Method for manufacturing an optical waveguide

Abstract

The method for manufacturing an optical waveguide according to the present invention comprises: a step of preparing a workpiece having a core layer including a core forming region and being sheet-shaped; and a step of cutting an optical waveguide from the inner side of the core forming region in the workpiece. The core layer is characterized by satisfying all of the following (a), (b), and (c): (a) The core layer comprises a polymer and monomers, and has a refractive index distribution based on the concentration difference of the monomers or the concentration difference derived from the structure of the monomers. (b) The core forming region comprises: a plurality of first cores; second cores disposed on both sides of the first cores; and a first side covering portion disposed between the first cores and the second cores. Furthermore, the core forming region is defined by a plurality of second cores positioned at the outer edge of the core forming region. (c) The core forming region is an area in which the combined area ratio of the first cores and the second cores within a 1 mm square area is 50% or more.

Description

Technical Field

[0001] This invention relates to a method for manufacturing an optical waveguide. Prior Technology

[0002] Patent Document 1 discloses a method for manufacturing an optical waveguide film, comprising: a step of preparing an optical waveguide sheet; and a step of cutting a strip of optical waveguide film from the optical waveguide sheet. Furthermore, it discloses that the optical waveguide sheet has a core layer having a plurality of core portions and two cladding layers sandwiching the core layer. The core layer is then formed by: a step of coating a composition for forming the core layer to obtain a film; a step of irradiating the obtained film with active light, such as ultraviolet light; and a step of heating the film in an oven. It discloses that the composition for forming the core layer includes a polymer and monomers. Furthermore, it discloses that when irradiated with active light, the monomers move along an in-plane direction orthogonal to the film thickness in the core layer, creating a refractive index difference between the irradiated and unirradiated areas. [Previous Technical Documents] [Patent Literature]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-084696 Summary of the Invention

[0004] [The problem that the invention aims to solve]

[0005] In the method for manufacturing an optical waveguide film described in Patent Document 1, a refractive index difference is generated between an irradiated area and a non-irradiated area by moving a monomer. Through the inventors' investigation, it was discovered that, when a refractive index difference is generated based on this principle, in areas with high density of the boundary line between the irradiated and non-irradiated areas, the refractive index difference through the boundary line tends to be larger compared to areas with low density of the boundary line.

[0006] Therefore, without taking into account the configuration of the boundary lines between the irradiated and unirradiated areas, the deviation of the refractive index difference across the boundary lines may become larger.

[0007] In the method for manufacturing an optical waveguide film described in Patent Document 1, the density of the boundary line between the irradiated and non-irradiated areas is not specifically considered during the manufacturing of the optical waveguide sheet. Therefore, the refractive index difference between the multiple cores of the optical waveguide sheet and adjacent cladding portions may deviate. Furthermore, while Patent Document 1 discloses cutting an optical waveguide film from the optical waveguide sheet, it does not disclose the positional relationship between the cutting line and the cores. Therefore, depending on the cutting position, it is possible to manufacture an optical waveguide film with multiple cores having refractive index differences that deviate from those of adjacent cladding portions. This deviation in refractive index difference becomes a cause of deviations in transmission loss between the cores.

[0008] The purpose of this invention is to provide a method for manufacturing an optical waveguide that can produce an optical waveguide with minimal deviation in transmission loss between channels. [Technical means to solve the problem]

[0009] This objective is achieved by the present invention described in (1) to (8) below. (1) A method for manufacturing an optical waveguide, characterized in that the method comprises: The steps for preparing a workpiece, which has a core layer including a core forming region and is sheet-shaped, Wherein, the aforementioned core layer satisfies all of the following (a), (b) and (c), (a) Contains polymers and monomers, and has a refractive index distribution based on the concentration difference of the aforementioned monomers or the concentration difference derived from the structure of the aforementioned monomers. (b) The aforementioned core forming region comprises: a plurality of first cores; second cores disposed on both sides of the aforementioned first cores; and a first side covering portion disposed between the aforementioned first cores and the aforementioned second cores, and the aforementioned core forming region is defined by the plurality of the aforementioned second cores being positioned at the outer edge of the aforementioned core forming region. (c) The aforementioned core-forming region is an area within a 1mm square region where the combined area ratio of the aforementioned first core and the aforementioned second core is 50% or more; and The step of cutting out the optical waveguide from the inside of the core forming region in the aforementioned workpiece.

[0010] (2) The optical waveguide manufacturing method as described in (1) above, wherein the width of at least one end of the second core is different from that of the first core.

[0011] (3) The optical waveguide manufacturing method as described in (1) or (2) above, wherein the optical waveguide has a first mark disposed at a position overlapping the aforementioned core forming region.

[0012] (4) The optical waveguide manufacturing method as described in (3) above, wherein the first mark has a low refractive index portion with a refractive index lower than that of the second core.

[0013] (5) The method for manufacturing an optical waveguide as described in any of (1) to (4) above, wherein, The aforementioned core layer includes: A plurality of the aforementioned core-forming regions that are separated from each other; and The blank area is located between adjacent core-forming areas and does not satisfy the aforementioned (c).

[0014] (6) The optical waveguide manufacturing method as described in (5) above, wherein the aforementioned blank area is further arranged in such a way as to surround the aforementioned core forming area.

[0015] (7) The optical waveguide manufacturing method as described in (5) or (6) above, wherein the workpiece has a second mark disposed at a position overlapping the aforementioned blank area.

[0016] (8) The optical waveguide manufacturing method as described in (7) above, wherein the aforementioned blank area has a second side covering portion integrally formed with the aforementioned first side covering portion. The aforementioned second mark has a high refractive index portion with a refractive index higher than that of the aforementioned second side covering portion. [Effects of the Invention]

[0017] According to the present invention, it is possible to manufacture optical waveguides with minimal deviation in transmission loss between channels. Simple Explanation of the Diagram

[0018] [Figure 1] is a top view of the workpiece used in the manufacturing method of the optical waveguide in the embodiment. [Figure 2] is a partial enlarged view of Figure 1. [Figure 3] is a cross-sectional view taken along line AA in Figure 2. [Figure 4] is a top view showing an example of an optical waveguide cut out from the inside of the core forming region in the workpiece shown in Figure 2. [Figure 5] is a top view used to illustrate the manufacturing method of the optical waveguide of the comparative example. [Figure 6] is a sectional view taken along line BB in Figure 5. [Figure 7] is a cross-sectional view used to illustrate the manufacturing method of the optical waveguide of the comparative example. [Figure 8] is a cross-sectional view used to illustrate the manufacturing method of the optical waveguide of the comparative example. [Figure 9] is a cross-sectional view used to illustrate the manufacturing method of the optical waveguide of the comparative example. [Figure 10] is a cross-sectional view used to illustrate the manufacturing method of the optical waveguide of the comparative example. [Figure 11] is a step diagram illustrating the manufacturing method of an optical waveguide in an embodiment. [Figure 12] is a cross-sectional view used to illustrate the manufacturing method of the optical waveguide in the embodiment. [Figure 13] is a cross-sectional view used to illustrate the manufacturing method of the optical waveguide in the embodiment. [Figure 14] is a cross-sectional view used to illustrate the manufacturing method of the optical waveguide in the embodiment. [Figure 15] is a cross-sectional view used to illustrate the manufacturing method of the optical waveguide in the embodiment. [Figure 16] is a top view of an optical waveguide manufactured by a modified optical waveguide manufacturing method. [Figure 17] is an enlarged view of part E in Figure 2. [Figure 18] is a top view showing the core of an evaluation optical waveguide. [Figure 19] is an enlarged view of part F in Figure 18. [Figure 20] is a graph showing the relative loss for each channel of the evaluation optical waveguide. Implementation

[0019] The manufacturing method of the optical waveguide of the present invention will now be described in detail with reference to the preferred embodiment shown in the figures.

[0020] Figure 1 is a top view of the workpiece used in the manufacturing method of the optical waveguide according to the embodiment. Figure 2 is a partial enlarged view of Figure 1. Figure 3 is a cross-sectional view taken along line AA in Figure 2.

[0021] Furthermore, in the figures of this application, the X-axis, Y-axis, and Z-axis are defined as three mutually orthogonal axes and are represented by arrows. The front end of the arrow is called the "positive side," and the rear end is called the "negative side." Moreover, the front end of the arrow representing the Z-axis is called the "up," and the rear end is called the "down."

[0022] 1. Workpiece The workpiece 100 shown in Figure 1 is a component used in the manufacture of the optical waveguide 1 shown in Figure 2. It is sheet-shaped and has two units 200. Each unit 200 has two pieces 300. One optical waveguide 1 can be cut from the piece 300. Therefore, workpiece 100 is a component that can manufacture four optical waveguides 1 at a time. Furthermore, there is no particular limitation on the number of optical waveguides 1 that can be manufactured at a time, as long as there is one or more. Also, the number of units 200 is not limited.

[0023] 1.1. Structure Figure 2 is a magnified view of the vicinity of piece 300 in workpiece 100.

[0024] As shown in Figure 2, the sheet 300 has 3 waveguide cores 14 (first cores), 10 dummy cores 16 (second cores), and 12 first side coverings 15. These are elongated strips extending along the X-axis and arranged along the Y-axis. Furthermore, in the following description, both the waveguide cores 14 and the dummy cores 16 are sometimes referred to simply as "cores." Also, the number of cores in the sheet 300 is not particularly limited, as long as the number of waveguide cores 14 is 2 or more and the number of dummy cores 16 is 3 or more.

[0025] Each waveguide core 14 has a first side cover 15 adjacent to each other on both sides in the Y-axis direction. Similarly, the virtual core 16 also has a first side cover 15 adjacent to each other on both sides in the Y-axis direction. Therefore, the first side cover 15 is disposed between the cores. Furthermore, a second side cover 17 in the shape of a frame is provided to surround these perimeters. In the following description, the first side cover 15 and the second side cover 17 are sometimes referred to simply as "side cover".

[0026] Virtual cores 16 are arranged adjacent to each waveguide core 14 on both sides via a first side covering portion 15. Optical signals are incident on the waveguide core 14 and transmitted along the Y-axis. This enables optical communication via the waveguide core 14. By arranging the virtual cores 16 adjacent to the waveguide cores 14, the increased transmission loss that easily occurs when the spacing between the waveguide cores 14 is too wide is suppressed. That is, the virtual cores 16 do not transmit optical signals, but rather serve to improve the transmission efficiency within the waveguide cores 14. Furthermore, two or more virtual cores 16 can be arranged between the waveguide cores 14, and the waveguide cores can be used to incident and transmit optical signals to the virtual cores 16.

[0027] In the Y-axis direction of the sheet 300 shown in Figure 1, three virtual cores 16 are arranged at both ends via the first side covering portion 15, without waveguide cores 14. This prevents the influence of the refractive index difference between the cores and the first side covering portion 15 from affecting the optical waveguide 1 cut from the sheet 300, even when the refractive index difference between the cores and the first side covering portion 15 is small at the ends of the sheet 300. This principle will be described in detail later.

[0028] As shown in Figure 3, the workpiece 100 has a laminated structure consisting of a first cover layer 18, a first coating layer 11, a core layer 13, a second coating layer 12, and a second cover layer 19, stacked sequentially. Each layer of the laminated structure extends along the XY plane. The workpiece 100 is a resin film and is flexible. Furthermore, Figures 1 and 2 are top views of the workpiece 100 viewed from above, and are views showing the core layer 13 through the second cover layer 19 and the second coating layer 12.

[0029] The aforementioned waveguide core 14, virtual core 16, first side cladding 15, and second side cladding 17 are disposed in the core layer 13. Therefore, the core is surrounded by the first side cladding 15, the second side cladding 17, the first cladding layer 11, and the second cladding layer 12, which can confine light inside.

[0030] Among them, the core layer 13 satisfies the following requirement (a). (a) The core layer 13 contains polymers and monomers and has a refractive index distribution based on the concentration difference of the monomers or the concentration difference of the structure of the monomers.

[0031] The refractive index distribution refers to the presence of portions with high and low refractive indices. In this embodiment, the refractive index varies depending on the polymer and monomer or the structure derived from the monomer. Furthermore, in this embodiment, the refractive index of the latter is lower than that of the former. Therefore, a refractive index distribution is formed along with the concentration difference. Furthermore, in the core layer 13, waveguide core 14, virtual core 16, first side covering portion 15, and second side covering portion 17 are formed corresponding to the refractive index distribution. Furthermore, the various portions of the core layer 13 can be formed based on the refractive index difference of the constituent materials. For example, by using different constituent materials for the core 14 and the side covering portions, a refractive index distribution can be formed in the core layer 13. Also, a polymer having detachable groups (detachable dangling groups) that can detach from the main chain branch by irradiation with active radiation can be used as the constituent material of the core layer 13. In this method, the refractive index of the polymer decreases due to the detachment of the detachable groups, thus the polymer can form a refractive index difference based on the presence or absence of active radiation irradiation, thereby forming a refractive index distribution in the core layer 13. Various methods exist for forming a refractive index distribution in the core layer 13, but in this embodiment, the core layer 13 comprises a polymer and monomers, and has a refractive index distribution based on the concentration difference of the monomers or the concentration difference derived from the structure of the monomers.

[0032] The widths of the waveguide cores 14 in the Y-axis direction and the widths of the virtual cores 16 in the Y-axis direction can be equal or different. Furthermore, the width of the waveguide cores 14 in the Y-axis direction and the width of the first side covering portion 15 can be equal or different.

[0033] Furthermore, waveguide core 14 can branch off midway or intersect with other waveguide cores 14 midway. Also, virtual core 16 can branch off midway, intersect with other virtual cores 16 midway, or be interrupted midway.

[0034] There is no particular limitation on the total length of workpiece 100 in the X-axis direction, but approximately 100~3000mm is preferred, and approximately 500~2000mm is even better. There is also no particular limitation on the total width of workpiece 100 in the Y-axis direction, but approximately 10~500mm is preferred, and approximately 50~200mm is even better.

[0035] The thickness of the core layer 13 in the Z-axis direction is not particularly limited, but approximately 1~200 μm is preferred, 5~100 μm is even better, and 10~70 μm is even better. This ensures the required optical properties and mechanical strength of the core layer 13.

[0036] The thicknesses of the first coating layer 11 and the second coating layer 12 along the Z-axis are preferably 1~200 μm, more preferably 3~100 μm, and even more preferably 5~60 μm. This ensures the required optical properties and mechanical strength of the first coating layer 11 and the second coating layer 12.

[0037] The first cover layer 18 is deposited on the lower surface of the first coating layer 11. The second cover layer 19 is deposited on the upper surface of the second coating layer 12. This improves the mechanical properties and durability of the workpiece 100.

[0038] The thickness of the film in the Z-axis direction of the workpiece 100 is preferably 50~300μm, more preferably 60~200μm, and even more preferably 70~150μm. This allows for improved flexibility of the workpiece 100 while ensuring its mechanical strength.

[0039] 1.2. Core Formation Region The core layer 13 includes the core forming region 130 shown in FIG2. The core forming region 130 is a region that satisfies the following requirements (b) and (c).

[0040] (b) The core forming region 130 includes: a plurality of waveguide cores 14 (first cores); virtual cores 16 (second cores) disposed on both sides of the waveguide cores 14; and a first side covering portion 15 disposed between the waveguide cores 14 and the virtual cores 16. Furthermore, the core forming region 130 is defined such that the plurality of virtual cores 16 (second cores) are positioned at the outer edge of the core forming region 130.

[0041] (c) The core forming region 130 is a region in which the combined area ratio of the waveguide core 14 and the virtual core 16 within a 1 mm square area is 50% or more.

[0042] The core layer 13 shown in Figure 2 has a waveguide core 14, a virtual core 16, a first side cladding 15, and a second side cladding 17. The core forming region 130 can be described as a region in which a plurality of virtual cores 16 (second cores) are positioned at the outer edge of the core forming region 130 within the core layer 13, and the cores are arranged in a high density such that the area ratio is 50% or more. In other words, the core forming region 130 can be described as a region in which a plurality of virtual cores 16 (second cores) are positioned on both sides (positive and negative sides of the Y-axis) of the core forming region 130, and the boundary lines between the cores and the side claddings are arranged in a high density. Specifically, when scanning a 1 mm square within the core layer 13, the scanning range in which the area ratio of the core within the square is 50% or more can be considered the core forming region 130. In the cutting step S108 described later, the optical waveguide 1 is cut out from the inside of the core forming region 130 in the workpiece 100. An example of the cutting line CL is shown in FIG2. As shown in FIG2, the cutting line CL is located inside the core forming region 130.

[0043] 1.3. Optical waveguide Figure 4 is a top view showing an example of an optical waveguide 1 cut out from the inside of the core forming region 130 in the workpiece 100 shown in Figure 2.

[0044] The optical waveguide 1 shown in Figure 4 has 3 waveguide cores 14, 6 virtual cores 16, 8 first-side coverings 15, and 2 second-side coverings 17. This type of optical waveguide 1 is used, for example, to connect with other optical components to construct optical wiring.

[0045] At least one of the two ends of the optical waveguide 1 may be equipped with an optical connector (not shown). The optical connector allows the optical waveguide 1 to be fixed and optically connected to other optical components. Furthermore, the optical waveguide 1 may have a reflector that converts the optical path of light passing through the waveguide core 14. By converting the optical path via the reflector, the waveguide core 14 can be optically connected to optical components disposed outside the optical waveguide 1. Alternatively, a curved waveguide may be used instead of a reflector.

[0046] 2. The problems that this implementation aims to solve. Next, the problem to be solved by this embodiment will be explained by describing the manufacturing method of the optical waveguide of the comparative example.

[0047] Figure 5 is a top view illustrating the manufacturing method of the optical waveguide in the comparative example. Figure 6 is a cross-sectional view taken along line BB of Figure 5. Figures 7 to 10 are cross-sectional views illustrating the manufacturing method of the optical waveguide in the comparative example. Furthermore, in Figures 5 to 10, for ease of explanation, structures identical to those in this embodiment are labeled with the same symbols. Also, Figures 7 to 10 correspond to enlarged views of section D in Figure 6.

[0048] In the workpiece 100X shown in Figure 5, the size of the comparison core forming region 130X is narrower than the core forming region 130 of the aforementioned workpiece 100, and the plurality of virtual cores 16 (second cores) are not positioned at the outer edge of the comparison core forming region 130X. Otherwise, it is substantially the same as the workpiece 100 in this embodiment. Therefore, in the workpiece 100X, the cutting line CL is located further outward than the comparison core forming region 130X. The problems arising from this configuration will be explained below.

[0049] As shown in Figure 6, workpiece 100X omits a portion of the virtual core 16 (the virtual core 16 located on the negative side of the Y-axis), otherwise it is basically the same as workpiece 100. As a result of omitting the virtual core 16, the comparison core forming region 130X is smaller than the core forming region 130, and consequently the cutting line CL extends outward beyond the comparison core forming region 130X.

[0050] In the comparative example of the optical waveguide manufacturing method, firstly, as shown in FIG7(a), a core film 600 is prepared as a laminate of substrate 500 and core forming layer 160.

[0051] Methods for forming the core forming layer 160 include, for example, applying a varnish-like core forming resin composition to a substrate 500 and then drying it, or depositing a resin film on the substrate 500.

[0052] Examples of resin compositions for core forming include compositions containing polymers, monomers, polymerization initiators, etc.

[0053] As a monomer, examples include photopolymerizable monomers that react in the irradiated area by irradiation with active radiation such as visible light, ultraviolet light, infrared light, laser light, electron beam, and X-rays to generate reactants. Alternatively, a structure could be formed where, upon irradiation with active radiation, the monomer can move in an in-plane direction orthogonal to the film thickness in the core-forming layer 160, resulting in a refractive index difference between the irradiated and unirradiated areas in the core layer 13X shown in FIG. 6.

[0054] Next, as shown in Figure 7(b), active radiation R is irradiated onto a portion of the core forming layer 160 via photomask 303. Figure 7(b) illustrates the polymer 131 and monomer 132 contained in the core forming layer 160. The refractive index of monomer 132, or the structure derived from monomer 132, is lower than that of polymer 131.

[0055] After irradiation with active radiation R, the core forming layer 160 is heated. This heating activates the polymerization initiator present in the irradiated region 301, causing a reaction of monomer 132. This creates a concentration gradient of monomer 132, resulting in the movement of monomer 132. As a result, as shown in FIG8(d), the concentration of monomer 132 in the irradiated region 301 increases, while the concentration of monomer 132 in the non-irradiated region 302 decreases. Consequently, the refractive index of the irradiated region 301 decreases due to the influence of monomer 132, while the refractive index of the non-irradiated region 302 increases due to the influence of polymer 131. As a result, as shown in FIG8(e), a core layer 13 comprising a waveguide core 14, a virtual core 16, a first side covering 15, and a second side covering 17 can be obtained.

[0056] In Figure 8(e), the distribution of refractive index n along the Y-axis is shown as a graph. The refractive index n distribution is determined by the concentration difference of monomer 132 or the structure derived from monomer 132. Regarding the refractive index n distribution shown in Figure 8(e), the refractive index n of the side coating becomes higher towards the negative Y-axis. Consequently, the refractive index difference between the core and the side coating decreases towards the negative Y-axis. Hereinafter, this decrease in the refractive index difference along the Y-axis will be referred to as "gradual decrease in refractive index difference".

[0057] Next, as shown in FIG8(f), a coating film 702, which serves as the coating forming layer 170 and the second cover layer 19, is deposited on the core layer 13. The resulting component is then heated. Thereby, the core layer 13 and the coating film 702 are bonded, and as shown in FIG9(g), a second coating layer 12 covering the core layer 13 is obtained. Next, as shown in Figure 9(h), the substrate 500 is peeled off from the core layer 13.

[0058] Next, as shown in FIG9(i), a coating film 701, which serves as a coating forming layer 170 and a first cover layer 18, is deposited on the core layer 13. The resulting component is then heated. Thereby, the core layer 13 and the coating film 701 are bonded, and as shown in FIG10(j), a first cover layer 11 covering the core layer 13 is obtained. As described above, the workpiece 100X shown in FIG10(j) can be obtained.

[0059] Next, as shown in Figure 10(k), the workpiece 100X is cut along the cutting line CL shown in Figure 6 using a dicing blade DB. Thus, as shown in Figure 10(L), the optical waveguide 1X is cut out.

[0060] In Figure 10(L), the distribution of refractive index along the Y-axis of the optical waveguide 1X is shown as a curve.

[0061] In the manufacturing method of the optical waveguide in the comparative example described above, as mentioned above, a portion of the dicing line CL is located outside the comparison core forming region 130X. The portion of the cut optical waveguide 1X located outside the comparison core forming region 130X is affected by the gradual decrease in the refractive index difference mentioned above. That is, in the optical waveguide 1X, the refractive index n2 of the side cladding portion located on the negative Y-axis side of the waveguide core 14 is higher than the refractive index n1 of the side cladding portion located on the positive Y-axis side. As a result, the deviation of the refractive index difference between the two sides in the Y-axis direction through the waveguide core 14 becomes larger. This deviation of the refractive index difference becomes the cause of the increased transmission loss of the waveguide core 14. As a result, in the plurality of waveguide cores 14, i.e., the plurality of channels, the transmission loss between channels deviates.

[0062] The manufacturing method of the optical waveguide according to the present embodiment, described later, can solve the problems mentioned above.

[0063] 3. Manufacturing method of optical waveguide Next, the manufacturing method of the optical waveguide in the implementation form will be explained.

[0064] Figure 11 is a step diagram illustrating the manufacturing method of the optical waveguide in the embodiment. Figures 12 to 15 are cross-sectional views illustrating the manufacturing method of the optical waveguide in the embodiment. Furthermore, Figures 12 to 15 correspond to enlarged views of part C in Figure 3.

[0065] The manufacturing method of the optical waveguide shown in Figure 11 includes a workpiece preparation step S106 and a cutting step S108.

[0066] In the workpiece preparation step S106, a workpiece 100 having a core layer 13 including a core forming region 130 and being in the form of a sheet is prepared. In the cutting step S108, the optical waveguide 1 is cut from the inside of the core forming region 130 in the workpiece 100. Therefore, the cutting line CL shown in FIG2 is located inside the core forming region 130. The following is a description of each step in sequence.

[0067] 3.1. Workpiece preparation steps As shown in Figure 11, the workpiece preparation step S106 includes the component preparation step S100, the core layer formation step S102, and the coating layer formation step S104.

[0068] 3.1.1. Component preparation steps In component preparation step S100, the core membrane 600 shown in FIG12(a) is prepared. Also, in component preparation step S100, the covering membrane 702 shown in FIG13(f) and the covering membrane 701 shown in FIG14(i) are prepared. Hereinafter, these components will be described sequentially.

[0069] 3.1.1.1. Core membrane As shown in Figure 12(a), the core film 600 is a laminate of the substrate 500 and the core forming layer 160. The core film 600 is in the shape of a film and can be a single sheet or a roll that can be wound up.

[0070] Methods for forming the core forming layer 160 include, for example, applying a varnish-like core forming resin composition to a substrate 500 and then drying it, or depositing a resin film on the substrate 500.

[0071] Methods for coating resin compositions include, for example, coating using various coating machines such as spin coaters, die coaters, comma coaters, and curtain coaters, as well as printing methods such as screen printing.

[0072] In methods for laminating resin films, methods such as using roller laminators, vacuum roller laminators, flat plate laminators, vacuum flat plate laminators, atmospheric pressure presses, and vacuum presses can be used to laminate a film-like resin composition formed from a varnish-like core.

[0073] 3.1.1.1.1. Substrate The substrate 500 may, for example, be a resin film. Examples of constituent materials of the substrate 500 include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyolefins such as polyethylene and polypropylene, polyimide, polyamide, polyetherimide, polyamideimide, fluoropolymers such as polytetrafluoroethylene (PTFE), polycarbonate, polyether sulfide, polyphenylene sulfide, liquid crystal polymers, etc.

[0074] Furthermore, depending on the need, the substrate 500 can be subjected to a demolding process that allows the core layer 13 to be easily peeled off from the substrate 500.

[0075] 3.1.1.1.2. Resin composition for core formation Examples of resin compositions for core formation include those comprising polymers, monomers, polymerization initiators, etc.

[0076] 3.1.1.1.2.1. Polymers Examples of polymers include acrylic resins, methacrylic resins, polycarbonate, polystyrene, cyclic ether resins such as epoxy resins or cyclobutane resins, polyamide, polyimide, polybenzoxazole, polysilane, polysilazane, polysiloxane, fluorinated resins, polyurethane, polyolefin resins, polybutadiene, polyisoprene, polychloroprene, polyesters such as PET or PBT, polyethylene glycol succinate, polyurethane, polyether, and cyclic olefin resins such as phenylcyclobutene resins or norbornene resins, phenoxy resins, etc. One or more of these can also be used in combination as polymer blends, polymer mixtures (mixtures), copolymers, etc.

[0077] Among these, the polymer can preferably be an acrylic resin, a phenoxy resin, or a cyclic olefin resin.

[0078] Examples of acrylic resins include polymers comprising one or more acrylic compounds selected from the group consisting of monofunctional acrylates, polyfunctional acrylates, monofunctional methacrylates, polyfunctional methacrylates, amine acrylates, amine methacrylates, epoxy acrylates, epoxy methacrylates, polyester acrylates, and urea acrylates. Furthermore, acrylic resins may have a polyester backbone, a polypropylene glycol backbone, a bisphenol backbone, a cyclohexane backbone, a tricyclodecane backbone, a dicyclopentadiene backbone, etc.

[0079] Examples of phenoxy resins include polymers comprising bisphenol A, bisphenol A-type epoxy compounds or their derivatives, and bisphenol F, bisphenol F-type epoxy compounds or their derivatives as copolymer components.

[0080] The polymer content is preferably 15% by mass or more of the total solid content of the core-forming resin composition, more preferably 40% by mass or more, and even more preferably 60% by mass or more. This improves the mechanical properties of the core layer 13. Furthermore, the polymer content in the core-forming resin composition is preferably 95% by mass or less of the total solid content of the core-forming resin composition, and more preferably 90% by mass or less. This improves the optical properties of the core layer 13.

[0081] The solid component of a resin composition for core formation refers to the non-volatile components in the composition, and specifically refers to the remaining portion after removing volatile components such as water or solvents.

[0082] 3.1.1.1.2.2. Monomer As a monomer, any compound that has a polymerizable site in its molecular structure is acceptable, and there are no particular limitations. However, examples include acrylic (methacrylic acid) monomers, epoxy monomers, cyclobutane monomers, norcamphene monomers, vinyl ether monomers, styrene monomers, photodimerizing monomers, etc., and one or more of these monomers may be used in combination.

[0083] Among these, acrylic (methacrylic acid) monomers or epoxy monomers are preferred as monomers.

[0084] Examples of acrylic acid (methacrylic acid) monomers include compounds having two or more vinyl unsaturated groups, and difunctional or trifunctional (meth)acrylates. Specifically, examples include aliphatic (meth)acrylates, alicyclic (meth)acrylates, aromatic (meth)acrylates, heterocyclic (meth)acrylates, or their ethoxylated, propoxylated, ethoxylated propoxylated, and caprolactone-modified forms. Furthermore, bisphenol skeletons and amine ester skeletons may also be present within the molecule.

[0085] Examples of epoxy monomers include alicyclic epoxy compounds, aromatic epoxy compounds, and aliphatic epoxy compounds.

[0086] As a monomer, a photopolymerizable monomer can be generated by reacting in the irradiated area under the influence of active radiation such as visible light, ultraviolet light, infrared light, laser light, electron beam, and X-ray. Alternatively, the structure can be such that, upon irradiation with active radiation, the monomer can move in an in-plane direction orthogonal to the film thickness in the core forming layer 160, resulting in a refractive index difference between the irradiated and unirradiated areas in the core layer 13.

[0087] The monomer content is preferably 1 part by mass or more and 70 parts by mass or less per 100 parts by mass of polymer, and more preferably 10 parts by mass or more and 60 parts by mass or less. This allows for a more reliable induction of the aforementioned refractive index difference, i.e., refractive index modulation.

[0088] 3.1.1.1.2.3. Polymerization initiator The polymerization initiator is selected appropriately based on the type of polymerization or crosslinking reaction of the monomer. Examples of polymerization initiators that can be used include free radical polymerization initiators such as acrylic (methacrylic acid) monomers and styrene monomers, as well as cationic polymerization initiators such as epoxy monomers, cyclobutane monomers, and vinyl ether monomers.

[0089] Examples of free radical polymerization initiators include benzophenones and acetophenones. Specifically, examples include Irgacure (Irgacure, a registered trademark) 651, Irgacure 819, Irgacure 2959, and Irgacure 184 (all manufactured by IGM Resins BV).

[0090] Examples of cationic polymerization initiators include Lewis acid-generating compounds such as diazonium salts, and Brinzyl acid-generating compounds such as styrene and strontium salts. Specifically, examples include Adeka Optomer SP-170 (manufactured by ADEKA CORPORATION), San-Aid SI-100L (manufactured by SANSHIN CHEMICAL INDUSTRY CO.,LTD.), and Rhodorsil 2074 (manufactured by Rhodia Japan Co., Ltd.).

[0091] The content of the polymerization initiator is preferably 0.01 parts by mass or more and 5 parts by mass or less per 100 parts by mass of the polymer, and more preferably 0.05 parts by mass or more and 3 parts by mass or less. This allows the monomer to react rapidly without reducing the optical or mechanical properties of the core layer 13.

[0092] 3.1.1.1.2.4. Others The resin composition for core forming may also include, for example, crosslinking agents, sensitizers (photosensitizers), catalyst precursors, co-catalysts, antioxidants, ultraviolet absorbers, light stabilizers, silane coupling agents, coating modifiers, thermal polymerization inhibitors, leveling agents, surfactants, colorants, storage stabilizers, plasticizers, lubricants, fillers, inorganic particles, deterioration inhibitors, wetting modifiers, antistatic agents, etc.

[0093] 3.1.1.1.2.5. Solvent By adding the above components to a solvent and stirring, a varnish-like core-forming resin composition can be obtained. The obtained composition can be used, for example, in filtration processing using a PTFE filter with a pore size of 0.2 μm. Furthermore, the obtained composition can be used in mixing processing using various mixers.

[0094] Examples of solvents contained in the resin composition for core forming include acetone, methyl ethyl ketone, methyl isobutyl ketone, toluene, ethyl acetate, cyclohexane, heptane, methylcyclohexane, cyclohexanone, tetrahydrofuran, dimethylformamide, dimethyl acetamide, dimethyl sulfoxide, ethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, diethylene glycol dimethyl ether, ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether acetate, cyroxene, carbitol, anisole, N-methylpyrrolidone, etc., or mixtures of one or more of these solvents may be used.

[0095] 3.1.1.2. Coating film As shown in Figure 14(i), the coating film 701 is a laminate of the first cover layer 18 and the coating forming layer 170. As shown in Figure 13(f), the coating film 702 is a laminate of the second cover layer 19 and the coating forming layer 170. The coating films 701 and 702 are film-shaped and can be single sheets or rolls that can be wound up.

[0096] Methods for forming the coating layer 170 include, for example, applying a varnish-like coating resin composition onto the coating layer and then drying it, or depositing a resin film on the coating layer.

[0097] Methods for coating resin compositions include, for example, coating using various coating machines such as spin coaters, die coaters, corner roller coaters, and curtain coaters, as well as printing methods such as screen printing.

[0098] In methods for laminating resin films, methods can be used, for example, to laminate a varnish-like coating to form a film-like resin film made of a resin composition using a roller laminator, a vacuum roller laminator, a flat plate laminator, a vacuum flat plate laminator, an atmospheric pressure press, a vacuum press, etc.

[0099] 3.1.1.2.1. Covering layer The thickness of the first capping layer 18 and the second capping layer 19 is not particularly limited, but approximately 1 to 200 μm is preferred, approximately 3 to 100 μm is more preferred, and approximately 5 to 50 μm is even more preferred. As long as the thickness of each capping layer is within the aforementioned range, it is possible to ensure the ability of the first capping layer 18 and the second capping layer 19 to protect the core layer 13, etc., while suppressing the disadvantages of the workpiece 100 becoming too thick, such as the reduction of the flexibility of the manufactured optical waveguide 1.

[0100] The thicknesses of the first capping layer 18 and the second capping layer 19 can be different, but it is preferable that they are the same. This can suppress the warping of the optical waveguide 1 caused by the difference in film thickness. Furthermore, the same film thickness means that the difference in film thickness is less than 5 μm.

[0101] The main materials for the first cover layer 18 and the second cover layer 19 can include, for example, various resins such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyolefins such as polyethylene and polypropylene, polyimide, polyamide, polyetherimide, polyamideimide, fluoropolymers such as polytetrafluoroethylene (PTFE), polycarbonate, polyether ether, polyphenylene sulfide, liquid crystal polymers, etc.

[0102] The primary materials of the first capping layer 18 and the second capping layer 19 may be different from each other, but it is preferable that they are the same. In this way, the warping of the optical waveguide 1 caused by the difference in the primary materials can be suppressed.

[0103] The elastic modulus of the first covering layer 18 and the second covering layer 19 is preferably 1~12 GPa, more preferably 2~11 GPa, and even more preferably 3~10 GPa. Furthermore, the above elastic modulus is set as the tensile elastic modulus.

[0104] 3.1.1.2.2. Resin composition for coating formation Examples of resin compositions for coating formation include those comprising polymers, monomers, polymerization initiators, etc.

[0105] 3.1.1.2.2.1. Polymers Examples of polymers include acrylic resins, methacrylic resins, polycarbonates, polystyrene, cyclic ether resins such as epoxy resins or cyclobutane resins, polyamides, polyimides, polybenzoxazoles, polysilanes, polysilazanes, polysiloxanes, fluorinated resins, polyurethanes, polyolefin resins, polybutadiene, polyisoprene, polychloroprene, polyesters such as PET or PBT, polyethylene glycol succinates, polyurethanes, polyethers, and cyclic olefin resins such as phenylcyclobutene resins or norbornene resins, phenoxy resins, etc. One or more of these can also be used in combination as polymer blends, polymer mixtures (mixtures), copolymers, etc.

[0106] Among these, the polymer can preferably be an acrylic resin, a phenoxy resin, or a cyclic olefin resin.

[0107] Examples of acrylic resins include polymers comprising one or more acrylic compounds selected from the group consisting of monofunctional acrylates, polyfunctional acrylates, monofunctional methacrylates, polyfunctional methacrylates, amine acrylates, amine methacrylates, epoxy acrylates, epoxy methacrylates, polyester acrylates, and urea acrylates. Furthermore, acrylic resins may have a polyester backbone, a polypropylene glycol backbone, a bisphenol backbone, a cyclohexane backbone, a tricyclodecane backbone, a dicyclopentadiene backbone, etc.

[0108] Examples of phenoxy resins include polymers comprising bisphenol A, bisphenol A-type epoxy compounds or their derivatives, and bisphenol F, bisphenol F-type epoxy compounds or their derivatives as copolymer components.

[0109] Furthermore, depending on the need, the polymer may include thermosetting resins. Examples of thermosetting resins include amine resins, isocyanate compounds, terminal isocyanate compounds, maleic diimide compounds, benzo[a]pyridine compounds, acezoline compounds, carbodiimide compounds, cyclic carbonate compounds, polyfunctional cyclobutane compounds, cyclic sulfur resins, epoxy resins, etc.

[0110] The polymer content is preferably 15% by mass or more of the total solid content of the coating-forming resin composition, more preferably 40% by mass or more, and even more preferably 60% by mass or more. This improves the mechanical properties of the first coating layer 11 and the second coating layer 12. Furthermore, the polymer content in the coating-forming resin composition is preferably 95% by mass or less of the total solid content of the coating-forming resin composition, and more preferably 90% by mass or less. This improves the optical properties of the first coating layer 11 and the second coating layer 12.

[0111] The solid components of a resin composition for coating formation refer to the non-volatile components in the composition, and specifically to the remaining portion after removing volatile components such as water or solvents.

[0112] 3.1.1.2.2.2. Monomer As a monomer, any compound that has a polymerizable site in its molecular structure is acceptable, and there are no particular limitations. However, examples include acrylic (methacrylic acid) monomers, epoxy monomers, cyclobutane monomers, norcamphene monomers, vinyl ether monomers, styrene monomers, photodimerizing monomers, etc., and one or more of these monomers may be used in combination.

[0113] Among these, acrylic (methacrylic acid) monomers or epoxy monomers are preferred as monomers.

[0114] Examples of acrylic acid (methacrylic acid) monomers include compounds having two or more vinyl unsaturated groups, and difunctional or trifunctional (meth)acrylates. Specifically, examples include aliphatic (meth)acrylates, alicyclic (meth)acrylates, aromatic (meth)acrylates, heterocyclic (meth)acrylates, or their ethoxylated, propoxylated, ethoxylated propoxylated, and caprolactone-modified forms. Furthermore, bisphenol skeletons and amine ester skeletons may also be present within the molecule.

[0115] Examples of epoxy monomers include alicyclic epoxy compounds, aromatic epoxy compounds, and aliphatic epoxy compounds.

[0116] The monomer content is preferably 1 part by mass or more and 70 parts by mass or less per 100 parts by mass of polymer, and even more preferably 10 parts by mass or more and 60 parts by mass or less.

[0117] 3.1.1.2.2.3. Polymerization initiator The polymerization initiator is selected appropriately based on the type of polymerization or crosslinking reaction of the monomer. Examples of polymerization initiators that can be used include free radical polymerization initiators such as acrylic (methacrylic acid) monomers and styrene monomers, as well as cationic polymerization initiators such as epoxy monomers, cyclobutane monomers, and vinyl ether monomers.

[0118] Examples of free radical polymerization initiators include benzophenones and acetophenones. Specifically, examples include Irgacure 651, Irgacure 819, Irgacure 2959, and Irgacure 184 (all manufactured by IGM Resins BV).

[0119] Examples of cationic polymerization initiators include Lewis acid-generating compounds such as diazonium salts, and Brinzyl acid-generating compounds such as styrene and strontium salts. Specifically, examples include Adeka Optomer SP-170 (manufactured by ADEKA CORPORATION), San-Aid SI-100L (manufactured by SANSHIN CHEMICAL INDUSTRY CO.,LTD.), and Rhodorsil 2074 (manufactured by Rhodia Japan Co., Ltd.).

[0120] The content of the polymerization initiator is preferably 0.01 parts by mass or more and 5 parts by mass or less per 100 parts by mass of the polymer, and more preferably 0.05 parts by mass or more and 3 parts by mass or less. In this way, the monomer can react rapidly without reducing the optical or mechanical properties of the first coating layer 11 and the second coating layer 12.

[0121] 3.1.1.2.2.4. Others The resin composition for coating formation may also include, for example, crosslinking agents, sensitizers (photosensitizers), catalyst precursors, co-catalysts, antioxidants, ultraviolet absorbers, light stabilizers, silane coupling agents, coating modifiers, thermal polymerization inhibitors, leveling agents, surfactants, colorants, preservation stabilizers, plasticizers, lubricants, fillers, inorganic particles, deterioration inhibitors, wettability modifiers, antistatic agents, etc.

[0122] 3.1.1.2.2.5. Solvent By adding the above components to a solvent and stirring, a varnish-like coating resin composition can be obtained. The obtained composition can be used, for example, in filtration processing using a PTFE filter with a pore size of 0.2 μm. Furthermore, the obtained composition can be used in mixing processing using various mixers.

[0123] Examples of solvents included in the resin composition for coating formation include acetone, methyl ethyl ketone, methyl isobutyl ketone, toluene, ethyl acetate, cyclohexane, heptane, methylcyclohexane, cyclohexanone, tetrahydrofuran, dimethylformamide, dimethyl acetamide, dimethyl sulfoxide, ethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, diethylene glycol dimethyl ether, ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether acetate, cyroxene, carbitol, anisole, N-methylpyrrolidone, etc., or mixtures of one or more of these solvents may be used.

[0124] Furthermore, the resin composition for forming the first coating layer 11 and the resin composition for forming the second coating layer 12 may be the same as each other or different from each other.

[0125] 3.1.2. Core Formation Steps In the core layer formation step S102, the core layer 13 is formed from the core forming layer 160. Specifically, the core layer 13 is obtained by irradiating a portion of the core forming layer 160 with active radiation R, which includes a waveguide core 14 and a virtual core 16 corresponding to the non-irradiated region 302, and a first side covering portion 15 and a second side covering portion 17 corresponding to the irradiated region 301.

[0126] In setting the irradiated area 301 and the non-irradiated area 302, for example, the method of using the photomask 303 shown in FIG12(b) can be used. By irradiating the active radiation R through the photomask 303, the irradiated area 301 and the non-irradiated area 302 can be set in accordance with the masking pattern of the photomask 303.

[0127] Furthermore, a direct exposure machine 304 can be used instead of a photomask 303. In Figure 12(c), active radiation R is irradiated by the direct exposure machine 304. Examples of direct exposure machines 304 include those that utilize various spatial light modulation elements, such as reflective spatial light modulation elements in digital micromirror devices (DMDs) or transmissive spatial light modulation elements in liquid crystal display (LCDs), to select the irradiation area. By using such a direct exposure machine 304, the irradiation area 301 and the non-irradiation area 302 can be set without using a photomask 303. This allows for adjustment of the size of the irradiation area 301 or the non-irradiation area 302 without changing the photomask 303, thereby reducing the manufacturing cost and increasing the efficiency of the optical waveguide 1.

[0128] Figures 12(b) and 12(c) illustrate the polymer 131 and monomer 132 contained in the core forming layer 160. In the core forming layer 160 before irradiation with active radiation R, the monomer 132 is substantially uniformly distributed in the polymer 131. Furthermore, the refractive index of the monomer 132, or the structure derived from the monomer 132, is lower than that of the polymer 131.

[0129] After irradiation with active radiation R, the core forming layer 160 is heated. This heating activates the polymerization initiator present in the irradiated region 301, causing a reaction of monomer 132. This creates a concentration gradient of monomer 132, resulting in the movement of monomer 132. As a result, as shown in FIG13(d), the concentration of monomer 132 in the irradiated region 301 increases, while the concentration of monomer 132 in the non-irradiated region 302 decreases. Consequently, the refractive index of the irradiated region 301 decreases due to the influence of monomer 132, while the refractive index of the non-irradiated region 302 increases due to the influence of polymer 131. As a result, as shown in FIG13(e), a core layer 13 comprising a waveguide core 14, a virtual core 16, a first side covering 15, and a second side covering 17 can be obtained.

[0130] Examples of heating conditions for the core forming layer 160 include a heating temperature of 100-200°C and a heating time of 10-180 minutes.

[0131] Furthermore, the refractive index may change as monomer 132 evaporates or polymer 131 changes with heating.

[0132] 3.1.3. Coating Layer Formation Steps In the coating layer forming step S104, the first coating layer 11 and the second coating layer 12 are deposited on the core layer 13, and the substrate 500 is peeled off. Thereby, the workpiece 100 is obtained.

[0133] In this embodiment, as shown in FIG13(f), a coating film 702 is deposited on the upper surface of the core layer 13. Then, the resulting laminate is heated. This bonds the core layer 13 to the coating film 702. As a result, as shown in FIG14(g), a second coating layer 12 covering the core layer 13 is obtained. Examples of heating conditions include a heating temperature of 100-200°C and a heating time of 10-180 minutes.

[0134] Next, as shown in FIG14(h), after the substrate 500 is peeled off from the core layer 13, as shown in FIG14(i), the coating film 701 is deposited on the lower surface of the core layer 13. Then, the resulting deposited body is heated. Herein, the core layer 13 and the coating film 701 are bonded. As a result, as shown in FIG15(j), a first coating layer 11 covering the core layer 13 can be obtained. Examples of heating conditions at this time include a heating temperature of 100~200°C and a heating time of 10~180 minutes, but it is preferable to set the temperature higher or the time longer than the heating conditions used to form the second coating layer 12. As described above, the workpiece 100 shown in FIG15(j) can be obtained.

[0135] 3.2. Cutting Step In the cutting step S108, as shown in FIG15(k), the workpiece 100 is cut. During cutting, for example, the cutting blade DB shown in FIG15(k) can be used. Alternatively, cutting based on a cutting saw, laser, planer, ultrasonic cutter, waterjet cutter, or blanking based on a blade mold can be used instead of cutting based on the cutting blade DB.

[0136] The workpiece 100 is cut along the cutting line CL shown in Figure 2. Thus, as shown in Figure 15(L), the optical waveguide 1 is cut out.

[0137] In Figure 15(L), the distribution of the refractive index n along the Y-axis of the optical waveguide 1 is shown by a curve.

[0138] In the manufacturing method of the optical waveguide of this embodiment, as described above, the dicing line CL is located inside the core forming region 130. Therefore, even if the aforementioned "gradual decrease in refractive index difference" occurs outside the core forming region 130, the cut optical waveguide 1 can be prevented from being affected by the gradual decrease in refractive index difference. That is, in the optical waveguide 1, the refractive index n2 of the side cladding on the negative Y-axis side of the waveguide core 14 becomes equal to or close to the refractive index n1 of the side cladding on the positive Y-axis side. As a result, the deviation of the refractive index difference on both sides in the Y-axis direction through the waveguide core 14 becomes smaller. Therefore, the problem of increased transmission loss of the waveguide core 14 due to the deviation of the refractive index difference can be solved. As a result, the optical waveguide 1 can be realized in which the deviation of transmission loss between channels in the plurality of waveguide cores 14, that is, the plurality of channels, is suppressed.

[0139] Furthermore, when setting the cutting line CL as shown in FIG2, it is preferable to set it at a position inside the core forming region 130, preferably at least two cores and more preferably at least three cores. This allows the boundary lines between the irradiated region 301 and the non-irradiated region 302 to be densely arranged, thus enabling the optical waveguide 1 to suppress the effect of "gradual decrease in refractive index difference". Furthermore, in FIG2, as an example, the cutting line CL is set at a position inside the core forming region 130, at least two cores, from the outer edge of the core forming region 130. The core forming region 130 satisfies requirement (b), thus this setting can be reliably implemented. As a result, the optical waveguide 1 can be reliably manufactured, especially suppressing the effect of "gradual decrease in refractive index difference".

[0140] As described above, the method for manufacturing an optical waveguide according to this embodiment includes a workpiece preparation step S106 and a cutting step S108. In the workpiece preparation step S106, a workpiece 100 having a core layer 13 including a core forming region 130 and being in the form of a sheet is prepared. In the cutting step S108, the optical waveguide 1 is cut out from the inside of the core forming region 130 in the workpiece 100. Furthermore, the core layer 13 satisfies all of the following requirements (a), (b) and (c).

[0141] (a) The core layer 13 comprises polymer 131 and monomer 132 and has a refractive index distribution based on the concentration difference of monomer 132 or the concentration difference of the structure of monomer 132.

[0142] (b) The core forming region 130 includes: a plurality of waveguide cores 14 (first cores); virtual cores 16 (second cores) disposed on both sides of the waveguide cores 14; and a first side covering portion 15 disposed between the waveguide cores 14 and the virtual cores 16, and the core forming region 130 is defined such that the plurality of virtual cores 16 (second cores) are positioned at the outer edge of the core forming region 130.

[0143] (c) The core forming region 130 is a region in which the combined area ratio of the waveguide core 14 and the virtual core 16 within a 1 mm square area is 50% or more.

[0144] Based on this structure, the optical waveguide 1 is cut out from the inside of the core forming region 130 in the workpiece 100, so the effect of the gradual decrease in refractive index difference mentioned above is less likely to affect the optical waveguide 1. Therefore, an optical waveguide 1 in which the refractive index difference is sufficiently ensured between the waveguide core 14 and the first side covering portion 15 can be obtained. As a result, an optical waveguide 1 with less deviation in transmission loss between channels can be manufactured.

[0145] Furthermore, the core layer 13 shown in Figure 2 comprises a plurality of mutually separated core forming regions 130 and blank regions 135. The blank region 135 is a region located between adjacent core forming regions 130 and does not satisfy the above (c). That is, the blank region 135 is a region that may have waveguide cores 14 and virtual cores 16, but whose combined area ratio does not reach 50%.

[0146] By including a plurality of core forming regions 130, a plurality of optical waveguides 1 can be cut from a single workpiece 100.

[0147] Furthermore, the blank area 135 shown in Figure 2 is the area where the waveguide core 14 and the virtual core 16 are not provided. Therefore, it is the area where the monomers 132 are polymerized in the core layer formation step S102, corresponding to the irradiation area 301. Therefore, in the blank area 135 corresponding to the irradiation area 301, the volume reduction caused by the reduction of monomers 132 is suppressed. In contrast, in the core formation area 130 corresponding to the non-irradiation area 302, the volume reduction caused by the reduction of monomers 132 is more likely to occur. Therefore, by providing blank areas 135 between the core formation areas 130, the overall deformation (warping) of the workpiece 100 can be suppressed.

[0148] Furthermore, the blank area 135 shown in Figure 2 is positioned to surround the core forming area 130.

[0149] By also providing a blank area 135 at this location, the workpiece 100 is supported by the blank area 135, thus effectively suppressing overall deformation of the workpiece 100. Furthermore, the entire edge of the core forming region 130 is adjacent to the blank area 135. Therefore, the influence of the blank area 135 on the core forming region 130 becomes more uniform, and the deviation in transmission loss between channels is particularly reduced.

[0150] 4. Variations Next, the manufacturing method of the modified optical waveguide will be explained.

[0151] Figure 16 is a top view of an optical waveguide 1B manufactured by a modified optical waveguide manufacturing method.

[0152] The following description provides examples of variations, focusing on the differences from the aforementioned embodiments and omitting descriptions of identical aspects. Furthermore, in each figure, structures identical to those in the aforementioned embodiments are labeled with the same symbols.

[0153] In the optical waveguide 1B shown in Figure 16, the virtual core 16 has a different shape and has a first mark 801, but otherwise it is the same as the optical waveguide 1 shown in Figure 2.

[0154] In the optical waveguide 1B, the width of at least one end of the virtual core 16 (the second core) differs from that of the waveguide core 14. In the example of FIG16, the width of the virtual core 16 at both ends in the X-axis direction is approximately half the width of the waveguide core 14. Specifically, the virtual core 16 shown in FIG16 is formed by dividing the width of the virtual core 16 shown in FIG2 into two parts by adding a new first side covering portion 15 at the center of the width.

[0155] Based on this structure, the width differs when viewed from the end face, making it easy to distinguish the waveguide core 14 from the virtual core 16. Therefore, the connection operation becomes easier when optically connecting the waveguide core 14 to optical components.

[0156] 5. Mark The optical waveguide 1B shown in Figure 16 has a first mark 801 disposed at a position overlapping with the core forming region 130. Specifically, in the optical waveguide 1B, in addition to the two ends in the X-axis direction, there is a portion where the width of the virtual core 16 is equal to the width of the waveguide core 14. Furthermore, the first mark 801 is disposed at this portion.

[0157] The first mark 801 is located at a position overlapping with the core forming region 130, thus increasing the likelihood that it will be included in the optical waveguide 1. Therefore, for example, when mounting an optical connector on the optical waveguide 1, the first mark 801 can be used as a position reference for aligning the optical waveguide 1 and the optical connector. As a result, the accuracy of the alignment can be improved. Furthermore, the method of using the first mark 801 is not limited to this. For example, in cases where an optical path conversion part such as a reflector is formed on the optical waveguide 1, or in cases where optical components are assembled on the optical waveguide 1, the first mark 801 can also be used as a position reference.

[0158] Furthermore, the first mark 801 can be applied, for example, by printing or transfer. Moreover, in this modified example, the constituent material of the first mark 801 is the same material as the side covering portion included in the core layer 13B. That is, the first mark 801 shown in FIG16 is set against the background of the virtual core 16 (second core) and has a low refractive index portion 802 with a refractive index lower than that of the virtual core 16. Specifically, the first mark 801 shown in FIG2 is composed of the low refractive index portion 802 that cuts across the virtual core 16.

[0159] Based on this structure, the way the first mark 801 is viewed against the background of the virtual core 16, such as the way light passes through, can be different. This improves the visibility of the first mark 801.

[0160] Furthermore, since the low-refractive-index portion 802 is made of the same material as the side-covering portion, it can be manufactured simultaneously with the side-covering portion. Therefore, the first mark 801 having the low-refractive-index portion 802 is easy to manufacture.

[0161] Furthermore, the low refractive index portion 802 can be formed according to the irradiation region 301 of the active radiation R. On the other hand, the waveguide core 14 and the dummy core 16 are also formed corresponding to the non-irradiation region 302 of the active radiation R. Therefore, the positional accuracy of the first mark 801 relative to the waveguide core 14 and the dummy core 16 is equivalent to the positional accuracy of the irradiation region 301, and is very high.

[0162] Furthermore, the shape of the first mark 801 is not limited to the shape shown in the figure, and can be any shape.

[0163] Furthermore, in the above-described method for manufacturing an optical waveguide, the workpiece 100 needs to be aligned with the device when irradiating with active radiation R or when cutting the workpiece 100. The workpiece 100 shown in Figure 1 has various markings for this alignment.

[0164] The workpiece 100 shown in Figure 2 has a second mark 803 located at a position overlapping with the blank area 135.

[0165] The second mark 803 is positioned overlapping the blank area 135, and can therefore be used as a position reference when cutting the optical waveguide 1 from the workpiece 100. Furthermore, the method of using the second mark 803 is not limited to this. For example, in cases where an optical path conversion part such as a reflector is formed on the workpiece 100 before cutting, or in cases where optical components are assembled on the optical waveguide 1, the second mark 803 can also be used as a position reference.

[0166] Figure 17 is an enlarged view of part E in Figure 2. Various examples of the second mark 803 are shown in Figure 2 or Figure 17.

[0167] For example, as shown in FIG17, a "+" shaped mark as the second mark 803 is provided on the outer side of unit 200 in workpiece 100 shown in FIG2. Also, as shown in FIG17, a concentric circle mark as the second mark 803 is provided on the inner side of unit 200 shown in FIG2. Furthermore, as shown in FIG17, a circular mark as the second mark 803 is provided on the inner side of unit 200 shown in FIG2 and at the center of the width of sheet 300.

[0168] Furthermore, the shape of the second mark 803 is not limited to the shape shown in the figure, and can be any shape.

[0169] The blank area 135 shown in Figure 2 has a second side covering portion 17 integrally formed with the first side covering portion 15. At this time, as shown in Figure 17, the second mark 803 provided at the position overlapping with the blank area 135 has a high refractive index portion 804 with a refractive index higher than that of the second side covering portion 17.

[0170] Based on this structure, the way the second mark 803 is viewed against the background of the second side covering portion 17, for example, the way light passes through, can be different. This improves the visibility of the second mark 803.

[0171] Furthermore, in this embodiment, the high refractive index portion 804 is made of the same material as the waveguide core 14 and the dummy core 16. This allows the high refractive index portion 804 to be manufactured simultaneously with the waveguide core 14 and the dummy core 16. Therefore, the second mark 803 of the high refractive index portion 804 is easily manufactured.

[0172] Furthermore, the high refractive index portion 804 can be formed according to the non-irradiated region 302 of the active radiation R. On the other hand, the waveguide core 14 and the dummy core 16 are also formed corresponding to the non-irradiated region 302 of the active radiation R. Therefore, the positional accuracy of the second mark 803 relative to the waveguide core 14 and the dummy core 16 is equivalent to the positional accuracy of the non-irradiated region 302, and is very high.

[0173] Furthermore, the number and arrangement of units 200 and pieces 300 in workpiece 100 shown in Figure 1 are not limited thereto.

[0174] The manufacturing method of the optical waveguide of the present invention has been described above based on the embodiments shown in the figures, but the present invention is not limited thereto.

[0175] For example, the method for manufacturing the optical waveguide of the present invention can be a manufacturing method that adds steps for any purpose to the aforementioned embodiments. [Example]

[0176] Next, specific embodiments of the present invention will be described. 6. Evaluation of the fabrication of optical waveguides Figure 18 is a top view showing the core of the evaluation optical waveguide 1D. Figure 19 is an enlarged view of part F of Figure 18.

[0177] As shown in Figure 19, 16 cores 14D are arranged side-by-side on the evaluation waveguide 1D shown in Figure 18. Furthermore, in the following description, the 16 cores 14D are also referred to as "core group 140D", and each core 14D is also referred to as a "channel". The 16 channels are labeled ch1 to ch16.

[0178] Furthermore, the total length of the optical waveguide 1D in the X-axis direction is 70 mm, the width of the core 14D in the Y-axis direction is 45 μm, and the spacing between the cores 14D in the Y-axis direction is 62.5 μm. Therefore, the width of the first side covering portion 15D located between the cores 14D is 17.5 μm in the Y-axis direction. Furthermore, a second side covering portion 17D with a width of 450 μm in the Y-axis direction is provided on both sides of the core group 140D.

[0179] Furthermore, the core assembly 140D bends midway along the X-axis. The bending radius r of the bent portion is set to 10 mm.

[0180] An evaluation optical waveguide 1D as described above was manufactured using the optical waveguide manufacturing method of the aforementioned embodiment. The cutting step is omitted. In the evaluation optical waveguide 1D, the area ratio of the cores within the core group 140D is 50% or more. Furthermore, a plurality of cores 14D (a plurality of cores that can be used as dummy cores) are located at both ends of the core group 140D. Therefore, this area corresponds to the "core forming region" in the aforementioned embodiment.

[0181] 7. Evaluation of optical waveguides The insertion loss was measured using an optical waveguide 1D to evaluate the results. Regarding the insertion loss, measurements were performed for each channel according to the measurement method specified in the JPCA (Japan Electronics Packaging Circuits Association) standard, "Test Methods for Polymer Optical Waveguides (JPCA-PE02-05-01S-2008)". Furthermore, the relative loss of each channel was calculated relative to the lowest loss among the 16 channels measured. Three identical measurements and calculations were performed, and the results were designated as #1, #2, and #3. The calculation results are shown in Figure 20.

[0182] Figure 20 shows the relative loss curves for each channel of the evaluation optical waveguide. As clearly shown in Figure 20, when comparing the relative losses among the 16 channels, it can be read that the relative losses tend to decrease from the ends of the core group 140D (i.e., ch1 or ch16) towards the center of the core group 140D (i.e., ch8 or ch9). Therefore, it can be said that the distribution of relative losses in the core group 140D is generally U-shaped. Therefore, it can be concluded that as long as the optical waveguide is cut out from the inside, avoiding both ends of the core group 140D, it is possible to manufacture an optical waveguide with low insertion loss in each channel and low deviation in insertion loss between channels.

[0183] In particular, the relative loss was suppressed to below 0.20 dB in the range of ch3 to ch14. Based on this result, it can be said that there is a tendency for the transmission loss to deteriorate due to the influence of the outer side of the core assembly 140D on the two quantities of the channel starting from the end of the core assembly 140D. As an influence of the outer side of the core assembly 140D, the aforementioned "gradual decrease in refractive index difference" can be considered, for example.

[0184] Furthermore, in the range of ch4 to ch13, the relative loss was suppressed to below 0.15 dB. On the other hand, in ch1 to ch3 and ch14 to ch16, the relative loss exceeded 0.15 dB.

[0185] Based on the above results, the following advantages are confirmed: When setting the cutting line CL as shown in FIG2, it is preferably set at a position inside the core forming region 130, preferably at least two cores, and more preferably at least three cores. By setting the cutting line CL at this position, an optical waveguide in which the effect of "gradual decrease in refractive index difference" can be suppressed. In other words, by cutting out a portion of the core remaining on the workpiece side, the effect of gradual decrease in refractive index difference is suppressed, and an optical waveguide with less transmission loss deviation can be obtained. On the other hand, when the cutting line CL is set at a position further outward than the outer edge of the core forming region 130, the cut optical waveguide is more susceptible to the effect of gradual decrease in refractive index difference. It can be said that the area ratio of the core in the aforementioned core forming region 130 is the threshold for the difference between whether such an effect occurs. [Industrial Applicability]

[0186] According to the present invention, it is possible to manufacture optical waveguides with low deviation in transmission loss between channels. Therefore, the present invention is industrially applicable.

[0187] 1: Optical waveguide 1B: Optical waveguide 1D: Evaluation of Optical Waveguides 1X: Optical waveguide 11: First cladding layer 12: Second cladding layer 13: Core layer 13B: Core layer 13X: Core layer 14: Waveguide Core 14D: Core 15: First side covering 15D: First side covering 16: Virtual Core 17: Second side covering 17D: Second side covering 18: First Covering Layer 19: Second Covering Layer 100: Workpiece 100X: Workpiece 130: Core Formation Region 130X: Comparison of core formation areas 131: Polymer 132: Monomer 135: Blank area 140D: Core Assembly 160: Core Cambium 170: Coating layer 200: Unit 300: pieces 301: Irradiation area 302: Non-irradiated area 303: Photomask 304: Direct Exposure Machine 500: Substrate 600: Core membrane 701: Coating film 702: Coating film 801: Mark 1 802: Low Refractive Index Section 803: Mark 2 804: High Refractive Index Section CL: Cutting line DB: Cutting knife R: Active radiation S100: Component Preparation Steps S102: Core Formation Steps S104: Steps for forming the coating layer S106: Workpiece preparation steps S108: Cutting Step n: Refractive index n1: Refractive index n2: Refractive index r: Bending radius

Claims

1. A method for manufacturing an optical waveguide, characterized in that the method comprises: a step of preparing a workpiece, the workpiece having a core layer including a core forming region and being sheet-shaped, wherein, The aforementioned core layer satisfies all of the following (a), (b), and (c): (a) it comprises a polymer and monomers and has a refractive index distribution based on the concentration difference of the aforementioned monomers or the concentration difference of the structure of the aforementioned monomers; (b) the aforementioned core forming region comprises: a plurality of first cores; second cores disposed on both sides of the aforementioned first cores; and a first side covering portion disposed between the aforementioned first cores and the aforementioned second cores, and the aforementioned core forming region further comprises a plurality of second cores located at both ends of the aforementioned core forming region in a direction orthogonal to the long side direction of the aforementioned first cores and the aforementioned second cores; (c) the aforementioned core forming region is a region in which the total area ratio of the aforementioned first cores and the aforementioned second cores in a 1 mm square area is 50% or more; and the step of cutting out the optical waveguide from the inside of the aforementioned core forming region in the aforementioned workpiece in a manner that avoids at least two of the aforementioned plurality of second cores located at the aforementioned ends of the aforementioned core forming region.

2. The method for manufacturing the optical waveguide as described in claim 1, wherein, The width of at least one end of the aforementioned second core is different from that of the aforementioned first core.

3. The method for manufacturing the optical waveguide as described in claim 1, wherein, The optical waveguide has a first mark located at a position overlapping the aforementioned core forming region.

4. The method for manufacturing the optical waveguide as described in claim 3, wherein, The aforementioned first mark has a low refractive index portion with a refractive index lower than that of the aforementioned second core.

5. A method for manufacturing an optical waveguide as described in claim 1, wherein, The aforementioned core layer comprises: a plurality of mutually separated aforementioned core forming regions; and a blank region located between adjacent aforementioned core forming regions, which does not satisfy the aforementioned (c).

6. The method for manufacturing the optical waveguide as described in claim 5, wherein, The aforementioned blank area is then set in such a way that it surrounds the aforementioned core forming area.

7. A method for manufacturing an optical waveguide as described in claim 5 or 6, wherein, The workpiece has a second mark located at a position overlapping the aforementioned blank area.

8. The method for manufacturing the optical waveguide as described in claim 7, wherein, The aforementioned blank area has a second side covering portion integrally formed with the aforementioned first side covering portion, and the aforementioned second mark has a high refractive index portion with a refractive index higher than that of the aforementioned second side covering portion.

9. A method for manufacturing an optical waveguide as claimed in claim 1, wherein, The aforementioned step of cutting out the optical waveguide is performed in a manner that avoids at least three of the aforementioned plurality of second cores located at both ends of the aforementioned core formation region.

10. A method for manufacturing an optical waveguide as claimed in claim 1, wherein, The cut-out optical waveguide includes the aforementioned first core and the aforementioned second core, each with a transmission loss of less than 0.20 dB.

11. The method for manufacturing the optical waveguide as described in claim 10, wherein, The aforementioned transmission loss is less than 0.15 dB.

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