Optical waveguide substrate, optical device, and method for manufacturing optical device

Abstract

An optical waveguide substrate (10) including a substrate body (101) and optical waveguides (102) formed on the substrate body (101) is configured such that: the substrate body (101) includes through holes (12a) that include one end surface (10d) of the substrate body (101) and that penetrate through the substrate body (101) in the thickness direction, and long groove parts (12b) that are contiguous to the through holes (12a) and that extend parallel to the main surface of the substrate body; the through holes (12a) are formed at positions corresponding to the optical waveguides (102); and the inner surfaces of the long groove parts (12b) include inclined surfaces (12c) which come into contact with optical fibers (23a) when the optical fibers (23a) are inserted into the long groove parts (12b) through the through holes (12a).

Description

[Technical field]

[0001] The present invention relates to an optical waveguide substrate, an optical device, and a method for manufacturing an optical device. [Background technology]

[0002] An optical waveguide structure using silicon photonics technology is formed by depositing SiO2 on a Si substrate, depositing a Si layer in the SiO2, and etching the Si layer into a desired pattern using photolithography. Wiring for driving devices such as photodiodes and pads for fixing the substrate are provided on the surface of the Si substrate. The wiring and pads are formed from metal layers such as Al and Au. To input and output optical signals to and from such a silicon photonics optical waveguide substrate, it is necessary to optically polish the optical waveguide end surface of the Si substrate and connect multiple optical fibers to each optical waveguide according to the function of the optical circuit.

[0003] The known optical polishing process is carried out in the same manner as the polishing process of other metal products, through a rough polishing process using different types and sizes of abrasive grains, a medium polishing process, and a finish polishing process using fine silica particles, and requires large-scale polishing equipment and a lot of work time. In addition, since the layers above the Si waveguide layer of the optical waveguide substrate are very thin, at about a few μm, there is a risk that small chips or cracks will occur in the upper layers of the substrate due to chipping that occurs during the optical polishing process. If the chips reach the end face of the optical waveguide, it will cause a large optical connection loss when the optical fiber is connected.

[0004] In addition, when optical fibers are connected and fixed to the end face of an optical waveguide, an optical fiber array is used to optically align and fix a plurality of optical fibers at once. The optical fiber array is configured to align the optical fibers with high precision according to the spacing of the optical waveguide when connected. The optical fibers are connected using an optical fiber array by placing the optical fibers with their coating removed on a glass substrate with a V-groove processing, pressing the glass substrate so that the optical fibers are in close contact with the slope of the V-groove, and further covering the coating of the optical fibers with a protective resin on the side opposite to the optical connection surface. This type of optical fiber connection can improve the bending resistance of the optical fibers and prevent them from falling out of the V-groove. If optical polishing is performed on the optical end face of the optical fiber array, the angle of the optical end face can be freely adjusted. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] NTT Advanced Technology Corporation, Internet, WEB page URL: https: / / keytech.ntt-at.co.jp / optservice / prd_0029.html Accessed November 29, 2021. Summary of the Invention

[0006] However, the above configuration requires a relatively long time for polishing, which leaves room for improvement. Specifically, the optical alignment process using an optical fiber array requires the adjustment of the parallelism and spacing between the connection end faces of the optical fiber array and the optical waveguide substrate, the alignment of the optical axis by active alignment, and the fixing with an ultraviolet-curing adhesive to achieve low-loss optical connection. The processing time, including the installation of the components, the alignment, and the ultraviolet curing of the adhesive, is more than 10 minutes.

[0007] Furthermore, silicon photonics optical waveguide substrates are mounted on control boards as the main components of optical transceivers. The mainstream mounting method is flip chip, which uses gold bumps or copper pillars on the surface of the optical waveguide substrate. Flip chip mounting is preferably performed without optical fiber, since it involves thermal processes. Therefore, it is preferable to connect the optical fiber after mounting using flip chip. However, when connecting the optical fiber after mounting, a problem occurs in that it becomes difficult to visually confirm the optical waveguide to be connected to the optical fiber. In other words, the optical waveguide substrate is turned upside down after mounting, making it difficult to confirm the side (top surface) on which the optical waveguide is visible.

[0008] As described above, in the known active alignment method of the end face of the optical waveguide in the optical fiber array, complicated steps are involved from the preparation including the polishing step to the alignment and fixing, and the preparation time and cost become an issue. In addition, in the flip-chip mounting, there is a problem that it is difficult to confirm the position of the optical waveguide at a stage before the active alignment. The present disclosure has been made in consideration of such points, and relates to an optical waveguide substrate, an optical device, and a manufacturing method of an optical device that shorten the time required for preparation including the polishing step and for the alignment of the optical fiber, and that allows the optical waveguide to be easily confirmed when connected to the optical fiber after mounting.

[0009] In order to achieve the above object, an optical waveguide substrate according to one embodiment of the present disclosure is an optical waveguide substrate including a substrate body and an optical waveguide formed in the substrate body, the substrate body including one end surface of the substrate body, Between the top and bottom of The substrate body includes a through hole that passes through the substrate, and a long groove portion that communicates with the through hole and extends parallel to the main surface of the substrate body, the through hole being formed at a position corresponding to the optical waveguide, and the inner surface of the long groove portion includes a slope that comes into contact with the optical fiber when the optical fiber is inserted into the long groove portion through the through hole.

[0010] An optical device of one embodiment of the present disclosure includes the above-mentioned optical waveguide substrate and an electronic circuit mounted on a mounting surface which is one of the main surfaces of the optical waveguide substrate, and the inclined surface of the through hole inclines from a center line along the extension direction of the long groove portion toward the mounting surface.

[0011] According to one embodiment of the present disclosure, there is provided a method for manufacturing an optical device including an optical waveguide substrate including a substrate body and an optical waveguide formed in the substrate body, and a plurality of optical fibers aligned and connected to the optical waveguide, the substrate body including one end face of the substrate body, Penetrates between the top and bottom of The optical fiber cable includes a through hole and a long groove portion that communicates with the through hole and extends parallel to a main surface of the substrate body, and includes aligning a plurality of the optical fibers to match the through hole, translating the aligned plurality of the optical fibers along the long groove portion, and fixing the plurality of the optical fibers inside the long groove portion.

[0012] Moreover, a manufacturing method for an optical device of one embodiment of the present disclosure is a manufacturing method for an optical device including an optical waveguide substrate and a plurality of optical fibers aligned and connected to an end face of the optical waveguide substrate, the optical waveguide substrate including the end face, the optical waveguide substrate having a through hole penetrating the optical waveguide substrate in a thickness direction and formed at a position corresponding to an optical waveguide of the optical waveguide substrate, and a long groove portion communicating with the through hole, extending parallel to a main surface of the optical waveguide substrate and including a slope whose inner surface contacts the optical fiber, the method including aligning the plurality of optical fibers to match the through hole, translating the aligned plurality of optical fibers along the long groove portion, and fixing the plurality of optical fibers inside the long groove portion.

[0013] According to the above-described embodiments, it is possible to provide an optical waveguide substrate, an optical device, and a method for manufacturing an optical device, which can shorten the time required for fabrication including a polishing step and for aligning the optical fiber, and which allows the optical waveguide to be easily confirmed when connected to the optical fiber after mounting. [Brief description of the drawings]

[0014] [Figure 1] FIG. 2 is a bottom perspective view of an optical device according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a top perspective view of the optical device shown in FIG. [Diagram 3] 2 is an enlarged perspective view of a portion shown in FIG. 1 as viewed from above. FIG. [Figure 4] (a) is a top view of the optical fiber connection part, (b) is a vertical cross-sectional view, and (c) is a horizontal cross-sectional view. [Diagram 5] 1A is a bottom view of the optical waveguide substrate, and FIG. [Figure 6] 1A, 1B, and 1C are diagrams for explaining the manufacturing process of an optical device. [Figure 7] 6(a), (b), and (c) are diagrams for explaining the manufacturing process of the optical device subsequent to FIG. 6(c). [Figure 8] FIG. 8 is a perspective view of the optical device shown in FIG. 7(b) as viewed from above. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, one embodiment of the present disclosure will be described. The drawings used in the description of this embodiment are intended to explain the technical ideas and components of the present disclosure, as well as the arrangement and relationship of the components, and do not necessarily accurately show the specific shape, size, length, width, and thickness ratio of the present disclosure.

[0016] (Optical Devices) FIG. 1 is a bottom perspective view of an optical device 100 according to an embodiment of the present disclosure, FIG. 2 is a top perspective view of the optical device 100 shown in FIG. 1, and FIG. 3 is a perspective view of an area A shown in FIG. 1, enlarged and viewed from above. The top and bottom surfaces of this embodiment are defined by the coordinate system in FIG. 1, and the side with a larger z-axis coordinate is referred to as "upper" or "upward" relative to the side with a smaller z-axis coordinate. The side with a smaller z-axis coordinate is referred to as "lower" or "downward" relative to the side with a larger z-axis coordinate. The bottom surface 10a is the surface opposite to the surface on which the optical waveguide (not shown) of the optical waveguide substrate 10 of the optical device 100 is visible. The top surface 10b is the back surface of the bottom surface 10a. The surface between the top surface 10a and the bottom surface 10b is referred to as the side surface 10c. The side surface 10c on the side to which the optical fiber 23a is connected is particularly referred to as the end surface 10d. The reason why the side with a larger z-axis coordinate is the lower surface 10a and the side with a smaller z-axis coordinate is the upper surface 10b is because the connection and alignment of the optical fiber 23a in this embodiment are performed by turning the optical waveguide substrate 10 upside down. Also, the perspective views of Figures 1, 2 and 3 all show a state in which the optical fiber 23a is close to the end face 10d, and do not show a state in which the optical fiber 23a is connected to the optical waveguide in the optical waveguide substrate 10.

[0017] 1 to 3, the optical waveguide substrate 10 includes a substrate body 101 and an optical waveguide 102 formed in the substrate body. The substrate body includes one end face 10d, a through hole 12a penetrating the substrate body in the thickness direction, and a long groove portion 12b communicating with the through hole 12a and extending parallel to the main surface (e.g., the lower surface 10a) of the substrate body 101. The through hole 12a is formed at a position corresponding to the optical waveguide 102, and the inner surface of the long groove portion 12b includes a slope 12c (FIG. 4) that comes into contact with the optical fiber 23a when the optical fiber 23a is inserted into the long groove portion 12b through the through hole 12a. Such through hole 12a and long groove portion 12b constitute an optical fiber connection portion 12 described later.

[0018] Here, "through hole 12a includes end face 10d" means that an edge portion of the through hole intersects with end face 10d in a top view. That is, through hole 12a is not formed at a position contained within the plane of optical waveguide substrate 10, and the inner surface is opened at the point where through hole 12a intersects with end face 10d. Optical fiber 23a engages with the opened inner surface of through hole 12a and is aligned in long groove portion 12b.

[0019] The optical waveguide substrate 10 further configures an optical device by connecting the optical fiber 23a to the electronic circuit 3 (FIG. 5). In this embodiment, as described in detail later, the optical fiber 23a aligned by the through hole 12a is connected with an optical waveguide (not shown) of the optical waveguide substrate 10 with high precision. For this reason, the through hole 12a is formed at a position corresponding to the optical waveguide (not shown). Therefore, in this embodiment, it is possible to indirectly confirm the position of the optical waveguide from the position of the through hole 12a. This point will also be described later.

[0020] In the above configuration, the optical waveguide substrate 10 may be a photonics substrate made of Si. The optical fiber 23a is composed of a core layer 24 as an optical waveguide and a cladding layer 25 that protects the core layer 24. The optical fibers 23a are bundled by a glass block 26 to form an optical fiber group 23. As shown in FIG. 2, the glass block 26 is formed with a holding hole 26a for holding the inserted optical fiber 23a. The holding hole 26a has an oval cross section, and the major axis is designed to be larger than the value obtained by multiplying the coating diameter of the optical fiber 23a by the number of cores. The optical fibers 23a inserted into the holding hole 26a are held parallel to each other and at equal intervals. In addition, the coating of the optical fiber 23a is partially removed from the side facing the optical waveguide substrate 10, exposing a crack layer 25. A plurality of bumps 13 for mounting a flip-flop are provided on the upper surface 10b of the optical waveguide substrate 10.

[0021] (Optical fiber connection) Next, the optical fiber connection part 12 will be described. Figures 4(a), 4(b), 4(c), 5(a) and 5(b) are diagrams for explaining the optical fiber connection part 12. Figure 4(a) is a top view showing the optical fiber connection part 12 seen from the upper surface 10b side of the optical waveguide substrate 10, Figure 4(b) is a cross-sectional view along the arrows IVb and IVb in Figure 4(a), and Figure 4(c) is a cross-sectional view along the arrows IVc and IVc in Figure 4(a). The long groove part 12b has an inclined apex angle 12e and an inclined surface 12c that extends obliquely from the apex angle 12e toward the lower surface 10a of the optical waveguide substrate. The successive vertices of the apex angle 12e coincide with the center line along the extension direction of the long groove part 12b. Therefore, it can be said that the inclined surface 12c is inclined from the center line along the extension direction of the long groove portion 12b toward the upper surface 10b (mounting surface) on which the electronic circuit 3 is mounted.

[0022] 4(c), the inclined surface 12c in this embodiment forms a V-groove having a V-shaped cross section perpendicular to the extending direction of the long groove portion 12b. When the optical fiber 23a is inserted into the long groove portion 12b, the optical fiber 23a comes into contact with the V-groove, and the movement of the optical fiber 23a in a direction away from the apex angle 12e is restricted by the inclined surfaces 12c on both sides of the apex angle 12e, so that the optical fiber 23a is aligned with the apex angle 12e.

[0023] 5(a) is a bottom view of the optical waveguide substrate 10 as viewed from the bottom surface 10a, and FIG. 5(b) is a cross-sectional view taken along the arrows Vb, Vb in FIG. 5(a). In FIG. 5(a) and FIG. 5(b), the optical fiber 23a is partially inserted into the through hole 12a, and is not inserted into the long groove portion 12b. As shown in FIG. 4(a) and FIG. 5(a), the edge of the through hole 12a in this embodiment is formed so as to extend from the end face 10d side toward the extension direction of the long groove portion 12b in a top view, and then draw an arc toward the end face 12d again. Such a shape is also referred to as a "U-shape" in this embodiment.

[0024] In this embodiment, as shown in FIG. 5(b), the electronic circuit 3 is mounted on the upper surface 10b of the optical waveguide substrate 10 via the bumps 13. Therefore, the upper surface 10b in this embodiment corresponds to the mounting surface. The mounting of the electronic circuit 3 is performed before the connection and alignment of the optical fibers 23a. Therefore, in this embodiment, the alignment of the multiple optical fibers 23a with the through holes 12a is performed on the optical waveguide substrate 10 on which the electronic circuit 3 is mounted. In this embodiment, the electronic circuit 3 can be mounted in a state in which the optical fibers 23a are not connected, making it easy to mount the electronic circuit 3.

[0025] As shown in FIG. 5(b), a slope 12f is formed on the inner surface of the through hole 12a, which slopes from the apex of the apex angle 12c, i.e., the center line along the extension direction of the long groove portion 12b, toward the upper surface 10b, which is the mounting surface. Such a slope 12f comes into contact with the optical fiber 23a aligned in parallel and at equal intervals by the through hole 12a when the optical fiber 23a moves downward, and has the function of smoothly guiding the optical fiber 23a to the lower part of the through hole 12a that continues to the long groove portion 12b. As shown in FIG. 5(c), the long groove portion 12b is formed at a position corresponding to the optical waveguide 102. The optical fiber 23a guided downward through the through hole 12a advances along the long groove portion 12b, and its end face is aligned with the end face of the optical waveguide 102. The "position where the long groove portion 12b and the optical waveguide 102 correspond to each other" refers to the position where the optical axis of the optical fiber 23a inserted into the long groove portion 23a and the optical axis of the optical waveguide 102 coincide with each other.

[0026] The V-shaped long groove portion 12b can be formed by known photolithography and wet etching. The long groove portion 12b is formed to match the position of the optical waveguide 102. The depth of the long groove portion 12b is adjusted so that the center of the core layer 24 of the optical fiber 23a coincides with the height of the optical waveguide 102. In this embodiment, by arranging the optical fiber 23a in the V-groove of the long groove portion 12b, it is possible to establish a low-loss optical connection while omitting an optical polishing process and an active alignment process.

[0027] (Optical device manufacturing method) Next, a method for manufacturing the optical device 100 described above will be described. FIGS. 6(a), 6(b), 6(c), 7(a), 7(b), and 7(c) are diagrams for explaining each step of manufacturing the optical device 100. In the method for manufacturing the optical device 100 of this embodiment, first, as shown in FIG. 6(a), a plurality of optical fibers 23a are passed through the holding holes 26a of the glass block 26 to form the optical fiber group 23. At this time, the coating material of the optical fibers 23a is removed from a part of the optical fiber 23a facing the optical waveguide substrate 10 and the optical fiber group 23 is cleaved off. Next, as shown in FIG. 6(b), the tips of the optical fiber group 23 are slid from above into the through holes 12a and aligned at equal intervals. Note that the electronic circuit 3 has already been mounted on the upper surface 10b as shown in FIG. 6(b) and FIG. 6(c).

[0028] At this time, since the through hole 12a has a relatively gentle U-shape, when the optical fiber 23a is pushed toward the long groove portion 12b, the horizontal position is regulated by the through hole 12a, and horizontal alignment is possible. Furthermore, the optical fiber 23a moves downward on the optical waveguide substrate 10 as shown in FIG. 6(c). The apex of the convex part of the U-shape of the through hole 12a coincides with the apex of the apex angle 12e of the long groove portion 12b in the surface direction of the optical waveguide substrate 10. Therefore, the optical fiber 23a that has moved downward smoothly descends toward the apex angle of the V-shaped groove while contacting the inner surface of the through hole 12a. At this time, as described above, the optical fiber 23a slides on the slope 12f provided on the inner surface of the through hole 12a, and is then smoothly loaded into the long groove portion 12b. Through the above steps, the manufacturing method of the optical device of this embodiment enables horizontal alignment of the optical fiber 23a and the optical waveguide.

[0029] In this embodiment, when the optical fiber 23a is pushed toward the long groove portion 12b, the optical fiber 23a may be inclined at an angle of 1 degree or more and 10 degrees or less with respect to the lower surface 10a of the optical waveguide substrate 10. In this case, it is preferable that the optical fiber 23a is inclined so that the optical fiber 23a faces upward relative to the lower surface 10a, that is, forms an elevation angle. This contributes to reducing optical loss by increasing the adhesion of the optical fiber 23a to the inner surface of the long groove portion 12b.

[0030] 7(a) shows a state in which, after the optical fiber 23a is loaded, the glass block 26 is brought close to the end face 10d of the optical waveguide substrate 10. In this state, in this embodiment, when the optical waveguide substrate 10 is viewed from the bottom face 10a to which the electronic circuit 3 is not attached, the position of the optical waveguide can be confirmed from the position of the through hole 12a.

[0031] Next, in this embodiment, as shown in Fig. 7(b), ultraviolet (UV) curing adhesive 9 is dripped into the inside of the holding hole 26a of the glass block 26 and fixed by irradiating an appropriate amount of ultraviolet light. The ultraviolet curing adhesive fills the entire through hole 12a and the long groove portion 12b, and firmly fixes the optical fiber 23a to the optical waveguide substrate 10. Fig. 7(c) shows a state in which the entire holding hole 26a of the glass block 26 is filled with the ultraviolet curing adhesive 9. Also, Fig. 8 shows the optical device shown in Fig. 7(b) as viewed from the side on which the electronic circuit 3 is mounted, that is, from the top surface 10b.

[0032] As described above, in this embodiment, the through hole 12a and the long groove portion 12b are provided, so that the optical fiber can be aligned at a proper angle to the optical waveguide of the optical waveguide substrate. Therefore, in this embodiment, the accuracy of rough alignment between the optical waveguide and the optical fiber 23a can be improved compared to known techniques, so that the time required for polishing the end face of the optical waveguide and the optical fiber or for core alignment can be shortened. In addition, since the through hole 12a is formed according to the position of the optical fiber to be aligned with the optical waveguide, it is necessarily formed at a position corresponding to the optical waveguide. Therefore, in this embodiment, the position of the optical waveguide can be confirmed from the side of the lower surface 10a of the optical device, and the work of aligning and connecting the optical fiber 23a can be made easy. The work of aligning and connecting the optical fiber 23a may be performed manually by an operator. In addition, it may be controlled automatically by a robot or the like, or by an operator watching a monitor or the like. [Explanation of symbols]

[0033] 10 Optical waveguide substrate 12a Through hole 12b Long groove 12c Slope 12d end face 12e vertical angle 12th floor slope 13. Bump 23 Optical Fiber Group 23a Optical Fiber 24 Core Layer 25 Crack Layer 26 Glass Blocks 26a Retaining hole 100 Optical Devices 101 Board body 102 Optical waveguide

Claims

1. An optical waveguide substrate including a substrate body and an optical waveguide formed in the substrate body, The substrate body is a through hole that includes one end surface of the substrate body and penetrates between an upper surface and a lower surface of the substrate body, and a long groove portion that communicates with the through hole and extends parallel to a main surface of the substrate body, an inner surface of the long groove portion including a slope that comes into contact with an optical fiber when the optical fiber is inserted into the long groove portion through the through hole.

2. 2. The optical waveguide substrate according to claim 1, wherein the inclined surface of the long groove portion is a V-groove having a V-shaped cross section perpendicular to the direction in which the long groove portion extends.

3. 3. The optical waveguide substrate according to claim 1, wherein the through hole has a shape in a top view that includes a U-shaped portion that is convex from the end face of the substrate body toward the extending direction of the long groove portion.

4. An optical waveguide substrate according to claim 1 , an electronic circuit mounted on a mounting surface which is one of the main surfaces of the optical waveguide substrate; Including, an inclined surface of the through hole inclined from a center line along the extending direction of the long groove portion toward the mounting surface;

5. The optical device according to claim 4 , further comprising a plurality of optical fibers inserted through the through hole and into the long groove portion.

6. A method for manufacturing an optical device including an optical waveguide substrate including a substrate body and an optical waveguide formed in the substrate body, and a plurality of optical fibers aligned and connected to the optical waveguide, the method comprising the steps of: the substrate body includes one end surface of the substrate body, a through hole penetrating between an upper surface and a lower surface of the substrate body, and a long groove portion communicating with the through hole and extending parallel to a main surface of the substrate body; aligning a plurality of the optical fibers with the through holes; translating the aligned optical fibers along the groove; Fixing a plurality of the optical fibers within the groove portion; A method for manufacturing an optical device, comprising:

7. The method for manufacturing an optical device according to claim 6 , wherein the optical fibers are fixed to a fixing block and aligned.

8. 8. The method for manufacturing an optical device according to claim 6, wherein the optical fiber makes an elevation angle of 1 degree or more and 10 degrees or less with respect to a surface direction of the optical waveguide substrate when the optical fiber translates along the long groove portion.

9. The method for manufacturing an optical device according to claim 6 , wherein the step of aligning the optical fibers with the through holes is performed on the optical waveguide substrate on which an electronic circuit is mounted.

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