Optical waveguide element

Abstract

The purpose of the present disclosure is to obtain an optical waveguide element in which return light is reduced and the size of which can be reduced.　An optical waveguide element (100) according to the present disclosure transmits light having a wavelength λ, and comprises: a substrate (10); a lower cladding layer (20) that is formed on the substrate (10) and has a refractive index of nc; an optical waveguide layer (30) that is formed on the lower cladding layer (20); an upper cladding layer (40) that is formed on the lower cladding layer (20) and the optical waveguide layer (30); and a return-light-blocking layer (50) that is formed inside the lower cladding layer (20), that is made of a material having a refractive index nb higher than the refractive index nc, and that has an end portion on the incident-end-face side located at a distance that is an odd multiple of λ / 4 from the light-emission end of the optical waveguide layer (30) toward the incident-end-face side.

Description

Optical waveguide element

[0001] This application relates to an optical waveguide element.

[0002] In an optical waveguide element, a technique is known in which a window structure having a space between the emission end of the optical waveguide layer and the emission end face of the optical waveguide element can reduce the return light from the element end face.

[0003] However, with a simple window structure, the return light due to reflection from the element end face can be reduced, but return light that is reflection at the emission end of the optical waveguide layer occurs. Therefore, a technique is known in which the return light from the emission end face is further reduced by forming a taper structure in which the width of the optical waveguide layer, that is, the optical waveguide width, gradually changes toward the emission end (for example, Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 05-027130

[0005] Since the taper structure needs to gradually change the optical waveguide width so that losses due to reflection and scattering of light do not occur, there is a problem that the total length of the taper structure becomes long, and thus the size of the optical waveguide element becomes large.

[0006] The present disclosure has been made to solve the above problems, and an object thereof is to obtain an optical waveguide element in which return light is reduced and miniaturization is possible.

[0007] The optical waveguide element according to the present disclosure is an optical waveguide element that propagates light having a wavelength λ, and includes a substrate, a lower cladding layer formed on the substrate and having a refractive index of nc, an optical waveguide layer formed on the lower cladding layer, an upper cladding layer formed on the lower cladding layer and the optical waveguide layer, and a return light blocking layer formed inside the lower cladding layer and made of a material having a refractive index nb higher than nc, and the end on the incident end face side is located at a distance that is an odd multiple of λ / 4 from the emission end of the optical waveguide layer toward the incident end face side.

[0008] The optical waveguide element disclosed herein has the effect of reducing reflected light and enabling miniaturization, as the phases of the light reflected at the exit end of the optical waveguide layer and the light reflected at the incident end face side of the return light blocking layer cancel each other out.

[0009] This is a cross-sectional view of the optical waveguide element according to Embodiment 1, along the direction of light propagation. This is a cross-sectional view of the optical waveguide element according to Embodiment 1, along the line A-A in Figure 1. This is a cross-sectional view of the optical waveguide element according to Embodiment 2, along the direction of light propagation. This is a top view of the optical waveguide element according to Embodiment 3. This is a cross-sectional view of the optical waveguide element according to Embodiment 3, along the line A-A in Figure 4. This is a top view of the optical waveguide element according to Embodiment 4.

[0010] Each embodiment of this disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts will be denoted by the same reference numerals, and redundant descriptions will not be repeated. Within the bounds of consistency, the following embodiments can be combined as appropriate, and parts thereof can be modified or omitted.

[0011] Embodiment 1. The optical waveguide element according to Embodiment 1 will be described below. The optical waveguide element according to Embodiment 1 will be referred to as the optical waveguide element 100. Figure 1 is a cross-sectional view of the optical waveguide element 100 according to Embodiment 1 along the direction of light propagation. Figure 2 is a cross-sectional view of the optical waveguide element 100 according to Embodiment 1 along the line A-A in Figure 1.

[0012] In Figure 1, the first direction DR1 is the direction perpendicular to the surface of the substrate 10, the second direction DR2 is the direction in which light propagates, and the third direction DR3 is the direction parallel to the surface of the substrate 10 and perpendicular to the direction in which light propagates. Let λ be the wavelength of light propagating within the optical waveguide element 100. Light enters the optical waveguide element 100 from the incident end face, propagates within the optical waveguide element 100 along the second direction DR2, and exits the optical waveguide element 100 toward the outside from the exit end face.

[0013] <Configuration of the optical waveguide element according to Embodiment 1> As shown in Figures 1 and 2, the optical waveguide element 100 comprises a substrate 10, a lower cladding layer 20 formed on the substrate 10 and made of a material with a refractive index of nc, an optical waveguide layer 30 formed on the lower cladding layer 20, an upper cladding layer 40 formed on the lower cladding layer 20 and the optical waveguide layer 30, and a return light blocking layer 50 formed inside the lower cladding layer 20 and made of a material with a refractive index of mb which is higher than the refractive index of nc, with its end on the incident end face side located at a distance of an odd multiple of λ / 4 from the exit end of the optical waveguide layer 30 toward the incident end face side.

[0014] An example of a substrate 10 is a semiconductor substrate. An example of a semiconductor substrate is a silicon (Si) substrate. However, the substrate 10 may be a substrate other than a Si substrate, for example, a glass substrate.

[0015] The lower cladding layer 20 and the upper cladding layer 40 are made of, for example, silicon dioxide (SiO2). The lower cladding layer 20 and the upper cladding layer 40 may also be made of a single cladding layer.

[0016] The optical waveguide layer 30 is made of, for example, Si. However, the optical waveguide layer 30 may be made of a material other than Si, for example, a silicon nitride (SiN) film. The optical waveguide layer 30 propagates light of wavelength λ incident from the outside and emits light to the outside from the exit end face.

[0017] The light-reflecting blocking layer 50 is made of Si, which is the same material as that used to make up the optical waveguide layer 30. However, it may be made of a material other than Si, which has a refractive index greater than that of the lower cladding layer 20. In other words, if the refractive index of the material making up the light-reflecting blocking layer 50 is nb and the refractive index of the lower cladding layer 20 is nc, the light-reflecting blocking layer 50 should be made of a material that satisfies the relationship that refractive index nb is greater than refractive index nc.

[0018] The return light blocking layer 50 is formed inside the lower cladding layer 20. The return light blocking layer 50 is located spaced apart directly below the substrate 10 side of the optical waveguide layer 30. The return light blocking layer 50 is provided spaced apart from the optical waveguide layer 30 at a distance that does not cause evanescent coupling with the light propagating through the optical waveguide layer 30. The return light blocking layer 50 only needs to be positioned around the optical waveguide layer 30. Alternatively, the return light blocking layer 50 may be positioned in contact with the optical waveguide layer 30.

[0019] The return light blocking layer 50 is formed such that the distance D between the end face position of the return light blocking layer 50 in the direction opposite to the second direction DR2 and the side of the optical waveguide layer 30 in the second direction DR2, that is, the end face on the side of the optical waveguide layer 30 that is opposite to the exit end of the optical waveguide layer 30 and the incident end face of the return light blocking layer 50, is an odd multiple of λ / 4, where λ is the wavelength of light propagating through the optical waveguide layer 30. Here, if the wavelength of light in a vacuum is λ0 and the effective refractive index of the light mode propagating through the optical waveguide layer 30 is neff, then the wavelength λ of the light propagating through the optical waveguide layer 30 can be expressed as λ0 / neff.

[0020] <Operation of the optical waveguide element according to Embodiment 1> The return light blocking layer 50 has an end on the incident end face side that is located at a distance of an odd multiple of λ / 4 from the exit end of the optical waveguide layer 30 toward the incident end face side. Therefore, the phases of the reflected light at the end of the return light blocking layer 50 and the reflected light at the exit end of the optical waveguide layer 30 cancel each other out. In other words, the return light blocking layer 50 functions to reduce the return light, which is the light that is reflected at the exit end of the optical waveguide layer 30 and returns in the negative direction of the second direction DR2, that is, toward the incident end face side.

[0021] <Effects of Embodiment 1> As described above, the optical waveguide element according to Embodiment 1 is provided such that a return light blocking layer is provided within the lower cladding layer, spaced apart directly below the optical waveguide layer, and the end on the incident end face side is located at a distance of an odd multiple of λ / 4 from the exit end of the optical waveguide layer toward the incident end face side. This provides the effect of obtaining an optical waveguide element with reduced return light.

[0022] Embodiment 2. The optical waveguide element according to Embodiment 2 will be described below. The optical waveguide element according to Embodiment 2 will be referred to as optical waveguide element 100A. In the following, the differences from the optical waveguide element 100 according to Embodiment 1 will be mainly described, and redundant explanations will not be repeated.

[0023] <Configuration of the optical waveguide element according to Embodiment 2> Figure 3 is a cross-sectional view of the optical waveguide element 100A according to Embodiment 2, along the direction of light propagation. The optical waveguide element 100A according to Embodiment 2 is composed of multiple return light blocking layers 50a instead of one return light blocking layer 50 of the optical waveguide element 100 according to Embodiment 1.

[0024] The return light blocking layer 50a of the optical waveguide element 100A according to Embodiment 2 is formed similarly to the return light blocking layer 50 of the optical waveguide element 100 according to Embodiment 1. Among the multiple return light blocking layers 50a, the return light blocking layer 50a closest to the output end of the optical waveguide layer 30 is formed such that the distance D between the end face position of the return light blocking layer 50a in the direction opposite to the second direction DR2 and the end face on the second direction DR2 side of the optical waveguide layer 30, i.e., the output end of the optical waveguide layer 30 and the input end face side of the return light blocking layer 50, is an odd multiple of λ / 4, where λ is the wavelength of light propagating through the optical waveguide layer 30.

[0025] The remaining return light blocking layers 50a, with the exception of the return light blocking layer 50a closest to the exit end of the optical waveguide layer 30, are arranged in the opposite direction to the second direction DR2, while maintaining a predetermined spacing.

[0026] As an arrangement of multiple return light blocking layers 50a, for example, if blocks are placed at positions λ × 1 / 4 and λ × 3 / 4, it is preferable that the length of the return light blocking layer 50a on the exit end side be less than λ / 2, and in this case, the distance between the multiple return light blocking layers 50a is preferably λ / 2.

[0027] Furthermore, as a method for arranging the multiple light-reflecting blocking layers 50a, they may be arranged not at odd multiples of λ / 4, i.e., at positions such as λ×1 / 4, λ×3 / 4, λ×5 / 4, but at any odd multiple of λ / 4, for example, λ×1 / 4, λ×5 / 4, λ×7 / 4).

[0028] <Operation of the Optical Waveguide Element According to Embodiment 2> Similar to the return light blocking layer 50 of the optical waveguide element 100 according to Embodiment 1, the return light blocking layer 50a of the optical waveguide element 100A according to Embodiment 2 has the effect of reducing return light due to end-face reflection at the exit end of the optical waveguide layer 30. Since the optical waveguide element 100A is composed of multiple return light blocking layers 50a, it is possible to further reduce the light intensity of the return light.

[0029] <Effects of Embodiment 2> As described above, the optical waveguide element according to Embodiment 2 has the effect of providing an optical waveguide element with further reduced reflected light because it is equipped with multiple reflected light blocking layers.

[0030] Embodiment 3. The optical waveguide element according to Embodiment 3 will be described below. The optical waveguide element according to Embodiment 3 will be referred to as optical waveguide element 100B. In the following, the differences from the optical waveguide element 100 according to Embodiment 1 will be mainly described, and redundant explanations will not be repeated.

[0031] Figure 4 is a top view of the optical waveguide element 100B according to Embodiment 3. Figure 5 is a cross-sectional view of the optical waveguide element 100B along the line A-A in Figure 4.

[0032] <Configuration of the optical waveguide element according to Embodiment 3> The optical waveguide element 100B according to Embodiment 3 comprises a substrate 10, a lower cladding layer 20 formed on the substrate 10 and made of a material with a refractive index of nc, an optical waveguide layer 30 formed on the lower cladding layer 20, an upper cladding layer 40 formed on the lower cladding layer 20 and the optical waveguide layer 30 and having a refractive index of nc, and two return light blocking layers 50b formed on the lower cladding layer 20 at positions spaced apart from both sides of the optical waveguide layer 30, made of a material with a refractive index nb that is higher than the refractive index of nc, and whose ends on the incident end face side are located at a distance of an odd multiple of λ / 4 from the exit end of the optical waveguide layer 30 toward the incident end face side.

[0033] The light reflection blocking layer 50b of the optical waveguide element 100B is made of the same material as the optical waveguide layer 30. The light reflection blocking layer 50b is located at the same height from the surface of the substrate 10 as the optical waveguide layer 30 and is formed with the same layer thickness as the optical waveguide layer 30. The material constituting the light reflection blocking layer 50b is, for example, Si.

[0034] <Operation of the optical waveguide element according to Embodiment 3> In the optical waveguide element 100B according to Embodiment 3, each of the two return light blocking layers 50b, which are spaced apart from both sides of the optical waveguide layer 30, has its end on the incident end face side located at a distance of an odd multiple of λ / 4 from the exit end of the optical waveguide layer 30 toward the incident end face side. As a result, the phases of the reflected light at the end of the return light blocking layer 50b and the reflected light at the exit end of the optical waveguide layer 30 cancel each other out. In other words, the return light blocking layer 50b functions to reduce the return light, which is the light that is reflected at the exit end of the optical waveguide layer 30 and returns in the negative direction of the second direction DR2, that is, toward the incident end face side.

[0035] <Effects of Embodiment 3> As described above, the optical waveguide element according to Embodiment 3 has the effect of providing an optical waveguide element with further reduced reflected light because two return light blocking layers are provided such that the ends on the incident end face side are located at a distance of an odd multiple of λ / 4 from the exit end of the optical waveguide layer toward the incident end face side, at positions spaced apart from both sides of the optical waveguide layer 30.

[0036] Embodiment 4. The optical waveguide element according to Embodiment 4 will be described below. The optical waveguide element according to Embodiment 4 will be referred to as optical waveguide element 100C. In the following, the differences from the optical waveguide element 100 according to Embodiment 1 will be mainly described, and redundant explanations will not be repeated.

[0037] Figure 6 is a top view of the optical waveguide element 100C according to Embodiment 4. Figure 5 is a cross-sectional view of the optical waveguide element 100C along the line A-A in Figure 4.

[0038] <Configuration of the optical waveguide element according to Embodiment 4> The optical waveguide element 100C according to Embodiment 4 is characterized in that it has a tapered optical waveguide layer 30a instead of the optical waveguide layer 30 of the optical waveguide element 100 according to Embodiment 1. In other words, the optical waveguide layer 30a of the optical waveguide element 100C has a tapered structure in which the optical waveguide width gradually narrows toward the exit end face.

[0039] <Operation of the optical waveguide element according to Embodiment 4> The tapered optical waveguide layer 30a functions to reduce reflected light. In the tapered structure, it is necessary to gradually change the optical waveguide width so that no loss occurs due to light reflection and scattering.

[0040] <Effects of Embodiment 4> As described above, the optical waveguide element according to Embodiment 4 has a tapered optical waveguide layer, and together with the application of the reflected light blocking layer, it has the effect of providing an optical waveguide element in which reflected light is synergistically reduced.

[0041] While this disclosure describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to the application of a particular embodiment, but can be applied individually or in various combinations to the embodiments.

[0042] Accordingly, countless variations not illustrated are conceivable within the scope of the art of this disclosure. These include, for example, modifying, adding or omitting at least one component, or extracting at least one component and combining it with components of other embodiments.

[0043] 10 Substrate, 20 Lower cladding layer, 30, 30a Optical waveguide layer, 40 Upper cladding layer, 50, 50a, 50b Reflection light blocking layer, 100, 100A, 100B, 100C Optical waveguide element

Claims

1. An optical waveguide element for propagating light of wavelength λ, comprising: a substrate; a lower cladding layer formed on the substrate and having a refractive index of nc; an optical waveguide layer formed on the lower cladding layer; an upper cladding layer formed on the lower cladding layer and the optical waveguide layer; and a return light blocking layer formed inside the lower cladding layer, made of a material having a refractive index nb higher than the refractive index of nc, with its end on the incident end face side located at a distance of an odd multiple of λ / 4 from the exit end of the optical waveguide layer toward the incident end face side.

2. The optical waveguide element according to claim 1, characterized in that the return light blocking layer is composed of a plurality of layers.

3. The optical waveguide element according to claim 1 or 2, characterized in that the return light blocking layer is located spaced apart directly below the substrate side of the optical waveguide layer.

4. An optical waveguide element for propagating light of wavelength λ, comprising: a substrate; a lower cladding layer formed on the substrate; an optical waveguide layer formed on the lower cladding layer; an upper cladding layer formed on the lower cladding layer and the optical waveguide layer, having a refractive index of nc; and at least two return light blocking layers, each formed on the lower cladding layer at positions spaced apart from both sides of the optical waveguide layer, made of a material with a refractive index nb higher than nc, and having their ends on the incident end face side located at an odd multiple of λ / 4 from the exit end of the optical waveguide layer toward the incident end face side.

5. The optical waveguide element according to any one of claims 1 to 4, characterized in that the optical waveguide layer has a tapered structure in which the optical waveguide width gradually narrows toward the exit end face.

6. The optical waveguide element according to any one of claims 1 to 4, characterized in that the optical waveguide layer and the return light blocking layer are spaced apart at a distance such that light propagating through the optical waveguide layer does not evanescently couple with the return light blocking layer.

7. The optical waveguide element according to any one of claims 1 to 4, characterized in that the light-return blocking layer is made of silicon.

8. The optical waveguide element according to any one of claims 1 to 4, characterized in that the substrate is a semiconductor substrate.

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