Abstract:
This optical receptacle comprises: a first optical surface through which light from a photoelectric conversion element is incident; a second optical surface through which the incident light is emitted to the optical transmitter side; an optical separation part which separates the incident light into monitor light that goes to a detection element and signal light that goes to the optical transmitter; and a third optical surface through which the monitor light is emitted to the detection element side. The securing part secures the optical transmitter such that the signal light from the second optical surface arrives at the end surface of the optical transmitter at a position farther than the focus of the second optical surface. The light flux diameter in the light separation part of the light incident through the second optical surface is smaller than the light flux diameter of the light in the second optical surface.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an optical receptacle and an optical module including the optical receptacle. 
       BACKGROUND ART 
       [0002]    Conventionally, in optical communications using an optical transmission member such as an optical fiber and an optical waveguide, an optical module including a light emitting element such as a surface-emitting laser (for example, VCSEL: Vertical Cavity Surface Emitting Laser) has been used. The optical module includes an optical receptacle which allows for incidence of light containing communication information emitted from a light emitting element on an end surface of the optical transmission member. 
         [0003]    In addition, for the purpose of adjusting the light output or stabilizing the output characteristics of a light emitting element against temperature variation, some optical modules include a detection element for checking (monitoring) the intensity and the quantity of the light emitted from the light emitting element. 
         [0004]    For example, PTL 1 discloses an optical module including a photoelectric conversion device in which a light emitting element and a detection element are disposed, and an optical receptacle configured to optically connect the light emitting element and an end surface of an optical transmission member. 
         [0005]    The optical module disclosed in PTL 1 includes the photoelectric conversion device and the optical receptacle. The optical receptacle includes a first optical surface on which light emitted from a light emitting element is incident; a second optical surface configured to emit light advanced through the inside of the optical receptacle is condensed at an end surface of the optical transmission member; a reflection surface configured to reflect, toward the second optical surface, light which is incident on the first optical surface; a light separation part configured to separate light reflected by the reflection surface into monitor light travelling toward the receiving element and signal light travelling toward an end surface of the optical transmission member; and a third optical surface configured to emit the monitor light toward the detection element. In addition, the light separation part includes a division reflection surface that is an inclined surface inclined to the optical axis of light reflected by the reflection surface and is configured to reflect a part of light reflected by the reflection surface toward the detection element; a division transmission surface that is a surface perpendicular to the optical axis and is configured to allow the other part of the light reflected by the reflection surface to pass therethrough toward the second optical surface; and a division step surface that is a surface parallel to the optical axis. 
         [0006]    In the optical module disclosed in PTL 1, the light which is emitted from the light emitting element and is incident on the first optical surface is reflected at the reflection surface toward the light separation part. The light reflected by the reflection surface is separated by the light separation part into signal light and monitor light. The monitor light separated by the light separation part is emitted from the third optical surface toward the light reception surface of the detection element. On the other hand, the signal light separated by the light separation part is emitted from the second optical surface toward an end surface of the optical transmission member. As described, PTL 1 discloses an optical module of the transmission side which includes an optical receptacle configured to couple light emitted from a light emitting element with an end surface of an optical transmission member. 
       CITATION LIST 
     Patent Literature 
       [0007]    PTL 1 
         [0008]    Japanese Patent Application Laid-Open No. 2013-137507 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0009]    It is conceivable to use the optical module disclosed in PTL 1 as an optical module of the reception side, or an optical module of the transmission side and the reception side. For example, by replacing all the light emitting elements with light receiving elements such as photodetectors, the optical module disclosed in PTL 1 can be used as an optical module of the reception side. In addition, by replacing some of the light emitting elements with light receiving elements, the optical module disclosed in PTL 1 can be used as an optical module of the transmission side and the reception side. In the above-mentioned cases, light emitted from an end surface of the optical transmission member reaches the light receiving element through the second optical surface, the light separation part, the reflection surface and the first optical surface. 
         [0010]    In the case where the optical module disclosed in PTL 1 is used also as an optical module of the reception side, light which is incident on the second optical surface passes through the light separation part. At this time, the light which is incident on the second optical surface is separated by the light separation part into light travelling toward light receiving element and light travelling in a direction opposite to the detection element (light not travelling toward the light receiving element or the detection element). As a result, there is a problem that, in the case where the optical module disclosed in PTL 1 is used also as the optical module of the reception side, the quantity of light that reaches the light reception surface of the light receiving element is significantly small relative to the quantity of light emitted from an end surface of the optical transmission member. 
         [0011]    In view of this, an object of the present invention is to provide an optical receptacle which includes a light separation part and can suppress reduction of the quantity of light which reaches the light receiving element even when used for reception. In addition, another object of the present invention is to provide an optical module including the optical receptacle. 
       Solution to Problem 
       [0012]    An optical receptacle according to embodiments of present invention is disposed between one or more optical transmission members and one or more photoelectric conversion devices including one or more photoelectric conversion elements and one or more detection elements for monitoring light emitted from the photoelectric conversion element, the optical receptacle being configured for optically coupling the photoelectric conversion element and an end surface of the optical transmission member, the optical receptacle including: one or more first optical surfaces configured to allow incidence of light emitted from the photoelectric conversion element, or emit, toward the photoelectric conversion element, light which is emitted from the end surface of the optical transmission member and is advanced through an inside of the optical receptacle; one or more second optical surfaces configured to emit, toward the end surface of the optical transmission member, light incident on the first optical surface, or allow incidence of light emitted from the end surface of the optical transmission member; a light separation part disposed on a light path between the first optical surface and the second optical surface, and configured to separate light incident on the first optical surface into monitor light travelling toward the detection element and signal light travelling toward the end surface of the optical transmission member, or allow at least a part of light incident on the second optical surface to pass therethrough toward the first optical surface side; one or more third optical surfaces configured to emit, toward the detection element, monitor light separated at the light separation part; and a fixing part configured to dispose the end surface of the optical transmission member such that the end surface faces the second optical surface. The fixing part fixes the optical transmission member such that signal light emitted from the second optical surface reaches the end surface of the optical transmission member at a remote position relative to a focus of the second optical surface, and a light flux diameter at the light separation part of light incident on the second optical surface is smaller than a light flux diameter of light at the second optical surface. 
         [0013]    An optical module according to embodiments of present invention includes: the optical receptacle; and a photoelectric conversion device including a substrate, one or more photoelectric conversion elements disposed on the substrate, and one or more detection elements disposed on the substrate and configured to monitor light emitted from the photoelectric conversion device. 
       Advantageous Effects of Invention 
       [0014]    According to the present invention, it is possible to provide an optical receptacle that includes a light separation part and can optically couple in an efficient manner the photoelectric conversion element (the light emitting element or the light receiving element) and an end surface of the optical transmission member in both of transmission and reception, and an optical module including the same. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]      FIGS. 1A and 1B  are sectional views of an optical module according to Embodiment 1; 
           [0016]      FIGS. 2A to 2D  illustrate a configuration of an optical receptacle according to Embodiment 1; 
           [0017]      FIGS. 3A and 3B  illustrate a configuration of a light separation part; 
           [0018]      FIGS. 4A and 4B  illustrate light paths of the transmission side in the optical module; 
           [0019]      FIGS. 5A and 5B  illustrate light paths of the reception side in the optical module; 
           [0020]      FIGS. 6A and 6B  illustrate a simulation of light which reaches an optical transmission member; 
           [0021]      FIGS. 7A and 7B  illustrate a simulation of light which reaches a light receiving element; 
           [0022]      FIGS. 8A and 8B  are sectional views of an optical module according to Embodiment 2; 
           [0023]      FIGS. 9A to 9C  illustrate a configuration of an optical receptacle according to Embodiment 2; 
           [0024]      FIG. 10A  illustrates light paths of the transmission side in an optical module, and 
           [0025]      FIG. 10B  illustrates light paths of the reception side in the optical module; and 
           [0026]      FIGS. 11A and 11B  illustrate a configuration of a light separation part according to a modification. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0027]    In the following, embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
       Embodiment 1 
     (Configuration of Optical Module) 
       [0028]      FIGS. 1A and 1B  are sectional views of optical module  100  according to Embodiment 1 of the present invention.  FIG. 1A  illustrates light paths in a transmission side region of optical module  100 , and  FIG. 1B  illustrates light paths in a reception side region of optical module  100 . It is to be noted that, in  FIG. 1A  and  FIG. 1B , the hatching of the cross section of optical receptacle  140  is omitted to illustrate light paths in optical receptacle  140 . 
         [0029]    As illustrated in  FIG. 1A  and  FIG. 1B , optical module  100  includes photoelectric conversion device  120  of substrate mounting type including a photoelectric conversion element (light emitting element  122  and/or light receiving element  123 ), and optical receptacle  140 . In optical module  100 , a plurality of optical transmission members  160  are connected to optical receptacle  140  through ferrule  162  when in use. The type of optical transmission member  160  is not limited, and optical transmission member  160  may be an optical fiber, a light waveguide or the like. In the present embodiment, a plurality of optical transmission members  160  are a plurality of optical fibers disposed in one line at a constant interval. The optical fiber may be of a single mode type, or a multiple mode type. It is to be noted that optical transmission members  160  may be disposed in two or more lines. 
         [0030]    Photoelectric conversion device  120  includes substrate  121 , four light emitting elements  122 , four light receiving elements  123 , and four detection elements  124 . Substrate  121  is a flexible substrate, for example. Four light emitting elements  122 , four light receiving elements  123  and four detection elements  124  are disposed on substrate  121 . 
         [0031]    Light emitting element  122  is disposed on substrate  121 , and emits laser light in a direction perpendicular to the installation part of substrate  121  where light emitting element  122  is disposed. The number of light emitting elements  122  is not limited. In the present embodiment, the number of light emitting elements  122  is four. In addition, the position of light emitting element  122  is not limited. In the present embodiment, four light emitting elements are disposed in one line at a constant interval. Light emitting element  122  is a vertical cavity surface emitting laser (VCSEL), for example. It is to be noted that, when optical transmission members  160  are disposed in two or more lines, the number of the lines of light emitting elements  122  may be identical to that of optical transmission members  160 . 
         [0032]    Light receiving element  123  is disposed on the same surface of substrate  121  on which light emitting element  122  is disposed, and is configured to receive reception light Lr from end surface  126  of optical transmission member  160 . The number of light receiving elements  123  is not limited. In the present embodiment, the number of light receiving elements  123  is four. In addition, the position of light receiving element  123  is also not limited. In the present embodiment, four light receiving elements  123  are disposed in one line at a constant interval. Light receiving element  123  is a photodetector, for example. In addition, in the present embodiment, four light emitting elements  122  and four light receiving elements  123  are disposed in one line at a constant interval. Although details are described later, light emitting surface  125  of light emitting element  122  and light reception surface  127  of light receiving element  123  may not be disposed on the same plane. 
         [0033]    Detection element  124  receives monitor light Lm for monitoring the output of emission light L emitted from light emitting element  122  (for example, the intensity and the quantity of the light). Detection element  124  is a photodetector, for example. The number of detection elements  124  is not limited. In the present embodiment, the number of detection elements  124  is four. Four detection elements  124  corresponding to four light emitting elements  122  are disposed in one line. 
         [0034]    Optical receptacle  140  is disposed on substrate  121  of photoelectric conversion device  120 . Disposed between photoelectric conversion device  120  and optical transmission member  160 , optical receptacle  140  optically connects light emitting surface  125  of light emitting element  122  or light reception surface  127  of light receiving element  123 , and end surfaces  126  of a plurality of optical transmission members  160 . In the following, a configuration of optical receptacle  140  is described in detail. 
       (Configuration of Optical Receptacle) 
       [0035]      FIGS. 2A to 2D  illustrate a configuration of optical receptacle  140  according to Embodiment 1.  FIG. 2A  is a plan view of optical receptacle  140 ,  FIG. 2B  is a bottom view of optical receptacle  140 ,  FIG. 2C  is a front view of optical receptacle  140 , and  FIG. 2D  is a rear view of optical receptacle  140 . 
         [0036]    As illustrated in  FIG. 1A  to  FIG. 2D , optical receptacle  140  is a member having a substantially cuboid shape. Optical receptacle  140  has light transmissivity, and emits, toward end surface  126  of optical transmission member  160 , emission light L emitted from light emitting surface  125  of emitting element  122 , and, emits, toward light reception surface  127  of light receiving element  123 , reception light Lr from optical transmission member  160 . Optical receptacle  140  includes a plurality of first optical surfaces  141 , light separation part  142 , transmission surface  143 , a plurality of second optical surfaces  144 , a plurality of third optical surfaces  145 , and fixing part  146 . Optical receptacle  140  is formed using a material having a transparency to light of the wavelength used in optical communications. Examples of such a material include transparent resins such as polyetherimide (PEI) and cyclic olefin resin. In addition, for example, optical receptacle  140  is manufactured by injection molding. 
         [0037]    First optical surface  141  refracts emission light L emitted from light emitting element  122  and allows the light to enter optical receptacle  140 , and, first optical surface  141  refracts reception light Lr from optical transmission member  160  and emits the light toward light receiving element  123  from optical receptacle  140 . In the present embodiment, first optical surface  141  has a shape of a convex lens protruding toward light emitting element  122 . First optical surface  141  converts emission light L emitted from light emitting element  122  into collimate light. In addition, in the present embodiment, a plurality of (twelve) first optical surfaces  141  are disposed in one line in the long side direction on the back surface of optical receptacle  140  in such a manner as to face light emitting surface  125  of light emitting element  122  or light reception surface  127  of light receiving element  123 . In addition, first optical surface  141  has a circular shape in plan view. The light incident on first optical surface  141  advances toward light separation part  142 . It is to be noted that, when the photoelectric conversion elements (light emitting element  122  and light receiving element  123 ) are disposed in two or more lines, the number of the lines of first optical surfaces  141  is identical to that of the photoelectric conversion devices. It is to be noted that, of twelve first optical surfaces  141  in  FIG. 2D  in the present embodiment, four transmission side first optical surfaces  141  on the left end side are used as first optical surface  141 , and other four first optical surfaces  141  on the right end side are used as the reception side first optical surface. That is, emission light L emitted from light emitting element  122  is incident on four transmission side first optical surfaces  141  on the left end, and reception light Lr having passed through the inside is emitted from four reception side first optical surfaces  141  on the right end. In this manner, in optical receptacle  140  according to the present embodiment, with respect to a plane that equally divides twelve first optical surfaces  141  and is perpendicular to substrate  121 , one region functions as the transmission side region, and the other region functions as the reception side region. 
         [0038]    Light separation part  142  separates emission light (collimate light) L of a predetermined light flux diameter incident on first optical surface  141  into monitor light Lm travelling toward detection element  124 , and signal light Ls travelling toward second optical surface (end surface  126  of optical transmission member  160 ) while allowing at least a part of reception light Lr incident on second optical surface  144  to pass therethrough. Light separation part  142  is a region composed of a plurality of surfaces, and is disposed on the top surface side of optical receptacle  140 . 
         [0039]      FIGS. 3A and 3B  illustrate a configuration of light separation part  142 .  FIG. 3A  is a perspective view of light separation part  142 , and  FIG. 3B  is a partially enlarged sectional view illustrating light paths of light separation part  142 . In  FIG. 3B , the hatching of the cross section of optical receptacle  140  is omitted to illustrate light paths in optical receptacle  140 . 
         [0040]    As illustrated in  FIGS. 3A and 3B , light separation part  142  includes a plurality of separation units  147 . While the number of separation units  147  is not limited, four to six separation units  147  are disposed in the region where emission light L incident on first optical surface  141  reaches. Each separation unit  147  includes one division reflection surface  148  and one division transmission surface  149 . That is, light separation parts  142  include a plurality of division reflection surfaces  148  and a plurality of division transmission surfaces  149 . In the following description, the inclination direction of division reflection surface  148  is referred to as first direction D 1  (see arrow D 1  of  FIGS. 1A and 1B  and  FIGS. 3A and 3B ). Division reflection surface  148  and division transmission surface  149  are divided in first direction D 1 . 
         [0041]    Division reflection surface  148  is an inclined surface that is inclined to the optical axis of emission light L incident on first optical surface  141 . Division reflection surface  148  reflects a part of emission light L incident on first optical surface  141  toward third optical surface  145 . In the present embodiment, division reflection surface  148  is tilted such that the distance to second optical surface  144  (optical transmission member  160 ) decreases from the top surface toward the bottom surface of optical receptacle  140 . The inclination angle of division reflection surface  148  is 45 degrees to the optical axis of emission light L incident on first optical surface  141 . Division reflection surface  148  is divided in first direction D 1  at a predetermined interval. Division reflection surfaces  148  are parallel to each other in first direction D 1 . 
         [0042]    Division transmission surface  149  is a surface which is formed at a position different from division reflection surface  148  and is perpendicular to the optical axis of emission light L incident on first optical surface  141  and the optical axis of reception light Lr incident on second optical surface  144 . Division transmission surface  149  allows a part of emission light L incident on first optical surface  141  to pass therethrough, and emits the light to the outside of optical receptacle  140  (see  FIG. 1A ). In addition, division transmission surface  149  allows at least a part of reception light Lr incident on second optical surface  144  to pass therethrough to first optical surface  141  side. Division transmission surface  149  is also divided in first direction D 1  at a predetermined interval. Division transmission surfaces  149  are parallel to each other in first direction D 1 . 
         [0043]    In one separation unit  147 , division reflection surface  148  and division transmission surface  149  are disposed in first direction (a direction from the top surface to the bottom surface) D 1  in the named order. Ridgeline  151  is formed between division reflection surface  148  and division transmission surface  149 . Ridgelines  151  adjacent to one another are parallel to one another in first direction D 1 . The smaller one of the angles between division transmission surface  149  and division step surface  150  is 135 degrees. In addition, the smaller one of the angles between division reflection surface  148  and division transmission surface  149  (of adjacent separation unit  147 ) is 135 degrees. In light separation part  142 , a plurality of separation units  147  are disposed in first direction D 1 . 
         [0044]    As illustrated in  FIG. 3B , a part of emission light L incident on first optical surface  141  is internally incident on division reflection surface  148  at an incident angle greater than the critical angle. Division reflection surface  148  reflects, toward third optical surface  145 , a part of emission light L incident on first optical surface  141 , and generates monitor light Lm. On the other hand, division transmission surface  149  allows a part of emission light L incident on first optical surface  141  to pass therethrough, and generates signal light Ls travelling toward end surface  126  of optical transmission member  160 . At this time, since division transmission surface  149  is perpendicular to emission light L, signal light Ls is emitted without being refracted. 
         [0045]    The ratio between the quantity of signal light Ls and the quantity of monitor light Lm is not limited as long as monitor light Lm capable of monitoring the intensity and the quantity of light L emitted from light emitting element  122  can be obtained while ensuring a desired quantity of signal light Ls. Preferably, the ratio of the quantity of signal light Ls to the quantity of monitor light Lm is 6 to 4, to 8 to 2, or more preferably, 7 to 3. 
         [0046]    Transmission surface  143  is disposed on the top surface side of optical receptacle  140  and is configured to allow signal light Ls emitted from light separation part  142  to again enter optical receptacle  140 . In addition, transmission surface  143  emits reception light Lr incident on second optical surface  144 . In the present embodiment, transmission surface  143  is a surface perpendicular to the optical axis of signal light Ls separated at light separation part  142  and the optical axis of reception light Lr incident on second optical surface  144 . With this configuration, it is possible to allow signal light Ls travelling toward end surface  126  of optical transmission member  160  to again enter optical receptacle  140  without refracting the light. In addition, it is possible to emit reception light Lr travelling toward light separation part  142  out of optical receptacle  140  without refracting the light. 
         [0047]    Second optical surface  144  is an optical surface that emits emission light L incident on first optical surface  141  toward end surface  126  of optical transmission member  160 , and refracts reception light Lr emitted from end surface  126  of optical transmission member  160  to allow the light to enter optical receptacle  140 . In the present embodiment, a plurality of second optical surfaces  144  are disposed in one line in the long side direction on the front surface of optical receptacle  140  in such a manner as to face end surface  126  of optical transmission member  160 . Second optical surface  144  has a shape of a convex lens protruding toward an end surface of optical transmission member  160 . With this configuration, signal light Ls which is incident on first optical surface  141  and separated at light separation part  142  can be condensed and efficiently connected to end surface  126  of optical transmission member  160 . In addition, reception light Lr emitted from optical transmission member  160  converges. It is to be noted that, in the case where optical transmission members  160  are disposed in two or more lines, the number of the lines of second optical surfaces  144  is identical to that of optical transmission members  160 . 
         [0048]    Third optical surface  145  is disposed on the bottom surface side of optical receptacle  140  in such a manner as to face detection element  124 . In the present embodiment, third optical surface  145  is a convex lens protruding toward detection element  124 . Third optical surface  145  causes monitor light Lm separated at light separation part  142  to converge, and emits the light toward detection element  124 . In this manner, it is possible to efficiently couple monitor light Lm to detection element  124 . Preferably, the central axis of third optical surface  145  is perpendicular to the light reception surface (substrate  121 ) of detection element  124 . 
         [0049]    Fixing part  146  fixes end surface  126  of optical transmission member  160  held by ferrule  162  at a predetermined position of optical receptacle  140 . Fixing part  146  fixes optical transmission member  160  such that signal light Ls emitted from second optical surface  144  reaches end surface  126  of optical transmission member  160  at a remote position relative to a focus of the second optical surface  144 . Fixing part  146  is disposed on the front surface of optical receptacle  140  and includes positioning recess  152  and positioning hole  153 . Positioning recess  152  is disposed at a center portion on the front surface of optical receptacle  140 . In addition, second optical surfaces  144  are disposed on the bottom of positioning recess  152 . The shape of positioning recess  152  in plan view is not limited. In plan view, the shape of positioning recess  152  and the shape of ferrule  162  are similar to each other. Step  154  for setting the position of ferrule  162  is disposed in positioning recess  152 . Step  154  is formed to protrude to the inside from the inner wall of positioning recess  152 . In addition, positioning hole  153  is disposed at outer end portions of positioning recess  152  in the long side direction in such a manner as to correspond to a positioning protrusion (omitted in the drawing) of ferrule  162 . The positioning protrusion of ferrule  162  is inserted to positioning hole  153  of optical receptacle  140 . With this configuration, when the positioning protrusion of ferrule  162  is inserted to positioning hole  153  of optical receptacle  140  and an end surface of ferrule  162  is brought into contact with step  154 , the position of ferrule  162  (end surface  126  of optical transmission member  160 ) is set with respect to optical receptacle  140 , and ferrule  162  (end surface  126  of optical transmission member  160 ) is fixed thereto. 
         [0050]    One feature of optical receptacle  140  and optical module  100  according to the present embodiment is the positional relationship between focus f of second optical surface  144  and end surface  126  of optical transmission member  160 . That is, the position where positioning recess  152  sets the position of end surface  126  of optical transmission member  160  with respect to focus f of second optical surface  144  is an important point. In view of this, the positional relationship between focus f of second optical surface  144  and end surface  126  of optical transmission member  160  is described in detail. 
         [0051]      FIG. 4A  illustrates light paths of emission light L of the transmission side in optical module  100  according to Embodiment 1, and  FIG. 4B  illustrates light paths of emission light L in a region around optical transmission member  160 . It is to be noted that, in  FIGS. 4A and 4B , only light emitting element  122 , first optical surface  141 , light separation part  142 , second optical surface  144 , and optical transmission member  160  are illustrated. 
         [0052]    As illustrated in  FIG. 1A  and  FIG. 4A , in the transmission side region in optical module  100  according to Embodiment 1, emission light L emitted from light emitting element  122  enters optical receptacle  140  from first optical surface  141 . At this time, emission light L is converted into collimate light by first optical surface  141 . Emission light L having entered optical receptacle  140  is separated by light separation part  142  into monitor light Lm travelling toward detection element  124  and signal light Ls travelling toward optical transmission member  160 . Monitor light Lm separated toward detection element  124  is emitted from third optical surface  145  and reaches detection element  124 . On the other hand, the light transmitted toward optical transmission member  160  is emitted from second optical surface  144 , and reaches end surface  126  of optical transmission member  160 . 
         [0053]    As illustrated in  FIG. 4B , signal light Ls separated at light separation part  142  is emitted toward end surface  126  of optical transmission member  160  while converging at second optical surface  144 . The emitted signal light Ls passes through focus f of second optical surface  144  and thereafter reaches end surface  126  of optical transmission member  160 . That is, positioning recess  152  sets the position of end surface  126  of optical transmission member  160  such that signal light Ls emitted from second optical surface  144  reaches end surface  126  of optical transmission member  160  at a remote position relative to focus f of second optical surface  144 . It is to be noted that the light flux diameter of signal light Ls emitted from second optical surface  144  gradually decreases toward focus f, and gradually increases after the light passes through focus f. In view of this, it is preferable to dispose end surface  126  of optical transmission member  160  at a position where the light flux diameter of signal light Ls after passing through focus f falls within the end surface of the core. With such a configuration, the use efficiency of signal light Ls emitted from light emitting element  122  and separated at light separation part  142  is not reduced. 
         [0054]    Next, light paths of reception light Lr of the reception side in optical module  100  according to Embodiment 1 will be described.  FIG. 5A  illustrates light paths of reception light Lr in the reception side region in optical module  100  according to Embodiment 1, and  FIG. 5B  illustrates light paths of reception light Lr in a region around light separation part  142 . It is to be noted that, in  FIGS. 5A and 5B , only light receiving element  123 , first optical surface  141 , light separation part  142 , second optical surface  144 , optical transmission member  160  are illustrated. 
         [0055]    As illustrated in  FIG. 1B  and  FIG. 5A , in the reception side region in optical module  100  according to the present embodiment, reception light L emitted from end surface  126  of optical transmission member  160  enters optical receptacle  140  from second optical surface  144 . The light flux diameter of the light having entered optical receptacle  140  decreases as the light travels toward light separation part  142 . That is, the light flux diameter at light separation part  142  of reception light Lr incident on second optical surface  144  is smaller than the light flux diameter at second optical surface  144  of reception light Lr. Here, when the position of an end surface of optical transmission member  160  is set such that signal light Ls (collimate light) having travelled through the inside of optical receptacle  140  is condensed at an end surface of optical transmission member  160  (such that the light flux diameter is minimized at end surface  126  of optical transmission member  160 ), reception light Lr emitted from end surface  126  of optical transmission member  160  is converted by second optical surface  144  into collimate light. However, in optical receptacle  140  according to the present embodiment, end surface  126  of optical transmission member  160  is disposed at a remote position relative to focus f of second optical surface  144 , and thus reception light Lr which is emitted from end surface  126  of optical transmission member  160  and is incident on second optical surface  144  can converge. In this manner, the quantity of reception light Lr which is reflected at division reflection surface  148  of light separation part  142  can be reduced. 
         [0056]    It is to be noted that the ratio of the light flux diameter at light separation part  142  of reception light Lr incident on second optical surface  144  to the light flux diameter at second optical surface  144  of reception light Lr is not limited as long as the above-described conditions are satisfied. From the viewpoint of efficiently causing reception light Lr to reach light receiving element  123 , the quantity of reception light Lr which reaches division transmission surface  149  is preferably greater than the quantity of reception light Lr which reaches division reflection surface  148 . In other words, regarding the irradiation spot (light flux) of reception light Lr which is incident on second optical surface  144  and reaches light separation part  142 , the area of the irradiation spot on division transmission surface  149  is preferably greater than the irradiation spot on division reflection surface  148 . With this configuration, the proportion of reception light Lr which passes through light separation part  142  can be increased, and the use efficiency of reception light Lr is not significantly reduced. 
         [0057]    It is to be noted that, in the present embodiment, the light incident on second optical surface  144  passes through one division transmission surface  149  (see  FIG. 5B ). That is, in the present embodiment, the light flux diameter on light separation part  142  of reception light Lr incident on second optical surface  144  is smaller than division transmission surface  149 . Thus, the whole reception light Lr emitted from optical transmission member  160  can be guided to light receiving element  123 . As described above, in light separation part  142 , the way of setting the light flux diameter of reception light Lr to a small value is not limited. For example, the light flux diameter of reception light Lr on light separation part  142  can be set to a small value by increasing (reducing) the lens diameter, or by reducing (increasing) the curvature. In addition, the light flux diameter of reception light Lr on light separation part  142  can be set to a small value by changing the distances among first optical surface  141 , light separation part  142  and second optical surface  144 . 
       Simulation 1 
       [0058]    In Simulation 1, the relationship between the quantity of signal light which reaches end surface  126  of optical transmission member  160 , and the distance between second optical surface  144  and end surface  126  of optical transmission member  160  in the transmission side region was simulated.  FIGS. 6A and 6B  show the simulation.  FIG. 6A  is a graph showing a relationship between the position of end surface  126  of optical transmission member  160 , and the quantity of signal light which reaches end surface  126  of optical transmission member  160 . The abscissa indicates the position (offset distance) of end surface  126  of optical transmission member  160  with respect to focus f of second optical surface  144 . The ordinate indicates the relative value (db) of the quantity of signal light Ls which reaches end surface  126  of optical transmission member  160  with respect to the quantity of signal light Ls which reaches end surface  126  of optical transmission member  160  in the case where the offset distance is 0 mm.  FIG. 6B  illustrates the luminous intensity distribution at end surface  126  of optical transmission member  160  at the position of the dashed line of  FIG. 6A  (the position remote from focus f by 0.175 mm). In addition, in  FIG. 6B , a measurement region of 50 μm×50 μm is used. In this simulation, the distance between light emitting element  122  and first optical surface  141  is 0.28 mm, the distance between first optical surface  141  and the center of light separation part  142  is 1.02 mm, the distance between the center of light separation part  142  and second optical surface  144  is 2.8 mm, and the distance between second optical surface  144  and optical transmission member  160  is 0.43 mm. 
         [0059]    As illustrated in  FIGS. 4B, 6A and 6B , it was confirmed that the quantity of signal light Ls is kept at a constant value in a region around focus f of second optical surface  144 . This means that the irradiation spot (light flux) of signal light Ls falls within end surface  126  of optical transmission member  160 . In addition, it was confirmed that, when the distance of focus f of second optical surface  144  from end surface  126  of optical transmission member  160  significantly increases, the quantity of received signal light Ls decreases. This means that the irradiation spot (light flux) of signal light Ls falls outside end surface  126  of second optical surface  144 , and that signal light Ls also reaches the region outside end surface  126  of optical transmission member  160 . It can be said from this simulation that the distance from focus f of second optical surface  144  may be set to 0.2 mm. 
       Simulation 2 
       [0060]    In Simulation 2, in the case where end surface  126  of optical transmission member  160  is fixed at a position remote from focus f of second optical surface  144  by 0.175 mm (the position of the dashed line in  FIG. 6A ), the relationship between the distance from end surface  126  of first optical surface  141  and light receiving element  123 , and the quantity of the reception light which reaches light reception surface  127  of light receiving element  123  was simulated. End surface  126  of optical transmission member  160  is set at a position remote from focus f of second optical surface  144  by 0.175 mm, because, under that condition, the light flux diameter of reception light Lr emitted from optical transmission member  160  is minimized at light separation part  142 .  FIGS. 7A and 7B  show the simulation.  FIG. 7A  is a graph illustrating the relationship between the position of light reception surface  127  of light receiving element  123 , and the quantity of the reception light which reaches light reception surface  127  of light receiving element  123 . The abscissa indicates the position (offset distance) of light reception surface  127  of light receiving element  123  to focus f of first optical surface  141 . The ordinate indicates the relative value (db) of the quantity of signal light Ls which reaches light reception surface  127  of light receiving element  123  with respect to the quantity of reception light Lr which reaches light reception surface  127  of light receiving element  123  in the case where the offset distance is 0 mm.  FIG. 7B  illustrates the luminous intensity distribution at light reception surface  127  of light receiving element  123  at the position of the dashed line of  FIG. 7A . In addition, in  FIG. 7B , a measurement region of 70 μm×70 μm is used. 
         [0061]    As illustrated in  FIGS. 5B, 7A and 7B , it was confirmed that the quantity of the received light is kept at a constant value in a region around focus f of first optical surface  141 . This means that the irradiation spot (light flux) of reception light Lr falls within light reception surface  127  of light receiving element  123 . In addition, it was confirmed that, when the position of light reception surface  127  of light receiving element  123  is significantly apart from the light reception surface  127  of light receiving element  123 , the quantity of received reception light Lr is reduced. This means that the irradiation spot (light flux) of reception light Lr falls outside light reception surface  127  of light receiving element  123 , and reception light Lr did not reached light reception surface  127  of light receiving element  123 . That is, under the condition where the light flux diameter of reception light Lr at light separation part  142  is minimized, the light flux diameter at light reception surface  127  of light receiving element  123  is not minimized, but falls within a diameter range of 70 μm (light reception surface  127  of light receiving element  123  for high-speed communication of 10 Gbps). It is to be noted that, when reception light Lr emitted from first optical surface  141  falls outside light reception surface  127  of light receiving element  123 , it suffices to adjust the height of light reception surface  127  of light receiving element  123 . 
         [0062]    As shown by Simulation 1 and Simulation 2, it was confirmed that there is a range where reception light Lr emitted from optical transmission member  160  can appropriately reach light reception surface  127  of light receiving element  123  even in the case where the position of end surface  126  of optical transmission member  160  is adjusted such that the light flux diameter of reception light Lr is minimized at light separation part  142 . 
         [0063]    (Effect) 
         [0064]    As described above, in optical module  100  according to Embodiment 1, emission light L which is emitted from light emitting element  122  and has entered optical receptacle  140  reaches end surface  126  of optical transmission member  160  at a position after focus f of second optical surface  144  from which light is emitted out of optical receptacle  140 . In addition, reception light Lr emitted from end surface  126  of optical transmission member  160  enters optical receptacle  140  toward light separation part  142  while converging at second optical surface  144 . The most part of reception light Lr having entered optical receptacle  140  passes through light separation part  142  (division transmission surface  149 ) and is emitted from first optical surface  141 . With this configuration, even when used as the transmission side and the reception side, optical module  100  can suppress reduction of the quantity of the light which is emitted from optical transmission member  160  and reaches light receiving element  123  while maintaining the quantity of emission light L of the transmission side reaching optical transmission member  160 . 
       Embodiment 2 
       [0065]    Optical module  200  according to Embodiment 2 is different from optical module  100  according to Embodiment 1 in configurations of photoelectric conversion device  220  and optical receptacle  240 . In view of this, the configurations similar to those of Embodiment 1 are denoted with the same reference numerals, and the description thereof will be omitted. 
         [0066]    (Configuration of Optical Module) 
         [0067]      FIGS. 8A and 8B  are sectional views of optical module  200  according to Embodiment 2 of the present invention.  FIG. 8A  illustrates light paths in the transmission side region of optical module  200 , and  FIG. 8B  illustrates light paths in the reception side region of optical module  200 . In  FIGS. 8A and 8B , the hatching of the cross section of optical receptacle  240  is omitted to illustrate light paths in optical receptacle  240 . 
         [0068]    As illustrated in  FIGS. 8A and 8B , optical module  200  according to Embodiment  2  includes photoelectric conversion device  220  and optical receptacle  240 . Photoelectric conversion device  220  includes substrate  221 , four light emitting elements  122 , four light receiving elements  123 , and four detection elements  124 . Substrate  221  has a shape of a flat plate, for example. Light emitting element  122 , light receiving element  123  and detection element  124  are disposed on one surface of substrate  221 . 
         [0069]    (Configuration of Optical Receptacle) 
         [0070]      FIGS. 9A to 9C  illustrate a configuration of optical receptacle  240  according to Embodiment 2.  FIG. 9A  is a plan view of optical receptacle  240 ,  FIG. 9B  is a bottom view of optical receptacle  240 , and  FIG. 9C  is a front view of optical receptacle  240 . 
         [0071]    As illustrated in  FIGS. 9A to 9C , optical receptacle  240  according to Embodiment 2 includes a plurality of first optical surfaces  141 , reflection surface  241 , light separation part  142 , transmission surface  143 , a plurality of second optical surfaces  144 , a plurality of third optical surfaces  145  and fixing part  146 . 
         [0072]    First optical surface  141  and third optical surface  145  are disposed on the bottom surface side of optical receptacle  240 . In addition, second optical surface  144  is disposed on the front surface of optical receptacle  240 . 
         [0073]    Reflection surface  241  is an inclined surface formed on the top surface side of the optical receptacle  240 . Reflection surface  241  reflects emission light L incident on first optical surface  141  toward light separation part  142 , and reflects reception light Lr having passed through light separation part  142  toward first optical surface  141 . Reflection surface  241  is tilted such that the distance to optical transmission member  160  decreases from the bottom surface toward the top surface of optical receptacle  240 . In the present embodiment, the inclination angle of reflection surface  241  is 45 degrees to the optical axis of emission light L incident on first optical surface  141 . Emission light L incident on first optical surface  141  is internally incident on reflection surface  241  at an incident angle greater than the critical angle, and reception light Lr having passed through light separation part  142  is internally incident on reflection surface  241  at an incident angle greater than the critical angle. In this manner, reflection surface  241  totally reflects the incident emission light L in the direction along the surface of substrate  221 , and totally reflects reception light Lr in the direction perpendicular to the surface of substrate  221 . 
         [0074]      FIG. 10A  illustrates light paths of emission light L of the transmission side in optical module  200  according to Embodiment 2, and  FIG. 10B  illustrates light paths of reception light Lr of the reception side in optical module  200  according to Embodiment 2. It is to be noted that  FIGS. 10A and 10B  illustrate only light emitting element  122  (light receiving element  123 ), first optical surface  141 , reflection surface  241 , light separation part  142 , second optical surface  144 , and optical transmission member  160 . 
         [0075]    As illustrated in  FIG. 10A , on the transmission side of optical module  200  according to Embodiment 2, emission light L emitted from light emitting element  122  enters optical receptacle  240  from first optical surface  141 . Emission light L having entered optical receptacle  240  is reflected by reflection surface  241  toward light separation part  142 . Emission light L reflected by reflection surface  241  is separated by light separation part  142  into monitor light Lm travelling toward detection element  124  and signal light Ls travelling toward optical transmission member  160 . Monitor light Lm separated toward detection element  124  is emitted from third optical surface  145 , and reaches detection element  124 . On the other hand, the light having passed therethrough toward optical transmission member  160  is emitted from second optical surface  144 , and reaches end surface  126  of optical transmission member  160 . 
         [0076]    As illustrated in  FIG. 10B , on the reception side of optical module  200  according to the present embodiment, reception light Lr emitted from optical transmission member  160  enters optical receptacle  240  from second optical surface  144 . The light flux diameter of reception light Lr having entered optical receptacle  240  decreases toward light separation part  142 , and the reception light Lr passes through light separation part  142  (division transmission surface  149 ). Reception light Lr having passed through light separation part  142  (division transmission surface  149 ) is reflected by reflection surface  241  toward first optical surface  141 . Reception light Lr reflected by reflection surface  241  is emitted from first optical surface  141 , and reaches light reception surface  127  of light receiving element  123 . 
         [0077]    (Effect) 
         [0078]    With this configuration, optical module  200  according to Embodiment 2 has an effect similar to that of optical module  200  according to Embodiment 1. In addition, since light emitting element  122 , light receiving element  123  and detection element  124  are disposed on the same plane, optical module  200  can be downsized. 
         [0079]    It is to be noted that, as illustrated in  FIG. 11A , light separation unit  247  of light separation part  242  may include, in addition to division reflection surface  148  and division transmission surface  149 , division step surface  250  disposed between division reflection surface  148  and division transmission surface  149 . In this case, division step surface  250  is parallel to the optical axis of emission light L incident on first optical surface  141 , and connects division reflection surface  148  and division transmission surface  149 . A plurality of division step surfaces  250  are disposed such that division step surfaces  250  are parallel to each other in first direction D 1 . 
         [0080]    In addition, as illustrated in  FIG. 11B , light separation units  347  of light separation part  342  are alternately disposed in first direction D 1  and second direction D 2  orthogonal to first direction D 1  in a matrix. Here, the “second direction” is direction D 2  which is orthogonal to first direction D 1  (see arrow D 2  of  FIG. 11 ) along division reflection surface  148 . 
         [0081]    In addition, in optical receptacles  140  and  240  of the embodiments, a reflection film such as a thin film formed of a metal having a high light reflectance (such as Al, Ag and Au) may be formed on reflection surface  241  and division reflection surface  148 . When reduction of the number of components is prioritized, it is preferable to employ a configuration using only a total reflection surface as in Embodiment 1 and of Embodiment 2. 
         [0082]    In optical receptacles  140  and  240  according to Embodiments 1 and 2, first optical surface  141  converts the incident light into collimate light, first optical surface  141  may convert the incident emission light L into light other than collimate light. To be more specific, incident light L may be converted into light whose light flux diameter gradually increases, or light whose light flux diameter gradually decreases. 
         [0083]    This application is entitled to and claims the benefit of Japanese Patent Application No. 2014-158787 filed on Aug. 4, 2014, the disclosure each of which including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
       INDUSTRIAL APPLICABILITY 
       [0084]    The optical receptacle and the optical module according to the embodiments of the present invention are suitable for optical communications using an optical transmission member. 
       REFERENCE SIGNS LIST 
       [0085]      100 ,  200  Optical module 
         [0086]      120 ,  220  Photoelectric conversion device 
         [0087]      121 ,  221  Substrate 
         [0088]      122  Light emitting element 
         [0089]      123  Light receiving element 
         [0090]      124  Detection elements 
         [0091]      125  Light emitting surface 
         [0092]      126  End surface 
         [0093]      127  Light reception surface 
         [0094]      140 ,  240  Optical receptacle 
         [0095]      141  First optical surface 
         [0096]      142 ,  242 ,  342  Light separation part 
         [0097]      143  Transmission surface 
         [0098]      144  Second optical surface 
         [0099]      145  Third optical surface 
         [0100]      146  Fixing part 
         [0101]      147  Separation unit 
         [0102]      148  Division reflection surface 
         [0103]      149  Division transmission surface 
         [0104]      151  Ridgeline 
         [0105]      152  Positioning recess 
         [0106]      153  Positioning hole 
         [0107]      154  Step 
         [0108]      160  Optical transmission member 
         [0109]      162  Ferrule 
         [0110]      241  Reflection surface 
         [0111]      247 ,  347  Light separation unit 
         [0112]      250  Division step surface 
         [0113]    f Focus 
         [0114]    L Emission light 
         [0115]    Lm Monitor light 
         [0116]    Ls Signal light 
         [0117]    Lr Reception light