Optical circuit board and optical component mounting structure

Abstract

An optical circuit board according to the present disclosure can easily determine an irradiation position of light when performing inspection and can efficiently perform the inspection of an optical waveguide.　An optical circuit board (1) according to the present disclosure includes a wiring board (2), and a first optical waveguide (31) and a second optical waveguide (32) positioned on the wiring board (2). The first optical waveguide (31) includes first lower cladding (311), a first core (312), and first upper cladding (313) covering at least a portion of the fire core. The second optical waveguide (32) includes second lower cladding (321), a second core (322), and second upper cladding (323) covering at least a portion of the second core. The second optical waveguide (32) has a first end face (3a) where a first core end face (322a) of a second core is exposed to an outer edge side of a wiring board, and a second end face (3b) where a second core end face (322b) of a second core is exposed to the central side of the wiring board. A gap (324) is present between the second core (322) and the second upper cladding (323) at the first end face (3a) and / or second end face (3b).

Description

Optical circuit board and optical component mounting structure

[0001] The present invention relates to an optical circuit board and an optical component mounting structure using the same.

[0002] In recent years, optical fibers capable of transmitting large volumes of data at high speeds have come to be used in information communications. Optical signals are transmitted and received between these optical fibers and optical components. Such optical components are mounted on, for example, optical circuit boards. The optical circuit boards are provided with optical waveguides. Optical signals are transmitted and received via these optical waveguides. Optical circuit boards used for transmitting and receiving optical signals need to be inspected to determine whether the transmission and reception of optical signals is performed normally, as described in Patent Document 1, for example.

[0003] Japanese Patent Application Laid-Open No. 2015-215469

[0004] The optical circuit board according to the present disclosure includes a wiring substrate, a first optical waveguide located on the wiring substrate, and a second optical waveguide located on the wiring substrate adjacent to the first optical waveguide. The first optical waveguide includes a first lower clad located on the wiring substrate, a first core extending on the first lower clad from the outer edge of the wiring substrate to the center of the wiring substrate, and a first upper clad covering at least a portion of the first core. The second optical waveguide includes a second lower clad located on the wiring substrate, a second core located on the second lower clad along the first core, and a second upper clad covering at least a portion of the second core. The second optical waveguide has a first end face at the outer edge of the wiring substrate where the first core end face of the second core is exposed, and a second end face at the center of the wiring substrate where the second core end face of the second core is exposed. A gap exists between the second core and the second upper clad at at least one of the first end face and the second end face.

[0005] An optical component mounting structure according to the present disclosure includes the optical circuit board and an optical component mounted on the optical circuit board.

[0006] Fig. 3 is a plan view showing an optical component mounting structure in which optical components and electronic components are mounted on an optical circuit board according to an embodiment of the present disclosure. Fig. 4 is an enlarged explanatory view for illustrating a cross section of region R1 shown in Fig. 1. Fig. 5 is a plan view seen from the direction of arrow A shown in Fig. 2. Fig. 6 is an explanatory view for illustrating a cross section cut along line X-X shown in Fig. 3. Fig. 7 is an explanatory view for illustrating a process of forming a first optical waveguide and a second optical waveguide in an optical circuit board according to an embodiment of the present disclosure.

[0007] Optical continuity testing requires that a thin beam of light (e.g., approximately 9 μm in diameter) be incident on each core included in an optical waveguide. However, with conventional optical circuit boards, it is difficult to visually identify the cores at the end face of the optical waveguide, and it is also difficult to determine the position for incident light. Therefore, there is a demand for an optical circuit board that allows easy determination of the light incident position during testing and has excellent optical waveguide testing efficiency.

[0008] The optical circuit board according to the present disclosure has a configuration as described in the section on means for solving the problem, which makes it easy to determine the incident position of light during inspection, thereby enabling efficient inspection of optical waveguides.

[0009] An optical circuit board according to an embodiment of the present disclosure will be described with reference to Figures 1 to 4. Figure 1 is a plan view showing an optical component mounting structure 10 in which an optical component 4 is mounted on an optical circuit board 1 according to an embodiment of the present disclosure.

[0010] An optical circuit board 1 according to an embodiment of the present disclosure includes a wiring board 2 and an optical waveguide 3. Examples of the wiring board 2 included in the optical circuit board 1 according to an embodiment include wiring boards that are generally used for optical circuit boards.

[0011] Although not specifically illustrated, such wiring board 2 includes, for example, a core substrate and build-up layers laminated on both sides of the core substrate. The core substrate is not particularly limited as long as it is made of an insulating material. Examples of insulating materials include resins such as epoxy resin, bismaleimide-triazine resin, polyimide resin, and polyphenylene ether resin. Two or more of these resins may be mixed and used. The core substrate usually has through-hole conductors to electrically connect the top and bottom surfaces of the core substrate.

[0012] The core substrate may contain a reinforcing material. Examples of the reinforcing material include insulating fabric materials such as glass fiber, glass nonwoven fabric, aramid nonwoven fabric, aramid fiber, and polyester fiber. Two or more types of reinforcing materials may be used in combination. Furthermore, the core substrate may have dispersed therein an inorganic filler such as silica, barium sulfate, talc, clay, glass, calcium carbonate, or titanium oxide.

[0013] The build-up layer has a structure in which insulating layers and conductor layers are alternately laminated. A portion of the conductor layer located on the outermost surface (the conductor layer located on the upper surface of the wiring substrate 2) includes a conductor layer 21a where the optical waveguide 3 is located. The conductor layer 21a is formed of a metal such as copper. Like the core substrate, the insulating layer included in the build-up layer is not particularly limited as long as it is made of an insulating material. Examples of insulating materials include resins such as epoxy resin, bismaleimide-triazine resin, polyimide resin, and polyphenylene ether resin. Two or more of these resins may be mixed and used.

[0014] When two or more insulating layers are present in the build-up layer, the insulating layers may be made of the same resin or different resins. The insulating layers included in the build-up layer and the core substrate may be made of the same resin or different resins. The build-up layer usually has via-hole conductors for electrically connecting the layers.

[0015] Furthermore, the insulating layer included in the build-up layer may have inorganic fillers such as silica, barium sulfate, talc, clay, glass, calcium carbonate, and titanium oxide dispersed therein.

[0016] As shown in Fig. 2, the optical waveguide 3 included in the optical circuit board 1 according to one embodiment is located on the upper surface of a conductor layer 21a that is present on the upper surface of the wiring board 2. Fig. 2 is an enlarged explanatory view illustrating a cross section of region R1 shown in Fig. 1. One end of the optical waveguide 3 faces an optical component 4 that includes an optical transmission line 41. The other end of the optical waveguide 3 is connected to an optical connector 5a that includes an optical fiber 5.

[0017] As shown in Fig. 3, the optical waveguide 3 includes a first optical waveguide 31 and a second optical waveguide 32. Fig. 3 is a plan view seen from the direction of arrow A shown in Fig. 2. As shown in Fig. 4, the first optical waveguide 31 includes a first lower clad 311, a first core 312, and a first upper clad 313. Fig. 4 is an explanatory diagram for describing a cross section taken along line X-X shown in Fig. 3.

[0018] The first lower clad 311 included in the first optical waveguide 31 is located on the upper surface of the wiring substrate 2, specifically on the upper surface of the conductor layer 21a present on the upper surface of the wiring substrate 2. The material forming the first lower clad 311 is not limited, and examples thereof include resins such as epoxy resin and silicone resin.

[0019] The first core 312 included in the first optical waveguide 31 is located on the upper surface of the first lower clad 311. The first core 312 extends from the outer edge side of the wiring board 2 to the center side of the wiring board 2. In other words, in FIG. 2 , the outer edge side of the wiring board 2 refers to the side (outer periphery) where the optical connector 5a is located, and the center side of the wiring board 2 refers to the side where the optical component 4 is located. The first core 312 is a portion through which light that has entered the first optical waveguide 31 propagates. That is, optical signals are transmitted and received between the first core 312 and the optical transmission path 41. Therefore, one end face of the first core 312 is located so as to face the end face of the optical transmission path 41 included in the optical component 4 mounted on the wiring board 2.

[0020] The material forming the first core 312 is not limited and may be appropriately selected taking into consideration, for example, the light transmittance and the wavelength characteristics of the propagating light. Examples of the material include resins such as epoxy resin and silicone resin. The first core 312 has a thickness of, for example, approximately 3 μm or more and 50 μm or less.

[0021] The first upper clad 313 included in the first optical waveguide 31 is positioned so as to cover at least a portion of the first core 312. Like the first lower clad 311, the first upper clad 313 is also formed of a resin such as an epoxy resin or a silicone resin. The first lower clad 311 and the first upper clad 313 may be made of the same material or different materials. Furthermore, the first lower clad 311 and the first upper clad 313 may have the same thickness or different thicknesses. The first lower clad 311 and the first upper clad 313 have a thickness of, for example, approximately 5 μm or more and 150 μm or less.

[0022] The second optical waveguide 32 is located adjacent to the first optical waveguide 31. Specifically, the second optical waveguide 32 is located along the first optical waveguide 31 so as to sandwich the first optical waveguide 31. The second optical waveguide 32 is used for positioning the first optical waveguide 31 for the incidence of light when performing an optical continuity test on the first optical waveguide 31.

[0023] The second lower clad 321 included in the second optical waveguide 32, like the first lower clad 311, is located on the upper surface of the wiring substrate 2, specifically on the upper surface of the conductor layer 21a present on the upper surface of the wiring substrate 2. The material forming the second lower clad 321 is not limited, and like the first lower clad 311, examples of the material include resins such as epoxy resin and silicone resin. The second lower clad 321 may be formed from the same material (resin) as the first lower clad 311, or may be formed from a different material (resin).

[0024] 4, the second lower cladding 321 may be integrated with the first lower cladding 311, or may be separate from the first lower cladding 311. For example, if the second lower cladding 321 and the first lower cladding 311 are integrated, the process of forming the first optical waveguide 31 and the second optical waveguide 32 can be simplified.

[0025] The second core 322 included in the second optical waveguide 32 is located on the upper surface of the second lower clad 321. The second core 322 is located along the first core 312 included in the first optical waveguide 31. The material forming the second core 322 is not limited, and examples thereof include resins such as epoxy resin and silicone resin, similar to the material forming the first core 312. Since the first core 312 and the second core 322 are typically formed simultaneously, the material (resin) forming the first core 312 and the material (resin) forming the second core 322 may be the same. Similar to the first core 312, the second core 322 has a thickness of, for example, approximately 3 μm or more and 50 μm or less.

[0026] The second optical waveguide 32 has a first end face 3a on the outer edge side of the wiring board 2 and a second end face 3b on the central side of the wiring board 2. That is, in Fig. 3, the end face located on the optical connector 5a side is the first end face 3a, and the end face located on the optical component 4 side is the second end face 3b. The second core 322 has a first core end face 322a on the outer edge side of the wiring board 2 and a second core end face 322b on the central side of the wiring board 2. That is, the first core end face 322a is a part of the first end face 3a, and the second core end face 322b is a part of the second end face 3b.

[0027] The second upper clad 323 included in the second optical waveguide 32 is positioned so as to cover at least a portion of the second core 322. Like the second lower clad 321, the second upper clad 323 is also formed of a resin such as an epoxy resin or a silicone resin. The second lower clad 321 and the second upper clad 323 may be made of the same material or different materials. Furthermore, the second lower clad 321 and the second upper clad 323 may have the same thickness or different thicknesses. The second lower clad 321 and the second upper clad 323 have a thickness of, for example, approximately 5 μm or more and 150 μm or less. The second upper clad 323 is usually formed simultaneously with the first upper clad 313 included in the first optical waveguide 31. Therefore, the second upper clad 323 may have the same thickness as the first upper clad 313.

[0028] As described above, the second lower cladding 321 may be integrated with the first lower cladding 311. On the other hand, as shown in Fig. 4, the second upper cladding 323 may be located independently from the first upper cladding 313. When the second upper cladding 323 is located independently from the first upper cladding 313, even if the second upper cladding 323 is separated from the second core 322, it is less likely to affect the first core 312, which transmits and receives optical signals.

[0029] 4 exists between the second core 322 and the second upper clad 323 at least on the first end face 3 a and the second end face 3 b of the second optical waveguide 32. The existence of such a gap 324 makes it possible to visually recognize the gap 324 when performing an optical continuity test. As a result, the position of the second core 322 can be recognized, and from the position of the second core 322, the position of the first core 312 for which an optical continuity test is to be performed can be easily recognized.

[0030] The reason why no gap 324 is formed between the first core 312 and the first upper clad 313 is that the presence of the gap 324 between the first core 312 and the first upper clad 313 increases transmission loss. Therefore, a second core 322 that does not transmit or receive optical signals is formed, and a visible gap 324 is formed near the second core 322. Positioning for making a light beam incident on the first core 312 is performed based on the visible gap 324.

[0031] The second core 322 may have multiple side surfaces connecting the first core end face 322a and the second core end face 322b. The number of side surfaces varies depending on the cross-sectional shape of the second core 322. For example, as shown in FIG. 4 , when the cross-sectional shape of the second core 322 is rectangular, there are two side surfaces. In other words, when the second core 322 is viewed in cross section, the surfaces other than the surface in contact with the second lower cladding 321 and the surface facing that surface are side surfaces. For example, when the cross-sectional shape of the second core 322 is hexagonal, there are four side surfaces.

[0032] A gap 324 may exist between at least one of the side surfaces of the second core 322 and the second upper clad 323. Due to the existence of the gap 324 between at least one of the side surfaces and the second upper clad 323, the lower surface of the second core 322 contacts the second lower clad 321 and the upper surface of the second core 322 contacts the second upper clad 323. As a result, separation of the second core 322 from the second lower clad 321 or the second upper clad 323 can be reduced.

[0033] The multiple side surfaces of the second core 322 may include, for example, a first side surface and a second side surface that face each other, and the gaps 324 may exist in both the first side surface and the second side surface. Specifically, when the cross-sectional shape of the second core 322 is rectangular, the two side surfaces face each other, with one side surface being the first side surface and the other being the second side surface. The presence of the gaps 324 in both the facing first side surface and second side surface allows the position of the second core 322 to be more accurately visually recognized. As a result, the incident position of the light beam can be determined with greater precision. There may be multiple gaps 324 on each of the first side surface and the second side surface, or multiple gaps on only one side. Furthermore, the gaps 324 may be located continuously or discontinuously between the first core end surface 322a and the second core end surface 322b.

[0034] A plurality of gaps 324 may be present on at least one of the first end face 3 a and the second end face 3 b. For example, in FIG. 4 , two gaps 324 are present, one on each side face (first side face and second side face) of the second core 322 and the second upper cladding 323. The presence of multiple gaps 324 can improve visibility. As a result, the incident position of the light beam can be determined with greater precision. In FIG. 4 , one gap 324 is present on one side face, but multiple gaps 324 may be present on one side face.

[0035] A gap 324 existing between at least one side surface of the second core 322 and the second upper clad 323 may be in contact with the second lower clad 321 or may be separated from the second lower clad 321. For example, when the gap 324 is in contact with the second lower clad 321, it is easy to identify the boundary between the second lower clad 321 and the second core 322. As a result, the positioning of the incident light beam in the height direction of the first optical waveguide 31 can be performed with higher accuracy.

[0036] The gap 324 may be present continuously from the first end face 3 a to the second end face 3 b, or may be present intermittently. If the gap 324 is present continuously, when forming the optical waveguide 3, for example, by cutting both end faces to form the first end face 3 a and the second end face 3 b, the gap 324 can be present at the first end face 3 a and the second end face 3 b even if any part is cut. If the gap 324 is present intermittently, this is advantageous in that adhesion between the second core 322 and the second upper clad 323 can be ensured.

[0037] As described above, according to the present disclosure, the second core 322 can improve the inspection efficiency of the optical waveguide 3, and an optical circuit board 1 with excellent optical transmission can be provided.

[0038] Next, one embodiment of a method for forming the first optical waveguide 31 and the second optical waveguide 32 will be described with reference to Fig. 5. Fig. 5 is an explanatory diagram for explaining the process of forming the first optical waveguide 31 and the second optical waveguide 32 in the optical circuit board 1 according to one embodiment. In Fig. 5, the diagram on the right side shows an enlarged view of the area surrounded by a dashed line in the diagram on the left side.

[0039] First, the first lower clad 311 and the second lower clad 321 are formed on the upper surface of the wiring substrate 2 (the conductor layer 21 a). The first lower clad 311 and the second lower clad 321 are as described above, and a detailed description thereof will be omitted. The first lower clad 311 and the second lower clad 321 shown in FIG. 5 are integrated.

[0040] 5A, the materials for the first core 312 and the second core 322 are disposed on the upper surfaces of the first lower clad 311 and the second lower clad 321. Examples of such materials include uncured resins such as epoxy resin and silicone resin.

[0041] Next, an exposure mask M1 is placed so as to cover the uncured resin. The exposure mask M1 has openings, and the first core 312 and the second core 322 are formed at the positions of these openings. After the exposure mask M1 is placed, exposure and development are performed to form the first core 312 on the upper surface of the first lower clad 311 and the second core 322 on the upper surface of the second lower clad 321, as shown in FIG. 5B . During exposure, even the portions covered by the exposure mask M1 are slightly affected by the exposure near the openings. As a result, insufficiently cured resin remains near the side surfaces of the first core 312 and the second core 322.

[0042] 5C, materials for the first upper clad 313 and the second upper clad 323 are disposed so as to cover the first core 312 and the second core 322. Examples of such materials include uncured resins such as epoxy resins and silicone resins. Next, a half-tone mask M2 is disposed so as to cover the uncured resins.

[0043] The half-tone mask M2 is a mask having a half-tone portion H in which the amount of exposure is suppressed by reducing the transmittance. The transmittance of the half-tone portion H is, for example, about 40% of the usual transmittance (specifically, about 40±10%). The boundary between the first upper clad 313 and the second upper clad 323 is shielded from exposure. After the half-tone mask M2 is placed, exposure and development are performed, whereby the first upper clad 313 is formed to cover the first core 312, and the second upper clad 323 is formed to cover the second core 322, as shown in FIG. 5(D). Because the boundary between the first upper clad 313 and the second upper clad 323 is shielded from exposure and does not harden, the first upper clad 313 and the second upper clad 323 are positioned independently of each other.

[0044] As described above, in the portion corresponding to the second optical waveguide 32, for example, insufficiently cured resin exists near the side surface of the second core 322. Furthermore, when the second upper clad 323 is exposed, the portion corresponding to the second optical waveguide 32 is exposed with a smaller amount of light than the amount of exposure of the first upper clad 313. As a result, the curing reaction does not progress particularly between the side surface of the second core 322 and the second upper clad 323, and gaps 324 are likely to form.

[0045] The portion corresponding to the first optical waveguide 31 is exposed to light with a transmittance required for curing when the first upper clad 313 is exposed to light. This allows a sufficient curing reaction to proceed between the insufficiently cured resin present near the side surface of the first core 312 and the first upper clad 313. As a result, the first core 312 and the first upper clad 313 are sufficiently adhered to each other, and no gap 324 is formed.

[0046] Next, an optical component mounting structure 10 in which an optical component 4 and an electronic component 6 are mounted on an optical circuit board 1 according to one embodiment will be described. As shown in Fig. 1 , the optical component 4 mounted on the optical component mounting structure 10 according to one embodiment includes an optical transmission line 41. Examples of the optical component 4 including such an optical transmission line 41 include a silicon photonics device. Examples of the electronic component 6 include an ASIC (Application Specific Integrated Circuit) and a driver IC.

[0047] 2, the optical component 4 is electrically connected to a pad 21b located in a mounting area (area for mounting the optical component 4) of the wiring board 2 via solder 7. The pad 21b is part of a conductor layer located on the upper surface of the wiring board 2.

[0048] A silicon photonics device will be described as an example of the optical component 4. The silicon photonics device has, for example, a silicon (Si) core and silicon dioxide (SiO ２The silicon photonics device is a type of optical component having an optical transmission line 41 with a cladding of Si (Si-based) waveguide. The silicon photonics device includes a Si waveguide as the optical transmission line 41, and further includes a passivation film, a light source unit, a photodetector unit, and the like, which are not shown. As described above, the optical transmission line 41 (Si waveguide 41) is located at one end of the first optical waveguide 31 so as to face the first core 312 included in the first optical waveguide 31.

[0049] For example, an electrical signal from wiring board 2 is propagated via solder 7 to a light source unit included in optical component 4 (silicon photonics device). The light source unit receives the propagated electrical signal and emits light. The emitted optical signal is propagated via optical transmission path 41 (Si waveguide 41) and first core 312 to optical fiber 5 connected via optical connector 5a. Optical component mounting structure 10 according to an embodiment of the present disclosure is capable of reducing optical transmission loss because optical component 4 is mounted on optical circuit board 1, which has excellent optical transmission properties.

[0050] Although the embodiments of the present disclosure have been described above, the invention according to the present disclosure is not limited to the above-described embodiments, and various modifications and improvements are possible within the scope of the present disclosure as shown in (1) and (8) below.

[0051] (1) An optical circuit board according to the present disclosure includes a wiring substrate, a first optical waveguide located on the wiring substrate, and a second optical waveguide located on the wiring substrate adjacent to the first optical waveguide. The first optical waveguide includes a first lower clad located on the wiring substrate, a first core extending on the first lower clad from the outer edge of the wiring substrate to the center of the wiring substrate, and a first upper clad covering at least a portion of the first core. The second optical waveguide includes a second lower clad located on the wiring substrate, a second core located on the second lower clad along the first core, and a second upper clad covering at least a portion of the second core. The second optical waveguide has a first end face at the outer edge of the wiring substrate where the first core end face of the second core is exposed, and a second end face at the center of the wiring substrate where the second core end face of the second core is exposed. A gap exists between the second core and the second upper clad at at least one of the first end face and the second end face.

[0052] The present disclosure further discloses the following embodiments (2) to (7).

[0053] (2) In the optical circuit board described in (1) above, the second core has a plurality of side surfaces connecting the first core end face and the second core end face, and a gap exists between at least one of the plurality of side surfaces of the second core and the second upper cladding. (3) In the optical circuit board described in (1) or (2) above, the gap exists continuously or intermittently from the first end face to the second end face. (4) In the optical circuit board described in any of (1) to (3) above, a plurality of gaps exist in at least one of the first end face and the second end face. (5) In the optical circuit board described in any of (1) to (4) above, the gaps contact the second lower cladding. (6) In the optical circuit board described in any of (2) to (5) above, the plurality of side surfaces of the second core include a first side face and a second side face facing each other, and the gaps exist on both sides of the first side face and the second side face. (7) In the optical circuit board according to any one of (1) to (6) above, the first lower clad and the second lower clad are integrated.

[0054] (8) An optical component mounting structure according to the present disclosure includes the optical circuit board according to any one of (1) to (7) above and an optical component mounted on the optical circuit board.

[0055] REFERENCE SIGNS LIST 1 Optical circuit board 2 Wiring board 21a Conductor layer 21b Pad 3 Optical waveguide 31 First optical waveguide 311 First lower clad 312 First core 313 First upper clad 32 Second optical waveguide 321 Second lower clad 322 Second core 322a First core end face 322b Second core end face 323 Second upper clad 324 Gap 3a First end face 3b Second end face 4 Optical component 41 Optical transmission path (silicon waveguide (Si waveguide)) 5 Optical fiber 5a Optical connector 6 Electronic component 7 Solder 10 Optical component mounting structure

Claims

1. A wiring board; a first optical waveguide located on the wiring substrate; a second optical waveguide located adjacent to the first optical waveguide on the wiring substrate; Including, the first optical waveguide includes a first lower clad located on the wiring board, a first core extending on the first lower clad from an outer edge side of the wiring board to a center side of the wiring board, and a first upper clad covering at least a portion of the first core, the second optical waveguide includes a second lower clad located on the wiring substrate, a second core located on the second lower clad along the first core, and a second upper clad covering at least a portion of the second core; the second optical waveguide has a first end face at which a first core end face of the second core is exposed on an outer edge side of the wiring board, and a second end face at which a second core end face of the second core is exposed on a central side of the wiring board, a gap exists between the second core and the second upper cladding at at least one of the first end face and the second end face; Optical circuit board.

2. the second core has a plurality of side surfaces connecting the first core end surface and the second core end surface, The optical circuit board according to claim 1 , wherein the gap exists between at least one of the plurality of side surfaces of the second core and the second upper cladding.

3. The optical circuit board according to claim 1 , wherein the gap exists continuously or discontinuously from the first end face to the second end face.

4. The optical circuit board according to claim 1 , wherein a plurality of the gaps are present in at least one of the first end face and the second end face.

5. The optical circuit board according to claim 1 , wherein the gap is in contact with the second lower clad.

6. the plurality of side surfaces of the second core include a first side surface and a second side surface opposed to each other, The optical circuit board according to claim 2 , wherein the gap exists on both the first side surface and the second side surface.

7. The optical circuit board according to claim 1 , wherein the first lower clad and the second lower clad are integrated together.

8. An optical circuit board according to any one of claims 1 to 7, an optical component mounted on the optical circuit board; An optical component mounting structure having: