess  21 , the adhesive  14  easily enters the recess  21  through the adhesive application slot  21   d . In the present embodiment, the opening size was increased in the longitudinal direction of the optical fiber  12  (a horizontal direction of the paper in  FIG. 7A ). When a smaller number of optical fibers  12  are arranged (there may be one optical fiber, i.e., the ferrule may be a single-core ferrule), the opening size may be increased in a direction perpendicular to the longitudinal direction of the optical fiber  12  (a vertical direction of the paper in  FIG. 7A ) to facilitate the application of the adhesive  14 . 
     The inclined surfaces  25   a  and  25   b  may be provided at least one of the first inner wall  21   b  and the second inner wall  21   a , and may be provided at both of the inner walls  21   a  and  21   b , as shown. An inclination angle of the inclined surfaces  25   a  and  25   b  is about 45° in the shown example, but the angle is not particularly limited. For example, the angle may be 30 to 60°. When the inclined surface  25   a  provided in the second inner wall  21   a  does not reach the front face  20   c  with the reflecting portion  24 , a flat part of the upper surface  20   b  is formed between the inclined surface  25   a  and the front face  20   c , which is advantageous in terms of molding of the ferrule body  20 . 
     An example of the structure in which the opening size of the adhesive application slot  21   d  is larger than the distance L between the first inner wall  21   b  and the second inner wall  21   a  includes a structure in which the above-described inclined surfaces  25   a  and  25   b  are not only formed, but also the entire inner walls  21   a  and  21   b  are curved or inclined, and the size of the recess  21  is gradually increased toward the upper surface in a tapered form. As long as the above-described requirement, L/D≦4, is satisfied, it does not matter that the recess  21  has an opening larger than four times the outer diameter D of the optical fiber  12 , at a height portion above the positioning mechanism  22  in which there is no optical fiber  12 . 
     A ferrule with an optical fiber  10 B shown in  FIGS. 8A and 8B  has a focusing lens  26  on a lower surface  20   a  of a ferrule body  20 . The focusing lens  26  is, for example, a convex lens. This focusing lens  26  is disposed between a reflecting portion  24  and an optical element  17 , and focuses light from the reflecting portion  24  toward the optical element  17 , or vice versa (i.e., from the optical element  17  toward the reflecting portion  24 ) to suppress connection loss. An outer face of the ferrule body  20  may be formed in a convex shape, such that the focusing lens  26  can be integral with the ferrule body  20 . Further, a lens separate from the ferrule body  20  may be fixed to the ferrule body  20 . 
     A concave portion  26   a  may be formed in the lower surface  20   a  of the ferrule body  20  and the focusing lens  26  may be formed in the concave portion  26   a  to prevent the focusing lens  26  from protruding from the lower surface  20   a  of the ferrule body  20  downward. It is preferable that when the depth of the concave portion  26   a  is larger than a protrusion size of the focusing lens  26 , the focusing lens  26  is accommodated inward from the lower surface  20   a  of the ferrule body  20  (in an upper direction of the paper in  FIG. 8B ). 
     When a plurality of optical fibers  12  are fixed to the ferrule body  20  as shown in  FIG. 8A , a focusing lens  26  is provided for each of the optical fibers  12 . In this case, the plurality of focusing lenses  26  are arranged in an arrangement direction of the optical fibers  12 . The concave portion  26   a  may be provided for each focusing lens  26 , or may be formed so that the plurality of focusing lenses  26  are disposed in one concave portion  26   a  as illustrated in  FIG. 8A . The concave portion  26   a  may be a groove portion that is formed in a rectangular shape on the lower surface  20   a.    
     A ferrule with an optical fiber  10 C shown in  FIGS. 9A and 9B  has a reflecting portion  27  with a curved surface provided on a front face  20   c  of a ferrule body  20 . The reflecting portion  27  may be, for example, a recessed reflecting surface and may be a spherical surface or a non-spherical surface. This reflecting portion  27  is located between a front end of the optical fiber  12  and an optical element  17 , and functions as a concave mirror with respect to the front end of the optical fiber  12  and the optical element  17 . 
     Accordingly, it is possible to focus light between the optical fiber  12  and the optical element  17  and suppress connection loss. That is, when the optical element  17  is a light emitting element, the reflecting portion  27  focuses, toward the front end of the optical fiber  12 , light emitted from the optical element  17  to the reflecting portion  27 . On the other hand, when the optical element  17  is a light receiving element, the reflecting portion  27  focuses, toward the optical element  17 , light emitted from the front end of the optical fiber  12  to the reflecting portion  27 . 
     A focal point of the reflecting portion  27  may be located on the front end face  12   a  of the optical fiber  12 , on a light-emitting face of the optical element  17 , or on a light-receiving face of the optical element  17 , with a small deviation allowed. 
     The reflecting portion  27  reflects light propagating inside the ferrule body  20  from its inner surface based on a difference in reflective index between the ferrule body  20  and an external medium (e.g., air). Further, a metal layer or a resin layer may be provided on the front face  20   c  to improve reflectance. It is preferable that the reflecting portion  27  has high reflectance. The reflecting portion  27  may have a concave shape, when viewed from light reflected by the inner surface thereof. That is, the ferrule body  20  may be formed integrally with the reflecting portion  27  so that the front face  20   c  of the ferrule body  20  has a convex shape, when viewed from the outside. Further, a concave mirror which is separate from the ferrule body  20  may be fixed to the ferrule body  20 . 
     When a plurality of optical fibers  12  are fixed to the ferrule body  20  as shown in  FIG. 9A , the reflecting portion  27  is provided to each optical fiber  12  and the plurality of reflecting portions  27  are arranged in an arrangement direction of the optical fibers  12 . 
     A positioning mechanism  22  may be an optical fiber hole  22   a  entirely surrounding the optical fiber  12 , as shown in  FIG. 10A . When a through hole with a small diameter, such as the optical fiber hole  22   a , is formed in a integral mold, a pin-shaped mold is disposed in the position of the optical fiber hole upon molding the ferrule body  20  to prevent the inflow of material, such that the optical fiber hole can be formed simultaneously with molding of the ferrule body  20 . Since this technique can easily form a high-precision optical fiber hole  22   a  in comparison with post-processing using, for example, a drill, the technique is particularly suitable for a multi-core ferrule  11  with a plurality of optical fiber holes  22   a.    
     The V-shaped groove  22   b  shown in  FIG. 10B , the U-shaped groove  22   c  shown in  FIG. 10C  or the like may be employed as the positioning mechanism  22 . 
     In this case, as shown in  FIG. 11 , a ferrule body  28  having an optical fiber-accommodating groove such as the V-shaped groove  22   b  or the U-shaped groove may be covered with a pressing lid  29  formed as a plate-shaped member, and the optical fibers  12  may be adhered and fixed between the ferrule body  28  and the pressing lid  29 . 
     While the preferred embodiments of the present invention have been described, the present invention is not limited to the above-described embodiments and variations may be made to the present invention without departing from the scope of the present invention. 
     While in  FIGS. 6 to 9B , the reflecting portion  24  or  27  of the ferrule body  20  is formed on the front face  20   c  that is an outer face of the ferrule body  20 , the present invention is not limited thereto. The reflecting portion may be formed inside the ferrule body  20 . For example, a concave portion having a cross-sectional surface of a V-shape may be formed from the upper surface  20   b  of the ferrule body between the front face  20   c  of the ferrule body  20  and the recess  21 , and used as the reflecting surface. Alternatively, a thin metal piece, as a reflecting mirror, may be implanted in the ferrule body to form the reflecting portion. 
     EXAMPLES 
     Hereinafter, an example of the present invention will be described in detail. The present invention is not limited to the examples. 
     In this example, a multi-core (12-core) tape-shaped optical fiber core wire with a silica optical fiber having an outer diameter of 0.125 mm was used as an optical fiber. The ferrule body  20  having the structure in which the front end portion of the optical fiber  12  is fixed in the recess  21  by the adhesive  14 , and the directions of the optical paths  12   b  and  17   a  are changed 90° by the reflecting portion  24  formed as a flat face on the front face of the ferrule body  20  to optically connect the optical fiber  12  with the optical element  17 , as shown in  FIGS. 12A and 12B , was used as a ferrule. An optical fiber hole having an inner diameter of 0.127 mm was used as the positioning mechanism  22  of the ferrule. 
     The distance L between the first inner wall  21   b  and the second inner wall  21   a  of the recess  21  in each sample was designed so that L/D was 0.5, 1, 2, 3, 4, 5 and 6, and these seven types of samples were manufactured, the number of the respective manufactured samples being about 30, as shown in Table 1. 12 optical fiber holes were formed in one ferrule to position and fix 12 optical fibers. 
     For each optical fiber, a beam angle α with respect to a reference direction perpendicular to the lower surface  20   a  as shown in  FIG. 12B  was measured. Here, the reference direction corresponds to an optical axial direction of the optical element  17  when the optical element  17  is optically connected to the optical fiber. The beam angle α corresponds to a beam angle with respect to the optical axial direction of the optical element  17 . In this example, the beam angle α is obtained by measuring an angle when light output from the optical fiber  12  is reflected and output by the reflecting portion  24 , as an angle deviating from the reference direction. When the front end portion of the optical fiber  12  is moved, for example, due to the shrinkage  14   a  of the adhesive  14 , the optical path  12   b  deviates from a regular direction and the beam angle α increases. 
     For about 30 ferrules with L/D=0.5, L/D=1, L/D=2, L/D=3, L/D=4, L/D=5, and L/D=6 and about 360 optical fibers, beam angles α were measured. For each L/D, a standard deviation of the beam angle α of each 12-core optical fiber was calculated and averaged to obtain a standard deviation of the beam angle α for each L/D. The result is shown in Table 1. In  FIG. 13 , the result of Table 1 is shown by a graph. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Standard deviation (°) 
               
               
                   
                 L/D 
                 of beam angle α 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 0.5 
                 0.07 
               
               
                   
                 1 
                 0.09 
               
               
                   
                 2 
                 0.08 
               
               
                   
                 3 
                 0.08 
               
               
                   
                 4 
                 0.09 
               
               
                   
                 5 
                 0.18 
               
               
                   
                 6 
                 0.22 
               
               
                   
                   
               
            
           
         
       
     
     As shown in Table 1 and  FIG. 13 , when the distance L between the inner walls  21   a  and  21   b  of the recess  21  is designed so that L/D≦4, the standard deviation of the beam angle α was decreased. On the other hand, when L/D is 5 or more, the standard deviation of the beam angle α was greatly increased. It has been found from this result that when L/D≦4, a ferrule with small connection loss can be manufactured with a higher yield.