Patent Publication Number: US-2021181439-A1

Title: Optical receptacle, optical module, and optical transmitter

Description:
TECHNICAL FIELD 
     The present invention relates to an optical receptacle, an optical module and an optical transmitter. 
     BACKGROUND ART 
     In optical communications using an optical transmission member such as an optical fiber, an optical module including a light emitting element such as a surface-emitting laser (e.g., Vertical Cavity Surface Emitting Laser (VCSEL)) is used. The optical module includes an optical receptacle that allows, to enter an end surface of the optical transmission member, transmission light having communication information emitted from the light emitting element. 
     In addition, in the case where two-way optical communications are performed, an optical module including a light receiving element (e.g., a photodiode (PD)) in addition to a light emitting element is used. The optical receptacle provided in the optical module for two-way optical communications has a configuration in which transmission light emitted from the light emitting element that has entered the optical receptacle reaches an end surface of the optical transmission member, and reception light having communication information emitted from the end surface of the optical transmission member that has entered the optical receptacle reaches the light receiving element. At this time, the optical path of the transmission light that enters the end surface of the optical transmission member and the optical path of the reception light that is entered from the end surface of the optical transmission member are common to each other and parallel to each other in a region near the end surface of the optical transmission member. Therefore, typically, the optical receptacle provided in the optical module for two-way optical communications includes an optical path separation part that separates the optical path of the transmission light and the optical path of the reception light from each other. 
     For example, PTL 1 discloses an optical member (optical receptacle) that optically couples a transmitting optical element, a receiving optical element, and an optical fiber, and includes an optical functional member such as a half mirror that separates transmitting optical signal and received optical signal from each other. The above-mentioned optical member includes an inclined surface inclined with respect to the optical axis of the optical fiber, and the optical functional member is disposed in the inclined surface. With such a configuration, the optical functional member can operate such that the transmitting optical signal is reflected at the inclined surface so as to be delivered to the optical fiber, and that the received optical signal passes through the inclined surface so as to reach the receiving optical element. 
     CITATION LIST 
     Patent Literature 
     PTL 1 
     Japanese Patent Application Laid-Open No. 2009-251375 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the optical member disclosed in PTL 1, it is necessary to dispose the optical functional member at an inclined surface. However, installation of the optical functional member at the inclined surface requires fine and exacting operation, and as such the optical member disclosed in PTL 1 easily causes positional displacement of optical functional members. Such positional displacement may result in inclination of the optical axis of the transmitting optical signal or the receiving optical signal, which results displacement of optical coupling between the transmitting optical element and the optical fiber, or between the optical fiber and the receiving optical element, and consequently, the accuracy of optical communications may be reduced. 
     In addition, in the optical member disclosed in PTL 1, it is necessary to dispose a refractive index adjuster whose refractive index is identical to that of the optical member at the back surface of the inclined surface in order to control the optical path of the received optical signal transmitted through the inclined surface. However, typically, the refractive index adjuster is formed with a material whose thermal expansion coefficient is different from that of the material of the main body of the optical member, and consequently crack may occur in a high temperature test and the like after manufacture of the optical member. 
     In view of the above-mentioned problems, an object of the present invention is to provide an optical receptacle, an optical module including the optical receptacle and an optical transmitter including the optical module that can separate a transmitting optical signal and a received optical signal from each other without disposing an optical functional member at the inclined surface and without using an refractive index adjuster. 
     Solution to Problem 
     An optical receptacle of the present invention optically couples a light emitting element and an end surface of an optical transmission member, and optically couples the end surface of the optical transmission member and a light receiving element. The optical receptacle includes a first optical surface configured to allow, to enter the optical receptacle, transmission light emitted from the light emitting element; a second optical surface configured to emit, to outside of the optical receptacle, the transmission light entered from the first optical surface such that the transmission light entered from the first optical surface reaches the end surface of the optical transmission member, the second optical surface being configured to allow, to enter the optical receptacle, reception light emitted from the end surface of the optical transmission member; a third optical surface configured to emit, to the outside of the optical receptacle, the reception light entered from the second optical surface such that the reception light entered from the second optical surface reaches the light receiving element; an optical path separation part configured to deliver, to the second optical surface, a part of the transmission light entered from the first optical surface, the optical path separation part being configured to deliver, to the third optical surface, a part of the reception light entered from the second optical surface; and a light attenuation member disposed on an optical path connecting between the first optical surface and the light emitting element, the light attenuation member being configured to attenuate the reception light that reaches the light emitting element from the optical path separation part, wherein the optical path separation part is an optical surface including a fourth optical surface, and a fifth optical surface inclined with respect to the fourth optical surface, wherein the fourth optical surface is disposed at an angle such that the part of the transmission light that has entered the optical receptacle and has reached the optical path separation part advances toward the second optical surface, and wherein the fifth optical surface is disposed at an angle such that the part of reception light that has entered the optical receptacle and has reached the optical path separation part advances toward the third optical surface. 
     An optical receptacle of the present invention optically couples a light emitting element and an end surface of an optical transmission member, and optically couples the end surface of the optical transmission member and a light receiving element. The optical receptacle includes a first optical surface configured to allow, to enter the optical receptacle, transmission light emitted from the light emitting element; a second optical surface configured to emit, to outside of the optical receptacle, the transmission light entered from the first optical surface such that the transmission light entered from the first optical surface reaches the end surface of the optical transmission member, the second optical surface being configured to allow, to enter the optical receptacle, reception light emitted from the end surface of the optical transmission member; a third optical surface configured to emit, to the outside of the optical receptacle, the reception light entered from the second optical surface such that the reception light entered from the second optical surface reaches the light receiving element; and an optical path separation part configured to deliver, to the second optical surface, a part of the transmission light entered from the first optical surface, the optical path separation part being configured to deliver, to the third optical surface, a part of the reception light entered from the second optical surface, wherein the optical path separation part is an optical surface including a fourth optical surface, and a fifth optical surface inclined with respect to the fourth optical surface, wherein the fourth optical surface is disposed at an angle such that the part of the transmission light that has entered the optical receptacle and has reached the optical path separation part advances toward the second optical surface, and wherein the fifth optical surface is disposed at an angle such that the part of reception light that has entered the optical receptacle and has reached the optical path separation part advances toward the third optical surface. The optical receptacle is used with a light attenuation member disposed on an optical path connecting between the first optical surface and the light emitting element, the light attenuation member being configured to attenuate the reception light that reaches the light emitting element from the optical path separation part. 
     An optical module of the present invention includes: a photoelectric conversion device including a light emitting element and a light receiving element; and the above-mentioned optical receptacle. 
     An optical module of the present invention includes: a photoelectric conversion device including a light emitting element and a light receiving element; an optical receptacle configured to optically couple the light emitting element and an end surface of an optical transmission member, and optically couple the end surface of the optical transmission member and the light receiving element, and a light attenuation member. The optical receptacle includes a first optical surface configured to allow, to enter the optical receptacle, transmission light emitted from the light emitting element; a second optical surface configured to emit, to outside of the optical receptacle, the transmission light entered from the first optical surface such that the transmission light entered from the first optical surface reaches the end surface of the optical transmission member, the second optical surface being configured to allow, to enter the optical receptacle, reception light emitted from the end surface of the optical transmission member; a third optical surface configured to emit, to the outside of the optical receptacle, the reception light entered from the second optical surface such that the reception light entered from the second optical surface reaches the light receiving element; and an optical path separation part configured to deliver, to the second optical surface, a part of the transmission light entered from the first optical surface, the optical path separation part being configured to deliver, to the third optical surface, a part of the reception light entered from the second optical surface, wherein the optical path separation part is an optical surface including a fourth optical surface, and a fifth optical surface inclined with respect to the fourth optical surface, wherein the fourth optical surface is disposed at an angle such that the part of the transmission light that has entered the optical receptacle and has reached the optical path separation part advances toward the second optical surface, wherein the fifth optical surface is disposed at an angle such that the part of reception light that has entered the optical receptacle and has reached the optical path separation part advances toward the third optical surface. The light attenuation member is disposed on an optical path connecting between the first optical surface and the light emitting element, the light attenuation member being configured to attenuate the reception light that reaches the light emitting element from the optical path separation part. 
     An optical transmitter of the present invention includes: an optical transmission member; and two optical modules disposed at both end portions of the optical transmission member, each of the two optical modules being the above-mentioned optical module. 
     Advantageous Effects of Invention 
     According to the present invention, an optical receptacle, an optical module including the optical receptacle and an optical transmitter including the optical module that can separate a transmitting optical signal and a received optical signal from each other without disposing an optical functional member at the inclined surface and without using an refractive index adjuster are provided. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a sectional view schematically illustrating a configuration of an optical module of a first embodiment of the present invention; 
         FIG. 2A  is a plan view of an optical receptacle of the first embodiment of the present invention,  FIG. 2B  is a bottom view of the optical receptacle,  FIG. 2C  is a front view of the optical receptacle,  FIG. 2D  is a back view of the optical receptacle,  FIG. 2E  is a left side view of the optical receptacle, and  FIG. 2F  is a right side view of the optical receptacle; 
         FIG. 3A  is a partially enlarged sectional view of an optical path separation part in a region indicated with a broken line in  FIG. 1 ,  FIG. 3B  is a partially enlarged sectional view illustrating optical paths of transmission light in a region near the optical path separation part, and  FIG. 3C  is a partially enlarged sectional view illustrating optical paths of reception light in a region near the optical path separation part; 
         FIG. 4  is a sectional view schematically illustrating a configuration of an optical module of a second embodiment of the present invention; 
         FIG. 5A  is a partially enlarged sectional view of an optical path separation part in a region indicated with a broken line in  FIG. 4 ,  FIG. 5B  is a partially enlarged sectional view illustrating optical paths of transmission light in a region near the optical path separation part, and  FIG. 5C  is a partially enlarged sectional view illustrating optical paths of reception light in a region near the optical path separation part; and 
         FIG. 6  is a sectional view schematically illustrating a configuration of an optical transmitter of a third embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention are elaborated below with reference to the accompanying drawings. 
     First Embodiment 
     Configuration of Optical Module 
       FIG. 1  is a sectional view schematically illustrating a configuration of optical module  100  of a first embodiment of the present invention. In  FIG. 1 , the dashed line indicates an optical axis, and the broken line indicates the outer diameter of light. 
     As illustrated in  FIG. 1 , optical module  100  includes photoelectric conversion device  200  and optical receptacle  300 . Optical module  100  is an optical module for two-way communications that can perform both transmission and reception. Optical module  100  is used in the state where optical transmission member  400  is connected to optical receptacle  300 . 
     Photoelectric conversion device  200  includes substrate  210 , light emitting element  220  and light receiving element  230 . 
     Substrate  210  holds light emitting element  220 , light receiving element  230  and optical receptacle  300 . Substrate  210  may be a glass composite substrate, a glass epoxy substrate, or a flexible substrate, for example. 
     Light emitting element  220  is a transmitting photoelectric conversion element disposed on substrate  210 . The number and position of light emitting element  220  are not limited, and may be appropriately set in accordance with the use. In the present embodiment, twelve light emitting elements  220  are arranged on the same straight line along the depth direction of  FIG. 1 . 
     Light emitting element  220  emits laser light that is transmission light in a direction perpendicular to the top surface of light emitting element  220 . Light emitting element  220  may be a vertical-cavity surface-emitting laser (VCSEL) that emits transmission light from a light-emitting surface (light emission region), for example. In the present embodiment, light emitting element  220  is a VCSEL that emits laser light having a wavelength of 850 nm. 
     Light receiving element  230  is a receiving photoelectric conversion element disposed on substrate  210 . The number and position of light receiving element  230  are not limited, and may be appropriately set in accordance with the use. In the present embodiment, twelve light receiving elements  230  are arranged on the same straight line along the depth direction of  FIG. 1 . 
     Light receiving element  230  receives laser light that is reception light emitted from the end surface of optical transmission member  400  and transmitted through the inside of optical receptacle  300 . Light receiving element  230  may be a photodiode (PD) that receives and senses reception light at a light reception surface (light reception region). In the present embodiment, light receiving element  230  is a PD that senses laser light having a wavelength of 910 nm. 
     Optical receptacle  300  is disposed between light emitting element  220  and light receiving element  230 , and a plurality of optical transmission members  400 , and optically couples light emitting element  220  and the end surface of optical transmission member  400 , and the end surface of optical transmission member  400  and light receiving element  230 . 
     Photoelectric conversion device  200  and optical receptacle  300  are fixed with each other with a publicly known fixing member such as an adhesive agent containing thermosetting resin, ultraviolet curing resin and the like, for example. 
     Optical transmission member  400  is attached to optical receptacle  300  through a publicly known attaching member in the state where an end portion thereof is housed inside a connector. Optical transmission member  400  may be a publicly known optical transmission member such as an optical fiber and a light waveguide. In the present embodiment, optical transmission member  400  is an optical fiber. The optical fiber may be of a single mode type, or a multiple mode type. The number of optical transmission member  400  is not limited, and may be appropriately changed in accordance with the use. 
     Configuration of Optical Receptacle 
       FIGS. 2A to 2F  illustrate a configuration of optical receptacle  300  of the present embodiment.  FIG. 2A  is a plan view of optical receptacle  300 ,  FIG. 2B  is a bottom view of optical receptacle  300 ,  FIG. 2C  is a front view of optical receptacle  300 ,  FIG. 2D  is a back view of optical receptacle  300 ,  FIG. 2E  is a left side view of optical receptacle  300 , and  FIG. 2F  is a right side view of optical receptacle  300 . 
     As illustrated in  FIG. 1 , optical receptacle  300  is disposed on substrate  210  in such a manner as to face light emitting element  220  and light receiving element  230 . 
     The rate of the intensity of transmission light emitted toward optical transmission member  400  from optical receptacle  300  with respect to the intensity of transmission light that enters optical receptacle  300  is 40% to 50%, for example. This rate can be adjusted by a factor such as the amount of a light attenuator and the planar dimension of a fourth optical surface, which will be described later. 
     Optical receptacle  300  is formed of a material that is optically transparent to light having a wavelength used for optical communications. Examples of such a material include transparent resins such as polyetherimide (PEI) and cyclic olefin resin. Typically, the inside of optical receptacle  300  is filled with the above-mentioned material. 
     Note that a light attenuator that reduces the intensity of the light (transmission light L 1  and reception light L 2 ) passing inside optical receptacle  300  may be added to the material of optical receptacle  300 . Examples of the light attenuator include a phthalocyanine organic pigment, and inorganic particles including carbon black, oxidation copper and the like. The amount of the light attenuator in the material of optical receptacle  300  is appropriately selected in accordance with the type of the light attenuator, the optical path length in optical receptacle  300 , the type of light emitting element  220  and the like. 
     In addition, it is preferable to dispose an antireflection film on the surface of optical receptacle  300  from the viewpoint of suppressing reflection of light at the surface. The antireflection film may be disposed over the entire surface of optical receptacle  300 , or may be disposed only on first optical surface  370  where transmission light L 1  emitted from light emitting element  220  impinges or on second optical surface  380  where reception light L 2  emitted from the end surface of optical transmission member  400  impinges. The method of disposing the antireflection film on the surface of optical receptacle  300  is not limited and it suffices to provide antireflection coating (AR coating) on the surface of optical receptacle  300 , for example. Examples of the material of the antireflection film include, SiO 2 , TiO 2  and MgF 2 . 
     In addition, optical receptacle  300  may include positioning part  302  for alignment of substrate  210  and optical receptacle  300 . From the viewpoint of increasing the visibility through optical receptacle  300 , it is preferable to provide positioning part  302   a  at a position where the top surface and the bottom surface of optical receptacle  300  are parallel to each other. From the viewpoint of ease of shaping and accuracy of alignment, it is preferable to dispose positioning part  302  at the bottom surface (the surface facing substrate  210 ) of optical receptacle  300 , except on the optical path. The shape and the size of positioning part  302  may be set as in a common positioning part. Examples of positioning part  302  may include a recess and a protrusion formed in the bottom surface of optical receptacle  300 , a pattern formed in the bottom surface of optical receptacle  300 , and the like. 
     As illustrated in  FIGS. 2A to 2F , optical receptacle  300  is a member having a substantially cuboid shape. In the present embodiment, first recess  310  having a shape of a substantially rectangular prism surrounded by leg part  305  from three directions is formed in the bottom surface (the surface facing substrate  210 ) of optical receptacle  300 . In the top surface (the surface opposite the bottom surface) of optical receptacle  300 , second recess  320  having a substantially pentagonal prism shape and third recess  330  having a substantially pentagonal prism shape are sequentially disposed in the direction toward the side on which optical transmission member  400  is attached in optical receptacle  300 . As elaborated later, a part of the inner surface of second recess  320  is transmission light reflection part  340 , the other part of the inner surface of third recess  330  is transmission surface  350 , and the other part of the inner surface of third recess  330  is optical path separation part  360 . The interiors of first recess  310 , second recess  320  and third recess  330  are filled with a material (e.g., the atmosphere) having a refractive index lower than that of the material of optical receptacle  300 . 
     Optical receptacle  300  includes first optical surface  370 , second optical surface  380 , third optical surface  390 , optical path separation part  360  and transmission light reflection part  340 . In addition, optical receptacle  300  includes light attenuation member  375  on the optical path connecting between first optical surface  370  and light emitting element  220 . Light attenuation member  375  may be attached to optical receptacle  300 , or may be attached to substrate  210  separately from optical receptacle  300 . 
     In optical receptacle  300 , transmission light L 1  emitted from light emitting element  220  enters optical receptacle  300  from first optical surface  370 , and then reaches second optical surface  380  through transmission light reflection part  340  and optical path separation part  360 , and thereafter, the light is emitted from second optical surface  380  to the end portion of optical transmission member  400 . 
     In addition, in optical receptacle  300 , reception light L 2  emitted from the end portion of optical transmission member  400  enters optical receptacle  300  from second optical surface  380  and travels to third optical surface  390  through optical path separation part  360 , and thereafter, the light is emitted from third optical surface  390  such that the light reaches light receiving element  230 . 
     First optical surface  370  is an optical surface that is disposed in the bottom surface of optical receptacle  300  in such a manner as to face light emitting element  220 , and first optical surface  370  allows, to enter optical receptacle  300 , transmission light L 1  emitted from light emitting element  220 . First optical surface  370  may be a lens that allows, to enter optical receptacle  300 , transmission light L 1  emitted from the light-emitting surface (light emission region) of light emitting element  220  while refracting the light so as to convert the light into collimated light. 
     The number of first optical surface  370  is not limited, and may be appropriately selected in accordance with the use, the number of light emitting elements  220  and the like. In the present embodiment, the number of first optical surfaces  370  is twelve as with light emitting elements  220 . Twelve first optical surfaces  370  are disposed in the bottom surface of optical receptacle  300  in such a manner as to face respective twelve light emitting elements  220 . 
     The shape of first optical surface  370  is not limited, and may be a flat surface or a curved surface. In the present embodiment, first optical surface  370  is a convex lens surface protruding toward light emitting element  220 . In addition, first optical surface  370  has a circular shape in plan view. Preferably, the central axis of first optical surface  370  is perpendicular to the light-emitting surface of light emitting element  220  (and the surface of substrate  210 ). In addition, preferably, first optical surface  370  is disposed at a position where the central axis of first optical surface  370  is aligned with the optical axis of transmission light L 1  emitted from light emitting element  220 . 
     Transmission light reflection part  340  is an optical surface that constitutes a part of the inner surface of second recess  320 , and is inclined such that it comes closer to second optical surface  380  in the direction from the bottom surface toward the top surface of optical receptacle  300 . Transmission light reflection part  340  is disposed at a position with an inclination angle such that transmission light reflection part  340  reflects, toward second optical surface  380 , transmission light L 1  entering optical receptacle  300  from first optical surface  370 , by the difference between the refractive index of the material (e.g., resin) of the inside of optical receptacle  300  and the refractive index of the material (e.g., the atmosphere) of the inside of second recess  320 . Preferably, the inclination angle of transmission light reflection part  340  is, but not limited to, an angle at which transmission light L 1  entering from first optical surface  370  impinges at an incident angle greater than the critical angle so as to be totally reflected. In the present embodiment, the inclination angle of reflection part  340  is 45° (note that in this specification, the angle between two surfaces means the angle smaller than the other) with respect to the optical axis of transmission light L 1  entering from first optical surface  370 . The shape of transmission light reflection part  340  is not limited, and may be a flat surface or a curved surface. In the present embodiment, the shape of transmission light reflection part  340  is a flat surface. 
     Transmission surface  350  is an optical surface that constitutes a part of the inner surface of third recess  330 , and emits transmission light L 1  reflected by transmission light reflection part  340  to the inside of third recess  330 , which is the outside of optical receptacle  300 . Preferably, transmission surface  350  is a surface perpendicular to the optical axis of transmission light L 1  reflected by transmission light reflection part  340 . With such a configuration, transmission surface  350  can deliver transmission light L 1  reflected by transmission light reflection part  340  to optical path separation part  360  and second optical surface  380  along the shortest route without refracting the light at transmission surface  350 , and as a result, the configuration of optical receptacle  300  can be simplified to increase the manufacturability and handleability. 
     Note that depending on the configuration of optical path separation part  360  and the like, transmission surface  350  may be a surface inclined with respect to the optical axis of transmission light L 1  reflected by transmission light reflection part  340  for adjusting the optical path of transmission light L 1  through refraction of transmission light L 1  reflected by transmission light reflection part  340 . In such a case, preferably, transmission surface  350  is inclined such that the distance from second optical surface  380  increases in the direction from the bottom surface toward the top surface of optical receptacle  300  for the purpose of increasing the releasability in injection molding. 
     Optical path separation part  360  is an optical surface that constitutes a part of the inner surface of third recess  330 , and is disposed at a position where transmission light L 1  entering from first optical surface  370  and reception light L 2  entering from second optical surface  380  reach. Optical path separation part  360  is disposed at a position with an inclination angle such that optical path separation part  360  allows, to reenter optical receptacle  300  and travel toward second optical surface  380 , a part of transmission light L 1  emitted from transmission surface  350  to the outside of optical receptacle  300  (the inside of third recess  330 ). Furthermore, optical path separation part  360  is disposed at a position with an inclination angle such that optical path separation part  360  reflects, toward third optical surface  390 , a part of reception light L 2  that has entered optical receptacle  300  from second optical surface  380 , by the difference between the refractive index of the material (e.g., resin) of the inside of optical receptacle  300  and the refractive index of the material (e.g., the atmosphere) of the inside of third recess  330 . 
     Second optical surface  380  is an optical surface disposed in the front surface of optical receptacle  300 , and second optical surface  380  emits, toward the end surface of optical transmission member  400 , a part of transmission light L 1  delivered by optical path separation part  360  to second optical surface  380 . At this time, preferably, second optical surface  380  emits, toward the end surface of optical transmission member  400 , the part of transmission light L 1  while converging the light. 
     In addition, second optical surface  380  is also a surface that allows, to enter optical receptacle  300 , reception light L 2  emitted from the end surface of optical transmission member  400 . Here, second optical surface  380  may be a lens that allows, to enter optical receptacle  300 , reception light L 2  emitted from the end surface of optical transmission member  400  while refracting the light so as to convert the light into collimated light. 
     The number of second optical surfaces  380  is not limited, and may be appropriately selected in accordance with the use. In the present embodiment, the number of second optical surfaces  380  is twelve as with the end surfaces of optical transmission member  400 . Twelve second optical surfaces  380  are disposed to face the respective twelve end surfaces of optical transmission member  400  in the front surface of the optical receptacle  300 . 
     The shape of second optical surface  380  is not limited, and may be a flat surface or a curved surface. In the present embodiment, the shape of second optical surface  380  is a convex lens surface protruding toward the end surface of optical transmission member  400 . Second optical surface  380  has a circular shape in plan view. Preferably, the central axis of second optical surface  380  is perpendicular to the end surface of optical transmission member  400 . 
     Third optical surface  390  is an optical surface disposed in the bottom surface of optical receptacle  300  in such a manner as to face light receiving element  230 , and third optical surface  390  emits reception light L 2  that has entered optical receptacle  300  from second optical surface  380  and is reflected by optical path separation part  360  such that the reception light L 2  reaches light receiving element  230 . 
     The number of third optical surfaces  390  is not limited, and may be appropriately selected in accordance with the use. In the present embodiment, the number of third optical surfaces  390  is twelve as with twelve light receiving elements  230 . Twelve third optical surfaces  390  are disposed in the bottom surface of optical receptacle  300  in such a manner as to face respective twelve light receiving elements  230 . 
     The shape of third optical surface  390  is not limited, and may be a flat surface or a curved surface. In the present embodiment, third optical surface  390  is a convex lens surface protruding toward light receiving element  230 . 
     Light attenuation member  375  may be an optical filter that selectively absorbs light having the wavelength of reception light L 2 , a half mirror that selectively reflects light having the wavelength of reception light L 2 , or the like. The attenuation member is not limited as long as the transmittance of the light of the wavelength of reception light L 2  is smaller than the light of the wavelength of transmission light L 1 . In the present embodiment, light attenuation member  375  is an optical filter that absorbs light having a wavelength of wavelength 910 nm while allowing light having a wavelength of 850 nm to pass therethrough. 
     Configuration and Function of Optical Path Separation Part 
       FIGS. 3A to 3C  illustrate a configuration of optical path separation part  360  of optical receptacle  300  of the present embodiment.  FIG. 3A  is a partially enlarged sectional view of the optical path separation part in the region indicated with the broken line in  FIG. 1 ,  FIG. 3B  is a partially enlarged sectional view illustrating optical paths of transmission light in a region near optical path separation part  360 , and  FIG. 3C  is a partially enlarged sectional view illustrating optical paths of reception light in a region near optical path separation part  360 . 
     Optical path separation part  360  is an optical surface provided with a plurality of separation units  365 . Each separation unit  365   a  has a shape that allows a part of transmission light L 1  to pass therethrough toward second optical surface  380  while reflecting a part of reception light L 2  toward third optical surface  390 . Each separation unit includes fourth optical surface  365   a , fifth optical surface  365   b  inclined with respect to fourth optical surface  365   a , and connection surface  365   c  connecting between fourth optical surface  365   a  and fifth optical surface  365   b . Optical path separation part  360  has a step shape in which a plurality of separation units  365  are arranged. 
     Fourth optical surface  365   a  is an optical surface disposed at an angle at which a part of transmission light L 1  emitted from transmission surface  350  to the outside of optical receptacle  300  is allowed to pass through fourth optical surface  365   a  toward second optical surface  380 . In the present embodiment, fourth optical surface  365   a  is a surface perpendicular to the optical axis of transmission light L 1  emitted from transmission surface  350  to the outside of optical receptacle  300 . 
     Fifth optical surface  365   b  is an optical surface disposed at an angle at which a part of reception light L 2  that has entered optical receptacle  300  from second optical surface  380  is reflected toward third optical surface  390 . In the present embodiment, fifth optical surface  365   b  is a surface inclined with respect to the optical axis of reception light L 2  that has entered optical receptacle  300  from second optical surface  380 . In the present embodiment, fifth optical surface  365   b  is a surface inclined such that the distance from second optical surface  380  (the end surface of optical transmission member  400 ) increases in the direction from the top surface toward the bottom surface of optical receptacle  300 , and fifth optical surface  365   b  has an inclination angle of 45° with respect to the optical axis of reception light L 2  that reaches fifth optical surface  365   b . In addition, fifth optical surface  365   b  has an inclination angle of 135° with respect to fourth optical surface  365   a , and an inclination angle of 135° with respect to connection surface  365   c.    
     Connection surface  365   c  is a surface that connects between fourth optical surface  365   a  and fifth optical surface  365   b , and is parallel to both the optical axis of transmission light L 1  that reaches fourth optical surface  365   a , and the optical axis of reception light L 2  that reaches fifth optical surface  365   b . Connection surface  365   c  has an inclination angle of 90° with respect to fourth optical surface  365   a.    
     Separation units  365  are arranged at an angle such that a plurality of fourth optical surfaces  365   a , fifth optical surfaces  365   b  and connection surfaces  365   c  thereof are respectively parallel to each other at predetermined intervals in the inclination direction of optical path separation part  360 . The number of separation units is not limited, and may be appropriately selected in accordance with the use as long as four to six separation units  365  are disposed within the arrival region of transmission light L 1  emitted from transmission surface  350  to the outside of optical receptacle  300  and within the arrival region of reception light L 2  emitted from second optical surface  380  to the inside of optical receptacle  300 . 
     As necessary, separation unit  365  may include an optical surface, other than fifth optical surface  365   b , that allows a part of transmission light L 1  to pass therethrough toward the top surface, the side surface or the bottom surface of optical receptacle  300  except for second optical surface  380 , or, an optical surface that reflects a part of reception light L 2  toward the top surface, the side surface or the bottom surface of optical receptacle  300  except for third optical surface  390 . In addition, as necessary, separation unit  365  may include an optical surface that reflects a part of transmission light L 1  toward the top surface, the side surface or the bottom surface of optical receptacle  300  except for second optical surface  380 , or, an optical surface that allows a part of reception light L 2  to pass therethrough toward the top surface, the side surface or the bottom surface of optical receptacle  300  except for first optical surface  370  and third optical surface  390 . Preferably, separation unit  365  includes only fourth optical surface  365   a  and connection surface  365   c  as the surface that allows transmission light L 1  to pass therethrough, and includes only fifth optical surface  365   b  as the surface that reflects a part of reception light L 2 , from a view point of the ease of shaping. In addition, from the viewpoint of suppressing occurrence of cross talk or the like, it is preferable not to include the optical surface that delivers, to third optical surface  390 , a part of transmission light L 1  entering from first optical surface  370  by reflecting or allowing the light to pass therethrough and separating the light from the other part of transmission light L 1 . 
     As illustrated in  FIG. 3B , transmission light L 1  that is emitted from transmission surface  350  to the outside of optical receptacle  300  so as to reach optical path separation part  360  reenters optical receptacle  300  from fourth optical surface  365   a  and fifth optical surface  365   b.    
     At this time, since fourth optical surface  365   a  is perpendicular to the optical axis of the above-mentioned transmission light L 1 , fourth optical surface  365   a  allows transmission light L 1   a  that is a part of the transmission light reaching fourth optical surface  365   a  to pass therethrough in the direction toward second optical surface  380  without refracting the light. With such a configuration, fourth optical surface  365   a  can deliver, to second optical surface  380  along the shortest route, transmission light L 1   a  that reaches fourth optical surface  365   a  from transmission light reflection part  340  through transmission surface  350  without refracting the light at fourth optical surface  365   a , and as a result, the configuration of optical receptacle  300  can be simplified to increase the manufacturability and handleability. Note that at this time, transmission light reflection part  340 , transmission surface  350 , optical path separation part  360  and second optical surface  380  are sequentially disposed in the direction toward the side on which optical transmission member  400  is attached in optical receptacle  300 , on a straight line that is parallel to the optical path of the transmission light emitted to optical transmission member  400  and the optical path of the reception light entering from optical transmission member  400 . In addition, the angles of transmission surface  350 , fourth optical surface  365   a  of optical path separation part  360 , and second optical surface  380  are parallel to each other. 
     On the other hand, fifth optical surface  365   b , which is also a surface inclined with respect to the optical axis of the above-mentioned transmission light L 1 , refracts transmission light L 1   b  that is a part of the transmission light reaching fifth optical surface  365   b , by the difference between the refractive index of the material (e.g., the atmosphere) of the inside of third recess  330  and the refractive index of the material (e.g., resin) of the inside of optical receptacle  300 . Fifth optical surface  365   b  functions also as an attenuation part that selectively attenuates transmission light L 1  by refracting transmission light L 1   b  in a direction different from second optical surface  380 . 
     Note that no transmission light L 1  impinges on connection surface  365   c  since connection surface  365   c  is parallel to the incident direction of transmission light L 1 . 
     As illustrated in  FIG. 3C , incident reception light L 2  that enters optical receptacle  300  from second optical surface  380  also reaches optical path separation part  360 . 
     At this time, since fifth optical surface  365   b  is a surface inclined with respect to the optical axis of the above-mentioned reception light L 2 , fifth optical surface  365   b  reflects, toward third optical surface  390 , reception light L 2   a  that is a part of the reception light reaching fifth optical surface  365   b.    
     Note that, as illustrated in  FIG. 3C , fourth optical surface  365   a  is a surface perpendicular to the optical axis of reception light L 2  that enters optical receptacle  300  from second optical surface  380 , and therefore reception light L 2   b  that is a part of the above-mentioned reception light may pass through fourth optical surface  365   a  so as to reach light emitting element  220  through transmission surface  350 , transmission reflection light section  340  and first optical surface  370 . In the present embodiment, for the purpose of suppressing occurrence of cross talk due to the above-mentioned reception light L 2   b  reaching light emitting element  220 , light attenuation member  375  is provided on the optical path connecting between first optical surface  370  and light emitting element  220 . 
     Note that no reception light L 2  impinges on connection surface  365   c  since connection surface  365   c  is parallel to the incident direction of reception light L 2 . 
     In this manner, in optical path separation part  360  disposed at a position on the optical path of transmission light L 1  and the optical path of reception light L 2 , fourth optical surface  365   a  functions as an optical surface that delivers, to second optical surface  380 , a part of transmission light L 1  that enters optical receptacle  300  and reaches optical path separation part  360 , and fifth optical surface  365   b  functions as an optical surface that delivers, to third optical surface  390 , a part of reception light L 2  that enters optical receptacle  300  and reaches optical path separation part  360 . Thus, optical path separation part  360  controls the optical paths inside optical receptacle  300  by separating at least one of the optical path of transmission light L 1  and the optical path of reception light L 2 . 
     It suffices that light attenuation member  375  is a member that attenuates reception light L 2   b  reaching light emitting element  220  from optical path separation part  360  (fourth optical surface  365   a ), and does not significantly attenuates delivery of transmission light L 1   a  from light emitting element  220  to optical path separation part  360  (fourth optical surface  365   a ). Light attenuation member  375  may be an optical filter that selectively absorbs the light of the wavelength of reception light L 2 , a half mirror that selectively reflects the light of the wavelength of reception light L 2  or the like. The above-mentioned attenuation member is not limited as long as the transmittance of the light of the wavelength of reception light L 2  is smaller than the transmittance of the light of the wavelength of transmission light L 1 . In the present embodiment, light attenuation member  375  is an optical filter that allows, to pass therethrough, light having a wavelength of 850 nm, and absorbs light having a wavelength of 910 nm. 
     In transmission light L 1 , the ratio between the light quantity of transmission light L 1  a delivered to second optical surface  380  through fourth optical surface  365   a  and the light quantity of transmission light L 1   b  refracted by fifth optical surface  365   b  so as not to reach second optical surface  380  is substantially the same as the area ratio between fourth optical surface  365   a  and fifth optical surface  365   b  in optical path separation part  360  as viewed from transmission light reflection part  340  side. In addition, in reception light L 2 , the ratio between the light quantity of reception light L 2   b  that passes through fourth optical surface  365   a  so as not to reach third optical surface  390  and the light quantity of reception light L 2   a  that is reflected by fifth optical surface  365   b  toward third optical surface  390  is substantially the same as the area ratio between fourth optical surface  365   a  and fifth optical surface  365   b  in optical path separation part  360  as viewed from second optical surface  380  side. In the present embodiment, transmission light reflection part  340 , transmission surface  350 , optical path separation part  360  and second optical surface  380  are sequentially disposed on a straight line, and therefore the ratio between the light quantity of transmission light L 1  a and the light quantity of transmission light L 1   b  is the same as the ratio between the light quantity of reception light L 2   b  and the light quantity of reception light L 2   a . The above-mentioned two light quantity ratios are substantially the same as the area ratio between fourth optical surface  365   a  and fifth optical surface  365   b  in optical path separation part  360  as viewed from transmission light reflection part  340  side (and is substantially the same as the length ratio between d 1  and d 2  of  FIGS. 3B and 3C ), and can be adjusted by changing the ratio between d 1  and d 2 . It is preferable that the proportion of d 2  be greater than the proportion of d 1  from the viewpoint of increasing the attenuation rate of transmission light L 1  by optical path separation part  360 , and also from the viewpoint of suppressing occurrence of cross talk due to reception light L 2   b  transmitted through fourth optical surface. From the above-mentioned viewpoints, d 1 :d 2  is preferably 5:5 to 9:1, more preferably 7:3 to 8:2. 
     Optical Paths in Optical Module 
     Transmission light L 1  that is laser light having a wavelength of 850 nm emitted from light emitting element  220  enters optical receptacle  300  from first optical surface  370 . At this time, transmission light L 1  is converted to collimated light by first optical surface  370 . Next, transmission light L 1  entering optical receptacle  300  from first optical surface  370  is reflected by transmission light reflection part  340  toward optical path separation part  360 . Transmission light L 1  reflected by transmission light reflection part  340  is emitted from transmission surface  350  to the outside of optical receptacle  300  so as to reach optical path separation part  360  and reenter optical receptacle  300 . At this time, transmission light L 1  a that is a part of transmission light L 1  reaching optical path separation part  360  passes through fourth optical surface  365   a  and reaches second optical surface  380 . At the same time, transmission light L 1   b  that is the other part of transmission light L 1  reaching optical path separation part  360  is refracted by fifth optical surface  365   b , and therefore does not reach second optical surface  380 . With such a configuration, transmission light L 1  is attenuated by optical path separation part  360 . Transmission light L 1   a  reaching second optical surface  380  through fourth optical surface  365   a  is emitted from second optical surface  380  to the outside of optical receptacle  300 , and reaches the end surface of optical transmission member  400 . 
     On the other hand, reception light L 2  that is laser light having a wavelength of 910 nm emitted from the end surface of optical transmission member  400  enters optical receptacle  300  from second optical surface  380 . At this time, reception light L 2  is converted to collimated light by second optical surface  380 . Next, reception light L 2   a  that is a part of reception light L 2  entering optical receptacle  300  from second optical surface  380  reaches optical path separation part  360  so as to be reflected by fifth optical surface  365   b , and reaches third optical surface  390 . Reception light L 2   a  that is reflected by fifth optical surface  365   b  so as to reach third optical surface  390  is emitted to the outside of optical receptacle  300  from third optical surface  390 , and reaches light receiving element  230 . On the other hand, reception light L 2   b  that is the other part of reception light L 2  entering optical receptacle  300  from second optical surface  380  is emitted to the outside of optical receptacle  300  through fourth optical surface  365   a  passes through transmission surface  350  and reenters optical receptacle  300  so as to be reflected by transmission light reflection part  340  toward first optical surface  370 . Reception light L 2   b  having reached first optical surface  370  is emitted to the outside of optical receptacle  300  toward light emitting element  220 , but is absorbed and attenuated by light attenuation member  375  that is an optical filter configured to selectively absorb light having a wavelength of 910 nm, and thus, occurrence of cross talk due to reception light L 2   b  reaching light emitting element  220  is suppressed. 
     Effect 
     As described above, in optical receptacle  300  according to the present embodiment, optical path separation part  360  separates the optical path of reception light L 2  from the optical path of transmission light L 1 , and thus separates light into a transmitting optical signal and a reception optical signal. Thus, optical receptacle  300  according to the present embodiment does not require an optical functional member such as a half mirror at the inclined surface corresponding to optical path separation part  360 , and therefore reduction in accuracy of optical communications due to positional displacement of the optical functional member is suppressed. 
     In addition, in optical receptacle  300  according to the present embodiment, it is not necessary to dispose an optical functional member such as a half mirror at the above-mentioned inclined surface, and therefore it is not necessary to use a refractive index adjuster for adjusting the optical path of light passing through the above-mentioned inclined surface. Therefore, optical receptacle  300  according to the present embodiment can suppress crack in a high temperature test after manufacture of optical receptacle  300  due to the difference between the thermal expansion coefficient of the material of the refractive index adjuster and the thermal expansion coefficient of the material of optical receptacle  300 . 
     Second Embodiment 
       FIG. 4  is a sectional view schematically illustrating a configuration of optical module 500 of a second embodiment of the present invention. In  FIG. 4 , the dashed line indicates an optical axis, and the broken line indicates the outer diameter of light. 
     Optical module  500  of the second embodiment differs from optical module  500  of the first embodiment in that the wavelength of laser light emitted by light emitting element  220  that is a VCSEL is 910 nm, and that the wavelength of the laser light sensed by light receiving element  230  that is a PD is 850 nm. Further, optical module  500  of the second embodiment differs from optical module  500  of the first embodiment in the configuration of optical receptacle  600 . Therefore, in the present embodiment, the component same as those of the first embodiment are denoted with the same reference numerals and the description thereof will be omitted. 
     Configuration of Optical Module 
     As illustrated in  FIG. 4 , optical module  500  includes photoelectric conversion device  200  in which light emitting element  220  and light receiving element  230  disposed on substrate  210 , and optical receptacle  600 . Optical module  500  is an optical module for two-way communications that can perform both transmission and reception. Optical module  500  is used in the state where optical receptacle  600  is connected to optical transmission member  400 . 
     Configuration of Optical Receptacle 
     As in the first embodiment, optical receptacle  600  is disposed over substrate  210  in such a manner as face light emitting element  220  and light receiving element  230 . 
     The ratio of the intensity of transmission light emitted from optical receptacle  600  to optical transmission member  400  to the intensity of transmission light that enters optical receptacle  600  is, for example, 40% to 50%. This ratio can be adjusted by the amount of the light attenuator, the planar dimension of a fourth optical surface described later, and the like. 
     As in the first embodiment, optical receptacle  600  is a member having a substantially cuboid shape, and in the bottom surface (the surface facing substrate  210 ), first recess  310  having a substantially rectangular prism shape that is surrounded by leg part  305  from three directions is formed. In the top surface (the surface opposite the bottom surface) of optical receptacle  600 , fourth recess  620  having a substantially pentagonal prism shape and fifth recess  630  having a substantially pentagonal prism shape are sequentially disposed in the direction away from the side on which optical transmission member  400  is attached in optical receptacle  600 . A part of the inner surface of fourth recess  620  is optical path separation part  660 , and another part of the inner surface of fourth recess  620  is transmission surface  650 , and, a part of the inner surface of fifth recess  630  is reception light reflection part  640 . The inside of first recess  310 , fourth recess  620  and fifth recess  630  is filled with a material (e.g., the atmosphere) whose refractive index is lower than that of the material of optical receptacle  600 . 
     Optical receptacle  600  includes first optical surface  370 , second optical surface  380 , third optical surface  390 , optical path separation part  660  and reception light reflection part  640 . In addition, optical receptacle  600  includes light attenuation member  375  on the optical path connecting between first optical surface  370  and light emitting element  220 . In addition, optical receptacle  600  includes positioning part  302  at a position in bottom surface (the surface facing substrate  210 ) except for the optical path. 
     Optical receptacle  600  allows transmission light L 3  emitted from light emitting element  220  to enter optical receptacle  600  from first optical surface  370 , and delivers the light to second optical surface  380  through optical path separation part  660  such that the light is emitted from second optical surface  380  to the end portion of optical transmission member  400 . 
     In addition, optical receptacle  600  allows reception light L 4  emitted from the end portion of optical transmission member  400  to enter optical receptacle  600  from second optical surface  380 , and delivers the light to third optical surface  390  through optical path separation part  660  and reception light reflection part  640  such that the light is emitted from third optical surface  390  and delivered to light receiving element  230 . 
     Note that the shape, function, position, number and the like of first optical surface  370 , second optical surface  380  and third optical surface  390  may be the same as those of first embodiment, and therefore detailed description thereof is omitted. 
     Optical path separation part  660  is an optical surface that constitutes a part of the inner surface of fourth recess  620 , and is disposed at a position where transmission light L 3  entered from first optical surface  370  and reception light L 4  entered from second optical surface  380  reach. Optical path separation part  660  is disposed at a position with an inclination angle such that optical path separation part  660  reflects, toward second optical surface  380 , a part of transmission light L 3  entering optical receptacle  600  from first optical surface  370 , by the difference between the refractive index of the material (e.g., resin) of the inside of optical receptacle  600  and the refractive index of the material (e.g., the atmosphere) of the inside of fourth recess  620 . Furthermore, optical path separation part  660  is disposed at a position with an inclination angle such that optical path separation part  660  emits a part of reception light L 4  entering optical receptacle  600  from second optical surface  380  toward the inside of fourth recess  620 , which is the outside of optical receptacle  600 . 
     Transmission surface  650  is another optical surface that constitutes a part of the inner surface of fourth recess  620 , and allows, to reenter optical receptacle  600 , reception light L 4  emitted to the outside of optical receptacle  600  from optical path separation part  660 . Preferably, transmission surface  650  is perpendicular to the optical axis of reception light L 4  that is emitted to the outside of optical receptacle  600  (inside of fourth recess  620 ) from optical path separation part  660 . With such a configuration, transmission surface  650  can allow, to reenter optical receptacle  600  along the shortest route, reception light L 4  emitted from optical path separation part  660  and can deliver the light to reception light reflection part  640  without refracting the light at transmission surface  650 . Thus, the configuration of optical receptacle  600  can be simplified and the manufacturability and handleability can be increased. 
     Note that depending on the configuration of optical path separation part  660  and the like, transmission surface  650  may be a surface that is inclined with respect to the optical axis of reception light L 4  emitted to the outside of optical receptacle  600  from optical path separation part  660  and is configured to adjust the optical path of reception light L 4  by refracting reception light L 4  emitted from optical path separation part  660 . In this case, preferably, transmission surface  650  is inclined such that the distance from second optical surface  380  increases in the direction from the bottom surface toward the top surface of optical receptacle  600  for the purpose of increasing the releasability in injection molding. 
     Reception light reflection part  640  is an optical surface that constitutes a part of the inner surface of fifth recess  630 , and is a surface that is inclined such that it comes closer to second optical surface  380  in the direction from the bottom surface toward the top surface of optical receptacle  600 . Reception light reflection part  640  is disposed at a position with an inclination angle such that reception light reflection part  640  reflects, toward third optical surface  390 , reception light L 4  reentering optical receptacle  600  from transmission surface  650 , by the difference between the refractive index of the material (e.g., resin) of the inside of optical receptacle  600  and the refractive index of the material (e.g., the atmosphere) of the inside of fifth recess  630 . Preferably, the inclination angle of reception light reflection part  640  is, but not limited to, an angle at which reception light L 4  reentering optical receptacle  600  from transmission surface  650  impinges thereto at an incident angle greater than the critical angle so as to be totally reflected. In the present embodiment, the inclination angle of reception light reflection part  640  is 45° with respect to the optical axis of reception light L 4  reentering optical receptacle  600  from transmission surface  650 . The shape of reception light reflection part  640  is not limited, and may be a flat surface or a curved surface. In the present embodiment, the shape of reception light reflection part  640  is a flat surface. 
     Configuration and Function of Optical Path Separation Part 
       FIGS. 5A to 5C  illustrate a configuration of optical path separation part  660  of optical receptacle  600  of the present embodiment.  FIG. 5A  is a partially enlarged sectional view of the region indicated with the broken line in  FIG. 4 ,  FIG. 5B  is a partially enlarged sectional view illustrating optical paths of transmission light in a region near optical path separation part  660 , and  FIG. 5C  is a partially enlarged sectional view illustrating optical paths of reception light in a region near optical path separation part  660 . 
     Optical path separation part  660  is an optical surface provided with a plurality of separation units  665 . Each separation unit  665  has a shape that reflects a part of transmission light L 3  toward second optical surface  380 , and allows a part of reception light L 4  to pass therethrough toward third optical surface  390 . Each separation unit includes fourth optical surface  665   a , fifth optical surface  665   b  inclined with respect to fourth optical surface  665   a , and connection surface  665   c  connecting between fourth optical surface  665   a  and fifth optical surface  665   b . Optical path separation part  660  has a step shape in which a plurality of separation units  665  are arranged. 
     Fourth optical surface  665   a  is an optical surface disposed at an angle at which a part of transmission light L 3  entering optical receptacle  600  from first optical surface  370  is reflected toward second optical surface  380 . In the present embodiment, fourth optical surface  665   a  is a surface inclined with respect to optical axis of transmission light L 3  entering optical receptacle  600  from first optical surface  370 . In the present embodiment, fourth optical surface  665   a  is a surface inclined such that the distance from second optical surface  380  (the end surface of optical transmission member  400 ) increases in the direction from the top surface toward the bottom surface of optical receptacle  600 , and fourth optical surface  665   a  has an inclination angle of 45° with respect to optical axis of transmission light L 3  reaching fourth optical surface  665   a . In addition, fourth optical surface  665   a  has an inclination angle of 135° with respect to fifth optical surface  665   b , and an inclination angle of 135° with respect to connection surface  665   c.    
     Fifth optical surface  665   b  is an optical surface disposed at an angle at which fifth optical surface  665   b  allows, to pass therethrough toward third optical surface  390 , a part of reception light L 4  entering optical receptacle  600  from second optical surface  380 , and in the present embodiment, fifth optical surface  665   b  is perpendicular to the optical axis of reception light L 4  entering optical receptacle  600  from second optical surface  380 . 
     Connection surface  665   c  is a surface connecting between fourth optical surface  665   a  and fifth optical surface  665   b . Connection surface  665   c  is perpendicular to the optical axis of transmission light L 3  reaching fourth optical surface  665   a , and is parallel to the optical axis of reception light L 4  reaching fifth optical surface  665   b . Connection surface  665   c  has an inclination angle of 90° with respect to fourth optical surface  665   a . Separation units  665  are arranged at an angle such that fourth optical surfaces  665   a , fifth optical surfaces  665   b  and connection surfaces  665   c  thereof are respectively parallel to each other at predetermined intervals in the inclination direction of optical path separation part  660 . The number of separation units is not limited, and may be appropriately selected in accordance with the use as long as four to six separation units  665  are disposed within the arrival region of transmission light L 3  entering optical receptacle  600  from first optical surface  370 , and within the arrival region of reception light L 4  entering optical receptacle  600  from second optical surface  380 . 
     As necessary, separation unit  665  may include an optical surface that reflects a part of transmission light L 3  toward the top surface, the side surface or the bottom surface of optical receptacle  600  except for second optical surface  380 , or an optical surface that allows a part of reception light L 4  to pass therethrough toward the top surface, the side surface or the bottom surface of optical receptacle  600  except for third optical surface  390 . In addition, as necessary, separation unit  665  may include an optical surface, other than connection surface  665   c , that allows a part of transmission light L 3  to pass therethrough toward the top surface, the side surface or the bottom surface of optical receptacle  600  except for second optical surface  380 , or, an optical surface that allows a part of reception light L 4  to pass therethrough toward the top surface, the side surface or the bottom surface of optical receptacle  600  except for first optical surface  370  and third optical surface  390 . From a view point of the ease of shaping, it is preferable that separation unit  665  include only fourth optical surface  665   a  as the surface that reflects a part of transmission light L 3 , and include only fifth optical surface  665   b  as the surface that allows a part of reception light L 4  to pass therethrough. In addition, from the viewpoint of suppressing occurrence of cross talk or the like, it is preferable not to include the optical surface that delivers, to third optical surface  390 , a part of transmission light L 3  entering from first optical surface  370  by reflecting or allowing the light to pass therethrough and separating the light from the other part of transmission light L 3 . 
     As illustrated in  FIG. 5B , transmission light L 3  entering optical receptacle  600  from first optical surface  370  reaches optical path separation part  660 . 
     At this time, since fourth optical surface  665   a  is a surface inclined with respect to the optical axis of the above-mentioned transmission light L 3 , fourth optical surface  665   a  reflects, in the direction toward second optical surface  380 , transmission light L 3   a  that is a part of the transmission light reaching fourth optical surface  665   a.    
     On the other hand, since fifth optical surface  665   b  is parallel to the incident direction of transmission light L 3 , no transmission light L 3  impinges on fifth optical surface  665   b.    
     In addition, since connection surface  665   c  is a surface perpendicular to the optical axis of the above-mentioned transmission light L 3 , connection surface  665   c  allows, to pass therethrough, transmission light L 3   b  that is a part of the above-mentioned transmission light. Connection surface  665   c  allows to pass therethrough transmission light L 3   b  such that the light travels in a direction different from second optical surface  380 , and thus functions also as an attenuation part that selectively attenuates transmission light L 3 . 
     As illustrated in  FIG. 5C , reception light L 4  entering optical receptacle  600  from second optical surface  380  also reaches optical path separation part  660 . 
     At this time, since fifth optical surface  665   b  is a surface perpendicular to the optical axis of the above-mentioned reception light L 4 , fifth optical surface  665   b  allows reception light L 4   a  that is a part of the transmission light reaching fifth optical surface  665   b  to pass therethrough toward the outside of optical receptacle  600  (the inside of fourth recess  620 ) and toward transmission surface  650  without refracting the light. With such a configuration, fifth optical surface  665   b  can deliver, to third optical surface  390  along the shortest route, reception light L 4   a  entering optical receptacle  600  from second optical surface  380  without refracting the light at fifth optical surface  665   b . Thus, the configuration of optical receptacle  600  can be simplified and the manufacturability and handleability can be increased. Note that, here, second optical surface  380 , optical path separation part  660 , transmission surface  650  and reception light reflection part  640  are sequentially disposed on a straight line parallel to the optical path of the transmission light emitted to optical transmission member  400  and the optical path of the reception light entering from optical transmission member  400  in the direction away from the side on which optical transmission member  400  is attached in optical receptacle  600 . In addition, the angles of second optical surface  380 , fifth optical surface  665   b  of optical path separation part  660 , and transmission surface  650  are parallel to each other. 
     On the other hand, since fourth optical surface  665   a  is a surface inclined with respect to the optical axis of the above-mentioned reception light L 4 , fourth optical surface  665   a  reflects reception light L 4   b  that is a part of the reception light reaching fourth optical surface  665   a , by the difference between the refractive index of the material (e.g., the atmosphere) of the inside of fourth recess  620  and the refractive index of the material (e.g., resin) of the inside of optical receptacle  600 . At this time, the reflected reception light L 4   b  may reach light emitting element  220  through first optical surface  370 . Also in the present embodiment, for the purpose of suppressing occurrence of cross talk due to reception light L 4   b  reaching light emitting element  220 , light attenuation member  375  is provided on the optical path connecting between first optical surface  370  and light emitting element  220 . The configuration, the position, the number and the like of light attenuation member  375  may be the same as in the first embodiment, and therefore the detailed description thereof is omitted. Note that in the present embodiment, light attenuation member  375  is an optical filter that allows light having a wavelength of 910 nm to pass therethrough, and absorbs light having a wavelength of 850 nm. 
     Note that since connection surface  665   c  is parallel to the incident direction of reception light L 4 , no reception light L 4  impinges on connection surface  665   c.    
     In this manner, in optical path separation part  660  disposed at a position on the optical path of transmission light L 3 , and on the optical path of reception light L 4 , fourth optical surface  665   a  functions as an optical surface that delivers, to second optical surface  380 , a part of transmission light L 3  entering optical receptacle  600  and reaching optical path separation part  660 , and fifth optical surface  665   b  functions as an optical surface that delivers, to third optical surface  390 , a part of reception light L 4  entering optical receptacle  600  and reaching optical path separation part  660 . Thus, optical path separation part  660  controls the optical paths inside optical receptacle  300  by separating the optical path of transmission light L 3  from the optical path of reception light L 4 . 
     The light quantity ratio between the light quantity of transmission light L 3   a  that is delivered by fourth optical surface  665   a  to second optical surface  380  and the light quantity of transmission light L 3   b  that passes through fifth optical surface  665   c  so as not to reach second optical surface  380  in transmission light L 3  is substantially the same as the area ratio between fourth optical surface  665   a  and connection surface  665   c  in optical path separation part  660  as viewed from first optical surface  370  side (and is substantially the same as the length ratio between d 3  and d 4  of  FIG. 5B ), and can be adjusted by changing the ratio between d 3  and d 4 . From the viewpoint of increasing the attenuation rate of transmission light L 3  by optical path separation part  660 , it is preferable that the proportion of d 4  be large. In view of this, preferably, d 3 :d 4  is 5:5 to 1:9, more preferably 3:7 to 2:8. 
     In addition, the light quantity ratio between the light quantity of reception light L 4   a  that passes through fifth optical surface  665   b  toward third optical surface  390  and the light quantity of reception light L 4   b  that is reflected by fourth optical surface  665   a  so as not to reach third optical surface  390  in reception light L 4  is substantially the same as the area ratio between fifth optical surface  665   b  and fourth optical surface  665   a  in optical path separation part  660  as viewed from second optical surface  380  side (and is substantially the same as the length ratio between d 5  and d 6  of  FIG. 5C ), and can be adjusted by changing the ratio between d 5  and d 6 . From the viewpoint of increasing the reception sensitivity by increasing the proportion of reception light L 4   a  that reaches light receiving element  230 , and the view point of suppressing occurrence of cross talk due to arrival of reception light L 4   b  of light emitting element  220 , it is preferable that the proportion of d 5  be large. In view of this, preferably, d 5 :d 6  is 5:5 to 9:1, more preferably 7:3 to 8:2. 
     Optical Paths in Optical Module 
     Transmission light L 3  that is laser light emitted from light emitting element  220  and having a wavelength of 910 nm enters optical receptacle  600  from first optical surface  370 . At this time, transmission light L 3  is converted to collimated light by first optical surface  370 . Next, transmission light L 3   a  that is a part of transmission light L 3  entering optical receptacle  600  from first optical surface  370  reaches optical path separation part  660 , and is reflected by fourth optical surface  665   a  toward second optical surface  380 . On the other hand, transmission light L 3   b  that is the other part of transmission light L 3  reaching optical path separation part  660  passes through connection surface  665   c  and as such does not reach second optical surface  380 . Thus, transmission light L 3  is attenuated by optical path separation part  660 . Transmission light L 3   a  reflected by fourth optical surface  665   a  so as to reach second optical surface  380  is emitted to the outside of optical receptacle  600  from second optical surface  380  so as to reach the end surface of optical transmission member  400 . 
     On the other hand, reception light L 4  that is laser light having a wavelength of 850 nm emitted from the end surface of optical transmission member  400  enters optical receptacle  600  from second optical surface  380 . At this time, reception light L 4  is converted to collimated light by second optical surface  380 . Next, reception light L 4   a  that is a part of reception light L 4  entering optical receptacle  600  from second optical surface  380  reaches optical path separation part  660  and is emitted to the outside of optical receptacle  600  (the inside of fourth recess  620 ) through fifth optical surface  665   b . Reception light L 4   a  emitted to the outside of optical receptacle  600  (the inside of fourth recess  620 ) reenters optical receptacle  600  through transmission surface  650 , and is reflected by reception light reflection part  640  toward third optical surface  390 . Reception light L 4   a  reflected toward third optical surface  390  is emitted from third optical surface  390  to the outside of optical receptacle  600 , and reaches light receiving element  230 . On the other hand, reception light L 4   b  that is the other part of reception light L 4  entering optical receptacle  600  from second optical surface  380  is reflected by fourth optical surface  665   a  toward first optical surface  370 . Reception light L 4   b  having reached first optical surface  370  is emitted to the outside of optical receptacle  600  toward light emitting element  220 , but is absorbed and attenuated by light attenuation member  375 , which is an optical filter that absorbs light having a wavelength of 850 nm. Thus, occurrence of cross talk due to reception light L 4   b  reaching light emitting element  220  is suppressed. 
     Effect 
     As described above, in optical receptacle  600  according to the present embodiment, optical path separation part  660  separates the optical path of reception light L 3  from the optical path of transmission light L 4 , and thus separates light into a transmitting optical signal and a reception optical signal. Thus, optical receptacle  600  according to the present embodiment does not require an optical functional member such as a half mirror at the inclined surface corresponding to optical path separation part  660 , and reduction in accuracy of optical communications due to positional displacement of the optical functional member is suppressed. 
     In addition, in optical receptacle  600  according to the present embodiment, it is not necessary to dispose an optical functional member such as a half mirror at the above-mentioned inclined surface, and therefore it is not necessary to use a refractive index adjuster for adjusting the optical path of light passing through the above-mentioned inclined surface. Therefore, optical receptacle  600  according to the present embodiment can suppress crack in a high temperature test after manufacture of optical receptacle  600  due to the difference between the thermal expansion coefficient of the material of the refractive index adjuster and the thermal expansion coefficient of the material of optical receptacle  600 . 
     In addition, in optical receptacle  600  according to the present embodiment, the attenuation rate of transmission light L 3  (proportion of d 4  to d 3 ) and the attenuation rate of reception light L 4  (the proportion of reception light L 4  that reaches light receiving element  230 : the proportion of d 5  to d 6 ) can be independently controlled. 
     Third Embodiment 
       FIG. 6  is a sectional view schematically illustrating a configuration of optical transmitter  700  of a third embodiment of the present invention. 
     As illustrated in  FIG. 6 , optical transmitter  700  includes optical transmission member  400 , and optical module  100  of the first embodiment and optical module  500  of the second embodiment which are disposed at both end portions of optical transmission member  400 . 
     Transmission light L 1  that is laser light having a wavelength of 850 nm emitted from light emitting element  220  of optical module  100  enters optical receptacle  300  from first optical surface  370  and passes through transmission light reflection part  340 , transmission surface  350 , optical path separation part  360 , and second optical surface  380  in this order. In this manner, transmission light L 1   a  that is a part of transmission light L 1  having passed through fourth optical surface  365   a  of optical path separation part  360  is emitted to the outside of optical receptacle  300  from second optical surface  380  so as to reach the end surface of optical transmission member  400 . Thereafter, transmission light L 1   a  passes through the inside of optical transmission member  400 , and reaches the end surface of optical transmission member  400  on optical module  500  side. The laser light having reached the end surface on optical module  500  side is emitted from the end surface, and becomes reception light L 4 . Reception light L 4  passes through second optical surface  380 , optical path separation part  660 , transmission surface  650 , reception light reflection part  640 , and third optical surface  390  in this order. With such a configuration, reception light L 4   a  that is a part of reception light L 4  having passed through fifth optical surface  660   b  of optical path separation part  660  is emitted to the outside of optical receptacle  600  from third optical surface  390 , and reaches light receiving element  230 . 
     On the other hand, transmission light L 3  that is laser light emitted from light emitting element  220  of optical module  500  and having a wavelength of 850 nm enters optical receptacle  600  from first optical surface  370 , and passes through optical path separation part  660  and second optical surface  380  in this order. In this manner, transmission light L 3   a  that is a part of transmission light L 3  that is reflected by fourth optical surface  665   a  of optical path separation part  660  is emitted to the outside of optical receptacle  600  from second optical surface  380 , and reaches the end surface of optical transmission member  400 . Thereafter, transmission light L 3   a  passes through the inside of optical transmission member  400 , and reaches the end surface of optical transmission member  400  on optical module  100  side. The laser light having reached the end surface on optical module  100  side is emitted from the end surface, and becomes reception light L 2 . Reception light L 2  passes through second optical surface  380  and optical path separation part  360  in this order. In this manner, reception light L 2   a  that is a part of reception light L 2  reflected by fifth optical surface  360   b  of optical path separation part  360  is emitted to the outside of optical receptacle  300  from third optical surface  390 , and reaches light receiving element  230 . 
     Effect 
     As described above, optical transmitter  700  according to the present embodiment separates a signal into a transmitting optical signal and a receiving optical signal in such a manner that optical path separation part  360  of optical receptacle  300  of optical module  100  separates the optical path of reception light L 2  from the optical path of transmission light L 1 , and that optical path separation part  660  of optical receptacle  600  of optical module  500  separates the optical path of transmission light L 3  from the optical path of reception light L 4 . Thus, optical transmitter  700  according to the present embodiment can achieve two-way communications while suppressing reduction in accuracy of optical communications due to positional displacement of the optical functional member. 
     Other Embodiments 
     While the invention made by the present inventor has been specifically described based on the preferred embodiments, it is not intended to limit the present invention to the above-mentioned preferred embodiments but the present invention may be further modified within the scope and spirit of the invention defined by the appended claims. 
     For example, while the optical receptacle includes four to six separation units in the first to third embodiments, the number of the separation units of the optical receptacle is not limited, and may be one to three, or seven or more. 
     In addition, while the light emitting element and the light receiving element are mounted on the same substrate and disposed on the same plane in the first to third embodiments, they may be mounted on different substrates, and may be disposed on different planes. For example, the light emitting element of the first embodiment may be disposed on a plane perpendicular to the light receiving element. In this manner, the light emitting element can be disposed on the same straight line as that of the transmission surface, the optical path separation part and the second optical surface, and the transmission light reflection part is not required, and therefore, the manufacturability and handleability can be increased by simplifying the configuration of the optical receptacle. Likewise, the light receiving element of the second embodiment may be disposed on a plane perpendicular to the light emitting element. 
     In addition, while the light attenuation member is disposed apart from both the first optical surface and the light emitting element on the optical path connecting between the first optical surface and the light emitting element in the first to third embodiments, it is also possible to dispose a light attenuation member at the first optical surface or the light-emitting surface of the light emitting element (light emission region) by coating the first optical surface or the light-emitting surface of the light emitting element (light emission region) with a material that selectively attenuates reception light through selective absorption of light of the wavelength of reception light and the like. 
     In addition, while the first optical surface is disposed at a position where the central axis thereof is aligned with the optical axis of the transmission light emitted from the light emitting element in the first to third embodiments, it may be disposed at a position deviated from the optical axis of the transmission light emitted from the light emitting element. At this time, an optical member such as a mirror or a filter that reflects or refracts light having the wavelength of the transmission light may be disposed between the light emitting element and the first optical surface such that the transmission light emitted from the light emitting element is delivered toward the first optical surface. Further, at this time, it is also possible to suppress the occurrence of cross talk due the reception light reaching the light emitting element by using, as the above-mentioned optical member, a member that does not reflect or refract the reception light entered from the second optical surface such that the light is not delivered to the first optical surface. 
     In addition, in the third embodiment, the two optical modules disposed at both end portions of optical transmission member  400  may each be optical module  100  of the first embodiment, or may each be optical module  500  of the second embodiment as long as the attenuation rate of transmission light at the optical path separation part (the attenuation rate of transmission light L 1  at optical path separation part  360  in optical module  100  of the first embodiment; the attenuation rate of transmission light L 3  at optical path separation part  660  in optical module  500  of the second embodiment), and the quantity of light from the optical path separation part to the light receiving element (the quantity of transmission light L 2   a  from optical path separation part  360  to light receiving element  230  in optical module  100  of the first embodiment; the quantity transmission light L 4   b  from optical path separation part  660  to light receiving element  220  in optical module  500  of the second embodiment) are appropriately adjusted. 
     In addition, a light attenuator, an antireflection film and the like may be disposed in the surface of the optical receptacle where transmission light refracted by the fifth optical surface reaches in the first and third embodiments. In this manner, it is possible to suppress reduction in sensitivity of light transmission and light reception due to the transmission light refracted at the fifth optical surface that is reflected to pass through the optical path of transmission light L 1  or reception light L 2 . Likewise, in the second and third embodiments, a light attenuator, an antireflection film and the like may be disposed in the surface of the optical receptacle where transmission light transmitted through the connection surface reaches. 
     This application is entitled to and claims the benefit of Japanese Patent Application No. 2017-213719 filed on Nov. 6, 2017, the disclosure each of which including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
     INDUSTRIAL APPLICABILITY 
     The optical receptacle, the optical module and the optical transmission member according to the present invention are suitable for optical communications using an optical transmission member, for example. 
     REFERENCE SIGNS LIST 
     
         
           100  Optical module 
           200  Photoelectric conversion device 
           210  Substrate 
           220  Light emitting element 
           230  Light receiving element 
           300  Optical receptacle 
           302  Positioning part 
           305  Leg part 
           310  First recess 
           320  Second recess 
           330  Third recess 
           340  Transmission light reflection part 
           350  Transmission surface 
           360  Optical path separation part 
           365  Separation unit 
           365   a  Fourth optical surface 
           365   b  Fifth optical surface 
           365   c  Connection surface 
           370  First optical surface 
           375  Light attenuation member 
           380  Second optical surface 
           390  Third optical surface 
           400  Optical transmission member 
           500  Optical module 
           600  Optical receptacle 
           620  Fourth recess 
           630  Fifth recess 
           640  Reception light reflection part 
           650  Transmission surface 
           660  Optical path separation part 
           665  Separation unit 
           665   a  Fourth optical surface 
           665   b  Fifth optical surface 
           665   c  Connection surface 
           700  Optical transmitter