Optical waveguide device and method for manufacturing optical waveguide device

Abstract

To provide an optical waveguide device with which it is possible to suppress an increase in optical connection losses, and a method for manufacturing the optical waveguide device.SOLUTION: An optical waveguide device 1 comprises: a clad 10 which has a first end face 11, a second end face 12 lined with the first end face in a first direction X, and a side face 16 extending in the first direction between the first and second end faces; and a core 20 which has a first core end face 21 exposed at the first end face and a second core end face 22 exposed at the second end face and extending from the first core end face to the second core end face within the clad. The second core end face is at a different height from the height of the first core end face from a side face in a second direction Z that is perpendicular to the side face, and is located at a position shifted from the first core end face in a third direction Y which is along the side face and perpendicular to the second direction. The shape of the core at a cross section perpendicular to the extension direction of the core maintains a uniform circular or elliptical shape at each position of the core along the extending direction.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to an optical waveguide device and a method for manufacturing an optical waveguide device. [Background technology]

[0002] Patent Documents 1 and 2 disclose a method for forming a three-dimensional optical waveguide by laser drawing. In such a method, for example, a laser beam is irradiated inside a glass material, thereby causing a refractive index change inside the glass material at the focal point of the laser beam. By utilizing this refractive index change and three-dimensionally scanning the focal point of the laser beam inside the glass material, it becomes possible to form an arbitrary three-dimensional optical waveguide inside the glass material. An optical waveguide device in which such a three-dimensional optical waveguide is formed is disposed, for example, between two optical waveguide components having different core arrangements, and is used to optically connect these optical waveguide components to each other. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 6-337320 [Patent Document 2] Special Publication No. 2004-503813 Summary of the Invention [Problem to be solved by the invention]

[0004] As another method for forming the above-mentioned three-dimensional optical waveguide, a method for forming an arbitrary three-dimensional optical waveguide using a needle is considered. In this method, the tip of a needle is inserted into a liquid cladding material applied on a substrate, and the needle is scanned three-dimensionally while discharging a liquid core material from the tip of the needle. The core material and the cladding material are then cured to form a three-dimensional optical waveguide. Unlike the laser drawing method, the method using such a needle does not require an optical system such as a laser light source, so that the equipment cost can be reduced. Furthermore, the method using a needle has the advantage that materials other than those whose refractive index changes due to irradiation with a laser beam can be used as the material of the three-dimensional optical waveguide, so that the selection of materials is wider than that of the laser drawing method.

[0005] However, the method using a needle has a problem in that it is difficult to maintain the cross-sectional shape of the core in a uniform shape (for example, a circular or elliptical shape). In this method, even if an attempt is made to maintain the cross-sectional shape of the core after ejection in a uniform shape, the cross-sectional shape of the core tends to deviate from the shape due to the behavior of the fluid when the liquid core material is ejected from the tip of the needle. If such a deformation of the cross-sectional shape of the core occurs, there is a risk of an increase in optical connection loss between two optical waveguide components when optically connecting the two optical waveguide components to each other via an optical waveguide device.

[0006] The present disclosure has been made in consideration of the above-mentioned problems, and provides an optical waveguide device and a method for manufacturing an optical waveguide device that can suppress an increase in optical connection loss. [Means for solving the problem]

[0007] An optical waveguide device according to an embodiment of the present disclosure includes a cladding having a first end face, a second end face aligned with the first end face in a first direction, and a side surface extending in the first direction between the first end face and the second end face, and a core having a first core end face exposed at the first end face and a second core end face exposed at the second end face, and extending within the cladding from the first core end face to the second core end face. The second core end face is at a height different from the height of the first core end face from the side surface in a second direction perpendicular to the side surface, and is disposed at a position offset from the first core end face in a third direction along the side surface and perpendicular to the second direction. The shape of the core in a cross section perpendicular to the extension direction of the core maintains a uniform circular or elliptical shape at each position of the core along the extension direction.

[0008] A method for manufacturing an optical waveguide device according to an embodiment of the present disclosure includes the steps of preparing a liquid core material and a clad material including an ultraviolet-curable resin composition containing a monomer, applying the clad material onto a substrate, inserting the tip of a needle into the clad material and scanning the tip of the needle while discharging the core material from the tip of the needle, and, after scanning the tip of the needle, extracting the tip of the needle from the clad material and irradiating the clad material and the core material with ultraviolet light to harden them, thereby obtaining an optical waveguide device including a clad and a core. In the step of scanning the tip of the needle, the tip of the needle is scanned so as to move from one end side of the clad material to the other end side in a first direction along the substrate, in a second direction perpendicular to the substrate, and in a third direction along the substrate and perpendicular to the second direction. When scanning the tip of the needle, the core material is discharged from the tip of the needle in a state in which the needle is tilted from the second direction perpendicular to the substrate starting from the tip of the needle in the scanning direction of the tip of the needle or in the opposite direction to the scanning direction.

[0009] A method for manufacturing an optical waveguide device according to another embodiment of the present disclosure includes the steps of preparing a liquid core material and a clad material including an ultraviolet-curable resin composition containing a monomer, applying the clad material onto a substrate, inserting the tip of a needle into the clad material and scanning the tip of the needle while discharging the core material from the tip of the needle, and, after scanning the tip of the needle, removing the tip of the needle from the clad material and irradiating the clad material and the core material with ultraviolet light to harden them, thereby obtaining an optical waveguide device including a clad and a core. In the step of scanning the tip of the needle, the tip of the needle is scanned so as to move from one end side of the clad material to the other end side in a first direction along the substrate, in a second direction perpendicular to the substrate, and in a third direction along the substrate and perpendicular to the second direction. The outer surface of the needle facing in the opposite direction to the scanning direction of the needle includes an inclined surface that starts from the tip of the needle and inclines in the opposite direction from the second direction perpendicular to the substrate. Effect of the Invention

[0010] According to the optical waveguide device and the method for manufacturing the optical waveguide device disclosed herein, an increase in optical connection loss can be suppressed. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a perspective view showing an optical waveguide device according to the first embodiment. [Diagram 2] FIG. 2 is a plan view showing the optical waveguide device of FIG. [Diagram 3] FIG. 3 is a side view showing the optical waveguide device of FIG. [Figure 4] FIG. 4 is a perspective view showing a manufacturing process of the optical waveguide device according to the first embodiment. [Diagram 5] FIG. 5 is a perspective view showing a step subsequent to that of FIG. [Figure 6] FIG. 6 is a perspective view showing a step subsequent to that of FIG. [Figure 7]FIG. 7 is a cross-sectional view showing a state in which the core material is discharged from the tip of the needle into the cladding material in the step shown in FIG. [Figure 8] Fig. 8(a) is a simulation result showing the cross-sectional shape of the core material at position a1 shown in Fig. 7. Fig. 8(b) is a simulation result showing the cross-sectional shape of the core material at position b1 shown in Fig. 7. Fig. 8(c) is a simulation result showing the cross-sectional shape of the core material at position c1 shown in Fig. 7. [Figure 9] FIG. 9 is another simulation result showing the cross-sectional shape of the core material at the position c1 shown in FIG. [Figure 10] FIG. 10 is a perspective view showing a manufacturing process of an optical waveguide device according to a modified example of the first embodiment. [Figure 11] FIG. 11 is a cross-sectional view showing the state in which the core material is discharged from the tip of the needle into the cladding material in the step shown in FIG. [Figure 12] Fig. 12(a) is a simulation result showing the cross-sectional shape of the core material at position a2 shown in Fig. 11. Fig. 12(b) is a simulation result showing the cross-sectional shape of the core material at position b2 shown in Fig. 11. Fig. 12(c) is a simulation result showing the cross-sectional shape of the core material at position c2 shown in Fig. 11. [Figure 13] FIG. 13 is a perspective view showing an optical waveguide device according to a modified example of the first embodiment. [Figure 14] FIG. 14 is a perspective view showing a manufacturing process of the optical waveguide device according to the second embodiment. [Figure 15] FIG. 15 is a cross-sectional view showing the state in which the core material is discharged from the tip of the needle into the cladding material in the step shown in FIG. [Figure 16] Fig. 16(a) is a simulation result showing the cross-sectional shape of the core material at position a3 shown in Fig. 15. Fig. 16(b) is a simulation result showing the cross-sectional shape of the core material at position b3 shown in Fig. 15. Fig. 16(c) is a simulation result showing the cross-sectional shape of the core material at position c3 shown in Fig. 15. [Figure 17] FIG. 17 is a graph showing the relationship between the cross-sectional shape of the core and the height of the needle tip. [Figure 18] FIG. 18 is a perspective view showing a manufacturing process of an optical waveguide device according to a comparative example. [Figure 19] FIG. 19 is a cross-sectional view showing the state in which the core material is discharged from the tip of the needle into the cladding material in the step shown in FIG. [Figure 20] Fig. 20(a) is a simulation result showing the cross-sectional shape of the core material at position a10 shown in Fig. 19. Fig. 20(b) is a simulation result showing the cross-sectional shape of the core material at position b10 shown in Fig. 19. Fig. 20(c) is a simulation result showing the cross-sectional shape of the core material at position c10 shown in Fig. 19. [Figure 21] FIG. 21 shows the results of an experiment showing that the cross-sectional shape of the core according to the comparative example changes depending on the height of the core from the substrate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] [Description of the embodiments of the present disclosure] First, the contents of the embodiments of the present disclosure will be listed and described. An optical waveguide device according to an embodiment of the present disclosure includes a clad having a first end face, a second end face aligned with the first end face in a first direction, and a side face extending in the first direction between the first end face and the second end face, and a core having a first core end face exposed at the first end face and a second core end face exposed at the second end face, and extending in the clad from the first core end face to the second core end face. The second core end face is at a height different from the height of the first core end face from the side face in a second direction perpendicular to the side face, and is disposed at a position offset from the first core end face along the side face in a third direction perpendicular to the second direction. The shape of the core in a cross section perpendicular to the extension direction of the core maintains a uniform circular or elliptical shape at each position of the core along the extension direction.

[0013] In this optical waveguide device, the core is configured to extend three-dimensionally in a path from the first core end face to the second core end face. In the above optical waveguide device, the cross-sectional shape of the core in a cross section perpendicular to the extension direction of the core maintains a uniform circular or elliptical shape at each position along the extension direction of the core. In other words, the cross-sectional shape of the core maintains a constant shape without collapsing from the first core end face to the second core end face. This makes it possible to suppress a situation in which the optical connection loss between the two optical waveguide components increases due to the collapse of the cross-sectional shape of the core when optically connecting two optical waveguide components together via an optical waveguide device.

[0014] In the above-mentioned optical waveguide device, the core and the clad may be composed of a hybrid material containing both an organic material and an inorganic material, an organic material, or an inorganic material. The core and the clad may be composed of a cured product of an ultraviolet-curable resin composition. With such a configuration, a configuration in which a three-dimensional core is formed inside the clad can be suitably obtained.

[0015] In the optical waveguide device, the shape of the core in a cross section perpendicular to the extension direction of the core may maintain a uniform circular shape at each position of the core along the extension direction. In this case, the cross-sectional shape of the core can be matched to the cross-sectional shapes of the cores of the two optical waveguide components to be connected, making it possible to more reliably suppress an increase in optical connection loss between the two optical waveguide components.

[0016] In the optical waveguide device, the shape of the core in a cross section perpendicular to the extension direction of the core may maintain a uniform elliptical shape at each position of the core along the extension direction, making it possible to guide light within the core while maintaining its polarization.

[0017] The optical waveguide device may include a plurality of cores. The first core end faces of the cores may be arranged in a row along the third direction at the first end face. The second core end faces of the cores may be arranged in a plurality of rows along the third direction at the second end face in the second direction. In this case, it is possible to suppress an increase in optical connection loss when connecting two optical waveguide components having different core arrangements.

[0018] A method for manufacturing an optical waveguide device according to an embodiment of the present disclosure includes the steps of preparing a liquid core material and a clad material including an ultraviolet-curable resin composition containing a monomer, applying the clad material onto a substrate, inserting the tip of a needle into the clad material and scanning the tip of the needle while discharging the core material from the tip of the needle, and, after scanning the tip of the needle, extracting the tip of the needle from the clad material and irradiating the clad material and the core material with ultraviolet light to harden them, thereby obtaining an optical waveguide device including a clad and a core. In the step of scanning the tip of the needle, the tip of the needle is scanned so as to move from one end side of the clad material to the other end side in a first direction along the substrate, in a second direction perpendicular to the substrate, and in a third direction along the substrate and perpendicular to the second direction. When scanning the tip of the needle, the core material is discharged from the tip of the needle in a state in which the needle is tilted from the second direction perpendicular to the substrate starting from the tip of the needle in the scanning direction of the tip of the needle or in the opposite direction to the scanning direction.

[0019] In this method for manufacturing an optical waveguide device, when the tip of the needle is scanned from one end side to the other end side of the cladding material in the first direction, the core material is discharged from the tip of the needle while scanning the tip of the needle so as to move in the second and third directions as well, thereby enabling the core material to be arranged three-dimensionally within the cladding material. Here, according to the study by the present inventors, the core material immediately after being discharged from the tip of the needle tends to rise slightly (i.e., move to the opposite side to the substrate in the second direction) due to the pressure difference occurring near the tip of the needle, and it was found that the cross-sectional shape of the core in a cross section perpendicular to the extension direction of the core after hardening depends on the degree of rise of the core material at this time. For example, when the tip of the needle is scanned with the needle standing vertically on the substrate, the top of the core material is rubbed by the tip of the needle as the core material rises immediately after being discharged, forming a localized depression in the cross-sectional shape of the core material. After that, the outer surface near the tip of the needle becomes an obstacle and the core material does not rise sufficiently, so the state in which the depression remains in the core material after being discharged is maintained. In this state, the core material is hardened to form a core having a cross-sectional shape with a localized depression. Therefore, the present inventors have found that it is effective to tilt the needle as described above when scanning the tip of the needle in order to eliminate the occurrence of such a depression. When the needle is tilted in this way, the core material after discharge is more likely to rise to a degree that eliminates the depression compared to when the needle is set vertically to the substrate, so that the formation of a depression in the cross-sectional shape of the core can be suppressed. Furthermore, the present inventors have found that by tilting the needle more greatly, the core material immediately after discharge is more likely to rise, and the cross-sectional shape of the core material is more likely to spread in the second direction. By utilizing this principle, it is possible to suppress the situation in which the core material after discharge is significantly deformed so as to spread in the third direction due to pressure from the substrate. In this way, in the above-mentioned method for manufacturing an optical waveguide device, the needle is tilted to suppress the collapse of the shape of the core material after discharge. As a result, the cross-sectional shape of the core after curing can be maintained in a uniform shape (specifically, a circular or elliptical shape) at each position along the extension direction of the core.This makes it possible to prevent an increase in optical connection loss between two optical waveguide components due to deformation of the cross-sectional shape of the core when optically connecting two optical waveguide components together via an optical waveguide device.

[0020] In the step of scanning the tip of the needle in the above-mentioned method for manufacturing an optical waveguide device, the core material may be discharged from the tip of the needle while the needle is tilted from the second direction in the direction opposite to the scanning direction with the tip of the needle as the starting point. In this case, the core material immediately after discharge can be more easily raised, so that the situation in which a depression remains in the core material after discharge can be more reliably prevented. As a result, it is possible to more reliably maintain a uniform cross-sectional shape of the core after hardening.

[0021] In the step of scanning the tip of the needle in the above-mentioned method for manufacturing an optical waveguide device, the inclination angle of the needle with respect to the second direction may be set to be larger as the height of the tip of the needle from the substrate in the second direction decreases. The cross-sectional shape of the core material after ejection tends to expand more in the third direction due to pressure from the substrate as it approaches the substrate in the second direction. Therefore, by setting the inclination angle of the needle to be larger as the height of the tip of the needle from the substrate decreases, it is possible to more reliably prevent the core material after ejection from being significantly deformed so as to expand in the third direction. As a result, it is possible to more reliably maintain the cross-sectional shape of the core after hardening in a uniform shape.

[0022] A method for manufacturing an optical waveguide device according to another embodiment of the present disclosure includes the steps of preparing a liquid core material and a clad material including an ultraviolet-curable resin composition containing a monomer, applying the clad material onto a substrate, inserting the tip of a needle into the clad material and scanning the tip of the needle while discharging the core material from the tip of the needle, and, after scanning the tip of the needle, removing the tip of the needle from the clad material and irradiating the clad material and the core material with ultraviolet light to harden them, thereby obtaining an optical waveguide device including a clad and a core. In the step of scanning the tip of the needle, the tip of the needle is scanned so as to move from one end side of the clad material to the other end side in a first direction along the substrate, in a second direction perpendicular to the substrate, and in a third direction along the substrate and perpendicular to the second direction. The outer surface of the needle facing in the opposite direction to the scanning direction of the needle includes an inclined surface that starts from the tip of the needle and inclines in the opposite direction from the second direction perpendicular to the substrate.

[0023] In this method for manufacturing an optical waveguide device, when the tip of the needle is scanned from one end side to the other end side of the cladding material in the first direction, the core material is discharged from the tip of the needle while scanning the tip of the needle so as to move in the second and third directions as well, thereby enabling the core material to be arranged three-dimensionally within the cladding material. Here, according to the study by the present inventors, the core material immediately after being discharged from the tip of the needle tends to rise slightly (i.e., move to the opposite side to the substrate in the second direction) due to the pressure difference occurring near the tip of the needle, and it was found that the cross-sectional shape of the core in a cross section perpendicular to the extension direction of the core after hardening depends on the degree of rise of the core material at this time. For example, when the tip of the needle is scanned with the needle standing vertically on the substrate, the top of the core material is rubbed by the tip of the needle as the core material rises immediately after being discharged, forming a localized depression in the cross-sectional shape of the core material. After that, the outer surface near the tip of the needle becomes an obstacle and the core material does not rise sufficiently, so the state in which the depression remains in the core material after being discharged is maintained. In this state, the core material is hardened to form a core having a cross-sectional shape with a localized depression. Therefore, the present inventors have found that it is effective to use a needle having an inclined surface as described above when scanning the tip of the needle in order to eliminate the occurrence of such a depression. When the needle has an inclined surface in this way, the core material after discharge is more likely to rise to a degree that eliminates the depression compared to when the needle does not have an inclined surface, so that the formation of a depression in the cross-sectional shape of the core can be suppressed. Furthermore, the present inventors have found that by increasing the inclination of the inclined surface of the needle, the core material immediately after discharge is more likely to rise, and the cross-sectional shape of the core material is more likely to spread in the second direction. By utilizing this principle, it is possible to suppress a situation in which the core material after discharge is significantly deformed so as to spread in the third direction due to pressure from the substrate. In this way, in the above-mentioned method for manufacturing an optical waveguide device, by using a needle having an inclined surface, it is possible to suppress a situation in which the shape of the core material after discharge collapses. As a result, the cross-sectional shape of the core after curing can be maintained in a uniform shape (specifically, a circular or elliptical shape) at each position along the extension direction of the core.This makes it possible to prevent an increase in optical connection loss between two optical waveguide components due to deformation of the cross-sectional shape of the core when optically connecting two optical waveguide components together via an optical waveguide device.

[0024] [Details of the embodiment of the present disclosure] Specific examples of optical waveguide devices and methods for manufacturing optical waveguide devices according to embodiments of the present disclosure will be described below with reference to the drawings. The present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims. In the following description, the same elements in the description of the drawings will be given the same reference numerals, and duplicate descriptions will be omitted as appropriate.

[0025] [First embodiment] FIG. 1 is a perspective view showing an optical waveguide device 1 according to a first embodiment. FIG. 2 is a plan view showing the optical waveguide device 1. FIG. 3 is a side view showing the optical waveguide device 1. In each drawing, an XYZ orthogonal coordinate system is shown for ease of understanding. The optical waveguide device 1 is used, for example, to optically connect two optical waveguide components having different core arrangements. The optical waveguide device 1 is disposed between the two optical waveguide components and optically connects the two optical waveguide components.

[0026] As shown in Fig. 1, the optical waveguide device 1 includes a clad 10 having a substantially rectangular parallelepiped appearance, and a plurality of (four in this embodiment) cores 20 surrounded by the clad 10. The clad 10 and the cores 20 include, for example, a hybrid material containing both an organic material and an inorganic material, an organic material, or an inorganic material. Examples of the organic material include acrylic, epoxy, and silicone. In this embodiment, the clad 10 and the cores 20 include a cured product of an ultraviolet-curable resin composition. A material having a higher refractive index than the clad 10 is selected as the material of the cores 20.

[0027] The cladding 10 has a first end face 11 and a second end face 12 aligned along the X-axis direction, and four side faces 13, 14, 15, and 16 extending along the X-axis direction between the first end face 11 and the second end face 12. The first end face 11 and the second end face 12 are, for example, planes along the YZ plane, and are arranged parallel to each other along the X-axis direction. The side face 13 and the side face 14 are, for example, planes along the XZ plane, and are arranged parallel to each other along the Y-axis direction. The side face 15 and the side face 16 are, for example, planes along the XZ plane, and are arranged parallel to each other along the Z-axis direction. The thickness of the cladding 10, i.e., the distance in the Z-axis direction between the side face 15 and the side face 16, is, for example, 0.05 mm or more and 3 mm or less.

[0028] The multiple cores 20 extend in the cladding 10 from the first end face 11 to the second end face 12. Each core 20 has a first core end face 21 exposed at the first end face 11 and a second core end face 22 exposed at the second end face 12. The first core end face 21 of each core 20 has, for example, a circular shape when viewed from the X-axis direction. The first core end face 21 of each core 20 is arranged so as to be point-symmetric with respect to a predetermined point on the first end face 11. In this embodiment, the first core end faces 21 of each core 20 are arranged in a row at equal intervals along the Y-axis direction on the first end face 11. The second core end face 22 of each core 20 has, for example, the same circular shape as the first core end face 21 when viewed from the X-axis direction. The second core end face 22 of each core 20 is arranged so as to be point-symmetric with respect to a predetermined point on the second end face 12. In this embodiment, the second core end faces 22 of each core 20 are arranged in two rows in the Z-axis direction on the second end face 12, with one row aligned along the Y-axis direction, and each second core end face 22 is, for example, arranged at equal intervals from each other.

[0029] As shown in FIG. 2, the second core end face 22 is disposed at a position shifted from the first core end face 21 as viewed from the X-axis direction. Specifically, the second core end face 22 is disposed at a height different from the height of the first end face 11 from the side surface 16 in the Z direction, and at a position different from the first core end face 21 in the Y-axis direction. That is, the second core end face 22 is disposed at a position shifted from the first core end face 21 in both the Y-axis direction and the Z-axis direction. In this way, since the position of the second core end face 22 is disposed at a position shifted three-dimensionally with respect to the first core end face 21, the core 20 extends three-dimensionally so as to move in the Y-axis direction and the Z-axis direction on the path from the first core end face 21 to the second core end face 22. The position of the first core end face 21 may be compared with the position of the second core end face 22 by comparing the center point of the first core end face 21 with the center point of the second core end face 22 as viewed from the X-axis direction.

[0030] The shape (cross-sectional shape) of the core 20 in a cross section perpendicular to the extension direction of the core 20 maintains a uniform circular shape at each position along the extension direction. In other words, the cross-sectional shape of each position of the core 20 from the first core end face 21 to the second core end face 22 has a constant circular shape. Hereinafter, when simply referring to the "cross-sectional shape of the core 20", it means the shape of the core 20 in a cross section perpendicular to the extension direction of the core 20. Hereinafter, the "circular shape" includes not only a perfect circular shape but also a circular shape close to a perfect circular shape. A circular shape close to a perfect circular shape refers to, for example, a state in which the aspect ratio of the circular shape is close to 1 in a cross section perpendicular to the extension direction of the core 20. The aspect ratio of the circular shape is the ratio of the width (diameter) of the circular shape in one direction (vertical direction) to the width (diameter) of the circular shape in the other direction (horizontal direction) perpendicular to the one direction. For example, when the cross section is a YZ cross section, the aspect ratio of the circle may be the ratio of the width of the circle in the Z axis direction to the width of the circle in the Y axis direction (for example, the width of the circle in the Z axis direction / the width of the circle in the Y axis direction).

[0031] The aspect ratio being close to 1 may be, for example, a state in which the aspect ratio is in the range of 0.9 to 1.1 (i.e., 1±0.1). The state in which the cross-sectional shape of the core 20 at each position along the extension direction maintains a uniform circular shape means that the aspect ratio of the cross-sectional shape of the core 20 at each position along the extension direction is close to 1 (for example, 0.9 to 1.1). Therefore, the cross-sectional shape of the core 20 at a certain position along the extension direction and the cross-sectional shape of the core 20 at another position along the extension direction do not need to have the exact same circular shape, and may be slightly different as long as they are circular shapes with an aspect ratio close to 1.

[0032] Next, a method for manufacturing the optical waveguide device 1 will be described with reference to Fig. 4 to Fig. 6. Fig. 4 is a perspective view showing a manufacturing process of the optical waveguide device 1. Fig. 5 is a perspective view showing a process subsequent to Fig. 4. Fig. 6 is a perspective view showing a process subsequent to Fig. 5.

[0033] First, a liquid cladding material 110 and a core material 120 are prepared, each of which includes an ultraviolet-curable resin composition containing a monomer and a photopolymerization initiator. A material having a higher refractive index than the cladding material 110 is selected as the core material 120. Next, as shown in FIG. 4, the cladding material 110 is applied onto a rectangular plate-shaped substrate 40. Specifically, the liquid cladding material 110 is poured into a rectangular frame 41 formed on the substrate 40. In order to make the thickness of the cladding material 110 in the frame 41 uniform, the cladding material 110 may be poured into the frame 41 using a microdispenser or the like. The substrate 40 is, for example, composed of the same material as the ferrule. That is, the substrate 40 is, for example, composed of a resin such as polyphenylene sulfide (PPS) filled with a glass filler.

[0034] Next, as shown in FIG. 5, the core material 120 is injected into the clad material 110 using a syringe 50. The syringe 50 contains the core material 120. A cylindrical needle 51 extending linearly is attached to the syringe 50. The core material 120 contained in the syringe 50 flows through the needle 51 and can be discharged to the outside from a tip 51a of the needle 51. When the core material 120 is injected into the clad material 110, the tip 51a of the needle 51 of the syringe 50 is inserted into the clad material 110. Then, while the tip 51a of the needle 51 is inserted into the clad material 110, the tip 51a of the needle 51 is scanned from one end 111 side to the other end 112 side of the clad material 110 in the X direction while discharging the core material 120 from the tip 51a of the needle 51. For example, the starting point of the scan of the tip 51 a of the needle 51 may be a position spaced apart from one end 111 of the clad material 110 , and the ending point of the scan of the tip 51 a of the needle 51 may be a position spaced apart from the other end 112 of the clad material 110 .

[0035] When the tip 51a of the needle 51 is scanned from the starting point to the end point, the tip 51a of the needle 51 is scanned so as to move in the Y direction and the Z direction on the path from the starting point to the end point of the scan. Therefore, the tip 51a of the needle 51 moves three-dimensionally not only in the horizontal direction (in the XY plane) but also in the height direction (Z direction). By injecting the core material 120 into the clad material 110 while scanning the tip 51a of the needle 51 in this manner, the three-dimensional core material 120 corresponding to the core 20 (see FIGS. 1 to 3) is arranged in the clad material 110. By repeatedly scanning the tip 51a of the needle 51 for each path corresponding to the multiple cores 20, the multiple core materials 120 corresponding to the multiple cores 20 are arranged in the clad material 110.

[0036] 6, the cladding material 110 and the core material 120 are irradiated with ultraviolet light L from an ultraviolet light source 60 to harden the cladding material 110 and the core material 120. Thereafter, the hardened cladding material 110 and the core material 120 are removed from the substrate 40, and one end 111 and the other end 112 of the cladding material 110 are cut off to expose both end faces of the core material 120 from the cladding material 110. In this way, an optical waveguide device 1 (see FIGS. 1 to 3) including a core 20 and a cladding 10 is obtained.

[0037] Here, the step of scanning the tip 51a of the needle 51 (the step shown in FIG. 5) will be described in more detail with further reference to FIG. 7 to FIG. 9. FIG. 7 is an XZ cross-sectional view showing how the core material 120 is discharged from the tip 51a of the needle 51 into the clad material 110 in the step shown in FIG. 5. In the following, a state in which the tip 51a of the needle 51 is scanned so as to move along the X-axis direction will be described as an example. In the following, the direction from one end 111 to the other end 112 of the clad material 110 in the X-axis direction (i.e., the scanning direction of the tip 51a of the needle 51) may be referred to as the front, and the direction from the other end 112 to one end 111 of the clad material 110 in the X-axis direction (i.e., the opposite direction to the scanning direction of the tip 51a of the needle 51) may be referred to as the rear. In addition, in the following, when referring to the "height" of a certain configuration, it means the height of that configuration from substrate 40 in the Z-axis direction, and the side of substrate 40 in the Z-axis direction may be referred to as the lower side, and the side opposite substrate 40 in the Z-axis direction may be referred to as the upper side.

[0038] In this embodiment, as shown in Fig. 7, when the tip 51a of the needle 51 is scanned, the core material 120 is discharged from the tip 51a of the needle 51 in a state in which the needle 51 is tilted forward or backward from the Z-axis direction perpendicular to the substrate 40 (i.e., the state in which the needle 51 is vertically erected on the substrate 40) with the tip 51a of the needle 51 as a starting point. The state in which the needle 51 is tilted forward or backward from the Z-axis direction perpendicular to the substrate 40 can also be rephrased as a state in which the center line CL of the needle 51 is tilted with respect to a reference line RL that passes through the tip 51a of the needle 51 and extends in the Z-axis direction when viewed from the Y-axis direction. In this case, the tilt angle of the needle 51 with respect to the Z-axis direction can be represented by the tilt angle θ of the center line CL of the needle 51 with respect to the reference line RL.

[0039] When the inclination angle θ of the reference line RL is defined as 0°, the rear side of the reference line RL is defined as positive, and the front side of the reference line RL is defined as negative, the inclination angle θ of the needle 51 when the needle 51 is inclined backward with respect to the reference line RL may be, for example, in a range greater than 0° and less than 90°. On the other hand, the inclination angle θ of the needle 51 when the needle 51 is inclined forward with respect to the reference line RL may be, for example, in a range greater than -90° and less than 0°. When the inclination angle θ of the needle 51 is defined in this way, the smaller the absolute value of the inclination angle θ, the smaller the inclination of the needle 51 with respect to the reference line RL. Conversely, the larger the absolute value of the inclination angle θ, the greater the inclination of the needle 51 with respect to the reference line RL.

[0040] The absolute value of the inclination angle θ may be set according to the height of the tip 51a of the needle 51. That is, the absolute value of the inclination angle θ when the tip 51a of the needle 51 is at a certain height (for example, a height near the substrate 40) may be set to be larger than the absolute value of the inclination angle θ when the tip 51a of the needle 51 is at a position higher than the certain height. Alternatively, the absolute value of the inclination angle θ may be set variably so as to gradually change according to the height of the tip 51a of the needle 51. That is, the absolute value of the inclination angle θ may be set to be larger as the height of the tip 51a of the needle 51 becomes lower, or may be set to be smaller as the height of the tip 51a of the needle 51 becomes higher.

[0041] In this embodiment, as shown in Figs. 5 and 7, a case where the needle 51 is tilted backward with respect to the reference line RL is illustrated. In this example, the inclination angle θ of the needle 51 is set constant at 20°. As shown in Fig. 7, the core material 120 after being discharged from the tip 51a of the needle 51 rises slightly behind the tip 51a of the needle 51, and then gradually descends and remains at a constant height. Thereafter, the core material 120 and the clad material 110 are irradiated with ultraviolet light L (see Fig. 6), thereby forming the core 20 and the clad 10. In this embodiment, the YZ cross-sectional shape of the core material 120 when it remains at a constant height is maintained in a uniform circular shape, and the YZ cross-sectional shape of the core 20 after hardening is also maintained in a uniform circular shape.

[0042] 8(a), 8(b), and 8(c) show the results of simulating the flow of the core material 120 after it is discharged from the tip 51a of the needle 51 using general-purpose fluid analysis software. FIG. 8(a) shows the simulation result of the YZ cross-sectional shape of the core material 120 at the position a1 shown in FIG. 7. FIG. 8(b) shows the simulation result of the YZ cross-sectional shape of the core material 120 at the position b1 shown in FIG. 7. FIG. 8(c) shows the simulation result of the YZ cross-sectional shape of the core material 120 at the position c1 shown in FIG. 7. In FIG. 7, the position a1 indicates the position of the rear end of the tip surface 51b (see FIG. 7) located at the tip 51a of the needle 51. The position b1 indicates a position shifted 0.1 mm backward from the reference line RL. The position c1 indicates a position shifted 9 mm backward from the reference line RL.

[0043] The core material 120 immediately after being discharged from the tip 51a of the needle 51 rises slightly upward due to a pressure difference occurring near the tip 51a of the needle 51. At this time, at the position a1 shown in FIG. 7, the upper part of the core material 120 is rubbed against the tip 51a of the needle 51. As a result, as shown in FIG. 8(a), a depression 120a is formed in the upper part of the core material 120. Thereafter, the core material 120 further rises from the position a1 to the position b1 shown in FIG. 7. At this time, as shown in FIG. 8(b), the core material 120 rises sufficiently to the extent that the depression 120a is eliminated, and the YZ cross section of the core material 120 becomes a circle without the depression 120a. Thereafter, even when the core material 120 reaches the position c1 from the position b1 shown in FIG. 7, the YZ cross section of the core material 120 similarly maintains a circle without the depression 120a. 8(c) is an enlarged view of the YZ cross section of the core material 120. In this manner, in this embodiment, the YZ cross section of the core material 120 is maintained in a circular shape.

[0044] The effects achieved by the optical waveguide device 1 and the manufacturing method of the optical waveguide device 1 according to the present embodiment described above will be described together with the problems of a comparative example. FIG. 18 is a perspective view showing a manufacturing process of an optical waveguide device according to the comparative example. FIG. 18 shows a process of scanning the tip 51a of the needle 51. FIG. 19 is an XZ cross-sectional view showing a state in which the core material 320 is discharged from the tip 51a of the needle 51 into the clad material 310 in the process shown in FIG. 18. In the comparative example, unlike the present embodiment, when scanning the tip 51a of the needle 51, the tip 51a of the needle 51 is moved from a start point on one end 311 side of the clad material 310 to an end point on the other end 312 side while discharging the core material 320 from the tip 51a of the needle 51 in a state in which the needle 51 is vertically erected on the substrate 40 (i.e., a state in which the center line CL of the needle 51 extends in the Z-axis direction).

[0045] 20(a), 20(b), and 20(c) show the results of simulating the flow of the core material 320 after it is discharged from the tip 51a of the needle 51 in the process shown in FIG. 19. FIG. 20(a) shows the simulation result showing the cross-sectional shape of the core material 320 at the position a10 shown in FIG. 19. FIG. 20(b) shows the simulation result showing the cross-sectional shape of the core material 320 at the position b10 shown in FIG. 19. FIG. 20(c) shows the simulation result showing the cross-sectional shape of the core material 320 at the position c10 shown in FIG. 19. In FIG. 19, the position a10 shows the position of the rear end of the tip surface 51b located at the tip 51a of the needle 51. The position b10 shows the position shifted 0.1 mm backward from the position of the center line CL shown in FIG. 19. The position c10 shows the position shifted 9 mm backward from the position of the center line CL shown in FIG.

[0046] As shown in (a) of FIG. 20, the core material 320 immediately after being discharged from the tip 51a of the needle 51 has an upper portion rubbed against the tip 51a of the needle 51, forming a depression 320a in the upper portion of the core material 320, as in the present embodiment. After that, the core material 320 rises slightly and reaches a position b10 shown in FIG. 19. At this time, as shown in (b) of FIG. 20, unlike the present embodiment, it can be seen that a depression 320a remains in the upper portion of the core material 320. As in the comparative example, when the core material 320 is discharged from the tip 51a of the needle 51 while the needle 51 is vertically erected on the substrate 40, the outer surface near the tip 51a of the needle 51 becomes an obstacle, and the core material 320 cannot rise sufficiently to eliminate the depression 320a. As a result, as shown in FIG. 20(c), even when the core material 320 reaches the position c10, the state in which the depression 320a remains in the core material 320 is similarly maintained.

[0047] When the core material 320 is located at position c10, the depression 320a formed in the core material 320 is smaller than when the core material 320 is located at positions a10 and b10. This is because the surface tension acts on the core material 320, causing the cross-sectional shape of the core material 320 to converge into a circular shape. However, during the period until the core material 320 is hardened, the depression 320a of the core material 320 cannot be eliminated, and the depression 320a remains in the core material 320. Part E shown in (c) of FIG. 20 is an enlarged view of the YZ cross section of the core material 320, and part F shown in (c) of FIG. 20 is an enlarged view of the YZ cross section of the core 220 obtained by an experiment. From the results of parts E and F shown in (c) of FIG. 20, it can be seen that the core material 320 is hardened in a state in which the depression 320a remains in the core material 320, and thus the core 220 having the YZ cross-sectional shape in which the depression 220a is formed is formed.

[0048] FIG. 21 shows an experimental result indicating that the YZ cross-sectional shape of the core 220 according to the comparative example changes depending on the height of the core 220 from the substrate 40. The height of the core 220 here corresponds to the height of the tip 51a of the needle 51 in the manufacturing process of the core 220. Part H1 of FIG. 21 shows the YZ cross-sectional shape of the core 220 when the height of the core 220 is 0.10 mm. Part H2 of FIG. 21 shows the YZ cross-sectional shape of the core 220 when the height of the core 220 is 0.15 mm. Part H3 of FIG. 21 shows the YZ cross-sectional shape of the core 220 when the height of the core 220 is 0.20 mm. Part H4 of FIG. 21 shows the YZ cross-sectional shape of the core 220 when the height of the core 220 is 0.25 mm.

[0049] As shown in parts H1 to H4 of FIG. 21, it can be seen that the YZ cross-sectional shape of the core 220 cannot maintain a circular shape at any height of the core 220, but is deformed into an elliptical shape spreading in the horizontal direction (Y-axis direction). Furthermore, as shown in part H4 of FIG. 21, when the height of the core 220 is low (i.e., when the core 220 is located near the substrate 40), it can be seen that the core 220 is greatly deformed so as to spread widely in the horizontal direction. When the core 220 is formed at such a height, the tip 51a of the needle 51 that discharges the core material 320 needs to be disposed near the substrate 40. In this case, the core material 320 discharged from the tip 51a of the needle 51 is likely to spread widely in the horizontal direction due to pressure from the substrate 40. In this way, the core material 320 deformed in this state is hardened, and thus the core 220 having the YZ cross-sectional shape spreading in the horizontal direction is formed. In this way, in the comparative example, the YZ cross-sectional shape of the core material 320 cannot be maintained as a uniform circle in the manufacturing process of the optical waveguide device 1, and therefore the YZ cross-sectional shape of the hardened core 220 cannot be maintained as a uniform circle either. If the cross-sectional shape of the core 220 is deformed in this way, there is a risk that the optical connection loss between the two optical waveguide components will increase when the two optical waveguide components are optically connected to each other via the optical waveguide device.

[0050] In response to this problem, the present inventors have investigated the cause of the collapse of the cross-sectional shape of the core material, and have found that the cross-sectional shape of the core material is determined depending on the degree of rise of the core material immediately after discharge. When the core material rises immediately after discharge, the top (upper part) of the core material is rubbed by the tip surface 51b of the needle 51, and a local depression is formed in the cross-sectional shape of the core material. Here, when the tip 51a of the needle 51 is scanned in a state where the needle 51 is vertically erected as in the comparative example, the outer surface near the tip 51a of the needle 51 is an obstacle and the core material 320 cannot rise sufficiently, so that the state in which the depression 320a remains in the core material 320 is maintained. When the core material 320 hardens in this state, a core 220 having a cross-sectional shape in which a local depression 220a is formed is formed. Therefore, the present inventors have found that in order to eliminate the occurrence of such a depression, it is effective to tilt the needle 51 as described above when scanning the tip 51a of the needle 51. When the needle 51 is tilted in this manner, the core material 120 after ejection is more likely to rise sufficiently to eliminate the depression compared to when the needle 51 is placed perpendicular to the substrate 40, thereby preventing the formation of a depression in the cross-sectional shape of the core 20.

[0051] Furthermore, the inventors have found that by inclining the needle 51 more, the core material 120 immediately after being discharged is more likely to rise, and the cross-sectional shape of the core material 120 is more likely to spread in the vertical direction (Z-axis direction). By utilizing this principle, it is possible to prevent the core material 120 after being discharged from being significantly deformed so as to spread in the horizontal direction (Y-axis direction) due to pressure from the substrate 40. That is, the cross-sectional shape of the core material 120 can be corrected to a circular shape so as not to spread in the horizontal direction. In this way, in the manufacturing method of the optical waveguide device 1, by inclining the needle 51, it is possible to prevent the shape of the core material 120 after being discharged from collapsing. That is, the cross-sectional shape of the core material 120 can be maintained in a uniform circular shape in the section from the start point to the end point of the scan of the tip 51a of the needle 51. By hardening the core material 120 in this state, the cross-sectional shape of the hardened core 20 can be maintained in a uniform circular shape at each position along the extension direction of the core 20. More specifically, regardless of the height of the core 20 from the side surface 16 (the depth of the core 20 from the side surface 15), that is, regardless of the height of the tip 51a of the needle 51 from the substrate 40, the core 20 can be formed while maintaining a uniform circular shape. For example, even when the tip 51a of the needle 51 is scanned in the vicinity of the substrate 40, it is possible to form the core 20 while maintaining a uniform circular shape. As a result, when two optical waveguide components are optically connected to each other via the optical waveguide device 1, it is possible to suppress a situation in which the optical connection loss between the two optical waveguide components increases due to the collapse of the cross-sectional shape of the core 20.

[0052] In this embodiment, the cross-sectional shape of the core 20 maintains a uniform circular shape at each position of the core 20 along the extension direction, so that the cross-sectional shape of the core 20 can be made to match the cross-sectional shapes of the cores of the two optical waveguide components to be connected. This makes it possible to more reliably suppress the situation in which the optical connection loss between the two optical waveguide components increases.

[0053] In this embodiment, the first core end faces 21 of each core 20 are arranged in a line along the Y-axis direction on the first end face 11, and the second core end faces 22 of each core 20 are arranged in a plurality of rows along the Y-axis direction on the second end face 12 in the Z-axis direction. This can prevent an increase in optical connection loss when connecting two optical waveguide components having different core arrangements. The first core end faces 21 of each core 20 do not need to be arranged in a line, and may be arranged in a plurality of rows along the Y-axis direction on the first end face 11 in the Z-axis direction, similar to the second core end face 22. In this case, the vertical position of the core 20 (i.e., the position of the core 20 in the Z-axis direction) changes on the way from the first end face 11 to the second end face 12, so that the arrangement of the first core end face 21 on the first end face 11 and the arrangement of the second core end face 22 on the second end face 12 may be vertically interchanged. For example, the core 20 may have a configuration in which the first core end face 21 is located in a lower layer (i.e., a layer on the side surface 16 side of the cladding 10) at the first end face 11, while the second core end face 22 is located in an upper layer (i.e., a layer on the side surface 15 side) at the second end face 12. Alternatively, the core 20 may have a configuration in which the first core end face 21 is located in an upper layer at the first end face 11, while the second core end face 22 is located in a lower layer at the second end face 12.

[0054] In this embodiment, when the tip 51a of the needle 51 is scanned, the needle 51 is tilted backward from the reference line RL, and the core material 120 is discharged from the tip 51a of the needle 51. This makes it easier to raise the core material 120 immediately after discharge, and more reliably prevents depressions from remaining in the discharged core material 120. As a result, it becomes possible to more reliably maintain the cross-sectional shape of the hardened core 20 in a uniform shape.

[0055] In this embodiment, when scanning the tip 51a of the needle 51, the inclination angle θ of the needle 51 may be set to be larger as the height of the tip 51a of the needle 51 becomes lower. As described above, the cross-sectional shape of the core material 120 after discharge tends to be expanded in the Y-axis direction by receiving pressure from the substrate 40 as it approaches the substrate 40 in the Z-axis direction. Therefore, by setting the inclination angle θ of the needle 51 to be larger as the height of the tip 51a of the needle 51 becomes lower, it is possible to more reliably prevent the core material 120 after discharge from being significantly deformed so as to expand in the Y-axis direction. As a result, it is possible to more reliably maintain the cross-sectional shape of the core 20 after hardening in a uniform shape.

[0056] In the above embodiment, the inclination angle θ of the needle 51 is set to 20°, but the inclination angle θ may be set to another angle. For example, when the height of the tip 51a of the needle 51 is relatively high, the inclination angle θ of the needle 51 may be set to a small angle, such as 10°. FIG. 9 is a simulation result showing the YZ cross-sectional shape of the core material 120 at the position c1 shown in FIG. 7 when the inclination angle θ is set to 10°. Part B of FIG. 9 is an enlarged view of the YZ cross-sectional shape of the core material 120. As shown in FIG. 9, it can be seen that the YZ cross-section of the core material 120 after ejection maintains a circular shape without a depression, as in the above embodiment. Therefore, even when the inclination angle θ is set to 10°, the cross-sectional shape of the core material 120 can be maintained in a uniform circular shape in the section from the start point to the end point of the scan of the tip 51a of the needle 51. By hardening the core material 120 in this state, the cross-sectional shape of the hardened core 20 can be maintained in a uniform circular shape at each position along the extension direction of the core 20. In other words, even with this configuration, the same effects as those of the above-mentioned embodiment can be obtained.

[0057] In the above-described embodiment, the needle 51 is inclined backward with respect to the reference line RL, but the needle 51 may be inclined forward with respect to the reference line RL. FIG. 10 is a perspective view showing a manufacturing process of the optical waveguide device 1 according to a modified example of the above-described embodiment. FIG. 11 is a cross-sectional view showing a state in which the core material 120 is discharged from the tip 51a of the needle 51 into the cladding material 110 in the process shown in FIG. 10. As shown in FIG. 11, the center line CL of the needle 51 may be inclined forward with respect to the reference line RL. In this case, the inclination angle θ of the needle 51 may be in a range greater than -90° and smaller than 0°, for example. In this modified example, the inclination angle θ of the needle 51 is set to a constant value of -20°. In this modified example, the inclination angle θ of the needle 51 may be set to an angle other than -20°, and the absolute value of the inclination angle θ may be set to be variable so as to gradually change depending on the height of the tip 51a of the needle 51.

[0058] FIG. 12(a) is a simulation result showing the cross-sectional shape of the core material 120 at position a2 shown in FIG. 11. FIG. 12(b) is a simulation result showing the cross-sectional shape of the core material 120 at position b2 shown in FIG. 11. FIG. 12(c) is a simulation result showing the cross-sectional shape of the core material 120 at position c2 shown in FIG. 11. In FIG. 11, position a2 indicates the position of the rear end of the tip surface 51b located at the tip 51a of the needle 51. Position b2 indicates a position shifted 0.1 mm rearward from the reference line RL. Position c2 indicates a position shifted 9 mm rearward from the reference line RL.

[0059] When the needle 51 is tilted forward with respect to the reference line RL, the tip surface 51b of the needle 51 is tilted from the horizontal direction (XY plane). Specifically, the tip surface 51b is tilted so as to be located rearward as it moves upward. Accordingly, the core material 120 immediately after being discharged from the tip 51a of the needle 51 is easily able to rise sufficiently along the inclination of the tip surface 51b. When the tip surface 51b is tilted in this manner, the upper part of the core material 120 is rubbed against the tip surface 51b of the needle 51, so that a flat part 120b is formed on the upper part of the core material 120 as shown in (a) of FIG. 12. Thereafter, the core material 120 gradually descends from position a2 to position b2 shown in FIG. 11. At this time, the flat part 120b of the core material 120 is gradually eliminated due to the action of surface tension. When the core material 120 reaches position b2, a small amount of flat portion 120b remains on the upper portion of the core material 120, but when the core material 120 reaches position c2, the flat portion 120b of the core material 120 disappears, and the YZ cross-sectional shape of the core material 120 maintains a circular shape without the flat portion 120b. Part C shown in (c) of FIG. 12 is an enlarged view of the YZ cross-section of the core material 120.

[0060] Therefore, in this modification as well, the cross-sectional shape of the core material 120 can be maintained in a uniform circular shape in the section from the start point to the end point of the scan of the tip 51a of the needle 51. By hardening the core material 120 in this state, the cross-sectional shape of the hardened core 20 can be maintained in a uniform circular shape at each position along the extension direction of the core 20. Therefore, according to this modification, the same effects as those of the above-mentioned embodiment can be obtained.

[0061] In the above-described embodiment, the cross-sectional shape of the core 20 is uniformly circular at each position along the extension direction of the core 20, but the cross-sectional shape of the core 20 may be uniformly elliptical at each position along the extension direction of the core 20. FIG. 13 is a perspective view showing an optical waveguide device 1A according to a modification of the above-described embodiment. In the example shown in FIG. 13, the cross section of the core 20A maintains a uniform elliptical shape at each position along the extension direction of the core 20A. In other words, the cross-sectional shape of the core 20A at each position from the first core end face 21 to the second core end face 22 has a constant elliptical shape. The "elliptical shape" here includes not only an ideal elliptical shape, but also an elliptical shape close to the ideal elliptical shape. The ideal elliptical shape refers to an elliptical shape when the aspect ratio of the elliptical shape is a target ideal value when the aspect ratio is specified in a cross section perpendicular to the extension direction of the core 20A.

[0062] The aspect ratio of the ellipse here is the ratio between the width of the ellipse in the longitudinal direction (Z-axis direction) and the width of the ellipse in the lateral direction (Y-axis direction) (for example, the width of the ellipse in the Z-axis direction / the width of the ellipse in the Y-axis direction). Close to an ideal ellipse means that the aspect ratio is close to the ideal value, for example, the aspect ratio is within the range of the ideal value ±0.1. Therefore, the state in which the cross-sectional shape of the core 20A at each position along the extension direction maintains a uniform elliptical shape means that the aspect ratio of the cross-sectional shape of the core 20A at each position along the extension direction is close to the ideal value (for example, the ideal value ±0.1). Therefore, the cross-sectional shape of the core 20A at a certain position along the extension direction and the cross-sectional shape of the core 20A at another position along the extension direction do not need to have the same elliptical shape in the strict sense, and may be slightly different as long as the aspect ratio is close to the ideal value.

[0063] In the example shown in FIG. 13, the cross-sectional shape of the core 20A is maintained as an ellipse with the Z-axis direction as the longitudinal direction (i.e., an ellipse spreading in the vertical direction). In order to form such a core 20A, in the process of scanning the tip 51a of the needle 51, the absolute value of the inclination angle θ (see FIG. 7) of the needle 51 may be set to be larger than that of the above-mentioned embodiment. As described above, by increasing the absolute value of the inclination angle θ of the needle 51, the core material 120 immediately after discharge is more likely to rise, and the cross-sectional shape of the core material 120 is more likely to spread in the horizontal direction (Y-axis direction). By utilizing this principle, the cross-sectional shape of the core material 120 can be corrected to a uniform ellipse spreading in the vertical direction in the section from the start point to the end point of the scanning of the tip 51a of the needle 51. By hardening the core material 120 in this state, the cross-sectional shape of the hardened core 20A can be maintained as a uniform ellipse spreading in the vertical direction at each position along the extension direction of the core 20A.

[0064] Conversely, by reducing the absolute value of the inclination angle θ of the needle 51, the cross-sectional shape of the core 20A can be maintained as an ellipse with the Y-axis direction as the longitudinal direction (i.e., an ellipse spreading in the horizontal direction). As described above, when the tip 51a of the needle 51 that discharges the core material 120 is disposed in the vicinity of the substrate 40, the core material 120 discharged from the tip 51a of the needle 51 is likely to spread widely in the horizontal direction due to pressure from the substrate 40. By utilizing this principle, the absolute value of the inclination angle θ of the needle 51 can be intentionally reduced to maintain the cross-sectional shape of the core material 120 as a uniform ellipse spreading in the horizontal direction in the section from the start point to the end point of the scanning of the tip 51a of the needle 51. By hardening the core material 120 in this state, the cross-sectional shape of the hardened core 20A can be maintained as a uniform ellipse spreading in the horizontal direction at each position along the extension direction of the core 20A. In this way, if the cross-sectional shape of core 20A can be maintained as a uniform elliptical shape at each position along the extension direction of core 20A, it is possible to guide light within core 20A while maintaining the polarization of the light.

[0065] [Second embodiment] Next, a second embodiment of the present disclosure will be described. In the second embodiment, unlike the first embodiment, in the step of scanning the tip 51a of the needle 51A of the syringe 50A, the needle 51A is vertically erected on the substrate 40, and the core material 120 is discharged from the tip 51a of the needle 51A. However, in the second embodiment, the needle 51A having a tapered surface 51c (inclined surface) near the tip 51a is used. Below, the differences from the first embodiment will be mainly described.

[0066] FIG. 14 is a perspective view showing a manufacturing process of an optical waveguide device according to the second embodiment. FIG. 15 is a cross-sectional view showing a state in which the core material 120 is discharged from the tip 51a of the needle 51A into the cladding material 110 in the process shown in FIG. 14. In this embodiment, as shown in FIG. 14 and FIG. 15, when the tip 51a of the needle 51A is scanned, the core material 120 is discharged from the tip 51a of the needle 51A in a state in which the needle 51A is vertically erected on the substrate 40, that is, in a state in which the center line CL of the needle 51A extends in the Z-axis direction. Here, as shown in FIG. 15, the needle 51A has a tapered surface 51c near the tip 51a. The tapered surface 51c constitutes the side surface (outer surface) of the needle 51A, and is inclined so as to gradually expand in diameter as it moves upward from the tip surface 51b located at the tip 51a of the needle 51A. As a result, the rear tapered surface 51c is an inclined surface that slopes rearward from the Z-axis direction, starting from the tip 51a of the needle 51A.

[0067] The inclination angle of the tapered surface 51c can be expressed by the inclination angle θ of the tapered surface 51c with respect to the center line CL of the needle 51A when viewed from the Y-axis direction. When the inclination angle θ of the center line CL is defined as 0°, the inclination angle θ of the tapered surface 51c may be, for example, in a range greater than 0° and less than 90°. The inclination angle θ may be set, for example, according to the height of the tip 51a of the needle 51A. That is, the inclination angle θ when the tip 51a of the needle 51A is at a certain height (for example, a height near the substrate 40) may be set to be greater than the inclination angle θ when the tip 51a of the needle 51A is at a position higher than the certain height. In this embodiment, the inclination angle θ of the tapered surface 51c is set to 20°. As shown in FIG. 15, the core material 120 after being discharged from the tip 51a of the needle 51A rises slightly behind the tip 51a of the needle 51A, and then gradually falls and remains at a constant height. The YZ cross-sectional shape of the core material 120 when it remains at a constant height is maintained in a circular shape, and the YZ cross-sectional shape of the core 20 after hardening is also maintained in a uniform circular shape.

[0068] 16(a), 16(b), and 16(c) show the results of simulating the flow of the core material 120 after it is discharged from the tip 51a of the needle 51A using general-purpose fluid analysis software. FIG. 16(a) shows the simulation result showing the cross-sectional shape of the core material 120 at the position a3 shown in FIG. 15. FIG. 16(b) shows the simulation result showing the cross-sectional shape of the core material 120 at the position b3 shown in FIG. 15. FIG. 16(c) shows the simulation result showing the cross-sectional shape of the core material 120 at the position c3 shown in FIG. 15. In FIG. 15, the position a3 indicates the position of the rear end of the tip surface 51b of the needle 51A. The position b3 indicates a position shifted 0.1 mm rearward from the center line CL. The position c3 indicates a position shifted 9 mm rearward from the center line CL.

[0069] The core material 120 immediately after being discharged from the tip 51a of the needle 51A rises slightly upward due to a pressure difference occurring near the tip 51a of the needle 51A. At this time, at the position a3 shown in FIG. 15, the upper part of the core material 120 is rubbed against the tip 51a of the needle 51A. As a result, as shown in FIG. 16(a), a depression 120a is formed in the upper part of the core material 120. Thereafter, the core material 120 further rises from the position a3 shown in FIG. 15 to the position b3. At this time, as shown in FIG. 16(b), the core material 120 rises sufficiently to the extent that the depression 120a is eliminated, and the YZ cross section of the core material 120 becomes a circle without the depression 120a. Thereafter, even when the core material 120 reaches the position c3 from the position b3 shown in FIG. 15, the YZ cross section of the core material 120 similarly maintains a circle without the depression 120a. 16(c) is an enlarged view of the YZ cross section of the core material 120. FIG.

[0070] The effects of the optical waveguide device and the manufacturing method of the optical waveguide device according to the present embodiment described above will be described. When the tip 51a of the needle 51 is scanned while the needle 51 is vertically erected on the substrate 40 as in the comparative example described above, the upper part of the core material 320 is rubbed by the tip 51a of the needle 51 when the core material 320 rises immediately after being discharged, and a local depression 320a is formed in the cross-sectional shape of the core material 320 (see Figs. 18 to 21). After that, the outer surface near the tip 51a of the needle 51 prevents the core material 320 from rising sufficiently, so that the state in which the depression 320a remains in the core material 320 after being discharged is maintained. In this state, the core material 320 is hardened to form a core 220 having a cross-sectional shape in which the local depression 320a is formed. Therefore, the present inventors have found that it is effective to use the needle 51A having the tapered surface 51c described above in order to eliminate the occurrence of such a depression 320a. When the needle 51A has a tapered surface 51c, the core material 120 after ejection is more likely to rise sufficiently to eliminate the depression compared to when the needle 51 does not have a tapered surface 51c, thereby preventing the formation of a depression in the cross-sectional shape of the core 20.

[0071] Furthermore, the inventors have found that by increasing the inclination angle θ of the tapered surface 51c of the needle 51A, the core material 120 immediately after being discharged is more likely to rise, and the cross-sectional shape of the core material 120 is more likely to spread in the vertical direction (Z-axis direction). By utilizing this principle, it is possible to prevent the core material 120 after being discharged from being significantly deformed so as to spread in the horizontal direction (Y-axis direction) due to pressure from the substrate 40. In this way, in the method for manufacturing an optical waveguide device according to this embodiment, by using the needle 51A having the tapered surface 51c, it is possible to prevent the shape of the core material 120 after being discharged from collapsing. As a result, the cross-sectional shape of the core 20 after hardening can be maintained in a uniform circular shape at each position along the extension direction of the core 20. More specifically, regardless of the height of the core 20 from the side surface 16 (the depth of the core 20 from the side surface 15), that is, regardless of the height of the tip 51a of the needle 51A from the substrate 40, the core 20 can be formed while maintaining a uniform circular shape. For example, it is possible to form the core 20 while maintaining a uniform circular shape even when the tip 51a of the needle 51A is scanned in the vicinity of the substrate 40. As a result, it is possible to suppress a situation in which the optical connection loss between the two optical waveguide components increases due to the deformation of the cross-sectional shape of the core 20 when optically connecting two optical waveguide components to each other via an optical waveguide device.

[0072] FIG. 17 is a graph showing the relationship between the cross-sectional shape of the core and the height of the tip of the needle. The horizontal axis of FIG. 17 shows the aspect ratio of the cross-sectional shape of the core (specifically, the width in the Z-axis direction of the circle / the width in the Y-axis direction). The vertical axis of FIG. 17 shows the height (mm) of the tip of the needle from the substrate 40. When the aspect ratio is 1, it means that the cross-sectional shape of the core is a perfect circle. When the aspect ratio is greater than 1, it means that the cross-sectional shape of the core is an ellipse whose longitudinal direction is the Z-axis direction (i.e., spreads in the vertical direction). When the aspect ratio is less than 1, it means that the cross-sectional shape of the core is an ellipse whose longitudinal direction is the Y-axis direction (i.e., spreads in the horizontal direction). Graph G11 shows the simulation results when a needle 51 without a tapered surface 51c is used. Graph G12 shows the simulation results when the inclination angle θ of the tapered surface 51c of the needle 51A is 10°. Graph G13 shows the simulation results when the inclination angle θ of the tapered surface 51c of the needle 51A is 20°. Plot P11 shows the experimental results when a needle 51 without a tapered surface 51c is used. Plot P12 shows the experimental results when the inclination angle θ of the tapered surface 51c of the needle 51A is 10°. All of the data shown in FIG. 17 show the results when the needle is placed perpendicular to the substrate 40 and scanned.

[0073] As shown in FIG. 17, the lower the height of the tip of the needle, the smaller the aspect ratio. That is, the closer the tip of the needle is to the substrate 40, the more likely the cross-sectional shape of the core is to be widened in the horizontal direction (Y-axis direction). On the other hand, when the height of the tip of the needle reaches a certain height (for example, 0.25 mm or more), the change in the aspect ratio becomes small. And, compared with the case where the needle 51 without the tapered surface 51c is used (see graphs G11 and plot P11), the aspect ratio is larger when the needle 51A with the tapered surface 51c is used (see graphs G12, G13, and plot P12). That is, by using the needle 51A with the tapered surface 51c, the cross-sectional shape of the core 20 is more likely to be widened in the vertical direction (Z-axis direction). Furthermore, by increasing the inclination angle θ of the tapered surface 51c, the cross-sectional shape of the core 20 is more likely to be widened in the vertical direction.

[0074] Therefore, it is possible to adjust the cross-sectional shape of the core 20 by adjusting the inclination angle θ of the tapered surface 51c according to the height of the tip 51a of the needle 51A. For example, when the height of the tip 51a of the needle 51A is 0.125 mm, the aspect ratio of the cross-sectional shape of the core 20 can be made close to 1 by setting the inclination angle θ of the tapered surface 51c to 20°. When the height of the tip 51a of the needle 51A is 0.2 mm, the aspect ratio of the cross-sectional shape of the core 20 can be made close to 1 by setting the inclination angle θ of the tapered surface 51c to 10°. In the first embodiment, when the absolute value of the inclination angle θ of the needle 51 with respect to the reference line RL (see FIG. 7) is set to a constant 10°, the same result as that of the graph G12 is obtained, and when the absolute value of the inclination angle θ of the needle 51 with respect to the reference line RL is set to a constant 20°, the same result as that of the graph G13 is obtained.

[0075] The optical waveguide device and the manufacturing method of the optical waveguide device of the present disclosure are not limited to the above-mentioned embodiments and modifications, and various other modifications are possible. For example, the above-mentioned embodiments and modifications may be combined with each other according to the required purpose and effect. For example, the needle 51A having the tapered surface 51c may be tilted from a state where it is vertically erected on the substrate 40, or the needle 51A having the tapered surface 51c may be used to maintain the cross-sectional shape of the core material 120 in a uniform elliptical shape in the section from the start point to the end point of the scanning of the tip 51a of the needle 51. In addition, in the above-mentioned embodiments and modifications, the optical waveguide device 1 is described as having four cores 20, but the number of cores 20 is not particularly limited. The number of cores 20 may be one or four or more. In addition, the arrangement of the cores 20 is not limited to the above-mentioned embodiments and modifications, and can be appropriately changed. [Explanation of symbols]

[0076] 1,1A...Optical waveguide device 10. Clad 11...First end surface 12…Second end surface 13,14,15,16…Side 20,20A…Core 21…First core end face 22…Second core end face 40…Substrate 41…Frame 50,50A…Syringe 51,51A…Needle 51a...Tip 51b…Tip surface 51c...Tapered surface (inclined surface) 60...UV light source 110...Clad material 111...one end 112...other end 120…Core material 120a…Depression 120b…Flat area 220…Core 310...Clad materials 320…Core material 320a…depression a1, a2, a3, a10…positions b1, b2, b3, b10…positions c1, c2, c3, c10…positions CL…center line L…ultraviolet ray RL…reference line θ…tilt angle

Claims

1. A step of preparing a liquid core material and a liquid clad material each including an ultraviolet-curable resin composition containing a monomer; applying the cladding material onto a substrate; a step of inserting a tip of a needle into the interior of the cladding material and scanning the tip of the needle while discharging the core material from the tip of the needle; and a step of extracting the tip of the needle from the cladding material after scanning the tip of the needle, and irradiating the cladding material and the core material with ultraviolet light to cure them, thereby obtaining an optical waveguide device having a cladding and a core comprising a cured product of the ultraviolet curable resin composition, In the step of scanning the tip of the needle, the tip of the needle is scanned so as to move from one end side to the other end side of the cladding material in a first direction along the substrate, in a second direction perpendicular to the substrate, and in a third direction along the substrate and perpendicular to the second direction; When scanning the tip of the needle, the core material is ejected from the tip of the needle in a state in which the needle is tilted from a second direction perpendicular to the substrate to a scanning direction of the tip of the needle or a direction opposite to the scanning direction, with the tip of the needle as a starting point; the cladding has a first end face, a second end face aligned with the first end face in the first direction, and a side face extending in the first direction between the first end face and the second end face, the core has a first core end face exposed at the first end face and a second core end face exposed at the second end face, and extends within the cladding from the first core end face to the second core end face; the second core end face has a height different from a height of the first core end face from the side face in the second direction perpendicular to the side face, and is disposed at a position shifted from the first core end face in the third direction along the side face and perpendicular to the second direction, The shape of the core in a cross section perpendicular to the extension direction of the core maintains a uniform circular or elliptical shape at each position of the core along the extension direction. A method for manufacturing an optical waveguide device.

2. 2. The method for manufacturing an optical waveguide device according to claim 1, wherein in the step of scanning the tip of the needle, the core material is ejected from the tip of the needle while tilting the needle from the second direction in a direction opposite to the scanning direction, with the tip of the needle as a starting point.

3. 3. The method for manufacturing an optical waveguide device according to claim 1, wherein in the step of scanning the tip of the needle, the inclination angle of the needle with respect to the second direction is set to increase as the height of the tip of the needle from the substrate in the second direction decreases.

4. A step of preparing a liquid core material and a liquid clad material each including an ultraviolet-curable resin composition containing a monomer; applying the cladding material onto a substrate; a step of inserting a tip of a needle into the interior of the cladding material and scanning the tip of the needle while discharging the core material from the tip of the needle; and a step of extracting the tip of the needle from the cladding material after scanning the tip of the needle, and irradiating the cladding material and the core material with ultraviolet light to cure them, thereby obtaining an optical waveguide device having a cladding and a core comprising a cured product of the ultraviolet curable resin composition, In the step of scanning the tip of the needle, the tip of the needle is scanned so as to move from one end side to the other end side of the cladding material in a first direction along the substrate, in a second direction perpendicular to the substrate, and in a third direction along the substrate and perpendicular to the second direction; an outer surface of the needle facing in a direction opposite to the scanning direction of the needle includes an inclined surface that is inclined from a tip of the needle to the opposite direction from a second direction perpendicular to the substrate, the cladding has a first end face, a second end face aligned with the first end face in the first direction, and a side face extending in the first direction between the first end face and the second end face, the core has a first core end face exposed at the first end face and a second core end face exposed at the second end face, and extends within the cladding from the first core end face to the second core end face; the second core end face has a height different from a height of the first core end face from the side face in the second direction perpendicular to the side face, and is disposed at a position shifted from the first core end face in the third direction along the side face and perpendicular to the second direction, The shape of the core in a cross section perpendicular to the extension direction of the core maintains a uniform circular or elliptical shape at each position of the core along the extension direction. A method for manufacturing an optical waveguide device.

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