Optical waveguide, and optical module

Abstract

To provide an optical waveguide that enables a part of light to be efficiently propagated, and an optical module.SOLUTION: An optical waveguide 30 comprises a substrate 31, a core 32, a clad 33, an underfill, and a light-guide portion 41. The substrate 31 has a groove 35. The light-guide portion 41 has a light-reflecting surface 41a. The light-reflecting surface 41a totally reflects a part of light propagating through the core 32 and guides the reflected light to the clad 33. The light-guide portion 41 is located inside the core 32. An inclination angle of the light-reflecting surface 41a satisfies the condition of expression 1. A condition for the distance between the middle portion of the light-reflecting surface 41a and a light extraction portion provided in the underfill is limited. A condition for the upper-limit value of the angle of light totally reflected on a first boundary surface of one of the core 32 and the clad 33 is limited. The light totally reflected on the first boundary surface on one side is totally reflected on the light-reflecting surface 41a and refracted without being totally reflected at the other of the first boundary surface and a second boundary surface. [Expression 1]SELECTED DRAWING: Figure 3

Description

Technical Field

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

Background Art

[0002] As a conventional example, the optical module described in Patent Document 1 is exemplified. The optical module described in Patent Document 1 includes a mount substrate, a light-emitting element attached to the mount substrate, and a light-receiving element for monitoring attached to the mount substrate. A groove for forming a waveguide is provided in the mount substrate. In the groove for forming a waveguide, a core portion through which light from the light-emitting element propagates and a cladding portion having a refractive index lower than that of the core portion are provided.

[0003] In the core portion, a light extraction portion (light guiding portion) that reflects a part of the propagating light toward the slope of the groove for forming a waveguide is provided. The light extraction portion is a slope of the core portion, and the end face of the core portion is inclined. The light extraction portion is inclined at 45 degrees with respect to the light propagation direction. The slope of the groove for forming a waveguide reflects a part of the light toward the light-receiving portion of the light-receiving element for monitoring.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the optical waveguide of an optical module as in the conventional example, it is desired to efficiently propagate a part of the light from the light-emitting element to the light-receiving portion of the light-receiving element for monitoring.

[0006] An object of the present disclosure is to provide an optical waveguide and an optical module capable of efficiently propagating a part of the light.

Means for Solving the Problem

[0007] An optical waveguide according to an aspect of the present disclosure includes a substrate, a core, a cladding, an underfill, and a light guiding portion. The substrate has a groove. At least a part of the core is disposed inside the groove, and light propagates through the core. The cladding covers the core and the groove and has a refractive index lower than that of the core. The underfill is disposed on the upper surface of the cladding. The light guiding portion has a reflecting surface. The reflecting surface totally reflects a part of the light propagating through the core and guides it to the cladding. The light guiding portion is disposed inside the core. The groove has an inclined surface. The inclined surface guides a part of the light totally reflected by the reflecting surface of the light guiding portion and guided to the cladding to a light extraction portion provided in the underfill. The inclination angle of the reflecting surface with respect to a straight line along the extending direction of the groove satisfies the following condition when the angle of the inclination angle is α1, the refractive index of the core is n1, and the refractive index of the cladding is n2.

[0008]

Equation

[0009] The distance between the central portion of the reflecting surface and the light extraction portion of the underfill satisfies the following condition when the length of the distance is L1, the refractive index of the underfill is n3, the width of the core is W1, the dimension from one of the pair of first interfaces between the core and the cladding in the width direction of the groove to the second interface between the cladding and the underfill through the inclined surface is W2, and the thickness of the underfill is W3.

[0010]

Equation

[0011] The upper limit value of the angle of the remaining part of the light that is totally reflected by the remaining first interface of the pair of first interfaces with respect to the remaining first interface is β, the upper limit value. MThen, it is an angle that satisfies the conditions of the following formula.

[0012]

Equation

[0013] The light that undergoes total internal reflection at the remaining first boundary surface is totally reflected at the reflecting surface and refracts without total internal reflection at the one first boundary surface and the second boundary surface.

[0014] The optical module according to one aspect of the present disclosure includes the optical waveguide and a light emitting element. The light emitting element emits the light toward the optical waveguide.

Advantages of the Invention

[0015] According to one aspect of the present disclosure, it becomes possible to efficiently propagate a part of the light.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

[0017] Hereinafter, the optical modules according to Embodiments 1 and 2 will be described with reference to the drawings. Each of the drawings described in the following embodiments is a schematic diagram, and the respective ratios of the sizes and thicknesses of the respective components do not necessarily reflect the actual dimensional ratios. Further, the configurations described in the following embodiments are merely examples of the present disclosure. The present disclosure is not limited to the following embodiments, and various modifications can be made according to the design and the like as long as the effects of the present disclosure can be achieved.

[0018] (Embodiment 1) (1) Optical module First, the optical module A1 according to Embodiment 1 will be described with reference to FIGS. 1 to 3.

[0019] The optical module A1 includes a light emitting element 10, a light receiving element 20, and an optical waveguide 30. In the optical module A1, the light emitted from the light emitting element 10 propagates through the optical waveguide 30, a part of the light propagating through the optical waveguide 30 is received by the light receiving element 20, and the light output of the light emitting element 10 is controlled by an APC (Automatic Power Control) circuit (not shown). Therefore, the optical module A1 can stabilize the light output of the light emitting element 10.

[0020] The optical module A1 is an optical module on the transmitting side that transmits optical signals. Optical signals other than the above-mentioned part of the light propagating through the optical waveguide 30 are received by a light receiving element (not shown) provided in an optical module (not shown) on the receiving side. The optical module A1 on the transmitting side and the above-mentioned optical module on the receiving side are connected by an external optical waveguide (not shown).

[0021] (2) Each component of the optical module Next, each component of the optical module A1 will be described with reference to FIGS. 1 to 3. In the following description, unless otherwise specified, the first direction D1, the second direction D2, and the third direction D3 indicated by arrows in FIG. 1 are defined as the front-rear direction, the left-right direction, and the up-down direction of the optical module A1. However, these directions are not intended to limit the direction of use of the optical module A1. Also, the arrows indicating "D1", "D2", and "D3" in the drawings are only shown for the purpose of explanation and do not have any physical entity. FIG. 2 represents the X-X cross-sectional view of FIG. 1. Also, the dotted line with an arrow in FIG. 2 represents a part of the optical path through which light propagates from the light emitting element 10 to the light receiving element 20 via the optical waveguide 30.

[0022] (2.1) Light emitting element The light emitting element 10 (see FIG. 1) emits light toward the optical waveguide 30. The light emitting element 10 is, for example, a semiconductor laser. The semiconductor laser is, for example, a vertical cavity surface emitting laser (VCSEL). The light emitting element 10 is arranged on the upper surface (one surface) 33a of the cladding 33 described later in the optical waveguide 30. Note that the semiconductor laser is not limited to a vertical cavity surface emitting laser.

[0023] (2.2) Light receiving element The light receiving element 20 has a light receiving portion 21 (see FIG. 2). The light receiving element 20 is, for example, a photodiode. The light receiving element 20 receives a part of the light propagated by the optical waveguide 30. The light receiving element 20 is arranged on the upper surface (one surface) 34b of the underfill 34 (see FIG. 2) described later in the optical waveguide 30.

[0024] (2.3) Optical waveguide As shown in Fig. 1, the optical waveguide 30 includes a substrate 31, a core 32, a cladding 33, an underfill 34 (see Fig. 2), and a light guiding portion 41 (see Fig. 3).

[0025] (2.3.1) Substrate The substrate 31 is a plate-shaped (e.g., rectangular plate-shaped) silicon substrate. The substrate 31 has a waveguide groove 35 (see Fig. 3). The groove 35 is provided at the central portion in the left-right direction (second direction D2) of the substrate 31 and in the portion from the rear end portion 31c to the front end surface 31b of the substrate 31 on the upper surface (one surface) 31a side of the substrate 31 (see Fig. 3). The groove 35 has a bottom surface 35a, a pair of first inclined surfaces 36a and 36b, a second inclined surface 37, and a pair of third inclined surfaces 38a and 38b.

[0026] (2.3.2) Core Light emitted from the light-emitting element 10 propagates through the core 32. The core 32 is, for example, in the shape of a rectangular parallelepiped. The cross-sectional shape of the core 32 viewed from the front-rear direction (first direction D1) is a square shape (see Fig. 2). The refractive index of the core 32 is higher than that of the cladding 33. The core 32 is disposed inside the groove 35 of the substrate 31. For example, the core 32 is disposed on the bottom surface 35a of the groove 35 of the substrate 31 (see Fig. 2). More specifically, the core 32 is disposed along the extending direction (first direction D1) of the groove 35 and at the central portion in the width direction (second direction D2) of the groove 35 on the bottom surface 35a of the groove 35 of the substrate 31. The height of the core 32 is larger than the depth of the groove 35 of the substrate 31. In short, the upper surface (first surface) 32a of the core 32 is higher than the upper surface 31a of the substrate 31 with reference to the bottom surface 35a of the groove 35 of the substrate 31 (see Fig. 2).

[0027] (2.3.3) Cladding The cladding 33 covers the core 32 and the groove 35. More specifically, the cladding 33 covers the upper surface 32a, the left side surface (second surface) 32b (see FIG. 3), and the right side surface (third surface) 32c (see FIG. 3) of the core 32. Further, the cladding 33 covers the bottom surface 35a of the groove 35 and the inclined surfaces (in FIG. 3, a pair of first inclined surfaces 36a, 36b, a second inclined surface 37, and a pair of third inclined surfaces 38a, 38b) of the substrate 31. Furthermore, the cladding 33 covers the outer peripheral portion of the groove 35 on the upper surface 31a of the substrate 31. That is, the upper surface 33a of the cladding 33 is higher than the upper surface 31a of the substrate 31 with reference to the bottom surface 35a of the groove 35 in the substrate 31 (see FIG. 2). In other words, the upper end portion 33b of the cladding 33 slightly protrudes above the upper surface 31a of the substrate 31. The refractive index of the cladding 33 is lower than that of the core 32. In short, the cladding 33 has a refractive index lower than that of the core 32.

[0028] The light-emitting element 10 is attached to the upper surface 33a of the cladding 33 (see FIG. 1). The light-emitting element 10 is disposed at the center in the left-right direction (second direction D2) on the upper surface 33a of the cladding 33 and is also disposed at the rear end portion 33c of the upper surface 33a of the cladding 33.

[0029] A control circuit (not shown) including the above APC circuit is mounted on the upper surface 31a of the substrate 31. The control circuit is electrically connected to the light-emitting element 10 and the light-receiving element 20. In the present embodiment, the control circuit is electrically connected to the light-emitting element 10 and the light-receiving element 20 via the substrate 31. The control circuit causes the light-emitting element 10 to emit light. Further, the control circuit detects the light received by the light-receiving element 20 and controls the light output of the light-emitting element 10 based on the detected light. Note that the control circuit may not be mounted on the upper surface 31a of the substrate 31 and may be mounted on, for example, another substrate different from the substrate 31. In this case, the other substrate on which the control circuit is mounted is electrically connected to the light-emitting element 10 and the light-receiving element 20 via the substrate 31.

[0030] (2.3.4) Underfill The underfill 34 is disposed on the upper surface 33a of the clad 33 (see FIG. 2). Also, the underfill 34 is disposed on the upper surface 31a of the substrate 31. That is, the underfill 34 is disposed across a part of the upper surface 33a of the clad 33 and a part of the upper surface 31a of the substrate 31.

[0031] The light-receiving element 20 is disposed on the upper surface 34b of the underfill 34. That is, the underfill 34 is disposed between the above-mentioned part of the upper surface 31a of the substrate 31 and the above-mentioned part of the upper surface 33a of the clad 33, and the light-receiving element 20. In the present embodiment, the portion of the upper end portion 34c of the underfill 34 that faces the light-receiving portion 21 of the light-receiving element 20 is the light extraction portion 34a. That is, the light extraction portion 34a is provided in the underfill 34. The light-receiving element 20 is disposed so as to face the light extraction portion 34a of the underfill 34. More specifically, the light-receiving element 20 is disposed such that the light-receiving portion 21 faces the light extraction portion 34a of the underfill 34.

[0032] (2.3.5) Light guiding portion As shown in FIG. 3, the light guiding portion 41 has a reflecting surface 41a. The reflecting surface 41a totally reflects a part of the light propagating through the core 32 and guides it to the clad 33. The light guiding portion 41 is disposed inside the core 32. Also, the light guiding portion 41 is disposed so as to divide the core 32 into two cores 50a and 50b (see FIG. 3). In the present embodiment, the light guiding portion 41 is provided integrally with the clad 33.

[0033] When the reflecting surface 41a of the light guide portion 41 is viewed in the extending direction of the groove 35 of the substrate 31, it has a polygonal shape such that both of the pair of first boundary surfaces 42a and 42b (see FIG. 2) between the core 32 and the cladding 33 are perpendicular to the bottom surface 35a of the groove 35. In the present embodiment, when the reflecting surface 41a of the light guide portion 41 is viewed in the extending direction of the groove 35 of the substrate 31, it has a rectangular shape (a square shape in FIG. 2) such that both of the pair of first boundary surfaces 42a and 42b are perpendicular to the bottom surface 35a of the groove 35. In short, the reflecting surface 41a of the light guide portion 41 has a rectangular shape when viewed from the front end surface 31b (see FIG. 1) of the substrate 31. In other words, the cross-sectional shape of the core 32 in the front-rear direction is rectangular. Here, the perpendicular includes not only 90°, but also an angle within a range where an error of about several degrees is allowed (an angle within the range of 90° ± 1°).

[0034] Incidentally, the first inclined surface 36a (see FIG. 3) of the groove 35 of the substrate 31 guides a part of the light that is totally reflected by the reflecting surface 41a of the light guide portion 41 and guided to the cladding 33 to the light extraction portion 34a of the underfill 34. Also, the second inclined surface 37 of the groove 35 of the substrate 31 guides the light emitted from the light emitting element 10 to the core 32 of the optical waveguide 30.

[0035] As shown in FIG. 3, the substrate 31 has a first mirror 39 and a second mirror 40.

[0036] The first mirror 39 changes the traveling path of a part of the light that is totally reflected by the reflecting surface 41a of the light guide portion 41 and guided to the cladding 33 to the light extraction portion 34a of the underfill 34 (see FIG. 2). The first mirror 39 is disposed on the first inclined surface 36a of the groove 35. The first mirror 39 is a metal film such as gold, for example, and is deposited on the first inclined surface 36a. Note that the first mirror 39 is not limited to gold.

[0037] The second mirror 40 changes the traveling path of the light emitted from the light emitting element 10 to the core 32 of the optical waveguide 30. The second mirror 40 is disposed on the second inclined surface 37 of the groove 35. The second mirror 40 is a metal film such as gold, for example, and is deposited on the second inclined surface 37. Note that the second mirror 40 is not limited to gold.

[0038] (3) Details of the optical waveguide As described above, in order to stabilize the light output of the light-emitting element 10, the optical module A1 needs to receive a part of the light propagating through the core 32 of the optical waveguide 30 with the light-receiving element 20. Further, in order not to reduce the amount of light (light quantity) received by the light-receiving element 20, the optical module A1 needs to efficiently propagate a part of the light to the light-receiving part 21 of the light-receiving element 20.

[0039] Hereinafter, the details of the optical waveguide 30, particularly, the inclination angle α1 of the reflection surface 41a of the light guiding part 41 (see FIG. 5), and the distance L1 (see FIG. 6) between the central part of the reflection surface 41a of the light guiding part 41 and the light extraction part 34a of the underfill 34 will be described with reference to FIGS. 1 to 10.

[0040] (3.1) Inclination angle of the reflection surface of the light guiding part In order for the optical waveguide 30 to efficiently propagate a part of the light (hereinafter referred to as the propagating light) propagating through the core 32 to the light-receiving part 21 of the light-receiving element 20, the propagating light needs to be totally reflected by the reflection surface 41a of the light guiding part 41. Therefore, the inclination angle α1 of the reflection surface 41a of the light guiding part 41 is important. Note that a part of the propagating light means the light from when the propagating light is totally reflected without passing through the reflection surface 41a of the light guiding part 41 until it reaches the light-receiving element 20.

[0041] Hereinafter, the inclination angle α1 of the reflection surface 41a of the light guiding part 41 will be described with reference to FIGS. 1 to 5. The inclination angle α1 of the reflection surface 41a of the light guiding part 41 is the inclination angle with respect to one of the pair of first boundary surfaces 42a and 42b, i.e., the first boundary surface 42a, as shown in FIG. 5. In other words, the inclination angle α1 of the reflection surface 41a of the light guiding part 41 is the inclination angle with respect to a straight line along the extending direction of the groove 35 of the substrate 31 (see FIG. 3). The inclination angle α1 is an angle greater than 0 (α1 > 0). The dotted line with an arrow in FIG. 5 represents the path of a part of the propagating light.

[0042] (3.1.1) Conditions for the traveling angle of the propagating light First, before explaining the details of the inclination angle α1 of the reflecting surface 41a of the light guide part 41, the condition of the traveling angle β1 of the propagating light will be explained with reference to FIG. 4. The dotted line with an arrow in FIG. 4 represents a part of the path of the propagating light.

[0043] The traveling angle β1 of the propagating light is, for example, the angle with respect to the first interface 42a, and as shown in FIG. 4, it is an angle representing the difference between the angle perpendicular to the first interface 42a (that is, 90°) and the incident angle θ1 of the propagating light. That is, the traveling angle β1 of the propagating light can be expressed as 90° - θ1.

[0044] In order for the propagating light to propagate to the reflecting surface 41a of the light guide part 41 with little loss, it is necessary for the propagating light to be totally reflected at the pair of first interfaces 42a and 42b. Hereinafter, the condition of the traveling angle β1 of the propagating light when the propagating light is totally reflected at the first interface 42a will be explained.

[0045] The incident angle θ1 of the propagating light that is totally reflected at the first interface 42a satisfies the condition of the following formula (1) according to Snell's law, where the refractive index of the core 32 is n1 and the refractive index of the cladding 33 is n2.

[0046]

Equation

[0047] Here, the critical angle θc is represented by the following formula (2).

[0048]

Equation

[0049] Also, the traveling angle βc of the propagating light at the critical angle θc is represented by the following formula (3) using formula (2).

[0050]

Equation

[0051] When the propagation light is totally reflected at the first interface 42a, the relationship between the propagation angle β1 and the propagation angle βc of the propagation light at the critical angle θc is β1 < βc. Therefore, the propagation angle β1 when the propagation light is totally reflected at the first interface 42a satisfies the condition of the following formula (4).

[0052]

Number

[0053] In order to efficiently propagate a part of the propagation light to the light-receiving part 21 of the light-receiving element 20, the light totally reflected at the first interface 42a needs to be totally reflected at the reflection surface 41a of the light guide part 41. That is, the propagation angle of the light totally reflected at the reflection surface 41a of the light guide part 41 (α1 - β1 in FIG. 5) needs to be the same angle as the propagation angle β1 of the propagation light, and is represented by the following formula (5). Here, in order to make the propagation angle β1 of the propagation light and the propagation angle of the light totally reflected at the reflection surface 41a of the light guide part 41 the same angle, the refractive index of the light guide part 41 is preferably the same as the refractive index of the cladding 33.

[0054]

Number

[0055] Therefore, the propagation angle of the light totally reflected at the reflection surface 41a of the light guide part 41 satisfies the condition of the following formula (6) from formula (4).

[0056]

Number

[0057] Here, formula (6) can be transformed into the following formula (7).

[0058]

Number

[0059] Therefore, the condition for the propagation angle β1 of the propagated light, using equations (4) and (7), is as shown in the following equation (8).

[0060] [Number]

[0061] That is, the propagation angle β1 of the propagated light needs to satisfy the condition of being larger than the critical angle of the light that is totally reflected by the reflecting surface 41a of the light guide portion 41 and smaller than the critical angle of the light that is totally reflected by the first boundary surface 42a in order to efficiently propagate a part of the propagated light to the light receiving portion 21 of the light receiving element 20. Note that the condition for the propagation angle β1 of the propagated light is the same not only when the propagated light is totally reflected by the first boundary surface 42a but also when the propagated light is totally reflected by the first boundary surface 42b.

[0062] (3.1.2) Details of the inclination angle of the reflecting surface of the light guide portion Next, the details of the inclination angle α1 of the reflecting surface 41a of the light guide portion 41 will be described.

[0063] Using equation (8), the condition of the following equation (9) can be obtained for the inclination angle α1 of the reflecting surface 41a of the light guide portion 41.

[0064] [Number]

[0065] Here, in order to propagate a part of the propagated light to the light receiving portion 21 of the light receiving element 20, the inclination angle α1 of the reflecting surface 41a of the light guide portion 41 needs to be inclined even slightly. That is, the inclination angle α1 of the reflecting surface 41a of the light guide portion 41 needs to satisfy the condition of α1 > 0. Therefore, the inclination angle α1 of the reflecting surface 41a of the light guide portion 41 needs to satisfy the condition of the following equation (10).

[0066] [Number]

[0067] On the one hand, the inclination angle α1 of the reflection surface 41a of the light guide portion 41 needs to be greater than the critical angle βc of the traveling angle of the light totally reflected at the first boundary surface 42a so that the light totally reflected at the first boundary surface 42a is also totally reflected at the reflection surface 41a. That is, the inclination angle α1 of the reflection surface 41a of the light guide portion 41 needs to satisfy the condition of α1 > βc so that the light totally reflected at the first boundary surface 42a is also totally reflected at the reflection surface 41a. Therefore, when using Equation (3), the following Equation (11) condition is obtained for the inclination angle α1 of the reflection surface 41a of the light guide portion 41.

[0068]

Equation

[0069] That is, the inclination angle α1 of the reflection surface 41a of the light guide portion 41 needs to be greater than the critical angle of the traveling angle of the light totally reflected at the first boundary surface 42a and less than twice this critical angle in order to efficiently propagate a part of the propagating light to the light receiving portion 21 of the light receiving element 20.

[0070] As described above, the light guide portion 41 of the optical waveguide 30 is disposed inside the core 32 such that the inclination angle α1 of the reflection surface 41a satisfies the condition of Equation (11).

[0071] (3.2) Propagation distance Hereinafter, the distance (hereinafter referred to as the propagation distance) L1 between the central portion of the reflection surface 41a of the light guide portion 41 and the light extraction portion 34a of the underfill 34 will be described with reference to FIGS. 6 to 10. Note that FIGS. 6 to 10 illustrate the case where the refractive index of the underfill 34 is lower than the refractive index of the cladding 33, but the refractive index of the underfill 34 may be equal to the refractive index of the cladding 33 or higher than the refractive index of the cladding 33.

[0072] In order to efficiently propagate a part of the propagated light that is totally reflected by the reflecting surface 41a of the light guide unit 41 to the light receiving unit 21 of the light receiving element 20, it is necessary to specify where on the underfill 34 the light totally reflected by the reflecting surface 41a of the light guide unit 41 reaches. That is, in order to efficiently propagate a part of the propagated light to the light receiving unit 21 of the light receiving element 20, the position of the light extraction unit 34a, that is, the propagation distance L1, is important.

[0073] (3.2.1) When the propagated light is totally reflected at the central part of the reflecting surface of the light guide unit First, the propagation distance L1 when the propagated light is totally reflected at the central part of the reflecting surface 41a of the light guide unit 41 will be described with reference to FIG. 6.

[0074] The relationship between the incident angle γ1 of the light incident on the first boundary surface 42b and the refraction angle δ1 of the light refracted at the first boundary surface 42b satisfies the condition of the following formula (12) according to Snell's law. Note that n1 and n2 in formula (12) are the same as those in formula (1). The dotted line with an arrow in FIG. 6 represents the path of a part of the propagated light.

[0075]

Equation

[0076] Here, formula (12) can be transformed into the following formula (13).

[0077]

Equation

[0078] In addition, the relationship between the incident angle δ2 of the light incident on the second boundary surface 43 and the refraction angle ζ1 of the light refracted at the second boundary surface 43 satisfies the condition of the following formula (14) according to Snell's law, assuming that the refractive index of the underfill 34 is n3. Note that n2 in formula (14) is the same as that in formula (1).

[0079]

Equation

[0080] Since the incident angle δ2 of the light incident on the second interface 43 is the same as the refraction angle δ1 of the light refracted at the first interface 42b, as shown in FIG. 6, Equation (14) can be transformed into the following Equation (15) from the relational expression of sinδ2 = sinδ1.

[0081]

Equation

[0082] Furthermore, Equation (15) can be transformed into the following Equation (16).

[0083]

Equation

[0084] The incident angle γ1 of the light incident on the first interface 42b is represented by the following Equation (17), as can be seen from FIG. 6.

[0085]

Equation

[0086] Therefore, when the propagated light totally reflects at the central part of the reflection surface 41a of the light guiding part 41, the propagation distance L1 is as shown in FIG. 6. Assuming the width of the core 32 is W1, the dimension from the first interface 42b to the second interface 43 through the first inclined surface 36a of the groove 35 (see FIG. 3) is W2, and the thickness of the underfill 34 is W3, it is as follows in Equation (18).

[0087]

Equation

[0088] (3.2.2) When the propagated light totally reflects at the first boundary Next, the propagation distance L2 when the propagated light totally reflects at the boundary (the first boundary) 44 between the reflection surface 41a of the light guiding part 41 and the first interface 42a will be described with reference to FIG. 7.

[0089] The propagation distance L2 is a distance representing the difference between the first distance Lm1 and the second distance Lm2, as shown in FIG. 7. The dotted line with an arrow in FIG. 7 represents a part of the path of the propagating light.

[0090] As shown in FIG. 7, the first distance Lm1 is given by the following equation (19) using the incident angle γ2 of the light incident on the first boundary surface 42b, the refraction angle δ3 of the light refracted at the first boundary surface 42b, the incident angle δ4 of the light incident on the second boundary surface 43, and the refraction angle ζ2 of the light refracted at the second boundary surface 43. Note that W1, W2, and W3 in equation (19) are the same as those in equation (18). Also, the incident angle δ4 of the light incident on the second boundary surface 43 is the same angle as the refraction angle δ3 of the light refracted at the first boundary surface 42b.

[0091] [Number]

[0092] As can be seen from FIG. 7, the second distance Lm2 is represented by the following equation (20).

[0093] [Number]

[0094] Therefore, when the propagating light is totally reflected at the first boundary portion 44, the propagation distance L2 is given by the following equation (21) using equations (19) and (20).

[0095] [Number]

[0096] (3.2.3) When the propagating light is totally reflected at the second boundary portion Next, the propagation distance L3 when the propagating light is totally reflected at the boundary portion (second boundary portion) 45 between the reflection surface 41a of the light guide portion 41 and the first boundary surface 42b will be described with reference to FIG. 8.

[0097] The propagation distance L3 is, as shown in FIG. 8, the distance representing the sum of the third distance Ln1 and the fourth distance Ln2. The dotted line with an arrow in FIG. 8 represents a part of the path of the propagating light.

[0098] As shown in FIG. 8, the third distance Ln1 is expressed by the following formula (22) using the refraction angle δ5 of the light refracted at the first boundary surface 2b, the incident angle δ6 of the light incident on the second boundary surface 43, and the refraction angle ζ3 of the light refracted at the second boundary surface 43. Note that W2 and W3 in formula (22) are the same as those in formula (18).

[0099] [Number]

[0100] As can be seen from FIG. 8, the fourth distance Ln2 is represented by the following formula (23).

[0101] [Number]

[0102] Therefore, when the propagating light is totally reflected at the second boundary portion 45, the propagation distance L3 is expressed by the following formula (24) using formulas (22) and (23).

[0103] [Number]

[0104] (3.2.4) Details of the propagation distance In order for the light totally reflected by the reflecting surface 41a of the light guide portion 41 to be received by the light receiving portion 21 of the light receiving element 20, the propagation distance L1 needs to be longer than the propagation distance L2 and shorter than the propagation distance L3. That is, the propagation distance L1 needs to satisfy the condition of L2 < L1 < L3. Therefore, using formulas (21) and (24), the following condition of formula (25) for the propagation distance L1 is obtained.

[0105] [Number]

[0106] Therefore, the propagation distance L1 may be the distance between the propagation distance L2 which is the lower limit value of the propagation distance L1 and the propagation distance L3 which is the upper limit value of the propagation distance L1.

[0107] Next, with regard to the condition of the propagation distance L1 when considering the lower limit value β N and the upper limit value β M of the propagation angle β1 of the propagated light, it will be described with reference to FIGS. 9 and 10. More specifically, the lower limit value β N of the propagation angle β1 of the propagated light at the propagation distance L2 which is the lower limit value of the propagation distance L1, and the upper limit value β M of the propagation angle β1 of the propagated light at the propagation distance L3 which is the upper limit value of the propagation distance L1, the condition of the propagation distance L1 will be described.

[0108] The lower limit value β N of the propagation angle β1 of the propagated light at the propagation distance L2 is represented by the following formula (26) using formula (8).

[0109]

Equation

[0110] Also, the lower limit value γ L (see FIG. 9) of the incident angle of the light incident on the first interface 42b is represented by the following formula (27) using formula (17) considering the lower limit value β N of the propagation angle β1 of the propagated light. Note that the dotted line with an arrow in FIG. 9 represents a partial path of the propagated light.

[0111]

Equation

[0112] Also, the lower limit value δ L (see FIG. 9) of the refraction angle of the light refracted at the first interface 42b is represented by the following formula (28) using formula (13) considering the lower limit value β N of the propagation angle β1 of the propagated light.

[0113] [Number]

[0114] Also, the lower limit value ζ of the refraction angle of the light refracted at the second boundary surface 43 L (see Fig. 9) is expressed by the following formula (29) using formula (16) in consideration of the lower limit value β of the traveling angle β1 of the propagating light. N Therefore, the propagation distance L when considering the lower limit value β of the traveling angle β1 of the propagating light

[0115] [Number]

[0116] Therefore, is expressed by the following formula (30) using formula (21), formula (27), formula (28) and formula (29). N when considering the lower limit value β of the traveling angle β1 of the propagating light L is expressed by the following formula (30) using formula (21), formula (27), formula (28) and formula (29).

[0117] [Number]

[0118] On the other hand, the upper limit value β of the traveling angle β1 of the propagating light at the propagation distance L3 M is expressed by the following formula (31) using formula (8).

[0119] [Number]

[0120] By the way, when considering the upper limit value β of the traveling angle β1 of the propagating light at the propagation distance L3 M the propagation distance L3 becomes longer than the case where the upper limit value β M is not considered, and it is difficult to efficiently propagate a part of the propagating light that has undergone total reflection at the reflection surface 41a of the light guide part 41 to the light receiving part 21 of the light receiving element 20.

[0121] Therefore, in order not to increase the propagation distance L3, a part of the propagated light that is totally reflected at the second boundary portion 45 needs to be refracted without total reflection at the first boundary surface 42b and also refracted without total reflection at the second boundary surface 43.

[0122] Further, the traveling angle βa (see FIG. 10) of the propagated light incident on the second boundary portion 45 may be the median value between the lower limit value β N and the upper limit value β M of the traveling angle β1 of the propagated light. Therefore, the traveling angle βa of the propagated light incident on the second boundary portion 45 is represented by the following formula (32). Note that the traveling angle βa of the propagated light incident on the second boundary portion 45 is, for example, the angle with respect to the first boundary surface 42b. Also, the dotted line with an arrow in FIG. 10 represents the path of a part of the propagated light.

[0123]

Equation

[0124] However, since a part of the propagated light that is totally reflected at the second boundary portion 45 needs to be refracted without total reflection at the first boundary surface 42b and the second boundary surface 43, the following condition of formula (33) is obtained from formula (31) for the upper limit value β M of the traveling angle β1 of the propagated light.

[0125]

Equation

[0126] Also, the upper limit value γ H (not shown) of the incident angle of the light incident on the first boundary surface 42b is represented by the following formula (34) using formula (17) in consideration of the upper limit value β M of the traveling angle β1 of the propagated light and the traveling angle βa of the propagated light incident on the second boundary portion 45.

[0127]

Equation

[0128] Also, the upper limit value δ of the refraction angle of the light refracted at the first interface 42b H (see Fig. 10) is expressed by the following formula (35) using formula (13), considering the upper limit value β of the traveling angle β1 of the propagating light M and the traveling angle βa of the propagating light incident on the second boundary portion 45.

[0129]

Equation

[0130] Also, the upper limit value ζ of the refraction angle of the light refracted at the second interface 43 H (see Fig. 10) is expressed by the following formula (36) using formula (16), considering the upper limit value β of the traveling angle β1 of the propagating light M and the traveling angle βa of the propagating light incident on the second boundary portion 45.

[0131]

Equation

[0132] Therefore, the propagation distance L M when considering the upper limit value β of the traveling angle β1 of the propagating light and the traveling angle βa of the propagating light incident on the second boundary portion 45 H is expressed by the following formula (37) using formula (24), formula (34), formula (35) and formula (36).

[0133]

Equation

[0134] Thus, in order to efficiently propagate a part of the propagating light that is totally reflected by the reflecting surface 41a of the light guide portion 41 to the light receiving portion 21 of the light receiving element 20, the propagation distance L1 satisfies the condition of the following formula (38).

[0135]

Equation

[0136] As described above, the light extraction portion 34a is provided at the upper end portion 34c of the underfill 34 such that the propagation distance L1 between the central portion of the reflection surface 41a of the light guiding portion 41 and the light extraction portion 34a of the underfill 34 satisfies the condition of Equation (38).

[0137] (4) Operation of the optical module The control board attached to the substrate 31 of the optical waveguide 30 (see FIG. 1) causes the light emitting element 10 to emit light. The light from the light emitting element 10 enters the core 32 of the optical waveguide 30. Part of the light propagating through the core 32 (propagating light) is totally reflected by the reflection surface 41a of the light guiding portion 41 (see FIG. 3). Part of the propagating light totally reflected by the reflection surface 41a of the light guiding portion 41 is guided to the cladding 33. Also, part of the propagating light guided to the cladding 33 is guided to the light extraction portion 34a of the underfill 34 (see FIG. 2) via the first mirror 39 disposed on the first inclined surface 36a of the substrate 31. Therefore, the light receiving element 20 receives part of the propagating light guided to the light extraction portion 34a. Accordingly, the control board detects part of the propagating light received by the light receiving portion 21 and controls the light output of the light emitting element 10 based on the detected part of the propagating light. Thereby, the optical module A1 can stabilize the light output of the light emitting element 10.

[0138] (5) Summary In the optical waveguide 30 of the optical module A1, in order to efficiently propagate part of the propagating light to the light receiving portion 21 of the light receiving element 20, the light guiding portion 41 is disposed inside the core 32 such that the inclination angle α1 of the reflection surface 41a satisfies the condition of Equation (11). Also, in the optical waveguide 30 of the optical module A1, in order to efficiently propagate part of the propagating light to the light receiving portion 21 of the light receiving element 20, the light extraction portion 34a is provided at the upper end portion 34c of the underfill 34 such that the propagation distance L1 satisfies the condition of Equation (38). Therefore, the optical waveguide 30 can efficiently propagate part of the light. Also, since the optical module A1 includes the optical waveguide 30, it can efficiently propagate part of the light.

[0139] The refractive index of the light guide portion 41 is the same as that of the cladding 33. Therefore, in the optical waveguide 30, it is possible to make the traveling angle β1 of the propagating light and the traveling angle of the light that is totally reflected by the reflecting surface 41a of the light guide portion 41 the same angle. Accordingly, in the optical waveguide 30, it is possible to propagate a part of the light more efficiently.

[0140] The substrate 31 has the first mirror 39. The first mirror 39 changes the traveling path of a part of the light that is totally reflected by the reflecting surface 41a of the light guide portion 41 and guided to the cladding 33 to the light extraction portion 34a of the underfill 34. Therefore, in the optical waveguide 30, since the traveling path of a part of the light can be changed by the first mirror 39, it is possible to increase the degree of freedom in the arrangement location of the light extraction portion 34a. In other words, in the optical waveguide 30, since the traveling path of a part of the light can be changed by the first mirror 39, it is possible to increase the degree of freedom in the arrangement location of the light receiving element 20.

[0141] The reflecting surface 41a of the light guide portion 41 is a polygonal shape such that both of the pair of first boundary surfaces 42a and 42b are perpendicular to the bottom surface 35a of the groove 35 when viewed from the extending direction of the groove 35 of the substrate 31. Therefore, in the optical waveguide 30, for example, it is possible to increase the amount of light that is totally reflected by the reflecting surface 41a compared to the case where the shape of the reflecting surface 41a of the light guide portion 41 is circular or elliptical, and it is possible to suppress a decrease in the amount of light that reaches the light extraction portion 34a. In other words, in the optical waveguide 30, for example, it is possible to increase the amount of light that is totally reflected by the reflecting surface 41a compared to the case where the shape of the reflecting surface 41a of the light guide portion 41 is circular or elliptical, and it is possible to suppress a decrease in the amount of light received by the light receiving element 20.

[0142] (6) Modification As a modification of the first embodiment, the light emitting element 10 is not limited to a semiconductor laser, and may be, for example, an LED or the like. The substrate 31 is not limited to a silicon substrate, and may be, for example, a ceramic substrate, a resin substrate, or the like.

[0143] The substrate 31 has the first mirror 39, but it may not have the first mirror 39. Also, the substrate 31 has the second mirror 40, but it may not have the second mirror 40.

[0144] The refractive index of the light guide portion 41 is the same as that of the cladding 33. However, if the traveling angle β1 of the propagating light and the traveling angle of the light that is totally reflected by the reflection surface 41a of the light guide portion 41 can be made the same angle, it may be different from the refractive index of the cladding 33.

[0145] The core 32 is disposed on the bottom surface 35a of the groove 35 of the substrate 31, but it may be other than the bottom surface 35a of the groove 35. For example, the core 32 may be disposed inside the groove 35 of the substrate 31 away from the bottom surface 35a of the groove 35.

[0146] The optical module A1 includes one light emitting element 10, but it may include a plurality of light emitting elements 10. In this case, the optical module A1 includes a plurality of grooves 35, and a core 32, a cladding 33, and an underfill 34 are provided in each groove 35. The plurality of light emitting elements 10 are electrically connected to the control substrate.

[0147] Also, the optical module A1 includes one light receiving element 20, but it may include a plurality of light receiving elements 20. In this case, the plurality of light receiving elements 20 are electrically connected to the control substrate.

[0148] Also, the optical module A1 includes the light receiving element 20, but it may not include the light receiving element 20.

[0149] Also in the optical waveguide 30 according to the above modification example, the same effects as those of the optical waveguide 30 according to Embodiment 1 are achieved. Also in the optical module A1 according to the above modification example, the same effects as those of the optical module A1 according to Embodiment 1 are achieved.

[0150] The above-described Embodiment 1 and modification examples are only a part of various embodiments and modification examples of the present disclosure.

[0151] (Embodiment 2) The optical module A2 according to Embodiment 2 is different from the optical module A1 (see FIG. 2) according to Embodiment 1 in that the cross-sectional shape of the core 32 viewed from the front-rear direction and the like are different.

[0152] (1) Optical module The optical module A2 according to Embodiment 2 has substantially the same configuration as the optical module A1 according to Embodiment 1. For the optical module A2 according to Embodiment 2, the same components as those of the optical module A1 (see FIGS. 1 to 10) according to Embodiment 1 are denoted by the same reference numerals, and the description thereof is omitted.

[0153] (2) Each component of the optical module Each component of the optical module A2 according to Embodiment 2 will be described with reference to FIG. 11. Note that the dotted line with an arrow in FIG. 11 represents a part of the optical path that propagates from the light-emitting element 10 to the light-receiving element 20 through the optical waveguide 30.

[0154] The reflecting surface 41a of the light guide part 41 is pentagonal such that both of the pair of first boundary surfaces 42a and 42b are perpendicular to the bottom surface 35a of the groove 35 when viewed from the extending direction of the groove 35 of the substrate 31 (see FIG. 11). In short, the reflecting surface 41a of the light guide part 41 is pentagonal when viewed from the front end surface 31b (see FIG. 1) of the substrate 31. In other words, the cross-sectional shape of the core 32 viewed from the front-rear direction is pentagonal.

[0155] (3) Operation of the optical module The operation of the optical module A2 is the same as the operation of the optical module A1 according to Embodiment 1. Therefore, the optical module A2 can stabilize the light output of the light-emitting element 10.

[0156] (4) Summary Also in the optical waveguide 30 in the optical module A2, in order to efficiently propagate a part of the propagating light to the light receiving part 21 of the light receiving element 20, the light guiding part 41 is arranged inside the core 32 such that the inclination angle α1 of the reflecting surface 41a satisfies the condition of the formula (11). Also in the optical waveguide 30 in the optical module A2, in order to efficiently propagate a part of the propagating light to the light receiving part 21 of the light receiving element 20, the light extraction part 34a is provided at the upper end part 34c of the underfill 34 such that the propagation distance L1 satisfies the condition of the formula (38). Therefore, also in the optical waveguide 30 of the optical module A2, it is possible to efficiently propagate a part of the light. Also in the optical module A2, since it is provided with the optical waveguide 30, it is possible to efficiently propagate a part of the light.

[0157] Also, in the optical waveguide 30 of the optical module A2, the reflecting surface 41a of the light guiding part 41 has a pentagonal shape such that both of the pair of first boundary surfaces 42a and 42b are perpendicular to the bottom surface 35a of the groove 35 when viewed from the extending direction of the groove 35 of the substrate 31. Therefore, in the optical waveguide 30 of the second embodiment, it is possible to increase the amount of light propagating through the core 32 as compared with the optical waveguide 30 of the first embodiment.

[0158] (5) Modification As a modification of the optical module A2 according to the second embodiment, the same modifications as those of the optical module A1 according to the modification of the first embodiment are possible.

[0159] The reflecting surface 41a of the light guiding part 41 is not limited to a pentagonal shape such that both of the pair of first boundary surfaces 42a and 42b are perpendicular to the bottom surface 35a of the groove 35 when viewed from the extending direction of the groove 35 of the substrate 31, and for example, it may be hexagonal.

[0160] Further, the reflecting surface 41a of the light guide portion 41 is not limited to a polygonal shape in which both of the pair of first boundary surfaces 42a and 42b are perpendicular to the bottom surface 35a of the groove 35 when viewed from the extending direction of the groove 35 of the substrate 31. The reflecting surface 41a of the light guide portion 41 may be a polygonal shape in which any one of the pair of first boundary surfaces (for example, the first boundary surface 42a) is perpendicular to the bottom surface 35a of the groove 35 when viewed from the extending direction of the groove 35 of the substrate 31. Therefore, also in the optical waveguide 30 of the optical module A2, for example, it becomes possible to increase the amount of light totally reflected by the reflecting surface 41a more than in the case where the shape of the reflecting surface 41a of the light guide portion 41 is circular or elliptical, and it becomes possible to suppress a decrease in the amount of light reaching the light extraction portion 34a. In other words, also in the optical waveguide 30 of the optical module A2, for example, it becomes possible to increase the amount of light totally reflected by the reflecting surface 41a more than in the case where the shape of the reflecting surface 41a of the light guide portion 41 is circular or elliptical, and it becomes possible to suppress a decrease in the amount of light received by the light receiving element 20.

[0161] Also in the optical waveguide 30 according to the above-described modification, the same effects as those of the optical waveguide 30 according to the second embodiment are exhibited. Further, also in the optical module A2 according to the above-described modification, the same effects as those of the optical module A2 according to the second embodiment are exhibited.

[0162] The second embodiment and the modification described above are only a part of various embodiments and modifications of the present disclosure.

[0163] (Aspect) The following aspects are disclosed in this specification.

[0164] The optical waveguide (30) according to the first aspect includes a substrate (31), a core (32), a cladding (33), an underfill (34), and a light guiding portion (41). The substrate (31) has a groove (35). The core (32) is at least partially disposed inside the groove (35) and light propagates therethrough. The cladding (33) covers the core (32) and the groove (35) and has a refractive index lower than that of the core (32). The underfill (34) is disposed on the upper surface (33a) of the cladding (33). The light guiding portion (41) has a reflecting surface (41a). The reflecting surface (41a) totally reflects a part of the light propagating through the core (32) and guides it to the cladding (33). The light guiding portion (41) is disposed inside the core (32). The groove (35) has an inclined surface (36a). The inclined surface (36a) guides a part of the light totally reflected by the reflecting surface (41a) of the light guiding portion (41) and guided to the cladding (33) to a light extraction portion (34a) provided in the underfill (34). The inclination angle (α1) of the reflecting surface (41a) with respect to a straight line along the extending direction of the groove (35) satisfies the following condition, where the angle of the inclination angle (α1) is α1, the refractive index of the core (32) is n1, and the refractive index of the cladding (33) is n2.

[0165]

Equation

[0166] The distance (L1) between the central portion of the reflecting surface (41a) and the light extraction portion (34a) of the underfill (34) satisfies the following condition, where the length of the distance (L1) is L1, the refractive index of the underfill (34) is n3, the width of the core (32) is W1, the dimension from one of the pair of first interfaces (42a, 42b) of the core (32) and the cladding (33) in the width direction of the groove (35) to the second interface (43) of the cladding (33) and the underfill (34) via the inclined surface (36a) is W2, and the thickness of the underfill (34) is W3.

[0167]

Equation

[0168] Of the pair of first interfaces (42a, 42b), the upper limit value (β M ) of the angle of the remaining light that totally reflects on the remaining first interface (42a) with respect to the remaining first interface (42a) is such that, when the upper limit value (β M ) is denoted as β M , it is an angle that satisfies the condition of the following equation.

[0169]

Equation

[0170] The light that totally reflects on the remaining first interface (42a) totally reflects on the reflecting surface (41a), and refracts without total reflection on one of the first interfaces (42b) and the second interface (43).

[0171] According to this aspect, it becomes possible to efficiently propagate a part of the light.

[0172] In the optical waveguide (30) according to the second aspect, in the first aspect, the refractive index of the light guiding portion (41) is the same as the refractive index of the cladding (33).

[0173] According to this aspect, it becomes possible to more efficiently propagate a part of the light.

[0174] In the optical waveguide (30) according to the third aspect, in the first or second aspect, the substrate (31) has a mirror (39). The mirror (39) changes the traveling path of a part of the light that totally reflects on the reflecting surface (41a) of the light guiding portion (41) and is guided to the cladding (33) to the light extraction portion (34a) of the underfill (34). The mirror (39) is disposed on the inclined surface (36a) of the groove (35).

[0175] According to this aspect, since the traveling path of a part of the light can be changed by the mirror (39), it becomes possible to increase the degree of freedom in the placement location of the light extraction portion (34a). In other words, since the traveling path of a part of the light can be changed by the mirror (39), it becomes possible to increase the degree of freedom in the placement location of the light receiving element (20).

[0176] In the fourth aspect, in any one of the first to third aspects, for the optical waveguide (30), the reflecting surface (41a) of the light guiding portion (41) has a polygonal shape such that, when viewed in the extending direction of the groove (35), one of the pair of first boundary surfaces (42a, 42b), i.e., either the first boundary surface (42a; 42b), is perpendicular to the bottom surface (35a) of the groove (35).

[0177] According to this aspect, for example, it is possible to increase the amount of light that is totally reflected by the reflecting surface (41a) compared to the cases where the shape of the reflecting surface (41a) of the light guiding portion (41) is circular or elliptical, and it is possible to suppress a decrease in the amount of light reaching the light extraction portion (34a). In other words, for example, it is possible to increase the amount of light that is totally reflected by the reflecting surface (41a) compared to the cases where the shape of the reflecting surface (41a) of the light guiding portion (41) is circular or elliptical, and it is possible to suppress a decrease in the amount of light received by the light receiving element (20).

[0178] In the fifth aspect, in any one of the first to third aspects, for the optical waveguide (30), the reflecting surface (41a) of the light guiding portion (41) has a polygonal shape such that, when viewed in the extending direction of the groove (35), both of the pair of first boundary surfaces (42a, 42b) are perpendicular to the bottom surface (35a) of the groove (35).

[0179] Also according to this aspect, for example, it is possible to increase the amount of light that is totally reflected by the reflecting surface (41a) compared to the cases where the shape of the reflecting surface (41a) of the light guiding portion (41) is circular or elliptical, and it is possible to suppress a decrease in the amount of light reaching the light extraction portion (34a). In other words, for example, it is possible to increase the amount of light that is totally reflected by the reflecting surface (41a) compared to the cases where the shape of the reflecting surface (41a) of the light guiding portion (41) is circular or elliptical, and it is possible to suppress a decrease in the amount of light received by the light receiving element (20).

[0180] The configurations according to the second to fifth aspects are not essential configurations of the optical waveguide (30) and can be omitted as appropriate.

[0181] The optical module (A1; A2) according to the sixth aspect includes any one of the optical waveguides (30) of the first to fifth aspects and a light emitting element (10). The light emitting element (10) emits light toward the optical waveguide (30).

[0182] According to this aspect, it becomes possible to efficiently propagate a part of the light.

[0183] The optical module (A1; A2) according to the seventh aspect further includes a light receiving element (20) in the sixth aspect. The light receiving element (20) receives a part of the light propagated by the optical waveguide (30). The light receiving element (20) is arranged to face the light extraction portion (34a) of the underfill (34).

[0184] Also according to this aspect, it becomes possible to efficiently propagate a part of the light.

[0185] The configuration according to the seventh aspect is not an essential configuration of the optical module (A1; A2) and can be omitted as appropriate.

Explanation of Reference Numerals

[0186] 10 Light emitting element 20 Light receiving element 30 Optical waveguide 31 Substrate 32 Core 33 Clad 33a Upper surface 34 Underfill 34a Light extraction portion 35 Groove 35a Bottom surface 36a First inclined surface (inclined surface) 39 First mirror (mirror) 41 Light guiding portion 41a Reflecting surface 42a First interface 42b First interface 43 Second interface A1 Optical module A2 Optical module L1 Propagation distance (distance) α1 inclination angle β M upper limit value

Claims

1. A substrate having a groove; A core at least partially disposed inside the groove through which light propagates; A cladding covering the core and the groove and having a refractive index lower than that of the core; An underfill disposed on the upper surface of the cladding; A light guiding portion having a reflecting surface that totally reflects a part of the light propagating through the core and guides it to the cladding, comprising: The light guiding portion is disposed inside the core; The groove has an inclined surface that guides a part of the light totally reflected by the reflecting surface of the light guiding portion and guided to the cladding to a light extraction portion provided in the underfill; The inclination angle of the reflecting surface with respect to a straight line along the extending direction of the groove satisfies the following condition, where the angle of the inclination angle is α1, the refractive index of the core is n1, and the refractive index of the cladding is n2; 【Number 1】 The distance between the central portion of the reflecting surface and the light extraction portion of the underfill satisfies the following condition, where the length of the distance is L1, the refractive index of the underfill is n3, the width of the core is W1, the dimension from one of the pair of first boundary surfaces between the core and the cladding in the width direction of the groove to the second boundary surface between the cladding and the underfill via the inclined surface is W2, and the thickness of the underfill is W3; 【Number 2】 The upper limit of the angle of the remaining light that totally reflects on the remaining first boundary surface among the pair of first boundary surfaces with respect to the remaining first boundary surface is the upper limit value β Ｍ If we denote it as β, it is an angle that satisfies the condition of the following equation, [Number 3] The light totally reflected at the remaining first boundary surface is totally reflected at the reflecting surface and refracts without total reflection at the one first boundary surface and the second boundary surface; An optical waveguide.

2. The refractive index of the light guiding portion is the same as that of the cladding; The optical waveguide according to Claim 1.

3. The substrate has a mirror that changes the path of a part of the light totally reflected by the reflecting surface of the light guiding portion and guided to the cladding to the light extraction portion of the underfill; The mirror is disposed on the inclined surface of the groove; The optical waveguide according to Claim 1 or Claim 2.

4. The reflecting surface of the light guiding portion has a polygonal shape such that one of the pair of first boundary surfaces is perpendicular to the bottom surface of the groove when viewed from the extending direction of the groove; The optical waveguide according to any one of Claims 1 to 3.

5. The reflecting surface of the light guiding portion has a polygonal shape such that both of the pair of first boundary surfaces are perpendicular to the bottom surface of the groove when viewed from the extending direction of the groove; The optical waveguide according to any one of Claims 1 to 3.

6. An optical waveguide according to any one of claims 1 to 5, and a light-emitting element that emits the light toward the optical waveguide, comprising an optical module.

7. further comprising a light-receiving element that receives a part of the light propagated by the optical waveguide, wherein the light-receiving element is disposed so as to face the light extraction portion of the underfill, the optical module according to claim 6.

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