Spot size converter and method for manufacturing a spot size converter

Abstract

To provide a spot size converter which can reduce loss generated when converting a mode field diameter and a method for manufacturing the spot size converter.SOLUTION: The spot size converter includes: a first clad layer; a first waveguide core on the first clad layer; a second waveguide core on the first clad layer, the second waveguide core covering the first waveguide core and having a lower index of refraction than the first waveguide core; and a second clad layer on the first clad layer, the second clad layer covering the first waveguide core and the second waveguide core and having a lower index of refraction than the second waveguide core. The second waveguide core has a first part having a first height in a laminate direction with respect to the first clad layer and a second part having a second height higher than the first height in a laminate direction with respect to the first clad layer.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a spot size converter and a method for manufacturing the spot size converter.

Background Art

[0002] With the progress of information technology (IT) or information and communication technology (ICT), the amount of information to be transmitted has been increasing significantly. In such a situation, optical wiring technology has attracted attention in recent years. In optical wiring technology, information transmission between elements, boards, or chips in an information processing device is performed by optical signals using an optical device such as an optical fiber and / or an optical waveguide element as a transmission medium.

[0003] It is desirable that the optical connection between the optical waveguide core of an optical device and an external element such as an optical fiber be performed with low loss and efficiently. For such a connection, when optically connecting between the optical waveguide core and an external element such as an optical fiber, the mode field diameter (MFD) of light may be converted between them. As an element for converting the MFD, for example, a spot size converter (SSC) is known. According to the spot size converter, the MFD of the light input and output between the external element and the optical waveguide core can be reduced or enlarged. For example, Patent Document 1 discloses a spot size converter including a first optical waveguide core having a tapered end portion and a second optical waveguide core covering the lower surface thereof. Patent Document 1 teaches that the refractive index of the second optical waveguide core is made larger than the refractive index of the cladding layer and smaller than the refractive index of the first optical waveguide core.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] In spot size converters, it is desirable to minimize losses when converting the mode field diameter as much as possible.

[0006] The object of this disclosure is to provide a spot size converter that can reduce losses when converting mode field diameters, and a method for manufacturing such a spot size converter. [Means for solving the problem]

[0007] A spot size converter according to one embodiment is: The first cladding layer, A first waveguide core formed on the first cladding layer, A second waveguide core, formed on the first cladding layer and covering the first waveguide core, has a lower refractive index than the first waveguide core, A second cladding layer is formed on the first cladding layer and covers the first waveguide core and the second waveguide core, having a lower refractive index than the second waveguide core. A third waveguide core is formed between the first cladding layer and the second cladding layer, covering the first waveguide core and the second waveguide core, It is equipped with. The second waveguide core is A first portion having a first height in the stacking direction relative to the first cladding layer, A second portion having a second height lower than the first height in the stacking direction relative to the first cladding layer, It holds.

[0008] A method for manufacturing a spot size converter according to one embodiment is as follows: The steps include forming the first cladding layer, The steps include forming a first waveguide core on the first cladding layer, The steps include forming a second waveguide core on the first cladding layer, such that it covers the first waveguide core and has a lower refractive index than the first waveguide core, The steps include forming a third waveguide core on the first cladding layer so as to cover the first waveguide core and the second waveguide core, The first waveguide core is placed on the first cladding layer. ,before Note: Second waveguide core and the third waveguide core The steps include forming a second cladding layer with a lower refractive index than the second waveguide core so as to cover the above, Includes. In the above manufacturing method, the second waveguide core is A first portion having a first height in the lamination direction relative to the first cladding layer, A second portion having a second height lower than the first height in the lamination direction relative to the first cladding layer, It is formed to have. [Effects of the Invention]

[0009] According to one embodiment, a spot size converter capable of reducing losses when converting mode field diameters, and a method for manufacturing such a spot size converter can be provided. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic plan view showing the configuration of a spot size converter according to one embodiment. [Figure 2] This figure shows a cross-section of a spot size converter according to one embodiment. [Figure 3] This figure shows a cross-section of a spot size converter according to one embodiment. [Figure 4] This figure shows a cross-section of a spot size converter according to one embodiment. [Figure 5A] This figure illustrates a method for manufacturing a spot size converter according to one embodiment. [Figure 5B] This figure illustrates a method for manufacturing a spot size converter according to one embodiment. [Figure 6A]This is a diagram for explaining a method of manufacturing a spot size converter according to an embodiment. [Figure 6B] This is a diagram for explaining a method of manufacturing a spot size converter according to an embodiment. [Figure 7A] This is a diagram for explaining a method of manufacturing a spot size converter according to an embodiment. [Figure 7B] This is a diagram for explaining a method of manufacturing a spot size converter according to an embodiment. [Figure 8] This is a diagram showing a cross section of a spot size converter according to another embodiment.

Embodiments for Carrying Out the Invention

[0011] In the embodiments described below, the "optical waveguide" may be an element that optically connects between the optical waveguide core of an optical device and an external element such as an optical fiber. Also, in the embodiments described below, the "optical waveguide" may be one having the function of the above-described spot size converter (SSC). Hereinafter, spot size converters according to several embodiments will be described with reference to the drawings. Here, the drawings showing the respective embodiments in the present disclosure are schematically shown with appropriate simplifications for the purpose of explanation. Therefore, the drawings showing the respective embodiments in the present disclosure do not necessarily show the actual sizes of each member, the actual size ratios between each member, or the actual size ratios in each direction of each member.

[0012] For example, in fields such as silicon photonics, reducing connection loss is crucial for achieving low-loss substrate mounting. In particular, in structures where a Si waveguide is optically coupled to an optical fiber with low loss, the core diameter changes significantly. Therefore, efficient substrate mounting is desirable in such structures. When butt coupling is performed, where the optical fiber is coupled by butting it against the end face of the substrate, the beam sizes (MFD) passing through the Si waveguide and the optical fiber differ significantly. Therefore, a spot size converter (SSC) is used to suppress optical loss during such coupling. Furthermore, it is desirable to reduce not only the loss when converting the MFD of the orthogonal polarization (TE wave (transverse electric wave)) component, but also the loss when converting the MFD of the parallel polarization (transverse magnetic wave (TM wave)) component.

[0013] In spot-size converters, to increase the MFD within the Si waveguide for both TE and TM polarization, a planarization process is generally used in the manufacturing process. For example, the spot-size converter disclosed in the aforementioned Patent Document 1 is also assumed to use a planarization process in its manufacturing process. Such a manufacturing process using a planarization process is complicated and increases manufacturing costs. However, without such a manufacturing process, it is difficult to improve coupling efficiency. Furthermore, such a manufacturing process creates constraints, such as not being able to be performed after metal wiring has been installed. A spot-size converter according to one embodiment achieves loss reduction for both TE and TM polarization without performing a planarization process during manufacturing.

[0014] First, a spot size converter according to one embodiment will be described.

[0015] Figures 1 to 3 show a schematic configuration of a spot size converter 1 according to one embodiment. Figure 1 is a plan view of the spot size converter 1 according to one embodiment. That is, Figure 1 shows the spot size converter 1 according to one embodiment viewed from above. Figures 2 and 3 are cross-sectional views of the spot size converter 1 according to one embodiment. That is, Figure 2 shows a cross-section of the spot size converter 1 shown in Figure 1 along the line II-II. Figure 3 shows a cross-section of the spot size converter 1 shown in Figure 1 along the line III-III.

[0016] As shown in Figures 1 to 3, a spot size converter 1 according to one embodiment may include a first cladding layer 11, a second cladding layer 12, a first waveguide core 21, and a second waveguide core 22.

[0017] In the spot size converter 1 shown in Figure 1, light is input from one end in the direction indicated by arrow A1. Light is also output from the other end of the spot size converter 1 in the direction indicated by arrow A2. That is, the spot size converter 1 shown in Figures 1 to 3 propagates light in the positive Z-axis direction. Hereinafter, in this specification, the end indicated by arrow A1 in the spot size converter 1 will also be referred to as the "first end" of the spot size converter 1. The end indicated by arrow A2 in the spot size converter 1 will also be referred to as the "second end" of the spot size converter 1. When light is input from the first end and output from the second end, the first end functions as the input end and the second end functions as the output end. When light is input from the second end and output from the first end, the second end functions as the input end and the first end functions as the output end. Here, the first and second ends of the light in the spot size converter 1 may be virtual ends or actual (physical) ends. The input terminal of the spot size converter 1 may be an end that is optically connected to, for example, an optical device, and the output terminal of the spot size converter 1 may be an end that is optically connected to, for example, an external element such as a semiconductor laser or an optical fiber.

[0018] In the following description, the direction of the Z-axis shown in Figures 1 to 3 may be the direction parallel to the direction in which light is guided (propagated) in the spot size converter 1. The spot size converter 1 can convert (magnify) the MFD of light input to the first end (the side indicated by arrow A1) and output it from the second end (the side indicated by arrow A2). In this case, in the spot size converter 1, light is guided (propagated) in the positive Z-axis direction. Conversely, the spot size converter 1 can convert (reduce) the MFD of light input to the second end (the side indicated by arrow A2) and output it from the first end (the side indicated by arrow A1). In this case, in the spot size converter 1, light is guided (propagated) in the negative Z-axis direction. Hereafter, the direction of the Z-axis shown in Figures 1 to 3 will indicate the direction (axial direction) of the axis of the spot size converter 1, as well as the first waveguide core 21 and the second waveguide core 22. Here, the axial direction of the spot size converter 1, and the first waveguide core 21 and the second waveguide core 22, etc., may be the direction in which light is guided (propagated) in these members, for example, the direction of the optical axis.

[0019] Furthermore, the direction of the Y-axis shown in Figures 1 to 3 may be parallel to the thickness direction of the spot size converter 1. Hereafter, the direction of the Y-axis shown in Figures 1 to 3 will indicate the thickness direction (thickness direction) of the spot size converter 1 and each component in the spot size converter 1. The positive direction of the Y-axis shown in Figures 1 to 3 may be, for example, vertically upward. Also, the negative direction of the Y-axis shown in Figures 1 to 3 may be, for example, vertically downward.

[0020] Furthermore, the direction of the X-axis shown in Figures 1 to 3 may be parallel to the direction of the width of the spot size converter 1. Here, the width of the spot size converter 1 may be the length perpendicular to the axis (Z-axis direction) of the spot size converter 1 in a plane parallel to the XZ plane. Hereafter, the direction of the X-axis shown in Figures 1 to 3 will indicate the direction of the width (width direction) of the spot size converter 1 and each component in the spot size converter 1.

[0021] As shown in Figures 2 and 3, the first cladding layer 11 may be the lower cladding or undercladding in the spot size converter 1. The first cladding layer 11 may be designed to have a lower refractive index than the first waveguide core 21 and the second waveguide core 22. The refractive index of the first cladding layer 11 is not particularly limited, but may be, for example, around 1.45 to 1.46.

[0022] As shown in Figures 2 and 3, the first waveguide core 21 is formed on the first cladding layer 11. The first waveguide core 21 may be partially formed on the upper surface of the first cladding layer 11. The first waveguide core 21 may be designed to have a higher refractive index than the first cladding layer 11. The refractive index of the first waveguide core 21 is not particularly limited, but may be, for example, around 1.463 to 1.467.

[0023] As shown in Figures 2 and 3, the second waveguide core 22 is formed on the first cladding layer 11. The second waveguide core 22 is formed to cover the first waveguide core 21. As shown in Figures 1 and 3, the second waveguide core 22 may be formed to cover the periphery of the first waveguide core 21, except for the portion at the first end of the spot size converter 1. The second waveguide core 22 may be designed to have a higher refractive index than the first cladding layer 11. The refractive index of the first waveguide core 21 is not particularly limited, but may be, for example, around 1.463 to 1.467. Alternatively, the second waveguide core 22 may be designed to have a lower refractive index than the first waveguide core 21.

[0024] As shown in Figures 1 to 3, the second cladding layer 12 may be the upper cladding or overcladding in the spot size converter 1. The second cladding layer 12 is formed on the first cladding layer 11. The second cladding layer 12 is formed to cover the first waveguide core 21 and the second waveguide core 22. As shown in Figures 1 and 3, the second cladding layer 12 may be formed to cover the periphery of the first waveguide core 21 and the second waveguide core 22, except for the portion at the first end of the spot size converter 1. More specifically, as described above, the second waveguide core 22 may be formed to cover the periphery of the first waveguide core 21, except for the portion at the first end of the spot size converter 1. The second cladding layer 12 may be formed to cover the periphery of the second waveguide core 22 (which covers the periphery of the first waveguide core 21), except for the portion at the first end of the spot size converter 1. The second cladding layer 12 may be designed to have a lower refractive index than the second waveguide core 22. The second cladding layer 12 may be designed to have a lower refractive index than both the first waveguide core 21 and the second waveguide core 22. The refractive index of the second cladding layer 12 is not particularly limited, but may be, for example, around 1.45 to 1.46.

[0025] As shown in Figure 3, the second waveguide core 22 has a first portion 221 and a second portion 222. The first portion 221 has a first height h1 in the stacking direction (Y-axis direction) relative to the first cladding layer 11. The second portion 222 has a second height h2 in the stacking direction (Y-axis direction) relative to the first cladding layer 11. In the spot size converter 1 according to one embodiment, the second height h2 may be lower than the first height h1.

[0026] In the second waveguide core 22, the first portion 221 and the second portion 222 are not physically separated and may be formed as a single unit. That is, in the second waveguide core 22, the division between the first portion 221 and the second portion 222 may be virtual. In Figure 3, the virtual boundary between the first portion 221 and the second portion 222 is shown as boundary B.

[0027] Furthermore, as shown in Figure 3, the boundary B between the first portion 221 and the second portion 222 in the direction of light propagation (Z-axis direction) by the second waveguide core 22 may be designed to be located between the termination T1 of the first waveguide core 21 and the termination T2 of the second waveguide core 22. Alternatively, the boundary B between the first portion 221 and the second portion 222 of the second waveguide core 22 may have a height difference (a step difference of height h1-height h2) in the stacking direction relative to the first cladding layer 11. Such a step in the second waveguide core 22 allows the spot size converter 1 to reduce losses when converting the MFD of the TM wave component.

[0028] Here, when forming the second waveguide core 22 having a first portion 221 and a second portion 222, it is not necessary to perform a process to flatten the upper surfaces of the first waveguide core 21 and / or the second waveguide core 22. For example, by forming the first waveguide core 21 on the first cladding layer 11 and then depositing the second waveguide core 22 on top of them, a film of a somewhat uniform thickness is formed on the first cladding layer 11 and the first waveguide core 21. As a result, a step is formed at the boundary B between the first portion 221 and the second waveguide core 22 without flattening the upper surfaces of the first waveguide core 21 and / or the second waveguide core 22.

[0029] Therefore, according to the spot size converter 1 of one embodiment, the loss when converting MFD can be reduced without performing a planarization process. Furthermore, because the spot size converter 1 of one embodiment does not perform a planarization process, it can be processed even after metal wiring has been installed.

[0030] Figure 4 shows a cross-section of the spot size converter 1 shown in Figure 1, specifically the III-III line. Figure 4 shows the same spot size converter 1 as shown in Figure 3. In Figure 3, the second waveguide core 22 was described in detail. In Figure 4, the second cladding layer 12 will be described in detail.

[0031] As shown in Figure 4, the second cladding layer 12 may have a third portion 123 and a fourth portion 124. The second cladding layer 12 may also have a fifth portion 125.

[0032] The third portion 123 may have a third height h3 in the stacking direction (Y-axis direction) relative to the first cladding layer 11. The fourth portion 124 may have a fourth height h4 in the stacking direction (Y-axis direction) relative to the first cladding layer 11. In one embodiment of the spot size converter 1, the fourth height h4 may be lower than the third height h3. The fifth portion 125 may have a fifth height h5 in the stacking direction (Y-axis direction) relative to the first cladding layer 11. In one embodiment of the spot size converter 1, the fifth height h5 may be lower than the fourth height h4.

[0033] In the second cladding layer 12, the third portion 123 and the fourth portion 124 may not be physically separated but formed as a single unit. That is, the distinction between the third portion 123 and the fourth portion 124 in the second cladding layer 12 may be virtual. Also, in the second cladding layer 12, the fourth portion 124 and the fifth portion 125 may not be physically separated but formed as a single unit. That is, the distinction between the fourth portion 124 and the fifth portion 125 in the second cladding layer 12 may be virtual.

[0034] As shown in Figure 4, in the second cladding layer 12, the boundary between the third portion 123 and the fourth portion 124 may be designed to be located between the boundary between the first portion 221 and the second portion 222 of the second waveguide core 22 and the end of the second waveguide core 22. Alternatively, the boundary between the third portion 123 and the fourth portion 124 of the second cladding layer 12 may have a height difference in the stacking direction relative to the first cladding layer 11 (a step difference of height h3-height h4). Also, in the second cladding layer 12, the boundary between the fourth portion 124 and the fifth portion 125 may be designed to be located between the end of the second waveguide core 22 and the end of the second cladding layer 12. Furthermore, the boundary between the fourth portion 124 and the fifth portion 125 of the second cladding layer 12 may have a height difference in the stacking direction relative to the first cladding layer 11 (a step difference of height h4-height h5).

[0035] Here, when forming the second cladding layer 12 having a third portion 123 and a fourth portion 124 (and a fifth portion 125), it is not necessary to perform a process to flatten the upper surface of the second waveguide core 22. For example, by forming the second waveguide core 22 on the first waveguide core 21 and then depositing the second cladding layer 12 on top of them, a film of a somewhat uniform thickness is formed on the first waveguide core 21 and the second waveguide core 22. As a result, even without flattening the upper surfaces of the first waveguide core 21 and the second waveguide core 22, a step is formed at the boundary between the third portion 123 and the fourth portion 124 (and a fifth portion 125).

[0036] Therefore, the spot size converter 1 according to one embodiment can simplify the manufacturing process by eliminating the need for a planarization process.

[0037] Next, a method for manufacturing the spot size converter 1 according to one embodiment will be described.

[0038] As described above, the spot size converter 1 according to one embodiment can be manufactured without performing a planarization process. Aside from the fact that it is manufactured without a planarization process, the spot size converter 1 according to one embodiment can be manufactured by the same or similar method as the cladding and / or waveguide core of known spot size converters. Therefore, explanations that are the same or similar as the cladding and / or waveguide core of known spot size converters may be simplified or omitted as appropriate.

[0039] When manufacturing the spot size converter 1 according to one embodiment, first, a first cladding layer 11 is formed. Figures 5A and 5B show the state in which the first cladding layer 11 has been formed. Figure 5A shows the manufacturing process of the spot size converter 1 from the same viewpoint as Figure 2. Figure 5B shows the manufacturing process of the spot size converter 1 from the same viewpoint as Figure 3.

[0040] Next, a first waveguide core 21 is formed on the first cladding layer 11. Figures 6A and 6B show the formation of the first waveguide core 21 on the first cladding layer 11. Figure 6A shows the formation of the first waveguide core 21 on the first cladding layer 11 shown in Figure 5A. Figure 6B shows the formation of the first waveguide core 21 on the first cladding layer 11 shown in Figure 5B.

[0041] Next, a second waveguide core 22 is formed on the first cladding layer 11. Figures 7A and 7B show the formation of the second waveguide core 22 on the first cladding layer 11. Figure 7A shows the formation of the second waveguide core 22 on the first cladding layer 11 and the first waveguide core 21 shown in Figure 6A. Figure 7B shows the formation of the second waveguide core 22 on the first cladding layer 11 and the first waveguide core 21 shown in Figure 6B. As described above, the formation of the second waveguide core 22 can be carried out without going through the process of flattening the upper surface of the first waveguide core 21.

[0042] As shown in Figures 7A and 7B, the second waveguide core 22 is formed on the first cladding layer 11 so as to cover the first waveguide core 21. Furthermore, as described above, the refractive index of the second waveguide core 22 may be lower than that of the first waveguide core 21.

[0043] In Figure 7B, the virtual boundary between the first part 221 and the second part 222 of the second waveguide core 22 is shown as boundary B. Similarly, in Figure 7A, the virtual boundary between the first part 221 and the second part 222 of the second waveguide core 22 is shown as boundary C.

[0044] Furthermore, in the X-axis direction shown in Figure 7A, the boundary C between the first portion 221 and the second portion 222 may be designed to be located between the widthwise end S1 of the first waveguide core 21 and the widthwise end S2 of the second waveguide core 22. Also, the boundary C between the first portion 221 and the second portion 222 of the second waveguide core 22 may have a height difference in the stacking direction relative to the first cladding layer 11 (a step difference of height h1 - height h2). Such a step in the second waveguide core 22 allows the spot size converter 1 to reduce losses when converting the MFD of the TE wave component.

[0045] Thus, in the X-axis direction shown in Figure 7A, the boundary C between the first part 221 and the second part 222 of the second waveguide core 22 may have a step in the stacking direction relative to the first cladding layer 11 (a step of height h1-h2). Here, the X-axis direction shown in Figure 7A may be the direction perpendicular to the direction of light propagation by the second waveguide core 22 shown in Figure 7A.

[0046] In a method for manufacturing a spot size converter 1 according to one embodiment, a second cladding layer 12 is then formed on the first cladding layer 11. The formation of the second cladding layer 12 on the first cladding layer 11, the first waveguide core 21, and the second waveguide core 22 shown in Figure 7A is shown in Figure 2. The formation of the second cladding layer 12 on the first cladding layer 11, the first waveguide core 21, and the second waveguide core 22 shown in Figure 7B is shown in Figure 3. As shown in Figures 2 and 3, the second cladding layer 12 may be formed on the first cladding layer 11 so as to cover the first waveguide core 21 and the second waveguide core 22. Furthermore, as described above, the refractive index of the second cladding layer 12 may be lower than that of the second waveguide core 22. As described above, the formation of the second cladding layer 12 may be carried out without going through the process of flattening the upper surfaces of the first waveguide core 21 and / or the second waveguide core 22.

[0047] By the manufacturing method described above, the second waveguide core 22 is formed to have a first portion 221 and a second portion 222. The first portion 221 has a first height h1 in the stacking direction relative to the first cladding layer 11. The second portion 222 has a second height h2 that is lower than the first height h1 in the stacking direction relative to the first cladding layer 11.

[0048] (Other embodiments) The spot size converter 1 according to one embodiment described above was described as comprising two waveguide cores, such as a first waveguide core 21 and a second waveguide core 22. However, in other embodiments, the waveguide cores are not limited to two, and may comprise three or more waveguide cores.

[0049] Figure 8 is a diagram showing a cross-section of a spot size converter 2 according to another embodiment. Figure 8 shows a spot size converter 2 according to another embodiment from the same viewpoint as Figure 3. As shown in Figure 8, in the spot size converter 2, a third waveguide core 23 may be formed so as to cover the first waveguide core 21 and the second waveguide core 22. The third waveguide core 23 may be formed between the first cladding layer 11 and the second cladding layer 12.

[0050] Thus, the spot size converter 2 according to a modified embodiment may include a third waveguide core 23 formed between the first cladding layer 11 and the second cladding layer 12, covering the first waveguide core 21 and the second waveguide core 22.

[0051] While embodiments of this disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art will find it easy to make various modifications or alterations based on this disclosure. Therefore, it should be noted that these modifications or alterations are within the scope of this disclosure. For example, the functions included in each component or step can be rearranged in a logically consistent manner, and multiple components or steps can be combined into one or separated. While embodiments of this disclosure have been described primarily in terms of optical waveguides, embodiments of this disclosure can also be realized as methods for manufacturing optical waveguides. [Explanation of Symbols]

[0052] 1,2 Spot Size Converter 11. First Cladding Layer 12. Second Cladding Layer 123 Part 3 124 Part 4 125 Part 5 21 Waveguide Core 22 Second waveguide core 23 Third waveguide core 221 Part 1 222 Part 2

Claims

1. The first cladding layer, A first waveguide core formed on the first cladding layer, A second waveguide core is formed on the first cladding layer and covers the first waveguide core, and has a lower refractive index than the first waveguide core. A second cladding layer is formed on the first cladding layer and covers the first waveguide core and the second waveguide core, having a lower refractive index than the second waveguide core. A third waveguide core is formed between the first cladding layer and the second cladding layer, covering the first waveguide core and the second waveguide core, Equipped with, The second waveguide core is A first portion having a first height in the stacking direction relative to the first cladding layer, A second portion having a second height lower than the first height in the stacking direction relative to the first cladding layer, A spot size converter having the following features.

2. The spot size converter according to claim 1, wherein, in the direction of light propagation by the second waveguide core, the boundary between the first portion and the second portion of the second waveguide core is located between the end of the first waveguide core and the end of the second waveguide core.

3. The spot size converter according to claim 1, wherein, in the direction of light propagation by the second waveguide core, the boundary between the first portion and the second portion of the second waveguide core has a step in the stacking direction relative to the first cladding layer.

4. The spot size converter according to claim 1, wherein, in a direction perpendicular to the direction of light propagation by the second waveguide core, the boundary between the first portion and the second portion of the second waveguide core has a step in the stacking direction relative to the first cladding layer.

5. The aforementioned second cladding layer is A third portion having a third height in the stacking direction relative to the first cladding layer, A fourth portion having a fourth height lower than the third height in the stacking direction relative to the first cladding layer, A spot size converter according to claim 1, having the following features.

6. The spot size converter according to claim 5, wherein the second cladding layer has a fifth portion having a fifth height lower than the fourth height in the stacking direction relative to the first cladding layer.

7. The steps include forming the first cladding layer, The steps include forming a first waveguide core on the first cladding layer, The steps include forming a second waveguide core on the first cladding layer, such that it covers the first waveguide core and has a lower refractive index than the first waveguide core, The steps include forming a third waveguide core on the first cladding layer so as to cover the first waveguide core and the second waveguide core, The steps include forming a second cladding layer on the first cladding layer, such that it covers the first waveguide core, the second waveguide core, and the third waveguide core, and having a lower refractive index than the second waveguide core, A method for manufacturing a spot size converter, including, The second waveguide core is A first portion having a first height in the lamination direction relative to the first cladding layer, A second portion having a second height lower than the first height in the lamination direction relative to the first cladding layer, A method for manufacturing which is formed to have

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