Optical module

Abstract

The present invention provides an optical module that can reduce the propagation of reflected light within the waveguide core and reduce the decrease in coupling efficiency with optical fibers. [Solution] The optical module A1 comprises a substrate 10 and a waveguide 20. The substrate 10 has a first groove 11 and a second groove 12. The first groove 11 is aligned with the left-right direction D1 of the substrate 10. The second groove 12 is aligned with the left-right direction D1 so as to connect with the first groove 11. The waveguide 20 has a first core 21 and a first cladding 22. The first core 21 is positioned within the first groove 11 along the left-right direction D1. The first cladding 22 covers the first core 21 and the first groove 11. The width W2 of the second groove 12 is greater than the width W1 of the first groove 11. The shortest distance K1 between the upper end 11a of the first groove 11 and the upper end 12a of the second groove 12 is shorter than the shortest distance K2 between the lower end 11b of the first groove 11 and the lower end 12b of the second groove 12. The right end of the first core 21 has an inclined surface 41 that is inclined with respect to the interface 60.

Description

Technical Field

[0001] The present disclosure generally relates to optical modules, and more particularly relates to an optical module including a waveguide. Background Art

[0002] An example is the optical module described in Patent Document 1. The optical module includes a silicon substrate and an optical waveguide. The silicon substrate has a groove in which an optical fiber is placed. The optical waveguide is disposed on the silicon substrate. One end face of the optical waveguide is formed into an inclined end face by inclined processing. One end face of the optical fiber is formed into an inclined end face by inclined processing. The optical fiber is disposed in the groove such that said one end face of the optical fiber faces said one end face of the optical waveguide. Prior Art Literature Patent Literature

[0003] Patent Literature 1 Japanese Patent Laid-Open No. 2004-151391 Summary of the Invention Problem to be Solved by the Invention

[0004] In the optical module described in Patent Document 1, light emitted from the optical waveguide to the optical fiber (hereinafter referred to as "emitted light") is refracted at said one end face of the optical waveguide, which may reduce the proportion of emitted light that enters the core of the optical fiber, and may reduce the coupling efficiency between the optical waveguide and the optical fiber.

[0005] Furthermore, in the above-described optical module, since said one end face of the optical fiber faces said one end face of the optical waveguide, return light from the optical fiber to the optical waveguide may propagate through the core of the optical waveguide.

[0006] The object of this disclosure is to provide an optical module that can reduce the propagation of reflected light within the waveguide core and reduce the decrease in coupling efficiency with optical fibers. [Means for solving the problem]

[0007] An optical module according to one aspect of the present disclosure comprises a substrate and a waveguide. Light propagates through the waveguide. The substrate has a first groove and a second groove. The first groove is formed on the main surface of the substrate along the left-right direction of the substrate. The second groove is formed on the main surface of the substrate along the left-right direction so as to connect with the first groove. The depth of the second groove is greater than the depth of the first groove. The waveguide has a first core and a first cladding. The first core is arranged in the first groove along the left-right direction. Light propagates through the first core. The first cladding covers the first core and the first groove. The vertical width of the substrate in the second groove is greater than the vertical width of the first groove. The shortest distance in the vertical direction between the upper end of the first groove and the upper end of the second groove is shorter than the shortest distance in the vertical direction between the lower end of the first groove and the lower end of the second groove. The right end of the first core has an inclined surface. The inclined surface is inclined with respect to the interface between the first groove and the second groove.

[0008] An optical module according to one aspect of the present disclosure comprises a substrate and a waveguide. Light propagates through the waveguide. The substrate has a first groove and a second groove. The first groove is formed on the main surface of the substrate along the left-right direction of the substrate. The second groove is formed on the main surface of the substrate along the left-right direction so as to connect with the first groove. The depth of the second groove is greater than the depth of the first groove. The waveguide has a core and a cladding. The core is disposed within the first groove along the left-right direction. Light propagates through the core. The cladding covers the core and the first groove. The vertical width of the substrate in the second groove is greater than the vertical width of the first groove. The shortest vertical distance between the upper end of the core and the upper end of the cladding is shorter than the shortest vertical distance between the lower end of the core and the lower end of the cladding. The right end of the core has an inclined surface. The inclined surface is inclined with respect to the interface between the first groove and the second groove. [Effects of the Invention]

[0009] According to one aspect of the present disclosure, the propagation of reflected light within the waveguide core can be reduced, and the decrease in coupling efficiency with the optical fiber can be reduced. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a plan view of an optical module according to an embodiment. [Figure 2] Figure 2 is an explanatory diagram illustrating the path of light in relation to the optical module described above. [Figure 3] Figure 3 is an explanatory diagram illustrating the first condition for determining the inclination angle of the inclined surface in the optical module described above. [Figure 4] Figure 4 is an explanatory diagram illustrating the second condition for determining the inclination angle of the inclined surface in the same optical module. [Figure 5]Figure 5 is an explanatory diagram illustrating the path of light incident on the waveguide core of the optical module described above. [Figure 6] Figure 6 is an explanatory diagram illustrating the third condition for determining the inclination angle of the inclined surface in the optical module described above. [Figure 7] Figure 7 is an explanatory diagram illustrating the fourth condition for determining the inclination angle of the inclined surface in the same optical module. [Figure 8] Figure 8 is an explanatory diagram illustrating the fifth condition for determining the inclination angle of the inclined surface in the same optical module. [Figure 9] Figure 9 is an explanatory diagram illustrating the sixth condition for determining the inclination angle of the inclined surface in the optical module described above. [Figure 10] Figure 10 is an explanatory diagram illustrating the positional relationship between the waveguide and the optical fiber in the optical module described above. [Figure 11] Figure 11 is a plan view of an optical module according to a first modified example of the embodiment. [Figure 12] Figure 12 is a plan view showing the shape of the waveguide core of an optical module according to a second modified example of the embodiment. [Figure 13] Figure 13 is a plan view showing the shape of the waveguide core of an optical module according to a third modified example of the embodiment. [Figure 14] Figure 14 is a plan view showing the shape of the waveguide core of an optical module according to a fourth modified example of the embodiment. [Modes for carrying out the invention]

[0011] The optical module according to the embodiment will be described below with reference to the drawings. The figures described in the embodiments below are schematic diagrams, and the ratios of the size and thickness of each component do not necessarily reflect the actual dimensional ratios. Furthermore, the configuration described in the embodiments is merely one example of the present disclosure. The present disclosure is not limited to the embodiments, and various modifications are possible depending on the design, etc., as long as the effects of the present disclosure can be achieved.

[0012] In the following description, unless otherwise specified, the first direction D1 and the second direction D2 indicated by arrows in the drawings are defined as the left-right direction and the up-down direction of the optical module, respectively, and the direction orthogonal to both the first direction D1 and the second direction D2 is defined as the front-rear direction of the optical module. However, the left-right direction, up-down direction, and front-rear direction of the optical module do not represent the direction when the optical module is in use. In addition, the arrows indicating "D1" and "D2" in the drawings are notations for description purposes, and none of them represent an actual entity.

[0013] Hereinafter, the optical module according to the embodiment will be described with reference to FIGS. 1 to 10.

[0014] (1) Optical module The optical module A1 of the embodiment is used as a transmission-side optical module for transmitting optical signals. An optical fiber 30 is disposed in the optical module A1. The optical module A1 includes a substrate 10, a waveguide 20, and the optical fiber 30.

[0015] (2) Components of the optical module (2.1) Substrate The substrate 10 is a plate-shaped (rectangular plate-shaped in the example of FIG. 1) silicon substrate. The substrate 10 has a first groove 11 and a second groove 12.

[0016] The first groove 11 is formed along the left-right direction D1 of the substrate 10 in a portion on the main surface 10a side of the substrate 10. The cross-sectional shape of the first groove 11 taken along the left-right direction D1 is a quadrilateral (for example, a trapezoid). Note that the cross-sectional shape of the first groove 11 taken along the left-right direction D1 is not limited to a quadrilateral, and may be, for example, a trilateral (such as an equilateral triangle).

[0017] The optical fiber 30 is positioned in the second groove 12. The second groove 12 is formed along the left-right direction D1 of the substrate 10 on the main surface 10a side of the substrate 10 so as to connect with the first groove 11. In other words, the second groove 12 is formed in the substrate 10 continuously with the first groove 11. The cross-sectional shape of the second groove 12 from the left-right direction D1 is a quadrilateral (for example, a rectangle). However, the cross-sectional shape of the second groove 12 from the left-right direction D1 is not limited to a quadrilateral; for example, it may be a triangular (for example, an equilateral triangle).

[0018] The depth of the second groove 12 is greater than the depth of the first groove 11. The width W2 in the vertical direction D2 of the second groove 12 is greater than the width (specifically, the maximum width) W1 of the first groove 11 in the vertical direction D2. In the following explanation, in the left-right direction D1 of the optical module A1 shown in Figure 1, the side of the second groove 12 as seen from the first groove 11 is defined as "right," and the opposite side is defined as "left." However, the left and right of the optical module A1 do not necessarily refer to the orientation in which the optical module A1 is used.

[0019] (2.2) Waveguides Waveguide 20 is through which light propagates. The material of waveguide 20 is a light-transmitting material (e.g., resin, glass, etc.). Waveguide 20 is located in the first groove 11 along the left-right direction D1. Waveguide 20 has a core 21 and a cladding 22.

[0020] Light propagates through the core 21. The core 21 is located within the first groove 11 along the left-right direction D1. More specifically, the core 21 is located at the bottom surface of the first groove 11 along the left-right direction D1.

[0021] The core 21 has a rectangular parallelepiped shape. The cross-sectional shape of the core 21 from the left-right direction D1 is a quadrilateral (for example, a square). However, the cross-sectional shape of the core 21 from the left-right direction D1 is not limited to a square; for example, it may be a trapezoid. Also, the cross-sectional shape of the core 21 from the left-right direction D1 is not limited to a quadrilateral; for example, it may be a triangular (for example, an equilateral triangle).

[0022] The height of the core 21 in the front-to-back direction is the same as the depth of the first groove 11. The width W3 of the core 21 in the vertical direction D2 is smaller than the width W1 of the first groove 11. Note that "the height of the core 21 in the front-to-back direction is the same as the depth of the first groove 11" does not only mean that the difference (absolute value of the difference) between the height of the core 21 and the depth of the first groove 11 is 0, but also includes, for example, the case where the difference between the height of the core 21 and the depth of the first groove 11 is 10% or less of the depth of the first groove 11.

[0023] The cladding 22 covers the core 21 and the first groove 11. In other words, the cladding 22 covers the core 21 located in the first groove 11, and also covers the opening of the first groove 11. The height of the cladding 22 in the front-rear direction is greater than the depth of the first groove 11. The width (specifically, the maximum width) W4 of the cladding 22 in the vertical direction D2 is the same as the width W1 of the first groove 11. The refractive index of the cladding 22 is lower than that of the core 21.

[0024] Furthermore, the statement "the width W4 of the cladding 22 in the vertical direction D2 is the same size as the width W1 of the first groove 11" is not limited to the case where the difference (absolute value of the difference) between the width W4 of the cladding 22 and the width W1 of the first groove 11 is 0, but also includes, for example, the case where the difference between the width W4 of the cladding 22 and the width W1 of the first groove 11 is 10% or less of the width W1 of the first groove 11.

[0025] The shortest distance K1 along the vertical direction D2 between the first end (upper end) 11a of the first groove 11 in the vertical direction D2 and the first end (upper end) 12a of the second groove 12 in the vertical direction D2 is shorter than the shortest distance K2 along the vertical direction D2 between the second end (lower end) 11b of the first groove 11 in the vertical direction D2 and the second end (lower end) 12b of the second groove 12 in the vertical direction D2. In the following explanation, in the vertical direction D2 of the optical module A1 shown in Figure 1, the side of the first end 12a as viewed from the second end 12b of the second groove 12 is defined as "up," and the opposite side is defined as "down." However, the up and down of the optical module A1 do not necessarily refer to the orientation in which the optical module A1 is used.

[0026] As shown in Figure 1, the upper end 11a and lower end 11b of the first groove 11 and the upper end 12a and lower end 12b of the second groove 12 are formed on the substrate 10 so that they are arranged in the order of upper end 12a of the second groove 12, upper end 11a of the first groove 11, lower end 11b of the first groove 11, and lower end 12b of the second groove 12, from top to bottom in the vertical direction D2 of the substrate 10.

[0027] The shortest distance K3 along the vertical direction D2 between the upper end 21a of the core 21 and the upper end 22a of the cladding 22 is shorter than the shortest distance K4 along the vertical direction D2 between the lower end 21b of the core 21 and the lower end 22b of the cladding 22. In other words, the central axis C1 of the core 21 is located above the central axis C11 of the first groove 11.

[0028] Furthermore, "the central axis C1 of the core 21" is the axis along the left-right direction D1 of the core 21 and passing through the center of the up-down direction D2 of the core 21. Also, "the central axis C11 of the first groove 11" is the axis along the left-right direction D1 of the first groove 11 and passing through the center of the up-down direction D2 of the first groove 11.

[0029] The rightmost end 6 of the core 21 in the left-right direction D1 has an inclined portion 40. The inclined portion 40 includes an inclined surface 41 for controlling the direction of light propagation. The inclined surface 41 is inclined with respect to the interface 60 between the first groove 11 and the second groove 12. The interface 60 is the inner surface of the second groove 12 located at the boundary between the first groove 11 and the second groove 12.

[0030] In this embodiment, an inclined portion 50 having an inclined surface 51 is provided at the right end 20a of the waveguide 20 in the left-right direction D1. That is, the right end 20a of the waveguide 20 is machined at an angle. In other words, the right end 6 of the core 21 is machined at an angle together with the right end of the cladding 22. Therefore, in this embodiment, the inclined portion 50 of the waveguide 20 includes the inclined portion 40 of the core 21, and the inclined surface 51 of the inclined portion 50 includes the inclined surface 41 of the inclined portion 40. Details of the inclined portion 40 will be described later.

[0031] (2.3) Optical fiber The optical fiber 30 is optically coupled to the waveguide 20. The optical fiber 30 is also positioned within the second groove 12 along the left-right direction D1. More specifically, the optical fiber 30 is positioned within the second groove 12 along the left-right direction D1 such that the left end 30a of the optical fiber 30 in the left-right direction D1 faces the right end 20a of the waveguide 20 (the inclined portion 50 in the example of Figure 1).

[0032] The optical fiber 30 has a core 31 and a cladding 32. Light propagates through the core 31. The core 31 has a cylindrical shape. The cladding 32 covers the outer surface of the core 31. The cross-sectional shape of the cladding 32 from the left-right direction D1 is annular. The refractive index of the cladding 32 is lower than that of the core 31. The refractive index of the core 31 is lower than that of the cladding 22 of the waveguide 20.

[0033] Incidentally, the shortest distance K5 in the left-right direction D1 between the first end (upper end) 1 of the inclination direction D3, which is one direction along the inclined surface 41 of the inclined section 40, and the left end 30a of the optical fiber 30 (more specifically, the end face of the left end 30a) is longer than the shortest distance K6 in the left-right direction D1 between the second end (lower end) 2 of the inclination direction D3 of the inclined surface 41 and the left end 30a of the optical fiber 30. In other words, as shown in Figure 1, the inclined surface 41 of the inclined section 40 is inclined diagonally downward to the right when the optical module A1 is viewed from the front-to-back direction.

[0034] The area of ​​the inclined surface 41 of the inclined section 40 is smaller than the area of ​​the end face 31a of the left end of the core 31 of the optical fiber 30 in the left-right direction D1. In other words, the area of ​​the inclined surface 41 of the inclined section 40 is smaller than the cross-sectional area of ​​the core 31 of the optical fiber 30. Also, the width W3 of the core 21 of the waveguide 20 is smaller than the diameter (core diameter) of the core 31 of the optical fiber 30. Furthermore, the height of the core 21 of the waveguide 20 in the front-back direction is smaller than the diameter of the core 31 of the optical fiber 30.

[0035] The central axis C2 of the core 31 of the optical fiber 30 is located below the central axis C1 of the core 21 of the waveguide 20. The "central axis C2 of the core 31 of the optical fiber 30" is defined as the axis along the left-right direction D1 of the core 31, and also the axis passing through the center of the up-down direction D2 of the core 31.

[0036] The upper end (i.e., the first end of the inclined surface 41) 1 in the vertical direction D2 at the right end 6 (i.e., the inclined portion 40) of the core 21 of the waveguide 20 is located at the same position in the vertical direction D2 as the upper end 3 in the vertical direction D2 at the left end 31a of the core 31 of the optical fiber 30. The lower end (i.e., the second end of the inclined surface 41) 2 in the vertical direction D2 at the right end 6 of the core 21 of the waveguide 20 is located above the lower end 4 in the vertical direction D2 at the left end 31a of the core 31 of the optical fiber 30.

[0037] The upper end (first end of the inclined surface 41) 1 of the right end 6 of the core 21 of the waveguide 20 is located at the same position as the upper end 3 of the left end 30a of the core 31 of the optical fiber 30 in the vertical direction D2, but it may also be located below the upper end 3 of the left end 30a of the core 31 of the optical fiber 30.

[0038] In the optical module A1 of this embodiment, the right end 20a of the waveguide 20 and the left end 30a of the optical fiber 30 are joined by an adhesive (for example, a UV adhesive).

[0039] For example, in optical module A1, the adhesive is applied to the right end 20a of the waveguide 20 located in the first groove 11 of the substrate 10 and to the left end 30a of the optical fiber 30 located in the second groove 12. Then, a pressing member (for example, a pressing glass) is pressed against the optical fiber 30 from the front and rear directions of the substrate 10, and the adhesive is cured. Note that the adhesive and pressing member are not shown in Figures 1 to 10.

[0040] The refractive index of the adhesive is preferably about the same as that of the cladding 22 of the waveguide 20 (including a 10% error). Furthermore, it is preferable that the refractive index of the adhesive is higher than that of the core 31 of the optical fiber 30.

[0041] (3) Inclination angle of the inclined surface of the inclined section The inclination angle θ of the inclined surface 41 of the inclined section 40 (see Figure 3) will be explained below.

[0042] The inclination angle θ of the inclined surface 41 of the inclined section 40 is set to satisfy at least one of the following multiple conditions.

[0043] As shown in Figure 3, when light propagating through the core 21 of the waveguide 20 (hereinafter referred to as "propagating light") travels in a straight line within the core 21, the conditions (first condition) for the light emitted from the inclined surface 41 of the inclined portion 40 of the core 21 (hereinafter referred to as "first emitted light") to undergo total internal reflection within the core 31 of the optical fiber 30, while the light totally reflected at the inclined surface 41 (hereinafter referred to as "reflected light") does not undergo total internal reflection within the core 21, and for the reflected light to be transmitted from the core 21 to the cladding 22, are expressed by the following equations (1) to (8).

[0044] In other words, the inclination angle θ of the inclined surface 41 of the inclined portion 40 is set such that equations (1) to (8) are satisfied, where Φ1 is the incident angle Φ1 of the propagating light with respect to the inclined surface 41, Φ2 is the refraction angle Φ2 of the first emitted light refracted at the inclined surface 41, Φ3 is the incident angle Φ3 of the first emitted light with respect to the end face of the left end 31a of the core 31 of the optical fiber 30, Φ4 is the refraction angle Φ4 of the light refracted at the end face of the left end 31a of the core 31, n1 is the refractive index of the core 21 of the waveguide 20, n2 is the refractive index of the cladding 22 of the waveguide 20, n3 is the refractive index of the adhesive placed in the optical path between the waveguide 20 and the optical fiber 30, n4 is the refractive index of the core 31 of the optical fiber 30, and n5 is the refractive index of the cladding 32 of the optical fiber 30.

[0045] In Figure 3, the optical fiber 30 is conceptually shown as a cross-sectional view to explain the path of light, and therefore, hatching is not applied to the cross-section of the optical fiber 30. Also, the dotted line with an arrow in Figure 3 represents a portion of the path of light propagating from the waveguide 20 to the optical fiber 30. Furthermore, the dashed line with an arrow in Figure 3 represents a portion of the path of reflected light that has undergone total internal reflection at the inclined surface 41 of the inclined section 40.

[0046]

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[0047] Furthermore, as shown in Figure 4, when the propagating light propagating through the core 21 of the waveguide 20 undergoes total internal reflection at the upper end 21a of the core 21, and then the first emitted light is emitted from the inclined surface 41 of the inclined section 40, the conditions (second condition) for the first emitted light to undergo total internal reflection within the core 31 of the optical fiber 30, and for the reflected light that underwent total internal reflection at the inclined surface 41 of the inclined section 40 to not undergo total internal reflection within the core 21, and for the reflected light to be transmitted from the core 21 to the cladding 22, are expressed by equations (2), (4), (6) to (8), in addition to the following equations (9) to (11).

[0048] In other words, the inclination angle θ of the inclined surface 41 of the inclined section 40 is set such that equations (2), (4), (6) to (11) are satisfied, where Φ0 is the angle at which the propagating light undergoes total internal reflection at the upper end 21a of the core 21.

[0049] In Figure 4, the optical fiber 30 is conceptually shown as a cross-sectional view to explain the path of light, and therefore hatching is not applied to the cross-section of the optical fiber 30. Also, the dotted line with an arrow in Figure 4 represents a portion of the path of light propagating from the waveguide 20 to the optical fiber 30. Furthermore, the dashed line with an arrow in Figure 4 represents a portion of the path of reflected light that has undergone total internal reflection at the inclined surface 41 of the inclined section 40.

[0050]

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[0051] Here, the angle Φ0 at which the propagating light undergoes total internal reflection at the upper end 21a of the core 21 is expressed by the following equation (12), as shown in Figure 5, where Φ9 is the angle of incidence of light from the light-emitting device 90 to the end face of the left end 5 of the core 21 of the waveguide 20, and n0 is the refractive index of the optical path (e.g., air layer) between the light-emitting device 90 and the end face of the left end 5 of the core 21. The light-emitting device 90 is, for example, a VCSEL (Vertical Cavity Surface Emitting Laser). The angle of incidence of light from the light-emitting device 90 Φ9 is an angle within the range of 0° to 20°. Note that the dotted line with an arrow in Figure 5 represents a part of the path of light propagating from the light-emitting device 90 through the waveguide 20 to the optical fiber 30.

[0052]

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[0053] Furthermore, as shown in Figure 6, when the propagating light propagating through the core 21 of the waveguide 20 undergoes total internal reflection at the lower end 21b of the core 21, and then the first emitted light is emitted from the inclined surface 41 of the inclined section 40, the conditions (third condition) for the first emitted light to undergo total internal reflection within the core 31 of the optical fiber 30, and for the reflected light that underwent total internal reflection at the inclined surface 41 of the inclined section 40 to not undergo total internal reflection within the core 21, and for the reflected light to be transmitted from the core 21 to the cladding 22, are expressed by equations (2), (4), (6) to (8), and (12), in addition to the following equations (13) to (15).

[0054] In other words, the inclination angle θ of the inclined surface 41 of the inclined section 40 is set to satisfy equations (2), (4), (6) to (8), and (12) to (15).

[0055] In Figure 6, the optical fiber 30 is conceptually shown as a cross-sectional view to explain the path of light, and therefore hatching is not applied to the cross-section of the optical fiber 30. Also, the dotted line with an arrow in Figure 6 represents a portion of the path of light propagating from the waveguide 20 to the optical fiber 30. Furthermore, the dashed line with an arrow in Figure 6 represents a portion of the path of reflected light that has undergone total internal reflection at the inclined surface 41 of the inclined section 40.

[0056]

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[0057] Furthermore, as shown in Figure 7, when the return light propagating through the core 31 of the optical fiber 30 travels in a straight line within the core 31, the conditions (fourth condition) for the light emitted from the end face of the left end 31a of the core 31 (hereinafter referred to as "second emitted light") to not undergo total internal reflection within the core 21 of the waveguide 20, and for the refracted light to be transmitted from the core 21 to the cladding 22, are expressed by the following equations (16) to (17).

[0058] In other words, the inclination angle θ of the inclined surface 41 of the inclined section 40 is set such that it satisfies equations (16) to (17), where Ψ1 is the refraction angle Ψ1 of the refracted light with respect to the inclined surface 41.

[0059] In Figure 7, the optical fiber 30 is conceptually shown as a cross-sectional view to explain the path of light, and therefore hatching is not applied to the cross-section of the optical fiber 30. Also, the dotted line with an arrow in Figure 7 represents a part of the path of the reflected light propagating from the optical fiber 30 to the waveguide 20. Furthermore, "reflected light" refers to the light that propagates from the waveguide 20 to the optical fiber 30, is reflected at the right end of the optical fiber 30 in the left-right direction D1, and returns towards the waveguide 20.

[0060]

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[0061] Furthermore, as shown in Figure 8, when the reflected light propagating through the core 31 of the optical fiber 30 undergoes total internal reflection at the upper end 3 of the core 31, and then a second emitted light is emitted from the end face of the left end 31a of the core 31, the conditions (fifth condition) for the refracted light, which is refracted at the inclined surface 41 of the inclined portion 40 of the waveguide 20 after it is incident on the inclined surface 41, not undergoing total internal reflection within the core 21 of the waveguide 20, and for the refracted light to be transmitted from the core 21 to the cladding 22, are expressed by the following equations (18) to (20).

[0062] In other words, the inclination angle θ of the inclined surface 41 of the inclined portion 40 is set such that equations (18) to (20) are satisfied, where Φ5 is the incident angle Φ5 of the reflected light with respect to the end face of the left end portion 31a of the core 31, Φ6 is the refraction angle Φ6 of the second emitted light refracted at the end face of the left end portion 31a of the core 31, and Ψ2 is the refraction angle Ψ2 of the refracted light refracted at the inclined surface 41.

[0063] In Figure 8, the optical fiber 30 is conceptually shown as a cross-sectional view to explain the path of light, and therefore, hatching is not applied to the cross-section of the optical fiber 30. Also, the dotted line with an arrow in Figure 8 represents a portion of the path of the return light propagating from the optical fiber 30 to the waveguide 20.

[0064]

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[0065] Furthermore, as shown in Figure 9, when the reflected light propagating through the core 31 of the optical fiber 30 undergoes total internal reflection at the lower end 4 of the core 31, and then a second emitted light is emitted from the end face of the left end 31a of the core 31, the conditions (sixth condition) for the refracted light, which is refracted at the inclined surface 41 of the inclined portion 40 of the waveguide 20 after being incident on the inclined surface 41, not undergoing total internal reflection within the core 21 of the waveguide 20, and for the refracted light to be transmitted from the core 21 to the cladding 22, are expressed by equations (21) to (22) below, in addition to equation (18).

[0066] In other words, the inclination angle θ of the inclined surface 41 of the inclined section 40 is set such that it satisfies equations (18) and (21) to (22), where Ψ3 is the refraction angle Ψ3 of the refracted light refracted by the inclined surface 41.

[0067] In Figure 9, the optical fiber 30 is conceptually shown as a cross-sectional view to explain the path of light, and therefore, hatching is not applied to the cross-section of the optical fiber 30. Also, the dotted line with an arrow in Figure 9 represents a portion of the path of the return light propagating from the optical fiber 30 to the waveguide 20.

[0068]

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[0069] (4) Positional relationship between the waveguide and the optical fiber As shown in Figure 10, the positional relationship between the waveguide 20 and the optical fiber 30 is determined such that the spread width of the first emitted light from the waveguide 20 fits within the diameter of the core 31 of the optical fiber 30. For example, the positional relationship between the waveguide 20 and the optical fiber 30 is determined by the shortest distance K6. Note that in Figure 10, the optical fiber 30 is conceptually illustrated as a cross-sectional view to explain the path of light, and therefore hatching is not applied to the cross-section of the optical fiber 30.

[0070] The shortest distance K6 is determined such that, given that W5 is the width W2 in the vertical direction of the core 31 of the optical fiber 30, W3 is the width W3 of the core 21 of the waveguide 20, θ is the inclination angle θ of the inclined surface 41 of the inclined section 40, Φ3 in equation (14) is Φ31, and Φ3 in equation (10) is Φ32, the following equations (23) to (24) are satisfied.

[0071]

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[0072] For example, if the width W3 of the core 21 of the waveguide 20 is 30 μm, the width W5 of the core 31 of the optical fiber 30 is 50 μm, and the inclination angle θ of the inclined surface 41 of the inclined section 40 is 70°, then the shortest distance K6 is 50 μm.

[0073] (5) Effects As shown in Figure 1, the optical module A1 comprises a substrate 10, a waveguide 20, and an optical fiber 30. The shortest distance K1 between the upper end 11a of the first groove 11 and the upper end 12a of the second groove 12 is shorter than the shortest distance K2 between the lower end 11b of the first groove 11 and the lower end 12b of the second groove 12. The right end 6 of the core 21 of the waveguide 20 has an inclined portion 40 including an inclined surface 41, and the inclined surface 41 is inclined with respect to the interface 60 between the first groove 11 and the second groove 12. That is, in the optical module A1, an inclined surface 41 is provided at the right end 6 of the core 21 of the waveguide 20, and the first groove 11 and the second groove 12 are formed in the substrate 10 such that the central axis C2 of the core 31 of the optical fiber 30 is located below the central axis C1 of the core 21 of the waveguide 20.

[0074] As a result, in optical module A1, as shown in Figure 2, when reflected light propagates from the optical fiber 30 toward the waveguide 20, the reflected light undergoes total internal reflection at the inclined surface 41 of the inclined section 40. Furthermore, in optical module A1, even if the reflected light does not undergo total internal reflection at the inclined surface 41 and is incident on the core 21 from the inclined surface 41, the reflected light does not undergo total internal reflection within the core 21 of the waveguide 20, but is transmitted from the core 21 to the cladding 22. Therefore, optical module A1 can reduce the propagation of reflected light within the core 21 of the waveguide 20. In addition, because optical module A1 can reduce the propagation of reflected light within the core 21 of the waveguide 20, it can reduce the degradation of communication performance.

[0075] In Figure 2, the optical fiber 30 is conceptually shown as a cross-sectional view to explain the path of light, and therefore hatching is not applied to the cross-section of the optical fiber 30. Also, the dotted line with an arrow in Figure 2 represents a portion of the path of light propagating from the waveguide 20 to the optical fiber 30. Also, the dashed line with an arrow in Figure 2 represents a portion of the path of the return light propagating from the optical fiber 30 to the waveguide 20.

[0076] In optical module A1, as shown in Figure 1, the central axis C2 of the core 31 of the optical fiber 30 is located below the central axis C1 of the core 21 of the waveguide 20. In other words, the central axes C2 and C1 are offset, which reduces the amount of reflected light traveling straight through the core 31 of the optical fiber 30 that enters the core 21 of the waveguide 20 (see Figure 2). Therefore, optical module A1 can reduce the propagation of reflected light within the core 21 of the waveguide 20.

[0077] Furthermore, in optical module A1, as shown in Figure 2, the first emitted light from waveguide 20 is refracted by the inclined surface 41, but since the central axis C2 is located below the central axis C1, all of the first emitted light from waveguide 20 can reach the core 31 of optical fiber 30. Therefore, optical module A1 can reduce the decrease in optical coupling efficiency between waveguide 20 and optical fiber 30. In addition, because optical module A1 can reduce the decrease in coupling efficiency with optical fiber 30, it can reduce the degradation of communication performance.

[0078] Therefore, in the optical module A1, the propagation of reflected light within the core 21 of the waveguide 20 can be reduced, and the decrease in coupling efficiency with the optical fiber 30 can be reduced.

[0079] As shown in Figure 1, the shortest distance K3 between the upper end 21a of the core 21 and the upper end 22a of the cladding 22 of the waveguide 20 is shorter than the shortest distance K4 between the lower end 21b of the core 21 and the lower end 22b of the cladding 22. In other words, the width of the cladding 22 above the core 21 is different from the width of the cladding 22 below the core 21. This allows the optical module A1 to have a longer shortest distance along the vertical direction D2 between the central axis C1 of the core 21 of the waveguide 20 and the central axis C2 of the core 31 of the optical fiber 30 than when the shortest distances K3 and K4 are the same. In other words, the amount by which the central axis C2 is offset from the central axis C1 in the optical module A1 can be greater than when the shortest distances K3 and K4 are the same. Therefore, the optical module A1 can reduce the propagation of reflected light within the core 21 of the waveguide 20 more than when the shortest distances K3 and K4 are the same. Furthermore, in the optical module A1, both the width W4 of the cladding 22 and the width W1 of the first groove 11 can be reduced, allowing for effective use of the space on the main surface 10a of the substrate 10.

[0080] The shortest distance K5 between the first end 1 of the inclined surface 41 of the inclined section 40 and the left end 30a of the optical fiber 30 is longer than the shortest distance K6 between the second end 2 of the inclined surface 41 and the left end 30a of the optical fiber 30. As a result, in the optical module A1, the inclination angle θ (see Figure 2) of the inclined surface 41 of the inclined section 40 can be set, allowing for better control over the direction of light propagation. Therefore, in the optical module A1, the propagation of reflected light within the core 21 of the waveguide 20 can be further reduced, and the decrease in coupling efficiency with the optical fiber 30 can be further reduced.

[0081] Furthermore, if the shortest distance K3 between the upper end 21a of the core 21 of the waveguide 20 and the upper end 22a of the cladding 22 is shorter than the shortest distance K4 between the lower end 21b of the core 21 and the lower end 22b of the cladding 22, the shortest distance K1 along the vertical direction D2 between the first end (upper end) 11a of the first groove 11 and the first end (upper end) 12a of the second groove 12 in the vertical direction D2 may be set to be approximately the same as the shortest distance K2 along the vertical direction D2 between the second end (lower end) 11b of the first groove 11 and the second end (lower end) 12b of the second groove 12 in the vertical direction D2. Even in this case, the incidence of reflected light traveling straight through the core 31 of the optical fiber 30 onto the core 21 of the waveguide 20 can be reduced. Furthermore, in optical module A1, by shifting both the shortest distances K1 and K2, and the shortest distances K3 and K4, the incidence of reflected light traveling in a straight line within the core 31 of the optical fiber 30 into the core 21 of the waveguide 20 can be further reduced.

[0082] The area of ​​the inclined surface 41 of the inclined portion 40 is smaller than the area of ​​the end face 31a of the left end of the core 31 of the optical fiber 30. The central axis C2 of the core 31 of the optical fiber 30 is located below the central axis C1 of the core 21 of the waveguide 20. As a result, in the optical module A1, the propagation of reflected light within the core 21 of the waveguide 20 can be further reduced, and the decrease in coupling efficiency with the optical fiber 30 can be further reduced.

[0083] The first end 1 of the inclined surface 41 of the inclined section 40 is located at the same position in the vertical direction D2 as the upper end 3 of the left end 31a of the core 31 of the optical fiber 30. The second end 2 of the inclined surface 41 of the inclined section 40 is located above the lower end 4 of the left end 31a of the core 31. As a result, in the optical module A1, the propagation of reflected light within the core 21 of the waveguide 20 can be further reduced, and the decrease in coupling efficiency with the optical fiber 30 can be further reduced.

[0084] The first end 1 of the inclined surface 41 of the inclined portion 40 is located at the same position as the upper end 3 of the left end 31a of the core 31 of the optical fiber 30 in the vertical direction D2, but it may also be located below the upper end 3 of the left end 31a of the core 31 of the optical fiber 30.

[0085] (6) Variant In this embodiment, the optical module A1 has the right end 20a of the waveguide 20 beveled, meaning that the right end 6 of the core 21 is beveled together with the right end of the cladding 22. However, as shown in Figure 11, for example, only the right end 6 of the core 21 may be beveled. In this case, the inclined surface 41 of the inclined portion 40 is covered by the cladding 22 of the waveguide 20, and the end face of the right end of the cladding 22 faces the end face of the left end 30a of the optical fiber 30.

[0086] As shown in Figure 12, the width W3 of the core 21 of the waveguide 20 may gradually decrease toward both ends (left end 5 and right end 6) in the left-right direction D1 of the core 21. That is, the core 21 may have a first portion 61 toward the right end 6 of the core 21, and a second portion 62 toward the left end 5 of the core 21.

[0087] In this case, the upper end (i.e., the first end of the inclined surface 41) 1 of the right end 6 (i.e., the inclined portion 40) of the core 21 of the waveguide 20 is located below the upper end 3 (see Figure 1) of the left end 31a of the core 31 of the optical fiber 30. The lower end (i.e., the second end of the inclined surface 41) 2 of the right end 6 of the core 21 of the waveguide 20 is located above the lower end 4 (see Figure 1) of the left end 31a of the core 31 of the optical fiber 30. Also, in this case, the rate at which the first portion 61 of the core 21 gradually decreases toward the right end 6 is smaller than the rate at which the second portion 62 of the core 21 gradually decreases toward the left end 5. As a result, the optical module A1 can further reduce the propagation of reflected light within the core 21 of the waveguide 20. Note that "W3" in Figure 12 refers to the largest width W3 of the width of the core 21 of the waveguide 20.

[0088] As shown in Figure 13, the waveguide 20 may have multiple (two in the example in Figure 13) cores 21. In this case, the multiple cores 21 are optically coupled to each other along the left-right direction D1 and are located within the first groove 11 (see Figure 1). This further reduces the propagation of reflected light within the cores 21 of the waveguide 20 in the optical module A1.

[0089] Note that the configuration and function of each of the multiple cores 21 are common. Also, in the example in Figure 13, it appears that the inclined portion 40 is provided only on the right end 6 of one of the multiple cores 21, but one of the multiple cores 21 (hereinafter referred to as the "right core 21") is optically coupled with the left core 21 such that the left end 5 of the right core 21 is a common part with the right end 6 of the remaining core 21 (hereinafter referred to as the "left core 21"). Therefore, in the example in Figure 13, it appears that the inclined portion 40 is not provided on the right end 6 of the left core 21, and that the inclined portion 40 is provided only on the right end 6 of the right core 21. In addition, "W3" in Figure 13 refers to the largest width W3 of the cores 21 of the waveguide 20.

[0090] The width W3 of the core 21 of the waveguide 20 may gradually decrease toward the left end 5 or the right end 6 of the core 21. That is, the core 21 may have a portion (first portion 61 or second portion 62) where the width W3 of the core 21 decreases toward the left end 5 or the right end 6 of the core 21.

[0091] For example, as shown in Figure 14, the waveguide 20 has a plurality of cores 21 (two in the example in Figure 14) optically coupled to each other along the left-right direction D1, and each of the plurality of cores 21 may have a first portion 61 in which the width W3 of the core 21 decreases towards the right end 6 of the core 21. This allows the optical module A1 to further reduce the propagation of reflected light within the cores 21 of the waveguide 20. Note that "W3" in Figure 14 refers to the largest width W3 of the cores 21 of the waveguide 20.

[0092] As shown in Figure 1, the upper ends 11a and 11b of the first groove 11 and the upper ends 12a and 12b of the second groove 12 are arranged in the order of upper end 12a of the second groove 12, upper end 11a of the first groove 11, lower end 11b of the first groove 11, and lower end 12b of the second groove 12, from top to bottom in the vertical direction D2 of the substrate 10, but the order is not limited to this. For example, they may be arranged in the order of upper end 11a of the first groove 11a, upper end 12a of the second groove 12, lower end 11b of the first groove 11, and lower end 12b of the second groove 12, from top to bottom in the vertical direction D2 of the substrate 10.

[0093] The number of waveguides 20 is not limited to one; there may be multiple waveguides. The number of optical fibers 30 is not limited to one; there may be multiple optical fibers.

[0094] Optical module A1 includes an optical fiber 30, but it does not have to include an optical fiber 30. In other words, optical module A1 only needs to include a substrate 10 and a waveguide 20. Even in this case, optical module A1 can reduce the propagation of reflected light within the core 21 of the waveguide 20 and reduce the decrease in coupling efficiency with the optical fiber 30.

[0095] Furthermore, the optical module A1 may further comprise the adhesive and a retaining member. The optical module A1 may further comprise an optical device (e.g., a light-emitting element or light-emitting device 90) and a mirror portion. The mirror portion is configured, for example, to bend the optical path of light from the light-emitting element by 90 degrees.

[0096] (Aspect) This specification discloses the following aspects:

[0097] An optical module (A1) according to the first embodiment comprises a substrate (10) and a waveguide (20). Light propagates through the waveguide (20). The substrate (10) has a first groove (11) and a second groove (12). The first groove (11) is formed on the main surface (10a) of the substrate (10) along the left-right direction (D1) of the substrate (10). The second groove (12) is formed on the main surface (10a) of the substrate (10) along the left-right direction (D1) so as to connect with the first groove (11). The depth of the second groove (12) is greater than the depth of the first groove (11). The waveguide (20) has a first core (21) and a first cladding (22). The first core (21) is arranged within the first groove (11) along the left-right direction (D1). Light propagates through the first core (21). The first cladding (22) covers the first core (21) and the first groove (11). The vertical width (W2) of the substrate (10) in the second groove (12) is greater than the vertical width (W1) of the first groove (11) in the vertical direction (D2). The shortest distance (K1) along the vertical direction (D2) between the upper end (11a) of the first groove (11) and the upper end (12a) of the second groove (12) is shorter than the shortest distance (K2) along the vertical direction (D2) between the lower end (11b) of the first groove (11) and the lower end (12b) of the second groove (12) in the vertical direction (D2). The right end (6) of the first core (21) has an inclined surface (41). The inclined surface (41) is inclined with respect to the interface surface (60) between the first groove (11) and the second groove (12).

[0098] According to this embodiment, the propagation of reflected light within the first core (21) of the waveguide (20) can be reduced, and the decrease in coupling efficiency with the optical fiber (30) can be reduced.

[0099] In the second embodiment of the optical module (A1), in the first embodiment, the shortest distance (K3) along the vertical direction (D2) between the upper end (21a) of the first core (21) in the vertical direction (D2) and the upper end (22a) of the first cladding (22) in the vertical direction (D2) is shorter than the shortest distance (K4) along the vertical direction (D2) between the lower end (21b) of the first core (21) in the vertical direction (D2) and the lower end (22b) of the first cladding (22) in the vertical direction (D2).

[0100] According to this embodiment, both the width (W4) of the cladding (22) and the width (W1) of the first groove (11) can be reduced, so that the space on the main surface (10a) of the substrate (10) can be effectively utilized.

[0101] In the third embodiment, the optical module (A1) has a first core (21) having a first portion (61) in which the width (W3) of the first core (21) in the vertical direction (D2) decreases towards the first end (6) located at one end of the first core (21) in the horizontal direction (D1).

[0102] According to this embodiment, the propagation of reflected light within the first core (21) of the waveguide (20) can be further reduced.

[0103] In the fourth embodiment, the optical module (A1) has, in the third embodiment, a first core (21) having a second portion (62) in which the width (W3) of the first core (21) decreases toward the second end (5) located at the other end in the left-right direction (D1) of the first core (21). The rate by which the first portion (61) of the first core (21) decreases toward the first end (6) is smaller than the rate by which the second portion (62) of the first core (21) decreases toward the second end (5).

[0104] According to this embodiment, the propagation of reflected light within the first core (21) of the waveguide (20) can be further reduced.

[0105] In the fifth embodiment, the optical module (A1) has, in the third or fourth embodiment, a waveguide (20) comprising a plurality of first cores (21), including a first core (21). The plurality of first cores (21) are optically coupled to one another along the left-right direction (D1) and are arranged within a first groove (11).

[0106] According to this embodiment, the propagation of reflected light within the first core (21) of the waveguide (20) can be further reduced.

[0107] The optical module (A1) according to the sixth embodiment further comprises an optical fiber (30) in any one of the first to fifth embodiments. The optical fiber (30) is arranged in the second groove (12) along the left-right direction (D1). The shortest distance (K5) between the upper end (1) of the inclined surface (41) and the left end (30a) of the optical fiber (30) is longer than the shortest distance (K6) between the lower end (2) of the inclined surface (41) and the left end (30a) of the optical fiber (30).

[0108] According to this embodiment, the propagation of reflected light within the first core (21) of the waveguide (20) can be further reduced, and the decrease in coupling efficiency with the optical fiber (30) can be further reduced.

[0109] The optical module (A1) according to the seventh embodiment, in the sixth embodiment, has an optical fiber (30) comprising a second core (31) and a second cladding (32). Light propagates through the second core (31). The second cladding (32) covers the second core (31) of the optical fiber (30). The area of ​​the inclined surface (41) of the waveguide (20) is smaller than the area of ​​the end face of the left end (31a) of the second core (31). The central axis (C2) of the second core (31) is located below the central axis (C1) of the first core (21) of the waveguide (20).

[0110] According to this embodiment, the propagation of reflected light within the first core (21) of the waveguide (20) can be further reduced, and the decrease in coupling efficiency with the optical fiber (30) can be further reduced.

[0111] In the optical module (A1) according to the eighth embodiment, in the seventh embodiment, the upper end (1) of the inclined surface (41) is located at the same position (D2) in the vertical direction as the upper end (3) of the left end (31a) of the second core (31), or is located below the upper end (3) of the left end (31a) of the second core (31). The lower end (2) of the inclined surface (41) is located above the lower end (4) of the left end (31a) of the second core (31).

[0112] According to this embodiment, the propagation of reflected light within the first core (21) of the waveguide (20) can be further reduced, and the decrease in coupling efficiency with the optical fiber (30) can be further reduced.

[0113] An optical module (A1) according to the ninth embodiment comprises a substrate (10) and a waveguide (20). Light propagates through the waveguide (20). The substrate (10) has a first groove (11) and a second groove (12). The first groove (11) is formed on the main surface (10a) of the substrate (10) along the left-right direction (D1) of the substrate (10). The second groove (12) is formed on the main surface (10a) of the substrate (10) along the left-right direction (D1) so as to connect with the first groove (11). The depth of the second groove (12) is greater than the depth of the first groove (11). The waveguide (20) has a core (21) and a cladding (22). The core (21) is located within the first groove (11) along the left-right direction (D1). Light propagates through the core (21). The cladding (22) covers the core (21) and the first groove (11). The vertical width (W2) of the substrate (10) in the second groove (12) is greater than the vertical width (W1) of the first groove (11) in the vertical direction (D2). The shortest distance (K3) along the vertical direction (D2) between the upper end (21a) of the core (21) and the upper end (22a) of the cladding (22) in the vertical direction (D2) is shorter than the shortest distance (K4) along the vertical direction (D2) between the lower end (21b) of the core (21) and the lower end (22b) of the cladding (22) in the vertical direction (D2). The right end (6) of the core (21) has an inclined surface (41). The inclined surface (41) is inclined with respect to the interface surface (60) between the first groove (11) and the second groove (12).

[0114] According to this embodiment, the propagation of reflected light within the first core (21) of the waveguide (20) can be reduced, and the decrease in coupling efficiency with the optical fiber (30) can be reduced. Furthermore, according to this embodiment, both the width (W4) of the cladding (22) and the width (W1) of the first groove (11) can be reduced, so that the space on the main surface (10a) of the substrate (10) can be effectively utilized. [Explanation of symbols]

[0115] 1 1st end (top end) 2 Second end (lower end) 3 Top edge 4 Bottom edge 5 Left end (second end) 6 Right end (first end) 10 circuit boards 10a Main surface 11 First groove 11a Top end 11b Bottom edge 12 Second groove 12a top end 12b Bottom edge 20 Waveguides 21 cores (1st core) 21a top end 21b Bottom end 22 Clad (First Clad) 22a top end 22b Bottom end 30 optical fibers 30a Left end 31 cores (second core) 31a Left end 32 Clad (Second Clad) 41 Slope 60 Interface 61 Part 1 62 Part 2 A1 Optical Module C1~C2 center axis D1 1st direction (left / right direction) D2 2nd direction (vertical direction) D3 Slope direction K1~K6 Shortest distance W1~W4 Width

Claims

1. circuit board and It comprises a waveguide through which light propagates, The aforementioned substrate is A first groove formed on the main surface of the substrate along the left-right direction of the substrate, It has a second groove formed on the main surface of the substrate along the left-right direction so as to connect with the first groove, The depth of the second groove is greater than the depth of the first groove. The waveguide is, A first core is arranged in the first groove along the left-right direction, through which the light propagates, It comprises a first cladding covering the first core and the first groove, The vertical width of the substrate in the second groove is greater than the vertical width of the first groove. The shortest distance along the vertical direction between the upper end of the first groove and the upper end of the second groove is shorter than the shortest distance along the vertical direction between the lower end of the first groove and the lower end of the second groove. The right end of the first core has an inclined surface that is inclined with respect to the interface between the first groove and the second groove. Optical module.

2. The shortest distance along the vertical direction between the upper end of the first core and the upper end of the first cladding is shorter than the shortest distance along the vertical direction between the lower end of the first core and the lower end of the first cladding. The optical module according to claim 1.

3. The first core is, The first core has a first portion in which the vertical width decreases towards the first end located at one end in the left-right direction of the first core. The optical module according to claim 1 or claim 2.

4. The first core is, The first core has a second portion in which the width decreases towards the second end located at the other end in the left-right direction of the first core, The ratio by which the first portion of the first core decreases toward the first end is smaller than the ratio by which the second portion of the first core decreases toward the second end. The optical module according to claim 3.

5. The waveguide has a plurality of first cores, including the first core. The plurality of first cores are optically coupled to each other along the left-right direction and are arranged within the first groove. The optical module according to claim 3 or claim 4.

6. Equipped with even more optical fibers, The optical fiber is arranged in the second groove along the left-right direction, The shortest distance between the upper end of the inclined surface and the left end of the optical fiber is longer than the shortest distance between the lower end of the inclined surface and the left end of the optical fiber. The optical module according to any one of claims 1 to 5.

7. The optical fiber is The second core through which the light propagates, The optical fiber has a second cladding covering the second core, The area of ​​the inclined surface of the waveguide is smaller than the area of ​​the end face of the left end of the second core. The central axis of the second core is located below the central axis of the first core of the waveguide. The optical module according to claim 6.

8. The upper end of the inclined surface is located at the same position in the vertical direction as the upper end of the left end of the second core, or is located below the upper end of the left end of the second core. The lower end of the inclined surface is located above the lower end of the left end of the second core. The optical module according to claim 7.

9. circuit board and It comprises a waveguide through which light propagates, The aforementioned substrate is A first groove formed on the main surface of the substrate along the left-right direction of the substrate, It has a second groove formed on the main surface of the substrate along the left-right direction so as to connect with the first groove, The depth of the second groove is greater than the depth of the first groove. The waveguide is, A core is arranged in the first groove along the left-right direction, through which the light propagates, The core and the cladding covering the first groove are included. The vertical width of the substrate in the second groove is greater than the vertical width of the first groove. The shortest distance along the vertical direction between the upper end of the core and the upper end of the cladding is shorter than the shortest distance along the vertical direction between the lower end of the core and the lower end of the cladding. The right end of the core has an inclined surface that is inclined with respect to the interface between the first groove and the second groove. Optical module.

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