Optical module

Abstract

To provide an optical module in which the loss of light reflected from the light-reflecting surface is sufficiently suppressed. [Solution] The optical module of the present invention comprises an optical waveguide having a core portion extending along an axis, a first light-reflecting surface intersecting the core portion, and a first surface and a second surface having a front-back relationship with each other, and a first optical element having a first light-receiving point arranged on the first surface side of the optical waveguide and optically connected to the core portion via the first light-reflecting surface, wherein, when the optical waveguide is cut by a plane that includes the axis and is perpendicular to the first surface, the shape of the first light-reflecting surface exposed on the cut surface is such that the first light-reflecting surface is the focal point and follows a parabola that intersects the axis at 45° at the first surface center.

Description

[Technical Field]

[0001] This invention relates to an optical module. [Background technology]

[0002] Patent Document 1 discloses a method for manufacturing an optical-electrical composite wiring board in which electrical wiring for propagating electrical signals and waveguides for propagating optical signals are mixed together. Patent Document 1 also discloses forming a reflective mirror in the core of the waveguide, making the reflective surface shape of the reflective mirror concave, and coupling the reflective mirror with an optical-electrical conversion element.

[0003] In such an optoelectronic composite circuit board, the reflective surface shape of the reflective mirror is concave, allowing the optical signal to be focused onto the light-receiving surface of the optical-electrical conversion element. Furthermore, the light from the light-emitting surface of the optical-electrical conversion element can be efficiently received by the reflective mirror. This improves the system's transmission efficiency. Additionally, since the reflective mirror has a focusing function, a coupling lens becomes unnecessary. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2004-205661 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Patent Document 1 discloses that the reflective surface of a reflective mirror should be concave, but it does not disclose what shape the concave surface should be. Since the shape of the concave surface affects the loss of light reflected by the reflective mirror, there is room for further consideration regarding the shape of the concave surface.

[0006] The object of the present invention is to provide an optical module in which the loss of light reflected from the light-reflecting surface is sufficiently suppressed. [Means for solving the problem]

[0007] These objectives are achieved by the present invention as described in (1) to (7) below. (1) An optical waveguide having a core portion extending along an axis, a first light-reflecting surface intersecting the core portion, and a first surface and a second surface that are in a front-back relationship with each other, A first optical element having a first light-receiving point, which is disposed on the first surface side of the optical waveguide and is optically connected to the core portion via the first light-reflecting surface, Equipped with, When the cross-section is made by a plane that includes the axis and is perpendicular to the first plane, and the intersection point of the axis and the first light-reflecting surface is defined as the center of the first plane, The optical module is characterized in that the shape of the first light-reflecting surface exposed on the cut surface is a shape that follows a parabola that has the first light-receiving point as its focal point and intersects the axis at a 45° angle at the center of the first surface.

[0008] (2) The optical module according to (1) above, wherein the shape of the first light reflecting surface is a shape that follows the paraboloid of revolution which includes the parabola.

[0009] (3) The optical module according to (1) or (2) above, wherein the first light reflecting surface is formed at the interface between the constituent material of the core and the external space.

[0010] (4) The optical module according to any one of (1) to (3) above, wherein the first light-emitting and receiving point is a light-emitting point that emits light toward the first light-reflecting surface.

[0011] (5) The optical waveguide further has a second optical reflecting surface located on the opposite side of the first optical reflecting surface via the core portion and optically connected to the first optical reflecting surface, The optical waveguide further comprises a second optical element having a second light-receiving point, which is disposed on the first surface side of the optical waveguide and is optically connected to the core portion via a second light-reflecting surface. In the aforementioned cross-section, when the intersection point of the axis and the second light-reflecting surface is defined as the second surface center, The shape of the second light reflection surface exposed on the cut surface is a shape along a parabola that focuses on the second light emitting and receiving point and intersects the axis at 45° at the second centroid, according to any one of the above (1) to (4) of the optical module.

[0012] (6) The optical module according to the above (5), wherein the shape of the second light reflection surface is a shape along a rotational paraboloid including the parabola.

[0013] (7) The optical module according to the above (5) or (6), wherein the second light reflection surface is formed at an interface between a constituent material of the core portion and an external space. [Advantages of the Invention]

[0014] According to the present invention, an optical module in which loss of light reflected by a light reflection surface is sufficiently suppressed can be obtained. [Brief Description of the Drawings]

[0015] [Figure 1] It is a cross-sectional view showing the configuration of an optical module according to the first embodiment. [Figure 2] It is a partially enlarged view of the vicinity of a light emitting element included in the optical module shown in FIG. 1. [Figure 3] It is a partially enlarged view of the vicinity of a light receiving element included in the optical module shown in FIG. 1. [Figure 4] It is a cross-sectional view when the optical module shown in FIG. 1 is cut by a plane passing through the first centroid and orthogonal to the a-axis. [Figure 5] It is a schematic diagram for explaining a method of quantifying the difference between the first light reflection surface and the paraboloid. [Figure 6] It is a diagram showing an example of the distribution of the z coordinate zm of the actually measured first light reflection surface. [Figure 7] It is a diagram showing an example of the distribution of the calculated difference zm - zp. [Figure 8] It is a conceptual diagram for explaining a method of forming a recess by a laser processing method. [Figure 9]Figure 8 is a schematic diagram showing the positional relationship between the irradiation range of the laser beam irradiated onto the movable mask and the transparent portion of the movable mask. [Figure 10] This is a cross-sectional view showing the configuration of an optical module according to the second embodiment. [Figure 11] This is a cross-sectional view showing the configuration of an optical module according to the second embodiment. [Figure 12] Figure 10 is a schematic diagram showing the irradiation range of the laser light irradiated onto the movable mask and the transmission area of ​​the movable mask when the first light-reflecting surface shown is formed by laser processing. [Modes for carrying out the invention]

[0016] The optical module according to the present invention will be described in detail below based on preferred embodiments shown in the attached drawings.

[0017] 1. First Embodiment An overview of the optical module according to the first embodiment will be described.

[0018] Figure 1 is a cross-sectional view showing the configuration of the optical module 1 according to the first embodiment. In the figures of this application, mutually orthogonal a-axis, b-axis, and c-axis are defined. Both directions along the a-axis are referred to as the "a-axis direction." The same applies to the b-axis and c-axis directions. Furthermore, the tip of the arrow representing each axis is referred to as "plus," and the base end as "minus." In addition, within the c-axis direction, the plus side is also referred to as "up," and the minus side as "down."

[0019] The optical module 1 shown in Figure 1 comprises an optical waveguide 2, a circuit board 3, a light-emitting element 41 (first optical element), and a light-receiving element 42 (second optical element). In the optical module 1, the circuit board 3 is arranged on the optical waveguide 2, and the light-emitting element 41 and the light-receiving element 42 are arranged on the circuit board 3.

[0020] The optical waveguide 2 has a core portion 24, a first optical reflective surface 262, a second optical reflective surface 266, and an upper surface 291 (first surface) and a lower surface 292 (second surface) that are in a front-back relationship with each other. The core portion 24 extends along the axis AX. The first optical reflective surface 262 and the second optical reflective surface 266 each intersect the core portion 24 and have an optical path conversion function that changes the direction of light propagation by light reflection. Furthermore, the first optical reflective surface 262 and the second optical reflective surface 266 are located on opposite sides of each other in the a-axis direction via the core portion 24 and are optically connected to each other.

[0021] The light-emitting element 41 is positioned on the upper surface 291 side of the optical waveguide 2. The light-emitting element 41 has a light-emitting point P1 (first light-receiving point) that is optically connected to the core portion 24 via a first light-reflecting surface 262. In other words, the first light-reflecting surface 262 optically connects the core portion 24 and the light-emitting point P1.

[0022] The light-receiving element 42 is positioned on the upper surface 291 side of the optical waveguide 2. The light-receiving element 42 has a light-receiving point P2 (second light-emitting point) that is optically connected to the core portion 24 via a second light-reflecting surface 266. In other words, the second light-reflecting surface 266 optically connects the core portion 24 and the light-receiving point P2.

[0023] Figure 1 shows a cross-section when the plane is cut by a plane that includes the axis AX within the plane and is perpendicular to the top surface 291 (first surface). In this cross-section, the intersection point of the axis AX and the first light-reflecting surface 262 is defined as the first surface center C1. This first surface center C1 corresponds to the center point of the first light-reflecting surface 262.

[0024] In the optical module 1, the shape of the first light-reflecting surface 262 exposed in the cross-section of Figure 1 is aligned with the parabola PA1. This parabola PA1 has a light-emitting point P1 as its focal point F1 and is set to intersect the axis AX at a 45° angle at the first surface center C1. In other words, when the parabola PA1 with the light-emitting point P1 as its focal point F1 passes through the first surface center C1 in Figure 1, the shape of the parabola PA1 is set such that the tangent line TL1 of the parabola PA1 at the first surface center C1 intersects the axis AX at a 45° angle. The shape of the first light-reflecting surface 262 is set to align with this parabola PA1. In the following explanation, the fact that the shape of the first light-reflecting surface 262 aligns with the parabola PA1 is also referred to as the first light-reflecting surface 262 aligning with the parabola.

[0025] Figure 2 is a magnified view of the vicinity of the light-emitting element 41 of the optical module 1 shown in Figure 1. Light L emitted from the light-emitting point P1 is reflected by the first light-reflecting surface 262 and introduced into the core section 24. In this case, the above configuration can suppress the propagation loss of light L propagating through the core section 24. Specifically, there are cases where light L emitted from the light-emitting point P1 spreads radially toward the first light-reflecting surface 262, as shown in Figure 2. In Figure 2, the line connecting the light-emitting point P1 and the center of the first surface C1 is called the perpendicular line PL. As an example, the light L shown in Figure 2 spreads toward the first light-reflecting surface 262 with a spreading angle θ relative to this perpendicular line PL.

[0026] In this case, if the first light reflection surface 262 is a flat surface, the light L reflected from the flat surface will continue to propagate while spreading at a spreading angle θ. As a result, a problem arises in which the propagation loss in the core portion 24 increases.

[0027] In contrast, in this embodiment, the shape of the first light reflecting surface 262 follows a parabola PA1. The parabola PA1 has a focal point F1 at the light emission point P1. Even when the light L emitted from the light emission point P1 (focal point F1) spreads radially, the parabola PA1 has the property of collimating the reflected light L by reflecting it off the first light reflecting surface 262, making the reflected light L closer to parallel light. This property suppresses propagation loss when the reflected light L propagates through the core portion 24. In other words, by reducing the ratio of higher-order propagation modes in the light propagating through the core portion 24, the generation of stray light can be suppressed. Therefore, an optical module 1 can be realized in which the loss of light L reflected by the first light reflecting surface 262 is sufficiently suppressed.

[0028] Furthermore, if the shape of the first light reflecting surface 262 shown in Figure 1 follows a shape other than a parabola, such as a circular arc or an elliptical arc, the reflected light L cannot be sufficiently parallelized. When the shape of the first light reflecting surface 262 shown in Figure 1 is a shape other than a parabola, the focal point is not fixed at a single point, resulting in so-called astigmatism and causing losses.

[0029] Furthermore, in the optical module 1 shown in Figure 1, the intersection point of the axis AX and the second light-reflecting surface 266 in the aforementioned cross-section is defined as the second surface center C2. This second surface center C2 corresponds to the center point of the second light-reflecting surface 266.

[0030] In the optical module 1, the shape of the second light-reflecting surface 266 exposed in the cross-section of Figure 1 is aligned with the parabola PA2. This parabola PA2 has a focal point F2 at the light-receiving point P2 and is set to intersect the axis AX at a 45° angle at the second surface center C2. In other words, when the parabola PA2 with the light-receiving point P2 as the focal point F2 passes through the second surface center C2 in Figure 1, the shape of the parabola PA2 is set such that the tangent line TL2 to the parabola PA2 at the second surface center C2 intersects the axis AX at a 45° angle. The shape of the second light-reflecting surface 266 is set to align with this parabola PA2. In the following explanation, the fact that the shape of the second light-reflecting surface 266 aligns with the parabola PA2 is also referred to as the second light-reflecting surface 266 aligning with the parabola.

[0031] Figure 3 is a magnified view of the vicinity of the photodetector 42 in the optical module 1 shown in Figure 1. Light L emitted from the light-emitting element 41 propagates through the core 24, is reflected by the second light-reflecting surface 266, and is incident on the photodetector 42. With the above configuration, the incident efficiency of light L incident on the photodetector 42 can be increased. In other words, coupling loss between the second light-reflecting surface 266 and the photodetector 42 can be suppressed. Specifically, when light L propagating through the core 24 is reflected by the second light-reflecting surface 266, the reflected light L is focused toward the focal point F2. Therefore, even when the light-receiving point P2 is small, the power loss of light L received by the photodetector 42 can be minimized.

[0032] Furthermore, due to the symmetry of light, when collimated light L is reflected by the second light-reflecting surface 266, the light L can be focused particularly well at the focal point F2. Therefore, the incident efficiency of light L to the light-receiving point P2 is increased, and an optical module 1 can be realized in which the loss of light L reflected by the second light-reflecting surface 266 is sufficiently suppressed.

[0033] The second light-reflecting surface 266 may be provided as needed, or it may be omitted. If the second light-reflecting surface 266 is omitted, the end face of the core portion 24 may be used as the light inlet and outlet surface.

[0034] 1.1.Optical waveguide The optical waveguide 2 shown in Figure 1 is constructed by stacking the lower cover layer 27, lower cladding layer 21, core layer 23, upper cladding layer 22, and upper cover layer 28 in the order shown from bottom to top.

[0035] Figure 4 is a cross-sectional view obtained when the optical module 1 shown in Figure 1 is cut by a plane passing through the first face center C1 and perpendicular to the a-axis.

[0036] The core layer 23 shown in Figure 4 includes a core portion 24 extending along axis AX (an axis parallel to the a-axis) and a side cladding portion 25 adjacent to its side surface (a side surface perpendicular to the b-axis). The core layer 23 is sandwiched between the lower cladding layer 21 and the upper cladding layer 22. Therefore, the core portion 24 is surrounded by cladding portions (side cladding portion 25, lower cladding layer 21, and upper cladding layer 22) with a lower refractive index.

[0037] The core layer 23 may include multiple core sections 24. Furthermore, the core sections 24 may intersect with other core sections 24, or they may branch into multiple parts along their course.

[0038] In the core layer 23, the refractive index distribution in the plane perpendicular to the axis AX may be any distribution, for example, a so-called step index (SI) type distribution in which the refractive index changes discontinuously, or a so-called graded index (GI) type distribution in which the refractive index changes continuously.

[0039] The shape of the core portion 24 in the plane perpendicular to the axis AX is not particularly limited and may be a circle such as a perfect circle, ellipse, or oblong, a polygon such as a triangle, square, pentagon, or hexagon, or other irregular shape.

[0040] The thickness of the core layer 23 is not particularly limited, but is preferably about 1 to 200 μm, more preferably about 5 to 100 μm, and even more preferably about 10 to 70 μm. This makes it possible to make the optical waveguide 2 thinner while maintaining the transmission efficiency of the optical waveguide 2.

[0041] The width of the core portion 24 is not particularly limited, but is preferably about 1 to 100 μm, more preferably about 5 to 80 μm, and even more preferably about 10 to 70 μm. This makes it possible to increase the density of the core portion 24 while maintaining the transmission efficiency of the optical waveguide 2.

[0042] Examples of materials that make up the core layer 23 include acrylic resins, methacrylic resins, polycarbonate, polystyrene, epoxy resins, cyclic ether resins such as oxetane resins, polyamides, polyimides, polybenzoxazoles, polysilanes, polysilazanes, silicone resins, fluororesins, polyurethanes, polyolefin resins, polybutadienes, polyisoprene, polychloroprene, polyesters such as PET and PBT, polyethylene succinates, polysulfones, polyethers, and cyclic olefin resins such as benzocyclobutene and norbornene resins, as well as glass materials and silicon materials. Composite materials combining different compositions are also used for the resin materials. Furthermore, flexibility can be imparted to the optical waveguide 2 by using resin materials.

[0043] The thickness of the lower cladding layer 21 and the upper cladding layer 22 is preferably about 1 to 200 μm, more preferably about 3 to 100 μm, and even more preferably about 5 to 60 μm. This prevents the optical waveguide 2 from becoming excessively thick while ensuring the functionality of the lower cladding layer 21 and the upper cladding layer 22.

[0044] The constituent materials for the lower cladding layer 21 and the upper cladding layer 22 are appropriately selected from, for example, the materials listed above as constituent materials for the core layer 23. Among these, using a resin material can impart flexibility to the optical waveguide 2.

[0045] The lower cladding layer 21 and the upper cladding layer 22 may be provided as needed, or they may be omitted.

[0046] The lower cover layer 27 is the lowest layer of the optical waveguide 2 and protects the lower cladding layer 21. The upper cover layer 28 is the highest layer of the optical waveguide 2 and protects the upper cladding layer 22. The lower cover layer 27 and the upper cover layer 28 may be provided as needed, and at least one of them may be omitted.

[0047] The optical waveguide 2 shown in Figure 1 has recesses 261 and 265 that open to the lower surface 292. The recesses 261 and 265 shown in Figure 1 are approximately triangular in the cross-sectional view shown in Figure 1, but they may have other shapes. The recesses 261 and 265 shown in Figure 1 each reach the upper cover layer 28, but it is sufficient that they penetrate at least the core layer 23.

[0048] The inner surface of recess 261 includes a first light-reflecting surface 262, and recess 265 includes a second light-reflecting surface 266. In other words, the optical waveguide 2 has a first light-reflecting surface 262 located on the inner surface of recess 261, and a second light-reflecting surface 266 located on the inner surface of recess 265.

[0049] The first light-reflecting surface 262 and the second light-reflecting surface 266 are, respectively, the portions of the curved surfaces formed to span the lower cover layer 27, the lower cladding layer 21, the core layer 23, the upper cladding layer 22, and the upper cover layer 28, that intersect with the core portion 24.

[0050] In Figure 1, the entire curved surface formed on the inner surface of the recess 261, excluding the first light-reflecting surface 262, that is, the surface that spans the lower cover layer 27, the lower cladding layer 21, the core layer 23, the upper cladding layer 22, and the upper cover layer 28, follows the parabolic plane. By making not only the part that intersects with the core portion 24 but also the parts located above and below it follow the parabolic plane in this way, the ease of formation and the stability of the surface shape of each curved surface, including the first light-reflecting surface 262, can be improved.

[0051] Similarly, in Figure 1, the entire curved surface formed on the inner surface of the recess 265, excluding the second light-reflecting surface 266, that is, the surface that spans the lower cover layer 27, the lower cladding layer 21, the core layer 23, the upper cladding layer 22, and the upper cover layer 28, follows a parabolic plane. By making not only the portion intersecting the core portion 24 but also the portions located above and below it follow a parabolic plane, the ease of formation and the stability of the surface shape of each curved surface, including the second light-reflecting surface 266, can be improved.

[0052] The first and second light-reflecting surfaces 262 and 266 shown in Figure 1 are each formed at the interface between the constituent material of the core portion 24 and the external space SP. As a result, total internal reflection occurs at the first and second light-reflecting surfaces 262 and 266 based on the refractive index difference at the interface. Consequently, the first and second light-reflecting surfaces 262 and 266 can each function as mirrors. Mirrors with this configuration have a simple structure, making them easy to form and offering excellent stability of surface shape.

[0053] Furthermore, a reflective film may be formed on the inner surfaces of the recesses 261 and 265 as needed. In other words, the first light-reflecting surface 262 and the second light-reflecting surface 266 may each be mirrors that utilize reflection by a reflective film. Examples of reflective films include metal films.

[0054] In this embodiment, the first light-reflecting surface 262 and the second light-reflecting surface 266 are aligned with parabolas. The first light-reflecting surface 262 shown in Figure 1 is a swept surface formed by translating the parabola PA1 in the b-axis direction. The second light-reflecting surface 266 shown in Figure 1 is a swept surface formed by translating the parabola PA2 in the b-axis direction.

[0055] The first light-reflecting surface 262 and the second light-reflecting surface 266 may each be slightly deviated from the parabolic surface described above. The acceptable amount of deviation can be quantified by the following method. If this amount of deviation is within a predetermined range, the first light-reflecting surface 262 and the second light-reflecting surface 266 can be considered to be aligned with the parabolic surface.

[0056] Figure 5 is a schematic diagram illustrating a method for quantifying the difference between the first light-reflecting surface 262 and the parabolic surface.

[0057] Figure 5 schematically shows an optical waveguide 2 having a first light-reflecting surface 262 in the same cross-section as in Figure 1. In Figure 5, the x, y, and z axes are set to be mutually orthogonal. The x axis passes through the first surface center C1 and is parallel to the a axis. The y axis passes through the first surface center C1 and is parallel to the b axis. The z axis passes through the first surface center C1 and the light-emitting point P1 and is parallel to the c axis. In Figure 5, the distance between the axis AX and the light-emitting point P1 is denoted as d. In the optical module 1, the distance d is preferably 50 to 2000 μm, and more preferably 100 to 1000 μm.

[0058] Ideally, the first light-reflecting surface 262 should coincide with the aforementioned parabolic surface; therefore, a first light-reflecting surface 262 that coincides with the parabolic surface is called an "ideal first light-reflecting surface 262".

[0059] The first light-reflecting surface 262 shown in Figure 1 is a swept surface formed by translating the parabola PA2 in the b-axis direction. Therefore, the z-coordinate of the ideal first light-reflecting surface 262 is expressed in terms of the distance d and the x-coordinate. In this case, the z-coordinate is z p When this is the case, the z coordinate z p This can be calculated using the following formula (1).

[0060]

number

[0061] Then, using equation (1) above, the z coordinate z in the xy plane p The distribution can be determined. On the other hand, the actual first light-reflecting surface 262 will deviate from the ideal first light-reflecting surface 262 due to manufacturing tolerances. This deviation can be measured using a laser microscope. The first light-reflecting surface 262 measured in this way is called the "measured first light-reflecting surface 262".

[0062] In a laser microscope, the in-plane distribution of the distance from the reference plane DP shown in FIG. 5 to the first light reflection surface 262 can be obtained. The data of this in-plane distribution is converted to the positions in the xyz coordinate system shown in FIG. 5. Thereby, the distribution of the z coordinate z of the actually measured first light reflection surface 262 is obtained. m is obtained.

[0063] FIG. 6 is a diagram showing an example of the distribution of the z coordinate z of the actually measured first light reflection surface 262. In FIG. 6, the shading changes according to the value of the z coordinate z in the xy plane. In FIG. 6, it can be seen that the value of the z coordinate z slopes along the x-axis direction. m In FIG. 6, the shading changes according to the value of the z coordinate z in the xy plane. In FIG. 6, it can be seen that the value of the z coordinate z slopes along the x-axis direction. m In FIG. 6, the shading changes according to the value of the z coordinate z in the xy plane. In FIG. 6, it can be seen that the value of the z coordinate z slopes along the x-axis direction. m is inclined.

[0064] Next, the difference z between the actually measured z coordinate z of the first light reflection surface 262 and the ideal z coordinate z of the first light reflection surface 262 is calculated. m and the ideal z coordinate z of the first light reflection surface 262 p is calculated. m -z <(0000011)>[ p is calculated.

[0065] FIG. 7 is a diagram showing an example of the distribution of the calculated difference z m -z p In FIG. 7, the shading changes according to the value of the difference z in the xy plane. In FIG. 7, the distribution of the difference z m -z p can be visually grasped. m -z p can be visually grasped.

[0066] Next, using the distribution of the difference z shown in FIG. 7, an index t that quantitatively represents the deviation amount between the actually measured first light reflection surface 262 and the ideal first light reflection surface 262 is calculated. The index t is obtained by the following formula (2). m -z p The index t represented by the above formula (2) is, in FIG. 7, the difference z at each point (each pixel).

[0067]

Equation

[0068] The index t represented by the above formula (2) is, in FIG. 7, the difference z at each point (each pixel). m -z pThis is the value obtained by averaging the squares of all values ​​and taking the square root. If the index t obtained in this way satisfies the relationship expressed by equation (3) below, then the first light reflection surface 262 can be considered to be along a parabolic surface.

[0069]

number

[0070] The index t is preferably 0.8 μm or less, and more preferably 0.5 μm or less. This makes it possible to further reduce various losses associated with reflection at the first light reflection surface 262.

[0071] Furthermore, the amount of displacement between the second light-reflecting surface 266 and the parabolic surface can be evaluated in the same manner as the first light-reflecting surface 262.

[0072] 1.2. Circuit board The circuit board 3 shown in Figure 1 comprises an insulating substrate 31, a conductive layer 32 provided on the lower surface of the insulating substrate 31, and a conductive layer 33 provided on the upper surface.

[0073] The insulating substrate 31 has insulating properties and insulates the conductive layer 32 and the conductive layer 33 from each other. Furthermore, the circuit board 3 shown in Figure 1 has through holes 341 and 342 that penetrate the insulating substrate 31 and the conductive layers 32 and 33 in the thickness direction. Through hole 341 is provided corresponding to the optical path connecting the light-emitting element 41 and the first light-reflecting surface 262. Through hole 342 is provided corresponding to the optical path connecting the light-receiving element 42 and the second light-reflecting surface 266.

[0074] The through holes 341 and 342 may be provided as needed, and may be omitted if, for example, the light transmittance in the thickness direction of the circuit board 3 is sufficiently high. Furthermore, the through holes 341 and 342 may be voids, but at least one of the through holes 341 and 342 may be filled with a resin that has high light transmittance.

[0075] The conductive layers 32 and 33 are patterned in the xy plane and function as wiring. This allows a circuit to be constructed on the circuit board 3. Alternatively, a board without a circuit may be used instead of the circuit board 3.

[0076] The circuit board 3 may be a flexible board that is pliable, or a rigid board that is rigid.

[0077] 1.3. Optical elements The upper surface of the circuit board 3 is a mounting surface on which the light-emitting element 41 and the light-receiving element 42 are mounted.

[0078] Examples of light-emitting elements 41 include a VCSEL (vertically opposed surface-emitting laser) and a light-emitting diode (LED).

[0079] Examples of the light-receiving element 42 include photodiodes (PD, APD) and phototransistors.

[0080] In addition to the above, the optical module 1 may also include any other electronic or optical components. Furthermore, optical elements such as optical fibers, other optical waveguides, or lenses may be provided between the light-emitting element 41 and the optical waveguide 2, as needed.

[0081] Furthermore, in this embodiment, the first light-reflecting surface 262 and the second light-reflecting surface 266 are shaped along a paraboloid, but it is also possible that only one of them is shaped along a paraboloid, and the other is shaped along a surface other than a paraboloid. Examples of surfaces other than paraboloids include flat surfaces, spheres, ellipsoids, hyperbolas, aspheric surfaces, etc.

[0082] Furthermore, since the light L emitted from the light-emitting point P1 tends to spread radially, it is preferable that the first light-reflecting surface 262 shown in Figure 1 has a shape that follows a parabolic surface. By providing the first light-reflecting surface 262 that follows a parabolic surface directly below the light-emitting element 41, the light L with a spreading angle θ can be collimated by the first light-reflecting surface 262. This makes it possible to realize an optical module 1 with further reduced losses.

[0083] On the other hand, if the first light-reflecting surface 262 shown in Figure 1 is shaped along a parabolic surface, the second light-reflecting surface 266 may be shaped along a surface other than a parabolic surface, but it is preferable that the second light-reflecting surface 266 is also shaped along a parabolic surface. In this case, the light L that radiates from the light-emitting point P1 can be collimated by the first light-reflecting surface 262 and then focused again to a single point by the second light-reflecting surface 266. This makes it possible to realize an optical module 1 with further reduced losses.

[0084] 2. Method for manufacturing optical modules Next, we will explain how to manufacture the optical module 1.

[0085] The optical module 1 shown in Figure 1 is manufactured, for example, by stacking an optical waveguide 2 and a circuit board 3, and then mounting a light-emitting element 41 and a light-receiving element 42.

[0086] The optical waveguide 2 is manufactured by stacking a lower cover layer 27, a lower cladding layer 21, a core layer 23, an upper cladding layer 22, and an upper cover layer 28, and then forming recesses 261 and 265. For example, laser processing, electron beam processing, and machining methods are used to form the recesses 261 and 265. In the following description, the method for forming the recess 261 will be explained. The method for forming the recess 265 is the same as the method for forming the recess 261.

[0087] Figure 8 is a conceptual diagram illustrating a method for forming a recess 261 by laser processing. In the laser processing method, as shown in Figure 8, the movable mask 96 is moved in a direction intersecting the optical path of the laser beam LB, thereby changing the projection pattern of the laser beam LB reaching the workpiece 10 and tilting the processing amount. This forms a recess 261 including the first light reflection surface 262. Figure 8 shows the processing marks M1, M2, and M3 that are sequentially formed on the workpiece 10 when laser processing is performed while moving the movable mask 96 in the movement direction SC. The workpiece 10 is a laminate consisting of a lower cover layer 27, a lower cladding layer 21, a core layer 23, an upper cladding layer 22, and an upper cover layer 28 before the formation of the recess 261.

[0088] Figure 9 is a schematic diagram showing the positional relationship between the irradiation range of the laser beam LB irradiated onto the movable mask 96 shown in Figure 8 and the transparent portion 962 of the movable mask 96.

[0089] As shown in Figure 8(a), the irradiation range of the laser beam LB emitted from a laser oscillator (not shown) is set so that a portion of the beam cross-section passes through the transparent portion 962 of the movable mask 96. As a result, a portion of the beam cross-section of the laser beam LB is cut off by the movable mask 96. The laser beam LB that has passed through the transparent portion 962 is then projected onto the surface 102 of the workpiece 10, forming the processing mark M1 shown by the thick line in Figure 8(a).

[0090] In Figure 8(b), the movable mask 96 is moved by a movement amount S1 toward the negative a-axis. This changes the position from which the laser beam LB is cut off, and consequently, the projection position of the laser beam LB onto the surface 102 of the workpiece 10 also shifts. As a result, as shown in Figure 8(b), a processing mark M2, indicated by a thick line, is formed at a position shifted toward the negative a-axis than the processing mark M1.

[0091] In Figure 8(c), the movable mask 96 is moved by a movement amount S2 toward the negative a-axis. As a result, as shown in Figure 8(c), a machining mark M3, indicated by a thick line, is formed at a position shifted toward the negative a-axis than the machining mark M2.

[0092] Based on the movement of the movable mask 96 as described above, and the resulting movement of the machining marks M1, M2, and M3, the amount of machining can be tilted in the direction of movement SC. This makes it possible to form a recess 261 having an inclined first light-reflecting surface 262 on its inner surface, as shown in Figure 2. The movable mask 96 may be moved in steps, but it is preferably moved continuously. This allows the machining marks to connect continuously, forming a smooth first light-reflecting surface 262.

[0093] Furthermore, when the sum of the displacement amounts S1 and S2 is S1+S2, and the sum of the depths of the processed marks M1 and M2 is M1+M2, the inclination angle of each part of the first light-reflecting surface 262 can be adjusted based on these ratios. For example, by bringing the ratio (S1+S2) / (M1+M2) closer to 1, the inclination angle (the angle between the first light-reflecting surface 262 and the axis AX in Figure 1) can be brought closer to 45°. Also, if the ratio (S1+S2) / (M1+M2) is less than 1, the inclination angle will be greater than 45°, and if the ratio (S1+S2) / (M1+M2) is greater than 1, the inclination angle will be less than 45°.

[0094] Based on the above, for example, by continuously changing the displacement amounts S1 and S2 and the depths of the processing marks M1 and M2, the shape of the first light-reflecting surface 262 can be brought closer to the desired shape. This makes it possible to make the first light-reflecting surface 262 conform to a parabolic surface.

[0095] Furthermore, when pulsed laser light is used as the laser light LB, the depths of the processed marks M1, M2, and M3 can be easily adjusted by changing the pulse repetition frequency. In other words, when forming the first light-reflecting surface 262, it is preferable to change the pulse repetition frequency while keeping the movement amounts S1 and S2 constant. Since the movement of the movable mask 96 involves mechanical changes, adjusting the movement speed is difficult. In contrast, changing the pulse repetition frequency is an electrical change, so it is easy to adjust. Therefore, by using a method of changing the pulse repetition frequency, it is particularly easy to form a first light-reflecting surface 262 with high shape accuracy that satisfies the relationship expressed in equation (3) above.

[0096] Examples of light sources for the laser beam LB include excimer lasers, gaseous lasers such as CO2 lasers, solid-state lasers such as YAG lasers, and semiconductor lasers such as GaAs lasers. Of these, excimer lasers are preferred. Because excimer lasers are inherently pulsed, they can efficiently emit high-power pulsed laser light. By using pulsed laser light, ablation processing can be performed on the workpiece while reducing thermal effects. As a result, the amount of processing residue adhering to the edges of the processing marks can be reduced, and a first light-reflecting surface 262 with high processing accuracy can be formed.

[0097] Alternatively, a focusing lens may be used to focus the pulsed laser light emitted from the light source. This allows the shape of the transparent portion 962 of the movable mask 96 to be projected onto the workpiece 10 while being reduced by a predetermined magnification. As a result, the effects of intensity distribution and positional displacement in the pulsed laser light before reduction can also be reduced, thereby stabilizing the shape of the first light reflecting surface 262.

[0098] On the other hand, the first light-reflecting surface 262 shown in Figure 1 is a swept surface formed by translating the parabola PA1 in the b-axis direction, as described above. The shape of the first light-reflecting surface 262 in the b-axis direction can be controlled by the shape of the transmissive portion 962 of the movable mask 96 shown in Figure 9. When forming the first light-reflecting surface 262 shown in Figure 1, the shape of the transmissive portion 962 can be, for example, a rectangle as shown in Figure 9. However, the shape of the transmissive portion 962 is not limited to this.

[0099] 3. Second Embodiment Next, we will describe the overview of the optical module according to the second embodiment.

[0100] Figures 10 and 11 are cross-sectional views showing the configuration of the optical module 1 according to the second embodiment. Figure 10 is a cross-sectional view taken when the optical module 1 is cut through a plane passing through the first face center C1 and perpendicular to the a-axis. Figure 11 is a cross-sectional view taken when the optical module 1 is cut through a plane passing through the second face center C2 and perpendicular to the a-axis.

[0101] The second embodiment will be described below, focusing on the differences from the first embodiment, and similar matters will be omitted from the description. In Figures 10 and 11, components similar to those in Figure 4 are denoted by the same reference numerals.

[0102] The first light-reflecting surface 262 shown in Figure 10 (a mirror provided on the light-emitting element 41 side) is similar to the first light-reflecting surface 262 shown in Figure 1 in that it follows a parabolic surface. On the other hand, the parabolic surface in the first embodiment is a swept surface formed by translating the parabola PA1 shown in Figure 1 in the b-axis direction, whereas the parabolic surface in the second embodiment is a swept surface formed by rotating the parabola PA1 shown in Figure 1 around the light-emitting point P1. Such a parabolic surface is also called a paraboloid of revolution. Therefore, the first light-reflecting surface 262 shown in Figure 10 follows a paraboloid of revolution that includes the parabola PA1 shown in Figure 1.

[0103] When a paraboloid of revolution is cut by a plane perpendicular to the axis AX, a circular arc is exposed in the cross-section. Therefore, in the optical module 1 shown in Figure 10, the cross-sectional shape of the first optical reflecting surface 262 follows the shape of the circular arc AR1. The center of this circular arc AR1 is set to the light emission point P1. With this configuration, the first optical reflecting surface 262 can be given the function of collimating light L with a divergence angle θ in the a-axis direction, as well as the function of making it nearly parallel in the b-axis direction. This makes it possible to realize an optical module 1 with further reduced losses.

[0104] When the cross-sectional shape of the first light-reflecting surface 262 follows the arc AR1 shown in Figure 10, the radius of curvature of the arc AR1 may vary depending on its position within the first light-reflecting surface 262, as shown in Figure 10, or it may be constant regardless of its position within the first light-reflecting surface 262. In the former case, the difficulty of forming the first light-reflecting surface 262 increases, but the focusing of light is easier to improve. In the latter case, the difficulty of forming the first light-reflecting surface 262 can be reduced while ensuring the focusing of light.

[0105] The second light-reflecting surface 266 (a mirror provided on the side of the light-receiving element 42) shown in Figure 11 is similar to the second light-reflecting surface 266 shown in Figure 1 in that it follows a parabolic surface. On the other hand, the parabolic surface in the first embodiment is a swept surface formed by translating the parabola PA2 shown in Figure 1 in the b-axis direction, whereas the parabolic surface in the second embodiment is a swept surface formed by rotating the parabola PA2 shown in Figure 1 around the light-receiving point P2. Therefore, the second light-reflecting surface 266 shown in Figure 11 follows a parabolic surface of rotation that includes the parabola PA2 shown in Figure 1.

[0106] In the optical module 1 shown in Figure 11, the cross-sectional shape of the second light-reflecting surface 266 follows the shape of the circular arc AR2. The center of this circular arc AR2 is set to the light-receiving point P2. With this configuration, the second light-reflecting surface 266 can be given the function of focusing the light L emitted from the core 24 not only in the a-axis direction but also in the b-axis direction. This makes it possible to realize an optical module 1 with further reduced losses.

[0107] The first light-reflecting surface 262 described above can also be formed using the laser processing method described earlier, but the cross-sectional shape of the first light-reflecting surface 262 shown in Figure 10 (shape along the arc AR1) can be formed based on the shape of the transparent portion 962 of the movable mask 96.

[0108] Figure 12 is a schematic diagram showing the irradiation range of the laser beam LB irradiated onto the movable mask 96 and the transparent portion 962 of the movable mask 96 when the first light-reflecting surface 262 shown in Figure 10 is formed by a laser processing method.

[0109] The shape of the transparent portion 962 shown in Figure 12 is a quadrilateral with a portion of its edge curved. The shape of this curved edge can be made into a parabola corresponding to the paraboloid of revolution to be formed. This allows the first light-reflecting surface 262 along the paraboloid of revolution to be formed by laser processing or the like.

[0110] In the second embodiment, when quantifying the difference between the first light-reflecting surface 262 and the paraboloid of revolution, the z-coordinate of the ideal first light-reflecting surface 262 is z p This is expressed as distance d, x-coordinate, and y-coordinate. Therefore, the z-coordinate of the ideal first light reflecting surface 262 is z p This can be calculated using the following formula (4).

[0111]

number

[0112] In the second embodiment described above, the same effects as in the first embodiment can be obtained. In addition, either the first light-reflecting surface 262 or the second light-reflecting surface 266 may be aligned with a paraboloid of revolution, while the other may be aligned with a paraboloid similar to that of the first embodiment, or with a non-paraboloid.

[0113] 4. Effects achieved by the above embodiment As described above, the optical module 1 according to the embodiment comprises an optical waveguide 2 and a light-emitting element 41 (first optical element). The optical waveguide 2 has a core portion 24, a first light-reflecting surface 262, and an upper surface 291 (first surface) and a lower surface 292 (second surface). The core portion 24 extends along the axis AX. The first light-reflecting surface 262 intersects with the core portion 24. The upper surface 291 and the lower surface 292 are in a front-back relationship with each other. The light-emitting element 41 is arranged on the upper surface 291 side of the optical waveguide 2 and has a light-emitting point P1 (first light-receiving point) that is optically connected to the core portion 24 via the first light-reflecting surface 262.

[0114] Furthermore, in the optical module 1 according to the above embodiment, when the module is cut by a plane that includes the axis AX and is perpendicular to the upper surface 291, the intersection point of the axis AX and the first light-reflecting surface 262 in the cut surface is defined as the first surface center C1. At this time, the shape of the first light-reflecting surface 262 exposed in the cut surface is such that the light-emitting point P1 is the focal point F1 and the shape follows a parabola PA1 that intersects the axis AX at a 45° angle at the first surface center C1.

[0115] With this configuration, even when the light L emitted from the light-emitting point P1 spreads radially, the light L reflected by the first light-reflecting surface 262 can be made closer to parallel light. This reduces the ratio of higher-order propagation modes in the light propagating through the core 24, thereby suppressing the generation of stray light. As a result, an optical module 1 can be realized in which the loss of light L reflected by the first light-reflecting surface 262 is sufficiently suppressed.

[0116] In the optical module 1 according to the above embodiment, the shape of the first light reflecting surface 262 may be a shape that follows a paraboloid of revolution that includes the parabola PA1.

[0117] With this configuration, the first optical reflective surface 262 can be given not only the function of collimating in the a-axis direction, but also the function of nearly parallelizing in the b-axis direction. This makes it possible to realize an optical module 1 with further reduced losses.

[0118] In the optical module 1 according to the above embodiment, the first light reflecting surface 262 may be formed at the interface between the constituent material of the core portion 24 and the external space SP.

[0119] This configuration simplifies the mirror's structure, resulting in superior ease of mirror formation and stability of the surface shape.

[0120] In the optical module 1 according to the above embodiment, the first light-receiving point may be a light-emitting point P1 that emits light L toward the first light-reflecting surface 262.

[0121] With this configuration, even if the light L emitted from the light source P1 spreads radially, the reflected light L can be made closer to parallel light by reflecting it off the first light reflecting surface 262.

[0122] In the optical module 1 according to the above embodiment, the optical waveguide 2 may further have a second optical reflecting surface 266. The second optical reflecting surface 266 is located on the opposite side from the first optical reflecting surface 262 via the core portion 24 and is optically connected to the first optical reflecting surface 262. The optical module 1 also further includes a light-receiving element 42 (second optical element). The light-receiving element 42 is arranged on the upper surface 291 (first surface) side of the optical waveguide 2 and has a light-receiving point P2 (second light-emitting point) that is optically connected to the core portion 24 via the second optical reflecting surface 266. When the optical waveguide 2 is cut by a plane that includes the axis AX and is perpendicular to the upper surface 291, the intersection point of the axis AX and the second optical reflecting surface 266 in the cut surface is defined as the second surface center C2. In this case, the shape of the second light-reflecting surface 266 exposed on the cut surface may be a shape that follows a parabola PA2 that intersects the axis AX at a 45° angle at the second surface center C2, with the light-receiving point P2 as the focal point F2.

[0123] With this configuration, when light L propagating through the core 24 is reflected by the second light reflecting surface 266, the reflected light L is focused toward the focal point F2. Therefore, even when the light receiving point P2 is small, the power loss of the light L received by the light receiving element 42 can be minimized.

[0124] In the optical module 1 according to the above embodiment, the shape of the second light reflecting surface 266 may be a shape that follows a paraboloid of revolution including the parabola PA2.

[0125] With this configuration, the second optical reflective surface 266 can be provided with a focusing function not only in the a-axis direction but also in the b-axis direction. This makes it possible to realize an optical module 1 with further reduced losses.

[0126] In the optical module 1 according to the above embodiment, the second light reflecting surface 266 may be formed at the interface between the constituent material of the core portion 24 and the external space SP.

[0127] This configuration simplifies the mirror's structure, resulting in superior ease of mirror formation and stability of the surface shape.

[0128] Although the optical module according to the present invention has been described above based on the illustrated embodiments, the present invention is not limited thereto.

[0129] For example, in the optical module according to the present invention, each component of the above embodiment may be replaced with any component capable of performing similar functions, or any component may be added to the above embodiment. [Explanation of Symbols]

[0130] 1 Optical module 2 Optical waveguide 3 Circuit board 10 Workpiece 21 Lower cladding layer 22 Upper cladding layer 23 Core Layers 24 Core section 25 Side cladding section 27 Lower cover layer 28 Upper cover layer 31 Insulating substrate 32 Conductive layer 33 Conductive layer 41 Light-emitting element 42 Photodetector 96 Movable Mask 102 Surface 261 recess 262 1st light reflecting surface 265 recesses 266 Second light reflecting surface 291 Top surface 292 Bottom surface 341 Through hole 342 Through hole 962 Transparent part AR1 Arc AR2 arc AX axis C1 1st side heart C2 Second face center DP reference plane F1 focus F2 focus L light LB laser light M1 machining marks M2 machining marks M3 machining marks P1 Light source P2 light receiving point PA1 Parabola PA2 Parabola PL perpendicular S1 Travel amount S2 Travel amount SC moving direction SP external space TL1 tangent TL2 tangent d distance θ: Angle of spread

Claims

1. An optical waveguide having a core portion extending along an axis, a first light-reflecting surface intersecting the core portion, and a first surface and a second surface that are in a front-back relationship with each other, A first optical element having a first light-receiving point, which is arranged on the first surface side of the optical waveguide and is optically connected to the core portion via the first light-reflecting surface, Equipped with, When the cross-section is made by a plane that includes the axis and is perpendicular to the first plane, and the intersection point of the axis and the first light-reflecting surface is defined as the center of the first plane, The optical module is characterized in that the shape of the first light-reflecting surface exposed on the cut surface is a shape that follows a parabola that has the first light-receiving point as its focal point and intersects the axis at a 45° angle at the center of the first surface.

2. The optical module according to claim 1, wherein the shape of the first light-reflecting surface is a shape that follows the paraboloid of revolution which includes the parabola.

3. The optical module according to claim 1 or 2, wherein the first light-reflecting surface is formed at the interface between the constituent material of the core portion and the external space.

4. The optical module according to claim 1 or 2, wherein the first light-receiving point is a light-emitting point that emits light toward the first light-reflecting surface.

5. The optical waveguide further has a second optical reflecting surface located on the opposite side of the first optical reflecting surface via the core portion and optically connected to the first optical reflecting surface. The optical waveguide further comprises a second optical element having a second light-receiving point, which is disposed on the first surface side of the optical waveguide and is optically connected to the core portion via the second light-reflecting surface. In the aforementioned cross-section, when the intersection point of the axis and the second light-reflecting surface is defined as the second surface center, The optical module according to claim 1 or 2, wherein the shape of the second light-reflecting surface exposed on the cut surface is a shape that follows a parabola that has the second light-receiving point as its focal point and intersects the axis at a 45° angle at the center of the second surface.

6. The optical module according to claim 5, wherein the shape of the second light-reflecting surface is a shape that follows the paraboloid of revolution which includes the parabola.

7. The optical module according to claim 5, wherein the second light-reflecting surface is formed at the interface between the constituent material of the core portion and the external space.

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