Optical waveguide device

Abstract

The present invention provides an optical waveguide apparatus that reduces variations in the thickness of the adhesive layer that optically couples the first waveguide and the second waveguide. [Solution] The optical waveguide apparatus comprises a first waveguide and a second waveguide disposed on the first waveguide, wherein the first waveguide includes a lower cladding layer, a first core disposed on the lower cladding layer, and an upper cladding layer disposed on the lower cladding layer and covering the first core, wherein the upper cladding layer includes a first surface on which the second waveguide is disposed, a second surface located on the side closer to the lower cladding layer with respect to the first surface in cross-sectional view and overlapping with the first core in plan view, and a recess located between the first surface and the second surface in plan view and recessed with respect to the second surface in cross-sectional view, wherein the second waveguide includes a second core and a cladding layer covering the second core, wherein the outer edge of the lower surface of the cladding layer is in contact with the first surface, the region of the cladding layer on which the second core is located is located on the second surface via an adhesive layer, and the second core overlaps with the first core in plan view and is optically coupled with the first core.

Description

[Technical Field]

[0001] The present invention relates to an optical waveguide device. [Background Art]

[0002] A technique for forming an adiabatic coupling by aligning a polymer waveguide formed on a polymer with a silicon waveguide formed on a silicon chip is disclosed. The coupling between the polymer waveguide and the silicon waveguide is performed via an adhesive layer for refractive index matching (see, for example, Patent Document 1). [Prior Art Documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Laid-Open No. 2014-81587 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] In adiabatic coupling, control of the thickness of the adhesive layer is important. However, the configuration of Patent Document 1 is not provided with a mechanism for controlling excess adhesive constituting the adhesive layer, and excess or deficiency of the adhesive causes variations in the thickness of the adhesive layer, which may affect coupling characteristics.

[0005] The present invention has been made in view of the above points, and an object of the present invention is to provide an optical waveguide device in which variation in thickness of an adhesive layer that optically couples a first waveguide and a second waveguide is reduced. [Means for Solving the Problem]

[0006] The optical waveguide apparatus comprises a first waveguide and a second waveguide disposed on the first waveguide, wherein the first waveguide includes a lower cladding layer, a first core disposed on the lower cladding layer, and an upper cladding layer disposed on the lower cladding layer and covering the first core, wherein the upper cladding layer includes a first surface on which the second waveguide is disposed, a second surface located on the side closer to the lower cladding layer with respect to the first surface in cross-sectional view and overlapping with the first core in plan view, and a recess located between the first surface and the second surface in plan view and recessed with respect to the second surface in cross-sectional view, wherein the second waveguide includes a second core and a cladding layer covering the second core, the outer edge of the lower surface of the cladding layer is in contact with the first surface, the region of the cladding layer on which the second core is located is located on the second surface via an adhesive layer, and the second core overlaps with the first core in plan view and is optically coupled with the first core. [Effects of the Invention]

[0007] According to the disclosed technology, it is possible to provide an optical waveguide apparatus that reduces variations in the thickness of the adhesive layer that optically couples the first waveguide and the second waveguide. [Brief explanation of the drawing]

[0008] [Figure 1] This is a plan view illustrating an optical waveguide device according to the first embodiment. [Figure 2] This is a cross-sectional view illustrating an optical waveguide device according to the first embodiment. [Figure 3] This is a diagram (part 1) illustrating the manufacturing process of an optical waveguide device according to the first embodiment. [Figure 4] This is a diagram (part 2) illustrating the manufacturing process of an optical waveguide device according to the first embodiment. [Figure 5] This is a plan view showing an example of the use of the optical waveguide device according to the first embodiment. [Figure 6] This is a cross-sectional view showing an example of use of the optical waveguide device according to the first embodiment. [Modes for carrying out the invention]

[0009] The embodiments for carrying out the invention will be described below with reference to the drawings. In each drawing, the same reference numerals are used for identical components, and redundant explanations may be omitted.

[0010] <First Embodiment> Figure 1 is a plan view illustrating an optical waveguide device according to the first embodiment. Figure 2 is a cross-sectional view illustrating an optical waveguide device according to the first embodiment, where Figure 2(a) shows a cross-section along line AA in Figure 1, and Figure 2(b) shows a cross-section along line BB in Figure 1. Referring to Figures 1 and 2, the optical waveguide device 1 includes a first waveguide 10, a second waveguide 20 arranged on the first waveguide 10, and an adhesive layer 30.

[0011] The first waveguide 10 includes a lower cladding layer 11, a first core 12, and an upper cladding layer 13.

[0012] The thickness of the lower cladding layer 11 can be, for example, about 10 μm to 30 μm. The refractive index of the lower cladding layer 11 can be, for example, about 1.5. The lower cladding layer 11 is formed from, for example, a resin. Examples of the resin include photosensitive resins such as polyimide resin, acrylic resin, epoxy resin, polyolefin resin, and polynorbornene resin.

[0013] The first core 12 is arranged on the lower cladding layer 11. There may be one or more first cores 12. In the illustrated example, three first cores 12 are arranged side by side on the lower cladding layer 11 at predetermined intervals. The first cores 12 may be straight or may include curved portions. The spacing between adjacent first cores 12 may be constant or not.

[0014] Each first core 12 is arranged, for example, parallel to each other. The width of each first core 12 can be, for example, about 2 μm to 10 μm. The thickness of each first core 12 can be, for example, about 2 μm to 10 μm. The refractive index of each first core 12 is higher than the refractive index of the lower cladding layer 11 and the upper cladding layer 13, for example, about 1.6. The first core 12 is made of, for example, resin, glass, silicon or its compounds (SiN, SiO X The first core 12 is formed from, for example, a material appropriately selected from among the materials exemplified for the lower cladding layer 11.

[0015] The upper cladding layer 13 is placed on the lower cladding layer 11 and covers the first core 12. The thickness of the thickest part of the upper cladding layer 13 can be, for example, about 10 μm to 30 μm. The thickness of the part of the upper cladding layer 13 that covers the upper surface of the first core 12 can be, for example, about 1 μm to 3 μm. The refractive index of the upper cladding layer 13 can be, for example, about 1.5. The upper cladding layer 13 is formed from, for example, a resin. The upper cladding layer 13 can be formed from, for example, a material appropriately selected from the materials exemplified for the lower cladding layer 11.

[0016] The upper cladding layer 13 comprises a first surface 13a on which the second waveguide 20 is arranged, and a second surface 13b located on the side closer to the lower cladding layer 11 relative to the first surface 13a in cross-sectional view, and overlapping with the first core 12 in plan view. The height difference between the first surface 13a and the second surface 13b can be, for example, about 0.5 μm to 2 μm. The upper cladding layer 13 comprises one or more recesses 13x located between the first surface 13a and the second surface 13b in plan view, and recessed relative to the second surface 13b in cross-sectional view.

[0017] Preferably, the upper cladding layer 13 includes a third surface 13c located on a side farther from the lower cladding layer 11 than the first surface 13a in a cross-sectional view, and located outside the first surface 13a in a plan view, and an inner side surface 13d connecting the third surface 13c to the first surface 13a and the second surface 13b. The difference in height between the first surface 13a and the third surface 13c can be, for example, approximately 10 µm to 30 µm.

[0018] In the illustrated example, the first surface 13a includes two regions opposing each other with the second surface 13b interposed therebetween in a plan view. Further, in a plan view, the upper cladding layer 13 includes two recesses 13x located between the second surface 13b and each region constituting the first surface 13a. The upper cladding layer 13 may include only one of the two illustrated recesses 13x. The upper cladding layer 13 may include three or more recesses 13x. The recess 13x may or may not penetrate the upper cladding layer 13.

[0019] In the illustrated example, the recess 13x penetrates the upper cladding layer 13, and a bottom surface of the recess 13x is constituted by an upper surface of the lower cladding layer 11. With this structure, since the recess 13x can be formed deep, when a part of the adhesive layer 30 enters into the recess 13x as described later, a larger amount of the adhesive layer 30 can be allowed to enter therein.

[0020] The second waveguide 20 includes a substrate 21, a second core 22, and a cladding layer 23. The second waveguide 20 is, for example, a SiN waveguide. The second waveguide 20 may be a silicon waveguide, a glass waveguide, or a polymer waveguide. The second waveguide 20 may be a part of a Planar Lightwave Circuit (PLC). Hereinafter, an example in which the second waveguide 20 is a silicon waveguide will be described.

[0021] The substrate 21 is a silicon substrate. The thickness of the substrate 21 is, for example, about 100 μm to 800 μm. The second core 22 is a fine optical waveguide and is located on one side of the substrate 21. There may be one or more second cores 22. In the illustrated example, three second cores 22 are arranged side by side on one side of the substrate 21 at predetermined intervals. The second cores 22 may be straight or may include curved portions. The spacing between adjacent second cores 22 may be constant or not.

[0022] Each second core 22 is arranged, for example, parallel to each other. The width of each second core 22 can be, for example, about 200 nm to 500 nm. In each second core 22, the region that photocouples with the first core 12 may have a tapered shape in which the width gradually narrows when viewed from above. The thickness of each second core 22 can be, for example, about 20 nm to 300 nm. The refractive index of the second core 22 is higher than the refractive index of the cladding layer 23, for example, about 3.5. The second core 22 is formed from, for example, silicon. The material of the second core 22 is not limited to silicon, and silicon nitride, gallium arsenide, lithium niobate, etc. may be used instead of silicon.

[0023] The cladding layer 23 covers the second core 22. The cladding layer 23 is, for example, a silicon oxide film (SiO2 or SiO2). X It can be formed from (etc.). The thickness of the cladding layer 23 can be, for example, about 2 μm to 6 μm. The refractive index of the cladding layer 23 can be, for example, about 1.5. The lower surface 23a of the cladding layer 23 is flat. In other words, no uneven structure like that shown in Patent Document 1 is formed on the lower surface 23a side of the cladding layer 23.

[0024] The outer edge of the lower surface 23a of the cladding layer 23 is in contact with the first surface 13a of the upper cladding layer 13. No adhesive layer or anything similar is placed between the outer edge of the lower surface 23a of the cladding layer 23 and the first surface 13a of the upper cladding layer 13; the two are in direct contact. The region where the second core 22 of the cladding layer 23 is located is on the second surface 13b via the adhesive layer 30. In a plan view, the second core 22 overlaps with the first core 12 and is photocoupled with the first core 12. The photocoupled between the first core 12 and the second core 22 is an adiabatic coupling.

[0025] The adhesive layer 30 is filled between the second surface 13b of the upper cladding layer 13 and the lower surface 23a of the cladding layer 23. A portion of the adhesive layer 30 protrudes from between the second surface 13b and the lower surface 23a and is located within the recess 13x. The thickness of the adhesive layer 30 located between the second surface 13b and the lower surface 23a is equal to the height difference between the first surface 13a and the second surface 13b of the upper cladding layer 13, and the excess adhesive layer 30 is placed within the recess 13x. The thickness of the adhesive layer 30 located between the second surface 13b and the lower surface 23a can be, for example, about 0.5 μm to 2 μm.

[0026] Preferably, a portion of the adhesive layer 30 protrudes from between the second surface 13b and the bottom surface 23a and is located between the inner surface 13d of the upper cladding layer 13 and the side surface 23d of the cladding layer 23. This suppresses leakage of light guiding the second core 22 from the cladding layer 23. In other words, if air is present between the inner surface 13d of the upper cladding layer 13 and the side surface 23d of the cladding layer 23, the refractive index of air is lower than that of the cladding layer 23, resulting in a discontinuity in the refractive index, which induces scattering loss and radiation loss. By positioning a portion of the adhesive layer 30 between the inner surface 13d of the upper cladding layer 13 and the side surface 23d of the cladding layer 23, the discontinuity in the refractive index can be suppressed.

[0027] As the adhesive layer 30, it is preferable to use a so-called optical adhesive that has good light transmittance and precise refractive index matching. Examples of optical adhesives include ultraviolet-curing adhesives mainly composed of epoxy resin. A thermosetting adhesive mainly composed of epoxy resin may also be used as the optical adhesive.

[0028] Figures 3 and 4 illustrate the manufacturing process of an optical waveguide device according to the first embodiment. To manufacture the optical waveguide device 1, first, as shown in Figure 3(a), a lower cladding layer 11 made of, for example, a film-like photosensitive resin is prepared, and a plurality of elongated first cores 12 are formed side by side on the lower cladding layer 11. Specifically, a photosensitive resin for obtaining the first cores 12 is formed on the lower cladding layer 11, the photosensitive resin is irradiated with ultraviolet light through a photomask, developed, and then cured by heat treatment.

[0029] Next, as shown in Figures 3(b) and 3(c), an upper cladding layer 13 is formed on the lower cladding layer 11 to cover the first core 12, thereby obtaining the first waveguide 10. Figure 3(b) is a plan view, and Figure 3(c) is a cross-sectional view along the CC line in Figure 3(b).

[0030] The upper cladding layer 13 can be formed, for example, by an imprint method. Specifically, a resin material to cover the first core 12 is placed on the lower cladding layer 11, and the resin material is softened by heating or other means to form a resin layer. A mold is prepared, having a fine uneven surface pattern corresponding to the desired shape of the upper cladding layer 13. The prepared mold is then pressed onto the softened resin layer to transfer the uneven surface pattern to the resin layer. Subsequently, the resin layer is cured by heating or ultraviolet irradiation, thereby integrally forming the upper cladding layer 13 of the desired shape. By using the imprint method, the upper cladding layer 13 can be formed with a simple manufacturing process and with small dimensional errors. For example, the height difference between the first surface 13a and the second surface 13b can be formed with an accuracy of ±1 μm or less.

[0031] The method for forming the upper cladding layer 13 is not limited to integral formation by imprinting, but any other method may be used. For example, a first resin film of a predetermined shape having a surface that will become the first surface 13a, a second resin film of a predetermined shape having a surface that will become the second surface 13b, and a third resin film of a predetermined shape having a surface that will become the third surface 13c may be prepared. The upper cladding layer 13 may then be formed by sequentially laminating the second resin film and the third resin film onto the first resin film and joining them together. Alternatively, a liquid or paste-like resin material may be used instead of a resin film.

[0032] Next, as shown in Figure 4(a), an adhesive is applied to the second surface 13b of the upper cladding layer 13 to form an adhesive layer 30. At this point, the adhesive layer 30 is not yet cured. For applying the adhesive, for example, a dispenser or an inkjet can be used.

[0033] Next, as shown in Figures 4(b) and 4(c), a second waveguide 20 is prepared, which includes a substrate 21, a second core 22, and a cladding layer 23. The second waveguide 20 is then placed on the first waveguide 10 via an uncured adhesive layer 30, and the uncured adhesive layer 30 is then cured. Figure 4(b) is a plan view, and Figure 4(c) is a cross-sectional view along the DD line in Figure 4(b).

[0034] Specifically, the second waveguide 20 is positioned on the first waveguide 10 such that the outer edge of the lower surface 23a of the cladding layer 23 is in direct contact with the first surface 13a of the upper cladding layer 13, and the region where the second core 22 of the cladding layer 23 is located is on the second surface 13b via the adhesive layer 30. At this time, the excess adhesive constituting the uncured adhesive layer 30 protrudes from between the second surface 13b and the lower surface 23a and enters the recess 13x. Preferably, the excess adhesive constituting the uncured adhesive layer 30 further protrudes from between the second surface 13b and the lower surface 23a, as shown in Figure 2(b), and enters between the inner surface 13d of the upper cladding layer 13 and the side surface 23d of the cladding layer 23.

[0035] After placing the second waveguide 20 on the first waveguide 10 via an uncured adhesive layer 30, the uncured adhesive layer 30 is cured by heating or ultraviolet irradiation. As a result, the second core 22 of the second waveguide 20 overlaps with the first core 12 of the first waveguide 10 in a plan view and is photocoupled with the first core 12. Through the above steps, an optical waveguide apparatus 1 is obtained.

[0036] Thus, in the optical waveguide device 1, the thickness of the adhesive layer 30, which is located between the second surface 13b and the bottom surface 23a and affects the optical coupling between the first core 12 and the second core 22, can be mechanically controlled in accordance with the height difference between the first surface 13a and the second surface 13b relative to the upper surface of the lower cladding layer 11. Therefore, variations in the thickness of the adhesive layer 30 can be reduced without depending on the amount of adhesive applied when forming the adhesive layer 30. For example, the thickness of the adhesive layer 30 located between the second surface 13b and the bottom surface 23a can be controlled to approximately 0.5 μm to 2 μm. By reducing variations in the thickness of the adhesive layer 30, the coupling efficiency between the first core 12 and the second core 22 can be stabilized.

[0037] Furthermore, when forming the adhesive layer 30, any excess adhesive seeps out from between the second surface 13b and the bottom surface 23a and enters the recess 13x. Therefore, it is possible to suppress the effect of excess adhesive on the thickness of the adhesive layer 30 located between the second surface 13b and the bottom surface 23a.

[0038] Furthermore, in the structure of the optical waveguide device 1, the lower surface 23a of the cladding layer 23 in the second waveguide 20 can be flat, and there is no need to process the optical waveguide to create an uneven structure, as in the structure of Patent Document 1. Therefore, a general-purpose optical waveguide can be selected as the second waveguide 20, which is advantageous in terms of cost. In addition, since the optical waveguide device 1 does not have a fitting structure like that in Patent Document 1, the degree of freedom in the structure and implementation method of the first waveguide 10 and the second waveguide 20 can be improved.

[0039] Furthermore, in the optical waveguide device 1, the first core 12 is always covered by the upper cladding layer 13, including during the manufacturing process of the optical waveguide device 1, making it less susceptible to external influences. For example, it is possible to suppress a decrease in yield caused by mechanical loads on the first core 12 or the adhesion of foreign matter.

[0040] Figure 5 is a plan view showing an example of use of the optical waveguide device according to the first embodiment. Figure 6 is a cross-sectional view showing an example of use of the optical waveguide device according to the first embodiment, and shows a cross-section along the EE line in Figure 1.

[0041] As shown in Figures 5 and 6, the optical waveguide device 1 can be mounted on a wiring board 110. Any wiring board can be used as the wiring board 110, such as a build-up board, an electronic component embedded board, a silicon board, or a ceramic board.

[0042] The electrodes of the wiring board 110 and the electrodes of the second waveguide 20 can be electrically connected via, for example, a columnar electrode 120 made of copper or the like. A resin portion 130 covering the columnar electrode 120 may be filled into the region where the wiring board 110 and the second waveguide 20 face each other.

[0043] In the illustrated example, a fiber array 140 is mounted on a wiring board 110. The fiber array 140 is positioned on the wiring board 110 so as to face the end face of the first waveguide 10. Specifically, the fiber array 140 has optical fibers, and the central axis of the optical fiber core is positioned to coincide with the central axis of the first core 12 of the first waveguide 10. This allows the two to be optically coupled. The fiber array 140 can be fixed to the wiring board 110, for example, with an adhesive.

[0044] It is preferable to place an optical adhesive between the opposing surfaces of the fiber array 140 and the first waveguide 10. This prevents air reflection and improves the coupling efficiency between the optical fiber cores of the fiber array 140 and the first core 12 of the first waveguide 10. The optical adhesive is as described above.

[0045] Electronic components electrically connected to the optical waveguide device 1 may be arranged on the wiring board 110. Examples of electronic components include IC chips incorporating a DSP (Digital Signal Processor) or amplifier for processing the output signal from the optical waveguide device 1.

[0046] Although preferred embodiments have been described in detail above, the invention is not limited to the embodiments described above, and various modifications and substitutions can be made to the embodiments described above without departing from the scope of the claims. [Explanation of symbols]

[0047] 1 Optical waveguide device 10 Waveguide 1 11 Lower cladding layer 12. First Core 13. Upper cladding layer 13a 1st page 13b Side 2 13c 3rd page 13d Inner surface 13x recess 20 Second Waveguide 21 circuit boards 22 Second Core 23 Clad Layer 23a Bottom side 30 Adhesive layer 110 Wiring board 120 Column electrode 130 Resin part 140 Fiber Array

Claims

1. It comprises a first waveguide and a second waveguide arranged on the first waveguide, The first waveguide is, Lower cladding layer, A first core disposed on the lower cladding layer, It includes an upper cladding layer disposed on the lower cladding layer and covering the first core, The aforementioned upper cladding layer is The first surface on which the second waveguide is arranged, A second surface located on the side closer to the lower cladding layer relative to the first surface in cross-sectional view, and overlapping with the first core in plan view, It comprises a recess located between the first surface and the second surface in a plan view, and recessed relative to the second surface in a cross-sectional view, The second waveguide includes a second core and a cladding layer covering the second core. The outer edge of the lower surface of the cladding layer is in contact with the first surface, The region of the cladding layer in which the second core is located is located on the second surface via the adhesive layer, The second core is an optical waveguide device in which the second core overlaps with the first core in a plan view and is optically coupled with the first core.

2. The aforementioned upper cladding layer is The optical waveguide apparatus according to claim 1, further comprising a third surface located on the side furthest from the lower cladding layer relative to the first surface in a cross-sectional view, and located outside the first surface in a plan view.

3. The upper cladding layer has an inner surface that connects the third surface and the second surface, The optical waveguide apparatus according to claim 2, wherein a portion of the adhesive layer is located between the inner surface and the side surface of the cladding layer.

4. The optical waveguide apparatus according to any one of claims 1 to 3, wherein a portion of the adhesive layer is located within the recess.

5. The optical waveguide apparatus according to any one of claims 1 to 3, wherein the lower surface of the cladding layer is flat.

6. The optical waveguide apparatus according to any one of claims 1 to 3, wherein the bottom surface of the recess is formed by the upper surface of the lower cladding layer.

7. The optical waveguide apparatus according to any one of claims 1 to 3, wherein the upper cladding layer comprises a plurality of recesses.

8. The optical waveguide apparatus according to any one of claims 1 to 3, wherein the upper cladding layer is integrally formed.

9. The optical waveguide apparatus according to any one of claims 1 to 3, wherein the first core, the lower cladding layer, and the upper cladding layer are formed from resin.

10. The optical waveguide apparatus according to claim 9, wherein the second core is formed from silicon and the cladding layer is formed from a silicon oxide film.

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