Patent Publication Number: US-11378763-B2

Title: Optical waveguide having support member, optical waveguide mounting substrate and optical transceiver

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from prior Japanese patent application No. 2018-095993 filed on May 18, 2018, the entire contents of which are incorporated herein by reference. This application is also a divisional application of parent U.S. application Ser. No. 16/411,656, filed May 14, 2019, the entire contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to an optical waveguide having a support member, an optical waveguide mounting substrate, and an optical transceiver. 
     RELATED ART 
     In an optical waveguide where a core layer is sandwiched by a first cladding layer and a second cladding layer, a technology has been known in which an opening (space) having an isosceles right angle-shaped section is provided from one side of the optical waveguide, so that an inclined surface, which is inclined by about 45° relative to a light propagation direction of the core layer, is formed. The inclined surface is a total reflection surface configured to convert a propagation direction of light to be propagated along the core layer into about a right angle. 
     Patent Document 1: WO2007/139155 
     Meanwhile, in the optical waveguide, the optical waveguide may be mounted on a wiring substrate with an adhesive layer being interposed therebetween in a state where an opened side of the isosceles right angle-shaped opening is made to face toward the adhesive layer. A width of the isosceles right angle-shaped opening is wide at the opened side, so that contaminants such as remnant of the adhesive layer, wastes and the like are likely to enter the opening. For this reason, the contaminants are attached to a reflection surface in the opening, so that reflection characteristics are deteriorated. 
     SUMMARY OF INVENTION 
     Aspect of non-limiting embodiments of the present disclosure relates to provide an optical waveguide having a support member, an optical waveguide mounting substrate, and an optical transceiver, which can reduce concerns that contaminants will be introduced into an opening provided to the optical waveguide. 
     Aspects of certain non-limiting embodiments of the present disclosure address the features discussed above and/or other features not described above. However, aspects of the non-limiting embodiments are not required to address the above features, and aspects of the non-limiting embodiments of the present disclosure may not address features described above. 
     According to an aspect of the present disclosure, there is provided an optical waveguide having a support member comprising:
         a support member; and   an optical waveguide formed on the support member,       

     wherein the optical waveguide comprises:
         a first cladding layer formed on a surface of the support member,   a core layer formed on a surface of the first cladding layer,   a second cladding layer formed on the surface of the first cladding layer so as to cover a periphery of the core layer and being thicker than the first cladding layer, and   an opening opened at the second cladding layer-side, penetrating the second cladding layer and the core layer, and closed at the first cladding layer-side, and       

     wherein the opening has a first surface and a second surface ranging from the opened side to the closed side, and in a vertical section taken along a longitudinal direction of the core layer, a first angle between a perpendicular line drawn from an opening end of the first surface to the surface of the first cladding layer and the first surface, and a second angle between a perpendicular line drawn from an opening end of the second surface to the surface of the first cladding layer and the second surface are all acute angles. 
     According to the present disclosure, it is possible to reduce concerns that contaminants will be introduced into the opening provided to the optical waveguide. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Exemplary embodiments of the present disclosure will be described in detail based on the following figures, wherein: 
         FIGS. 1A and 1B  are views illustrating an optical waveguide having a support member according to a first exemplary embodiment; 
         FIG. 2  is a partially enlarged sectional view in the vicinity of an opening  25  of  FIG. 1B ; 
         FIGS. 3A to 3D  are views illustrating manufacturing processes of the optical waveguide having a support member according to the first exemplary embodiment; 
         FIG. 4  is a plan view exemplifying an optical waveguide mounting substrate according to a second exemplary embodiment; 
         FIG. 5  is a sectional view exemplifying the optical waveguide mounting substrate according to the second exemplary embodiment; 
         FIGS. 6A and 6B  are views illustrating a manufacturing process of the optical waveguide mounting substrate according to the second exemplary embodiment (1 thereof); 
         FIGS. 7A and 7B  are views illustrating the manufacturing process of the optical waveguide mounting substrate according to the second exemplary embodiment (2 thereof); and 
         FIG. 8  is a sectional view exemplifying an optical transceiver according to a third exemplary embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, exemplary embodiments of the present disclosure will be described with reference to the drawings. In the meantime, in the drawings, the same constitutional parts are denoted with the same reference numerals, and the overlapping descriptions thereof may be omitted. 
     First Exemplary Embodiment 
     [Structure of Optical Waveguide Having Support Member According to First Exemplary Embodiment] 
     First, a structure of an optical waveguide having a support member according to a first exemplary embodiment is described.  FIGS. 1A and 1B  are views illustrating an optical waveguide having a support member according to the first exemplary embodiment.  FIG. 1A  is a plan view.  FIG. 1B  is a sectional view taken along a line A-A of  FIG. 1A , depicting a longitudinal section taken along a longitudinal direction of a core layer  22  (a section taken along a direction perpendicular to one surface  10   a  of a support member  10 ).  FIG. 2  is a partially enlarged sectional view in the vicinity of an opening  25  of  FIG. 1B . 
     Referring to  FIG. 1B , an optical waveguide  1  having a support member includes a support member  10 , and an optical waveguide  2  formed on the support member  10 . Referring to  FIGS. 1B and 2 , the optical waveguide  2  has a first cladding layer  21 , core layers  22 , a second cladding layer  23 , and openings  25 ,  26 . 
     The support member  10  is a base member for forming the optical waveguide  2  having the first cladding layer  21 , the core layers  22  and the second cladding layer  23 , and for example, may be formed by a resin substrate made of polycarbonate or the like. The support member  10  may be formed by a glass substrate, a silicon substrate or the like, too. A thickness of the support member  10  may be set to about 200 to 500 μm, for example. 
     The first cladding layer  21  is formed on one surface  10   a  of the support member  10 . The first cladding layer  21  may be formed of a polyimide-based resin, an acryl-based resin, an epoxy-based resin, a polyolefin-based resin, a polynorbornene-based resin, or the like, for example. A thickness T 1  of the first cladding layer  21  may be set to about 10 to 30 μm, for example. 
     The core layers  22  are selectively formed on one surface  21   a  of the first cladding layer  21 . In the example of  FIG. 1A , three elongated core layers  22  are arranged on one surface  21   a  of the first cladding layer  21 . This is just exemplary. That is, one, two or four or more core layers  22  may be formed. A pitch of the adjacent core layers  22  may be set to about 200 to 300 μm, for example. The core layer  22  may be formed of the same material as the first cladding layer  21 . A thickness T 2  of the core layer  22  may be set to 25 to 35 μm, for example. A sectional shape of the core layer  22  in a width direction may be a square, for example. 
     The second cladding layer  23  is formed on one surface  21   a  of the first cladding layer  21  so as to cover peripheries of the core layers  22 . The second cladding layer  23  may be formed of the same material as the first cladding layer  21 . A thickness T 3  of the second cladding layer  23  is larger than the thickness T 1  of the first cladding layer  21 . The thickness T 3  of the second cladding layer  23  may be set to be equal to or more than a value (T 1 +15 μm) obtained by adding 15 μm to the thickness T 1  of the first cladding layer  21 , for example. In the meantime, the thickness T 3  of the second cladding layer  23  indicates a thickness of an upper part of the second cladding layer  23  above an upper surface of the core layer  22 . 
     As described above, the first cladding layer  21 , the core layer  22 , and the second cladding layer  23  may be formed of the same material. A refractive index of the core layer  22  is required to be set higher than refractive indexes of the first cladding layer  21  and the second cladding layer  23 . When an additive for refractive index control such as Ge is added to the core layer  22 , it is possible to make the refractive index of the core layer  22  larger than the refractive indexes of the first cladding layer  21  and the second cladding layer  23 . The refractive indexes of the first cladding layer  21  and the second cladding layer  23  may be set to 1.5, and the refractive index of the core layer  22  may be set to 1.6, for example. 
     The optical waveguide  1  having a support member is formed with the openings  25 ,  26  opened at the second cladding layer  23 -side, penetrating the second cladding layer  23  and the core layers  22 , and closed at the first cladding layer  21 -side. A width W of each of the openings  25 ,  26  may be set to about 30 to 80 μm, for example. 
     As shown in  FIG. 2 , the opening  25  has a wedge-shaped section of which a width gradually decreases from the second cladding layer  23  toward the core layer  22 . The opening  25  has a first surface  251  and a second surface  252  ranging from the opened side to the closed side, and the first surface  251  and the second surface  252  substantially face each other. 
     An angle between a perpendicular line P 1  drawn from an opening end  251   e  of the first surface  251  to one surface  21   a  of the first cladding layer  21  and the first surface  251  is denoted as θ 1 . Also, an angle between a perpendicular line P 2  drawn from an opening end  252   e  of the second surface  252  to one surface  21   a  of the first cladding layer  21  and the second surface  252  is denoted as θ 2 . In this case, the angle θ 1  and the angle θ 2  are all acute angles. The acute angle is an angle which is less than 90 degrees (90°) but more than 0 degrees (0°). 
     The angle θ 1  is, for example, 45°±1°, and a portion  251   m  of the first surface  251  belonging to the core layer  22  is a reflection surface (hereinafter, also referred to as ‘reflection surface  251   m ’) on which a propagation direction of incident light is to be converted. The angle θ 2  is, for example, 31°±1°. An absolute value of a difference between the angle θ 1  and the angle θ 2  is, for example, 14±1°. 
     Although not shown in detail, the opening  26  has a line-symmetric shape to the opening  25  with respect to the perpendicular lines P 1 , P 2 . Therefore, values of the angle θ 1  and the angle θ 2  are the same as the opening  25 . A portion  261   m  of the first surface  261  belonging to the core layer  22  is a reflection surface (hereinafter, also referred to as ‘reflection surface  261   m ’) on which a propagation direction of incident light is to be converted. 
     Meanwhile, in the subject application, a shape where a wedge angle (absolute value of a difference between the angle θ 1  and the angle θ 2 ) is equal to or smaller than 40° is referred to as a wedge-shaped section. That is, the isosceles right angle-shaped section (the wedge angle is 45°) is not included in the wedge-shaped section of the subject application. 
     [Manufacturing Method of Optical Waveguide Having Support Member According to First Exemplary Embodiment] 
     Subsequently, a manufacturing method of the optical waveguide having a support member according to the first exemplary embodiment is described.  FIGS. 3A to 3D  are views illustrating manufacturing processes of the optical waveguide having a support member according to the first exemplary embodiment. 
     First, in a process of  FIG. 3A , the support member  10  is prepared, and the first cladding layer  21  is formed on one surface  10   a  of the support member  10 . The material and thickness of the support member  10  are as described above. The first cladding layer  21  may be formed by applying a liquid or paste resin material to one surface  10   a  of the support member  10 , irradiating the material with ultraviolet, and heating and curing the same, for example. Instead of coating the liquid or paste resin material, a film-shaped resin material may be laminated. The material and thickness of the first cladding layer  21  are as described above. 
     Then, in a process of  FIG. 3B , the core layer  22  is formed on one surface  21   a  of the first cladding layer  21 . The core layer  22  may be formed by applying a liquid or paste resin material to one entire surface  21   a  of the first cladding layer  21 , irradiating the material with ultraviolet, and heating and curing the same, for example. Instead of coating the liquid or paste resin material, a film-shaped resin material may be laminated. The material and thickness of the core layer  22  are as described above. 
     Then, in a process of  FIG. 3C , the second cladding layer  23  is formed on one surface  21   a  of the first cladding layer  21  so as to cover the core layer  22 . Thereby, a periphery of the core layer  22  is covered with the first cladding layer  21  and the second cladding layer  23 . The second cladding layer  23  may be formed by the same method as the first cladding layer  21 . The material and thickness of the second cladding layer  23  are as described above. 
     Then, in a process of  FIG. 3D , the openings  25 ,  26  that are opened at the second cladding layer  23 -side, penetrate the second cladding layer  23  and the core layer  22  and are closed at the first cladding layer  21 -side are formed. Thereby, the optical waveguide  2  in which the first cladding layer  21 , the core layer  22 , and the second cladding layer  23  are sequentially stacked on one surface  10   a  of the support member  10  is formed, so that the optical waveguide  1  having a support member is completed. 
     The openings  25 ,  26  may be formed by irradiation of laser light. As the laser light, for example, ArF excimer laser (wavelength 193 nm), KrF excimer laser (wavelength 248 nm), XeCl excimer laser (wavelength 308 nm), XeF excimer laser (wavelength 351 nm) and the like may be used. The excimer laser is favorable because it can form one opening by one time irradiation. 
     In the meantime, when the excimer laser is used, the opening  25  is formed so that an angle between the first surface  251  and the second surface  252  (refer to  FIG. 2 ) is to be about 14°. The opening  26  is also the same. Therefore, when the laser light is irradiated at an angle of about 38° relative to one surface  21   a  of the first cladding layer  21 , the angle θ 1  (refer to  FIG. 2 ) becomes about 45° and the angle θ 2  (refer to  FIG. 2 ) becomes about 31°. 
     In this way, in the optical waveguide  1  having a support member, the openings  25 ,  26  are formed using the excimer laser, so that it is possible to accurately form one opening by one time irradiation. 
     Second Exemplary Embodiment 
     In a second exemplary embodiment, an example of an optical waveguide mounting substrate on which the optical waveguide of the first exemplary embodiment is mounted is described. In the meantime, in the second exemplary embodiment, the descriptions of the same constitutional parts as the first exemplary embodiment may be omitted. 
     [Structure of Optical Waveguide Mounting Substrate According to Second Exemplary Embodiment] 
     First, a structure of an optical waveguide mounting substrate according to the second exemplary embodiment is described.  FIG. 4  is a plan view exemplifying the optical waveguide mounting substrate according to the second exemplary embodiment.  FIG. 5  is a sectional view exemplifying the optical waveguide mounting substrate according to the second exemplary embodiment, depicting a section taken along a line B-B of  FIG. 4 . 
     Referring to  FIGS. 4 and 5 , an optical waveguide mounting substrate  5  includes a wiring substrate  3 , and the optical waveguide  2  mounted on the wiring substrate  3  with an adhesive layer  4  being interposed therebetween. 
     In the wiring substrate  3 , wiring layers and insulation layers are stacked on both surfaces of a core substrate  30 . Specifically, in the wiring substrate  3 , a wiring layer  32 , an insulation layer  33 , a wiring layer  34 , and a solder resist layer  35  are sequentially stacked on one surface (upper surface) of the core substrate  30 . Also, a wiring layer  42 , an insulation layer  43 , a wiring layer  44 , and a solder resist layer  45  are sequentially stacked on the other surface (lower surface) of the core substrate  30 . 
     As the core substrate  30 , for example, a so-called glass epoxy substrate in which an insulating resin such as an epoxy-based resin is impregnated in glass cloth, and the like may be used. As the core substrate  30 , a substrate in which an epoxy-based resin, a polyimide-based resin or the like is impregnated in woven fabric or non-woven fabric of glass fiber, carbon fiber, aramid fiber or the like, and the like may also be used. A thickness of the core substrate  30  may be set to about 60 to 400 μm, for example. The core substrate  30  is formed with through-holes  30   x  penetrating the core substrate  30  in a thickness direction. A planar shape of the through-hole  30   x  is circular, for example. 
     The wiring layer  32  is formed on one surface of the core substrate  30 . Also, the wiring layer  42  is formed on the other surface of the core substrate  30 . The wiring layer  32  and the wiring layer  42  are electrically connected by through-wirings  31  formed in the through-holes  30   x . The wiring layers  32 ,  42  are respectively patterned into a predetermined planar shape. For the wiring layers  32 ,  42  and the through-wiring  31 , copper (Cu) or the like may be used, for example. A thickness of each of the wiring layers  32 ,  42  may be set to about 10 to 30 μm, for example. In the meantime, the wiring layer  32 , the wiring layer  42  and the through-wiring  31  may be integrally formed. 
     The insulation layer  33  is formed on one surface of the core substrate  30  so as to cover the wiring layer  32 . As a material of the insulation layer  33 , for example, an insulating resin of which a main component is an epoxy-based resin or a polyimide-based resin, and the like may be used. A thickness of the insulation layer  33  may be set to about 30 to 40 μm, for example. The insulation layer  33  may contain filler such as silica (SiO 2 ). 
     The wiring layer  34  is formed on one side of the insulation layer  33 . The wiring layer  34  includes via wirings filled in via holes  33   x  penetrating the insulation layer  33  and formed to expose one surface of the wiring layer  32 , and a wiring pattern formed on one surface of the insulation layer  33 . The wiring layer  34  is electrically connected to the wiring layer  32 . The via hole  33   x  may be formed as a concave portion having an inverted conical shape of which a diameter of an opening opened to the solder resist layer  35 -side is larger than a diameter of a bottom surface of an opening formed by one surface of the wiring layer  32 . A material of the wiring layer  34  and a thickness of the wiring pattern configuring the wiring layer  34  may be made to be the same as the wiring layer  32 , for example. 
     The solder resist layer  35  is an outermost layer formed at one side of the wiring substrate  3 , and is formed on one surface of the insulation layer  33  so as to cover the wiring layer  34 . The solder resist layer  35  may be formed of a photosensitive resin such as an epoxy-based resin and an acryl-based resin, and the like. A thickness of the solder resist layer  35  may be set to about 15 to 35 μm, for example. 
     The solder resist layer  35  has openings  35   x , and portions of one surface of the wiring layer  34  are exposed to bottom portions of the openings  35   x . A planar shape of the opening  35   x  may be circular, for example. If necessary, one surface of the wiring layer  34  exposed into the openings  35   x  may be formed with a metal layer or may be subjected to oxidation prevention processing such as OSP (Organic Solderability Preservative) processing. As the metal layer, an Au layer, a Ni/Au layer (a metal layer having a Ni layer and an Au layer stacked in corresponding order), a Ni/Pd/Au layer (a metal layer having a Ni layer, a Pd layer and an Au layer stacked in corresponding order), and the like may be exemplified. 
     The insulation layer  43  is formed on the other surface of the core substrate  30  so as to cover the wiring layer  42 . A material and a thickness of the insulation layer  43  may be made to be the same as the insulation layer  33 , for example. The insulation layer  43  may contain filler such as silica (SiO 2 ). The wiring layer  44  is formed on the other side of the insulation layer  43 . The wiring layer  44  includes via wirings filled in via holes  43   x  penetrating the insulation layer  43  and formed to expose the other surface of the wiring layer  42 , and a wiring pattern formed on the other surface of the insulation layer  43 . The wiring layer  44  is electrically connected to the wiring layer  42 . The via hole  43   x  may be formed as a concave portion having an inverted conical shape of which a diameter of an opening opened to the solder resist layer  45 -side is larger than a diameter of a bottom surface of an opening formed by the other surface of the wiring layer  42 . A material and a thickness of the wiring layer  44  may be made to be the same as the wiring layer  32 , for example. 
     The solder resist layer  45  is an outermost layer formed at the other side of the wiring substrate  3 , and is formed on the other surface of the insulation layer  43  so as to cover the wiring layer  44 . A material and a thickness of the solder resist layer  35  may be made to be the same as the solder resist layer  35 , for example. The solder resist layer  45  has openings  45   x , and portions of the other surface of the wiring layer  44  are exposed into the openings  45   x . A planar shape of the opening  45   x  may be circular, for example. The wiring layer  44  exposed into the openings  45   x  may be used as a pad for electrical connection with a mounting substrate (not shown) such as a motherboard. If necessary, the other surface of the wiring layer  44  exposed into the openings  45   x  may be formed with the above-described metal layer or may be subjected to oxidation prevention processing such as OSP processing. 
     On the solder resist layer  35  of the wiring substrate  3 , the optical waveguide  2  is mounted via the adhesive layer  4 . The second cladding layer  23  of the optical waveguide  2  faces the solder resist layer  35  of the wiring substrate  3  via the adhesive layer  4 . The optical waveguide  2  is formed with the openings  28  configured to communicate with the openings  35   x  of the solder resist layer  35 . The adhesive layer  4  is a thermosetting epoxy-based adhesive, for example. 
     One surface of the wiring layer  34  exposed into the openings  35   x  and the openings  28  to communicate with each other is formed with external connection terminals  39 . The external connection terminal  39  is a solder bump, for example. As a material of the solder bump, for example, an alloy including Pb, an alloy of Sn and Cu, an alloy of Sn and Ag, an alloy of Sn, Ag and Cu, and the like may be used. The external connection terminal  39  is a terminal to be electrically connected to a light-emitting element and a light-receiving element. 
     [Manufacturing Method of Optical Waveguide Mounting Substrate According to Second Exemplary Embodiment] 
     Subsequently, a manufacturing method of the optical waveguide mounting substrate according to the second exemplary embodiment is described.  FIGS. 6A to 7B  exemplify manufacturing processes of the optical waveguide mounting substrate according to the second exemplary embodiment. In the meantime, here, an example of the process of manufacturing one optical waveguide mounting substrate is described. However, a plurality of parts becoming the optical waveguide mounting substrate may be manufactured and then individually separated to form each optical waveguide mounting substrate. 
     First, in a process of  FIG. 6A , the wiring substrate  3  is prepared. The wiring substrate  3  may be manufactured using a well-known buildup technology, for example. 
     Then, in a process of  FIG. 6B , the optical waveguide  1  having a support member is prepared, and the optical waveguide  1  having a support member is mounted on the solder resist layer  35  of the wiring substrate  3  via the adhesive layer  4 . In the meantime, the optical waveguide  1  having a support member is mounted so that the second cladding layer  23  of the optical waveguide  2  is to face the solder resist layer  35  of the wiring substrate  3  via the adhesive layer  4 . 
     In this process, the openings  25 ,  26  are blocked at sides facing toward the second cladding layer  23  by the adhesive layer  4 , but a space is formed around the reflection surface  251   m  in the opening  25 . Thereby, the reflection surface  251   m  can perform an original function of converting a propagation direction of incident light. Likewise, the opening  26  is blocked at a side facing toward the second cladding layer  23  by the adhesive layer  4 , but a space is formed around the reflection surface  261   m  in the opening  26 . Thereby, the reflection surface  261   m  can perform an original function of converting a propagation direction of incident light. 
     Then, in a process of  FIG. 7A , the support member  10  is removed, and the optical waveguide  2  is formed with the openings  28  to communicate with the openings  35   x  of the solder resist layer  35 . In the openings  35   x  and the openings  28  to communicate with each other, one surface of the wiring layer  34  is exposed. The openings  28  may be formed by a laser processing method of using CO 2  laser, for example. 
     Then, in a process of  FIG. 7B , one surface of the wiring layer  34  exposed into the openings  35   x  and the openings  28  to communicate with each other is formed with the external connection terminals  39 . The external connection terminal  39  is a solder bump, for example. The material of the solder bump is as described above. By the above processes, the optical waveguide mounting substrate  5  shown in  FIGS. 4 and 5  is completed. 
     In the meantime, before the process of  FIG. 6B , the support member  10  may be removed from the optical waveguide  1  having a support member, and only the optical waveguide  2  from which the support member  10  has been removed may be mounted on the solder resist layer  35  of the wiring substrate  3  with the adhesive layer  4  being interposed therebetween. 
     Meanwhile, in the related art, the openings corresponding to the openings  25 ,  26  have an isosceles right angle-shaped section (θ 1 =45°, θ 2 =0°). Therefore, an opening-side width W of the opening is wide, so that contaminants such as remnant of the adhesive layer  4 , wastes and the like are likely to enter the opening. For this reason, the contaminants are attached to the reflection surface in the opening (corresponding to the reflection surface  251   m  in the opening  25  and the reflection surface  261   m  in the opening  26 ), so that reflection characteristics are deteriorated. 
     In contrast, in the second exemplary embodiment, the openings  25 ,  26  have a wedge-shaped section, other than the isosceles right angle-shaped section, and an opening-side width W of each of the openings  25 ,  26  is considerably smaller, as compared to the openings having the isosceles right angle-shaped section. For this reason, for example, in the process of  FIG. 6B , the contaminants such as remnant of the adhesive layer  4 , wastes and the like are difficult to enter the opening  25  and the opening  26 , so that it is possible to reduce the concerns that the reflection characteristics will be deteriorated, which is caused when the contaminants are attached to the reflection surface  251   m  and the reflection surface  261   m.    
     Also, in the related art, the thicknesses of the first cladding layer and the second cladding layer are generally the same. However, in the second exemplary embodiment, the second cladding layer  23  closer to the adhesive layer  4  is made thicker than the first cladding layer  21 . For this reason, as compared to the structure of the related art, it is possible to increase distances between the adhesive layer  4  and the reflection surfaces  251   m ,  261   m , so that it is possible to further reduce the concerns that the remnant of the adhesive layer  4  will be attached to the reflection surfaces  251   m ,  261   m.    
     Also, in the optical waveguide mounting substrate  5 , the openings  25 ,  26  do not penetrate the first cladding layer  21 . For this reason, since the openings  25 ,  26  do not interfere with the openings  28 , it is possible to improve a degree of design freedom of mounting of optical elements (a light-emitting element and a light-receiving element to be described later). 
     Third Exemplary Embodiment 
     In a third exemplary embodiment, an example of an optical transceiver where a light-emitting element and a light-receiving element are mounted on the optical waveguide mounting substrate of the second exemplary embodiment is described. Meanwhile, in the third exemplary embodiment, the descriptions of the same constitutional components as the above exemplary embodiments may be omitted. 
       FIG. 8  is a sectional view exemplifying an optical transceiver according to the third exemplary embodiment. Referring to  FIG. 8 , an optical transceiver  8  includes the optical waveguide mounting substrate  5 , a light-emitting element  110 , a light-receiving element  120 , and under-fill resins  150 ,  160 . 
     The light-emitting element  110  includes a bump  111  and a light-emitting part  112 , and is configured to emit light toward the optical waveguide  2 . The bump  111  is an Au bump, for example, is inserted in the opening  35   x  and the opening  28 , and is electrically connected to the external connection terminal  39  exposed in the opening  35   x  and the opening  28 . The light-emitting part  112  is arranged at a position at which the light can be irradiated toward the reflection surface  251   m . As the light-emitting element  110 , for example, a planar light-emitting laser (VCSEL: Vertical Cavity Surface Emitting Laser), a light-emitting diode (LED), and the like may be used. 
     The under-fill resin  150  is provided in the opening  35   x  and the opening  28 , and between the light-emitting element  110  and the solder resist layer  35 . As the under-fill resin  150 , for example, a light-transmittable resin through which the light emitted from the light-emitting element  110  can pass may be used. 
     The light-receiving element  120  includes a bump  121  and a light-receiving part  122 , and the light emitted from the optical waveguide  2  is incident thereon. The bump  121  is, for example, an Au bump, is inserted in the opening  35   x  and the opening  28 , and is electrically connected to the external connection terminal  39  exposed in the opening  35   x  and the opening  28 . The light-receiving part  122  is arranged at a position at which the light reflected on the reflection surface  261   m  can be received. As the light-receiving element  120 , for example, a photo diode, an avalanche photodiode (APD), and the like may be used. 
     The under-fill resin  160  is provided in the opening  35   x  and the opening  28 , and between the light-receiving element  120  and the solder resist layer  35 . As the under-fill resin  160 , for example, a light-transmittable resin through which the light to be received by the light-receiving element  120  can pass may be used. 
     In  FIG. 8 , the light L emitted from the light-emitting part  112  of the light-emitting element  110  passes through the under-fill resin  150  and the first cladding layer  21 , is incident on the core layer  22 , reaches the reflection surface  251   m , and is totally reflected on the reflection surface  251   m , so that a light propagation direction is converted by about 90°. Then, the light is propagated in the core layer  22 , reaches the reflection surface  261   m , and is totally reflected on the reflection surface  261   m , so that the light propagation direction is converted by about 90°. Then, the light is emitted from the core layer  22 , passes through the first cladding layer  21  and the under-fill resin  160 , and is received by the light-receiving part  122  of the light-receiving element  120 . 
     The reason that the light L is totally reflected on the reflection surfaces  251   m ,  261   m  is described. The total reflection indicates a phenomenon that when light is incident on a medium B having a small refractive index from a medium A having a large refractive index, the light is all reflected without passing through a boundary surface between the medium A and the medium B. Also, as is well known as Snell&#39;s law, a magnitude of a critical angle (the maximum incidence angle at which the refraction is to occur) is determined by the refractive index. When the light is incident on the medium B (the refractive index N 2 ) from the medium A (the refractive index N 1 ), the total reflection conditions are N 1 &gt;N 2  and θb&gt;θm where the critical angle θm=sin −1 (N 2 /N 1 ), and θb is the incidence angle from the medium A onto the medium B. 
     In  FIG. 8 , the core layer  22  corresponds to the medium A, and the air in the openings  25 ,  26  corresponds to the medium B. For example, when the refractive index N 1  of the core layer  22  is 1.6 and the refractive index N 2  of the air is 1.0, the critical angle θm at the reflection surfaces  251   m ,  261   m  is θm=sin −1 (1.0/1.6)=38°. In this case, when the incidence angle θb is larger than 38°, the light L is totally reflected on the reflection surfaces  251   m ,  261   m.    
     In the optical transceiver  8 , since the openings  25 ,  26  do not penetrate the first cladding layer  21 , the openings are not opened at the mounting side of the light-emitting element  110  and the light-receiving element  120 . For this reason, even when a special manufacturing process is not used, the under-fill resins  150 ,  160  do not enter the openings  25 ,  26 . That is, when mounting the light-emitting element  110  and the light-receiving element  120 , it is possible to use a manufacturing process that is the same as a case of mounting a normal semiconductor chip. 
     Although the preferred exemplary embodiments have been described in detail, the present disclosure is not limited to the exemplary embodiments, and the exemplary embodiments can be diversely modified and replaced without departing from the scope of the claims. 
     For example, in the exemplary embodiments, the optical waveguide mounting substrate including the light-emitting element and the light-receiving element has been described. However, an optical waveguide mounting substrate including the light-emitting element without the light-receiving element can also be implemented. In this case, a configuration where only the reflection surface  251   m  for converting the propagation direction of the light incident from the light-emitting element into a direction parallel with the core layer  22  is provided may be possible. Also, an optical waveguide mounting substrate including the light-receiving element without the light-emitting element can also be implemented. In this case, a configuration where only the reflection surface  261   m  for converting the propagation direction of the light to be propagated in the core layer  22  toward the light-receiving element is provided may be possible. 
     Also, in the exemplary embodiments, as the wiring substrate  3 , the wiring substrate having the core layer and manufactured by the buildup technology has been exemplified. However, as the wiring substrate  3 , a coreless wiring substrate manufactured by the buildup technology may also be used. Also, the wiring substrate  3  is not limited thereto, and a variety of wiring substrates may be used. For example, one side (one layer) wiring substrate of which only one surface is formed with a wiring layer, a both-sided (two-layered) wiring substrate of which both surfaces are formed with wiring layers, a through-multi layered wiring substrate where the respective wiring layers are connected by through-vias, an IVH (Interstitial Via Hole) multi-layered wiring substrate where a specific wiring layer is connected by an IVH, and the like may be used. 
     Also, in the exemplary embodiments, as the opening opened at the second cladding layer-side, penetrating the second cladding layer and the core layer, and closed at the first cladding layer-side, the opening  25 ,  26  is formed so as to be extended from the second cladding layer  23  to a portion of the first cladding layer  21  while it penetrates the second cladding layer  23  and the core layer  22 . However, the opening may be formed so as to be extended from the second cladding layer  23  to the core layer  22  while it penetrates the second cladding layer  23  and the core layer  22  and may not be extended to the portion of the first cladding layer  21 . In this case, the surface of the first cladding layer  21  facing the core layer  22  will be a surface which closes the opening.