Optical waveguide and wiring board

Abstract

To provide an optical waveguide capable of being optically coupled with an optical component with good coupling efficiency, and a wiring board.SOLUTION: A lower clad 21, a core 3 and an upper clad 22 are stacked on an optical waveguide 1 in this order, and part of the core 3 on which an optical signal enters and from which the optical signal is emitted is exposed. The optical waveguide 1 includes an upper clad non-formation area 1a and an upper clad formation area 1b. The upper clad non-formation area 1a includes core exposed parts 3aa, 3ab on which top face of the core 3 is exposed at one end 3α and an other end 3β of the core 3. The upper clad formation area 1b includes a core non-exposed part 3b on which the top face of the core 3 is not exposed. The core 3 has width W11 on the core exposed part 3aa positioned at the one end 3α, width W12 on the core exposed part 3ab positioned at the other end 3β, width W21 on a core non-exposed part 3b1 at the one end 3α side, and width W22 on the core non-exposed part 3b2 at the other end 3β side. The widths W11-W22 of the core 3 satisfy the relations of W11>W21 and W12>W22.SELECTED DRAWING: Figure 2C

Description

[Technical field]

[0001] The present invention relates to an optical waveguide and a wiring board. [Background technology]

[0002] Patent Document 1 discloses a polymer waveguide array formed on a polymer film and a silicon waveguide array formed on a silicon chip. The cores of the polymer waveguide and the silicon waveguide are arranged to overlap over a predetermined distance in the optical axis direction and are optically coupled by adiabatic coupling. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-81586 A Summary of the Invention [Problem to be solved by the invention]

[0004] The one disclosed in Patent Document 1 is a combination in which a silicon chip on which a polymer waveguide and a silicon waveguide are formed is placed face down and adiabatically combined. In the polymer waveguide, at the optically combined portion with the silicon waveguide, the width of the core of the polymer waveguide is not large enough relative to the width of the core of the silicon waveguide, and therefore the tolerance range for the alignment of the polymer waveguide and the silicon waveguide may be narrow. Therefore, the polymer waveguide and the silicon waveguide may not be optically combined with sufficient coupling efficiency. In the combination of the polymer waveguide and the silicon waveguide, it is considered that the core of the polymer waveguide and the core of the silicon waveguide may be misaligned due to the thermal history during use, resulting in poor coupling. [Means for solving the problem]

[0005] The optical waveguide of the present invention is an optical waveguide in which a lower clad, a core, and an upper clad are laminated in this order, and a part of the core on the side where an optical signal is input and a part of the core on the side where an optical signal is output are exposed. The optical waveguide is composed of an upper clad non-forming region and an upper clad forming region, the upper clad non-forming region has a core exposed portion at one end and the other end of the core where the upper surface of the core is exposed, the upper clad forming region has a core non-exposed portion where the upper surface of the core is not exposed, the core of the core exposed portion located at the one end has a width (W11), the core of the core exposed portion located at the other end has a width (W12), the core of the core non-exposed portion at the one end has a width (W21), the core of the core non-exposed portion at the other end has a width (W22), and the core width (W11), the core width (W12), the core width (W21), and the core width (W22) satisfy the relationships of the following formulas 1 and 2. W11>W21 (Formula 1) W12>W22...(Formula 2)

[0006] The wiring board of the present invention is a wiring board including an insulating layer and a conductor layer, the wiring board including the optical waveguide and a component mounting pad, the optical waveguide being disposed on a surface of the wiring board.

[0007] According to the embodiment of the present invention, it is possible to expand the tolerance of the alignment between the optical waveguide and the optical component that transmits and receives an optical signal to and from the optical waveguide, and therefore it is considered that the optical waveguide and the optical component can be optically coupled with good coupling efficiency. It is also considered that poor coupling due to misalignment between the optical waveguide and the optical component is suppressed even with the thermal history during use. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a plan view showing an example of an optical waveguide according to an embodiment of the present invention. [Figure 2A] FIG. 2 is a cross-sectional view of the example optical waveguide of FIG. 1 taken along line IIA-IIA. [Figure 2B] FIG. 2 is a cross-sectional view of the example optical waveguide of FIG. 1 taken along line IIB-IIB. [Figure 2C]2 is a plan view showing the width of each portion of a core in the optical waveguide of the example of FIG. 1; [Figure 2D] FIG. 11 is a plan view showing a first modified example of a connection portion of a core in the optical waveguide according to the embodiment. [Figure 2E] FIG. 11 is a plan view showing a second modified example of the connection portion of the cores in the optical waveguide according to the embodiment. [Diagram 3] FIG. 4 is a cross-sectional view showing another example of the clad of the optical waveguide according to the embodiment. [Figure 4] FIG. 4 is a plan view showing a first modified example of the optical waveguide according to the embodiment. [Diagram 5] FIG. 11 is a plan view showing a second modified example of the optical waveguide according to the embodiment. [Figure 6A] FIG. 4 is a plan view showing a first modified example of the optical waveguide according to the embodiment. [Figure 6B] FIG. 11 is a plan view showing a second modified example of the optical waveguide according to the embodiment. [Figure 7] FIG. 1 is a cross-sectional view showing an example of a wiring board according to an embodiment of the present invention. [Figure 8A] 5A to 5C are front views showing an example of a manufacturing process of the optical waveguide according to the embodiment. [Figure 8B] 5A to 5C are plan views showing an example of a manufacturing process of the optical waveguide according to the embodiment. [Figure 8C] 5A to 5C are front views showing an example of a manufacturing process of the optical waveguide according to the embodiment. [Figure 8D] 5A to 5C are front views showing an example of a manufacturing process of the optical waveguide according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The optical waveguide and the wiring board according to the embodiment of the present invention will be described with reference to the drawings. In each drawing referred to in the following description, a specific portion may be drawn enlarged to facilitate understanding of the disclosed embodiment, and each component may not be drawn at the exact ratio between each other in terms of size or length.

[0010] <Structure of optical waveguide according to embodiment> Fig. 1 shows a plan view of an optical waveguide 1, which is an example of an optical waveguide of an embodiment. Fig. 2A shows a cross section of the optical waveguide 1 of Fig. 1 taken along line IIA-IIA. Fig. 2B shows a cross section of the optical waveguide 1 of Fig. 1 taken along line IIB-IIB. Note that the optical waveguide 1 illustrated in Fig. 1 and other figures is merely an example of the optical waveguide of this embodiment. The structure of the optical waveguide of the embodiment is not limited to the structure shown in each drawing such as Fig. 1.

[0011] 1 and 2A to 2B, the optical waveguide 1 of this embodiment includes a core 3 that transmits an optical signal, and a clad 2 that surrounds the core 3. The clad 2 is composed of a lower clad 21 and an upper clad 22. The core 3 is sandwiched between the lower clad 21 and the upper clad 22. That is, in the optical waveguide 1, the lower clad 21, the upper clad 22, and the core 3 are laminated in the order of the lower clad 21, the core 3, and the upper clad 22.

[0012] The core 3 has an upper surface 31 facing in a direction along the stacking direction of the clad 2 and the core 3, and a lower surface 32 opposite to the upper surface 31. The stacking direction of the clad 2 and the core 3 is also referred to as the "Z direction" (see FIG. 2A) below. The upper surface 31 may be a surface facing either of two directions (+Z and -Z) along the Z direction. In the example of FIG. 2A, the upper surface 31 is a surface facing the +Z direction in the core 3, and the lower surface 32 is a surface facing the -Z direction in the core 3. Hereinafter, in the optical waveguide 1, the lower clad 21 side is also referred to as the "lower side" or simply "lower", and the upper clad 22 side is also referred to as the "upper side" or simply "upper".

[0013] The lower clad 21 is located on the lower surface 32 side of the core 3 and is in contact with the lower surface 32. The upper clad 22 is located on the upper surface 31 side of the core 3 and is in contact with the upper surface 31. The upper clad 22 covers the upper surface 31 of the core 3. The upper clad 22 also covers the upper surface 211 of the lower clad 21 (the surface facing the upper clad 22). As shown in FIG. 2B , in the optical waveguide 1, the upper clad 22 also covers the side surface 35 of the core 3. The side surface 35 is a surface that is along the extending direction of the core 3, among the surfaces connecting the upper surface 31 and the lower surface 32.

[0014] In the optical waveguide 1 of FIG. 1 and FIG. 2A, the core 3 extends along the +X direction and the -X direction. An optical signal propagating through the core 3 propagates in the +X direction or the -X direction. Hereinafter, the propagation direction of the optical signal is also simply referred to as the "X direction" collectively for the +X direction and the -X direction. The optical waveguide 1 of FIG. 1 and the like has two opposing ends (one end 11 and the other end 12). In the example of FIG. 1, the one end 11 and the other end 12 are opposed to each other in the X direction. In the optical waveguide 1, an optical signal is incident on the one end 11 or the other end 12, and the optical signal is emitted from the other end 12 or the one end 11. When an optical signal is incident on the one end 11 side, the optical signal is emitted from the other end 12 side. When an optical signal is incident on the other end 12 side, the optical signal is emitted from the one end 11 side.

[0015] In the optical waveguide 1, a part of the core 3 on the side where an optical signal is incident and a part of the core 3 on the side where an optical signal is output are exposed. In the optical waveguide 1, an optical signal may be input to one end 11, and an optical signal may be output from the one end 11. Similarly, an optical signal may be input to the other end 12, and an optical signal may be output from the other end 12. In the optical waveguide 1, a part of the core 3 is exposed at both the one end 11 and the other end 12. As shown in FIG. 1, FIG. 2A, and FIG. 2B, at the one end 11, the top surface 31 of the core 3, one end surface 33 of the core 3 in the X direction, and a side surface 35 are exposed from the cladding 2. And at the other end 12, as shown in FIG. 1 and FIG. 2A, the other end surface of the core 3 in the X direction, the end surface 34 opposite to the end surface 33, the top surface 31, and the side surface 35 are exposed from the cladding 2.

[0016] As shown in FIG. 1 and FIG. 2A, in the optical waveguide 1, the upper clad 22 covers the upper surface 31 of the core 3 and the upper surface 211 of the lower clad 21. The optical waveguide 1 is composed of an upper clad-free region 1a, which is a region where the upper clad 22 is not formed in a planar view, and an upper clad-formed region 1b, which is a region where the upper clad 22 is formed in a planar view. That is, the optical waveguide 1 is composed of the upper clad-free region 1a and the upper clad-formed region 1b. In the upper clad-free region 1a in a planar view, the upper surface 31 of the core 3 and the upper surface 211 of the lower clad 21 are exposed. In the example of FIG. 1, the side surface 35 of the core 3 is also exposed in the upper clad-free region 1a. Note that "planar view" means that an object is viewed with a line of sight along the Z direction.

[0017] The optical waveguide 1 has upper cladding non-forming regions 1a at both ends in the X direction. That is, the optical waveguide 1 has two upper cladding non-forming regions 1a in a predetermined region on one end 11 side of the optical waveguide 1 and a predetermined region on the other end 12 side of the optical waveguide 1. A first upper cladding non-forming region 1aa is located on one end 11 side of the optical waveguide 1, and a second upper cladding non-forming region 1ab is located on the other end 12 side of the optical waveguide 1. Therefore, in the optical waveguide 1, the respective regions are arranged in the order of the first upper cladding non-forming region 1aa-the upper cladding non-forming region 1b-the second upper cladding non-forming region 1ab from the one end 11 toward the other end 12. The first upper cladding non-forming region 1aa, the upper cladding non-forming region 1b, and the second upper cladding non-forming region 1ab are arranged over the entire length of the optical waveguide 1 in a direction perpendicular to the X direction in a plan view. In the optical waveguide 1, the entire region between the first upper cladding free region 1aa and the second upper cladding free region 1ab is the upper cladding free region 1b.

[0018] In the upper cladding non-forming region 1a of the optical waveguide 1, there are exposed core portions 3a at one end 3α of the core 3 and the other end 3β of the core 3, where the top surface 31 of the core 3 is exposed. In the upper cladding forming region 1b, there is a non-exposed core portion 3b where the top surface 31 of the core 3 is not exposed. Both the one end 3α of the core 3 and the other end 3β of the core 3 are ends where an optical signal is emitted from the core 3 or where an optical signal is incident on the core 3. The one end 3α of the core 3 and the other end 3β of the core 3 are ends on opposite sides of the core 3. When an optical signal is incident on one end 3α, the optical signal is emitted from the other end 3β, and when an optical signal is incident on the other end 3β, the optical signal is emitted from the one end 3α.

[0019] The core exposed portion 3a refers to a portion where the top surface 31 of the core 3 is exposed in the upper cladding non-forming region 1a and where the width (W11, W12 (see FIG. 2C)) of the core 3 is greater than the width (W21, W22 (see FIG. 2C)) of the core 3 in the upper cladding forming region 1b. The end of the core exposed portion 3a refers to the portion where the width of the core 3 is widest from the core 3 in the core non-exposed portion 3b along the core exposed portion 3a. The core exposed portion 3a is overlapped with the light receiving portion or light emitting portion E1a of the component E1 or the light receiving portion or light emitting portion E2a of the component E2 to couple optical signals.

[0020] The "width" of core 3 is the length of core 3 in a direction perpendicular to the propagation direction of the optical signal propagating within core 3 (X direction in FIG. 1) and the lamination direction of optical waveguide 1 (Z direction). The direction along the width of core 3 is also referred to as the +Y direction or -Y direction below. The +Y direction and -Y direction are also collectively referred to simply as the "Y direction". When core 3 is bent along the way, the propagation direction of the optical signal within core 3 is not constant but changes depending on the part (section) of core 3. Therefore, the direction along which core 3 is width may change from one end of core 3 to the other.

[0021] In the optical waveguide 1 of FIG. 1, one end 3α of the core 3 is in the first upper cladding non-forming region 1aa, and the other end 3β of the core 3 is in the second upper cladding non-forming region 1ab. The exposed core portion 3a includes a first exposed core portion 3aa in the first upper cladding non-forming region 1aa and a second exposed core portion 3ab in the second upper cladding non-forming region 1ab. Thus, in the core 3, the non-exposed portion and the two exposed portions are arranged in the order of the first exposed core portion 3aa-non-exposed core portion 3b-second exposed core portion 3ab from the one end 3α toward the other end 3β. The first exposed core portion 3aa is a part of the core 3 on the one end 3α side, and the second exposed core portion 3ab is a part of the core 3 on the other end 3β side. The non-exposed core portion 3b is a part of the core 3 between the two exposed core portions 3a, i.e., the first exposed core portion 3aa and the second exposed core portion 3ab.

[0022] The optical waveguide 1, i.e., the core 3 and the clad 2, are formed of any light-transmitting material. The optical waveguide 1 may be formed of, for example, an organic material (organic matter), an inorganic material (inorganic matter), or a hybrid material including an organic material and an inorganic material such as an inorganic polymer. Examples of inorganic materials include quartz glass and silicon, and examples of organic materials include acrylic resins such as polymethyl methacrylate (PMMA), polyimide resins, polyamide resins, polyether resins, and epoxy resins. An optical waveguide 1 formed of an organic material is likely to be lightweight and have high toughness. In addition, an optical waveguide 1 formed of an organic material is likely to be flexible. Therefore, the optical waveguide 1 formed of an organic matter may increase the degree of freedom of the relative arrangement positions in the Z direction between an optical component optically coupled at one end 11 of the optical waveguide 1 and an optical component optically coupled at the other end 12. In addition, "optically coupled" is also referred to as "optically coupled" hereinafter.

[0023] The core 3 and the clad 2 may be made of different materials or may be made of the same material. However, the core 3 is made of a material having a higher refractive index than the material used for the clad 2 so that the optical signal can be totally reflected at the interface between the core 3 and the clad 2. The core 3 and the clad 2 may be made of materials having the same refractive index, and then subjected to an appropriate process to make their refractive indices different from each other. That is, the optical waveguide 1 may be formed by using a forming method called a photobleaching method, for example. The optical waveguide 1 may be formed on a support that supports the optical waveguide 1 during the manufacturing process, and then may be used by separating it from the support, or may be used together with the support.

[0024] When the optical waveguide 1 is used, the core 3 is optically coupled at one end 11 and the other end 12 of the optical waveguide 1 to optical components such as a photoelectric conversion component, such as a semiconductor device including a photoelectric conversion element, and / or a connector member, such as an optical fiber or an optical connector, that connects the waveguide to the outside. That is, the core 3 is positioned with respect to each optical component so that the core 3 and these optical components have a positional relationship that allows transmission and reception of optical signals between them. In Figures 1 and 2A, components E1 and E2 equipped with a photoelectric conversion element (not shown) are shown by two-dot chain lines as examples of optical components optically coupled to the core 3 at one end 11 and the other end 12.

[0025] The component E1 includes a light receiving section or a light emitting section E1a, which is a portion where an optical signal is incident on the component E1 or a portion where an optical signal is emitted from the component E1. The component E1 is optically coupled to the core 3 at the light receiving section or the light emitting section E1a. The component E2 includes a light receiving section or a light emitting section E2a, which is a portion where an optical signal is incident on the component E2 or a portion where an optical signal is emitted from the component E2, and the component E2 is optically coupled to the core 3 at the light receiving section or the light emitting section E2a. As an example, an optical signal emitted from the light receiving section or the light emitting section E2a of the component E2 functioning as a light emitting section enters the core 3 from the second core exposed section 3ab at the other end 12 and propagates in the core non-exposed section 3b. Then, the optical signal is emitted from the first core exposed section 3aa at one end 11 and enters the component E1 from the light receiving section or the light emitting section E1a of the component E1 functioning as a light receiving section. Conversely, an optical signal emitted from the light receiving portion or light emitting portion E1a of component E1 enters the core 3 from the first core exposed portion 3aa, propagates through the core non-exposed portion 3b, exits from the second core exposed portion 3ab, and enters the component E2 from the light receiving portion or light emitting portion E2a.

[0026] In the example of Fig. 1 and Fig. 2A, the core 3 is positioned such that the upper surface 31 of the core 3 faces the light receiving unit or light emitting unit E1a of the component E1 and the upper surface 31 of the core 3 faces the light receiving unit or light emitting unit E2a of the component E2 at one end 11 and the other end 12 of the optical waveguide 1, and is optically coupled (adiabatic coupled). That is, a part of the optical signal propagating inside the core 3 toward one end 3α or the other end 3β leaks out of the core 3 from the upper surface 31 as evanescent light and enters the light receiving unit or light emitting unit E1a of the component E1 or the light receiving unit or light emitting unit E2a of the component E2. Since the upper surface 31 of the core 3 faces the light receiving unit or light emitting unit E1a of the component E1 and the light receiving unit or light emitting unit E2a of the component E2 without the cladding 2, it is considered that highly efficient optical coupling is realized.

[0027] The optical waveguide 1 illustrated in FIG. 1 and the like has four cores 3 arranged in parallel. The optical waveguide 1 of the embodiment may have any number of cores 3, not limited to four, and one or more. For example, the number of cores 3 is in the range of 2 to 64. When multiple cores 3 are provided, the arrangement pitch P1 of the cores 3 is, for example, 10 μm or more and 300 μm or less, and preferably 20 μm or more and 250 μm or less. Note that the arrangement pitch P1 of the multiple cores 3 is not limited to these numerical examples. In the example of FIG. 1, the arrangement pitch P1 of the multiple cores 3 is constant between one end 3α and the other end 3β of the cores 3. However, the arrangement pitch P1 of the cores 3 may change between the one end 3α and the other end 3β. The arrangement pitch P1 of the cores 3 is the distance between the centers of the cores 3.

[0028] <Connection> In the optical waveguide 1 shown in FIG. 1, the core 3 has a connection portion 3c between the core exposed portion 3a and the core non-exposed portion 3b, connecting the core exposed portion 3a and the core non-exposed portion 3b. The core 3 of the optical waveguide 1 in FIG. 1 has two connection portions 3c. That is, the connection portions 3c are disposed both between the first core exposed portion 3aa and the core non-exposed portion 3b and between the second core exposed portion 3ab and the core non-exposed portion 3b. In the example of FIG. 1, the connection portion 3c in contact with the first core exposed portion 3aa is disposed in the first upper cladding non-forming region 1aa. The connection portion 3c in contact with the second core exposed portion 3ab is disposed in the second upper cladding non-forming region 1ab.

[0029] As shown in FIG. 1, the connection portion 3c refers to the core 3 formed in the upper cladding non-forming region 1a between the core exposed portion 3a and the core non-exposed portion 3b in a plan view. Here, the shape of the core 3 in the connection portion 3c may be a shape having a constant width, a tapered shape tapering toward the core non-exposed portion 3b, or a combination of a shape with a constant width and a tapered shape. That is, the connection portion 3C may have a taper in a plan view, may be arranged in a straight line of a constant width, or may be arranged in a combination of a straight line of a constant width and a taper. The tapered shape of the core 3 in the connection portion 3c may be a shape in which the width gradually increases linearly (or smoothly) on both sides (i.e., both +Y direction side and -Y direction side with respect to a line passing through the midpoint of the width of the core 3) from the core non-exposed portion 3b toward the core exposed portion 3a, a shape in which the width gradually increases linearly only on one side (+Y direction side or -Y direction side), or a shape in which the width gradually increases stepwise on both sides or only on one side.

[0030] <Core width> The relationship in width between the various portions of the core 3 of the optical waveguide 1 will be described with reference to Fig. 2C. Fig. 3 shows the optical waveguide 1 in the same manner as Fig. 1, and is given a reference symbol such as "W11" indicating the length of each portion of the core 3. In Fig. 3, the components shown in Fig. 1 are given the same reference symbols as those in Fig. 1 or are omitted as appropriate, and repeated explanations of the components will be omitted.

[0031] The core 3 has a width W11 at a first core exposed portion 3aa located at one end 3α. The core 3 has a width W12 at a second core exposed portion 3ab located at the other end 3β. The first core exposed portion 3aa is a portion of the core 3 that is located in the first upper cladding non-forming region 1aa and has the width W11. The second core exposed portion 3ab is a portion of the core 3 that is located in the second upper cladding non-forming region 1ab and has the width W12.

[0032] When a virtual line X1 is provided at the middle of the upper cladding forming region 1b in the X direction, a region on the first upper cladding non-forming region 1aa side of the virtual line X1 in the upper cladding forming region 1b becomes an upper cladding forming region 1ba (first upper cladding forming region). A region on the second upper cladding non-forming region 1ab side of the virtual line X1 in the upper cladding forming region 1b becomes an upper cladding forming region 1bb (second upper cladding forming region). Note that the virtual line X1 is not formed in the optical waveguide 1, but is provided for convenience in explaining the embodiment.

[0033] The upper cladding forming region 1ba has a core non-exposed portion 3b1 (first core non-exposed portion) of the core non-exposed portion 3b, and the upper cladding forming region 1bb has a core non-exposed portion 3b2 (second core non-exposed portion) of the core non-exposed portion 3b. That is, the portion of the core non-exposed portion 3b that is closer to one end 3α than the middle in the X direction (the midpoint between one end 3α and the other end 3β of the core 3) is the core non-exposed portion 3b1, and the portion of the core non-exposed portion 3b that is closer to the other end 3β than the middle in the X direction is the core non-exposed portion 3b2.

[0034] The core 3 has a width W21 at the core unexposed portion 3b1 and a width W22 at the core unexposed portion 3b2. The core unexposed portion 3b1 is a portion of the core 3 that is located within the upper cladding formation region 1ba and has the width W21. The core unexposed portion 3b2 is a portion of the core 3 that is located within the upper cladding formation region 1bb and has the width W22.

[0035] In the optical waveguide of the embodiment, the width W11 of the core 3 in the first core exposed portion 3aa, the width W21 of the core 3 in the non-core exposed portion 3b1, the width W12 of the core 3 in the second core exposed portion 3ab, and the width W22 of the core 3 in the non-core exposed portion 3b2 satisfy the relationship of the following formula 1 and the following formula 2. W11>W21 (Formula 1) W12>W22...(Formula 2)

[0036] That is, the width W11 of the first core exposed portion 3aa is different from the width W21 of the core non-exposed portion 3b1. The width W11 of the first core exposed portion 3aa is larger than the width W21 of the core non-exposed portion 3b1. The width W12 of the second core exposed portion 3ab is different from the width W22 of the core non-exposed portion 3b2. The width W12 of the second core exposed portion 3ab is larger than the width W22 of the core non-exposed portion 3b2. Therefore, the difference between the width W11 of the first core exposed portion 3aa and the width We1 of the light receiving portion or light emitting portion E1a of the component E1 is larger than the difference between the width W21 of the core non-exposed portion 3b1 and the width We1 of the light receiving portion or light emitting portion E1a. Similarly, the difference between the width W12 of the second core exposed portion 3ab and the width We2 of the light receiving portion or light emitting portion E2a of the component E2 is larger than the difference between the width W22 of the core non-exposed portion 3b2 and the width We2 of the light receiving portion or light emitting portion E2a.

[0037] Therefore, in the optical waveguide 1, compared with a case where the core 3 has the same width W21 as the width W21 of the core non-exposed portion 3b1 in the first core exposed portion 3aa, the allowable range of positional deviation in the direction along the width of the core 3 when aligning the light guiding portion of the optical component such as the light receiving portion or the light emitting portion E1a with the core 3 is larger. That is, when the core 3 and the light receiving portion or the light emitting portion E1a of the component E1 are overlapped in the first core exposed portion 3aa as shown in FIG. 2C, the width Wg of the marginal portion of the core 3 that does not overlap with the light receiving portion or the light emitting portion E1a in a plan view is larger than the width of the marginal portion of the core 3 when the core 3 and the light receiving portion or the light emitting portion E1a are overlapped in the core non-exposed portion 3b1.

[0038] Similarly, in the optical waveguide 1, compared with the case where the core 3 has the same width W22 as the core non-exposed portion 3b2 in the second core exposed portion 3ab, the allowable range of positional deviation in the direction along the width of the core 3 when aligning the light guiding portion of the optical component such as the light receiving portion or the light emitting portion E2a with the core 3 is larger. That is, when the core 3 and the light receiving portion or the light emitting portion E2a of the component E2 are overlapped in the second core exposed portion 3ab as shown in FIG. 2C, the width Wg of the marginal portion of the core 3 that does not overlap with the light receiving portion or the light emitting portion E2a in a plan view is larger than the width of the marginal portion of the core 3 when the core 3 and the light receiving portion or the light emitting portion E2a are overlapped in the core non-exposed portion 3b2.

[0039] Therefore, in the optical waveguide 1, even if the alignment between the optical components such as components E1 and E2 and the core 3 is slightly shifted in the direction along the width of the core 3 (the +Y direction or the -Y direction in FIG. 2C), it is believed that an optical signal emitted from one of the optical components and the core 3 is likely to be incident on the other. In other words, even if such a positional shift occurs, it is believed that the substantial optical coupling efficiency between the optical components and the core 3 is likely to be maintained.

[0040] Therefore, in this embodiment, it is considered that alignment is easy to perform for appropriate optical coupling between optical components such as component E1 and component E2 and core 3. In particular, it is considered that alignment in the direction along the width of core 3 is easy. Therefore, according to the optical waveguide of the embodiment, it is considered that high coupling efficiency is easily achieved in coupling with optical components. Also, it is considered that poor coupling due to misalignment between core 3 and optical components such as component E1 and component E2 is suppressed even with thermal history during use.

[0041] In addition, in this embodiment, the core non-exposed portion 3b1 has a width W21 smaller than the width W11 of the first core exposed portion 3aa, and the core non-exposed portion 3b2 has a width W22 smaller than the width W12 of the second core exposed portion 3ab, so that the desired transmission mode may be easily realized in the core non-exposed portion 3b. For example, in a light guide member such as the optical waveguide 1, the size of the cross section of the optical path such as the core 3 is selected according to the refractive index difference between the constituent material of the optical path and the constituent material of the covering body such as the cladding 2 surrounding the optical path. That is, by realizing the core 3 having a cross section of an appropriate size according to the refractive index of each material, an optical signal can be propagated in a desired transmission mode. In this regard, in this embodiment, the core 3 is not formed over the entire length with the width (width W11) of the first core exposed portion 3aa or the width (width W12) of the second core exposed portion 3ab, which have a large width for high coupling efficiency with optical components, but the core non-exposed portion 3b1 has a width W21 and the core non-exposed portion 3b2 has a width W22. The width W21 is smaller than the width W11, and the width W22 is smaller than the width W12. Therefore, it is considered that optical transmission in a mode requiring a small core cross section is easily realized. For example, optical transmission in a single mode requiring a core diameter of several μm may be possible. In a plan view, the core unexposed portion 3b1 and the core unexposed portion 3b2 may have a shape of a constant width. In addition, the shape of the core unexposed portion 3b1 and the shape of the core unexposed portion 3b2 may be a combination of a tapered portion and a portion of a constant width.

[0042] In this way, the optical waveguide of this embodiment may be optically coupled (particularly adiabatic coupled) with external optical components such as the components E1 and E2 at the first core exposed portion 3aa and the second core exposed portion 3ab with excellent coupling efficiency, and may transmit an optical signal in a desired transmission mode in a portion other than the optically coupled portion with the optical components. For example, an optical signal may be propagated in a high-speed, low-loss transmission mode such as a single mode. In other words, it is considered that the optical waveguide of this embodiment can provide high-speed optical transmission with high efficiency and low loss between two or more optical components optically coupled to the optical waveguide.

[0043] In particular, in this embodiment, a first core exposed portion 3aa is provided at one end 3α of the core 3, and a second core exposed portion 3ab is provided at the other end 3β of the core 3, so it is believed that high-speed optical transmission with high efficiency and low loss can be provided between optical components such as semiconductor devices including photoelectric conversion elements.

[0044] The core width W11 in the first core exposed portion 3aa and the core width W12 in the second core exposed portion 3ab may be substantially the same. The core width W21 in the core non-exposed portion 3b1 and the core width W22 in the core non-exposed portion 3b2 may be substantially the same. Furthermore, the core width W11 may be larger than the core width W22, and the core width W12 may be larger than the core width W21.

[0045] The width W11 of the first core exposed portion 3aa and the width W21 of the core non-exposed portion 3b1 are not particularly limited as long as the width W11 is greater than the width W21, but it is desirable that the width W11 of the core 3 in the first core exposed portion 3aa and the width W21 of the core 3 in the core non-exposed portion 3b1 satisfy the relationship of the following formula 3. Furthermore, the width W12 of the second core exposed portion 3ab and the width W22 of the core non-exposed portion 3b2 are not particularly limited as long as the width W12 is greater than the width W22, but it is desirable that the width W12 of the core 3 in the second core exposed portion 3ab and the width W22 of the core 3 in the core non-exposed portion 3b2 satisfy the relationship of the following formula 4. 1.0<(W11 / W21)≦3.0 (Formula 3) 1.0<(W12 / W22)≦3.0 (Formula 4) That is, the first core exposed portion 3aa preferably has a width W11 that is greater than the width W21 of the core non-exposed portion 3b1 and is three times or less than the width W21. The second core exposed portion 3ab preferably has a width W12 that is greater than the width W22 of the core non-exposed portion 3b2 and is three times or less than the width W22.

[0046] The width W11 of the core 3 in the first core exposed portion 3aa is preferably 3 μm or more and 30 μm or less, more preferably 5 μm or more and 20 μm or less. When the core 3 in the first core exposed portion 3aa has a width in this range, it is considered that the effect of facilitating alignment with an optical component such as the component E1 can be obtained, and an excessively large area for optical coupling with the optical component is not required. The width W21 of the core non-exposed portion 3b1 can be, for example, 1 μm or more and 10 μm or less.

[0047] The width W12 of the core 3 in the second core exposed portion 3ab is preferably 3 μm or more and 30 μm or less, and more preferably 5 μm or more and 20 μm or less. When the core 3 in the second core exposed portion 3ab has a width in this range, it is considered that the effect of facilitating alignment with an optical component such as the component E2 can be obtained, and an excessively large area for optical coupling with the optical component is not required. The width W22 of the core unexposed portion 3b2 can be, for example, 1 μm or more and 10 μm or less.

[0048] The width of the core 3 is determined by the average value of the length measurements at three points in the X direction. The width of the core in the first core exposed portion 3aa and the second core exposed portion 3ab may be constant or may vary. As an example, the width of the first core exposed portion 3aa and the second core exposed portion 3ab may gradually increase or decrease from one end to the other end. When the width of the first core exposed portion 3aa varies, the width of the core of the first core exposed portion 3aa is determined by the average value of the length measurements at three points in the first core exposed portion 3aa in the X direction. When the width of the second core exposed portion 3ab varies, the width of the core of the second core exposed portion 3ab is determined by the average value of the length measurements at three points in the second core exposed portion 3ab in the X direction.

[0049] The core widths in the core unexposed portion 3b1 and the core unexposed portion 3b2 may be constant or may vary. As an example, the core unexposed portion 3b1 and the core unexposed portion 3b2 may have widths that gradually increase or decrease from one end to the other end. When the width of the core unexposed portion 3b1 varies, the core width of the core unexposed portion 3b1 is determined by the average value of length measurements at three points in the core unexposed portion 3b1 in the X direction. When the width of the core unexposed portion 3b2 varies, the core width of the core unexposed portion 3b2 is determined by the average value of length measurements at three points in the core unexposed portion 3b2 in the X direction.

[0050] The thickness of the core 3 is determined as the average value of values ​​measured at three points in the Z direction (see FIG. 2A). The thickness of the core 3 is not particularly limited, but is 3 μm or more and 100 μm or less, and preferably 5 μm or more and 20 μm or less.

[0051] The cross-sectional shape of the core 3 in the first core exposed portion 3aa and the second core exposed portion 3ab is a square or a rectangle. The ratio of the width of the core 3 to the thickness of the core 3 in the first core exposed portion 3aa and the second core exposed portion 3ab (width of the core 3: thickness of the core 3) is preferably 0.5:1 to 1:0.5. The cross-sectional shape of the core 3 in the core non-exposed portion 3b1 and the core non-exposed portion 3b2 is a square or a rectangle. The ratio of the width of the core 3 to the thickness of the core 3 in the core non-exposed portion 3b1 and the core non-exposed portion 3b2 (width of the core 3: thickness of the core 3) is preferably 0.5:1 to 1:0.5.

[0052] The length L11 of the core 3 at the first core exposed portion 3aa is preferably 100 μm or more and 3000 μm or less, and more preferably 100 μm or more and 2500 μm or less. When the first core exposed portion 3aa has a length in this range, it is considered that there is a high degree of freedom in selecting an optical component to be optically coupled at the first core exposed portion 3aa, and a necessary and sufficient tolerance is obtained in the alignment with the optical component in the direction perpendicular to the direction along the width of the core 3.

[0053] Furthermore, the length L12 of the core 3 at the second core exposed portion 3ab is preferably 100 μm or more and 3000 μm or less, and more preferably 100 μm or more and 2500 μm or less. If the second core exposed portion 3ab has a length in this range, it is considered that there is a high degree of freedom in selecting an optical component to be optically coupled at the second core exposed portion 3ab, and a necessary and sufficient tolerance can be obtained in the alignment with the optical component in the direction perpendicular to the direction along the width of the core 3.

[0054] <Lower cladding> The thickness of the lower cladding 21 is determined by the average value of measurements taken at three points in the Z direction (see FIG. 2A). The thickness of the lower cladding 21 is not particularly limited, but is in the range of 5 μm to 100 μm, and preferably 10 μm to 50 μm.

[0055] <Upper cladding> The thickness of the upper cladding 22 is determined by the average value of values ​​measured at three points in the Z direction. The thickness of the upper cladding 22 is not particularly limited, but is in the range of 5 μm to 100 μm, and preferably 10 μm to 50 μm.

[0056] An example of a combination of dimensions of each part of the optical waveguide 1 of the embodiment is as follows. The core width in the first core exposed portion 3aa is 10 μm, the core width in the second core exposed portion 3ab is 10 μm, and the thickness of the core 3 is 7 μm. The core width in the non-core exposed portion 3b1 is 7 μm, the core width in the non-core exposed portion 3b2 is 7 μm, and the core thickness is 7 μm. The lower cladding is 20 μm thick, and the upper cladding is 25 μm thick.

[0057] Note that the width of core 3, the thickness of core 3, the length of first core exposed portion 3aa and the length of second core exposed portion 3ab, as well as the thickness of lower cladding 21 and upper cladding 22 exemplified above are merely examples, and the dimensions of each portion of core 3 and the thickness of each cladding are not limited to the numerical values ​​exemplified above.

[0058] <Width and shape of connection part> The connection portion 3c of the core 3 shown in FIG. 2C includes two connection portions 3c1 (first connection portion) and 3c2 (second connection portion), and each connection portion 3c has a tapered portion tapered toward the core non-exposed portion 3b. The connection portion 3c1 (first connection portion) in contact with the first core exposed portion 3aa has a core width W31. The connection portion 3c2 (second connection portion) in contact with the second core exposed portion 3ab has a core width W32. The core width W31 at the connection portion 3c1 is smaller than the core width W11 of the first core exposed portion 3aa and is equal to or larger than the core width W21 of the core non-exposed portion 3b1 in the upper cladding forming region 1ba. The core width W32 at the connection portion 3c2 is smaller than the core width W12 of the second core exposed portion 3ab and is equal to or larger than the core width W22 of the core non-exposed portion 3b2 in the upper cladding forming region 1bb. In other words, core width W11, core width W21, and core width W31 satisfy the relationship of formula 5 below, and core width W12, core width W22, and core width W32 satisfy the relationship of formula 6 below. Core width W11>Core width W31≧Core width W21 (Equation 5) Core width W12>Core width W32≧Core width W22 (Equation 6)

[0059] It is considered that the unintended leakage of the optical signal from the first core exposed portion 3aa toward the core non-exposed portion 3b1 is suppressed by the width W31 of the core of the connecting portion 3c1 having a tapered shape. Also, it is considered that the unintended leakage of the optical signal from the second core exposed portion 3ab toward the core non-exposed portion 3b2 is suppressed by the width W32 of the core of the connecting portion 3c2 having a tapered shape. That is, in the optical waveguide of the embodiment, since the width W11 of the first core exposed portion 3aa is larger than the width W21 of the core non-exposed portion 3b1, it is considered that the connecting portion 3c1 having a tapered shape suppresses the unintended leakage of the optical signal from the first core exposed portion 3aa toward the core non-exposed portion 3b1. Similarly, since the width W12 of the second core exposed portion 3ab is larger than the width W22 of the core non-exposed portion 3b2, it is considered that the connecting portion 3c2 having a tapered shape suppresses the unintended leakage of the optical signal from the second core exposed portion 3ab toward the core non-exposed portion 3b2. Note that the width W31 of the core of the connecting portion 3c1 is not particularly limited, but is preferably 1 μm to 30 μm. The width W32 of the core of the connecting portion 3c2 is not particularly limited, but is preferably 1 μm to 30 μm.

[0060] The taper ratio ((W11 - W21) / L21 or (W12 - W22) / L22) of the tapered shape of the core 3 is, for example, 1 or more and 2 or less. Note that L21 is the length of the tapered shape portion of the connecting portion 3c1 along the X direction, and L22 is the length of the tapered shape portion of the connecting portion 3c2 along the X direction. When the connecting portion 3c1 and the connecting portion 3c2 have a taper ratio within this range, it may be possible to efficiently suppress the leakage of the optical signal from the core 3 within a limited length. At this time, the formation ratio R of the tapered shape in the core 3 is preferably 0.01 < R < 0.2, and more preferably 0.03 < R < 0.15. Note that the formation ratio R of the tapered shape is the ratio of the length of one tapered shape portion (length L21 or length L22 in FIG. 2C) to the total length of the core 3.

[0061] <Planar shape of core 3> The planar shape of the core 3 will be described with reference to Fig. 2D and Fig. 2E. Fig. 2D and Fig. 2E show a first modified example and a second modified example as modified examples of the connection portion 3c of the core 3 in the optical waveguide of the embodiment. Although two cores 3 are depicted in Fig. 2D and Fig. 2E, any number of cores 3 (e.g., 2 or more and 64 or less) may be arranged in both the first modified example and the second modified example. In Fig. 2D and Fig. 2E, components similar to those shown in Fig. 2C are denoted by the same reference numerals as those in Fig. 2C or omitted as appropriate, and repeated explanations thereof will be omitted.

[0062] The planar shape of the core 3, when viewed in combination with the upper clad 22, is a combination of the first core exposed portion 3aa, the connection portion 3c1, the core non-exposed portion 3b1, the core non-exposed portion 3b2, the connection portion 3c2, and the second core exposed portion 3ab. When viewed by itself, the planar shape of the core 3 has a portion having a certain width corresponding to the first core exposed portion 3aa, a portion having a certain width corresponding to the second core exposed portion 3ab, and a portion corresponding to the core non-exposed portion 3b in FIG. 2C. The connection portion 3c1 is disposed between the first core exposed portion 3aa and the core non-exposed portion 3b1. The connection portion 3c2 is disposed between the second core exposed portion 3ab and the core non-exposed portion 3b2. The connection portion 3c1 can have a shape having a certain width, a tapered shape, or a shape that is a combination of a portion with a certain width and a portion with a tapered shape. The connecting portion 3c2 may have a shape having a constant width, a tapered shape, or a shape that combines a portion with a constant width and a tapered shape.

[0063] That is, the shape of the connection portion 3c may include a portion with a constant width and a tapered portion as in Fig. 2C, or may have a shape with a constant width as in the first modified example shown in Fig. 2D. Also, as in the second modified example shown in Fig. 2E, the shape of the connection portion 3c1 may be tapered over the entire area between the first core exposed portion 3aa and the core non-exposed portion 3b1, and the shape of the connection portion 3c2 may be tapered over the entire area between the second core exposed portion 3ab and the core non-exposed portion 3b2.

[0064] Also, the shape of the core 3 may have a part having a constant width corresponding to the first core exposed portion 3aa and a part having a constant width corresponding to the second core exposed portion 3ab, and a part having a shape of a combination of a tapered shape and a shape having a constant width corresponding to the core non-exposed portion 3b1 and the core non-exposed portion 3b2 (see Figs. 4 and 5). A connecting portion 3c1 having a shape having a constant width, a tapered shape, or a shape of a combination of a part having a constant width and a tapered shape may be disposed between the first core exposed portion 3aa and the core non-exposed portion 3b1. Also, a connecting portion 3c2 having a shape having a constant width, a tapered shape, or a shape of a combination of a part having a constant width and a tapered shape may be disposed between the second core exposed portion 3ab and the core non-exposed portion 3b2.

[0065] When both the connection portion 3c1 and the core non-exposed portion 3b1 have a tapered shape, the shape of the core 3 in a planar view may be a tapered shape whose width changes continuously from the connection portion 3c1 to the core non-exposed portion 3b1 (see FIG. 5). When both the connection portion 3c2 and the core non-exposed portion 3b2 have a tapered shape, the shape of the core 3 in a planar view may be a tapered shape whose width changes continuously from the connection portion 3c2 to the core non-exposed portion 3b2 (see FIG. 5). In addition, the tapered shape of the core 3 in a planar view may be a shape whose width changes linearly on both sides, a shape whose width changes linearly on one side, or a shape whose width changes stepwise on both sides or one side.

[0066] <Core surrounded by lower cladding> Fig. 3 shows another example of the cladding 2 in the optical waveguide 1 of the embodiment. Fig. 3 shows a cross section of the example of Fig. 3 taken along a cutting line corresponding to line IIB-IIB shown in Fig. 1. In the example shown in Fig. 3, the core 3 is surrounded within the lower cladding 21. Therefore, the side surface 35 of the core 3 is covered by the lower cladding 21. Therefore, the side surface 35 of the core 3 is covered by the cladding 2 (specifically, by the lower cladding 21) not only in the upper cladding-formed region 1b (see Fig. 1) but also in the upper cladding-free region 1a (see Fig. 1). Therefore, it is considered that the transmission mode of the optical signal is less likely to be disturbed in the upper cladding-free region 1a.

[0067] On the other hand, the upper surface 31 of the core 3 is substantially flush with the upper surface 211 of the lower cladding 21. This can prevent unintended contact between the core 3 and an optical component optically coupled to the core 3. In addition, the core 3 can be easily formed by a photobleaching method.

[0068] <Modification of optical waveguide> FIG. 4 shows an optical waveguide 10a which is a first modified example of the optical waveguide of the embodiment. In the optical waveguide 10a, a first core exposed portion 3aa is arranged in the first upper cladding non-forming region 1aa, and a second core exposed portion 3ab is arranged in the second upper cladding non-forming region 1ab. The core exposed portion 3b1 in the upper cladding forming region 1ba is a combination of a tapered shape and a shape having a constant width. The core exposed portion 3b2 in the upper cladding forming region 1bb is also a combination of a tapered shape and a shape having a constant width. When the tapered shape of the core exposed portion 3b1 and the tapered shape of the core exposed portion 3b2 are covered by the upper cladding 22 in this way, it is considered that there is little disturbance in the transmission mode of the optical signal in the core 3.

[0069] Fig. 5 shows an optical waveguide 10b which is a second modified example of the optical waveguide of the embodiment. In the optical waveguide 10b shown in Fig. 5, the core of the connection portion 3c has a tapered shape tapered toward the core non-exposed portion 3b1 or the core non-exposed portion 3b2. The first upper cladding non-forming region 1aa has a first core exposed portion 3aa and a connection portion 3c1 having a tapered shape, and the second upper cladding non-forming region 1ab has a second core exposed portion 3ab and a connection portion 3c2 having a tapered shape. The core non-exposed portion 3b1 in the upper cladding forming region 1ba and the core non-exposed portion 3b2 in the upper cladding forming region 1bb each have a shape that combines a tapered shape with a shape of a constant width.

[0070] The tapered shape of the core of the connecting portion 3c1 may be a shape in which the width gradually increases linearly on both sides from the core non-exposed portion 3b1 toward the first core exposed portion 3aa, a shape in which the width gradually increases linearly on only one side, or a shape in which the width gradually increases in a step-like manner on both sides or only one side. The tapered shape of the core of the connecting portion 3c2 may be a shape in which the width gradually increases linearly on both sides from the core non-exposed portion 3b2 toward the second core exposed portion 3ab, a shape in which the width gradually increases linearly on only one side, or a shape in which the width gradually increases in a step-like manner on both sides or only one side.

[0071] In the optical waveguide 10b shown in Fig. 5, the shape of the core 3 includes a portion corresponding to the first core exposed portion 3aa having a certain width, a portion corresponding to the second core exposed portion 3ab having a certain width, a portion corresponding to the core non-exposed portion 3b1 having a shape that is a combination of a tapered shape and a shape that has a certain width, and a portion corresponding to the core non-exposed portion 3b2 having a shape that is a combination of a tapered shape and a shape that has a certain width. A connecting portion 3c1 having a tapered shape is disposed between the first core exposed portion 3aa and the core non-exposed portion 3b1, and a connecting portion 3c2 having a tapered shape is disposed between the second core exposed portion 3ab and the core non-exposed portion 3b2. The shape of the core 3 in a plan view includes a tapered shape whose width changes continuously from the connecting portion 3c1 to the core non-exposed portion 3b1, and also includes a tapered shape whose width changes continuously from the connecting portion 3c2 to the core non-exposed portion 3b2.

[0072] 6A and 6B show modified examples of the optical waveguide of the embodiment. FIG. 6A shows an optical waveguide 10c of a first modified example, and FIG. 6B shows an optical waveguide 10d of a second modified example. In the optical waveguide 10c shown in FIG. 6A, the core 3 has an L-shape in a plan view. That is, each core 3 has one bent portion 3d, and is bent at an angle of approximately 90° at the bent portion 3d. The angle of the bent portion 3d can be in the range of 45° to 135°. The optical components optically coupled to the optical waveguide 10c can be freely arranged, and the optical waveguide can be designed accordingly. The bent portion 3d may be straight or curved, but is preferably a curved portion, and if the bent portion 3d is curved, it becomes easier to transmit an optical signal near the bent portion 3d.

[0073] The optical waveguide 10c is formed in a shape having a side S1 of the optical waveguide 10c that is rectangular in plan view and a side S2 that is substantially perpendicular to the side S1. The lower cladding 21 is formed in a shape having a side S1 and a side S2. The upper cladding non-forming region 1a is formed in a shape that is along the sides S1 and S2. When a virtual line X2 is provided along the bent portion 3d of the core 3 in the upper cladding forming region 1b, the upper cladding forming region 1b is divided into an A1 region and an A2 region by the virtual line X2. The A1 region is a region where the core 3 of the core non-exposed portion 3b is formed along the side S2 (i.e., substantially parallel to the side S2), and the A2 region is a region where the core 3 of the core non-exposed portion 3b is formed along the side S1 (i.e., substantially parallel to the side S1). Note that the virtual line X2 is not formed in the optical waveguide 10c, but is provided for convenience in explaining the embodiment.

[0074] In FIG. 6A, the first core exposed portion 3aa at one end 3α of the core 3 is disposed outside the A1 region. The second core exposed portion 3ab at the other end 3β of the core 3 is disposed outside the A2 region. The four first core exposed portions 3aa at one end 3α of the core 3 are arranged along the side S1. The four second core exposed portions 3ab at the other end 3β of the core 3 are arranged along the side S2. As shown in FIG. 6A, the core 3 has an L-shape, so that the component E1 (see FIG. 2C) can be arranged in the region between the A1 region and the side S1, and the component E2 (see FIG. 2C) can be arranged in the region between the A2 region and the side S2. It is considered that the component E1 and the first core exposed portion 3aa can be easily aligned. It is considered that the component E2 and the second core exposed portion 3ab can be easily aligned. In addition, even if the components E1 and E2 are exposed to heat history during use after they are mounted, poor coupling due to misalignment is suppressed, so it is believed that optical coupling can be performed with good coupling efficiency. It is also believed that it is easy to realize a desired transmission mode.

[0075] The core 3 has a first core exposed portion 3aa outside the A1 region and a second core exposed portion 3ab outside the A2 region. The width of the first core exposed portion 3aa is W11, and the width of the second core exposed portion 3ab is W12. The upper cladding forming region 1b has a non-exposed core portion 3b1 in the A1 region and a non-exposed core portion 3b2 in the A2 region of the upper cladding forming region 1b. The width of the non-exposed core portion 3b1 is W21, and the width of the non-exposed core portion 3b2 is W22. The widths W11, W12, W21, and W22 of the core 3 satisfy the relationships of the following formulas 7 and 8. W11>W21...(Formula 7) W12>W22 (Formula 8)

[0076] That is, the width W11 of the first core exposed portion 3aa is different from the width W21 of the core non-exposed portion 3b1. The width W11 of the first core exposed portion 3aa is larger than the width W21 of the core non-exposed portion 3b1. The width W12 of the second core exposed portion 3ab is different from the width W22 of the core non-exposed portion 3b2. The width W12 of the second core exposed portion 3ab is larger than the width W22 of the core non-exposed portion 3b2.

[0077] In the optical waveguide 10d shown in FIG. 6B, the core 3 has a U-shape as a whole in a plan view. That is, each core 3 has a turn-back portion 3dd, and the turn-back portion 3dd has two bends 3d, and each bend 3d is bent at an angle of approximately 90°. The turn-back portion 3dd may be formed by a curve, a combination of straight lines, or a combination of a curve and a straight line. The turn-back portion 3dd is preferably curved, and when the turn-back portion 3dd is curved, it becomes easier to transmit an optical signal near the turn-back portion 3dd. The optical waveguide 10d has an upper cladding-free region 1a along a side S1 of the optical waveguide 10d that is rectangular in a plan view. That is, in the optical waveguide 10d, the core 3 has a first core exposed portion 3aa at one end 3α and a second core exposed portion 3ab at the other end 3β, but the upper cladding non-forming region 1a is provided only in the region near one end 11 of the optical waveguide 10d (the region along side S1 in Figure 6B).

[0078] The optical waveguide 10d is formed in a shape having a side S1 of the optical waveguide 10d that is rectangular in plan view and a side S2 that is approximately perpendicular to the side S1. The lower cladding 21 is formed in a shape having sides S1 and S2. The upper cladding forming region 1b is divided into an A1 region and an A2 region by a virtual line X3 that passes through the middle of the folded-back portion 3dd of each core 3. The A1 region is a region where the core 3 of the core non-exposed portion 3b is formed in the upper half (the half on the first core exposed portion 3aa side) of the upper cladding forming region 1b, and the A2 region is a region where the core 3 of the core non-exposed portion 3b is formed in the lower half (the half on the second core exposed portion 3ab side) of the upper cladding forming region 1b. Note that the virtual line X3 is not formed in the optical waveguide 10d, but is provided for the convenience of explaining the embodiment.

[0079] In FIG. 6B, the first core exposed portion 3aa at one end 3α of the core 3 is disposed outside the A1 region. The second core exposed portion 3ab at the other end 3β of the core 3 is disposed outside the A2 region. Outside the A1 region, the four first core exposed portions 3aa at one end 3α of the core 3 are lined up along the side S1. Outside the A2 region, the four second core exposed portions 3ab at the other end 3β of the core 3 are lined up along the side S1. As shown in FIG. 6B, the core 3 has a U-shape, so that the component E1 (see FIG. 2C) can be disposed outside the A1 region, and the component E2 (see FIG. 2C) can be disposed outside the A2 region. It is considered that the alignment of the component E1 and the first core exposed portion 3aa is easy. It is considered that the alignment of the component E2 and the second core exposed portion 3ab is easy. In addition, even if the components E1 and E2 are exposed to a thermal history during use after mounting, poor coupling due to misalignment is suppressed, so that optical coupling can be performed with good coupling efficiency. It is also believed that it is easy to realize a desired transmission mode.

[0080] The core 3 has a first core exposed portion 3aa on the outside of the A1 region (side S1 side) and a second core exposed portion 3ab on the outside of the A2 region (side S1 side). The width of the first core exposed portion 3aa is W11, and the width of the second core exposed portion 3ab is W12. The A1 region of the upper cladding forming region 1b has a core unexposed portion 3b1, and the A2 region of the upper cladding forming region 1b has a core unexposed portion 3b2. The width of the core unexposed portion 3b1 is W21, and the width of the core unexposed portion 3b2 is W22. The widths W11, W12, W21, and W22 of the core 3 satisfy the relationships of the following formulas 9 and 10. W11>W21...(Formula 9) W12>W22 (Formula 10)

[0081] That is, the width W11 of the first core exposed portion 3aa is different from the width W21 of the core non-exposed portion 3b1. The width W11 of the first core exposed portion 3aa is larger than the width W21 of the core non-exposed portion 3b1. The width W12 of the second core exposed portion 3ab is different from the width W22 of the core non-exposed portion 3b2. The width W12 of the second core exposed portion 3ab is larger than the width W22 of the core non-exposed portion 3b2.

[0082] In the optical waveguide 10c and the optical waveguide 10d, each core 3 has one or two bent portions 3d that are bent at approximately 90 degrees. However, in the optical waveguide of the embodiment, the core 3 may have any number of bent portions that are bent at any angle. Also, the core 3 may be rounded at the bent portions. That is, in the optical waveguide of the embodiment, each core 3 may have any shape in plan view, not limited to a straight line (I-shape) as shown in FIG. 1, or an L-shape or U-shape as shown in FIGS. 6A and 6B.

[0083] <Structure of wiring board according to embodiment> Next, a wiring board of an embodiment will be described with reference to the drawings. Fig. 7 shows a cross-sectional view of a wiring board 100, which is an example of a wiring board of an embodiment. Note that the wiring board 100 shown in Fig. 7 is merely an example of the wiring board of this embodiment. The laminated structure of the wiring board of the embodiment and the number of each of the conductor layers and the insulating layers are not limited to the laminated structure of the wiring board 100 of Fig. 7 and the number of each of the conductor layers and the insulating layers included in the wiring board 100.

[0084] 7, wiring board 100 is a wiring board composed of conductor layers and insulating layers, and includes conductor layers 41-43 as the conductor layers and insulating layers 51, 52 as the insulating layers. Wiring board 100 has optical waveguide 101 and component mounting pad 4. Wiring board 100 has first surface 100a which is a mounting surface for component E1, and second surface 100b which is the surface opposite first surface 100a. Optical waveguide 101 is disposed on the surface (first surface 100a) of wiring board 100.

[0085] The conductor layers 41 to 43 and the insulating layers 51 and 52 are laminated in the order of the conductor layer 43, the insulating layer 52, the conductor layer 42, the insulating layer 51, and the conductor layer 41 from the second surface 100b side of the wiring board 100 toward the first surface 100a side. The conductor layer 41 and the conductor layer 42 are connected by a via conductor 7 that penetrates the insulating layer 51. The conductor layer 42 and the conductor layer 43 are connected by a via conductor 7 that penetrates the insulating layer 52. The wiring board 100 includes a solder resist 62 that covers the conductor layer 43 and the insulating layer 52, and a solder resist 61 that covers the conductor layer 41 and the insulating layer 51. The wiring board 100 also includes bumps 8 that are connected to the respective conductor pads of the conductor layer 43 and protrude from the solder resist 62. The bumps 8 are made of a conductor such as solder, and are used for electrical and mechanical connection between the wiring board 100 and an external component located on the second surface 100b side. Incidentally, wiring board 100 may be used as a motherboard on which bumps 8 are not arranged.

[0086] The insulating layers 51 and 52 may be formed using a thermosetting insulating resin such as an epoxy resin, a bismaleimide triazine resin (BT resin), or a phenol resin. The insulating layers 51 and 52 may be formed using a thermoplastic insulating resin such as a fluororesin, a liquid crystal polymer (LCP), a fluoroethylene (PTFE) resin, a polyester (PE) resin, and a modified polyimide (MPI) resin. Note that the resins listed as the materials of the insulating layers are merely examples of materials that can form the insulating layers. The insulating layers may be formed of any material that can provide insulation between the conductor layers in the wiring board 100. Although not shown, each insulating layer may include a core material (reinforcing material) formed of glass fiber, aramid fiber, or the like, and may include an inorganic filler made of fine particles such as silica (SiO2), alumina, or mullite.

[0087] The solder resists 61 and 62 are formed of, for example, a photosensitive epoxy resin or a polyimide resin.

[0088] The conductor layers 41-43 and the via conductor 7 may be formed using any metal having suitable conductivity, such as copper or nickel. Although each of these conductors is depicted as a single layer in Fig. 7 for simplicity, they may have a multi-layer structure including two or more films. For example, the conductor layers 41-43 and the via conductor 7 may have a two-layer structure including an electroless plating film and an electrolytic plating film.

[0089] The component mounting pad 4 is a conductive pad formed on the conductive layer 41. An opening 61a is provided in the solder resist 61, and the component mounting pad 4 is exposed in the opening 61a. An optical waveguide 101 is disposed on the solder resist 61. Although not shown, the optical waveguide 101 is fixed to the surface of the wiring board 100 by any fixing member such as an adhesive.

[0090] The optical waveguide 101 is the optical waveguide of the embodiment described above. The optical waveguide 101 may be the optical waveguide 1 shown in FIG. 1 and FIG. 3, etc., or may be the optical waveguides 10a, 10b, 10c, and 10d shown in FIG. 4, FIG. 5, FIG. 6A, and FIG. 6B, respectively. FIG. 7 shows an optical waveguide 101 having a structure similar to that of the optical waveguide 1 of FIG. 1, as an example. Thus, the optical waveguide 101 of FIG. 7 includes a lower clad 21, a core 3, and an upper clad 22, which are stacked, and has an upper clad non-forming region 1a (a first upper clad non-forming region 1aa and a second upper clad non-forming region 1ab) and an upper clad forming region 1b. The core 3 has a core exposed portion 3a exposed to the upper clad non-forming region 1a. The first upper cladding non-forming region 1aa has a first core exposed portion 3aa, and the second upper cladding non-forming region 1ab has a second core exposed portion 3ab. The width of the core exposed portion 3a is greater than the width of the core non-exposed portion 3b.

[0091] The wiring board 100 is mounted with a component E1 and a component E2. Both the component E1 and the component E2 are optical components such as a semiconductor device including a photoelectric conversion element, as described in the description of the optical waveguide 1 in FIG. 1 and the like. The component E1 includes a light receiving portion or a light emitting portion E1a and a ball-shaped electrode E1b. The component E2 includes a light receiving portion or a light emitting portion E2a and a ball-shaped electrode E2b. Examples of the components E1 and E2 include a light receiving element such as a photodiode, and a light emitting element such as a light emitting diode (LED), an organic light emitting diode (OLED), a laser diode (LD), and a vertical cavity surface emitting laser (VCSEL). When the components E1 and E2 are light emitting elements, the components E1 and E2 generate an optical signal based on an electrical signal input to the electrode E1b or the electrode E2b, and emit the optical signal toward the core 3 from the light receiving portion or the light emitting portion E1a or the light receiving portion or the light emitting portion E2a functioning as a light emitting portion. In addition, when components E1 and E2 are light receiving elements, an electrical signal is generated based on an optical signal incident from a light receiving unit or light emitting unit E1a functioning as a light receiving unit or a light receiving unit or light emitting unit E2a, and is output from electrode E1b or electrode E2b.

[0092] Components E1 and E2 are mounted on the wiring board 100 by connecting the electrodes E1b or electrodes E2b to component mounting pads 4 using, for example, solder. In Fig. 7, components E1 and E2 are flip-chip mounted. The light receiving portion or light emitting portion E1a of component E1 and the first core exposed portion 3aa of the optical waveguide 101 are positioned to face each other and are optically coupled. The light receiving portion or light emitting portion E2a of component E2 and the second core exposed portion 3ab of the optical waveguide 101 are positioned to face each other and are optically coupled. Since the optical waveguide 101 is an embodiment of the optical waveguide such as the optical waveguide 1 illustrated in FIG. 1, it is easy to align the first core exposed portion 3aa with the light receiving portion or light emitting portion E1a of the component E1, and the second core exposed portion 3ab with the light receiving portion or light emitting portion E2a of the component E2, and therefore it is considered that optical coupling (especially adiabatic coupling) with excellent coupling efficiency is possible. In addition, an optical signal from the component E1 to the component E2, or an optical signal from the component E2 to the component E1, may be transmitted through the optical waveguide 101 in a desired transmission mode such as single mode. That is, according to the wiring board 100 of this embodiment, it may be possible to provide high-speed optical transmission with high efficiency and low loss to the optical components optically coupled to the optical waveguide 101.

[0093] <Method of Manufacturing Optical Waveguide of the Embodiment> A method for manufacturing an optical waveguide according to an embodiment will be described with reference to FIGS. 8A to 8D, taking the optical waveguide 1 of FIG. 1 as an example. In the following, a method for directly forming an optical waveguide on a wiring board (for example, wiring board 100 of FIG. 7) will be described as an example. As shown in FIG. 8A, wiring board 100 is prepared, and lower clad 21 is formed on a surface of a solder resist (not shown) of wiring board 100. Lower clad 21 is formed, for example, by thermocompression bonding a constituent material of lower clad 21 formed in a film shape to wiring board 100, or by applying a resin composition by spin coating to form a film. A constituent material of lower clad 21, such as PMMA, is formed in a film shape and thermocompression bonded to wiring board 100.

[0094] As shown in FIG. 8B, the core 3 is formed in a desired shape in plan view. The core 3 is formed by any method. As an example, the core 3 is formed by using a photolithography technique. That is, a layer made of the material of the core 3, such as PMMA, which has photosensitivity, is formed on the entire surface of the lower clad 21. As an example, the material of the core 3 is applied by spin coating to form a film made of the material of the core 3. The material of the core 3 may be formed in a film shape and thermocompressed on the surface of the lower clad 21. The material of the core 3 having a higher refractive index than the lower clad 21 may be applied, or a film-like material having a higher refractive index than the lower clad 21 may be thermocompressed. Then, the layer made of the material of the core 3 on the lower clad 21 is patterned by exposing through a mask according to the shape of the core 3 to be formed and developing. As a result, a desired number of cores 3 having a desired shape are formed.

[0095] Each core 3 is formed with a portion corresponding to the first core exposed portion 3aa having a width W11, a portion corresponding to the connection portion 3c1, a portion corresponding to the core non-exposed portion 3b1 having a width W21, a portion corresponding to the core non-exposed portion 3b2 having a width W22, a portion corresponding to the connection portion 3c2, and a portion corresponding to the second core exposed portion 3ab having a width W12. The width W11 is larger than the width W21, and the width W12 is larger than the width W22. The portion corresponding to the connection portion 3c1 connects the portion corresponding to the first core exposed portion 3aa and the portion corresponding to the core non-exposed portion 3b1. The portion corresponding to the connection portion 3c2 connects the portion corresponding to the core non-exposed portion 3b2 and the portion corresponding to the second core exposed portion 3ab. In the example of FIG. 8B, the portion corresponding to the connection portion 3c1 and the portion corresponding to the connection portion 3c2 are formed by combining a tapered shape and a shape of a constant width. In addition, the portion corresponding to connecting portion 3c1 and the portion corresponding to connecting portion 3c2 may have only a tapered shape or only a shape of a constant width, rather than simply having a combination of a tapered shape and a shape of a constant width.

[0096] The portion corresponding to the first core exposed portion 3aa is formed to be located in a first upper cladding non-forming region 1aa (see FIG. 8D) that will be provided in a later process, and the portion corresponding to the second core exposed portion 3ab is formed to be located in a second upper cladding non-forming region 1ab (see FIG. 8D) that will be provided in a later process. The portion corresponding to the core non-exposed portion 3b1 is formed to be located in an upper cladding forming region 1ba (see FIG. 8D) that will be provided in a later process, and the portion corresponding to the core non-exposed portion 3b2 is formed to be located in an upper cladding forming region 1bb (see FIG. 8D) that will be provided in a later process. The portion corresponding to the connecting portion 3c1 is formed to connect the first core exposed portion 3aa and the core non-exposed portion 3b1 in the first upper cladding non-forming region 1aa. The portion corresponding to the connecting portion 3c2 is formed to connect the second core exposed portion 3ab and the core non-exposed portion 3b2 in the second upper cladding non-forming region 1ab.

[0097] In addition to the photolithography technique, the method of forming the core 3 in the desired shape includes the photobleaching method and the core cutting method. In the photobleaching method, a layer having a higher refractive index than the lower clad 21 and formed on the entire surface of the lower clad 21 is irradiated with ultraviolet light or the like in the non-masked region using a mask that shields the region where the core 3 is formed. The core 3 is formed by lowering the refractive index of the irradiated region. In the core cutting method, the layer having a higher refractive index than the lower clad 21 and formed on the entire surface of the lower clad 21 is cut into the desired shape with a laser beam or the like to form the core 3. The core 3 may be formed by such a photobleaching method or core cutting method.

[0098] As shown in FIG. 8C, the upper clad 22 is formed on the core 3 and the lower clad 21. For example, similar to the formation of the lower clad 21, the constituent material of the upper clad 22, such as PMMA, is applied to the lower clad 21 and the core 3 by spin coating to form a film made of the constituent material of the upper clad 22. The constituent material of the upper clad 22, such as PMMA, may be formed into a film and then thermocompressed. The upper clad 22 is integrated with the lower clad 21 or at least closely adheres to the lower clad 21 to form the clad 2 surrounding the core 3. At the stage shown in FIG. 8C, the upper clad 22 is in contact with the upper surface 31 of the core 3 and the side surface of the core 3, the upper clad 22 is formed to surround the core 3, and the lower clad 21 is formed on the lower surface 32 of the core 3. As a result, the clad 2 is formed to surround the core 3. Alternatively, the clad 2 may be formed so that the upper clad 22 is formed on the upper surface 31 of the core 3 , and the lower clad 21 is in contact with the side surface of the core 3 and the lower surface 32 of the core 3 , surrounding the core 3 .

[0099] As shown in FIG. 8D, in the upper cladding 22, a portion covering the first core exposed portion 3aa and the connecting portion 3c1 of the core 3, and a portion covering the second core exposed portion 3ab and the connecting portion 3c2 are removed. For example, a portion of the upper cladding 22 on the first core exposed portion 3aa and a portion on the connecting portion 3c1 are removed over the entire length in the direction along the width of the core 3, such as width W11 (see FIG. 8B). In addition, a portion of the upper cladding 22 on the second core exposed portion 3ab and a portion on the connecting portion 3c2 are removed over the entire length in the direction along the width of the core 3, such as width W12 (see FIG. 8B). As a result, the first core exposed portion 3aa and the second core exposed portion 3ab of the core 3 are exposed from the cladding 2. That is, by removing a portion of the upper cladding 22, an upper cladding non-forming region 1a and an upper cladding forming region 1b are provided.

[0100] The upper cladding non-forming region 1a includes a first upper cladding non-forming region 1aa where the first core exposed portion 3aa is exposed, and a second upper cladding non-forming region 1ab where the second core exposed portion 3ab is exposed. The upper cladding forming region 1b includes an upper cladding forming region 1ba located closer to the first upper cladding non-forming region 1aa than the middle of the upper cladding forming region 1b, and an upper cladding forming region 1bb located closer to the second upper cladding non-forming region 1ab than the middle of the upper cladding forming region 1b. The portion of the core 3 that is covered with the upper cladding 22 in the upper cladding forming region 1ba is a core non-exposed portion 3b1, and the portion of the core 3 that is covered with the upper cladding 22 in the upper cladding forming region 1bb is a core non-exposed portion 3b2.

[0101] The portion of the upper cladding 22 to be removed is removed by using a photolithography technique, for example. The portion of the upper cladding 22 to be removed may be removed by laser processing, and the removal method is not limited to these methods. In addition, a film that is a constituent material of the upper cladding 22 may be thermocompression bonded so that the portion corresponding to the first core exposed portion 3aa and the portion corresponding to the second core exposed portion 3ab are not covered.

[0102] A support plate (not shown) may be prepared instead of the wiring board 100, and the optical waveguide may be formed on the support plate. The optical waveguide being manufactured is supported and given appropriate rigidity. A support plate having approximately the same size and shape as the optical waveguide to be manufactured in a plan view may be prepared, or a support plate slightly larger than the optical waveguide to be manufactured in a plan view may be prepared. The support plate may have an adhesive layer (not shown) on the surface on which the lower clad 21 is formed. In this case, after the optical waveguide is completed, the support plate may be peeled off from the completed optical waveguide at the adhesive layer. The optical waveguide to be manufactured may be used with the support plate attached after completion.

[0103] The support plate is preferably made of a material having a higher rigidity than the optical waveguide to be manufactured. The support plate may be made of a material having a lower thermal expansion coefficient than the optical waveguide to be manufactured. The displacement of the optical waveguide due to temperature changes may be suppressed. Examples of materials for the support plate include glasses such as soda-lime glass, borosilicate glass, and quartz glass, various metals such as tungsten, titanium, and molybdenum, and various ceramics such as alumina, silicon nitride, and silicon oxide.

[0104] The support plate may have a suitable degree of flexibility, and may be made of, for example, a resin film. When the optical waveguide is used with the support plate, the degree of freedom in the shape of the optical waveguide during use may be increased.

[0105] When the optical waveguide to be manufactured is used without a support plate, the support plate is removed after the upper clad non-forming region 1a is defined as shown in FIG. 8D. By removing the support plate, a single optical waveguide is completed. The support plate is removed by any method. For example, when the support plate and the lower clad 21 are bonded with an adhesive layer (not shown) made of a thermoplastic adhesive, the optical waveguide with the support plate is heated, the adhesiveness of the adhesive is reduced, and then the support plate is peeled off from the lower clad 21. Also, when the lower clad 21 is bonded to the light-transmitting support plate with an adhesive layer (not shown) made of a photoplastic adhesive, light may be irradiated from the support plate side toward the lower clad 21, the adhesiveness of the adhesive is reduced, and then the support plate may be peeled off from the lower clad 21. The optical waveguide after the support plate is peeled off is arranged on the wiring board 100 as described with reference to FIG. 7, for example.

[0106] <Method of Manufacturing a Wiring Board According to an Embodiment> 7 may be manufactured by sequentially forming conductor layer 43, insulating layer 52, conductor layer 42, insulating layer 51, and conductor layer 41, and forming optical waveguide 101 on the laminate of these layers by the manufacturing method described with reference to FIGS. 8A to 8D. Optical waveguide 101 may be separately manufactured on a support plate (not shown) that supports optical waveguide 101 during manufacture, and then disposed on wiring board 100 before optical waveguide arrangement, after removing the support plate or with the support plate still attached.

[0107] The conductor layer 43 is formed on a support substrate (not shown) such as a double-sided copper-clad laminate by, for example, a semi-additive method. After the conductor layer 43 is formed, an insulating layer 52 covering the conductor layer 43 is formed by, for example, laminating and thermocompression bonding an insulating resin such as a film-like epoxy resin. A through hole is formed in the insulating layer 52 by, for example, irradiation with a carbon dioxide laser beam. After the through hole is formed, the conductor layer 42 is formed on the insulating layer 52 by, for example, a semi-additive method, and the via conductor 7 is formed in the through hole of the insulating layer 52. Furthermore, an insulating layer 51 is formed on the conductor layer 42 and the insulating layer 52 by the same method as the insulating layer 52. A conductor layer 41 is formed on the insulating layer 51 by the same method as the conductor layer 42. In the insulating layer 51, a via conductor 7 is formed by the same method as the via conductor 7 in the insulating layer 52. After the support substrate is removed by peeling or the like, solder resists 61 and 62 are formed by applying or spraying a photosensitive epoxy resin. The solder resists 61 and 62 are exposed and developed to form openings such as opening 61a that expose parts of the conductor layer 41 and parts of the conductor layer 43.

[0108] Then, the optical waveguide 101 is manufactured on the surface of the conductor layer 41 side of the laminate of the conductor layers 41-42 and the insulating layers 51, 52 by the method described with reference to Figs. 8A-8D. Alternatively, the optical waveguide 101 may be separately manufactured on an arbitrary support plate (not shown) and then disposed thereon. For example, an arbitrary adhesive (not shown), such as a thermosetting, room temperature curing, or photocuring adhesive, is supplied onto the surface of the solder resist 61, and the optical waveguide 101 is mounted thereon. If necessary, the adhesive is cured by heating or the like, and the optical waveguide 101 is fixed onto the laminate of the conductor layers and the insulating layers. After the optical waveguide 101 is manufactured or disposed, the bump 8 is formed by mounting a conductive ball by solder or the like and performing a reflow process. Through the above steps, the wiring board 100 of the example of Fig. 7 is completed.

[0109] 7, the optical waveguide 101 may be manufactured on an area on the surface of the insulating layer 51 where the solder resist 61 and the conductor layer 41 are not provided, or may be disposed on an area on the surface of the insulating layer 51 where the solder resist 61 and the conductor layer 41 are not provided. The optical waveguide 101 may be disposed on the surface of a laminate of a conductor layer and an insulating layer while still including a support plate (not shown) used in manufacturing the optical waveguide 101.

[0110] The optical waveguide and wiring board of the embodiment are not limited to those having the structures illustrated in the drawings and the structures, shapes, and materials illustrated in this specification. The wiring board of the embodiment may have any laminated structure and may include any number of conductor layers and insulating layers. For example, the wiring board of the embodiment may be a build-up wiring board including a core substrate, a multilayer wiring board without a build-up layer, or a double-sided or single-sided wiring board. The bump 8 may not be formed, and the via conductor 7 is not necessarily provided. In addition, the thickness of the core of the optical waveguide of the embodiment may vary in each of the core exposed portion and the core unexposed portion. [Explanation of symbols]

[0111] 1, 10a~10d, 101 optical waveguide 100 wiring board 1a Upper cladding-free region 1aa First upper cladding-free region 1ab Second upper cladding-free region 1b, 1ba, 1bb Upper cladding formation region 2. Clad 21 Lower Cladding 22 Upper Cladding 3 Cores 3α One end of the core 3β The other end of the core 3a Exposed core 3aa First core exposed part 3ab Second core exposed part 3b, 3b1, 3b2 Core non-exposed part 3c, 3c1, 3c2 connection 31 Top of the core 4 Component mounting pads 41~43 Conductor layer 51~52 Insulation layer L11 Length of exposed part of first core L12 Length of exposed part of second core W11 Width of exposed first core W12 Width of exposed second core W21 Width of non-exposed core part 3b1 W22 Width of non-exposed core part 3b2 W31 Width of core joint 3c1 W32 Width of core joint 3c2

Claims

1. An optical waveguide in which a lower clad, a core, and an upper clad are laminated in this order, and a part of the core on the side where an optical signal is incident and a part of the core on the side where an optical signal is emitted are exposed, the optical waveguide comprises an upper cladding non-forming region and an upper cladding forming region, the upper cladding non-forming region has a core exposed portion at one end of the core and at the other end of the core, where an upper surface of the core is exposed; the upper cladding region has a core non-exposed portion where the upper surface of the core is not exposed; The core of the core exposed portion located at the one end has a width (W11), The core of the core exposed portion located at the other end has a width (W12), The core of the non-exposed core portion on the one end side has a width (W21), The core of the non-exposed portion on the other end has a width (W22), The core width (W11), the core width (W12), the core width (W21), and the core width (W22) satisfy the relationships of the following formulas 1 and 2. W11>W21...(Formula 1) W12>W22...(Formula 2)

2. 2. The optical waveguide according to claim 1, The width (W11) of the core and the width (W21) of the core satisfy the relationship of the following formula 3, 1.0<W11 / W21≦3.0 (Formula 3) The width (W12) of the core and the width (W22) of the core satisfy the relationship of the following formula 4. 1.0<W12 / W22≦3.0 (Formula 4)

3. 2. The optical waveguide according to claim 1, wherein the core width (W11) and the core width (W12) are 3 μm or more and 30 μm or less, respectively.

4. 2. The optical waveguide according to claim 1, wherein the length of the core of the core exposed portion located on the one end side and the length of the core of the core exposed portion located on the other end side are 100 μm or more and 3000 μm or less.

5. 2. The optical waveguide according to claim 1, The core has a connection portion that connects the core exposed portion and the core unexposed portion.

6. 2. The optical waveguide according to claim 1, the core has a connection portion connecting the core exposed portion and the core unexposed portion, The connection portion has a taper in a plan view.

7. 6. The optical waveguide according to claim 5, The connection portions are arranged in a straight line of a constant width in a plan view.

8. 6. The optical waveguide according to claim 5, The connection portions are arranged as a combination of straight lines of a constant width and tapers in a plan view.

9. 6. The optical waveguide according to claim 5, A width (W31) of the core of the connection portion in contact with the core exposed portion located at the one end, a width (W11) of the core, and a width (W21) of the core satisfy the relationship of the following formula 5, The width (W32) of the core of the connection portion in contact with the core exposed portion located at the other end, the width (W12) of the core, and the width (W22) of the core satisfy the relationship of the following formula 6. W11>W31≧W21 (Formula 5) W12>W32≧W22 (Formula 6)

10. A wiring board having an insulating layer and a conductor layer, the wiring board comprising the optical waveguide according to claim 1 and a component mounting pad, The optical waveguide is disposed on a surface of the wiring board.

Images