WO2024142894A1

WO2024142894A1 - Spot size converter, and method for manufacturing spot size converter

Info

Publication number: WO2024142894A1
Application number: PCT/JP2023/044304
Authority: WO
Inventors: 玲緒奈泉二; 紘崇上村
Original assignee: 京セラ株式会社
Priority date: 2022-12-26
Filing date: 2023-12-11
Publication date: 2024-07-04
Also published as: JP2024092720A

Abstract

This spot size converter comprises: a first cladding layer; a first waveguide core formed on the first cladding layer; a second waveguide core formed on the first cladding layer in a manner covering the first waveguide core, and having a lower refractive index than the first waveguide core; and a second cladding layer formed on the first cladding layer in a manner covering the first waveguide core and the second waveguide core, and having a lower refractive index than the second waveguide core. The second waveguide core comprises a first portion having the first height in the lamination direction in relation to the first cladding layer, and a second portion having the second height in the lamination direction in relation to the first cladding, the second height being shorter than the first height.

Description

Spot size converter and method for manufacturing the spot size converter

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No. 2022-208848, filed on December 26, 2022, the entire disclosure of which is incorporated herein by reference.

This disclosure relates to a spot size converter and a method for manufacturing a spot size converter.

With the advancement of information technology (IT) and information and communication technology (ICT), the amount of information that needs to be transmitted has been increasing dramatically. In this situation, optical wiring technology has been attracting attention in recent years. Optical wiring technology uses optical devices that use optical fiber and/or optical waveguide elements as the transmission medium to transmit information between elements, boards, or chips in information processing equipment using optical signals.

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 efficiently with low loss. For such a connection, when optically connecting an optical waveguide core and an external element such as an optical fiber, the mode field diameter (MFD) of light between them may be converted. For example, a spot size converter (SSC) is known as an element that converts MFD. The spot size converter can reduce or expand the MFD of light input/output between the external element and the optical waveguide core. For example, Patent Document 1 discloses a spot size converter that includes a first optical waveguide core having a tapered end and a second optical waveguide core that covers the lower surface of the first optical waveguide core. Patent Document 1 teaches that the refractive index of the second optical waveguide core is greater than the refractive index of the cladding layer and less than the refractive index of the first optical waveguide core.

JP 2016-18191 A

The spot size converter according to one embodiment includes:
A first cladding layer;
a first waveguide core formed on the first cladding layer;
a second waveguide core formed on the first cladding layer, covering the first waveguide core, and having a refractive index lower than that of the first waveguide core;
a second clad layer formed on the first clad layer, covering the first waveguide core and the second waveguide core, the second clad layer having a refractive index lower than that of the second waveguide core;
Equipped with.
The second waveguide core is
a first portion having a first height in a stacking direction relative to the first cladding layer;
a second portion having a second height in a stacking direction relative to the first cladding layer that is lower than the first height;
has.

A method for manufacturing a spot size converter according to one embodiment includes the steps of:
forming a first cladding layer;
forming a first waveguide core on the first cladding layer;
forming a second waveguide core having a lower refractive index than the first waveguide core on the first cladding layer so as to cover the first waveguide core;
forming a second clad layer on the first clad layer so as to cover the first waveguide core and the second waveguide core, the second clad layer having a refractive index lower than that of the second waveguide core;
including.
In the manufacturing method, the second waveguide core is
a first portion having a first height in a lamination direction relative to the first cladding layer;
a second portion having a second height in a stacking direction relative to the first cladding layer that is lower than the first height;
The substrate is formed so as to have

FIG. 1 is a plan view illustrating a schematic configuration of a spot size converter according to an embodiment. FIG. 2 illustrates a cross-section of a spot size converter according to an embodiment. FIG. 2 illustrates a cross-section of a spot size converter according to an embodiment. FIG. 2 illustrates a cross-section of a spot size converter according to an embodiment. 1A to 1C are diagrams illustrating a method for manufacturing a spot size converter according to an embodiment. 1A to 1C are diagrams illustrating a method for manufacturing a spot size converter according to an embodiment. 1A to 1C are diagrams illustrating a method for manufacturing a spot size converter according to an embodiment. 1A to 1C are diagrams illustrating a method for manufacturing a spot size converter according to an embodiment. 1A to 1C are diagrams illustrating a method for manufacturing a spot size converter according to an embodiment. 1A to 1C are diagrams illustrating a method for manufacturing a spot size converter according to an embodiment. FIG. 13 is a cross-sectional view of a spot size converter according to another embodiment.

In a spot size converter, it is desirable to reduce losses as much as possible when converting the mode field diameter. An object of the present disclosure is to provide a spot size converter that can reduce losses when converting the mode field diameter, and a method for manufacturing such a spot size converter. According to one embodiment, it is possible to provide a spot size converter that can reduce losses when converting the mode field diameter, and a method for manufacturing such a spot size converter.

In the embodiments described below, the "optical waveguide" may be an element that optically connects between an optical waveguide core of an optical device and an external element such as an optical fiber. In the embodiments described below, the "optical waveguide" may have the function of the spot size converter (SSC) described above. Below, the spot size converter according to several embodiments will be described with reference to the drawings. Here, the drawings showing each embodiment in this disclosure are schematic diagrams that have been appropriately simplified for the purpose of explanation. Therefore, the drawings showing each embodiment in this disclosure do not necessarily show the actual size of each component, the ratio of the actual sizes of each component, or the ratio of the actual sizes of each component in each direction.

For example, in fields such as silicon photonics, it is important to reduce connection loss in order to achieve low-loss board mounting. In particular, in a structure in which optical coupling from a Si waveguide to an optical fiber is performed with low loss, the core diameter changes significantly. Therefore, in such a structure, efficient board mounting is desirable. When butt coupling is performed by butting the end face of the substrate with an optical fiber, the size (MFD) of the beam passing through the Si waveguide and the optical fiber respectively differs significantly. Therefore, a spot size converter (SSC) is used to suppress the loss of light during such coupling. In addition, it is desirable to reduce not only the loss when converting the MFD of the orthogonal polarization (transverse electric wave (TE wave)) component, but also the loss when converting the MFD of the parallel polarization (transverse magnetic wave (TM wave)) component.

In order to increase the MFD in the Si waveguide for both TE and TM polarization in a spot size converter, a planarization process is generally used in the manufacturing process. For example, the spot size converter disclosed in the above-mentioned Patent Document 1 is also expected to use a planarization process in the manufacturing process. A manufacturing process using a planarization process in this way is cumbersome and increases manufacturing costs. However, it is difficult to increase the coupling efficiency without going through such a manufacturing process. In addition, such a manufacturing process creates restrictions such as not being able to be performed after metal wiring is applied. The spot size converter of one embodiment achieves reduced loss for both TE and TM polarization without performing a planarization process during manufacturing.

First, we will explain the spot size converter according to one embodiment.

FIGS. 1 to 3 are diagrams showing a schematic configuration of a spot size converter 1 according to one embodiment. FIG. 1 is a plan view of the spot size converter 1 according to one embodiment. That is, FIG. 1 is a diagram showing the spot size converter 1 according to one embodiment as viewed from above. FIGs. 2 and 3 are cross-sectional views of the spot size converter 1 according to one embodiment. That is, FIG. 2 is a diagram showing a cross-section of the spot size converter 1 shown in FIG. 1 taken along line II-II. FIG. 3 is a diagram showing a cross-section of the spot size converter 1 shown in FIG. 1 taken along line III-III.

As shown in Figures 1 to 3, the 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.

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

In the following description, the direction of the Z axis shown in Figures 1 to 3 may be parallel to the direction in which light is guided (propagated) in the spot size converter 1. The spot size converter 1 can convert (enlarge) the MFD of light input to the first end (side indicated by arrow A1) and output it from the second end (side indicated by arrow A2). In this case, in the spot size converter 1, light is guided (propagated) in the positive direction of the Z axis. Conversely, the spot size converter 1 can convert (reduce) the MFD of light input to the second end (side indicated by arrow A2) and output it from the first end (side indicated by arrow A1). In this case, in the spot size converter 1, light is guided (propagated) in the negative direction of the Z axis. Hereinafter, the direction of the Z axis shown in Figures 1 to 3 refers to the axial direction (axial direction) of the spot size converter 1, the first waveguide core 21, the second waveguide core 22, etc. Here, the axial direction (axis direction) of the spot size converter 1 and the first and

second waveguide cores

21 and 22 may be the direction in which light is guided (propagated) in these components, for example, the direction of the optical axis.

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. Hereinafter, the direction of the Y-axis shown in Figures 1 to 3 indicates 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. The negative direction of the Y-axis shown in Figures 1 to 3 may be, for example, vertically downward.

The direction of the X-axis shown in Figures 1 to 3 may be parallel to the width direction of the spot size converter 1. Here, the width of the spot size converter 1 may be the length in a plane parallel to the XZ plane, in a direction perpendicular to the axis (Z-axis direction) of the spot size converter 1. Hereinafter, the direction of the X-axis shown in Figures 1 to 3 indicates the width direction (width direction) of the spot size converter 1 and each component in the spot size converter 1.

As shown in Figures 2 and 3, the first cladding layer 11 may be a 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, about 1.45 to 1.46.

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, about 1.463 to 1.467.

As shown in Figs. 2 and 3, the second waveguide core 22 is formed on the first clad layer 11. The second waveguide core 22 is formed so as to cover the first waveguide core 21. As shown in Figs. 1 and 3, the second waveguide core 22 may be formed so as to cover the periphery of the first waveguide core 21 except for the first end portion of the spot size converter 1. The second waveguide core 22 may be designed to have a higher refractive index than the first clad layer 11. The refractive index of the first waveguide core 21 is not particularly limited, but may be, for example, about 1.463 to 1.467. The second waveguide core 22 may be designed to have a lower refractive index than the first waveguide core 21.

As shown in Figures 1 to 3, the second cladding layer 12 may be an 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 of 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 of 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 (covering the periphery of the first waveguide core 21) except for the portion of 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 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, about 1.45 to 1.46.

As shown in FIG. 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 smaller than the first height h1.

In the second waveguide core 22, the first portion 221 and the second portion 222 may not be physically separated and may be formed integrally. That is, in the second waveguide core 22, the division between the first portion 221 and the second portion 222 may be virtual. In FIG. 3, the virtual boundary between the first portion 221 and the second portion 222 is shown as boundary B.

3, in the direction of light propagation through the second waveguide core 22 (Z-axis direction), the boundary B between the first portion 221 and the second portion 222 may be designed to be located between the end T1 of the first waveguide core 21 and the end T2 of the second waveguide core 22. The boundary B between the first portion 221 and the second portion 222 of the second waveguide core 22 may have a height difference (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.

Here, when forming the second waveguide core 22 to have the first portion 221 and the second portion 222, there is no need to perform a process of flattening the upper surface of the first waveguide core 21 and/or the second waveguide core 22. For example, after the first waveguide core 21 is formed on the first cladding layer 11, the second waveguide core 22 is deposited on the first cladding layer 11, so that a film of a relatively uniform thickness is formed on the first cladding layer 11 and the first waveguide core 21. As a result, even if the upper surface of the first waveguide core 21 and/or the second waveguide core 22 is not flattened, a step is formed at the position of the boundary B between the first portion 221 and the second portion 222.

Therefore, the spot size converter 1 according to one embodiment can reduce losses when converting MFD without performing a planarization process. Furthermore, by not performing a planarization process, the spot size converter 1 according to one embodiment can be processed even after metal wiring.

FIG. 4 is a diagram showing a cross section of the spot size converter 1 shown in FIG. 1 taken along line III-III. FIG. 4 shows the same spot size converter 1 as shown in FIG. 3. In FIG. 3, the second waveguide core 22 has been mainly described. In FIG. 4, the second cladding layer 12 has been mainly described.

As shown in FIG. 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.

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 the spot size converter 1 according to one embodiment, 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 the spot size converter 1 according to one embodiment, the fifth height h5 may be lower than the fourth height h4.

In the second cladding layer 12, the third portion 123 and the fourth portion 124 may not be physically separated, but may be integrally formed. That is, in the second cladding layer 12, the division between the third portion 123 and the fourth portion 124 may be virtual. In addition, in the second cladding layer 12, the fourth portion 124 and the fifth portion 125 may not be physically separated, but may be integrally formed. That is, in the second cladding layer 12, the division between the fourth portion 124 and the fifth portion 125 may be virtual.

As shown in FIG. 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. In addition, the boundary between the third portion 123 and the fourth portion 124 of the second cladding layer 12 may have a step in height in the stacking direction relative to the first cladding layer 11 (step of height h3-height h4). In addition, 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. In addition, the boundary between the fourth portion 124 and the fifth portion 125 of the second cladding layer 12 may have a step in height in the stacking direction relative to the first cladding layer 11 (step of height h4-height h5).

Here, when forming the second cladding layer 12 to have the third portion 123 and the fourth portion 124 (and further the fifth portion 125), there is no need to carry out a process of planarizing the upper surface of the second waveguide core 22. For example, after the second waveguide core 22 is formed on the first waveguide core 21, the second cladding layer 12 is deposited on these, so that a film of a relatively uniform thickness is formed on the first waveguide core 21 and the second waveguide core 22. As a result, even if the upper surfaces of the first waveguide core 21 and the second waveguide core 22 are not planarized, a step is formed at the boundary between the third portion 123 and the fourth portion 124 (and further the fifth portion 125).

Therefore, the spot size converter 1 according to one embodiment can simplify the manufacturing process by not requiring a flattening process.

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

As described above, the spot size converter 1 according to one embodiment can be manufactured without performing a planarization process. In all respects other than being manufactured without performing a planarization process, the spot size converter 1 according to one embodiment can be manufactured by a method that is the same as or similar to the cladding and/or waveguide core of a known spot size converter. Therefore, descriptions that are the same as or similar to the cladding and/or waveguide core of a known spot size converter are appropriately simplified or omitted.

When manufacturing the spot size converter 1 according to one embodiment, first, the first cladding layer 11 is formed. Figures 5A and 5B are diagrams showing the state in which the first cladding layer 11 has been formed. Figure 5A is a diagram showing the manufacturing process of the spot size converter 1 from the same perspective as Figure 2. Figure 5B is a diagram showing the manufacturing process of the spot size converter 1 from the same perspective as Figure 3.

Next, a first waveguide core 21 is formed on the first cladding layer 11. Figures 6A and 6B are diagrams showing the first waveguide core 21 formed on the first cladding layer 11. Figure 6A is a diagram showing the first waveguide core 21 formed on the first cladding layer 11 shown in Figure 5A. Figure 6B is a diagram showing the first waveguide core 21 formed on the first cladding layer 11 shown in Figure 5B.

Next, the second waveguide core 22 is formed on the first cladding layer 11. Figures 7A and 7B are diagrams showing the second waveguide core 22 formed on the first cladding layer 11. Figure 7A is a diagram showing the second waveguide core 22 formed on the first cladding layer 11 and the first waveguide core 21 shown in Figure 6A. Figure 7B is a diagram showing the second waveguide core 22 formed on the first cladding layer 11 and the first waveguide core 21 shown in Figure 6B. As described above, the second waveguide core 22 can be formed without going through a process of flattening the top surface of the first waveguide core 21.

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. As described above, the second waveguide core 22 may have a lower refractive index than the first waveguide core 21.

In FIG. 7B, the imaginary boundary between the first portion 221 and the second portion 222 of the second waveguide core 22 is shown as boundary B. In FIG. 7A, the imaginary boundary between the first portion 221 and the second portion 222 of the second waveguide core 22 is shown as boundary C.

Also, in the X-axis direction shown in FIG. 7A , the boundary C between the first portion 221 and the second portion 222 may be designed to be located between the end S1 in the width direction of the first waveguide core 21 and the end S2 in the width direction 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 step in height (step 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 TE wave component.

In this way, in the X-axis direction shown in Figure 7A, the boundary C between the first portion 221 and the second portion 222 of the second waveguide core 22 may have a height difference (a step of height h1-h2) in the stacking direction relative to the first cladding layer 11. Here, the X-axis direction shown in Figure 7A may be a direction perpendicular to the propagation direction of light through the second waveguide core 22 shown in Figure 7A.

In the manufacturing method of the spot size converter 1 according to one embodiment, the second cladding layer 12 is then formed on the first cladding layer 11. The state in which the second cladding layer 12 is formed on the first cladding layer 11, the first waveguide core 21, and the second waveguide core 22 shown in FIG. 7A is as shown in FIG. 2. The state in which the second cladding layer 12 is formed on the first cladding layer 11, the first waveguide core 21, and the second waveguide core 22 shown in FIG. 7B is as shown in FIG. 3. As shown in FIG. 2 and FIG. 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. Also, as described above, the second cladding layer 12 may have a lower refractive index than the second waveguide core 22. As described above, the second cladding layer 12 may be formed without a process of planarizing the upper surface of the first waveguide core 21 and/or the second waveguide core 22.

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.

Other Embodiments
The spot size converter 1 according to the embodiment described above has been described as including two waveguide cores, such as the first waveguide core 21 and the second waveguide core 22. However, in other embodiments, the number of waveguide cores is not limited to two, and three or more waveguide cores may be included.

FIG. 8 is a diagram showing a cross section of a spot size converter 2 according to another embodiment. FIG. 8 is a diagram showing a spot size converter 2 according to another embodiment from the same perspective as FIG. 3. As shown in FIG. 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.

In this way, 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 and covering the first waveguide core 21 and the second waveguide core 22.

Although the embodiments of the present disclosure have been described based on the drawings and examples, it should be noted that a person skilled in the art would be able to easily make various modifications or amendments based on the present disclosure. Therefore, it should be noted that these modifications or amendments are included in the scope of the present disclosure. For example, the functions included in each component or step can be rearranged so as not to cause logical inconsistencies, and multiple components or steps can be combined into one or divided. Although the embodiments of the present disclosure have been described mainly with respect to optical waveguides, the embodiments of the present disclosure can also be realized as a manufacturing method for optical waveguides.

REFERENCE SIGNS

LIST

1, 2 Spot size converter 11 First cladding layer 12 Second cladding layer 123 Third portion 124 Fourth portion 125 Fifth portion 21 First waveguide core 22 Second waveguide core 23 Third waveguide core 221 First portion 222 Second portion

Claims

A first cladding layer;
a first waveguide core formed on the first cladding layer;
a second waveguide core formed on the first cladding layer, covering the first waveguide core, and having a refractive index lower than that of the first waveguide core;
a second clad layer formed on the first clad layer, covering the first waveguide core and the second waveguide core, the second clad layer having a refractive index lower than that of the second waveguide core;
Equipped with
The second waveguide core is
a first portion having a first height in a stacking direction relative to the first cladding layer;
a second portion having a second height in a stacking direction relative to the first cladding layer that is lower than the first height;
A spot size converter having a
The spot size converter of claim 1, wherein in the direction of light propagation through the second waveguide core, the boundary between the first portion and the second portion of the second waveguide core is located between an end of the first waveguide core and an end of the second waveguide core.
The spot size converter of claim 1, wherein in the direction of light propagation through the second waveguide core, the boundary between the first and second portions of the second waveguide core has a step in height in the stacking direction relative to the first cladding layer.
The spot size converter of claim 1, wherein the boundary between the first and second portions of the second waveguide core has a step in height in the stacking direction relative to the first cladding layer in a direction perpendicular to the propagation direction of light through the second waveguide core.
The spot size converter of claim 1, further comprising a third waveguide core formed between the first cladding layer and the second cladding layer and covering the first waveguide core and the second waveguide core.
The second cladding layer is
a third portion having a third height in a stacking direction relative to the first cladding layer;
a fourth portion having a fourth height that is lower than the third height in a stacking direction with respect to the first cladding layer;
The spot size converter of claim 1 , further comprising:
The spot size converter of claim 6, wherein the second cladding layer has a fifth portion having a fifth height that is lower than the fourth height in the stacking direction relative to the first cladding layer.
forming a first cladding layer;
forming a first waveguide core on the first cladding layer;
forming a second waveguide core having a lower refractive index than the first waveguide core on the first cladding layer so as to cover the first waveguide core;
forming a second clad layer on the first clad layer so as to cover the first waveguide core and the second waveguide core, the second clad layer having a refractive index lower than that of the second waveguide core;
A method for manufacturing a spot size converter, comprising:
The second waveguide core is
a first portion having a first height in a lamination direction relative to the first cladding layer;
a second portion having a second height in a stacking direction relative to the first cladding layer that is lower than the first height;
The method of manufacturing the same.