Composite substrate

Abstract

A composite substrate (10A) includes a wiring substrate (11A) and an optical waveguide-equipped substrate (12A). The wiring substrate (11A) includes an insulating layer and a conductor pattern. One surface of the wiring substrate includes a first region (R1) and a second region (R2) recessed with respect to the first region, and the height of the second region (R2) is lower than the lower surface of the conductor pattern (113) located in the first region (R1). The optical waveguide-equipped substrate (12A) includes a substrate (121) and an optical waveguide layer (122). The optical waveguide layer (122) includes a first cladding layer (122A), a second cladding layer (122C), and a core (122B) provided therebetween. The optical waveguide-equipped substrate (12A) is installed on the second region (R2) such that the optical waveguide layer (122) is located above the substrate (121), and the height of the lower surface of the core (122B) is higher than the first region (R1).

Description

Composite substrate 【0001】 The present invention relates to a composite substrate. 【0002】 In recent years, as a technology to achieve high-speed and high-capacity communication with low power consumption, introducing photonics-based technology into all components from the network to the terminal has attracted attention. 【0003】 In particular, the optoelectronic integration technology that replaces part of the electric circuit in the terminal with a circuit that handles optical signals is one of the important technologies. In the optoelectronic integration technology, for example, an optical waveguide is provided on a circuit board, and a device for performing photoelectric conversion and a device for processing electrical signals are mounted thereon, and the optical waveguide and the former device are optically coupled, and these devices are electrically connected by a circuit provided on the circuit board to use an optoelectronic integration device (Patent Document 1). 【0004】 Japanese Patent Application Laid-Open No. 2024-13031 【0005】 An object of the present invention is to provide a technology that can facilitate optical coupling and electrical connection in mounting a functional device on a composite substrate including a conductor pattern and an optical waveguide. 【0006】 According to one aspect of the present invention, there is provided a wiring substrate including one or more insulating layers and one or more conductor patterns, having a first surface and a second surface which is the back surface thereof, the first surface including one or more first regions and one or more second regions each recessed with respect to the one or more first regions, one of the one or more conductor patterns being located in the one or more first regions, the height of the one or more second regions being lower than the lower surface of the conductor pattern located in the one or more first regions; a substrate and an optical waveguide layer provided thereon, each of the optical waveguide layers including a first cladding layer provided on the substrate, a second cladding layer provided on the first cladding layer, and one or more cores provided between the first cladding layer and the second cladding layer, the optical waveguide layers being respectively installed on the one or more second regions so as to be located above the substrate, and the height of the lower surface of the one or more cores being higher than the one or more first regions, a composite substrate is provided. 【0007】 According to another aspect of the present invention, a composite substrate is provided in which the height of the upper surface of the substrate is lower than that of the one or more first regions. 【0008】 According to yet another aspect of the present invention, a composite substrate is provided in which the lower surface of the one or more cores relates to any of the above-mentioned sides, wherein the height of the one or more first regions is 100 μm or less. 【0009】 According to yet another aspect of the present invention, a composite substrate according to any of the above aspects is provided, further comprising one or more stress-relaxing layers interposed between the one or more optical waveguide substrates and the one or more second regions. 【0010】 According to yet another aspect of the present invention, a composite substrate is provided in which each of the one or more stress relaxation layers has an elastic modulus in the range of 0.1 MPa to 3 GPa. 【0011】 According to yet another aspect of the present invention, a composite substrate is provided in which each of the one or more stress relaxation layers has a thickness in the range of 5 μm or more and 50 μm or less, according to any of the above aspects. 【0012】 According to yet another aspect of the present invention, a composite substrate is provided which comprises one or more insulating layers including insulating resin layers and the substrate including a glass substrate, according to any of the above aspects. 【0013】 In yet another aspect of the present invention, a composite substrate relating to any of the above aspects, which is an interposer, is provided. 【0014】 According to yet another aspect of the present invention, at least one of the one or more optical waveguide substrates is provided, wherein the surface on which the optical waveguide layer is provided includes a third region on which the second cladding layer is provided and a fourth region on which the second cladding layer is not provided, the fourth region has a groove extending along the boundary between the third region and the fourth region, and the one or more cores have end faces adjacent to the upper space of the groove, in any of the above aspects. 【0015】 According to yet another aspect of the present invention, a composite substrate relating to the above aspect is provided, wherein the depth of the groove is in the range of 20 μm or more and 50 μm or less. 【0016】 According to yet another aspect of the present invention, a composite substrate relating to any of the above aspects is provided, wherein the width of the groove is within the range of 20 μm to 200 μm. 【0017】 According to yet another aspect of the present invention, a composite substrate is provided in which the upper surface of the substrate is recessed at the position of the groove, corresponding to any of the above-mentioned sides. 【0018】 According to yet another aspect of the present invention, a composite substrate is provided relating to any of the above aspects, wherein in at least one of the one or more substrates with optical waveguides, the first cladding layer includes a first portion provided at the location of the third region and a second portion provided at the location of the fourth region. 【0019】 According to yet another aspect of the present invention, a composite substrate is provided in which the bottom surface of the groove is part of the upper surface of the second portion. 【0020】 Alternatively, according to yet another aspect of the present invention, a composite substrate is provided in which the bottom surface of the groove is part of the top surface of the substrate. 【0021】 According to yet another aspect of the present invention, the first surface has one or more rectangular recesses, the one or more rectangular recesses divide the first surface into a first region located outside the one or more rectangular recesses and one or more second regions which are the bottom surfaces of the one or more rectangular recesses, the openings of each of the one or more rectangular recesses have rounded corners at both ends of the short side separating the first region and the second region, and the composite substrate further comprises one or more adhesive layers interposed between the one or more optical waveguide substrates and the inner surfaces of the one or more rectangular recesses, respectively, to provide a composite substrate according to any of the above aspects. 【0022】 According to yet another aspect of the present invention, a composite substrate is provided relating to the above-mentioned side, wherein the radius of curvature R of each of the corners is within the range of 200 μm to 2000 μm. 【0023】According to yet another aspect of the present invention, a composite substrate is provided wherein, in each of the one or more rectangular recesses, the ratio R / D of the radius of curvature R to the shortest distance D from each of the corners to the substrate with the optical waveguide is in the range of 0.8 or more and 1.2 or less. 【0024】 According to yet another aspect of the present invention, a composite substrate is provided in which the rectangular recess extends from the position of the contour of the first surface to any of the above-mentioned surfaces. 【0025】 A composite substrate is provided relating to any of the above aspects, wherein the wiring substrate has a first metal pattern at least partially exposed at the bottom surface of the one or more rectangular recesses, and the substrate with one or more optical waveguides further includes a second metal pattern facing the optical waveguide layer with the substrate in between, and the first metal pattern and the second metal pattern are joined to each other via a solder layer. 【0026】 According to yet another aspect of the present invention, the wiring substrate has a first magnetic layer that is at least partially exposed at the bottom surface of the one or more rectangular recesses, the substrate with one or more optical waveguides further includes a second magnetic layer that faces the optical waveguide layer with the substrate in between, and the first magnetic layer and the second magnetic layer are coupled to each other by magnetic force, providing a composite substrate according to any of the above aspects. 【0027】 According to yet another aspect of the present invention, a composite substrate is provided relating to any of the above aspects, wherein each of the one or more adhesive layers has an elastic modulus in the range of 0.1 MPa to 3 GPa. 【0028】 According to yet another aspect of the present invention, a composite substrate is provided in which each of the one or more adhesive layers has a thickness in the range of 5 μm to 50 μm. 【0029】 According to yet another aspect of the present invention, a photoelectric fusion device is provided comprising a composite substrate according to any of the above aspects, a first functional device mounted on the composite substrate and optically coupled to at least one of the one or more optical waveguide substrates, and a second functional device mounted on the composite substrate and electrically connected to the first functional device. 【0030】 According to yet another aspect of the present invention, a photoelectric fusion apparatus is provided that further comprises a refractive index adjusting layer having a portion interposed between the first functional device and at least one of the one or more optical waveguide substrates. 【0031】 According to the present invention, a technique is provided that facilitates optical coupling and electrical connection in the mounting of a functional device on a composite substrate including a conductor pattern and an optical waveguide. 【0032】Figure 1 is a top view of a composite substrate according to the first embodiment of the present invention. Figure 2 is a cross-sectional view of the composite substrate shown in Figure 1 along the line II-II. Figure 3 is a top view of a substrate with an optical waveguide included in the composite substrates shown in Figures 1 and 2. Figure 4 is a cross-sectional view of the substrate with an optical waveguide shown in Figure 3. Figure 5 is a top view of a photoelectric fusion apparatus including the composite substrates shown in Figures 1 and 2. Figure 6 is a cross-sectional view of the photoelectric fusion apparatus shown in Figure 5 along the line VI-VI. Figure 7 is a top view of a photoelectric fusion apparatus with a connector including the photoelectric fusion apparatus shown in Figures 5 and 6. Figure 8 is a cross-sectional view showing a modified example of the photoelectric fusion apparatus shown in Figures 5 and 6. Figure 9 is a top view of a composite substrate according to the second embodiment of the present invention. Figure 10 is a cross-sectional view of the composite substrate shown in Figure 9 along the line X-X. Figure 11 is a top view of a substrate with an optical waveguide included in the composite substrates shown in Figures 9 and 10. Figure 12 is a cross-sectional view of the substrate with an optical waveguide shown in Figure 11. Figure 13 is a top view of a photoelectric fusion apparatus including the composite substrate shown in Figures 9 and 10. Figure 14 is a cross-sectional view of the photoelectric fusion apparatus shown in Figure 13 along the line XIV-XIV. Figure 15 is a top view of a photoelectric fusion apparatus with a connector including the photoelectric fusion apparatus shown in Figures 13 and 14. Figure 16 is a cross-sectional view showing a modified example of the photoelectric fusion apparatus shown in Figures 13 and 14. Figure 17 is a top view of a composite substrate according to the third embodiment of the present invention. Figure 18 is a top view of a photoelectric fusion apparatus with a connector including the composite substrate shown in Figure 17. Figure 19 is a top view of a composite substrate according to the fourth embodiment of the present invention. Figure 20 is a cross-sectional view of the composite substrate shown in Figure 19 along the line XX-XX. Figure 21 is a top view of a photoelectric fusion apparatus including the composite substrate shown in Figures 19 and 20. Figure 22 is a cross-sectional view of the photoelectric fusion apparatus shown in Figure 21 along the line XXII-XXII. Figure 23 is a top view of a composite substrate according to the fifth embodiment of the present invention. Figure 24 is a cross-sectional view of the composite substrate shown in Figure 23 along the line XXIV-XXIV. Figure 25 is a top view of the optical waveguide substrate included in the composite substrates shown in Figures 23 and 24. Figure 26 is a cross-sectional view of the optical waveguide substrate shown in Figure 25. Figure 27 is a top view of the photoelectric fusion apparatus including the composite substrates shown in Figures 23 and 24. Figure 28 is a cross-sectional view of the photoelectric fusion apparatus shown in Figure 27 along the line XXVIII-XXVIII.Figure 29 is a partially enlarged cross-sectional view of the photoelectric fusion apparatus shown in Figure 28. Figure 30 is a cross-sectional view showing one modified example of the substrate with optical waveguides shown in Figures 25 and 26. Figure 31 is a cross-sectional view showing one modified example of the photoelectric fusion apparatus shown in Figures 27 and 28. Figure 32 is a top view of the photoelectric fusion apparatus with connectors, including the photoelectric fusion apparatus shown in Figures 27 and 28. Figure 33 is a cross-sectional view showing one modified example of the photoelectric fusion apparatus shown in Figures 27 and 28. Figure 34 is a top view of the composite substrate according to the sixth embodiment of the present invention. Figure 35 is a top view of the photoelectric fusion apparatus with connectors, including the composite substrate shown in Figure 34. Figure 36 is a top view of the composite substrate according to the seventh embodiment of the present invention. Figure 37 is a cross-sectional view of the composite substrate shown in Figure 36 along the line XXXVII-XXXVII. Figure 38 is a top view of the photoelectric fusion apparatus including the composite substrates shown in Figures 36 and 37. Figure 39 is a cross-sectional view of the photoelectric fusion apparatus shown in Figure 38 along the line XXXIX-XXXIX. Figure 40 is a top view of a composite substrate according to the eighth embodiment of the present invention. Figure 41 is a top view of a photoelectric fusion apparatus including the composite substrate shown in Figure 40. Figure 42 is an enlarged view of the composite substrate shown in Figure 40. Figure 43 is a cross-sectional view showing one modified example of the composite substrate shown in Figure 40. Figure 44 is a cross-sectional view showing another modified example of the composite substrate shown in Figure 40. Figure 45 is a top view of a photoelectric fusion apparatus with a connector including the photoelectric fusion apparatus shown in Figure 41. Figure 46 is a cross-sectional view showing one modified example of the photoelectric fusion apparatus shown in Figure 41. Figure 47 is a top view of a composite substrate according to the ninth embodiment of the present invention. Figure 48 is a top view of a photoelectric fusion apparatus including the composite substrate shown in Figure 47. Figure 49 is a top view of a photoelectric fusion apparatus with a connector including the photoelectric fusion apparatus shown in Figure 48. Figure 50 is a top view of a composite substrate according to the tenth embodiment of the present invention. Figure 51 is a top view of a photoelectric fusion apparatus with a connector including the composite substrate shown in Figure 50. Figure 52 is a top view of a composite substrate according to the eleventh embodiment of the present invention. Figure 53 is a top view of the photoelectric fusion apparatus including the composite substrate shown in Figure 52. 【0033】Embodiments of the present invention will be described below with reference to the drawings. The embodiments described below are more specific to any of the above aspects. The matters described below can be incorporated into each of the above aspects, individually or in combination. 【0034】 The embodiments described below illustrate examples that embody the technical concept of the present invention, and the technical concept of the present invention is not limited to the materials, shapes, structures, and arrangements of the components described below. Various modifications can be made to the technical concept of the present invention within the technical scope defined by the claims described in the patent claims. 【0035】 In the drawings referenced in the following description, components having similar or identical functions are given the same reference numerals. It should be noted that the drawings are schematic, and the relationships between dimensions in the thickness direction and dimensions perpendicular to the thickness direction (i.e., in-plane direction), as well as the relationships between dimensions in the thickness direction of multiple layers, may differ from reality. Therefore, specific dimensions should be determined by referring to the following description. It should also be noted that the dimensional relationships between two or more components may differ across multiple drawings. 【0036】 In this disclosure, "upper surface" and "lower surface" refer to the two main surfaces of the plate-like member or the layer contained therein, namely the surface perpendicular to the thickness direction and having the largest area, and the back surface thereof, which are shown at the top and bottom in the drawings, respectively. Furthermore, "end surface" refers to the surface of the plate-like member or the layer contained therein that is located on the outer periphery when viewed from a direction parallel to the thickness direction. And "side surface" refers to a surface that is perpendicular to or inclined with respect to the in-plane direction. 【0037】 Furthermore, in this disclosure, the phrase "AA on BB" is used independently of the direction of gravity. The state specified by the phrase "AA on BB" includes the state in which AA is in contact with BB. The phrase "AA on BB" does not exclude the interposition of one or more other components between AA and BB. 【0038】<1> First Embodiment <1.1> Composite Substrate FIG. 1 is a top view of a composite substrate according to the first embodiment of the present invention. FIG. 2 is a cross-sectional view taken along line II-II of the composite substrate shown in FIG. 1. FIG. 3 is a top view of a substrate with an optical waveguide included in the composite substrate shown in FIGS. 1 and 2. FIG. 4 is a cross-sectional view of the substrate with an optical waveguide shown in FIG. 3. 【0039】 In these figures and other figures, the X direction and the Y direction are perpendicular to the thickness direction of the composite substrate and are orthogonal to each other. Also, in these figures, the Z direction is a direction perpendicular to the X direction and the Y direction, that is, the thickness direction of the composite substrate. 【0040】 The composite substrate 10A shown in FIGS. 1 and 2 is an interposer. The composite substrate 10A includes a wiring substrate 11A, a substrate 12A with an optical waveguide, and an adhesive layer 13 that bonds them to each other. 【0041】 The wiring substrate 11A includes a core insulating layer 111, an insulating layer 112, a conductor pattern 113, and an insulating layer 114. 【0042】 The core insulating layer 111 is, here, an insulating resin layer. According to one example, the core insulating layer 111 is a composite material containing glass fibers and a resin cured product. The core insulating layer 111 may be a glass plate. The core insulating layer 111 may have a single-layer structure or a multilayer structure. A plurality of through holes each extending in the thickness direction thereof are provided in the core insulating layer 111. 【0043】 The insulating layer 112 is laminated on each of the main surfaces of the core insulating layer 111. The insulating layer 112 is, here, an insulating resin layer. The insulating layer 112 is, for example, made of a resin cured product. Each of the insulating layers 112 may have a single-layer structure or a multilayer structure. A plurality of through holes each extending in the thickness direction thereof are provided in each of the insulating layers 112. 【0044】Here, two insulating layers 112 are laminated on each main surface of the core insulating layer 111. The number of insulating layers 112 provided on each main surface of the core insulating layer 111 may be 1, or may be 3 or more. Also, on at least one of the main surfaces of the core insulating layer 111, the insulating layer 112 may not be provided. 【0045】 The conductor pattern 113 is a wiring layer including a main conductor layer. The conductor pattern 113 may have a single-layer structure or a multilayer structure. Here, the "main conductor layer" is the layer with the largest thickness among the conductive layers included in the wiring layer. The main conductor layer is made of a metal material such as copper. Each of the conductor patterns 113 can further include one or more other layers such as an adhesion layer and a seed layer. 【0046】 The conductor pattern 113 includes a first conductor pattern (not shown) including a portion interposed between the core insulating layer 111 and the insulating layer 112 adjacent thereto, a second conductor pattern including a portion interposed between adjacent insulating layers 112, and a third conductor pattern including a portion interposed between the insulating layer 112 and the insulating layer 114. 【0047】 The portion of the first conductor pattern interposed between the core insulating layer 111 and the insulating layer 112 adjacent thereto includes a land portion, a pad portion, and a wiring portion. Each of the wiring portions has one end connected to the land portion and the other end connected to the pad portion. The first conductor pattern further includes a through electrode as a portion covering the side wall of the through hole provided in the core insulating layer 111. Each of the through electrodes is connected to the above-mentioned land portion on both surfaces of the core insulating layer 111. The first conductor pattern may fill the through hole provided in the core insulating layer 111. 【0048】Each of the second and third conductor patterns includes pad portions, wiring portions, and via portions. In each of the second and third conductor patterns, the pad portions include those positioned to cover or surround one opening of a through-hole provided in the insulating layer 112 adjacent to the core insulating layer 111 side, and those positioned away from the through-hole. The wiring portions connect the former pad portions to the latter pad portions. The via portions fill the through-holes provided in the insulating layer 112 adjacent to the pad portions of the second or third conductor pattern, and connect the pad portions facing each other with the insulating layer 112 in between. The third conductor pattern located below has a greater distance between pad portions compared to the third conductor pattern located above. 【0049】 The insulating layer 114 is an organic insulating layer. The insulating layer 114 is made of, for example, solder resist. Each insulating layer 114 covers one of the insulating layers 112 and one of the conductor patterns 113. Each insulating layer 114 has through holes at the positions of the pad portions of the conductor pattern 113 it covers. 【0050】 The wiring board 11A has a first surface S1 and a second surface S2 which is its back surface. Here, the first surface S1 is the top surface of the wiring board 11A, and the second surface S2 is the bottom surface of the wiring board 11A. 【0051】 The first surface S1 includes a first region R1 and a second region R2 that is recessed relative to the first region R1. That is, the first surface S1 has a recess at the location of the second region R2. 【0052】 Here, the wiring board 11A has a shape that, when orthogonally projected onto a plane perpendicular to the Z direction, is a square or rectangle with sides parallel to the X direction and sides parallel to the Y direction. The dimensions of the wiring board 11A in the X and Y directions are, in one example, within the range of 30 mm to 150 mm, and in another example, within the range of 50 mm to 100 mm. 【0053】The shape of the second region R2 is, in this case, a rectangle extending from the edge of the first surface S1, which is parallel to the Y direction, in a direction parallel to the X direction. The dimensions of the second region R2 in the X direction, i.e., the length direction, are preferably within the range of 5 mm to 50 mm, and more preferably within the range of 10 mm to 30 mm. The dimensions of the second region R2 in the Y direction, i.e., the width direction, are preferably within the range of 1 mm to 10 mm, and more preferably within the range of 2 mm to 5 mm. 【0054】 The uppermost conductor pattern 113 is located in the first region R1. A portion of the through-holes provided in the insulating layer 114 located above it is located near the second region R2. 【0055】 The height of the second region R2 is lower than the lower surface of the conductor pattern 113 located in the first region R1, i.e., the uppermost conductor pattern 113. The difference between the height of the lower surface of the uppermost conductor pattern 113 and the height of the second region R2 is preferably in the range of 70 μm to 250 μm, and more preferably in the range of 100 μm to 200 μm. 【0056】 The optical waveguide substrate 12A includes a substrate 121 and an optical waveguide layer 122 provided thereon. 【0057】 The substrate 121 is made of, for example, glass, ceramic, plastic, metal, or a combination of two or more of these materials. The substrate 121 only needs to have a smooth surface. Here, as an example, the substrate 121 is assumed to be a glass plate. 【0058】 The shape of the orthogonal projection of the substrate 121 onto a plane perpendicular to its thickness direction is approximately equal to the shape of the second region R2. Here, the shape of the orthogonal projection of the substrate 121 is a rectangle corresponding to the shape of the second region R2. Furthermore, the dimensions of the orthogonal projection of the substrate 121 are slightly smaller than those of the second region R2. 【0059】The difference between the lengthwise dimension of the second region R2 and the lengthwise dimension of the orthogonal projection of the substrate 121 is, in one example, within the range of 5 μm to 300 μm, and in another example, within the range of 10 μm to 200 μm. The difference between the widthwise dimension of the second region R2 and the widthwise dimension of the orthogonal projection of the substrate 121 is, in one example, within the range of 5 μm to 300 μm, and in another example, within the range of 10 μm to 200 μm. 【0060】 The thickness of the substrate 121 is preferably in the range of 50 μm to 150 μm, and more preferably in the range of 80 μm to 100 μm. 【0061】 The optical waveguide layer 122 includes a first cladding layer 122A, a core 122B, and a second cladding layer 122C. 【0062】 The first cladding layer 122A is provided on one main surface of the substrate 121. The first cladding layer 122A is made of a first low refractive index material. In one example, the first low refractive index material is a cured resin. The first low refractive index material preferably has a refractive index for light with a wavelength of 1300 nm in the range of 1.4 to 1.7, and more preferably in the range of 1.5 to 1.6. 【0063】 The first cladding layer 122A includes a first portion with greater thickness and a second portion with less thickness. The first and second portions are arranged in the longitudinal direction of the substrate 121. 【0064】 The thickness of the first portion is preferably in the range of 120 μm to 170 μm, and more preferably in the range of 130 μm to 160 μm. The difference between the thickness of the first portion and the thickness of the second portion is preferably in the range of 60 μm to 140 μm, and more preferably in the range of 80 μm to 120 μm. 【0065】 The second cladding layer 122C is provided on the first portion of the first cladding layer 122A. The second cladding layer 122C covers the first portion of the first cladding layer 122A without covering the second portion of the first cladding layer 122A. 【0066】The second cladding layer 122C is made of a second low refractive index material. In one example, the second low refractive index material is a cured resin. Preferably, the second low refractive index material has the refractive index described above for the first low refractive index material. Preferably, the second low refractive index material is the same as the first low refractive index material. 【0067】 The core 122B is provided between the first cladding layer 122A and the second cladding layer 122C. Here, the number of cores 122B included in the optical waveguide substrate 12A is 2, but the number of cores 122B included in the optical waveguide substrate 12A may be 1 or 3 or more. 【0068】 Each of the cores 122B has a shape that extends in the longitudinal direction of the substrate 121. These cores 122B are arranged in the width direction. Each of the cores 122B preferably has a diameter in the range of 6 μm to 60 μm, and more preferably in the range of 8 μm to 50 μm. 【0069】 The core 122B is made of a high refractive index material. For example, the high refractive index material is a cured resin. The high refractive index material preferably has a refractive index for light of the above wavelength in the range of 1.4 to 1.7, and more preferably in the range of 1.5 to 1.6. 【0070】 The difference between the refractive index of the high refractive index material for the above wavelength and the refractive index of the first low refractive index material for the above wavelength is preferably within the range of 0.5% to 5.0%, and more preferably within the range of 1.0% to 3.0%, when the refractive index of the high refractive index material is set to 100%. The difference between the refractive index of the high refractive index material for the above wavelength and the refractive index of the second low refractive index material for the above wavelength is also preferably within these ranges. 【0071】 The optical waveguide substrate 12A is installed on the second region R2 such that the optical waveguide layer 122 is located above the substrate 121. As described above, the wiring board 11A has a recess at the location of the second region R2. The optical waveguide substrate 12A is installed within this recess. 【0072】The height of the lower surface of the core 122B is higher than that of the first region R1. The height of the lower surface of the core 122B relative to the first region R1, in this case, the height relative to the upper surface of the insulating layer 114 located above it, is preferably 100 μm or less, and more preferably 80 μm or less. Furthermore, the height of the lower surface of the core 122B relative to the first region R1 is preferably 50 μm or more, and more preferably 60 μm or more. 【0073】 The height of the upper surface of the substrate 121 is preferably lower than that of the first region R1. The difference between the height of the first region R1 and the height of the upper surface of the substrate 121 is preferably in the range of 10 μm to 30 μm, and more preferably in the range of 15 μm to 25 μm. 【0074】 The adhesive layer 13 is interposed between the wiring board 11A and the optical waveguide substrate 12A. The adhesive layer 13 fixes the optical waveguide substrate 12A to the wiring board 11A. The adhesive layer 13 includes a layer made of adhesive. The adhesive layer 13 may have a single-layer structure or a multi-layer structure. 【0075】 <1.2> Photoelectric Fusion Device Figure 5 is a top view of the photoelectric fusion device including the composite substrate shown in Figures 1 and 2. Figure 6 is a cross-sectional view of the photoelectric fusion device shown in Figure 5 along the line VI-VI. 【0076】 The photoelectric fusion apparatus 1A shown in Figures 5 and 6 includes the composite substrate 10A, the bonding conductor 14, the first functional device 20A, and the second functional device 30. 【0077】 The joining conductor 14 covers the pad portion of the conductor pattern 113 covered by the insulating layer 114 at the location of the through-hole provided in the insulating layer 114. Each of the joining conductors 14 includes a portion located within the through-hole provided in the insulating layer 114 and a portion protruding from the insulating layer 114. The joining conductor 14 is, for example, a solder bump. 【0078】The first functional device 20A is a device that includes an optical integrated circuit and an optical waveguide. The optical integrated circuit includes a photoelectric conversion element and performs conversion of optical signals to electrical signals, conversion of electrical signals to optical signals, or both. Here, as an example, the optical integrated circuit is assumed to perform both conversion of optical signals to electrical signals and conversion of electrical signals to optical signals. Each optical waveguide has one end face exposed to the end face of the first functional device 20A and is optically coupled to the photoelectric conversion element at the other end. Here, the number of optical waveguides included in the first functional device 20A is 2. The number of optical waveguides included in the first functional device 20A may be 1 or 3 or more. 【0079】 The first functional device 20A is flip-chip mounted on the wiring board 11A via a bonding conductor 14 in the vicinity of the optical waveguide substrate 12A. Furthermore, the first functional device 20A is positioned such that the end face of the core 21 of its optical waveguide faces the end face of the core 122B of the optical waveguide layer 122. In other words, the optical waveguide of the first functional device 20A is optically coupled to the optical waveguide layer 122 by butt coupling. 【0080】 The second functional device 30 is, for example, a device that operates when at least one of power and an electrical signal is supplied, a device that outputs at least one of power and an electrical signal in response to an external stimulus, or a device that operates when at least one of power and an electrical signal is supplied and outputs at least one of power and an electrical signal in response to an external stimulus. The second functional device 30 is in the form of a chip, for example, a semiconductor chip or a chip on which circuits and elements are formed on a substrate made of a material other than a semiconductor, such as a glass substrate. The second functional device 30 may include, for example, one or more large-scale integrated circuits (LSIs), memory, image sensors, light-emitting elements, and MEMS (Micro Electro Mechanical Systems). The MEMS is, for example, one or more of a pressure sensor, an acceleration sensor, a gyroscope, a tilt sensor, a microphone, and an acoustic sensor. In one example, the second functional device 30 is a semiconductor chip including an LSI. 【0081】The second functional device 30 is flip-chip mounted on the wiring board 11A via a connecting conductor 14. The second functional device 30 is electrically connected to the first functional device 20A via a conductor pattern 113 and a connecting conductor 14. 【0082】 Here, the number of second functional devices 30 included in the photoelectric fusion device 1A is 1. The number of second functional devices 30 included in the photoelectric fusion device 1A may be 2 or more. 【0083】 <1.3> Method for Manufacturing a Photoelectric Fusion Device The above-described photoelectric fusion device 1A can be manufactured, for example, by the following method. <1.3.1> Method for Manufacturing a Wiring Board The wiring board 11A can be manufactured, for example, by the following method. That is, first, a composite material including a core insulating layer 111 and first conductor layers provided on both sides thereof is prepared. Here, as will be described later, first, a composite substrate is manufactured, and this composite substrate is divided into multiple wiring boards 11A. Therefore, the dimensions of the composite material prepared here are slightly larger than the dimensions of the aggregate formed by arranging multiple wiring boards 11A. The first conductor layer is, for example, copper foil attached to the core insulating layer 111. 【0084】 Next, through-holes are formed in this composite material to electrically connect its front and back surfaces. These through-holes are formed, for example, using a drill. 【0085】 Next, a second conductor layer is formed on the side walls of the through-holes and on the surface of the first conductor layer. The second conductor layer may be formed so that the through-holes in the core insulating layer 111 are not completely filled, or it may be formed so that these through-holes are completely filled. 【0086】 The second conductive layer can be obtained, for example, by forming a seed layer by electroless plating and then forming a plating layer by electroplating, in that order. As the material for the seed layer, metallic materials such as Cu, Pd, Al, Sn, Ni, and Cr can be used. As the material for the plating layer, metallic materials such as Cu, Cu alloy, Ag, Ag alloy, Sn, Pd, Au, Ni, Cr, Pt, Fe, and combinations of two or more of these can be used. 【0087】Next, the through-holes in the core insulating layer 111 are filled with a hole-filling resin. For example, the through-holes are filled with resin, allowed to harden, and then any excess hardened resin that has protruded from the through-holes is removed by buffing or the like. If the through-holes in the core insulating layer 111 are completely filled with the conductive layer, this step and the following step can be omitted. 【0088】 Next, a third conductive layer is formed on both sides of the composite material obtained as described above. The third conductive layer is, for example, a laminate of a seed layer and a plating layer provided thereon. These seed layer and plating layer can be formed, for example, using the method and materials described above for the second conductive layer. 【0089】 The seed layer of the third conductor layer can also be formed by sputtering. When the seed layer is formed by sputtering, the materials used can be, for example, Cu, Ni, Al, Ti, Cr, Mo, W, Ta, Au, Ir, Ru, Pd, Pt, AlSi, AlSiCu, AlCu, NiFe, ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), AZO (Aluminum-doped Zinc Oxide), ZnO, PZT (Lead Zirconate Titanate), TiN, Cu ３ N ４ A Cu alloy, or a combination of two or more of these can be used. 【0090】 Next, a resist resin is applied to both sides of the composite material obtained as described above, or a dry film resist is laminated onto it. Then, pattern exposure and development are sequentially performed on these resist layers to obtain a resist pattern. 【0091】 Next, etching is performed using the resist pattern as an etching mask to remove portions of the first to third conductive layers corresponding to the openings in the resist pattern. In this way, a conductive pattern including the portion covering the upper surface of the core insulating layer 111 and a conductive pattern including the portion covering the lower surface of the core insulating layer 111 are obtained. 【0092】Next, an insulating layer 112 having through holes is formed on both sides of the composite material obtained as described above. The insulating layer 112 is formed using, for example, a thermosetting resin or a photosensitive resin. When using a thermosetting resin, a coating film made of the thermosetting resin is cured, and CO2 is applied to this cured film. ２ An insulating layer 112 having through holes is obtained by laser processing, such as laser processing and UV laser processing. When using a photosensitive resin, an insulating layer 112 having through holes is obtained by pattern exposure and development of a coating film made of the photosensitive resin. These through holes are formed at the positions of the pad portions of the conductor pattern covered by the insulating layer 112. 【0093】 Next, the seed layer is formed to cover the main surface of the insulating layer 112, the side walls of the through holes in the insulating layer 112, and the area of ​​the pad portion of the conductor pattern covered by the insulating layer 112 that is adjacent to the internal space of the through holes in the insulating layer 112. The seed layer can be formed using the method and materials described above for the seed layers of the second and third conductor layers. 【0094】 Next, a resist resin is applied to both sides of the composite material obtained as described above, or a dry film resist is laminated onto it. Then, pattern exposure and development are sequentially performed on these resist layers to obtain a resist pattern. 【0095】 Next, a plating layer is formed by an electroplating method using the seed layer as a power supply layer. The metal materials mentioned above can be used for these plating layers. 【0096】 Next, the resist pattern is removed, and then the portion of the seed layer that is not covered by the plating layer is removed by etching. This yields a conductive pattern 113 consisting of the seed layer and the plating layer, respectively. 【0097】 Subsequently, an insulating layer 112 and a conductor pattern 113 are formed on the upper and lower surfaces of the composite material obtained as described above. 【0098】Next, insulating layers are provided as continuous films on both sides of the composite material obtained as described above. These insulating layers are solder resist layers. The solder resist layers can be provided on the composite material by applying liquid solder resist or by laminating a dry film type solder resist. The solder resist is, for example, a photosensitive epoxy resin or a non-photosensitive thermosetting resin. The solder resist may further contain inorganic fillers. 【0099】 Next, through-holes are formed in the solder resist layer to obtain an insulating layer 114. These through-holes are formed at the positions of the pad portions of the conductor pattern 113 covered by the solder resist layer. When using a solder resist containing a photosensitive resin, through-holes can be formed by pattern exposure and development of the solder resist layer. When using a solder resist containing a thermosetting resin, CO2 is applied to the solder resist layer. ２ Through-holes can be formed by laser processing, such as laser processing and UV laser processing. 【0100】 Next, a surface treatment layer is formed on the surface of the pad portion of the conductor pattern 113 so as to cover the area adjacent to the internal space of the through-hole of the insulating layer 114. The surface treatment layer is provided for the purpose of preventing oxidation of the surface of the conductor pattern 113 and improving its wettability to solder. 【0101】 The surface treatment layer is, for example, an electroless Ni / Pd / Au plating layer. Alternatively, an OSP (Organic Solderability Preservative) film, i.e., a surface treatment layer using a water-soluble preflux, may be formed as the surface treatment layer. Alternatively, an electroless tin plating or an electroless Ni / Au plating layer may be formed as the surface treatment layer. 【0102】Next, a bonding conductor 14 is formed on the surface treatment layer. The bonding conductor 14 is, for example, a metal bump such as a solder bump. The bonding conductor 14 can be formed, for example, by printing a metal paste such as solder paste onto the surface treatment layer using a screen printing method. Alternatively, the bonding conductor 14 can be formed by printing flux onto the surface treatment layer using a screen printing method, placing metal balls such as solder balls into the through-holes of the insulating layer 114 using a ball-filling method or the like, melting them, and then cooling them. 【0103】 Subsequently, a recess corresponding to the second region R2 is formed on one surface of the composite material obtained as described above to obtain a composite substrate. These recesses are formed, for example, by cutting or laser ablation. When recesses are formed by laser ablation, it is preferable that the composite material includes a stopper film that defines the position of the bottom of the recess. The stopper film is preferably a metal layer that exhibits high reflectivity at the wavelength of the laser beam. This metal layer may also be part of the conductor pattern described above. 【0104】 Next, the assembled substrate is divided into multiple individual wiring boards. Specifically, dicing is performed along the dicing lines. In this way, wiring board 11A is obtained. 【0105】 <1.3.2> Method for Manufacturing a Substrate with Optical Waveguides The substrate with optical waveguides 12A is manufactured, for example, by the following method. That is, first, a substrate 121 is prepared. Here, as will be described later, a composite substrate is first manufactured, and this composite substrate is divided into multiple individual substrates with optical waveguides 12A. Therefore, the dimensions of the substrate 121 prepared here are slightly larger than the dimensions of the composite formed by arranging multiple substrates with optical waveguides 12A. To facilitate handling, the substrate 121 may be supported by a support that can be removed from the substrate 121. 【0106】 Next, an optical waveguide layer 122 is formed on the substrate 121. Specifically, a first cladding layer 122A, a core 122B, and a second cladding layer 122C are formed on the substrate 121 in this order. 【0107】The first cladding layer 122A can be obtained, for example, by coating an ionizing radiation-curable resin onto the substrate 121 and curing it by irradiating the entire surface of the coating with ionizing radiation, thereby obtaining a continuous film with substantially uniform thickness. Alternatively, the first cladding layer 122A can be obtained by coating a thermosetting resin onto the substrate 121 and curing it by heating the entire coating. The core 122B can be obtained, for example, by coating an ionizing radiation-curable resin onto the first cladding layer 122A, irradiating the portion of the coating where the core 122B is to be formed with ionizing radiation to cure these portions, and then subjecting the coating to a developing process. The second cladding layer 122C can be obtained, for example, by the same method as described above for the first cladding layer 122A. 【0108】 Subsequently, the portion of the optical waveguide layer 122 obtained as described above that is located directly above the second portion of the first cladding layer 122A is removed to obtain a composite substrate. For example, laser ablation, dry etching, or cutting can be used for this removal. This creates a first portion with a greater thickness and a second portion with a smaller thickness in the first cladding layer 122A, and exposes the end face of the core 122B at the boundary between the first and second portions. 【0109】 The first cladding layer 122A may be a multilayer structure including a continuous film and a patterned film provided thereon. In this case, if the core 122B and the second cladding layer 122C are formed only on the patterned film, the removal process described above is unnecessary. 【0110】 Next, the assembled substrate is divided into multiple individual substrates with optical waveguides. Specifically, dicing is performed along the dicing lines. In this way, a substrate 12A with optical waveguides is obtained. 【0111】 <1.3.3> Method for Manufacturing a Composite Substrate The composite substrate 10A is manufactured, for example, by the following method. First, an adhesive is applied to the second region R2 of the wiring board 11A. Next, the substrate 12A with optical waveguides is placed on the adhesive layer. Subsequently, the adhesive is cured. This results in a composite substrate 10A in which the substrate 12A with optical waveguides is fixed to the wiring board 11A via the adhesive layer 13. 【0112】 <1.3.4> Method for Manufacturing a Photoelectric Fusion Device The photoelectric fusion device 1A is manufactured, for example, by the following method. First, the first functional device 20A and the second functional device 30 are flip-chip mounted onto the composite substrate 10A. Next, preferably, the joints between them are sealed. For example, an underfill agent is injected between the composite substrate 10A and the first functional device 20A, and between the composite substrate 10A and the second functional device 30, and cured to form an underfill layer. For example, a thermosetting epoxy resin is used as the underfill agent. The underfill agent is injected in a manner that prevents it from flowing between the end face of the core 122B and the first functional device 20A. In this way, the photoelectric fusion device 1A is obtained. 【0113】 <1.4> Effects In the above-described photoelectric fusion apparatus 1A, a composite substrate 10A is formed by a wiring board 11A and a substrate with an optical waveguide 12A. Therefore, for example, a low-cost manufacturing configuration can be adopted for the wiring board 11A, and a substrate 121 with a smooth surface can be used for the substrate with an optical waveguide 12A to obtain an optical waveguide with excellent optical performance. 【0114】 This effect can be obtained even when the surface on which the optical waveguide substrate 12A is mounted on the wiring board 11A is substantially flat. However, in this case, in order to optically couple the first functional device 20A and the core 122B, the height of the bonding conductor 14 that connects the first functional device 20A and the wiring board 11A must be extremely large. It is difficult to form a bonding conductor 14 with such a large height with high dimensional accuracy. Furthermore, a photoelectric fusion device 1A in which the bonding conductor 14 has a large height has poor connection reliability between the first functional device 20A and the wiring board 11A. 【0115】In the composite substrate 10A, as described above, the height of the second region R2 is lower than the lower surface of the conductor pattern 113 located in the first region R1, i.e., the uppermost conductor pattern 113. When this configuration is adopted, the position of the core 122B can be lowered compared to the case where the surface on which the optical waveguide substrate 12A is mounted on the wiring substrate 11A is substantially flat. Therefore, the first functional device 20A and the core 122B can be optically coupled without increasing the height of the bonding conductor 14 that joins the first functional device 20A and the wiring substrate 11A to each other. In other words, by adopting the above configuration, optical coupling and electrical connection can be easily performed when mounting a functional device on a composite substrate including a conductor pattern and an optical waveguide. 【0116】 Furthermore, by adopting the above-described configuration, the joining conductor 14 can be formed with high dimensional accuracy. In addition, the photoelectric integration device 1A employing the above-described configuration exhibits excellent connection reliability between the first functional device 20A and the wiring board 11A. 【0117】 <1.5> Modifications The above photoelectric fusion device 1A can be modified in various ways. 【0118】 Figure 7 is a top view of a photoelectric fusion apparatus with a connector, including the photoelectric fusion apparatus shown in Figures 5 and 6. The photoelectric fusion apparatus with a connector 1AC shown in Figure 7 is the same as the photoelectric fusion apparatus 1A described above, except for the following: The photoelectric fusion apparatus with a connector 1AC further includes a connector 15. The composite substrate 10A and the connector 15 constitute the composite substrate 10AC with a connector. The connector 15 is configured to allow the optical wiring 40 to be detachably connected, facilitating optical coupling between the optical wiring 40 and the core 122B. 【0119】 Figure 8 is a cross-sectional view showing a modified example of the photoelectric fusion apparatus shown in Figures 5 and 6. The photoelectric fusion apparatus 1A2 shown in Figure 8 is the same as the photoelectric fusion apparatus 1A described above, except for the following point. That is, in the photoelectric fusion apparatus 1A2, the adhesive layer 13 of the composite substrate 10A is a stress relaxation layer. 【0120】In the photoelectric integration device 1A, most of the conductor pattern 113 is located in the portion of the wiring board 11A corresponding to the first region R1, and the first functional device 20A and the second functional device 30 are mounted in this portion. Furthermore, the portion of the wiring board 11A corresponding to the first region R1 is thicker than the portion corresponding to the second region R2. Therefore, for example, in a situation where the wiring board 11A warps due to the heat generated by the operation of the second functional device 30, the amount of deformation in the portion of the wiring board 11A corresponding to the second region R2 is greater than the amount of deformation in the portion of the wiring board 11A corresponding to the first region R1. 【0121】 In the photoelectric integration device 1A, the first functional device 20A is fixed to the portion of the wiring board 11A corresponding to the first region R1 via a bonding conductor 14, and the electrical connection between the first functional device 20A and the wiring board 11A is not impaired by the aforementioned warping. However, if an adhesive layer 13 with a small stress relaxation effect is used, the aforementioned warping will also cause warping in the substrate 12A with the optical waveguide, and as a result, the optical axis between the first functional device 20A and the core 122B may be misaligned. 【0122】 If the adhesive layer 13 is a stress relaxation layer, even if the wiring board 11A warps, the optical waveguide substrate 12A will not warp significantly as a result. Therefore, the photoelectric fusion device 1A2 is less likely to experience optical axis misalignment due to the warping of the wiring board 11A, and consequently, it is less likely to experience increased optical coupling loss or loss of optical coupling due to this optical axis misalignment. 【0123】 In this configuration, the stress relaxation layer is provided between the second region R2 and the end of the optical waveguide substrate 12A that is closer to the center of the wiring substrate 11A, but not between the second region R2 and the end of the optical waveguide substrate 12A that is further from the center of the wiring substrate 11A. This structure is advantageous in reducing the warping of the optical waveguide substrate 12A. 【0124】 The stress relaxation layer may be provided over the entire area between the second region R2 and the substrate 12A with the optical waveguide. This structure is advantageous for securely fixing the substrate 12A with the optical waveguide to the wiring board 11A. 【0125】The elastic modulus of the stress relaxation layer is preferably in the range of 0.1 MPa to 3 GPa, and more preferably in the range of 0.3 MPa to 1 GPa. Here, "elastic modulus" is the dynamic storage modulus at 25°C. Materials with a low elastic modulus often have a significantly different coefficient of thermal expansion from the wiring board 11A, etc., and therefore, if such a material is used for the stress relaxation layer, it may not be possible to sufficiently suppress the warping of the optical waveguide substrate 12A. If a material with a high elastic modulus is used for the stress relaxation layer, the deformation of the stress relaxation layer in response to stress will be insufficient, and therefore, it may not be possible to sufficiently suppress the warping of the optical waveguide substrate 12A. 【0126】 The thickness of the stress relaxation layer is preferably in the range of 5 μm to 50 μm, and more preferably in the range of 10 μm to 40 μm. If the stress relaxation layer is made thinner, it may become difficult to securely fix the substrate 12A with the optical waveguide to the wiring substrate 11A. If the stress relaxation layer is made thicker, the thickness of the composite substrate 10A increases. 【0127】 <2> Second Embodiment <2.1> Composite Substrate Figure 9 is a top view of a composite substrate according to a second embodiment of the present invention. Figure 10 is a cross-sectional view of the composite substrate shown in Figure 9 along the line X-X. Figure 11 is a top view of a substrate with an optical waveguide included in the composite substrate shown in Figures 9 and 10. Figure 12 is a cross-sectional view of the substrate with an optical waveguide shown in Figure 11. 【0128】 The composite substrate 10B shown in Figures 9 and 10 is the same as the composite substrate 10A described above, except that it includes a substrate 12B with an optical waveguide instead of the substrate 12A with an optical waveguide. Furthermore, the substrate 12B with an optical waveguide is the same as the substrate 12A with an optical waveguide, except for the following points. 【0129】 In other words, in the optical waveguide substrate 12B, the first cladding layer 122A has a uniform thickness throughout. The core 122B includes the portion sandwiched between the first cladding layer 122A and the second cladding layer 122C, as well as the portion not covered by the second cladding layer 122C. In the composite substrate 10B, similar to the composite substrate 10A, the height of the lower surface of the core 122B is higher than that of the first region R1. 【0130】 <2.2> Photoelectric Fusion Device Figure 13 is a top view of the photoelectric fusion device including the composite substrate shown in Figures 9 and 10. Figure 14 is a cross-sectional view of the photoelectric fusion device shown in Figure 13 along the line XIV-XIV. 【0131】 The photoelectric fusion apparatus 1B shown in Figures 13 and 14 is the same as the photoelectric fusion apparatus 1A described above, except that it includes a composite substrate 10B instead of composite substrate 10A, and includes a first functional device 20B instead of first functional device 20A. Furthermore, the first functional device 20B is the same as the first functional device 20A, except that a core 21 is provided so as to be exposed on its main surface. 【0132】 In the photoelectric fusion apparatus 1B, the first functional device 20B is mounted on the composite substrate 10B such that the region of the core 21's surface located on the main surface of the first functional device 20B is in contact with the upper surface of the core 122B. In other words, in the photoelectric fusion apparatus 1B, the optical waveguide of the first functional device 20B is optically coupled with the optical waveguide layer 122 by adiaptic coupling. 【0133】 <2.3> Effects In the second embodiment, the same effects as in the first embodiment can be obtained. Also, as shown in the first and second embodiments, the optical waveguide of the first functional device and the optical waveguide layer 122 and optical coupling may be performed by any method. 【0134】 <2.4> Modifications The above photoelectric fusion device 1B can be modified in various ways. 【0135】 Figure 15 is a top view of a photoelectric fusion apparatus with a connector, including the photoelectric fusion apparatus shown in Figures 13 and 14. The photoelectric fusion apparatus with a connector 1BC shown in Figure 15 is the same as the photoelectric fusion apparatus 1B described above, except for the following: The photoelectric fusion apparatus with a connector 1BC further includes a connector 15 connected to a substrate 12B with an optical waveguide. The composite substrate 10B and the connector 15 constitute the composite substrate 10BC with a connector. The connector 15 is the same as that described above for the photoelectric fusion apparatus with a connector 1AC. 【0136】 Figure 16 is a cross-sectional view showing a modified example of the photoelectric fusion apparatus shown in Figures 13 and 14. 【0137】 The photoelectric fusion apparatus 1B2 shown in Figure 16 is the same as the photoelectric fusion apparatus 1B described above, except for the following point. That is, in the photoelectric fusion apparatus 1B2, the adhesive layer 13 of the composite substrate 10B is the stress relaxation layer described above for the photoelectric fusion apparatus 1A2. 【0138】 If the wiring board 11A of the photoelectric fusion device 1B experiences warping similar to that described above, at least a portion of the surface of the core 21 that was in contact with the core 122B may separate from the core 122B. Adiabattic coupling is optical coupling that utilizes evanescent waves. Therefore, if the contact area between the core 21 and the core 122B decreases, the optical coupling loss increases, and in some cases, the optical coupling between the optical waveguide of the first functional device 20B and the optical waveguide layer 122 may be lost. 【0139】 If the adhesive layer 13 is a stress relaxation layer, even if the wiring board 11A warps, the optical waveguide substrate 12B will not warp significantly as a result. Therefore, the photoelectric fusion device 1B2 is less likely to experience a decrease in the contact area between the core 21 and the core 122B due to the warping of the wiring board 11A, and consequently, is less likely to experience an increase in optical coupling loss or loss of optical coupling due to this decrease in contact area. 【0140】 <3> Figure 17 of the third embodiment is a top view of a composite substrate according to the third embodiment of the present invention. 【0141】 The composite substrate 10C shown in Figure 17 is the same as the composite substrate 10A described above, except for the following: The composite substrate 10C includes a wiring board 11B instead of a wiring board 11A. The wiring board 11B is the same as the wiring board 11A described above, except for the following: The first surface S1 has four second regions R2. These second regions R2 are arranged so as to be adjacent to each of the four edges of the first surface S1. And, four optical waveguide substrates 12A are arranged in each of these four second regions R2. 【0142】Figure 18 is a top view of a photoelectric fusion apparatus with connectors, including the composite substrate shown in Figure 17. The photoelectric fusion apparatus with connectors 1CC shown in Figure 18 is the same as the photoelectric fusion apparatus with connectors 1AC, except for the following: The photoelectric fusion apparatus with connectors 1CC includes a composite substrate 10C instead of a composite substrate 10A. Four first functional devices 20A are mounted on the composite substrate 10C. Each of these first functional devices 20A is electrically connected to a second functional device 30 via a wiring board 11B. Four connectors 15 are also attached to the composite substrate 10C. The composite substrate 10C and the connectors 15 constitute the composite substrate with connectors 10CC. 【0143】 In the third embodiment, the same effects as in the first embodiment can be obtained. Furthermore, as shown in the third embodiment, the number of first functional devices included in the photoelectric fusion device may be two or more. 【0144】 <4> Figure 19 of the fourth embodiment is a top view of a composite substrate according to the fourth embodiment of the present invention. Figure 20 is a cross-sectional view of the composite substrate shown in Figure 19 along the line XX-XX. 【0145】 The composite substrate 10D shown in Figures 19 and 20 is the same as the composite substrate 10A, except for the following: The composite substrate 10D includes a wiring substrate 11C and a substrate 12C with an optical waveguide instead of a wiring substrate 11A and a substrate 12A with an optical waveguide. 【0146】 The wiring board 11C is the same as the wiring board 11A, except for the following: The wiring board 11C is configured to mount two first functional devices 20A and two second functional devices 30. The second region R2 is provided between the region on which one second functional device 30 is to be mounted and the region on which the other second functional device 30 is to be mounted. 【0147】The optical waveguide substrate 12C is the same as the optical waveguide substrate 12A, except for the following: In the optical waveguide substrate 12C, the first cladding layer 122A has two smaller second portions. The thicker first portion of the first cladding layer 122A is interposed between the two second portions. The second cladding layer 122C covers the first portion of the first cladding layer 122A without covering the second portion of the first cladding layer 122A. Each of the cores 122B is interposed between the first portion of the first cladding layer 122A and the second cladding layer 122C and extends in the direction of the arrangement of the second portions. The optical waveguide substrate 12C is placed in the second region R2 such that the length direction of the cores 122B coincides with the arrangement direction of the area on which the two second functional devices 30 are to be mounted. 【0148】 Figure 21 is a top view of the photoelectric fusion apparatus including the composite substrate shown in Figures 19 and 20. Figure 22 is a cross-sectional view of the photoelectric fusion apparatus shown in Figure 21 along the line XXII-XXII. 【0149】 The photoelectric fusion apparatus 1D shown in Figures 21 and 22 is the same as the photoelectric fusion apparatus 1A, except for the following: the photoelectric fusion apparatus 1D includes a composite substrate 10D instead of composite substrate 10A. Also, in the photoelectric fusion apparatus 1D, the number of first functional devices 20A is 2, and the number of second functional devices 30 is also 2. 【0150】 In the fourth embodiment, the same effects as in the first embodiment can be obtained. Also, as shown in the fourth embodiment, the number of first functional devices included in the photoelectric fusion device may be two or more, and the number of second functional devices included in the photoelectric fusion device may also be two or more. Also, as shown in the fourth embodiment, instead of optically coupling the optical waveguide layer 122 to the first functional device and the optical wiring, it may optically couple to a plurality of first functional devices. 【0151】<5> Fifth Embodiment <5.1> Composite Substrate Figure 23 is a top view of a composite substrate according to the fifth embodiment of the present invention. Figure 24 is a cross-sectional view of the composite substrate shown in Figure 23 along the line XXIV-XXIV. Figure 25 is a top view of a substrate with an optical waveguide included in the composite substrate shown in Figures 23 and 24. Figure 26 is a cross-sectional view of the substrate with an optical waveguide shown in Figure 25. 【0152】 The composite substrate 10AX shown in Figures 23 and 24 is the same as the composite substrate 10A described with reference to Figures 1 and 2, except that it includes a substrate 12AX with an optical waveguide instead of the substrate 12A with an optical waveguide. Furthermore, the substrate 12AX with an optical waveguide shown in Figures 23 to 26 is the same as the substrate 12A with an optical waveguide described with reference to Figures 1 to 4, except for the following points. 【0153】 In other words, in the optical waveguide substrate 12AX, as shown in Figure 26, the first cladding layer 122A includes a first portion P1 which is thicker and a second portion P2 which is thinner. The first portion P1 and the second portion P2 are arranged in the longitudinal direction of the substrate 121. The second portion P2 includes a portion that forms a groove GR. 【0154】 The thickness of the first portion P1 is preferably in the range of 120 μm to 170 μm, and more preferably in the range of 130 μm to 160 μm. The difference between the thickness of the first portion P1 and the thickness of the second portion P2 is preferably in the range of 60 μm to 140 μm, and more preferably in the range of 80 μm to 120 μm. Here, the thickness of the second portion P2 refers to the thickness measured in the portion where the groove GR is not formed. 【0155】 The second cladding layer 122C is provided on the first portion P1 of the first cladding layer 122A. The second cladding layer 122C covers the first portion P1 of the first cladding layer 122A without covering the second portion P2 of the first cladding layer 122A. That is, the second cladding layer 122C is provided such that a portion of the upper surface of the first cladding layer 122A is exposed. 【0156】As shown in Figure 26, the surface of the optical waveguide substrate 12AX on which the optical waveguide layer 122 is provided (i.e., the upper surface of the optical waveguide layer 122) includes a third region R3 on which the second cladding layer 122C is provided, and a fourth region R4 on which the second cladding layer 122C is not provided. The fourth region R4 has a groove GR extending along the boundary between the third region R3 and the fourth region R4. Details of the groove will be described later. 【0157】 <5.2> Photoelectric Fusion Device Figure 27 is a top view of the photoelectric fusion device including the composite substrate shown in Figures 23 and 24. Figure 28 is a cross-sectional view of the photoelectric fusion device shown in Figure 27 along the line XXVIII-XXVIII. 【0158】 The photoelectric fusion apparatus 1AX shown in Figures 27 and 28 is the same as the photoelectric fusion apparatus 1A described with reference to Figures 5 and 6, except that it includes the above-mentioned composite substrate 10AX instead of the composite substrate 10A. 【0159】 <5.3> Groove As described above, in the photoelectric fusion apparatus 1AX, the surface of the optical waveguide substrate 12AX on which the optical waveguide layer 122 is provided (i.e., the upper surface of the optical waveguide layer 122) includes a third region R3 on which the second cladding layer 122C is provided and a fourth region R4 on which the second cladding layer 122C is not provided, and the fourth region R4 has a groove GR that extends along the boundary between the third region R3 and the fourth region R4. Figure 29 is a partially enlarged view of the cross-sectional view of the photoelectric fusion apparatus shown in Figure 28, showing an enlarged view of the vicinity of the groove GR. 【0160】 In Figure 29, the bottom surface of groove GR is covered by the first cladding layer 122A. That is, the bottom surface of groove GR is part of the upper surface of the second portion P2 of the first cladding layer 122A. 【0161】 The upper surface of the substrate 121 is recessed at the location of the groove GR, corresponding to the groove GR. When a recess corresponding to the groove GR is provided on the upper surface of the substrate 121 at the location of the groove GR, the depth of the groove GR, i.e., the depth represented by the symbol D in Figure 29, can be increased. Alternatively, a recess corresponding to the groove GR is not required on the upper surface of the substrate 121 at the location of the groove GR. In this case, the depth D of the groove GR cannot be greater than the thickness of the second portion P2. 【0162】 The core 122B of the optical waveguide layer 122 has an end face EF1 adjacent to the upper space of the groove GR. The core 21 of the optical waveguide of the first functional device 20 has an end face EF2 adjacent to the upper space of the groove GR. 【0163】 The distance between the first functional device 20 and the substrate 12AX with the optical waveguide, i.e., the distance represented by the symbol G in Figure 29, is preferably narrowed in order to reduce the loss of optical signals. This distance G is preferably in the range of 1 μm to 10 μm, and more preferably in the range of 2 μm to 8 μm. 【0164】 Furthermore, in order to reduce the loss of optical signals, it is preferable to flow a cleaning solution into the narrow gap between the first functional device 20 and the optical waveguide substrate 12AX to clean the end faces of the optical waveguide, that is, the end face EF1 of the core 122B of the optical waveguide layer 122 of the optical waveguide substrate 12AX and the end face EF2 of the core 21 of the optical waveguide of the first functional device 20. As described above, the surface of the optical waveguide substrate 12AX on which the optical waveguide layer 122 is provided has grooves GR. When cleaning solution is flowed into the narrow gap between the first functional device 20 and the optical waveguide substrate 12AX from above the photoelectric fusion apparatus 1AX, the cleaning solution flows more easily, improving the cleanability of the end faces of the optical waveguide. In particular, it is possible to improve the difficulty of cleaning the end faces of the optical waveguide when the above-mentioned gap G is narrowed. Improving the cleanability of the end faces of the optical waveguide enhances the effect of reducing the loss of optical signals. For example, it is possible to improve the flux cleaning performance when a flux cleaning solution is applied after reflow. 【0165】The depth of the groove GR, i.e., the depth represented by the symbol D in Figure 29, is preferably within the range of 20 μm to 50 μm, and more preferably within the range of 30 μm to 45 μm. The width of the groove GR, i.e., the width represented by the symbol W in Figure 29, is preferably within the range of 20 μm to 200 μm, and more preferably within the range of 50 μm to 180 μm. When the depth D and width W of the groove GR are within the above ranges, the cleaning solution can be easily flowed into the narrow gap between the first functional device 20 and the optical waveguide substrate 12AX from above the photoelectric fusion apparatus 1AX. If the depth D and width W of the groove GR are too large, deformation of the optical waveguide substrate 12AX is more likely to occur. 【0166】 <5.4> Method for Manufacturing the Photoelectric Fusion Apparatus The above-described photoelectric fusion apparatus 1AX can be manufactured, for example, by the following method. <5.4.1> Method for Manufacturing the Optical Waveguide Substrate The optical waveguide substrate 12AX can be manufactured, for example, by the following method. That is, first, a substrate 121 is prepared. Here, as will be described later, a composite substrate is first manufactured, and this composite substrate is divided into multiple optical waveguide substrates 12AX. Therefore, the dimensions of the substrate 121 prepared here are slightly larger than the dimensions of the aggregate formed by arranging multiple optical waveguide substrates 12AX. To facilitate handling, the substrate 121 may be supported by a support that can be removed from the substrate 121. 【0167】 On the upper surface of the substrate 121, a recess corresponding to the groove GR is provided at the location of the groove GR, if necessary. For example, if the depth D of the groove GR is greater than the thickness of the second portion P2 of the first cladding layer 122A, a recess corresponding to the groove GR is provided on the upper surface of the substrate 121 at the location of the groove GR. This recess can be formed by etching, laser processing, a combination of laser and etching processing, cutting, etc. This recess may be provided with a size slightly larger than the depth D and width W of the groove GR, and the first cladding layer 122A may be interposed between the substrate 121 and the groove GR. In this case, the recessed portion provided on the upper surface of the substrate 121 can be protected by the first cladding layer 122A. 【0168】Next, an optical waveguide layer 122 is formed on the substrate 121. Specifically, a first cladding layer 122A, a core 122B, and a second cladding layer 122C are formed on the substrate 121 in this order. 【0169】 The first cladding layer 122A can be obtained, for example, by coating an ionizing radiation-curable resin onto the substrate 121 and curing it by irradiating the entire surface of the coating with ionizing radiation, thereby obtaining a continuous film with substantially uniform thickness. Alternatively, the first cladding layer 122A can be obtained by coating a thermosetting resin onto the substrate 121 and curing it by heating the entire coating. The core 122B can be obtained, for example, by coating an ionizing radiation-curable resin onto the first cladding layer 122A, irradiating the portion of the coating where the core 122B is to be formed with ionizing radiation to cure these portions, and then subjecting the coating to a developing process. The second cladding layer 122C can be obtained, for example, by the same method as described above for the first cladding layer 122A. 【0170】 Subsequently, the portion of the optical waveguide layer 122 obtained as described above that is located directly above the second portion P2 of the first cladding layer 122A is removed to obtain a composite substrate. For example, laser ablation, dry etching, or cutting can be used for this removal. This creates a first portion P1 with a greater thickness and a second portion P2 with a smaller thickness in the first cladding layer 122A, and exposes the end face EF1 of the core 122B at the boundary between the first portion P1 and the second portion P2. 【0171】 Subsequently, grooves GR are formed in the second portion P2 of the first cladding layer 122A. The grooves GR can be formed by, for example, router processing, laser ablation, dry etching, or photolithography. 【0172】 The first cladding layer 122A may be a multilayer structure including a continuous film and a patterned film provided thereon. In this case, if the core 122B and the second cladding layer 122C are formed only on the patterned film, the removal process described above is unnecessary. 【0173】Next, the assembled substrate is divided into multiple individual substrates with optical waveguides. Specifically, dicing is performed along the dicing lines. In this way, the substrate 12AX with optical waveguides is obtained. 【0174】 <5.4.2> Method for Manufacturing a Composite Substrate The composite substrate 10AX can be manufactured in the same manner as described above for the composite substrate 10A, except that, for example, the optical waveguide substrate 12AX is used instead of the optical waveguide substrate 12A. 【0175】 <5.4.3> Method for Manufacturing the Photoelectric Fusion Device The photoelectric fusion device 1AX is manufactured in the same manner as described above for the photoelectric fusion device 1A, except that, for example, the composite substrate 10AX is used instead of the composite substrate 10A. The underfill material is injected in such a way that the underfill material does not flow between the end face EF1 of the core 122B and the first functional device 20. 【0176】 <5.5> Effects In the fifth embodiment, the same effects as in the first embodiment can be obtained. 【0177】 Furthermore, as described above, in the photoelectric fusion apparatus 1AX, the surface of the optical waveguide substrate 12AX on which the optical waveguide layer 122 is provided has grooves GR. In this case, compared to the case where grooves GR are not provided, when cleaning liquid is flowed from above the photoelectric fusion apparatus 1AX into the narrow gap between the first functional device 20 and the optical waveguide substrate 12AX, the cleaning liquid can flow more easily. This improves the cleanability of the end faces of the optical waveguide (i.e., the end face EF1 of the core 122B of the optical waveguide layer 122 of the optical waveguide substrate 12AX and the end face EF2 of the core 21 of the optical waveguide of the first functional device 20), and reduces the loss of optical signals. 【0178】 <5.6> Modifications The above photoelectric fusion device 1AX can be modified in various ways. 【0179】Figure 30 is a cross-sectional view showing a modified example of the optical waveguide substrate shown in Figures 25 and 26. The optical waveguide substrate 12BX shown in Figure 30 may be used in place of the optical waveguide substrate 12AX of the above-mentioned photoelectric fusion device 1AX. The optical waveguide substrate 12BX shown in Figure 30 is the same as the optical waveguide substrate 12AX shown in Figures 25 and 26, except for the following point. That is, in the optical waveguide substrate 12AX, the bottom surface of the groove GR is covered by the first cladding layer 122A, but in the optical waveguide substrate 12BX, the bottom surface of the groove GR is not covered by the first cladding layer 122A. In other words, in the optical waveguide substrate 12AX, the bottom surface of the groove GR is part of the upper surface of the second portion P2 of the first cladding layer 122A, whereas in the optical waveguide substrate 12BX, the bottom surface of the groove GR is part of the upper surface of the substrate 121. 【0180】 Comparing the optical waveguide substrate 12AX and the optical waveguide substrate 12BX, in the optical waveguide substrate 12AX, the bottom surface of the groove GR is covered by the first cladding layer 122A, so the substrate 121 can be protected by the first cladding layer 122A at the bottom surface of the groove GR. Also, in the optical waveguide substrate 12AX, the entire top surface of the substrate 121 is covered by the first cladding layer 122A, so the surface of the flow path for the cleaning liquid can be made a surface with uniform affinity to the cleaning liquid, and the ease of flow of the cleaning liquid can be kept constant. On the other hand, in the optical waveguide substrate 12BX, the bottom surface of the groove GR is not covered by the first cladding layer 122A, so deeper grooves GR can be formed. 【0181】 Figure 31 is a cross-sectional view showing a modified example of the photoelectric fusion apparatus shown in Figures 27 and 28. The photoelectric fusion apparatus 1A2X shown in Figure 31 is the same as the photoelectric fusion apparatus 1AX described above, except for the following: The photoelectric fusion apparatus 1A2X further includes a refractive index adjusting agent layer RIL. The refractive index adjusting agent layer RIL is provided between the end face EF1 of the core 122B of the optical waveguide layer 122 of the optical waveguide substrate 12AX and the end face EF2 of the core 21 of the optical waveguide of the first functional device 20. 【0182】The refractive index adjusting agent layer RIL is made of a material having a refractive index approximately equal to that of the high refractive index material used in core 122B and core 21. For example, the refractive index adjusting agent layer RIL is made of a cured resin having a refractive index approximately equal to that of the high refractive index material used in core 122B and core 21. By providing the refractive index adjusting agent layer RIL, the loss of optical signals can be reduced. 【0183】 The refractive index adjusting agent layer RIL can be formed, for example, by the following procedure. The refractive index adjusting agent liquid is dropped from above the photoelectric fusion apparatus 1A2X into the narrow gap between the first functional device 20 and the substrate 12AX with optical waveguides, filling this gap with the refractive index adjusting agent liquid. This refractive index adjusting agent liquid is then cured, and any uncured portions are removed by washing. This allows the refractive index adjusting agent layer RIL to be formed as shown in Figure 31. Alternatively, the refractive index adjusting agent liquid may be injected into the groove GR from the side of the photoelectric fusion apparatus 1A2X and ejected from below to above the narrow gap between the first functional device 20 and the substrate 12AX with optical waveguides, filling this gap with the refractive index adjusting agent liquid. 【0184】 In the photoelectric fusion apparatus 1A2X, the surface of the optical waveguide substrate 12AX on which the optical waveguide layer 122 is provided has grooves GR. Thanks to these grooves GR, whether the refractive index adjusting agent liquid is dropped into the narrow gap between the first functional device 20 and the optical waveguide substrate 12AX from above the photoelectric fusion apparatus 1A2X and applied to this gap, or whether the refractive index adjusting agent liquid is applied to this narrow gap from the side of the photoelectric fusion apparatus 1A2X via the grooves GR, the refractive index adjusting agent liquid flows easily and is easy to apply to the narrow gap. 【0185】 Figure 32 is a top view of a photoelectric fusion apparatus with a connector, including the photoelectric fusion apparatus shown in Figures 27 and 28. The photoelectric fusion apparatus with a connector 1ACX shown in Figure 32 is the same as the photoelectric fusion apparatus 1AX described above, except for the following: The photoelectric fusion apparatus with a connector 1ACX further includes a connector 15. The composite substrate 10AX and the connector 15 constitute the composite substrate 10ACX with a connector. The connector 15 is configured to allow the optical wiring 40 to be detachably connected, facilitating optical coupling between the optical wiring 40 and the core 122B. 【0186】Figure 33 is a cross-sectional view showing a modified example of the photoelectric fusion apparatus shown in Figures 27 and 28. The photoelectric fusion apparatus 1A3X shown in Figure 33 is the same as the photoelectric fusion apparatus 1AX described above, except for the following point. That is, in the photoelectric fusion apparatus 1A3X, the adhesive layer 13 of the composite substrate 10AX is the stress relaxation layer described with reference to Figure 8. 【0187】 <6> Figure 34 of the sixth embodiment is a top view of a composite substrate according to the sixth embodiment of the present invention. 【0188】 The composite substrate 10CX shown in Figure 34 is the same as the composite substrate 10AX described above, except for the following point. That is, the composite substrate 10CX includes a wiring board 11B, which was described with reference to Figure 17, instead of a wiring board 11A. Furthermore, four optical waveguide substrates 12AX are arranged in each of the four second regions R2. 【0189】 Figure 35 is a top view of a photoelectric fusion apparatus with connectors, including the composite substrate shown in Figure 34. The photoelectric fusion apparatus with connectors 1CCX shown in Figure 35 is the same as the photoelectric fusion apparatus with connectors 1ACX, except for the following: The photoelectric fusion apparatus with connectors 1CCX includes a composite substrate 10CX instead of the composite substrate 10AX. Four first functional devices 20 are mounted on the composite substrate 10CX. Each of these first functional devices 20 is electrically connected to a second functional device 30 via a wiring board 11B. Four connectors 15 are also attached to the composite substrate 10CX. The composite substrate 10CX and the connectors 15 constitute the composite substrate with connectors 10CCX. 【0190】 In the sixth embodiment, the same effects as in the fifth embodiment can be obtained. Also, as shown in the sixth embodiment, the number of first functional devices included in the photoelectric fusion device may be two or more. 【0191】 <7> Figure 36 of the seventh embodiment is a top view of a composite substrate according to the seventh embodiment of the present invention. Figure 37 is a cross-sectional view of the composite substrate shown in Figure 36 along the line XXXVII-XXXVII. 【0192】The composite substrate 10DX shown in Figures 36 and 37 is the same as the composite substrate 10AX, except for the following: The composite substrate 10DX includes the wiring substrate 11C and the optical waveguide substrate 12CX, as described with reference to Figures 19 and 20, instead of the wiring substrate 11A and the optical waveguide substrate 12AX. 【0193】 The optical waveguide substrate 12CX is the same as the optical waveguide substrate 12AX, except for the following: In the optical waveguide substrate 12CX, the first cladding layer 122A has two smaller second portions P2. The thicker first portion P1 of the first cladding layer 122A is interposed between the two second portions P2. The second cladding layer 122C covers the first portion P1 of the first cladding layer 122A without covering the second portion P2 of the first cladding layer 122A. Each of the cores 122B is interposed between the first portion P1 of the first cladding layer 122A and the second cladding layer 122C and extends in the direction of the arrangement of the second portions P2. The optical waveguide substrate 12CX is positioned in the second region R2 such that the longitudinal direction of the core 122B coincides with the alignment direction of the regions on which the two second functional devices 30 are to be mounted. 【0194】 Figure 38 is a top view of the photoelectric fusion apparatus including the composite substrate shown in Figures 36 and 37. Figure 39 is a cross-sectional view of the photoelectric fusion apparatus shown in Figure 38 along the line XXXIX-XXXIX. 【0195】 The photoelectric fusion apparatus 1DX shown in Figures 38 and 39 is the same as the photoelectric fusion apparatus 1AX, except for the following: the photoelectric fusion apparatus 1DX includes a composite substrate 10DX instead of composite substrate 10AX. Also, in the photoelectric fusion apparatus 1DX, the number of first functional devices 20 is 2, and the number of second functional devices 30 is also 2. 【0196】In the seventh embodiment, the same effects as in the fifth embodiment can be obtained. Also, as shown in the seventh embodiment, the number of first functional devices included in the photoelectric fusion device may be two or more, and the number of second functional devices included in the photoelectric fusion device may also be two or more. Furthermore, as shown in the seventh embodiment, instead of optically coupling the optical waveguide layer 122 to the first functional device and the optical wiring, it may optically couple to a plurality of first functional devices. 【0197】 <8> Eighth Embodiment <8.1> Composite Substrate Figure 40 is a top view of a composite substrate according to the eighth embodiment of the present invention. The composite substrate 10AY shown in Figure 40 is the same as the composite substrate 10A described with reference to Figures 1 and 2, except that it includes a wiring substrate 11AY instead of a wiring substrate 11A. Furthermore, the wiring substrate 11AY is the same as the wiring substrate 11A, except for the following points. 【0198】 Specifically, in the wiring board 11AY, the first surface S1 has a rectangular recess. Here, the rectangular recess extends from the contour of the first surface S1. The rectangular recess divides the first surface S1 into a first region R1 located outside the rectangular recess and a second region R2, which is the bottom surface of the rectangular recess. As shown in Figure 40, the opening of the rectangular recess has rounded corners at both ends of the short side that separates the first region R1 and the second region R2. Here, the corners located away from the contour of the first surface S1 are rounded. Details of the corners will be described later. 【0199】 <8.2> Photoelectric Fusion Device Figure 41 is a top view of the photoelectric fusion device including the composite substrate shown in Figures 40 and 41. 【0200】 The photoelectric fusion apparatus 1AY shown in Figure 41 is the same as the photoelectric fusion apparatus 1A described with reference to Figures 5 and 6, except that it includes the composite substrate 10AY instead of the composite substrate 10A. 【0201】<8.3> Method for Manufacturing the Photoelectric Fusion Apparatus The above-described photoelectric fusion apparatus 1AY can be manufactured, for example, by the following method. <8.3.1> Method for Manufacturing the Wiring Substrate The wiring substrate 11AY is manufactured, for example, by the same method as described above for the wiring substrate 11A, except for the following point. That is, a rectangular recess is formed as a recess corresponding to the second region R2, in which each of the corners located away from the contour of the wiring substrate 11AY is rounded. 【0202】 <8.3.2> Method for Manufacturing a Composite Substrate The composite substrate 10AY is manufactured in the same manner as described above for the composite substrate 10A, except that, for example, the wiring board 11AY is used instead of the wiring board 11A. 【0203】 <8.3.3> Method for Manufacturing a Photoelectric Fusion Device The photoelectric fusion device 1AY is manufactured in the same manner as described above for the photoelectric fusion device 1A, except that, for example, the composite substrate 10AY is used instead of the composite substrate 10A. 【0204】 <8.4> The corner section diagram 42 is an enlarged view of the composite substrate 10AY shown in Figure 40. In Figure 42, the contour of the rectangular recess consists of a first long side LS1 and a second long side LS2 that are parallel to each other, a short side SS perpendicular to the first long side LS1, and two corner sections CP, each of which one end of the first long side LS1 and the second long side LS2 is connected to the short side SS. Circle C is centered at point O, with radius R being the value of the radius of curvature of the corner section CP, and is tangent to the corner section CP. Distance D indicates the shortest distance from the corner section CP to the substrate 12A with the optical waveguide. 【0205】 The radius of curvature R is preferably in the range of 200 μm to 2000 μm, and more preferably in the range of 400 μm to 1500 μm. If the radius of curvature R is too small, cracks are likely to occur in the wiring board 11AY, and the substrate 12A with optical waveguides is likely to deform. If the radius of curvature R is too large, it is difficult to increase the ratio of the area of ​​the substrate 12A with optical waveguides to the area of ​​the second region R2 when trying to keep the ratio R / D, described later, within the range below. 【0206】The shortest distance D is preferably within the range of 250 μm to 1700 μm, and more preferably within the range of 450 μm to 1400 μm. 【0207】 The ratio R / D of the radius of curvature R to the shortest distance D is preferably in the range of 0.8 to 1.2, more preferably in the range of 0.9 to 1.1, and even more preferably 1. When the ratio R / D is within the above range, the distance between the contour of the opening of the rectangular recess and the contour of the substrate 12A with the optical waveguide can be kept almost constant, so that the light propagation loss described later is particularly unlikely to occur. 【0208】 <8.4> Effects In the eighth embodiment, the same effects as in the first embodiment can be obtained. 【0209】 Furthermore, in the aforementioned wiring board 11AY, the corners CP of the rectangular recess are rounded, making it less prone to cracking at the corners CP compared to the wiring board 11AY in which the corners CP are not rounded. 【0210】 In Figure 42, when the corner CP is not rounded, for example, when the corner CP is right-angled, the distance between the contour of the rectangular recess opening and the contour of the optical waveguide substrate 12A is larger near the vertex of the corner CP compared to other parts of the rectangular recess contour. Therefore, when the corner CP is right-angled, a larger amount of adhesive is applied to the corner compared to when the corner is rounded. Consequently, when the adhesive shrinks during its curing process, a larger amount of adhesive moves from the corner CP toward the corner of the optical waveguide substrate 12 compared to the latter case. In this case, deformation occurs in the optical waveguide substrate 12, which can result in loss of light propagation. On the other hand, in the wiring board 11AY described above, the corner CP is rounded, making the above-mentioned deformation less likely to occur. 【0211】<8.5> Modified Examples The composite substrate 10AY described above can be modified in various ways. Figure 43 is a cross-sectional view showing one modified example of the composite substrate 10AY. The composite substrate 10A1Y according to this modified example is the same as the composite substrate 10AY except for the following points. That is, the composite substrate 10A1Y includes a wiring board 11A1 instead of a wiring board 11AY, and includes a substrate with an optical waveguide 12A1 instead of a substrate with an optical waveguide 12A. The wiring board 11A1 is the same as the wiring board 11AY except that it has a first metal pattern 115. The substrate with an optical waveguide 12A1 is the same as the substrate with an optical waveguide 12A except that it further includes a second metal pattern 123. The first metal pattern 115 and the second metal pattern 123 are joined to each other via a solder layer 16. 【0212】 The first metal pattern 115 is at least partially exposed at the location of the rectangular recess. The first metal pattern 115 is a metal pattern provided for bonding with the second metal pattern 123. Therefore, the first metal pattern 115 is not electrically connected to the conductor pattern 113 of the wiring board 11A1. 【0213】 The second metal pattern 123 faces the optical waveguide layer 122 with the substrate 121 in between. The second metal pattern 123 is a metal pattern provided for bonding with the first metal pattern 115. 【0214】 The composite substrate 10A1Y is manufactured, for example, by the following method. 【0215】 First, the wiring substrate 11A1 is prepared in the same manner as the manufacturing method of the wiring substrate 11AY described above, except that the first metal pattern 115 is formed so as to be at least partially exposed on the second region R2. The first metal pattern 115 can be formed, for example, by plating. 【0216】 Next, the optical waveguide substrate 12A1 is prepared in the same manner as the manufacturing method for the optical waveguide substrate 12A described above, except that the second metal pattern 123 is formed so as to be at least partially exposed on the surface of the substrate 121. The second metal pattern 123 can be formed, for example, by plating. 【0217】 Next, a solder layer 16 is formed on the first metal pattern 115. Then, the first metal pattern 115 and the second metal pattern 123 are joined together via the solder layer 16. In this way, the substrate 12A1 with an optical waveguide is placed on the wiring board 11A1. 【0218】 Next, adhesive is supplied between the wiring board 11A1 and the optical waveguide board 12A1 and allowed to cure. The manufacturing method of the composite substrate 10A1Y has now been described. 【0219】 In Figure 43, the number of each of the first metal pattern 115 and the second metal pattern 123 was 2, but this number may be 1 or 3 or more. 【0220】 Figure 44 is a cross-sectional view showing another modified example of the composite substrate 10AY. The composite substrate 10A2Y according to this modified example is the same as the composite substrate 10AY except for the following: That is, the composite substrate 10A2Y includes a wiring substrate 11A2 instead of a wiring substrate 11AY, and includes a substrate with an optical waveguide 12A2 instead of a substrate with an optical waveguide 12A. The wiring substrate 11A2 is the same as the wiring substrate 11AY except that it has a first magnetic layer 116. The substrate with an optical waveguide 12A2 is the same as the substrate with an optical waveguide 12A except that it further includes a second magnetic layer 124. In addition, the first magnetic layer 116 and the second magnetic layer 124 are coupled to each other by magnetic force. 【0221】 The first magnetic layer 116 is at least partially exposed at the bottom of the rectangular recess. The second magnetic layer 124 faces the optical waveguide layer 122 with the substrate 121 in between. The combination of the first magnetic layer 116 and the second magnetic layer 124 is, for example, a combination of two magnets, or a combination of a magnet and a ferromagnetic material. 【0222】The composite substrate 10A2Y can be manufactured by the same method as the composite substrate 10A1Y, except that, for example, a first magnetic layer 116 and a second magnetic layer 124 are provided instead of the first metal pattern 115 and the second metal pattern 123, the solder layer 16 is omitted, and the first magnetic layer 116 and the second magnetic layer 124 are coupled to each other by magnetic force. 【0223】 The configurations shown in Figures 43 and 44 make it possible to improve the positional accuracy of the substrate with the optical waveguide relative to the wiring board. In this case, for example, it is possible to easily achieve the aforementioned ratio R / D range. 【0224】 In Figure 44, the number of the first magnetic layer 116 and the second magnetic layer 124 were both 2, but this number may be 1 or 3 or more. 【0225】 Furthermore, the above-mentioned photoelectric fusion device 1AY can be modified in various ways. 【0226】 Figure 45 is a top view of a photoelectric fusion apparatus with a connector, including the photoelectric fusion apparatus shown in Figure 41. The photoelectric fusion apparatus with a connector 1ACY shown in Figure 45 is the same as the photoelectric fusion apparatus 1AY described above, except for the following: The photoelectric fusion apparatus with a connector 1ACY further includes a connector 15. The composite substrate 10AY and the connector 15 constitute the composite substrate 10ACY with a connector. The connector 15 is configured to allow the optical wiring 40 to be detachably connected, facilitating optical coupling between the optical wiring 40 and the core 122B. 【0227】 Figure 46 is a cross-sectional view showing a modified example of the photoelectric fusion apparatus shown in Figure 41. The photoelectric fusion apparatus 1A2 shown in Figure 46 is the same as the photoelectric fusion apparatus 1AY described above, except for the following point. That is, in the photoelectric fusion apparatus 1A2, the adhesive layer 13 of the composite substrate 10AY is the stress relaxation layer described above for the photoelectric fusion apparatus 1A2. 【0228】 <9> Ninth Embodiment <9.1> Composite Substrate Figure 47 is a top view of a composite substrate according to the ninth embodiment of the present invention. 【0229】The composite substrate 10BY shown in Figure 47 is the same as the composite substrate 10AY described above, except that it includes a substrate 12B with an optical waveguide instead of a substrate 12A with an optical waveguide. 【0230】 <9.2> Photoelectric Fusion Device Figure 48 is a top view of the photoelectric fusion device including the composite substrate shown in Figures 47 and 52. 【0231】 The photoelectric fusion apparatus 1BY shown in Figure 48 is the same as the photoelectric fusion apparatus 1AY described above, except that it includes a composite substrate 10BY instead of composite substrate 10AY, and includes a first functional device 20B instead of first functional device 20A. 【0232】 In the photoelectric fusion apparatus 1BY, the first functional device 20B is mounted on the composite substrate 10BY such that the region of the core 21 located on the main surface of the first functional device 20B is in contact with the upper surface of the core 122B. In other words, in the photoelectric fusion apparatus 1BY, the optical waveguide of the first functional device 20B is optically coupled to the optical waveguide layer 122 by adiaptic coupling. 【0233】 <9.3> Effects In the ninth embodiment, the same effects as in the eighth embodiment can be obtained. Also, as shown in the eighth and ninth embodiments, the optical waveguide of the first functional device and the optical waveguide layer 122 and optical coupling may be performed by any method. 【0234】 <9.4> Modifications The above photoelectric fusion device 1BY can be modified in various ways. 【0235】 Figure 49 is a top view of a photoelectric fusion apparatus with a connector, including the photoelectric fusion apparatus shown in Figure 48. The photoelectric fusion apparatus with a connector 1BCY shown in Figure 49 is the same as the photoelectric fusion apparatus 1BY described above, except for the following: The photoelectric fusion apparatus with a connector 1BCY further includes a connector 15 connected to the optical waveguide substrate 12B. The composite substrate 10BY and the connector 15 constitute the composite substrate 10BCY with a connector. The connector 15 is the same as that described above for the photoelectric fusion apparatus with a connector 1AC. 【0236】 <10> Figure 50 of the 10th embodiment is a top view of a composite substrate according to the 10th embodiment of the present invention. 【0237】 The composite substrate 10CY shown in Figure 50 is the same as the composite substrate 10AY described above, except for the following: The composite substrate 10CY includes a wiring board 11BY instead of a wiring board 11AY. The wiring board 11BY is the same as the wiring board 11AY described above, except for the following: The first surface S1 has four second regions R2. These second regions R2 are arranged so as to be adjacent to each of the four edges of the first surface S1. And, four optical waveguide substrates 12A are arranged in each of these four second regions R2. 【0238】 Figure 51 is a top view of a photoelectric fusion apparatus with connectors, including the composite substrate shown in Figure 50. The photoelectric fusion apparatus with connectors 1CCY shown in Figure 51 is the same as the photoelectric fusion apparatus with connectors 1AC, except for the following: The photoelectric fusion apparatus with connectors 1CCY includes a composite substrate 10CY instead of a composite substrate 10AY. Four first functional devices 20A are mounted on the composite substrate 10CY. Each of these first functional devices 20A is electrically connected to a second functional device 30 via a wiring board 11BY. Four connectors 15 are also attached to the composite substrate 10CY. The composite substrate 10CY and the connectors 15 constitute the composite substrate 10CCY with connectors. 【0239】 In the tenth embodiment, the same effects as in the eighth embodiment can be obtained. Also, as shown in the tenth embodiment, the number of first functional devices included in the photoelectric fusion device may be two or more. 【0240】 <11> Figure 52 of the 11th embodiment is a top view of a composite substrate according to the 11th embodiment of the present invention. 【0241】 The composite substrate 10DY shown in Figure 52 is the same as the composite substrate 10AY, except for the following: The composite substrate 10DY includes a wiring substrate 11CY and a substrate 12C with an optical waveguide instead of a wiring substrate 11AY and a substrate 12A with an optical waveguide. 【0242】The wiring board 11CY is the same as the wiring board 11AY, except for the following: The wiring board 11CY is configured to mount two first functional devices 20A and two second functional devices 30. The second region R2 is provided between the region on which one second functional device 30 is to be mounted and the region on which the other second functional device 30 is to be mounted. 【0243】 The optical waveguide substrate 12C is positioned in the second region R2 such that the longitudinal direction of the core 122B coincides with the alignment direction of the regions on which the two second functional devices 30 are to be mounted. 【0244】 Figure 53 is a top view of the photoelectric fusion apparatus including the composite substrate shown in Figure 52. 【0245】 The photoelectric fusion apparatus 1DY shown in Figure 53 is the same as the photoelectric fusion apparatus 1AY, except for the following: the photoelectric fusion apparatus 1DY includes a composite substrate 10DY instead of composite substrate 10AY. Also, in the photoelectric fusion apparatus 1DY, the number of first functional devices 20A is 2, and the number of second functional devices 30 is also 2. 【0246】 In the 11th embodiment, the same effects as in the 8th embodiment can be obtained. Also, as shown in the 11th embodiment, the number of first functional devices included in the photoelectric fusion device may be two or more, and the number of second functional devices included in the photoelectric fusion device may also be two or more. Also, as shown in the 11th embodiment, the optical waveguide layer 122 may be optically coupled to a plurality of first functional devices instead of optically coupling to the first functional device and the optical wiring. 【0247】 <12> Modifications Various modifications are possible for the composite substrate and photoelectric fusion device described above. For example, in the composite substrate 10C, composite substrate 10D, photoelectric fusion device 1D, and photoelectric fusion device 1CC with connector, instead of adopting a configuration in which the optical coupling between the optical waveguide of the first functional device 20A and the optical waveguide layer 122 is performed by butt coupling, a configuration in which this optical coupling is performed by adiabatic coupling may be adopted. Also, in the composite substrate 10C, composite substrate 10D, photoelectric fusion device 1D, and photoelectric fusion device 1CC with connector, the adhesive layer 13 may be used as a stress relaxation layer. 【0248】In the photoelectric fusion apparatus 1A2X (Figure 31), the photoelectric fusion apparatus 1ACX with connector (Figure 32), the photoelectric fusion apparatus 1A3X (Figure 33), the composite substrate 10CX (Figure 34), the photoelectric fusion apparatus 1CCX with connector (Figure 35), the composite substrate 10DX (Figures 36 and 37), and the photoelectric fusion apparatus 1DX (Figures 38 and 39), the groove GR configuration shown in Figure 30, that is, the groove GR configuration in which the bottom surface is not covered by the first cladding layer 122A, may be adopted. 【0249】 A refractive index adjusting layer RIL may be provided in the photoelectric fusion apparatus 1ACX with connector (Figure 32), the photoelectric fusion apparatus 1A3X (Figure 33), the composite substrate 10CX (Figure 34), the photoelectric fusion apparatus 1CCX with connector (Figure 35), the composite substrate 10DX (Figures 36 and 37), and the photoelectric fusion apparatus 1DX (Figures 38 and 39). 【0250】 In the photoelectric fusion apparatus 1ACX with connector (Figure 32), composite substrate 10CX (Figure 34), photoelectric fusion apparatus 1CCX with connector (Figure 35), composite substrate 10DX (Figures 36 and 37), and photoelectric fusion apparatus 1DX (Figures 38 and 39), the adhesive layer 13 may be used as a stress relaxation layer. 【0251】 In the composite substrates 10CY and 10DY, the photoelectric fusion device 1DY, and the photoelectric fusion device 1CCY with connector, instead of employing a configuration in which the optical coupling between the optical waveguide of the first functional device 20A and the optical waveguide layer 122 is performed by butt coupling, a configuration in which this optical coupling is performed by adiabatic coupling may be adopted. Furthermore, in the composite substrates 10CY, 10DY, the photoelectric fusion device 1DY, and the photoelectric fusion device 1CCY with connector, the adhesive layer 13 may be used as a stress relaxation layer. 【0252】 In the composite substrates 10BY, 10CY, and 10DY, the photoelectric fusion device 1DY, and the photoelectric fusion device with connector 1CCY, the wiring substrate and the substrate with optical waveguides may be fixed to each other via a solder layer, as shown in Figure 43. 【0253】 In the composite substrates 10BY, 10CY, and 10DY, the photoelectric fusion device 1DY, and the photoelectric fusion device with connector 1CCY, the wiring substrate and the substrate with optical waveguides may be fixed to each other via magnetic force, as shown in Figure 44. 【0254】1A...Photoelectric Fusion Device, 1A2...Photoelectric Fusion Device, 1A2X...Photoelectric Fusion Device, 1A3X...Photoelectric Fusion Device, 1AC...Photoelectric Fusion Device with Connector, 1ACX...Photoelectric Fusion Device with Connector, 1ACY...Photoelectric Fusion Device with Connector, 1AX...Photoelectric Fusion Device, 1AY...Photoelectric Fusion Device, 1B...Photoelectric Fusion Device, 1B2...Photoelectric Fusion Device, 1BC...Photoelectric Fusion Device with Connector, 1BCY...Photoelectric Fusion Device with Connector, 1BY...Photoelectric Fusion Device, 1CC...Photoelectric Fusion Device with Connector, 1CCX...Photoelectric Fusion Device with Connector, 1CCY...Photoelectric Fusion Device with Connector, 1D...Photoelectric Fusion Device , 1DX...Photoelectric fusion device, 1DY...Photoelectric fusion device, 10A...Composite substrate, 10A1Y...Composite substrate, 10A2Y...Composite substrate, 10AC...Composite substrate with connector, 10ACX...Composite substrate with connector, 10ACY...Composite substrate with connector, 10AX...Composite substrate, 10AY...Composite substrate, 10B...Composite substrate, 10BC...Composite substrate with connector, 10BCY...Composite substrate with connector, 10BY...Composite substrate, 10C...Composite substrate, 10CC...Composite substrate with connector, 10CCY...Composite substrate with connector, 10CX...Composite substrate, 10CY...Composite substrate, 10D...Composite substrate, 10 DX...Composite substrate, 10DY...Composite substrate, 11A...Wiring board, 11A1...Wiring board, 11A2...Wiring board, 11AY...Wiring board, 11B...Wiring board, 11BY...Wiring board, 11C...Wiring board, 11CY...Wiring board, 12A...Substrate with optical waveguide, 12A1...Substrate with optical waveguide, 12A2...Substrate with optical waveguide, 12AX...Substrate with optical waveguide, 12B...Substrate with optical waveguide, 12BX...Substrate with optical waveguide, 12C...Substrate with optical waveguide, 12CX...Substrate with optical waveguide, 13...Adhesive layer, 14...Conductor for bonding, 15...Connector, 16...Solder layer, 20A...First functional device , 20B...First functional device, 21...Core, 30...Second functional device, 40...Optical wiring, 111...Core insulating layer, 112...Insulating layer, 113...Conductor pattern, 114...Insulating layer, 115...First metal pattern, 116...First magnetic layer, 121...Substrate, 122...Optical waveguide layer, 122A...First cladding layer, 122B...Core, 122C...Second cladding layer, 123...Second metal pattern, 124...Second magnetic layer, C...Circle, CP...Corner, D...Distance, LS1...First long side, LS2...Second long side, O...Point, R...Radius of curvature, R1...First region, R2...Second region, S1...First surface, S2...Second surface,SS... Short side.

Claims

1. A wiring board comprising one or more insulating layers and one or more conductor patterns, having a first surface and a second surface which is its back surface, wherein the first surface comprises one or more first regions and one or more second regions which are recessed from the one or more first regions, one of the one or more conductor patterns is located in the one or more first regions, and the height of the one or more second regions is lower than the lower surface of the conductor pattern located in the one or more first regions; and one or more optical waveguide substrates comprising a substrate and an optical waveguide layer provided thereon, each of which comprises a first cladding layer provided on the substrate, a second cladding layer provided on the first cladding layer, and one or more cores provided between the first cladding layer and the second cladding layer, wherein the optical waveguide layers are each installed on the one or more second regions such that they are located above the substrate, and the height of the lower surface of the one or more cores is higher than the one or more first regions; and one or more optical waveguide substrates.

2. The composite substrate according to claim 1, wherein the height of the upper surface of the substrate is lower than the height of the one or more first regions.

3. The composite substrate according to claim 1, wherein the lower surface of the one or more cores has a height of 100 μm or less relative to the one or more first regions.

4. The composite substrate according to claim 1, further comprising one or more stress-relaxing layers interposed between the one or more optical waveguide substrates and the one or more second regions.

5. The composite substrate according to claim 4, wherein each of the one or more stress relaxation layers has an elastic modulus in the range of 0.1 MPa to 3 GPa.

6. The composite substrate according to claim 4, wherein each of the one or more stress relaxation layers has a thickness in the range of 5 μm or more and 50 μm or less.

7. The composite substrate according to claim 1, wherein the one or more insulating layers include an insulating resin layer, and the substrate includes a glass substrate.

8. The composite substrate according to claim 1, which is an interposer.

9. The composite substrate according to claim 1, wherein at least one of the one or more substrates with optical waveguides has a surface on which the optical waveguide layer is provided, comprising a third region on which the second cladding layer is provided and a fourth region on which the second cladding layer is not provided, the fourth region having a groove extending along the boundary between the third region and the fourth region, and the one or more cores having end faces adjacent to the space above the groove.

10. The composite substrate according to claim 9, wherein the depth of the groove is in the range of 20 μm or more and 50 μm or less.

11. The composite substrate according to claim 9, wherein the width of the groove is within the range of 20 μm or more and 200 μm or less.

12. The composite substrate according to claim 9, wherein the upper surface of the substrate is recessed at the position of the groove, corresponding to the groove.

13. The composite substrate according to claim 9, wherein in at least one of the one or more substrates with optical waveguides, the first cladding layer includes a first portion provided at the location of the third region and a second portion provided at the location of the fourth region.

14. The composite substrate according to claim 13, wherein the bottom surface of the groove is part of the upper surface of the second portion.

15. The composite substrate according to claim 13, wherein the bottom surface of the groove is part of the upper surface of the substrate.

16. The composite substrate according to any one of claims 1 to 15, wherein the first surface has one or more rectangular recesses, the one or more rectangular recesses divide the first surface into a first region located outside the one or more rectangular recesses and one or more second regions which are the bottom surfaces of the one or more rectangular recesses, and the openings of each of the one or more rectangular recesses have rounded corners at both ends of the short side separating the first region and the second region, and the composite substrate further comprises one or more adhesive layers interposed between the one or more optical waveguide substrates and the inner surfaces of the one or more rectangular recesses.

17. The composite substrate according to claim 16, wherein the radius of curvature R of each of the corners is within the range of 200 μm or more and 2000 μm or less.

18. The composite substrate according to claim 17, wherein in each of the one or more rectangular recesses, the ratio R / D of the radius of curvature R to the shortest distance D from each of the corners to the substrate with the optical waveguide is in the range of 0.8 or more and 1.2 or less.

19. The composite substrate according to claim 16, wherein the rectangular recess extends from the position of the contour of the first surface.

20. The composite substrate according to claim 16, wherein the wiring board has a first metal pattern at least partially exposed at the bottom surface of the one or more rectangular recesses, the one or more substrates with optical waveguides further include a second metal pattern facing the optical waveguide layer with the substrate in between, and the first metal pattern and the second metal pattern are joined to each other via a solder layer.

21. The composite substrate according to claim 16, wherein the wiring board has a first magnetic layer at least partially exposed at the bottom surface of the one or more rectangular recesses, the one or more substrates with optical waveguides further include a second magnetic layer facing the optical waveguide layer with the substrate in between, and the first magnetic layer and the second magnetic layer are coupled to each other by magnetic force.

22. The composite substrate according to claim 16, wherein each of the one or more adhesive layers has an elastic modulus in the range of 0.1 MPa to 3 GPa.

23. The composite substrate according to claim 22, wherein each of the one or more adhesive layers has a thickness in the range of 5 μm or more and 50 μm or less.

24. A photoelectric fusion apparatus comprising: a composite substrate according to any one of claims 1 to 15; a first functional device mounted on the composite substrate and optically coupled to at least one of the one or more optical waveguide substrates; and a second functional device mounted on the composite substrate and electrically connected to the first functional device.

25. The photoelectric fusion apparatus according to claim 24, further comprising a refractive index adjusting layer having a portion interposed between the first functional device and at least one of the one or more optical waveguide substrates.

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