Abstract:
This optical module comprises a substrate, light-emitting elements, a ferrule, an optical receptacle, through-holes and an adhesive. The optical receptacle includes two support units, and an optical receptacle body that has a first optical surface and a second optical surface. The through-holes include two first through-holes surrounded by the leading ends of the support units and the ferrule, and two second through-holes which are surrounded by the optical receptacle body, the support units and the ferrule. Thus, even using the adhesive to fix the optical receptacle and the ferrule to the substrate, it is possible to optically connect multiple optical transmission bodies with multiple light-emitting elements or multiple light-receiving elements in a suitable manner.

Description:
TECHNICAL FIELD 
     The present invention relates to an optical module including an optical receptacle. 
     BACKGROUND ART 
     In optical communications using optical transmission members such as optical fibers and light waveguides, optical modules have been used, provided with a light emitting element such as a surface-emitting laser (for example, VCSEL: Vertical Cavity Surface Emitting Laser). Such an optical module includes an optical receptacle that allows light including communication information emitted from a light emitting element to be incident on the end surface of an optical transmission member. 
     For example, PTL 1 discloses an optical module including an optical connector and a substrate with light emitting elements disposed thereon. The optical connector includes optical fibers and a connector part including a lens array (optical receptacle) disposed between the tips of the plurality of the optical fibers and the light emitting elements. The lens array includes a reflecting mirror that reflects light emitted from the light emitting elements toward the optical fiber tips, and a condenser lens that concentrates the light reflected by the reflecting mirror toward the optical fiber tips. 
     In the optical module disclosed in PTL 1, the optical connector is fixed to the substrate by positioning the optical connector at a certain position in the substrate, putting a thermosetting epoxy resin adhesive on the boundary between the lens array edges and the substrate, and heat curing the adhesive. 
     In an optical module produced in such a manner, light emitted from a light emitting element is reflected by a reflecting mirror toward an optical fiber tip, and reaches the optical fiber tip via a condenser lens. 
     CITATION LIST 
     Patent Literature 
     PTL 1 
     Japanese Patent Application Laid-Open No. 2010-175942 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, when the epoxy resin adhesive is cured in the optical module disclosed in PTL 1, the lens array (condenser lens and reflecting mirror) is deformed as if the lens array is pulled toward the epoxy resin adhesive side (i.e., laterally) by the shrinkage of the epoxy resin adhesive. The epoxy resin adhesive is cured with the lens array in the deformed state. The lens array is thus kept in the deformed state after fixed to the substrate, which may lead to light emitted from the light emitting element not properly guided to the end surface of the optical fiber. As described above, the lens array (optical receptacle) disclosed in PTL 1 is disadvantageously deformed when fixed with an adhesive. 
     An object of the present invention is to provide an optical module including an optical receptacle that is not easily deformed even when the optical receptacle is fixed using an adhesive. 
     Solution to Problem 
     An optical module of the present invention includes: a substrate; a plurality of light emitting elements or a plurality of light receiving elements arrayed on the substrate; a ferrule which holds a plurality of optical transmission members being configured to receive light respectively from the plurality of light emitting elements or to emit light respectively to the plurality of light receiving elements; an optical receptacle which is disposed on the substrate, with the ferrule being fixed to the optical receptacle, the optical receptacle being configured to optically couple the plurality of light emitting elements or the plurality of light receiving elements to the plurality of optical transmission members, respectively; four through holes formed in a boundary between the ferrule and the optical receptacle in a direction substantially perpendicular to the substrate; and an adhesive filled into the four through holes to adhere the ferrule and the optical receptacle to the substrate, in which the optical receptacle includes: an optical receptacle body including a plurality of first optical surfaces which are configured such that light emitted from the plurality of light emitting elements is respectively incident on the first optical surface or are configured to emit light propagating inside the optical receptacle body respectively toward the plurality of light receiving elements, and a plurality of second optical surfaces which are configured to emit the light incident on the plurality of first optical surfaces respectively toward an end surface of the plurality of optical transmission members or are configured such that light from the plurality of optical transmission members is respectively incident on the second optical surface, the optical receptacle body having the ferrule being fixed to a rear surface thereof such that the plurality of optical transmission members face the plurality of second optical surfaces, respectively, and two supporters disposed on both side surfaces of the ferrule, respectively, the two supporters each having a base end connected to the optical receptacle body, and the four through holes include: two first through holes each surrounded by a tip portion of each of the supporters and the ferrule, and two second through holes each surrounded by the optical receptacle body, each of the supporters, and the ferrule. 
     Advantageous Effects of Invention 
     According to the present invention, a plurality of light emitting elements or a plurality of light receiving elements can be optically coupled suitably to a plurality of optical transmission members even when an optical receptacle and a ferrule are fixed to a substrate using an adhesive. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIGS. 1A and 1B  illustrate a configuration of an optical module according to an embodiment of the present invention; 
         FIGS. 2A to 2D  illustrate a configuration of a ferrule; 
         FIGS. 3A to 3E  illustrate a configuration of an optical receptacle; 
         FIGS. 4A and 4B  illustrate deforming directions of optical modules at the time of curing an adhesive; and 
         FIG. 5  shows simulation results of the deformation of the optical module. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
     (Configuration of Optical Module) 
       FIGS. 1A and 1B  illustrate the configuration of optical module  100  according to an embodiment of the present invention.  FIG. 1A  is a plan view of optical module  100 , and  FIG. 1B  is a cross-sectional view along line A-A illustrated in  FIG. 1A . Note that, in  FIG. 1B , hatching is omitted in the cross-section of optical receptacle  130  to show an optical path in optical receptacle  130 . 
     As illustrated in  FIGS. 1A and 1B , optical module  100  includes substrate-mounted photoelectric conversion device  110  including substrate  112  and light emitting elements  114 , ferrule  120  holding optical transmission members  121 , optical receptacle  130  which includes optical receptacle body  131  and two supporters  132  and is configured to optically couple light emitting elements  114  to end surfaces of optical transmission members  121 , through holes  140  for fixing ferrule  120  and optical receptacle  130  to substrate  112  of photoelectric conversion device  110 , and adhesive  150  filled into through holes  140 . In optical module  100 , optical receptacle  130  is fixed (adhered) onto photoelectric conversion device  110  (substrate  112 ) with adhesive  150 , and ferrule  120  holding optical transmission members  121  is fixed to optical receptacle  130  with adhesive cured product  150 . Thus, optical module  100  in which light emitting elements  114  and optical transmission members  121  are optically coupled together is used. 
     Photoelectric conversion device  110  includes substrate  112  and a plurality of light emitting elements  114 . Substrate  112  is a plate-like member. A plurality of light emitting elements  114  are arrayed on substrate  112 . Further, ferrule  120  and optical receptacle  130  are fixed (adhered) to substrate  112  with an adhesive. The mode in which light emitting elements  114  are arrayed on substrate  112  is not particularly limited. In the present embodiment, light emitting elements  114  are disposed in a line on substrate  112  so as to emit laser light in the direction perpendicular to the surface of substrate  112 . Light emitting element  114  is, e.g., Vertical Cavity Surface Emitting Laser (VCSEL). 
       FIGS. 2A to 2D  illustrate the configuration of ferrule  120 .  FIGS. 2A, 2B, 2C , and  2 D are, respectively, a plan view, a front view, a rear view, and a right side view of ferrule  120 . In  FIGS. 2A and 2D , optical transmission members  121  are illustrated by dashed-dotted lines. 
     As illustrated in  FIGS. 2A to 2D , ferrule  120  holds a plurality of optical transmission members  121 . Ferrule  120  is a substantially rectangular member having a predetermined thickness, and is fixed to the rear surface side of optical receptacle  130  (the rear surface of optical receptacle body  131 ). Ferrule  120  includes insertion ports  122 , recesses  123 , two first cutout grooves  124  and two second cutout grooves  125 . Ferrule  120  can be molded by injection molding (transfer molding as necessary) using a thermosetting resin such as epoxy resin or a thermoplastic resin such as PPST, for example. 
     Optical transmission member  121  is inserted into insertion port  122 . The shape of insertion port  122  may be in any shape as long as insertion port  122  can hold optical transmission member  121  so as to receive light emitted from optical receptacle  130 . Insertion port  122  may either be a through hole or a bottomed recess. In the present embodiment, insertion port  122  is a through hole opening at the front surface and the rear surface of ferrule  120  and being parallel to the surface of substrate  112 . The number of insertion ports  122  and the mode in which insertion ports  122  are arrayed are not particularly limited. In the present embodiment, insertion ports  122  are disposed in a line with the same number as that (twelve) of optical transmission members  121 . 
     Recess  123  is designed to position ferrule  120  to optical receptacle  130 . The shape of recess  123  is a shape complementary to projection  136  disposed on optical receptacle  130 . The number of recesses  123  is the same as that of projection  136 . In the present embodiment, two recesses  123  are disposed such that arrayed insertion ports  122  are disposed therebetween. 
     Two first cutout grooves  124  are disposed at both side surfaces of supporter  132  on the tip portion side. First cutout groove  124  is disposed along the direction perpendicular to the axial direction of insertion port  122  when ferrule  120  is viewed laterally (see  FIG. 2D ). The cross-sectional shape of first cutout groove  124  parallel to the surface of substrate  112  is ½ of a circle (semicircle). First cutout groove  124  is disposed to face third cutout groove  137  to be described later in optical module  100 . First cutout groove  124  constitutes first through hole  141  together with third cutout groove  137  in optical module  100 . 
     Two first cutout grooves  125  are disposed at both ends of the side surface on optical receptacle body  131  side (on the base end side of supporter  132 ). Second cutout groove  125  is disposed along the direction perpendicular to the axial direction of insertion port  122  when ferrule  120  is viewed laterally (see  FIG. 2D ). The cross-sectional shape of second cutout groove  125  parallel to the surface of substrate  112  is ¼ of a circle (sector). Second cutout groove  125  is disposed to face fourth cutout groove  138  to be described later in optical module  100 . Second cutout groove  125  constitutes second through hole  142  together with fourth cutout groove  138  in optical module  100 . 
     Optical transmission members  121  receive light emitted from optical receptacle  130 . The end portions of optical transmission members  121  are held by ferrule  120 . Thus, optical transmission members  121  are disposed at such positions where optical transmission members  121  can receive light emitted from optical receptacle  130 . The number of optical transmission members  121  and the mode in which optical transmission members  121  are arrayed are not particularly limited. In the present embodiment, twelve optical transmission members  121  are disposed in a line in parallel with the surface of substrate  112  so as to receive light emitted from optical receptacle  130 . The type of optical transmission members  121  is not particularly limited, and examples thereof include optical fibers and light waveguides. In the present embodiment, optical transmission members  121  are optical fibers. The optical fibers may be single-mode optical fibers or multi-mode optical fibers. 
       FIGS. 3A to 3E  illustrate the configuration of optical receptacle  130  according to an embodiment.  FIGS. 3A, 3B, 3C, 3D, and 3E  are, respectively, a plan view, a bottom view, a front view, a rear view, and a right side view of the optical receptacle. 
     As illustrated in  FIGS. 3A to 3E , optical receptacle  130  is a squarely U-shaped member when viewed in plan view. Optical receptacle  130  includes optical receptacle body  131  and two supporters  132 . Optical receptacle body  131  and supporters  132  together have a plane symmetrical shape with respect to a symmetry plane parallel to the optical axis of light emitted from each of second optical surfaces  135 . 
     Optical receptacle body  131  is light transmissive, and is configured such that light emitted from light emitting element  114  is incident thereon and that optical receptacle body  131  emits the incident light toward the end surface of optical transmission member  121 . The shape of optical receptacle body  131  is a substantially rectangular parallelepiped. Optical receptacle body  131  includes a plurality of first optical surfaces (incidence surfaces)  133 , third optical surface (reflection surface)  134 , a plurality of second optical surfaces (emission surfaces)  135 , and two projections  136 . Optical receptacle body  131  is formed of a material transmitting light with a wavelength used for optical communications. Examples of the materials include transparent resins such as polyetherimide (PEI) and cyclic olefin resins. Optical receptacle body  131  can be made by injection molding, for example. 
     First optical surface  133  is an incidence surface that refracts laser light emitted from light emitting element  114  to allow the light to enter inside optical receptacle body  131 . The number of first optical surfaces  133  and the mode in which first optical surfaces  133  are arrayed are not particularly limited. A plurality of first optical surfaces  133  may be arrayed either in a line or in two or more lines. In the present embodiment, twelve first optical surfaces  133  are disposed in a line on the bottom surface side of optical receptacle body  131  so as to face respective light emitting elements  114 . First optical surface  133  may be in any shape. In the present embodiment, the shape of first optical surface  133  is that of a convex lens protruding toward light emitting element  114 . The shape of first optical surface  133  in plan view is a circle. The central axis of first optical surface  133  is preferably perpendicular to the light emitting surface of light emitting element  114  (and to the surface of substrate  112 ). Further, the central axis of first optical surface  133  preferably coincides with the optical axis of the laser light emitted from light emitting element  114 . The light incident on first optical surface  133  (incidence surface) propagates toward third optical surface  134  (reflection surface). 
     Third optical surface  134  is a reflection surface that reflects the light incident on first optical surface  133  toward second optical surface  135 . Third optical surface  134  is tilted such that the distance from optical transmission member  121  decreases in the direction from the bottom surface to the top surface of optical receptacle body  131 . The inclination angle of third optical surface  134  relative to the optical axis of light emitted from light emitting element  114  is not particularly limited. In the present embodiment, the inclination angle of third optical surface  134  is 45° relative to the optical axis of light incident on first optical surface  133 . Third optical surface  134  may be in any shape. In the present embodiment, the shape of third optical surface  134  is a flat surface. The light incident on first optical surface  133  is incident on third optical surface  134  at an incident angle larger than the critical angle. Third optical surface  134  totally reflects the incident light toward second optical surface  135 . That is, light with a predetermined light flux diameter is incident on third optical surface  134  (reflection surface), and the light with the predetermined light flux diameter is emitted toward second optical surface  135  (emission surface) from third optical surface  134 . 
     Second optical surface  135  is an emission surface that emits the light totally reflected by third optical surface  134  toward the end surface of optical transmission member  121 . The number of second optical surfaces  135  and the mode in which second optical surfaces  135  are arrayed are not particularly limited. A plurality of second optical surfaces  135  may be arrayed either in a line or in two or more lines. In the present embodiment, twelve second optical surfaces  135  are disposed in a line on the rear surface of optical receptacle body  131  so as to face respective end surfaces of optical transmission members  121 . Second optical surface  135  may be in any shape. In the present embodiment, the shape of second optical surface  135  is that of a convex lens protruding toward the end surface of optical transmission member  121 . This enables the light having the predetermined light flux diameter reflected by third optical surface  134  to be efficiently coupled to the end surface of optical transmission member  121 . The central axis of second optical surface  135  preferably coincides with the central axis of the end surface of optical transmission member  121 . 
     Two projections  136  are disposed on the rear surface of the optical receptacle body  131 . Two projections  136  are disposed at positions corresponding to recesses  123 , respectively. Optical transmission members  121  can be positioned to optical receptacle body  131  by respectively engaging two projections  136  of optical receptacle body  131  with two recesses  123  in ferrule  120  holding optical transmission members  121 . 
     Supporters  132  have the shape of a substantially rectangular parallelepiped, and are disposed on both sides of ferrule  120  fixed to the rear surface of optical receptacle body  131 . The base ends (front surface) of supporters  132  are connected to the both ends of optical receptacle body  131 , respectively. That is, supporter  132  is disposed in a direction the same as the optical axis of light emitted from second optical surface  135 . Supporter  132  may be formed of the same light transmissive material as optical receptacle body  131 , or of a different non-light transmissive material. For example, supporters  132  can be integrally formed with optical receptacle  130  by injection molding using the same material. Supporter  132  has two third cutout grooves  137  and two fourth cutout grooves  138 . 
     Third cutout groove  137  is disposed at a tip portion on a side surface of supporter  132  on ferrule  120  side. Specifically, third cutout groove  137  is preferably disposed at a position within 20%, which is a distance from the tip of supporter  132 , of a distance from the tip of supporter  132  to the center of first optical surface  133  in the optical axis direction of light emitted from second optical surface  135 . The cross-sectional shape of third cutout groove  137  in the same direction as the optical axis of the light emitted from second optical surface  135  is not particularly limited. In the present embodiment, the cross-sectional shape of third cutout groove  137  parallel to the surface of substrate  112  is ½ of a circle (semicircle). Third cutout groove  137  is disposed to face the above-mentioned first cutout groove  124  in optical module  100 . Further, third cutout groove  137  constitutes first through hole  141  together with first cutout groove  124  in optical module  100 . 
     Fourth cutout groove  138  is disposed at a connection portion between optical receptacle body  131  and supporter  132  and at a side surface of supporter  132  on ferrule  120  side. The cross-sectional shape of fourth cutout groove  138  in the same direction as the optical axis of the light emitted from second optical surface  135  is not particularly limited. In the present embodiment, the cross-sectional shape of fourth cutout groove  138  parallel to the surface of substrate  112  is ¾ of a circle (sector). Fourth cutout groove  138  is disposed to face the above-mentioned second cutout groove  125  in optical module  100 . Further, the inner surface of fourth cutout groove  138  constitutes second through hole  142  together with second cutout groove  125  in optical module  100 . 
     Returning to the description of optical module  100 , an adhesive is retained in through hole  140  in order to mount (fix) ferrule  120  and optical receptacle  130  onto substrate  112 . Therefore, through hole  140  is filled with adhesive cured product  150 . As illustrated in  FIG. 1A , through holes  140  include two first through holes  141  and two second through holes  142 . By fixing ferrule  120  to optical receptacle  130 , first cutout groove  124  and third cutout groove  137  constitute first through hole  141 , and second cutout groove  125  and fourth cutout groove  138  constitute second through hole  142 . 
     First through hole  141  is disposed at a boundary between ferrule  120  and supporter  132 . The inner surface of first through hole  141  includes the inner surface of first cutout groove  124  and the inner surface of third cutout groove  137 . The inner surface of first through hole  141  on ferrule  120  side is the inner surface of first cutout groove  124 , and the inner surface of first through hole  141  on supporter  132  side is the inner surface of third cutout groove  137 . First through hole  141  is disposed at a tip portion of supporter  132 . Specifically, first through hole  141  is preferably disposed at a position within 20%, which is a distance D 2  from the tip of supporter  132 , of a distance D 1  from the tip of supporter  132  to the center of first optical surface  133  in the optical axis direction of light between second optical surface  135  and the plurality of optical transmission members  121  (see  FIG. 1A ). The shape of first through hole  141  may be in any shape. In the present embodiment, the shape of first through hole  141  is a cylindrical shape. The opening of first through hole  141  may have any size. The size of the opening of first through hole  141  can be appropriately set depending on the material or size of optical receptacle  130  and ferrule  120  or the nature of the adhesive to be filled. The adhesive is not particularly limited as long as the adhesive can adhere optical receptacle  130  onto photoelectric conversion device  110  (substrate  112 ) without deformation. For example, the adhesive may be a filler to fill first through hole  141 , or a sealant charged into first through hole  141 . Further, known thermosetting epoxy resin adhesives, ultraviolet curable resin adhesives, or the like can also be used. 
     Second through hole  142  is disposed at a boundary among ferrule  120 , supporter  132 , and optical receptacle body  131 . The inner surface of second through hole  142  includes the inner surface of second cutout groove  125  and the inner surface of fourth cutout groove  138 . The inner surface of second through hole  142  on ferrule  120  side is the inner surface of second cutout groove  125 , and the inner surface of second through hole  142  on supporter  132  side is the inner surface of fourth cutout groove  138 . The shape of second through hole  142  may be in any shape. In the present embodiment, the shape of second through hole  142  is a cylindrical shape. The opening of second through hole  142  may have any size. The size of the opening of second through hole  142  can be appropriately set depending on the material or size of optical receptacle  130  and ferrule  120  or the nature of the adhesive to be filled. As the adhesive to fill second through hole  142 , the same adhesive as that to fill first through hole  141  can be used. 
     Ferrule  120  and optical receptacle  130  are fixed to substrate  112  by positioning ferrule  120  and optical receptacle  130  on substrate  112 , then filling an adhesive into through holes  140  (two first through holes  141  and two second through holes  142 ), and curing the adhesive. 
     More specifically, optical receptacle  130  is positioned on substrate  112  such that the central axis of each first optical surface  133  coincides with the optical axis of laser light emitted from corresponding light emitting element  114 . Next, ferrule  120  is positioned relative to optical receptacle  130  such that the central axis of each second optical surface  135  coincides with the central axis of the light receiving surface of optical transmission member  121 . Then, first through hole  141  and second through hole  142  are filled with an adhesive such that the adhesive is brought in contact with the entire circumferences of the inner peripheral surfaces of first through hole  141  and second through hole  142  as well as with substrate  112 , and subsequently the adhesive is cured. When a thermosetting epoxy resin adhesive is used, for example, the adhesive is heated. These steps enable optical receptacle  130  and ferrule  120  to be fixed to substrate  112 . Note that ferrule  120  and optical receptacle  130  may be positioned on substrate  112  after ferrule  120  is positioned relative to optical receptacle  130 . 
       FIGS. 4A and 4B  illustrate deforming directions of optical module  100  (optical receptacle  130  and ferrule  120 ) at the time of curing the adhesive.  FIG. 4A  is a schematic view illustrating deforming directions of optical module  100 ′ without through holes  140  when the adhesive is put on the outside of optical receptacle  130 ′.  FIG. 4B  is a schematic view illustrating deforming directions of optical module  100  according to the present invention. Note that optical transmission member  121  is omitted in  FIGS. 4A and 4B . 
     As indicated by solid arrows in  FIG. 4A , when the outer side surface of supporter  132 ′ is fixed with an adhesive in optical module  100 ′ including optical receptacle  130 ′ without through holes  140 , supporter  132 ′ is undesirably deformed as if it is pulled outward (toward adhesive cured product  150  side). At that time, optical receptacle body  131 ′ is connected to the base end of supporter  132 ′, and thus the tip side is undesirably deformed more largely than the base end side. In addition, in association with the outward deformation of supporter  132 ′, optical receptacle body  131 ′ is undesirably deformed to be convex toward ferrule  120 ′ side. 
     On the other hand, as illustrated in  FIG. 4B , in optical module  100  according to the present embodiment, ferrule  120  (the inner surface of first cutout grove  124 ; see dashed arrows) and supporter  132  (the inner surface of third cutout grove  137 ; see solid arrows) which are in contact with adhesive cured product  150  are pulled toward the center of first through hole  141  by the shrinkage of the adhesive caused by the curing. Further, as illustrated in  FIG. 4B , ferrule  120  (the inner surface of second cutout grove  125 ; see dashed arrows), optical receptacle body  131 , and supporter  132  (the inner surface of fourth cutout grove  138 ; see solid arrows) which are in contact with the adhesive are pulled toward the center of second through hole  142  by the shrinkage of the adhesive caused by the curing. In the present embodiment, the adhesive is in contact with the inner peripheral surface of through hole  141 . Thus, forces in a planar direction derived from the adhesive shrinkage, which cause deformation of ferrule  120  and optical receptacle  130 , are offset by each other. Accordingly, it can be found that, by reducing the deformation of optical receptacle body  131  toward ferrule  120  side, first optical surface  133 , second optical surface  135 , and third optical surface  134  are less likely to be deformed, so that the deformation of optical module  100  can be reduced. 
     (Simulation) 
     Next, the deformation of the optical receptacle body toward the ferrule side was studied. The moving distances of first optical surface  133  (deformation amount of optical receptacle  130 ) were simulated for optical module  100  according to the present invention when the optical module  100  was fixed with a thermosetting epoxy resin adhesive (after heating). The moving distances of each of first optical surfaces  133  in a planer direction (X axis direction) by heating were analyzed by a finite element method. For comparison, module  100 ′ without through holes  140  was also simulated. Parameters set for the simulation are shown in Table 1. The curing temperature and curing time of the thermosetting epoxy resin adhesive were set at 100° C. and at 1 hour, respectively, in the simulation. Further, first through hole  141  was disposed at a position within 14%, which is a distance from the tip of supporter  132 , of a distance from the tip of supporter  132  to the center of first optical surface  133 . Since the optical receptacle has a plane symmetrical shape with respect to a symmetry plane, only the right half of the optical receptacle was simulated. First optical surfaces  133  were numbered 1 to 12 with first optical surface  133  at the right most side as number one. Therefore, the moving distances of first optical surfaces  133  with numbers 7 to 12 were simulated. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                   
                 Adhesive 
               
               
                   
                 Substrate 
                 Optical  
                 Ferrule 
                 Thermosetting  
               
               
                   
                 Glass  
                 Receptacle 
                 Epoxy  
                 epoxy 
               
               
                 Material 
                 epoxy 
                 Polyetherimide 
                 resin 
                 resin adhesive 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Young&#39;s  
                 24.6 
                 3.4 
                 22 
                 8.8 
               
               
                 modulus 
                   
                   
                   
                   
               
               
                 (GPa) 
                   
                   
                   
                   
               
               
                 Poisson&#39;s ratio 
                 0.2 
                 0.4 
                 0.3 
                 0.3 
               
               
                 Linear  
                 1.1 × 10 −5   
                 5.6 × 10 −5   
                 1.1 × 10 −5   
                 4.0 × 10 −5   
               
               
                 expansion 
                   
                   
                   
                   
               
               
                 coefficient  
                   
                   
                   
                   
               
               
                 (/° C.) 
               
               
                   
               
             
          
         
       
     
       FIG. 5  is a graph showing the relationship between first optical surface (incidence surface) numbers and the respective moving distances of first optical surfaces caused by the curing of the adhesive. As used herein, “X axis direction” refers to the direction along the central axis of the second optical surface (vertical direction in  FIGS. 3A and 3B ). In the graph, the abscissa represents the numbers of the first optical surfaces given as described above. The ordinate represents the moving distance of the first optical surface  133  from a position before curing the adhesive to a position after curing the adhesive. Black circle symbols show simulation results for optical module  100 ′ of Comparative Example in  FIG. 4A , whereas white circle symbols show simulation results for optical module  100  according to the present invention in  FIGS. 1A and 1B . 
     As shown in  FIG. 5 , movements of first optical surfaces  133  in optical module  100 ′ of Comparative Example without through holes  140  by the curing of the adhesive were large in X axis direction. On the other hand, movements of first optical surfaces  133  in optical module  100  having through holes  140  were reduced. The moving distances in X axis direction did not change significantly when the center of first through hole  141  was at a position within 20%, from the tip of supporter  132 , of a distance from the tip of supporter  132  to the center of first optical surface  133 . 
     (Effects) 
     As described above, optical module  100  according to the present invention includes two first through holes  141  each disposed at a tip portion of supporter  132  and having an inner surface surrounded by supporter  132  and ferrule  120 , and two second through holes  142  each having an inner surface surrounded by supporter  132 , ferrule  120 , and optical receptacle body  131 . Thus, forces in a planar direction derived from the adhesive shrinkage, which cause deformation of ferrule  120  and optical receptacle  130 , are offset by each other. Accordingly, the deformation of optical module  100  according to the present invention can be reduced even when optical receptacle  130  and ferrule  120  are fixed to substrate  112  using an adhesive. 
     Note that a plurality of first optical surfaces  133  may be disposed on the front side of optical receptacle body  131 , and a plurality of second optical surfaces  135  may be disposed on the rear side of optical receptacle body  131  so as to face first optical surfaces  133 . In this case, a reflection surface is unnecessary. Further, first through hole  141  is disposed at a tip portion of supporter  132 . 
     Optical module  100  according to the embodiments may monitor output of laser light (e.g., intensity and amount of the light) emitted from light emitting elements  114 . In this case, photoelectric conversion device  110  of optical module  100  includes substrate  112 , light emitting element  114 , a light receiving element disposed on substrate  112 , and a control section that controls output of laser light emitted from light emitting element  114  based on the intensity and amount of monitoring light received by the light receiving element, although not illustrated. Optical receptacle  130  further includes a separating section that separates light incident on the first optical surface into signal light propagating toward optical transmission member  121  and monitoring light propagating toward the light receiving element. 
     In the above embodiments, first optical surface  133  and second optical surface  135  in the optical receptacle are convex lenses, but first optical surface  133  and second optical surface  135  may be flat surfaces. Specifically, only first optical surface  133  may be a flat surface, or only second optical surface  135  may be a flat surface. When first optical surface  133  is formed in a flat surface, third optical surface  134  is formed to function as a concave mirror, for example. When light immediately before reaching second optical surface  135  is effectively converged by first optical surface  133 , third optical surface  134  or the like, second optical surface  135  may be formed in a flat surface. 
     Further, the optical receptacle according to any one of the embodiments may be used also for an optical module on receiving side. In this case, the receiving optical module includes a plurality of light receiving elements for receiving light instead of the plurality of light emitting elements  114 . The light receiving elements are arrayed on the same positions as the respective corresponding light emitting elements. The receiving optical module has second optical surfaces  135  as incidence surfaces, and first optical surfaces  133  as emission surfaces. Light emitted from the end surface of optical transmission member  121  enters the optical receptacle from second optical surface  135 . The light having entered the optical receptacle is reflected by third optical surface  134  to be emitted from first optical surface  133  toward the light receiving element. In the case of an optical module not having a reflection surface, light having entered the optical receptacle is emitted from first optical surface  133  toward the light receiving element. 
     This application is entitled to and claims the benefit of Japanese Patent Application No. 2013-265288, filed on Dec. 24, 2013, the disclosure of which including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
     INDUSTRIAL APPLICABILITY 
     The optical module according to the present invention is advantageous for optical communications using optical transmission members. 
     REFERENCE SIGN LIST 
     
         
           100 ,  100 ′ Optical module 
           110  Photoelectric conversion device 
           112  Substrate 
           114  Light emitting element 
           120 ,  120 ′ Ferrule 
           121  Optical transmission member 
           122  Insertion port 
           123  Recess 
           124  First cutout groove 
           125  Second cutout groove 
           130 ,  130 ′ Optical receptacle 
           131 ,  131 ′ Optical receptacle body 
           132 ,  132 ′ Supporter 
           133  First optical surface 
           134  Third optical surface 
           135  Second optical surface 
           136  Projection 
           137  Third cutout groove 
           138  Fourth cutout groove 
           140  Through hole 
           141  First through hole 
           142  Second through hole 
           150  Adhesive cured product (adhesive)