Optical Module

Abstract

An optical module capable of improving connection reliability is provided. [Solution] The optical module (10) includes an optical component (40) having a single core (51) and an optical waveguide (30) having multiple cores (32) optically coupled to the single core (51) by adiabatic coupling. The optical module (10) includes cladding layers (33, 52) that separate the single core (51) from the multiple cores (32) in the Z-axis direction. The optical component (40) is a separate component from the optical waveguide (30). The single core (51) and the multiple cores (32) are arranged so as to be optically coupled from the single core (51) to the multiple cores (32). The multiple cores (32) are arranged side by side along the X-axis direction. The single core (51) and the multiple cores (32) have overlapping regions in the Y-axis direction where they overlap. A first separation distance (L1) between two adjacent cores (32) along the X-axis direction is equal to or greater than a second separation distance (L2) between the single core (51) and the multiple cores (32) along the Z-axis direction.

Description

[Technical Field]

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

[0002] Conventionally, optical modules used in optical communications have been known that include a wiring board, a first optical component such as an optical waveguide stacked on the wiring board, and a second optical component optically connected to the first optical component (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-018409 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned optical module, it is desired to improve the reliability of the connection between the first optical component and the second optical component. [Means for solving the problem]

[0005] According to one aspect of the present invention, there is provided a first optical component having a single first core, a second optical component having a plurality of second cores optically coupled to the single first core by adiabatic coupling, and a separating member separating the single first core and the plurality of second cores in a first direction, wherein the first optical component is a separate component from the second optical component, the single first core and the plurality of second cores are arranged so as to be optically coupled from the single first core to the plurality of second cores, the plurality of second cores are arranged side by side along a second direction perpendicular to the first direction, the single first core and the plurality of second cores have an overlap region in which they overlap each other in a third direction perpendicular to both the first direction and the second direction, and a first separation distance along the second direction between two adjacent second cores is equal to or greater than a second separation distance along the first direction between the single first core and the plurality of second cores. [Effects of the Invention]

[0006] According to one aspect of the present invention, an effect is achieved in that connection reliability can be improved. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an optical module according to an embodiment. [Figure 2] FIG. 2 is a schematic perspective view showing an optical module according to an embodiment. [Figure 3] FIG. 3 is a schematic plan view showing an optical module according to an embodiment. [Figure 4] FIG. 4 is a schematic cross-sectional view showing an optical module according to an embodiment. [Figure 5] FIG. 5(a) is a schematic plan view showing an optical module according to an embodiment, and FIGS. 5(b) to 5(g) are diagrams showing the light intensity distribution at various points in the optical module. [Figure 6] FIG. 6(a) is a schematic plan view showing an optical module according to an embodiment, and FIGS. 6(b) to 6(g) are diagrams showing the light intensity distribution at various points in the optical module. [Figure 7]FIG. 7 is a graph showing the relationship between misalignment and coupling loss. [Figure 8] FIG. 8 is a schematic cross-sectional view showing an optical module according to a modified example. [Figure 9] FIG. 9 is a schematic cross-sectional view showing an optical module according to a modified example. [Figure 10] FIG. 10 is a schematic plan view showing an application example of the optical module according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] An embodiment will be described below with reference to the accompanying drawings. For convenience, the accompanying drawings may show characteristic portions enlarged to make the features more clearly visible, and the dimensional ratios of each component may differ from one drawing to another. In cross-sectional views, some components are shown with matte finish instead of hatching, and some components are omitted to make the cross-sectional structure of each component more clearly visible. Each drawing also illustrates mutually orthogonal X, Y, and Z axes. In the following description, for convenience, the direction extending along the X axis will be referred to as the X-axis direction, the direction extending along the Y axis will be referred to as the Y-axis direction, and the direction extending along the Z axis will be referred to as the Z-axis direction. In this specification, "planar view" refers to viewing an object from the Z-axis direction unless otherwise specified. In this specification, "planar shape" refers to the shape of an object viewed from the Z-axis direction unless otherwise specified. In this specification, the terms "up-down direction" and "left-right direction" refer to the direction in which the symbols indicating each component in each drawing can be correctly read, assuming the normal position. In addition, "facing" in this specification refers to surfaces or components facing each other, and includes not only cases where they are completely facing each other, but also cases where they are partially facing each other. In this specification, "facing" includes not only cases where two components are separated from each other, but also cases where two components are in contact with each other.

[0009] (Overall configuration of optical module 10) As shown in FIGS. 1 and 2, the optical module 10 includes a wiring substrate 20, an optical waveguide 30 formed on the wiring substrate 20, and an optical component 40 mounted on the wiring substrate 20.

[0010] (Configuration of wiring board 20) 1, the wiring board 20 includes a substrate body 21, a wiring layer 22, and a solder resist layer 23. The substrate body 21 is formed, for example, in a flat plate shape. The substrate body 21 is formed, for example, in a rectangular shape in a plan view.

[0011] The wiring layer 22 is provided on the upper surface of the substrate body 21. The wiring layer 22 has connection pads 22P that are electrically connected to the optical component 40. The wiring layer 22 may be made of, for example, copper (Cu) or a copper alloy.

[0012] The solder resist layer 23 is formed on the upper surface of the substrate body 21 so as to cover the wiring layer 22. The solder resist layer 23 has openings 23X formed therein for exposing parts of the wiring layer 22 as connection pads 22P.

[0013] If necessary, a surface treatment layer may be formed on the wiring layer 22 exposed from the opening 23X. Examples of the surface treatment layer include a gold (Au) layer, a nickel (Ni) layer / Au layer (a metal layer formed by laminating a Ni layer and an Au layer in this order), and a Ni layer / palladium (Pd) layer / Au layer (a metal layer formed by laminating a Ni layer, a Pd layer, and an Au layer in this order). Here, the Au layer is a metal layer made of Au or an Au alloy, the Ni layer is a metal layer made of Ni or an Ni alloy, and the Pd layer is a metal layer made of Pd or a Pd alloy. The Au layer, Ni layer, and Pd layer may be, for example, a metal layer formed by electroless plating (electroless plated metal layer). Alternatively, the surface treatment layer may be an OSP (organic solderability preservative) film formed by applying an anti-oxidation treatment such as an OSP treatment to the surface of the connection pad 22P. For example, an organic coating such as an azole compound or an imidazole compound may be used as the OSP film.

[0014] An optical component 40 serving as a first optical component is mounted on the wiring board 20. An optical waveguide 30 serving as a second optical component is mounted on the wiring board 20. Components other than the optical component 40 and the optical waveguide 30, such as optical functional elements and electronic components, may also be mounted on the wiring board 20. Examples of optical functional elements include a light-emitting element, an optical modulator, an optical amplifier, and an optical attenuator.

[0015] (Configuration of optical waveguide 30) The optical waveguide 30 is formed, for example, on the upper surface of the substrate body 21 of the wiring substrate 20. The optical waveguide 30 is, for example, a polymer optical waveguide. The optical waveguide 30 has a cladding layer 31, a core 32, a cladding layer 33, and a cladding layer 34.

[0016] The cladding layer 31 is formed on the upper surface of the substrate main body 21. The cladding layer 31 is formed, for example, so as to cover the upper surface of the substrate main body 21 exposed from the solder resist layer 23. A plurality of cores 32 are formed on the upper surface of the cladding layer 31.

[0017] As shown in FIGS. 2 and 3 , three cores 32 are formed on the upper surface of the cladding layer 31 of this embodiment. Each core 32 is for propagating an optical signal. Each core 32 is formed, for example, in an elongated shape. Each core 32 is formed, for example, to extend along the Y-axis direction. Each core 32 has, for example, a predetermined width along the X-axis direction. That is, in this embodiment, the length direction (extension direction) of each core 32 coincides with the Y-axis direction, and the width direction of each core 32 coincides with the X-axis direction. Each core 32 is formed, for example, in the shape of a quadrangular prism. As shown in FIG. 3 , the three cores 32 are arranged side by side along the X-axis direction, which is orthogonal to the length direction of the cores 32. The three cores 32 are spaced apart from each other along the X-axis direction by a first separation distance L1. That is, two adjacent cores 32 are spaced apart from each other by the first separation distance L1 in the X-axis direction. In other words, the first separation distance L1 is the separation distance along the X-axis direction between two adjacent cores 32 among the three cores 32. The three cores 32 are formed, for example, to extend parallel to one another.

[0018] For ease of explanation, the core 32 disposed at the top of the three cores 32 in FIG. 3 may be referred to as "core 32A," and the core 32 disposed in the middle (center) of the three cores 32 may be referred to as "core 32B." Furthermore, the core 32 disposed at the bottom of the three cores 32 in FIG. 3 may be referred to as "core 32C." Furthermore, in the following explanation, the cores 32A to 32C will be collectively referred to as "core 32."

[0019] Each core 32 has an end 32D in the length direction of the core 32 and a tapered portion 32E that becomes thinner toward the end 32D. The end 32D is the end of each core 32 on the left side in the figure. The tapered portion 32E is formed so that the cross-sectional area becomes smaller toward the end 32D. Specifically, the tapered portion 32E is formed so that the width becomes smaller toward the end 32D. Note that FIG. 3 is a plan view of the optical module 10 shown in FIG. 1 as seen from above, and the cladding layer 34 and the like are drawn perspectively. Also, in FIG. 2, the solder resist layer 23 is not shown to simplify the drawing.

[0020] 4, the cladding layer 33 is formed on the upper surface of the cladding layer 31 so as to cover the cores 32. The cladding layer 33 is formed so as to fill the space between adjacent cores 32. The cladding layer 33 is formed so as to cover the entire side surface of each core 32. The cladding layer 33 is formed so as to cover the entire upper surface of each core 32.

[0021] 1, the cladding layer 34 is formed on the upper surface of the cladding layer 33. The cladding layer 34 is formed so as to cover a portion of the upper surface of the cladding layer 33. The cladding layer 34 is formed so as to expose the region of the upper surface of the cladding layer 33 on the left side in the figure.

[0022] As described above, the optical waveguide 30 has a structure in which the cladding layer 31, the plurality of cores 32, the cladding layer 33, and the cladding layer 34 are laminated in this order on the upper surface of the substrate body 21. Furthermore, the optical waveguide 30 has a structure in which each of the plurality of cores 32 is surrounded by the cladding layer 31 and the cladding layer 33.

[0023] The cladding layers 31, 33, 34 and each core 32 can basically be made of the same material. Examples of materials that can be used for the cladding layers 31, 33, 34 and each core 32 include acrylic resins such as polymethyl methacrylate (PMMA), epoxy resins, and silicone resins. However, to ensure that optical signals propagate only within the core 32, a material having a higher refractive index than the material of the cladding layers 31, 33 formed on both the top and bottom surfaces of the core 32 is selected for the material making up each core 32. The difference in refractive index between each core 32 and the cladding layers 31, 33, 34 is not particularly limited, but is preferably about 0.3% to 5.5%, and more preferably about 0.8% to 2.2%.

[0024] In each drawing, the cladding layers 31, 33, and 34 are distinguished by solid lines to make them easier to understand. However, in the actual optical module 10, the boundaries between the cladding layers 31, 33, and 34 may disappear, and the boundaries may not be clear.

[0025] As shown in FIG. 2, the optical waveguide 30 is a multi-waveguide having multiple waveguides each formed by multiple cores 32. Each of the multiple waveguides each formed by multiple cores 32 has its own propagation mode. That is, the multiple waveguides each formed by multiple cores 32 have propagation modes independent of each other. However, the multiple waveguides each formed by multiple cores 32 have the same propagation constant in the fundamental mode. Note that, for ease of explanation, hereinafter, "a waveguide each formed by cores 32" may be simply referred to as "core 32."

[0026] The cores 32 are, for example, optically connected (optically coupled) to one another. The cores 32 are, for example, optically coupled to one another by a supermode. The thickness of the cladding layer 31 can be, for example, about 2 μm to 50 μm. The dimensions of each core 32 and the first separation distance L1 are set so that each of the three cores 32 has its own propagation mode. The thickness of the core 32 can be, for example, about 0.2 μm to 10 μm. The width of the core 32 can be, for example, about 0.2 μm to 10 μm. In the optical waveguide 30 of this embodiment, the dimensions (thickness and width) of the three cores 32A, 32B, and 32C are set to be the same so that the three cores 32 have the same propagation constant in the fundamental mode.

[0027] The first separation distance L1 between two adjacent cores 32 can be, for example, about 0.5 μm to 10 μm. The first separation distance L1 between core 32A and core 32B and the first separation distance L1 between core 32B and core 32C may be the same distance or different distances. In other words, the arrangement intervals of the multiple cores 32 may or may not be constant.

[0028] The thickness of the cladding layer 33 can be, for example, about 0.2 μm to 5 μm, and the thickness of the cladding layer can be, for example, about 2 μm to 50 μm. (Configuration of optical component 40) The optical component 40 is a component separate from the optical waveguide 30. The optical component 40 is, for example, a photonic integrated circuit (PIC) element. The PIC element has, for example, an optical circuit. The optical circuit has, for example, an optical element and an optical modulation circuit.

[0029] As shown in FIG. 1 , the optical component 40 has, for example, a main body 41, an optical waveguide 50, and a connection terminal 60. The main body 41 is formed, for example, in the shape of a rectangular parallelepiped. The optical waveguide 50 is formed so as to protrude downward from the lower surface of the main body 41. The optical waveguide 50 is optically connected to the optical waveguide 30. The optical waveguide 50 is optically coupled to the optical waveguide 30 by adiabatic coupling. Note that, for example, a silicon optical waveguide or a spot size converter can be used as the optical waveguide 50.

[0030] The optical waveguide 50 has a single core 51 and a cladding layer 52. The core 51 is formed, for example, on the lower surface of the main body 41. The core 51 is for propagating an optical signal. The cladding layer 52 is formed on the lower surface of the main body 41 so as to cover the core 51. The cladding layer 52 is formed so as to cover the entire side surface of the core 51. The cladding layer 52 is formed so as to cover the entire lower surface of the core 51. For example, silicon oxide (SiO2) or the like can be used as the material for the cladding layer 52. For the material of the core 51, a material having a higher refractive index than the cladding layer 52 made of SiO2 is selected so that the propagation of the optical signal occurs only within the core 51. For example, silicon (Si) can be used as the material for the core 51.

[0031] The optical waveguide 50 is a single waveguide formed by a single core 51. Note that, hereinafter, the "waveguide formed by the core 51" may be simply referred to as the "core 51".

[0032] The propagation constant of the core 51 may be, for example, the same as or different from the propagation constant of each of the cores 32. For example, the propagation constant of the core 51 is preferably larger than the propagation constant of each of the cores 32. For example, it is more preferable that the propagation constant of the core 51 is equal to the propagation constant when the three cores 32 are optically coupled.

[0033] As shown in Fig. 3, in the optical module 10 of this embodiment, three cores 32 are provided for a single core 51. The single core 51 is optically coupled to the three cores 32 by adiabatic coupling. Here, the core 51 is provided for the multiple cores 32 so that the core 51 is optically coupled to the multiple cores 32. Note that in Fig. 3, the main body 41 of the optical component 40 is drawn perspectively.

[0034] The core 51 is formed, for example, in an elongated shape. The core 51 is formed, for example, so as to extend along the Y-axis direction. The core 51 has, for example, a predetermined width along the X-axis direction. That is, in this embodiment, the length direction (extension direction) of the core 51 coincides with the Y-axis direction, and the width direction of the core 51 coincides with the X-axis direction. The core 51 of this embodiment is provided so as to partially overlap with the central core 32B of the three cores 32 in a planar view. Note that the core 51 may be misaligned in the X-axis direction due to mounting accuracy when the optical component 40 is mounted on the optical waveguide 30. For example, as shown in FIG. 6, the core 51 may be disposed between two cores 32A and 32B in a planar view.

[0035] As shown in FIG. 4 , the core 51 of this embodiment is disposed opposite the core 32B. The core 51 is disposed away from the core 32 by a second separation distance L2 in the Z-axis direction. That is, the core 51 and the core 32 are disposed away from each other by the second separation distance L2 in the Z-axis direction. In other words, the second separation distance L2 is the separation distance between the core 51 and the core 32 along the Z-axis direction. The core 51 and the core 32 of this embodiment are separated from each other by the cladding layer 52 and the cladding layer 33. That is, the cladding layer 52 and the cladding layer 33 function as a separation member that separates the core 51 and the core 32 in the Z-axis direction. Here, the second separation distance L2 is set to be equal to or less than the first separation distance L1 between two adjacent cores 32. In other words, the first separation distance L1 is set to be equal to or greater than the second separation distance L2. By setting the first separation distance L1 in this manner, the arrangement interval between the three cores 32 can be set wide, and each of the three cores 32 can be formed to have its own propagation mode. The second separation distance L2 can be easily adjusted by adjusting the thickness from the lower surface of the core 51 to the lower surface of the cladding layer 52 and the thickness from the upper surface of the core 32 to the upper surface of the cladding layer 33. The second separation distance L2 can be set to, for example, about 0.2 μm to 5 μm. The first separation distance L1 can be set to, for example, about 0.2 μm to 10 μm.

[0036] As shown in Fig. 3, the core 51 has an end portion 51A in the longitudinal direction of the core 51 and a tapered portion 51B that becomes thinner toward the end portion 51A. The end portion 51A is the end portion of the core 51 on the right side in the figure. The tapered portion 51B is formed so that the cross-sectional area becomes smaller toward the end portion 51A. Specifically, the tapered portion 51B is formed so that the width becomes smaller toward the end portion 51A.

[0037] The core 51 is provided so as to overlap the core 32 in the length direction of the core 51 (i.e., the Y-axis direction). That is, in the optical module 10, an overlap region R1 is provided in which a single core 51 overlaps multiple cores 32 in the length direction of the cores 32, 51. In the overlap region R1, for example, the tapered portion 51B of the core 51 and the tapered portion 32E of the core 32 overlap. That is, the tapered portion 51B and the tapered portion 32E are provided in the overlap region R1. Furthermore, the end portion 51A of the core 51 and the end portion 32D of the core 32 are provided in the overlap region R1.

[0038] The thickness of the core 51 can be set to, for example, about 0.2 μm to 10 μm. The width of the core 51 can be set to, for example, about 0.5 μm to 10 μm. The thickness of the cladding layer 52 can be set to, for example, about 0.2 μm to 5 μm.

[0039] 1, the connection terminal 60 is provided, for example, on the lower surface of the cladding layer 52. The connection terminal 60 is formed so as to protrude downward from the lower surface of the cladding layer 52. The connection terminal 60 is formed in a columnar shape. Although not shown in the drawings, the connection terminal 60 is electrically connected, for example, to an optical circuit provided in the main body 41.

[0040] The optical component 40 described above is mounted on the wiring substrate 20 and on the optical waveguide 30. The optical component 40 is, for example, flip-chip mounted on the upper surface of the wiring substrate 20 and mounted on the upper surface of the cladding layer 33 exposed from the cladding layer 34. For example, the connection terminals 60 of the optical component 40 are electrically connected to the connection pads 22P of the wiring substrate 20 via the solder layers 61. As a result, the optical component 40 is electrically connected to the connection pads 22P via the connection terminals 60 and the solder layers 61. The optical component 40 is also mounted on the optical waveguide 30 such that the cladding layer 52 is bonded to the upper surface of the cladding layer 33 exposed from the cladding layer 34. In the optical module 10 of this embodiment, for example, the cladding layer 52 is mounted on the upper surface of the cladding layer 33 in an uncured state (rubber state), and then the cladding layer 33 is cured, thereby bonding the cladding layer 33 and the cladding layer 52 to each other.

[0041] Furthermore, the optical component 40 is mounted on the upper surface of the cladding layer 33, for example, so that the end face of the optical component 40 in the Y-axis direction abuts against the end face of the cladding layer 34 in the Y-axis direction. This allows the position of the optical component 40 in the Y-axis direction to be accurately determined by abutting the end face of the optical component 40 in the Y-axis direction against the end face of the cladding layer 34 in the Y-axis direction.

[0042] (About the propagation of light) Next, an example of light propagation in the optical module 10 will be described with reference to FIG. 5. Here, light propagation will be described when the optical component 40 is mounted so that the central core 32B of the three cores 32 and the core 51 overlap in a planar view. Note that FIGS. 5(b) to 5(g) show, using contour lines, the calculation results of the light intensity distribution (mode profile) of the optical waveguides 30 and 50 at each of the points b to g shown in FIG. 5(a). The light intensity distributions shown in FIGS. 5(b) to 5(g) are light intensity distributions in a cross section perpendicular to the longitudinal direction (here, the Y-axis direction) of the optical waveguides 30 and 50. Furthermore, the light intensity in the light intensity distributions shown in FIGS. 5(b) to 5(g) is stronger on the inner contour lines than on the outer contour lines.

[0043] 5(a), light input to a single core 51 is propagated from the single core 51 to three cores 32 as a whole (see the arrows in the figure). Such light propagation will be described in detail below.

[0044] Light input to a single core 51 propagates within the core 51 as single-mode light. This propagated light propagates within the core 51 along the length of the core 51 (here, to the right in the figure). Next, when the propagated light enters the overlap region R1 where the core 51 and the core 32 overlap, it transfers from the core 51 to the central core 32B and propagates further. More specifically, the width of the core 51 narrows in the direction of light propagation in the tapered portion 51B of the core 51, causing the light to leak out and increase in spot size. This causes the optical mode to expand in the tapered portion 51B of the core 51. The light with an increased spot size, i.e., the light with an expanded mode, is then affected by the central core 32B located below the core 51 with the cladding layers 52 and 33 (see FIG. 4) sandwiched therebetween, and is adiabatically coupled to the core 32B (see FIGS. 5(b) to 5(d)). That is, as the optical intensity is adiabatically coupled from the core 51 to the central core 32B, the light propagating within the core 51 is transferred to the core 32B in the overlap region R1 and continues to propagate. As a result, the propagating light propagating within the core 51 is adiabatically coupled with the central core 32B at an arbitrary coupling length. In this way, the propagating light shifts in the thickness direction and propagates three-dimensionally (stereoscopically) from the core 51 toward the central core 32B, which is provided below the core 51 with the cladding layers 52 and 33 (see FIG. 4) sandwiched therebetween.

[0045] As described above, each of the three cores 32 has its own propagation mode. That is, in the optical waveguide 30, the dimensions of each core 32 and the first separation distance L1 between two adjacent cores 32 are set so that each of the three cores 32 has its own propagation mode. Specifically, the first separation distance L1 is set to be equal to or greater than the second separation distance L2 (see FIG. 4 ) between the core 51 and the core 32 along the Z-axis direction, thereby widening the gap between two adjacent cores 32. As a result, in the optical waveguide 30, three independent waveguides are formed by the three cores 32. Therefore, the propagating light propagating through the core 51 is not optically coupled immediately from the core 51 to the three cores 32, but is first optically coupled only to the central core 32B of the three cores 32, which is located directly below the core 51. This optical coupling converts the single-peaked light intensity distribution at the location shown in FIG. 5(b) into a bi-peaked light intensity distribution having a peak for light propagating through core 51 and a peak for light propagating through central core 32B at the location shown in FIG. 5(d).

[0046] Next, as shown in FIG. 5(a), the propagated light propagated to the central core 32B propagates within the core 32B along the length direction of the core 32B (here, the right direction in the figure). Next, the propagated light is distributed from the central core 32B to the two cores 32A and 32C arranged on either side of the central core 32B and propagates therethrough. More specifically, the propagated light propagating within the central core 32B is affected by the cores 32A and 32C arranged on either side of the core 32B with the cladding layer 33 (see FIG. 4) sandwiched therebetween, and is adiabatically coupled to the cores 32A and 32C (see FIGS. 5(e) to 5(g)). That is, the light intensity is adiabatically coupled from the central core 32B to the cores 32A and 32C on either side, and the light propagating within the central core 32B propagates while being distributed to the cores 32A and 32C on either side. As a result, the propagating light propagating through the central core 32B is adiabatically coupled with the cores 32A and 32C on either side at an arbitrary coupling length. Note that the coupling length when one core 32B is adiabatically coupled with the two cores 32A and 32C is longer than the coupling length when one core 51 is adiabatically coupled with one core 32B. Here, the core 32B and the cores 32A and 32C have the same propagation constant in the fundamental mode. Specifically, the three cores 32A, 32B, and 32C are formed to have the same dimensions and are made of the same material so as to have the same propagation constant in the fundamental mode. Therefore, the propagating light propagating through the central core 32B is optically coupled appropriately with the cores 32A and 32C on either side, which have the same propagation constant as the core 32B in the fundamental mode. This optical coupling converts the bimodal light intensity distribution at the location shown in Figure 5(d) into a trimodal light intensity distribution at the location shown in Figure 5(g), which has three peaks of light propagating through each of the three cores 51.

[0047] In this way, when core 51 is arranged overlapping core 32B, light input to the single core 51 is propagated from core 51 to core 32B, and then distributed to the remaining cores 32A and 32C, and propagated to the three cores 32A, 32B, and 32C. In this way, the optical waveguide 50 having the single core 51 and the optical waveguide 30 having the three cores 32 are optically connected by adiabatic coupling.

[0048] Next, another example of the propagation of light in the optical module 10 will be described with reference to Fig. 6. Here, the propagation of light will be described when the optical component 40 is mounted so that the core 51 is positioned between the two cores 32A and 32B in a plan view. That is, the propagation of light will be described when the optical component 40 is displaced in the X-axis direction from the desired position shown in Fig. 5. Note that Figs. 6(b) to 6(g) show, using contour lines, the calculation results of the light intensity distribution (mode profile) of the optical waveguides 30 and 50 at each of the positions b to g shown in Fig. 6(a). The light intensity distributions shown in Figs. 6(b) to 6(g) are light intensity distributions in a cross section perpendicular to the length direction (here, the Y-axis direction) of the optical waveguides 30 and 50.

[0049] 6(a), light input to a single core 51 is propagated from the single core 51 to three cores 32 as a whole (see the arrows in the figure). Such light propagation will be described in detail below.

[0050] Light input to a single core 51 propagates within the core 51 as single-mode light. This propagated light propagates within the core 51 along the length of the core 51 (here, to the right in the figure). Next, when the propagated light enters an overlap region R1 where the core 51 and the core 32 overlap, it transfers from the core 51 to the two cores 32A and 32B and propagates there. More specifically, since the width of the core 51 narrows in the direction of light propagation at the tapered portion 51B of the core 51, the light leaks out and the spot size increases. Then, the light with an increased spot size is affected by the cores 32A and 32B provided near the core 51 below the core 51 with the cladding layers 52 and 33 (see FIG. 4) sandwiched therebetween, and is adiabatically coupled to the cores 32A and 32B (see FIGS. 6(b) to 6(d)). That is, the light intensity is adiabatically coupled from the core 51 to the two cores 32A and 32B, and the light propagating within the core 51 is transferred to the two cores 32A and 32B in the overlap region R1 and propagates there. As a result, the propagating light propagating within the core 51 is adiabatically coupled at an arbitrary coupling length with the two cores 32A and 32B provided on both sides of the core 51 in a planar view. In this case, because the light is coupled with the two cores 32A and 32B, the apparent propagation constant increases and the coupling length becomes longer compared to when the light is coupled with one core 32B.

[0051] In this way, the propagating light shifts in the thickness direction and propagates three-dimensionally (stereoscopically) from the core 51 toward the two cores 32A and 32B provided below the core 51 with the cladding layers 52 and 33 (see FIG. 4) sandwiched between them. As a result, the propagating light that has propagated within the core 51 is optically coupled from the core 51 to two of the three cores 32, the cores 32A and 32B, which are provided near the core 51. This optical coupling converts the single-peaked light intensity distribution at the location shown in FIG. 6(b) into a tri-peaked light intensity distribution having a peak for light propagating through the core 51 and two peaks for light propagating through the two cores 32A and 32B at the location shown in FIG. 6(d).

[0052] Next, as shown in FIG. 6(a), the propagated light propagated to the cores 32A and 32B propagates within the cores 32A and 32B along the length direction of the cores 32A and 32B (here, the right direction in the figure). Next, the propagated light propagating within the central core 32B is distributed from the core 32B to the core 32C arranged below the core 32B in the figure and propagates therethrough. More specifically, the propagated light propagating within the central core 32B is affected by the core 32C arranged on the side of the core 32B with the cladding layer 33 (see FIG. 4) sandwiched therebetween, and is adiabatically coupled to the core 32C (see FIGS. 6(e) to 6(g)). That is, as the light intensity is adiabatically coupled from the central core 32B to the core 32C, the light propagating within the core 32B is distributed to the core 32C and propagates therethrough. As a result, the propagating light propagating through core 32B is adiabatically coupled with core 32C at an arbitrary coupling length. Here, core 32B and core 32C have the same propagation constant in the fundamental mode. Therefore, the propagating light propagating through core 32B is suitably optically coupled with core 32C, which has the same propagation constant in the fundamental mode as core 32B. By such optical coupling, the trimodal light intensity distribution at the location shown in FIG. 6(d) is converted into a quadrupled light intensity distribution at the location shown in FIG. 6(g), which has a peak for light propagating through core 51 and three peaks for light propagating through each of the three cores 51.

[0053] In this way, even if the core 51 is misaligned in the X-axis direction, light input to a single core 51 propagates from the core 51 to two cores 32A and 32B, and then is distributed to the remaining core 32C and propagates to the three cores 32A, 32B, and 32C. At this time, the coupling length when the propagating light propagating through the core 51 is adiabatically coupled to the two cores 32A and 32B becomes long. However, because a portion of the light transferred to the two cores 32A and 32B is transferred to the other core 32C, an increase in coupling loss can be suppressed. Furthermore, by adjusting the first separation distance L1 between two adjacent cores 32 and the second separation distance L2 between the cores 32 and 51 along the Z-axis direction so that the variation in the equivalent refractive index in the X-axis direction is minimized, the amount of coupling loss can be kept small. Furthermore, by making the propagation constant of the core 51 larger than that of each core 32 and bringing the propagation constant of the core 51 closer to the propagation constant when the three cores 32 are coupled, the coupling efficiency can be improved. In this way, even if the core 51 is misaligned in the X-axis direction, deterioration of the coupling loss can be effectively suppressed. Therefore, when mounting the optical component 40 on the optical waveguide 30, the tolerance range for the misalignment of the core 51 in the X-axis direction relative to the three cores 32 can be expanded. In other words, by arranging multiple cores 32, each having a propagation mode, at intervals along the X-axis direction, the manufacturing tolerance range for the accuracy of the core 51 in the X-axis direction can be expanded. As a result, the manufacturing yield can be improved while reducing the coupling loss (propagation loss).

[0054] Fig. 7 is a graph showing the relationship between the amount of misalignment of the core 51 in the X-axis direction and the coupling loss. Fig. 7 shows simulation results for an example (see solid line) in which a single core 51 is adiabatically coupled to six cores 32, each having a single propagation mode, and a comparative example (see dashed line) in which a single core 51 is adiabatically coupled to a single core 32. In the simulation of Fig. 7, the length of the overlap region R1 where the cores 32 and 51 overlap is set to 1.6 mm.

[0055] As shown in FIG. 7 , in the comparative example in which a single core 51 is adiabatically coupled to a single core 32, the coupling loss increases as the misalignment of the core 51 in the X-axis direction increases. For example, assuming a coupling loss of −1.0 dB, the comparative example can only tolerate a misalignment of about ±5 μm. In contrast, in the embodiment, six cores 32 each having a single propagation mode are arranged in a line along the X-axis direction, thereby achieving a relatively flat coupling loss over a wide range. As a result, in the embodiment, assuming a coupling loss of −1.0 dB, a misalignment of up to about ±20 μm can be tolerated. Note that the tolerance for such misalignment can be expanded by increasing the number of cores 32 arranged along the X-axis direction. Therefore, by increasing the number of cores 32 arranged along the X-axis direction, the misalignment of the cores 51 in the X-axis direction can theoretically be tolerated infinitely.

[0056] (Effects of this embodiment) Next, the effects of this embodiment will be described. (1) The optical module 10 includes an optical component 40 having a single core 51 and an optical waveguide 30 having multiple cores 32 optically coupled to the single core 51 by adiabatic coupling. The optical module 10 includes a separator, here cladding layers 33 and 52, that separates the single core 51 from the multiple cores 32 in a first direction (here, the Z-axis direction). The optical component 40 is a separate component from the optical waveguide 30 and is mounted on the optical waveguide 30. The single core 51 and the multiple cores 32 are provided so as to be optically coupled from the single core 51 to the multiple cores 32. The multiple cores 32 are arranged side by side along a second direction (here, the X-axis direction) perpendicular to the first direction. The single core 51 and the multiple cores 32 have an overlap region R1 where they overlap each other in a third direction (here, the Y-axis direction) perpendicular to both the first and second directions. A first separation distance L1 along the X-axis direction between two adjacent cores 32 among the multiple cores 32 is equal to or greater than a second separation distance L2 along the Z-axis direction between the single core 51 and the multiple cores 32.

[0057] According to this configuration, multiple cores 32, each having a single propagation mode, are arranged side by side along the X-axis direction, and the single core 51 is adiabatically coupled to the multiple cores 32. This makes it possible to preferably prevent the coupling loss between the single core 51 and the multiple cores 32 from increasing even if the single core 51 is misaligned in the X-axis direction. Therefore, when mounting the optical component 40 on the optical waveguide 30, it is possible to expand the allowable range for misalignment of the core 51 in the X-axis direction relative to the multiple cores 32. As a result, even if the single core 51 is misaligned in the X-axis direction, the single core 51 and the multiple cores 32 can be optically coupled in a preferable manner, thereby improving the connection reliability between the single core 51 and the multiple cores 32.

[0058] (2) By arranging the multiple cores 32, each having a propagation mode, at intervals along the X-axis, the manufacturing tolerance for the accuracy of the cores 51 in the X-axis direction can be expanded. Specifically, by adjusting the number of the multiple cores 32, the first separation distance L1, and the like, the manufacturing tolerance for the accuracy of the cores 51 in the X-axis direction can be expanded to be greater than the mounting accuracy required when flip-chip mounting the optical component 40 on the wiring substrate 20. This contributes to realizing passive alignment, which simultaneously achieves flip-chip mounting of the optical component 40 on the wiring substrate 20 and optical coupling between a single core 51 and the multiple cores 32. Note that, unlike active alignment, passive alignment is an alignment method that does not use optical monitoring. Compared to active alignment, passive alignment is superior in productivity due to a reduced number of processes and shorter adjustment time. Therefore, realizing passive alignment can improve the productivity of the optical module 10.

[0059] (3) Incidentally, when a single core 51 is adiabatically coupled to multiple cores 32, it is possible to set the spacing between the multiple cores 32 and the dimensions of each core 32 so that the multiple cores 32 propagate in a single optical mode. However, in this case, there are significant structural constraints on each core 32. Furthermore, in this case, the first separation distance L1 between adjacent cores 32 needs to be set very narrow, making it difficult to significantly expand the manufacturing tolerance for the accuracy of the core 51 in the X-axis direction. Specifically, it is difficult to expand the manufacturing tolerance for the accuracy of the core 51 in the X-axis direction to a value greater than the mounting accuracy required when the optical component 40 is flip-chip mounted on the wiring substrate 20.

[0060] In contrast, in the optical module 10 of this embodiment, so that each core has its own propagation mode, the first separation distance L1 along the X-axis direction between two adjacent cores 32 is set to be equal to or greater than the second separation distance L2 along the Z-axis direction between the single core 51 and the multiple cores 32. This allows the first separation distance L1 to be set to be greater than when the multiple cores 32 are formed to propagate in a single optical mode, and makes it possible to suitably expand the manufacturing tolerance for accuracy of the core 51 in the X-axis direction.

[0061] (4) The optical component 40 has a cladding layer 52 that covers a single core 51. The optical waveguide 30 has a cladding layer 33 that covers multiple cores 32. The optical component 40 is mounted on the optical waveguide 30 so that the cladding layer 52 is bonded onto the cladding layer 33. The separation member is composed of the cladding layer 52 and the cladding layer 33. With this configuration, the cladding layers 33 and 52 that function as separation members can suitably separate the single core 51 and the multiple cores 32 in the Z-axis direction.

[0062] (5) The tapered portion 51B of the single core 51 and the tapered portions 32E of the multiple cores 32 are arranged to overlap each other in the longitudinal direction of the cores 51 and 32. With this configuration, the propagation constant of the core 51 can be made to suitably match the propagation constant of the core 32 at any location in the overlap region R1 where the tapered portion 51B and the tapered portion 32E overlap. This allows for suitable optical coupling between the single core 51 and the multiple cores 32.

[0063] (6) The propagation constant of the single core 51 is set to be larger than the propagation constant of each of the multiple cores 32. With this configuration, the propagation constant of the single core 51 can be made closer to the propagation constant when the three cores 32 are coupled, thereby improving the coupling efficiency between the cores 51 and 32.

[0064] (Example of change) The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0065] In the above embodiment, the separating member separating the core 32 from the core 51 in the Z-axis direction is embodied as the clad layer 33 and the clad layer 52. That is, in the above embodiment, the separating member is formed into a two-layer structure of the clad layer 33 and the clad layer 52. However, the structure of the separating member is not limited to this.

[0066] For example, as shown in FIG. 8 , the separating member separating the cores 32 and 51 in the Z-axis direction may be embodied as a three-layer structure including a cladding layer 33, an adhesive 55, and a cladding layer 52. In this optical module 10, the cladding layer 52 of the optical component 40 is bonded to the cladding layer 33 of the optical waveguide 30 with the adhesive 55. The adhesive 55 is bonded to the upper surface of the cladding layer 33 exposed from the cladding layer 34, and also to the lower surface of the cladding layer 52. In the optical module 10 of this modified example, for example, the cured cladding layer 33 and the cured cladding layer 52 are bonded to each other with the adhesive. Note that, for example, an optical adhesive can be used as the adhesive 55. For example, an ultraviolet-curing optical adhesive can be used as the optical adhesive.

[0067] 9, the separating member separating the core 32 from the core 51 in the Z-axis direction may be embodied as a single-layer structure consisting of only the clad layer 33. In this case, in the optical module 10, the core 51 exposed from the clad layer 52 is directly bonded to the upper surface of the clad layer 33 exposed from the clad layer 34. In the optical module 10 of this modification, the core 51 is mounted on the upper surface of the uncured (rubber-like) clad layer 33, and then the clad layer 33 is cured, thereby bonding the clad layer 33 and the core 51 to each other.

[0068] The structure of the optical component 40 in the above embodiment can be modified as needed. The structure of the optical waveguide 50 in the optical component 40 of the above embodiment may be modified as appropriate. For example, the optical waveguide 50 may be modified to have a structure including a cladding layer provided on the lower surface of the main body 41, a core 51 formed on the lower surface of the cladding layer, and a cladding layer 52 formed to cover the core 51.

[0069] In the above embodiment, the core 51 has a structure including the tapered portion 51B, but this is not limitative and the core 51 may be modified to have a structure that does not include the tapered portion 51B. Although the optical component 40 of the above embodiment is provided with one optical waveguide 50, there is no particular limitation on the number of optical waveguides 50. For example, the number of optical waveguides 50 may be two or more.

[0070] In the above embodiment, the optical waveguide 50 is embodied as a silicon optical waveguide, but is not limited to this. For example, the optical waveguide 50 may be embodied as a glass optical waveguide or a polymer optical waveguide.

[0071] In the above embodiment, the optical component 40 is mounted on the wiring substrate 20 by flip-chip mounting, but this is not limiting. For example, the optical component 40 may be mounted on the wiring substrate 20 by wire bonding or solder mounting.

[0072] In the optical module 10 of the above embodiment, the optical component 40 as the first optical component is embodied as a PIC element, but this is not limiting. For example, the optical component 40 may be embodied as an optical component other than a PIC element. For example, the optical component 40 may be embodied as a planar lightwave circuit (PLC).

[0073] The structure of the optical waveguide 30 in the above embodiment can be modified as appropriate. The cladding layer 34 in the above embodiment may be omitted. Although the optical waveguide 30 of the above embodiment is provided with three cores 32, there is no particular limitation on the number of cores 32. For example, the number of cores 32 may be two, or may be four or more.

[0074] In the above embodiment, the core 32 has a structure including the tapered portion 32E, but this is not limiting, and the core 32 may be modified to have a structure that does not include the tapered portion 32E. In the above embodiment, the optical waveguide 30 is formed on the upper surface of the substrate body 21 exposed from the solder resist layer 23, but this is not limiting. For example, the optical waveguide 30 may be formed on the upper surface of the solder resist layer 23.

[0075] In the above embodiment, the optical waveguide 30 is embodied as a polymer optical waveguide, but is not limited to this. For example, the optical waveguide 30 may be embodied as a silicon optical waveguide or a glass optical waveguide.

[0076] In the optical module 10 of the above embodiment, the second optical component is embodied as the optical waveguide 30, but this is not limiting. For example, the second optical component may be embodied as an optical component other than the optical waveguide 30.

[0077] Although the optical module 10 of the above embodiment is provided with one optical waveguide 30, there is no particular limitation on the number of optical waveguides 30. For example, the number of optical waveguides 30 may be two or more.

[0078] Although the optical module 10 of the above embodiment is provided with one optical component 40, there is no particular limitation on the number of optical components 40. For example, the number of optical components 40 may be two or more.

[0079] In the optical module 10 of the above embodiment, the optical component 40 is provided with an optical waveguide 50 having a single core 51, and the wiring substrate 20 is provided with an optical waveguide 30 having multiple cores 32, but this is not limiting. For example, the optical component 40 may be provided with an optical waveguide 50 having a single core 51 on the wiring substrate 20, and the optical component 40 may be provided with an optical waveguide 30 having multiple cores 32.

[0080] The structure of the wiring board 20 in the above embodiment can be modified as needed. For example, the solder resist layer 23 may be omitted. (Application example of optical module 10) Fig. 10 shows an application example of the optical module 10 according to the above embodiment. Fig. 10 is a plan view of the optical module 10 as seen from the Z-axis direction, and the wiring substrate 20, cladding layers 33 and 34, main body 41, etc. are depicted perspectively. The arrows in Fig. 10 indicate the direction of light propagation.

[0081] The optical module 10 of this application example includes an optical waveguide 30A and an optical component 40A mounted on the optical waveguide 30A. (Configuration of optical waveguide 30A) The optical waveguide 30A has, for example, one or more (here, one) optical waveguide portions 70 and one or more (here, one) optical waveguide portions 71.

[0082] The optical waveguide section 70 has multiple (here, four) cores 32, an optical multiplexer 35, and one core 36. The four cores 32 are arranged side by side along the X-axis direction. Each of the four cores 32 extends along the Y-axis direction.

[0083] The optical multiplexer 35 may be, for example, a Y-shaped optical coupler, a multi-mode interference (MMI) coupler, a directional coupler, or the like. The optical multiplexer 35 in this application example has a two or more stage (two stages in this case) tournament tree structure. The optical multiplexer 35 optically couples four cores 32 and one core 36. The optical multiplexer 35 optically couples four cores 32 to one core 36. The optical multiplexer 35 combines four propagating lights respectively propagating within the four cores 32, and outputs the combined light to one core 36. One core 36 extends, for example, along the Y-axis direction.

[0084] The optical waveguide portion 71 has a single core 37. The core 37 extends along the Y-axis direction. (Configuration of optical component 40A) Optical component 40A has, for example, one or more (here, one) optical waveguide section 80 optically connected to optical waveguide section 70, and one or more (here, one) optical waveguide section 81 optically connected to optical waveguide section 71.

[0085] The optical waveguide section 80 has a single core 51. The core 51 extends along the Y-axis direction. The core 51 is provided so as to overlap with four cores 32 in the length direction of the core 51 (here, the Y-axis direction). The single core 51 is optically coupled to the four cores 32 by adiabatic coupling. The single core 51 and the four cores 32 are arranged so that the single core 51 is optically coupled to the multiple cores 32.

[0086] Here, light input to a single core 51 is transferred to four cores 32. Thereafter, the light transferred to the four cores 32 is combined by an optical combiner 35 and propagated to one core 36. This forms a pair of channels each made up of an optical waveguide section 70 and an optical waveguide section 80. Note that the optical module 10 may be provided with a plurality of pairs of channels each made up of an optical waveguide section 70 and an optical waveguide section 80.

[0087] The optical waveguide section 81 has multiple (here, four) cores 56, an optical multiplexer 57, and one core 58. The four cores 56 are arranged side by side along the X-axis direction. Each of the four cores 56 extends along the Y-axis direction.

[0088] The optical multiplexer 57 may be, for example, a Y-shaped optical coupler, an MMI coupler, or a directional coupler. The optical multiplexer 57 optically couples four cores 56 to one core 58. The optical multiplexer 57 optically couples four cores 56 to one core 58. The optical multiplexer 57 combines four propagating lights respectively propagating within the four cores 56, and outputs the combined light to one core 58. One core 58 extends, for example, along the Y-axis direction.

[0089] The four cores 56 are arranged so as to overlap with the single core 37 in the length direction of the cores 56 (here, the Y-axis direction). The single core 37 is optically coupled to the four cores 56 by adiabatic coupling. The single core 37 and the four cores 56 are arranged so that the single core 37 is optically coupled to the multiple cores 56.

[0090] Here, light input to the single core 37 is transferred to the four cores 56. Thereafter, the light transferred to the four cores 56 is combined by the optical combiner 57 and propagated to one core 58. This forms a pair of channels each made up of the optical waveguide portion 71 and the optical waveguide portion 81. Note that the optical module 10 may be provided with a plurality of pairs of channels each made up of the optical waveguide portion 71 and the optical waveguide portion 81. [Explanation of symbols]

[0091] 10 Optical Modules 20 Wiring board 22P connection pad 30 Optical waveguide (second optical component) 31 Cladding layer 32, 32A, 32B, 32C core (second core) 32D end (second end) 32E Tapered section (second tapered section) 32X Cores 33 Cladding layer (separator) 34 Cladding layer 35 Optical multiplexer 36 cores (3rd core) 37 cores (first core) 40 Optical component (first optical component) 50 Optical waveguide 51 cores (first core) 51A End (1st end) 51B Tapered portion (first tapered portion) 52 Cladding layer (separator) 55 Adhesive (separator) 56 cores (second core) 57 Optical multiplexer 58 cores (3rd core) L1 1st separation distance L2 Second separation distance R1 overlap region

Claims

1. a first optical component having a single first core; a second optical component having a plurality of second cores optically coupled to the single first core by adiabatic coupling; a separating member separating the single first core and the plurality of second cores in a first direction, the first optical component is a separate component from the second optical component, the single first core and the plurality of second cores are provided to be optically coupled from the single first core to the plurality of second cores, the plurality of second cores are arranged side by side along a second direction perpendicular to the first direction, the single first core and the plurality of second cores have overlapping regions in which they overlap with each other in a third direction orthogonal to both the first direction and the second direction, An optical module, wherein a first separation distance along the second direction between two adjacent second cores is equal to or greater than a second separation distance along the first direction between the single first core and the plurality of second cores.

2. the first optical component has a first clad layer covering the single first core, the second optical component has a second clad layer covering the plurality of second cores, the first optical component is mounted on the second optical component such that the first clad layer is bonded onto the second clad layer; 2. The optical module according to claim 1, wherein the separating member has a two-layer structure including the first cladding layer and the second cladding layer.

3. the first optical component has a first clad layer covering the single first core, the second optical component has a second clad layer covering the plurality of second cores, the first optical component is mounted on the second optical component such that the first clad layer is bonded onto the second clad layer via an adhesive; 2. The optical module according to claim 1, wherein the separating member has a three-layer structure including the first cladding layer, the adhesive, and the second cladding layer.

4. the second optical component has a second clad layer covering the plurality of second cores, the first optical component is mounted on the second optical component such that the single first core is bonded onto the second cladding layer; 2. The optical module according to claim 1, wherein the separating member has a single-layer structure including only the second cladding layer.

5. the single first core has a first end in a longitudinal direction of the single first core and a first tapered portion whose cross-sectional area decreases toward the first end, The optical module according to claim 1 , wherein the first end and the first tapered portion are provided in the overlap region.

6. Each of the plurality of second cores has a second end portion in a longitudinal direction of the second core and a second tapered portion whose cross-sectional area decreases toward the second end portion, The optical module according to claim 1 , wherein the second end and the second tapered portion are provided in the overlap region.

7. 2. The optical module according to claim 1, wherein the propagation constant of the single first core is set to be larger than the propagation constant of each of the plurality of second cores.

8. 2. The optical module according to claim 1, wherein the second optical component has one third core and an optical multiplexer that optically couples the plurality of second cores to the one third core.

9. A wiring board is provided. the second optical component is an optical waveguide formed on the wiring substrate, 2. The optical module according to claim 1, wherein the first optical component is mounted on the wiring board and on the second optical component.

10. the wiring board has connection pads; The optical module according to claim 9 , wherein the first optical component is flip-chip mounted on the connection pad.

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