Optical circuit board

Abstract

An optical circuit board (1) according to the present disclosure comprises: a wiring board (2); a lower clad (31) that is positioned on the wiring board (2) and has a first region (311) and a second region (312); an optical waveguide (3) that is positioned on the first region (311) and includes a core (32) and an upper clad (33); and a guide structure (34) that is positioned on the second region (312) so as to be adjacent to the optical waveguide (3). The guide structure (34) has at least: a first portion (341) and a second portion (342) that are adjacent to each other and extend from the outer edge side of the wiring board (2) toward the central side in plane view; a third portion (343) extending from the end on the central side of the first portion (341) so as to go away from the second portion (342); and a fourth portion (344) extending from the end on the central side of the second portion (342) so as to go away from the first portion (341). The third portion (343) and the fourth portion (344) each include at least one of a first protrusion (34a) and a second protrusion (34b).

Description

[Technical Field]

[0001] The present invention relates to an optical circuit board and an optical module using the same. [Background technology]

[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 the optical fibers and optical components. Such optical components are mounted on optical circuit boards, as described in Patent Document 1, for example. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6264832 Summary of the Invention [Means for solving the problem]

[0004] The optical circuit board according to the present disclosure includes a wiring substrate, a lower clad located on the wiring substrate and having a first region and a second region, an optical waveguide located on the first region and including a core and an upper clad, and a guide structure located on the second region adjacent to the optical waveguide. The guide structure has at least a first portion and a second portion extending adjacent to each other from the outer edge of the wiring substrate toward the center in a plan view, a third portion extending from the center end of the first portion away from the second portion, and a fourth portion extending from the center end of the second portion away from the first portion. The third portion and the fourth portion include at least one of a first protrusion and a second protrusion. The first protrusion protrudes from at least one of two side edges of the third portion opposite the side adjacent to the first portion and one of two side edges of the fourth portion opposite the side adjacent to the second portion in a plan view. The second protrusion is a protrusion that protrudes into the lower clad from at least one of the third portion and the fourth portion in a cross-sectional view.

[0005] An optical module according to the present disclosure includes the above-described optical circuit board, and an optical connector abutting against the guide structure and connected to the optical circuit board. [Brief explanation of the drawings]

[0006] [Figure 1] 1 is a plan view showing an optical module in which optical components and electronic components are mounted on an optical circuit board according to an embodiment of the present disclosure. [Figure 2] 2 is an enlarged explanatory view for illustrating a cross section passing through an optical waveguide core in a region R1 shown in FIG. 1. FIG. [Figure 3] 3 is an enlarged explanatory view for explaining the state of a region R2 shown in FIG. 2 before and after connecting the optical waveguide and the optical connector. FIG. [Figure 4] FIG. 4 is a plan view seen from the direction of arrow A shown in FIG. [Figure 5] FIG. 5 is an enlarged explanatory view for explaining a region R3 shown in FIG. 4. [Figure 6] 6 is an explanatory diagram for explaining various embodiments of a cross section taken along line aa shown in FIG. 5. FIG. [Figure 7] 6A to 6C are explanatory views for explaining various embodiments of the cross section taken along line bb shown in FIG. 5. [Figure 8] 1 is an enlarged cross-sectional view of a main part of an optical connector connected to an optical circuit board. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0007] Conventional optical waveguides may not be mounted accurately due to poor formation of connector guides arranged at the edge of the substrate or peeling of the connector guide, as described in Patent Document 1. Therefore, there is a demand for an optical circuit board that can be connected to a connector with high accuracy even at the edge of the substrate.

[0008] The optical circuit board according to the present disclosure has a configuration as described in the section on means for solving the problems, and thus can be connected to a connector with high precision even at the edge of the board.

[0009] An optical circuit board according to an embodiment of the present disclosure will be described with reference to Figures 1 to 8. Figure 1 is a plan view showing an optical module 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 shown, such a 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 reinforcing materials include insulating fabric materials such as glass fiber, glass nonwoven fabric, aramid nonwoven fabric, aramid fiber, and polyester fiber. Two or more 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 part of the conductor layer located on the outermost surface (the conductor layer located on the upper surface of the wiring board 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, an optical waveguide 3 included in an optical circuit board 1 according to one embodiment is located on the surface of a conductor layer 21a that is present on the surface of a wiring board 2. Fig. 2 is an enlarged explanatory view illustrating a cross section of region R1 shown in Fig. 1. The optical waveguide 3 has a structure in which a lower clad 31, an optical waveguide core 32, and an upper clad 33 are laminated in this order from the conductor layer 21a side.

[0017] The lower clad 31 included in the optical waveguide 3 is located on the surface of the wiring board 2, specifically on the surface of the conductor layer 21a present on the surface of the wiring board 2. The lower clad 31 has a first region 311 in which an optical waveguide core 32 (described later) is located and a second region 312 in which a guide structure 34 (described later) is located. The material from which the lower clad 31 is formed is not limited, and examples include resins such as epoxy resin and silicone resin.

[0018] The upper clad 33 included in the optical waveguide 3 is located in the first region 311. Like the lower clad 31, the upper clad 33 is also formed of a resin such as an epoxy resin or a silicone resin. The lower clad 31 and the upper clad 33 may be made of the same material or different materials. Furthermore, the lower clad 31 and the upper clad 33 may have the same thickness or different thicknesses. The lower clad 31 and the upper clad 33 each have a thickness of, for example, about 5 μm or more and 150 μm or less.

[0019] The optical waveguide core 32 included in the optical waveguide 3 is located in the first region 311. The optical waveguide core 32 is a portion through which light that has entered the optical waveguide 3 propagates. Specifically, the optical waveguide core 32 is located so that an end face of the optical transmission line 41 included in the optical component 4 mounted on the wiring board 2 faces an end face of the optical waveguide core 32 of the optical waveguide 3. As shown in FIG. 2 , the end face of the optical waveguide 3 including the end face of the optical waveguide core 32 facing the optical component 4 mounted on the wiring board 2 is referred to as a first end face 3a.

[0020] Optical signals are transmitted and received between the optical waveguide core 32 and the optical transmission line 41 at this first end face 3a. The material forming the optical waveguide core 32 is not limited and is 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 optical waveguide core 32 has a thickness of, for example, approximately 3 μm or more and 50 μm or less.

[0021] In the optical waveguide 3, the end face located opposite to the first end face 3a is the second end face 3b, and the end face of the lower clad 31, the end face of the optical waveguide core 32, and the end face of the upper clad 33 are included in the same plane. Specifically, as shown in Fig. 2, in the optical waveguide 3, the end face facing the optical connector 5a is the second end face 3b.

[0022] Region R2 shown in Fig. 2 will be described with reference to Figs. 3 and 4. Fig. 3 is an enlarged explanatory view (perspective view) for describing the state of region R2 shown in Fig. 2 before and after connecting the optical waveguide 3 and the optical connector 5a. Fig. 4 is a plan view seen from the direction of arrow A shown in Fig. 3, and the portion covered by the optical connector 5a is depicted as a perspective view. For ease of explanation, the direction parallel to the optical waveguide core 32 is defined as the X direction, and the direction perpendicular to the optical waveguide core 32 is defined as the Y direction.

[0023] As shown in FIGS. 3 and 4, the lower clad 31 included in the optical waveguide 3 has a first region 311 and a second region 312. An optical waveguide core 32 and an upper clad 33 (not shown for convenience of explanation) are located in the first region 311 of the lower clad 31, thereby constituting the optical waveguide 3. Meanwhile, a guide structure 34 is located in the second region 312 of the lower clad 31 so as to be adjacent to the optical waveguide 3 (the first region 311 of the lower clad 31, the optical waveguide core 32, and the upper clad 33). For example, as shown in FIGS. 3 and 4, the guide structures 34 may be located on both sides of the optical waveguide 3 so as to sandwich the optical waveguide 3 therebetween. The guide structure 34 is used to position the optical connector 5a. The material forming the guide structure 34 is not limited, and examples thereof include resins such as epoxy resin and silicone resin.

[0024] 4, the guide structure 34 has at least a first portion 341 and a second portion 342 that extend adjacent to each other from the outer edge side to the center side of the wiring substrate 2 in a plan view, a third portion 343 that extends from the center end of the first portion 341 away from the second portion 342, and a fourth portion 344 that extends from the center end of the second portion 342 away from the first portion 341. "Extending away from the second portion" means extending in a direction different from the second portion side with respect to an imaginary extension line of the first portion. "Extending away from the first portion" means extending in a direction different from the first portion side with respect to an imaginary extension line of the second portion.

[0025] 8, the optical connector 5a has, for example, a first recess C1 for accommodating the guide structure 34 on the side of the lower clad 31, and a second recess C2 for accommodating the upper clad 33. The position of the optical connector 5a in the Y direction is determined by fitting the first portion 341 and the second portion 342 of the guide structure 34 into the first recess C1, and the position of the optical connector 5a in the X direction is determined by abutting the side surfaces of the optical connector 5a against the third portion 343 and the fourth portion 344 of the guide structure 34. This allows the optical connector 5a to be connected to a predetermined position with high precision.

[0026] The lengths of the first portion 341 and the second portion 342 included in the guide structure 34 are set appropriately depending on the size of the optical connector 5a. The widths of the first portion 341 and the second portion 342 are, for example, 10 μm or more and 50 μm or less. The lengths of the third portion 343 and the fourth portion 344 are set appropriately depending on the size of the optical connector 5a. The widths of the third portion 343 and the fourth portion 344 are, for example, 10 μm or more and 50 μm or less. The widths of the first portion 341 and the third portion 343 may be the same or different. The widths of the second portion 342 and the fourth portion 344 may be the same or different.

[0027] The angle θ between the first portion 341 and the third portion 343 is not limited and may be approximately 90 degrees as shown in Fig. 4. Similarly, the angle between the second portion 342 and the fourth portion 344 is not limited and may be approximately 90 degrees.

[0028] The first portion 341 and the third portion 343 will be described with reference to Fig. 5. Fig. 5 is an enlarged explanatory view for describing the region R3 shown in Fig. 4. As shown in Fig. 5, the third portion 343 includes a first protrusion 34a.

[0029] The first protrusion 34a is a protrusion that protrudes from one of two side edges of the third portion 343 in a plan view, opposite the side that is adjacent to the first portion 341. The first protrusion 34a is formed from the material that forms the above-described guide structure 34. The length L1 of the first protrusion 34a, i.e., the length from the side edge of the third portion 343 opposite the side that is adjacent to the first portion 341 in a plan view to the tip, is, for example, not less than 30 μm and not more than 150 μm, and may be approximately the same as the width of the third portion 343.

[0030] FIG. 6 is an explanatory diagram illustrating various embodiments of a cross section taken along line aa in FIG. 5. As shown in FIGS. 5 and 6A, the third portion 343 has a first protrusion 34a protruding from one of two side edges of the third portion 343 opposite the side adjacent to the first portion 341. As shown in FIG. 6B, the third portion 343 may include a second protrusion 34b protruding from the third portion 343 into the lower cladding 31 (second region 312) in a cross-sectional view. FIG. 6B illustrates a case where the third portion 343 does not have the first protrusion 34a. Like the first protrusion 34a, the second protrusion 34b is also formed from the material forming the guide structure 34. The thickness (depth) L2 of the second protrusion 34b is not limited and may be, for example, approximately 10% or more of the thickness of the lower cladding 31.

[0031] 6(C), both the first protrusion 34a and the second protrusion 34b may protrude from the third portion 343. That is, the third portion 343 only needs to include at least one of the first protrusion 34a and the second protrusion 34b.

[0032] 6(D), the first protrusion 34a may further include a third protrusion 34c that protrudes from the first protrusion 34a into the lower cladding 31 (second region 312) in a cross-sectional view. Similar to the second protrusion 34b, the third protrusion 34c is formed from the same material as the guide structure 34. The thickness (depth) L3 of the third protrusion 34c is not limited and may be, for example, approximately 10% or more of the thickness of the lower cladding 31. The third protrusion 34c may have the same thickness as the second protrusion 34b, or may have a different thickness.

[0033] As shown in FIG. 6(E), both the first protrusion 34a and the second protrusion 34b may protrude from the third portion 343, and the third protrusion 34c may protrude from the first protrusion 34a.

[0034] The fourth portion 344 also includes at least one of the first protrusion 34a and the second protrusion 34b, similar to the third portion 343. Furthermore, a third protrusion 34c may protrude from the first protrusion 34a located in the fourth portion 344.

[0035] In a plan view, the extending direction of the third portion 343 and the protruding direction of the first protruding portion 34a may be orthogonal. That is, in a plan view, the angle formed between the first protruding portion 34a located in the third portion 343 and the third portion 343 may be 90 degrees. In a plan view, the extending direction of the fourth portion 344 and the protruding direction of the first protruding portion 34a may be orthogonal. That is, in a plan view, the angle formed between the first protruding portion 34a located in the fourth portion 344 and the fourth portion 344 may be 90 degrees.

[0036] 5, the first portion 341 may include a fourth protrusion 34d. The fourth protrusion 34d is a protrusion that protrudes from the first portion 341 toward the region sandwiched between the first portion 341 and the second portion 342 in a plan view. The fourth protrusion 34d is formed from the material that forms the guide structure 34. The length L4 of the fourth protrusion 34d, i.e., the length from the side edge of the first portion 341 on the second portion 342 side to the tip in a plan view, is, for example, not less than 30 μm and not more than 150 μm, and may be approximately the same as the width of the first portion 341.

[0037] FIG. 7 is an explanatory diagram illustrating various embodiments of a cross section taken along line bb in FIG. 5. As shown in FIGS. 5 and 7A, the first portion 341 has a fourth protrusion 34d protruding from the first portion 341 toward the region sandwiched between the first portion 341 and the second portion 342. As shown in FIG. 7B, the first portion 341 may include a fifth protrusion 34e protruding from the first portion 341 into the lower cladding 31 (second region 312) in a cross-sectional view. FIG. 7B illustrates a case in which the first portion 341 does not have the fourth protrusion 34d. Like the fourth protrusion 34d, the fifth protrusion 34e is also formed from the material forming the guide structure 34. The thickness (depth) L5 of the fifth protrusion 34e is not limited and may be, for example, approximately 10% or more of the thickness of the lower cladding 31 or may be the same depth as the second protrusion 34b and the third protrusion 34c.

[0038] 7(C), both the fourth protrusion 34d and the fifth protrusion 34e may protrude from the first portion 341. That is, the first portion 341 may include at least one of the fourth protrusion 34d and the fifth protrusion 34e.

[0039] 7(D), the sixth protrusion 34f may be included, protruding from the fourth protrusion 34d into the lower cladding 31 (second region 312) in a cross-sectional view. Like the fifth protrusion 34e, the sixth protrusion 34f is formed from the same material as the guide structure 34. The thickness (depth) L6 of the sixth protrusion 34f is not limited and may be, for example, approximately 10% or more of the thickness of the lower cladding 31. The sixth protrusion 34f may have the same thickness as the fifth protrusion 34e, or may have a different thickness.

[0040] As shown in FIG. 7(E), both the fourth protrusion 34d and the fifth protrusion 34e may protrude from the first portion 341, and the sixth protrusion 34f may protrude from the fourth protrusion 34d.

[0041] The second portion 342 also includes at least one of the fourth protrusion 34d and the fifth protrusion 34e, similar to the first portion 341. Furthermore, a sixth protrusion 34f may protrude from the fourth protrusion 34d located in the second portion 342.

[0042] In a plan view, the extending direction of the first portion 341 and the protruding direction of the fourth protruding portion 34d may be orthogonal. That is, in a plan view, the angle formed between the fourth protruding portion 34d located on the first portion 341 and the first portion 341 may be 90 degrees. In a plan view, the extending direction of the second portion 342 and the protruding direction of the fourth protruding portion 34d may be orthogonal. That is, in a plan view, the angle formed between the fourth protruding portion 34d located on the second portion 342 and the second portion 342 may be 90 degrees.

[0043] Next, an embodiment of a method for forming the guide structure 34 in the second region 312 of the lower cladding 31 will be described.

[0044] First, the wiring board 2 is prepared. The wiring board 2 has, on its upper surface, a mounting region for the optical components 4 and a forming region for the optical waveguide 3, which are adjacent to each other. The forming region for the optical waveguide 3 of the wiring board 2 includes a conductor layer 21a, which is part of the conductor layer located on the uppermost surface (the conductor layer located on the upper surface of the wiring board 2). The mounting region of the wiring board 2 includes a pad 21b, which is part of the conductor layer located on the uppermost surface. The conductor layer 21a and the pad 21b are formed of a metal such as copper.

[0045] Next, the lower cladding 31 is formed in a region including the region where the optical waveguide 3 is to be formed. Specifically, a resin layer made of a resin such as epoxy resin or silicone resin is laminated so as to cover the region where the optical waveguide 3 is to be formed. Next, exposure and development are performed to form the lower cladding 31.

[0046] Next, the optical waveguide core 32 is formed in the first region 311 of the lower clad 31, and the guide structure 34 is formed in the second region 312 of the lower clad 31. The optical waveguide core 32 and the guide structure 34 may be formed simultaneously or separately. In order to reduce the number of steps, it is preferable to form the guide structure 34 simultaneously with the optical waveguide core 32.

[0047] Before forming the optical waveguide core 32 and the guide structure 34, recesses for forming the second protrusion 34b, the third protrusion 34c, the fifth protrusion 34e, and the sixth protrusion 34f that protrude into the second region 312 of the lower cladding 31 are formed in the second region 312 of the lower cladding 31. The method for forming these recesses is not limited, and examples thereof include an exposure method and a laser method. Examples of the exposure method include a method using a halftone mask and a method for forming a very small diameter hole. Examples of the laser method include a method using an excimer laser.

[0048] If necessary, a recess is formed in the second region 312 of the lower clad 31, and then a material (resin such as epoxy resin or silicone resin) for forming the optical waveguide core 32 and the guide structure 34 is applied to or attached to the first region 311 and the second region 312 of the lower clad 31. Thereafter, exposure processing and development processing are performed to form the optical waveguide core 32 and the guide structure 34.

[0049] Next, the upper clad 33 is formed in the first region 311 of the lower clad 31 to cover the optical waveguide core 32. Like the lower clad 31, the upper clad 33 is also formed by exposing and developing a resin such as an epoxy resin or a silicone resin. The lower clad 31 and the upper clad 33 may be made of the same material or different materials. Furthermore, the lower clad 31 and the upper clad 33 may have the same thickness or different thicknesses.

[0050] In this way, the guide structure 34 is formed in the second region 312 of the lower cladding 31. The optical circuit board 2 including such a guide structure 34 is used, for example, as an optical module. That is, the optical module according to the present disclosure includes the optical circuit board 1 according to one embodiment and an optical connector 5a that abuts against the guide structure 34 and is connected to the optical circuit board 3.

[0051] Next, an optical module 10 in which optical components 4 and electronic components 6 are mounted on an optical circuit board 1 according to one embodiment will be described. As shown in FIG. 1, the optical components 4 mounted on the optical module 10 include an optical transmission line 41. Examples of the optical components 4 including such an optical transmission line 41 include silicon photonics devices. Examples of the electronic components 6 include an ASIC (Application Specific Integrated Circuit), a driver IC, etc. Examples include:

[0052] 2, the optical component 4 is electrically connected to a pad 21b located in the optical component mounting region 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.

[0053] A silicon photonics device will be described as an example of the optical component 4. A silicon photonics device is a type of optical component having an optical transmission line 41 with, for example, a silicon (Si) core and silicon dioxide (SiO2) cladding. 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, although not shown. As described above, the optical transmission line 41 (Si waveguide 41) is located at one end of the optical waveguide 3 so as to face the optical waveguide core 32 included in the optical waveguide 3.

[0054] For example, an electrical signal from the wiring board 2 is propagated to a light source unit included in the optical component 4 (silicon photonics device) via the solder 7. The light source unit receives the propagated electrical signal and emits light. The emitted optical signal is propagated via the optical transmission path 41 (Si waveguide 41) and the optical waveguide core 32 to the optical fiber 5 connected via the optical connector 5a.

[0055] 8 is an enlarged cross-sectional view of a main part showing the state (left half) in which the connector 5a is connected to the optical circuit-board 1. The connector 5a has, for example, on the lower clad 31 side, a first recess C1 for accommodating the guide structure 34 and a second recess C2 for accommodating the upper clad 33. The first recess C1 has approximately the same width as the guide structure 34. This allows the connector 5a to be connected to a specified position on the optical circuit-board 1 in the Y direction shown in FIG.

[0056] The optical circuit board according to the present disclosure is not limited to the optical circuit board 1 according to the above-described embodiment. In the optical circuit board 1 according to the embodiment, the angle between the first portion 341 and the third portion 343 is approximately 90 degrees, and the angle between the second portion 342 and the fourth portion 344 is also approximately 90 degrees.

[0057] However, in the optical circuit board according to the present disclosure, the angle θ between the first portion and the third portion does not necessarily have to be 90 degrees. For example, the angle between the first portion and the third portion may be an obtuse angle (e.g., greater than 90 degrees and less than 180 degrees). The angle between the second portion and the fourth portion may also be an obtuse angle, similar to the angle between the first portion and the third portion. [Explanation of symbols]

[0058] 1 Optical circuit board 2. Wiring board 21a Conductor layer 21b pad 3 Optical waveguide 31 Lower Cladding 311 First area 312 Second area 32 Optical waveguide core 33 Upper Cladding 34 Guide structure 341 Part 1 342 Part 2 343 Part 3 344 Part 4 34a 1st protrusion 34b Second protrusion 34c Third protrusion 34d 4th protrusion 34e 5th protrusion 34f 6th protrusion 4 Optical Components 41 Optical transmission line (silicon waveguide (Si waveguide)) 5. Optical Fiber 5a optical connector 6. Electronic Components 7. Solder 10 Optical Modules

Claims

1. A wiring board; a lower clad located on the wiring substrate and having a first region and a second region; an optical waveguide located on the first region and including a core and an upper clad; a guide structure located on the second region adjacent to the optical waveguide; Including, The guide structure has at least a first portion and a second portion extending adjacent to each other from an outer edge side to a center side of the wiring substrate in a plan view, a third portion extending from an end of the first portion on the center side so as to move away from the second portion, and a fourth portion extending from the end of the second portion on the center side so as to move away from the first portion, the third portion and the fourth portion include at least one of a first protrusion and a second protrusion, the first protrusion protrudes from at least one of two side edge portions of the third portion opposite to a side adjacent to the first portion and one of two side edge portions of the fourth portion opposite to a side adjacent to the second portion in a plan view, the second protrusion is a protrusion protruding into the lower clad from at least one of the third portion and the fourth portion in a cross-sectional view. Optical circuit board.

2. 2. The optical circuit board according to claim 1, wherein at least one of the third portion and the fourth portion has a third protrusion protruding from the first protrusion into the lower clad in a cross-sectional view.

3. An optical circuit board as described in claim 1, wherein, when at least one of the third part and the fourth part includes the first protrusion, in a planar view, the extension direction of the third part and the direction in which the first protrusion protrudes are perpendicular to each other, and the extension direction of the fourth part and the direction in which the first protrusion protrudes are perpendicular to each other.

4. An optical circuit board as described in claim 1, wherein, when at least one of the third part and the fourth part includes the first protrusion, the protruding length of the first protrusion in a planar view is the same as the width of at least one of the third part and the fourth part that includes the first protrusion.

5. the first portion and the second portion include at least one of a fourth protrusion and a fifth protrusion, the fourth protrusion protrudes from at least one of the first portion and the second portion toward a region sandwiched between the first portion and the second portion in a plan view, the fifth protrusion is a protrusion protruding into the lower clad from at least one of the first portion and the second portion in a cross-sectional view; The optical circuit board according to claim 1 .

6. 6. The optical circuit board according to claim 5, wherein at least one of the first portion and the second portion has a sixth protrusion protruding from the fourth protrusion into the lower clad in a cross-sectional view.

7. The optical circuit board according to claim 1 , wherein the first portion and the second portion are positioned so as to sandwich the optical waveguide therebetween.

8. An optical circuit board according to any one of claims 1 to 7; an optical connector that is in contact with the guide structure and connected to the optical circuit board; an optical module including:

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