Patent Publication Number: US-2021173157-A1

Title: Optical receptacle and optical module

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is entitled to and claims the benefit of Japanese Patent Application No. 2019-213215, filed on Nov. 26, 2019, the disclosure of which including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The present invention relates to an optical receptacle and an optical module. 
     BACKGROUND ART 
     In the related art, an optical module including a light emitting element such as a surface emitting laser (e.g., vertical cavity surface emitting laser (VCSEL)) is used for optical communications using an optical transmission member such as an optical fiber and an optical waveguide. The optical module includes one or more photoelectric conversion elements (light emitting elements or light reception elements), and an optical receptacle (coupling lens) configured for transmission, reception, or transmission and reception. 
     In addition, for safety purposes, an optical module configured for light speed communication may attenuate the quantity of light emitted from a transmitting optical receptacle (see, for example, PTL 1). In addition, as a method for attenuating light emitted from a transmitting optical receptacle, an attenuation coating may be provided on the optical surface. 
     PTL 1 discloses a coupling lens for optically coupling a light source and an optical fiber. The coupling lens disclosed in PTL 1 includes an incidence surface on the light source side, and an emission surface on the optical fiber side. The emission surface is a so-called diffraction lens, and includes a ring-band that is concentric about the optical axis of the emission surface. 
     The coupling lens disclosed in PTL 1 adjusts the refraction efficiency of the diffraction lens such that zero-order diffraction light and primary diffraction light transmitted through the diffraction lens are utilized without utilizing secondary and subsequent diffraction light. 
     CITATION LIST 
     Patent Literature 
     PTL 1 
     
         
         WO00/17691 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     The coupling lens disclosed in PTL 1 utilizes the zero-order diffraction light and the primary diffraction light, and therefore requires an optical design in consideration of adjustment of light of two diffraction orders, thus making it difficult to adjust the quantity of light in some cases. In addition, in the optical surface provided with the attenuation coating, the attenuation coating may be cracked, and attenuation of the light quantity of light may not be achieved. 
     In view of this, an object of the present invention is to provide an optical receptacle that can accurately attenuate light emitted from a light emitting element without using other members such as an optical filter and an attenuation coating. In addition, another object of the present invention is to provide such an optical module including the optical receptacle. 
     Solution to Problem 
     To achieve the above-mentioned object, an optical receptacle of an embodiment of the present invention is configured to be disposed between a light emitting element and an optical transmission member and configured to optically couple the light emitting element and the optical transmission member, the optical receptacle including a first optical surface configured to allow incidence of light emitted from the light emitting element; a second optical surface configured to emit, toward the optical transmission member, light emitted from the light emitting element and advanced inside the optical receptacle; and a diffraction surface disposed on the first optical surface, on the second optical surface, or on a light path between the first optical surface and the second optical surface. The diffraction surface is configured such that primary diffraction light of the light emitted from the light emitting element reaches an end portion of the optical transmission member, and that zero-order diffraction light of the light emitted from the light emitting element does not reach the end portion of the optical transmission member. 
     In addition, to achieve the above-mentioned object, an optical module of an embodiment of the present invention includes a photoelectric conversion device including a light emitting element; and an optical receptacle configured to optically couple, to an optical transmission member, light emitted from the light emitting element. The optical receptacle is the optical receptacle. 
     Advantageous Effects of Invention 
     An optical receptacle of an embodiment of the present invention can accurately attenuate the quantity of light emitted from the light emitting element. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a sectional view of an optical module according to Embodiment 1; 
         FIGS. 2A to 2C  illustrate a configuration of an optical receptacle according to Embodiment 1; 
         FIGS. 3A to 3C  illustrate a configuration of an optical receptacle according to Modification 1 of Embodiment 1; 
         FIGS. 4A to 4C  illustrate a configuration of an optical receptacle according to Modification 2 of Embodiment 1; 
         FIGS. 5A to 5C  illustrate a configuration of an optical receptacle according to Modification 3 of Embodiment 1; 
         FIG. 6  is a sectional view of an optical module according to Embodiment 2; 
         FIGS. 7A to 7C  illustrate a configuration of an optical receptacle according to Embodiment 2; 
         FIG. 8  is a sectional view illustrating a configuration of an optical module according to Embodiment 3; and 
         FIGS. 9A to 9D  illustrate a configuration of an optical receptacle according to Embodiment 3. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An optical receptacle and an optical module according to an embodiment of the present invention are elaborated below with reference to the accompanying drawings. 
     Embodiment 1 
     Configuration of Optical Module 
       FIG. 1  is a sectional view of optical module  100  according to Embodiment 1 of the present invention. Note that in  FIG. 1 , the hatching of optical receptacle  120  is omitted for illustration of light paths. In  FIG. 1 , the center of the light flux is illustrated with a dashed line, and the outline of the light flux is illustrated with a dotted line. 
     As illustrated in  FIG. 1 , optical module  100  includes photoelectric conversion device  110  including one or more photoelectric conversion elements  112 , and optical receptacle  120 . Optical module  100  is used in the state where optical transmission member  130  is connected to optical receptacle  120 . 
     Photoelectric conversion device  110  includes substrate  111  and photoelectric conversion element  112 . 
     On substrate  111 , one or more photoelectric conversion elements  112  and optical receptacle  120  are disposed. On substrate  111 , a protrusion (omitted in the drawing) for setting the position of optical receptacle  120  may be formed. By fitting a recess (omitted in the drawing) of optical receptacle  120  to the protrusion, optical receptacle  120  can be positioned at a predetermined position with respect to photoelectric conversion element  112  disposed on substrate  111 . The material of substrate  111  is not limited. Substrate  111  is a glass composite substrate, a glass epoxy substrate, or the like, for example. 
     Photoelectric conversion element  112  emits light of a predetermined wavelength, or receives light of a predetermined wavelength. Photoelectric conversion element  112  is light emitting element  113  or light reception element  114 , and is disposed on substrate  111 . In transmitting optical module  100 , light emitting element  113  is used as photoelectric conversion element  112 . In receiving optical module  100 , light reception element  114  is used as photoelectric conversion element  112 . Light emitting element  113  is a vertical cavity surface emitting laser (VCSEL), for example. Light reception element  114  is a photodetector, for example. In the present embodiment, optical module  100  is transmitting and receiving optical module  100 , and therefore photoelectric conversion element  112  includes four light emitting elements  113  and four light reception elements  114 . 
     On substrate  111 , optical receptacle  120  is disposed opposite to photoelectric conversion element  112 . Optical receptacle  120  optically couples photoelectric conversion element  112  and the end surface of optical transmission member  130  in the state where optical receptacle  120  is disposed between photoelectric conversion element  112  and optical transmission member  130 . In the present embodiment, optical receptacle  120  emits, toward the end surface of optical transmission member  130 , light emitted from photoelectric conversion element  112  (light emitting element  113 ), and emits, toward photoelectric conversion element  112  (light reception element  114 ), light emitted from the end surface of optical transmission member  130 . The configuration of optical receptacle  120  will be elaborated later. 
     The type of optical transmission member  130  is not limited. Examples of the type of optical transmission member  130  include an optical fiber and an optical waveguide. Optical transmission member  130  is connected to optical receptacle  120  through ferrule  131 . In the present embodiment, optical transmission member  130  is an optical fiber. In addition, the optical fiber may be of a single mode type, or a multiple mode type. In the case where optical transmission member  130  is an optical fiber, optical transmission member  130  includes a core and a cladding. 
     Configuration of Optical Receptacle 
       FIGS. 2A to 2C  illustrate a configuration of optical receptacle  120  according to Embodiment 1.  FIG. 2A  is a plan view of optical receptacle  120  according to the present embodiment,  FIG. 2B  is a bottom view of optical receptacle  120 , and  FIG. 2C  is a sectional view taken along line A-A of  FIG. 2B . 
     As illustrated in  FIGS. 2A to 2C , optical receptacle  120  is a member having a substantially cuboid shape. Optical receptacle  120  includes first optical surface  121 , second optical surface  122 , and a diffraction surface (diffraction grating)  123 . Optical receptacle  120  according to the present embodiment is a transmitting and receiving optical receptacle, and therefore includes a region (transmission region) that serves a function of transmitting, to optical transmission member  130 , light emitted from light emitting element  113 , and a region (light reception region) that serves a function of receiving, at light reception element  114 , light emitted from optical transmission member  130 . In the example illustrated in  FIGS. 2A to 2C , the left side in the drawing is the transmission region, and the right side in the drawing is the reception region. 
     Optical receptacle  120  is formed of a material that is optically transparent to light of a wavelength used for optical communications. Examples of the material of optical receptacle  120  include polyetherimide (PEI) such as ULTEM (registered trademark) and a transparent resin such as cyclic olefin resin. Optical receptacle  120  may be produced by injection molding, for example. Optical receptacle  120  is molded as one piece including diffraction surface  123 . 
     First optical surface  121  is an optical surface that allows light emitted from photoelectric conversion element  112  (light emitting element  113 ) to enter optical receptacle  120 , or is an optical surface that emits, toward photoelectric conversion element  112  (light reception element  114 ), light entered from second optical surface  122 . In the present embodiment, first optical surfaces  121  are disposed opposite to photoelectric conversion element  112  in a line along the longitudinal direction. In the present embodiment, twelve first optical surfaces  121  are disposed in a line. In the example illustrated in  FIG. 2B , four first optical surfaces  121  on the left side in the drawing function as incidence surfaces, four first optical surfaces  121  on the right side in the drawing function as emission surfaces, and four first optical surfaces  121  at the center are not used. 
     The shape of first optical surface  121  is not limited. The shape of first optical surface  121  may be a flat surface, a convex lens surface protruding toward photoelectric conversion element  112 , or a concave lens surface recessed toward photoelectric conversion element  112 . In the present embodiment, the shape of first optical surface  121  is a convex lens surface protruding toward photoelectric conversion element  112 . In addition, first optical surface  121  has a circular shape in plan view. Preferably, the central axis of first optical surface  121  is perpendicular to the light-emitting surface or the light-receiving surface of photoelectric conversion element  112  (and the front surface of substrate  111 ). In addition, preferably, the central axis of first optical surface  121  coincides with the optical axis of light emitted from photoelectric conversion element  112  (light emitting element  113 ), or light incident on photoelectric conversion element  112  (light reception element  114 ). 
     Second optical surface  122  is an optical surface that emits, toward the end surface of optical transmission member  130 , light entered from first optical surface  121 , or is an optical surface that allows, to enter optical receptacle  120 , light emitted from the end surface of optical transmission member  130 . In the present embodiment, diffraction surface  123  is formed in a part of second optical surface  122 . The shape of second optical surface  122  is not limited. The shape of second optical surface  122  may be a flat surface, a convex lens surface protruding toward the end surface of optical transmission member  130 , or a concave lens surface recessed toward photoelectric conversion element  112 . In the present embodiment, the shape of second optical surface  122  is a flat surface. In the example illustrated in  FIG. 2A , the region on the left side in the drawing functions as the emission surface, the region on the right side in the drawing functions as the incidence surface, and the region at the center is not used. 
     Diffraction surface  123  focuses predetermined diffraction light toward the end portion of optical transmission member  130 . In the present embodiment, preferably, diffraction surface  123  is configured such that primary diffraction light reaches the end portion of optical transmission member  130  whereas zero-order diffraction light does not reach the end portion of optical transmission member  130  such that only primary diffraction light reaches the end portion of optical transmission member  130 . 
     The shape of diffraction surface  123  is appropriately set in accordance with the proportion of light to be attenuated. In diffraction surface  123 , a blazed shape (saw-tooth shape) may be formed by applying a hologram technique capable of freely shaping the focal point position and/or the focusing shape of laser light (https://www.science-academy.jp/showcase/15/list.html, General Poster Presentation, No. p-44), for example. The shape of the surface (in the present embodiment, the second optical surface) where the blazed shape is formed is not limited. The shape of the surface where the blazed shape is formed may be a flat surface, or a curved surface. That is, in diffraction surface (transmission (type) diffraction grating)  123  of the present embodiment, the blaze number, the blaze angle, the shape of the installation surface are appropriately set in accordance with the attenuation rate and the focusing position of the diffraction light. In addition, it may be appropriately set such that the light intensity differs depending on the focusing position. For example, light may be focused such that higher intensity light reaches the center of the optical transmission member than in the outer edge. 
     Next, light paths in optical module  100  according to the present embodiment are described. Light emitted from photoelectric conversion element  112  (light emitting element  113 ) enters optical receptacle  120  from first optical surface  121 . At this time, light entered into optical receptacle  120  is converted to collimated light by first optical surface  121 , and advances inside optical receptacle  120 . Next, the light entered into optical receptacle  120  is emitted by second optical surface  122  toward the end portion of optical transmission member  130 . Here, diffraction surface  123  is disposed in second optical surface  122 , and therefore, of the diffraction light generated from light advanced inside optical receptacle  120 , only primary diffraction light reaches the end portion of optical transmission member  130  (see  FIG. 1 ). Note that, preferably, the primary diffraction light reaches the core, rather than the cladding of optical transmission member (optical fiber)  130 . With such a configuration, the quantity of the light emitted from light emitting element  113  can be correctly adjusted. Note that in the present embodiment, no zero-order diffraction light is generated. In addition, secondary and subsequent diffraction light is generated, but the quantity of the light of the order higher than the secondary diffraction light is significantly small, and therefore such light is not required to be taken into consideration. 
     On the other hand, light emitted from the end surface of optical transmission member  130  enters optical receptacle  120  from second optical surface  122  where no diffraction surface  123  is formed in the reception region. Next, the light entered into optical receptacle  120  is emitted, at first optical surface  121 , to the outside of optical receptacle  120  toward photoelectric conversion element  112  (light reception element  114 ). The light emitted to the outside of optical receptacle  120  at first optical surface  121  reaches photoelectric conversion element  112  (light reception element) while being converged (see  FIG. 1 ). 
     Effect 
     Optical receptacle  120  according to the present embodiment generates only primary diffraction light with diffraction surface  123 , and thus attenuates the quantity of the light that enters optical transmission member  130  from light emitting element  113 . With this configuration, the quantity of the light emitted from the light emitting element can be accurately attenuated without using another member. 
     Modification 1 
     Next, an optical module according to Modification 1 of the present embodiment is described. The optical module according to the present modification differs from optical module  100  according to Embodiment 1 only in the configuration of optical receptacle  220 . In view of this, the components similar to those of optical module  100  according to Embodiment 1 are denoted with the same reference numerals and the description thereof is omitted. 
       FIGS. 3A to 3C  illustrate a configuration of optical receptacle  220  according to Modification 1 of Embodiment 1.  FIG. 3A  is a plan view of optical receptacle  220  according to Modification 1 of the present embodiment,  FIG. 3B  is a bottom view of optical receptacle  220 , and  FIG. 3C  is a sectional view taken along line A-A of  FIG. 3B . 
     Configuration of Optical Receptacle 
     As illustrated in  FIGS. 3A to 3C , optical receptacle  220  includes first optical surface  121 , second optical surface  222 , and diffraction surface  123 . In the present embodiment, in the reception region, second optical surface  222  is a convex lens surface protruding toward optical transmission member  130 . In the reception region, second optical surfaces  222  are disposed opposite to the end surface of optical transmission member  130  in a line along the longitudinal direction. Preferably, the central axis of second optical surface  222  coincides with the central axis of the end surface of optical transmission member  130 . 
     Also in the optical module according to Modification 1 of the present embodiment, diffraction surface  123  is preferably configured such that primary diffraction light reaches the end portion of optical transmission member  130  whereas zero-order diffraction light does not reach the end portion of optical transmission member  130  such that only primary diffraction light reaches the end portion of optical transmission member  130 . 
     Effect 
     The optical module according to the present embodiment can achieve an increased coupling efficiency on the reception side while achieving the same effect as that of optical module  100  according to Embodiment 1. 
     Modification 2 
     Next, an optical module according to Modification 2 of the present embodiment is described. The optical module according to the present modification differs from optical module  100  according to Embodiment 1 only in the configuration of optical receptacle  320 . In view of this, the components similar to those of optical module  100  according to Embodiment 1 are denoted with the same reference numerals and the description thereof is omitted. 
       FIGS. 4A to 4C  illustrate a configuration of optical receptacle  320  according to Modification 2 of Embodiment 1.  FIG. 4A  is a plan view of optical receptacle  320  according to Modification 2 of the present embodiment,  FIG. 4B  is a bottom view of optical receptacle  320 , and  FIG. 4C  is a sectional view taken along line A-A of  FIG. 4B . 
     Configuration of Optical Receptacle 
     As illustrated in  FIGS. 4A to 4C , optical receptacle  320  includes first optical surface  121 , second optical surface  322 , and diffraction surface  323 . In the present embodiment, in the transmission region, first optical surface  121  is a flat surface disposed opposite to photoelectric conversion element  112 . In addition, in the present embodiment, diffraction surface  323  is formed in first optical surface  121  in the transmission region. In the present embodiment, no diffraction surface  323  is formed in second optical surface  322 . 
     Also in the optical module according to Modification 2 of the present embodiment, diffraction surface  323  is preferably configured such that primary diffraction light reaches the end portion of optical transmission member  130  whereas zero-order diffraction light does not reach the end portion of optical transmission member  130  such that only primary diffraction light reaches the end portion of optical transmission member  130 . 
     Effect 
     The optical module according to the present embodiment has an effect similar to that of optical module  100  according to Embodiment 1. 
     Modification 3 
     Next, an optical module according to Modification 3 of the present embodiment is described. The optical module according to the present modification differs from optical module  100  according to Embodiment 1 only in the configuration of optical receptacle  420 . In view of this, the components similar to those of optical module  100  according to Embodiment 1 are denoted with the same reference numerals and the description thereof is omitted. 
       FIGS. 5A to 5C  illustrate a configuration of optical receptacle  420  according to Modification 3 of Embodiment 1.  FIG. 5A  is a plan view of optical receptacle  420  according to Modification 3 of the present embodiment,  FIG. 5B  is a bottom view of optical receptacle  420 , and  FIG. 5C  is a sectional view taken along line A-A of  FIG. 5B . 
     Configuration of Optical Receptacle 
     As illustrated in  FIGS. 5A to 5C , optical receptacle  420  includes first optical surface  121 , second optical surface  222 , and diffraction surface  323 . In the present embodiment, in the transmission region, first optical surface  121  is a flat surface disposed opposite to photoelectric conversion element  112 . In addition, in the present embodiment, in the transmission region, diffraction surface  323  is formed in first optical surface  121 . In the present embodiment, no diffraction surface  323  is formed in second optical surface  222 . 
     In the present embodiment, in the reception region, second optical surface  222  is a convex lens surface protruding toward optical transmission member  130 . They are disposed opposite to the end surface of optical transmission member  130  in a line along the longitudinal direction. Preferably, the central axis of second optical surface  222  coincides with the central axis of the end surface of optical transmission member  130 . 
     Also in the optical module according to Modification 3 of the present embodiment, diffraction surface  323  is preferably configured such that primary diffraction light reaches the end portion of optical transmission member  130  whereas zero-order diffraction light does not reach the end portion of optical transmission member  130  such that only primary diffraction light reaches the end portion of optical transmission member  130 . 
     Effect 
     The optical module according to the present embodiment has an effect similar to that of optical module  100  according to Embodiment 1. 
     Embodiment 2 
     Configuration of Optical Module 
     Optical module  500  according to Embodiment 2 differs from optical module  100  according to Embodiment 1 only in the configuration of optical receptacle  520 . In view of this, the same configurations as those of optical module  100  are denoted with the same reference numerals and the description thereof is omitted. 
       FIG. 6  is a sectional view of optical module  500  according to Embodiment 2.  FIGS. 7A to 7C  illustrate a configuration of optical receptacle  520  according to Embodiment 2.  FIG. 7A  is a plan view of optical receptacle  520  according to Embodiment 2,  FIG. 7B  is a bottom view of optical receptacle  520 , and  FIG. 7C  is a sectional view taken along line A-A of  FIG. 7B . Note that in  FIG. 6 , the hatching of optical receptacle  520  is omitted for illustration of light paths. In  FIG. 6 , the center of the light flux is illustrated with a dashed line, and the outline of the light flux is illustrated with a dotted line. 
     As illustrated in  FIG. 6 , optical module  500  according to Embodiment 2 includes photoelectric conversion device  510  and optical receptacle  520 . Optical module  500  according to the present embodiment is transmitting optical module  500 . As such, photoelectric conversion element  112  of the present embodiment is light emitting element  113 . 
     Configuration of Optical Receptacle 
     Optical receptacle  520  according to the present embodiment is a transmitting optical receptacle. Optical receptacle  520  includes first optical surface  521 , second optical surface  522 , and diffraction surface  523 . In the present embodiment, first optical surface  521  is a convex lens surface disposed opposite to light emitting element  113 . In the present embodiment, second optical surface  522  is a flat surface disposed opposite to the end surface of optical transmission member  130 . In addition, diffraction surface  523  is disposed in second optical surface  522 . In optical receptacle  520  of the present embodiment, first optical surface  521  and second optical surface  522  are not arrays. That is, in the present embodiment, one light emitting element  113 , one first optical surface  521  and one second optical surface  522  are provided. 
     Also in the optical module according to the present embodiment, diffraction surface  523  is preferably configured such that primary diffraction light reaches the end portion of optical transmission member  130  whereas zero-order diffraction light does not reach the end portion of optical transmission member  130  such that only primary diffraction light reaches the end portion of optical transmission member  130 . 
     Next, light paths in optical module  500  according to the present embodiment are described. Light emitted from photoelectric conversion element  112  (light emitting element  113 ) enters optical receptacle  520  from first optical surface  521 . At this time, light entered into optical receptacle  520  is converted into collimated light by first optical surface  521 , and advances inside optical receptacle  520 . Next, the light entered into optical receptacle  520  is emitted by second optical surface  522  toward the end portion of optical transmission member  130 . Here, diffraction surface  523  is disposed in second optical surface  522 , and therefore, of the diffraction light generated from light advanced inside optical receptacle  520 , only primary diffraction light reaches the end portion of optical transmission member  130 . 
     Effect 
     Optical module  500  according to the present embodiment has an effect similar to that of optical module  100  according to Embodiment 1. 
     While first optical surface  521  is a convex lens surface and second optical surface  522  is a flat surface in optical receptacle  520  according to Embodiment 2, first optical surface  521  may be a flat surface, and second optical surface  522  may be a convex lens surface. In this case, it is preferable to form diffraction surface  523  in first optical surface  521 . 
     Embodiment 3 
     Configuration of Optical Module 
     Optical module  600  according to Embodiment 3 differs from optical module  100  according to Embodiment 1 only in the configuration of optical receptacle  620 . In view of this, the same configurations as those of optical module  100  are denoted with the same reference numerals and the description thereof is omitted. 
       FIG. 8  is a sectional view of optical module  600  according to Embodiment 3.  FIGS. 9A to 9D  illustrate a configuration of optical receptacle  620  according to Embodiment 3.  FIG. 9A  is a plan view of optical receptacle  620  according to Embodiment 3,  FIG. 9B  is a bottom view of optical receptacle  620 , and  FIG. 9C  is a right side view of optical receptacle  620 , and  FIG. 9D  is a sectional view taken along line A-A of  FIG. 9B . Note that in  FIG. 8 , the hatching of optical receptacle  620  is omitted for illustration of light paths. In  FIG. 8 , the center of the light flux is illustrated with a dashed line, and the outline of the light flux is illustrated with a dotted line. 
     As illustrated in  FIG. 8 , optical module  600  according to Embodiment 3 includes photoelectric conversion device  610  and optical receptacle  620 . 
     Configuration of Optical Receptacle 
     Optical receptacle  620  according to the present embodiment is a transmitting and receiving optical receptacle. Optical receptacle  620  includes first optical surface  621 , second optical surface  622 , diffraction surface  623 , and third optical surface  624 . 
     Third optical surface  624  is a reflecting surface that reflects, toward second optical surface  622 , light entered from first optical surface  621 , or is a reflecting surface that emits, toward first optical surface  621 , light entered from second optical surface  622 . Third optical surface  624  is tilted to approach optical transmission member  130  in the direction from the bottom surface toward the top surface of optical receptacle  620 . The inclination angle of third optical surface  624  is not limited. In the present embodiment, the inclination angle of third optical surface  624  is 45° with respect to the optical axis of light incident on third optical surface  624 . The shape of third optical surface  624  is not limited. In the present embodiment, the shape of third optical surface  624  is a flat surface. Light entered from first optical surface  621  or second optical surface  622  impinges on third optical surface  624  at an incident angle equal to or greater than a critical angle. Diffraction surface  623  is disposed in third optical surface  624 . 
     Also in optical module  600  according to the present embodiment, diffraction surface  623  is preferably configured such that primary diffraction light reaches the end portion of optical transmission member  130  whereas zero-order diffraction light does not reach the end portion of optical transmission member  130  such that only primary diffraction light reaches the end portion of optical transmission member  130 . 
     Next, light paths in optical module  600  according to the present embodiment are described. Light emitted from photoelectric conversion element  112  (light emitting element  113 ) enters optical receptacle  620  from first optical surface  621 . At this time, light entered into optical receptacle  620  is converted by first optical surface  621  into collimated light, and advances inside optical receptacle  620 . The light entered into optical receptacle  620  is reflected by third optical surface  624  toward second optical surface  622 . Here, diffraction surface  623  is disposed in third optical surface  624 , and therefore, of the diffraction light generated from light advanced inside optical receptacle  520 , only primary diffraction light is reflected toward second optical surface  622 . The light reflected by third optical surface  624  (primary diffraction light) is emitted toward optical transmission member  130  at the end portion of second optical surface  522  (see  FIG. 8 ). On the other hand, light emitted from optical transmission member  130  enters optical receptacle  620  from second optical surface  622 . The light entered into optical receptacle  620  is reflected by third optical surface  624  toward first optical surface  621 . The light reflected by third optical surface  624  is emitted to the outside from first optical surface  621 . The light emitted at first optical surface  621  reaches light reception element  114 . 
     Effect 
     Optical module  600  according to the present embodiment has an effect similar to that of optical module  100  according to Embodiment 1. 
     While diffraction surface  623  is disposed in third optical surface  624  in optical receptacle  620  according to Embodiment 3, diffraction surface  623  may be disposed in first optical surface  621 , or in second optical surface  622 . In addition, while first optical surface  621  is a convex lens surface protruding toward photoelectric conversion element  112  in optical receptacle  620  according to Embodiment 3, first optical surface  621  may be a flat surface. In addition, while second optical surface  622  is a flat surface in optical receptacle  620  according to Embodiment 3, second optical surface  622  may be a convex lens surface protruding toward the end surface of optical transmission member  130 , or a concave lens surface recessed toward the end surface of optical transmission member  130 . 
     INDUSTRIAL APPLICABILITY 
     The optical receptacle and the optical module according to the embodiments of the present invention are suitable for optical communications using an optical transmission member. 
     REFERENCE SIGNS LIST 
     
         
           100 ,  500 ,  600  Optical module 
           110 ,  510 ,  610  Photoelectric conversion device 
           111  Substrate 
           112  Photoelectric conversion element 
           113  Light emitting element 
           114  Light reception element 
           120 ,  220 ,  320 ,  420 ,  520 ,  620  Optical receptacle 
           121 ,  521 ,  621  First optical surface 
           122 ,  222 ,  322 ,  522 ,  622  Second optical surface 
           123 ,  323 ,  523 ,  623  Diffraction surface 
           130  Optical transmission member 
           131  Ferrule 
           624  Third optical surface