JP7735786B2 - Optical waveguide manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing an optical waveguide.

Patent Document 1 discloses a method for manufacturing an optical waveguide, which includes the steps of forming a lower cladding layer on a polyimide laminate, forming a core layer on the lower cladding layer, forming a core pattern from the core layer, forming an upper cladding layer on the core pattern, and cutting out a linear optical waveguide. The core pattern forming step also includes the steps of spin-coating a fluorinated polyamic acid solution onto the lower cladding layer, heating this at 300°C or higher to form a core layer, forming a core pattern from the core layer using photoresist, and dry-etching the core pattern to obtain a core ridge.

Japanese Patent Application Laid-Open No. 2003-103738

Optical waveguides made from such organic materials are prone to dimensional changes due to the characteristics of organic materials. In particular, when the manufacturing process for optical waveguides involves a resin curing reaction, the reaction rate can change due to various external factors. As a result, the dimensional accuracy of the core ridge decreases after heating, posing the problem of reduced accuracy in the spacing between cores in the final optical waveguide.

The object of the present invention is to provide a method for manufacturing optical waveguides that can appropriately set the size of at least one of the irradiated and non-irradiated regions in anticipation of deformation of the core layer caused by the cladding layer, and that can efficiently manufacture optical waveguides with high core pitch accuracy.

These objects can be achieved by the present invention described below in (1) to (6).
(1) preparing a core-forming layer and a cladding-forming layer;
irradiating a portion of the core-forming layer with active radiation to obtain a core layer including a plurality of core portions corresponding to non-irradiated regions and aligned in a predetermined direction , and side clad portions positioned between the core portions and corresponding to the irradiated regions;
a step of laminating the cladding layer on the core layer and heating the resulting layer to obtain an optical waveguide having the core layer and the cladding layer;
and
A method for manufacturing an optical waveguide, characterized in that the size of at least one of the irradiated area and the non-irradiated area in the direction in which the core portions are arranged is adjusted depending on the elapsed time from the time of manufacturing the cladding forming layer.

(2) The elapsed time is the number of days stored at room temperature,
The method for manufacturing an optical waveguide according to (1) above, wherein the correction factor when adjusting the size is y and the number of days of storage at room temperature is x, and the correction factor is set so as to satisfy the following correction formula (1):
y = x ^A (1)
[In the correction formula (1), A is 0.00015 to 0.00045.]

(3) The method for manufacturing an optical waveguide according to (1) or (2) above, wherein the cladding layer has a thickness of 1 to 200 μm.

(4) The optical waveguide is
the core layer;
a first clad layer and a second clad layer, which are the clad layers laminated on both sides of the core layer;
Equipped with
the core layer is provided on a substrate before the step of obtaining the optical waveguide;
The step of obtaining the optical waveguide includes:
laminating the cladding layer on the core layer to obtain a laminate;
peeling the substrate from the laminate;
laminating the cladding layer on the core layer and heating the cladding layer to obtain the optical waveguide;
The method for manufacturing an optical waveguide according to any one of (1) to (3) above,

(5) The optical waveguide is
a first cover layer laminated on the first clad layer on the opposite side of the core layer;
a second cover layer laminated on the second clad layer on the opposite side of the core layer;
The method for manufacturing an optical waveguide according to (4) above, further comprising:

(6) A method for manufacturing an optical waveguide according to any one of (1) to (5) above, wherein the film thickness of the optical waveguide is 50 to 300 μm.

This invention makes it possible to efficiently manufacture optical waveguides with highly accurate core pitch.

1 is a plan view showing an optical waveguide manufactured by a method for manufacturing an optical waveguide according to an embodiment. 2 is a cross-sectional view taken along line AA in FIG. 1. 5A to 5C are process diagrams illustrating a method for manufacturing an optical waveguide according to an embodiment. 4 is a diagram for explaining a method for manufacturing the optical waveguide shown in FIG. 3, and is an enlarged view of a part of the optical waveguide shown in FIG. 2. FIG. 4 is a diagram for explaining a method for manufacturing the optical waveguide shown in FIG. 3, and is an enlarged view of a part of the optical waveguide shown in FIG. 2. FIG. 4 is a diagram for explaining a method for manufacturing the optical waveguide shown in FIG. 3, and is an enlarged view of a part of the optical waveguide shown in FIG. 2. FIG. FIG. 10 is a scatter diagram showing the correlation between the number of days that a clad film having a second clad layer is stored at room temperature and the pitch of the core portion. 8 is a scatter diagram showing the correlation between the number of days of storage at room temperature of a clad film having a second clad layer and the correction factor required to correct the shrinkage of the core layer shown in FIG. 7. FIG. 1 is a graph showing how the pitch of the core portion changes when the number of days of room temperature storage of a clad film having a first clad layer and the number of days of room temperature storage of a clad film having a second clad layer are the same and different from each other.

The method for manufacturing an optical waveguide of the present invention will now be described in detail based on a preferred embodiment shown in the accompanying drawings.

Figure 1 is a plan view showing an optical waveguide manufactured by a method for manufacturing an optical waveguide according to an embodiment. Figure 2 is a cross-sectional view taken along line A-A in Figure 1.

In each figure of this application, three mutually perpendicular axes are set: the X-axis, the Y-axis, and the Z-axis, and are indicated by arrows. The tip of the arrow is referred to as the "plus side," and the base is referred to as the "minus side." Furthermore, the tip of the arrow representing the Z-axis is referred to as the "upper" side, and the base is referred to as the "lower" side.

1. Optical Waveguide The optical waveguide 1 shown in FIGS. 1 and 2 is sheet-shaped and has a laminated structure in which a first cover layer 18, a first cladding layer 11, a core layer 13, a second cladding layer 12, and a second cover layer 19 are laminated in this order. Each layer of the laminated structure extends along the X-Y plane. As will be described later, the optical waveguide 1 is a long resin film with its major axis along the X-axis and is flexible. Therefore, the optical waveguide 1 can be used even when bent, for example, along the Z-axis.

As shown in FIG. 1, the core layer 13 contains nine elongated cores 14 extending along the X-axis, and side clads 15 adjacent to the side of each core 14. Therefore, a side clad 15 is adjacent to each of the cores 14 on both sides in the Y-axis direction. As shown in FIG. 2, the first clad layer 11 is adjacent to the bottom surface of the core 14, and the second clad layer 12 is adjacent to the top surface of the core 14. This stably maintains a sufficiently large refractive index difference between the core 14 and the clads (side clads 15, first clad layer 11, and second clad layer 12), increasing the transmission efficiency of the core 14. The cores 14 may branch or intersect with other cores 14 along the way within the core layer 13.

The number of core portions 14 provided in the core layer 13 is not particularly limited, and may be, for example, approximately 1 to 100. The total length of the optical waveguide 1 along the X axis is also not particularly limited, but is preferably approximately 10 to 3,000 mm. Furthermore, the total width of the optical waveguide 1 along the Y axis is also not particularly limited, but is more preferably approximately 2 to 200 mm.

The film thickness of the core layer 13 along the Z axis is not particularly limited, but is preferably approximately 1 to 200 μm, more preferably approximately 5 to 100 μm, and even more preferably approximately 10 to 70 μm. This ensures that the core layer 13 has the optical properties and mechanical strength required.

The film thickness along the Z-axis of the first cladding layer 11 and the second cladding layer 12 is preferably approximately 1 to 200 μm, more preferably approximately 3 to 100 μm, and even more preferably approximately 5 to 50 μm. This ensures that the first cladding layer 11 and the second cladding layer 12 have the optical properties and mechanical strength required. Furthermore, when the first cladding layer 11 and the second cladding layer 12 are formed from the cladding forming layer, excessive cure shrinkage of the cladding forming layer can be prevented, and this effect can be prevented from affecting the core layer 13.

The optical waveguide 1 has an end face 101 located at the end on the negative side of the X-axis and an end face 102 located at the end on the positive side of the X-axis. The end faces 101 and 102 each function as a light input/output surface.

An optical connector (not shown) may be attached to at least one of the ends of the optical waveguide 1. The optical connector can be used to secure the optical waveguide 1 to other optical components and to optically connect the end faces 101, 102 to other optical components. The optical waveguide 1 may also have a mirror that converts the optical path of light passing through the core 14. By converting the optical path via the mirror, the core 14 can be optically connected to an optical component located outside the optical waveguide 1.

The first cover layer 18 is laminated on the lower surface of the first cladding layer 11. The second cover layer 19 is laminated on the upper surface of the second cladding layer 12. This improves the mechanical properties and durability of the optical waveguide 1.

The film thickness of the optical waveguide 1 along the Z axis is preferably 50 to 300 μm, more preferably 60 to 200 μm, and even more preferably 70 to 150 μm. This increases the flexibility of the optical waveguide 1 while ensuring sufficient mechanical strength of the optical waveguide 1.

Each part of the optical waveguide 1 will be described in more detail below.
2. Method for Manufacturing Optical Waveguide Next, a method for manufacturing an optical waveguide according to an embodiment will be described. In the following description, a method for manufacturing the optical waveguide 1 shown in FIGS. 1 and 2 will be described as an example.

Figure 3 is a process diagram illustrating a method for manufacturing an optical waveguide according to an embodiment. Figures 4 to 6 are diagrams illustrating a method for manufacturing the optical waveguide shown in Figure 3, and are enlarged views of a portion of the optical waveguide shown in Figure 2.

The method for manufacturing the optical waveguide 1 shown in Figure 3 includes a preparation step S102, a core layer formation step S104, and a cladding layer formation step S106.

In the preparation step S102, the core-forming layer 160 and the cladding layer 170 are prepared. In the core-layer formation step S104, a portion of the core-forming layer 160 is irradiated with active radiation R to obtain the core layer 13 including the core portion 14 and the side cladding portion 15. In the cladding layer formation step S106, the cladding layer 170 is laminated on the core layer 13 and heated to obtain the optical waveguide 1.

In the method for manufacturing the optical waveguide 1 according to this embodiment, the size of at least one of the irradiation area 301 to be irradiated with active radiation R and the non-irradiation area 302 is adjusted depending on the time elapsed since the cladding forming layer 170 was manufactured.

With this configuration, the size of at least one of the irradiated region 301 and non-irradiated region 302 can be adjusted to anticipate deformation of the core layer 13 caused by the cladding layer 170. This allows the size of at least one of the core portion 14 and the side cladding portion 15 to approach the desired size even if the core layer 13 is deformed. As a result, it is possible to efficiently manufacture an optical waveguide 1 with a highly accurate pitch P of the core portion 14, as shown in Figure 2.

Each step will be explained below in order.
2.1. Preparation Step In the preparation step S102, the core forming layer 160 and the cladding forming layer 170 are prepared.

In this embodiment, as shown in Figure 4(a), a core film 200 is prepared, which has a substrate 100 and a core-forming layer 160 laminated on the upper surface of the substrate 100.

In this embodiment, as shown in FIG. 5(f), a clad film 402 is prepared, which includes a second cover layer 19 and a clad-forming layer 170 laminated on the lower surface of the second cover layer 19. Similarly, as shown in FIG. 6(i), a clad film 401 is prepared, which includes a first cover layer 18 and a clad-forming layer 170 laminated on the upper surface of the first cover layer 18.

2.1.1 Core Film As described above, the core film 200 is a laminate of the substrate 100 and the core-forming layer 160. The core film 200 is in the form of a film, and may be in the form of a sheet or a roll that can be wound up.

Examples of methods for forming the core-forming layer 160 include applying a varnish-like core-forming resin composition to the substrate 100 and then drying it, and laminating a resin film on the substrate 100.

Methods for applying the resin composition include, for example, coating using various coaters such as a spin coater, die coater, comma coater, or curtain coater, or printing methods such as screen printing.

Methods for laminating resin films include laminating a film-like resin film made from a varnish-like core-forming resin composition using, for example, roll lamination, vacuum roll lamination, flat lamination, vacuum flat lamination, atmospheric pressing, vacuum pressing, etc.

The core film 200 may include multiple regions corresponding to the optical waveguides 1 so that multiple optical waveguides 1 can ultimately be cut out. In this case, adding a process for cutting out the optical waveguides 1 allows the optical waveguides 1 to be manufactured more efficiently.

For example, a resin film is used for the substrate 100. Examples of materials that can be used for the substrate 100 include polyolefins such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethylene, and polypropylene, fluororesins such as polyimide, polyamide, polyetherimide, polyamideimide, and polytetrafluoroethylene (PTFE), polycarbonate, polyethersulfone, polyphenylene sulfide, and liquid crystal polymers.

If necessary, the substrate 100 may be subjected to a release treatment or the like to facilitate separation of the core layer 13 from the substrate 100.

2.1.1.2. Core-Forming Resin Composition Examples of the core-forming resin composition include compositions containing a polymer, a monomer, a polymerization initiator, and the like.

2.1.1.2.1 Polymers Examples of polymers include acrylic resins, methacrylic resins, polycarbonate, polystyrene, cyclic ether resins such as epoxy resins and oxetane resins, polyamide, polyimide, polybenzoxazole, polysilane, polysilazane, silicone resins, fluorine-containing resins, polyurethane, polyolefin resins, polybutadiene, polyisoprene, polychloroprene, polyesters such as PET and PBT, polyethylene succinate, polysulfone, polyether, cyclic olefin resins such as benzocyclobutene resins and norbornene resins, and phenoxy resins. One or more of these may be combined and used as a polymer alloy, polymer blend (mixture), copolymer, etc.

Among these, acrylic resins, phenoxy resins, or cyclic olefin resins are preferably used as polymers.

Examples of acrylic resins include polymers of acrylic compounds containing one or more compounds selected from the group consisting of monofunctional acrylates, polyfunctional acrylates, monofunctional methacrylates, polyfunctional methacrylates, urethane acrylates, urethane methacrylates, epoxy acrylates, epoxy methacrylates, polyester acrylates, and urea acrylates. Acrylic resins may also have a polyester skeleton, polypropylene glycol skeleton, bisphenol skeleton, fluorene skeleton, tricyclodecane skeleton, dicyclopentadiene skeleton, etc.

Examples of phenoxy resins include those containing bisphenol A, bisphenol A-type epoxy compounds, or derivatives thereof, and bisphenol F, bisphenol F-type epoxy compounds, or derivatives thereof as copolymerization component units.

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

The total solids content of the core-forming resin composition refers to the non-volatile content in the composition, i.e., the remainder excluding volatile components such as water and solvents.

2.1.1.2.2. Monomer The monomer is not particularly limited as long as it is a compound having a polymerizable moiety in its molecular structure, but examples thereof include acrylic acid (methacrylic acid)-based monomers, epoxy-based monomers, oxetane-based monomers, norbornene-based monomers, vinyl ether-based monomers, styrene-based monomers, and photodimerization monomers, and one or more of these may be used in combination.

Among these, acrylic acid (methacrylic acid)-based monomers or epoxy-based monomers are preferably used as monomers.

Examples of acrylic acid (methacrylic acid)-based monomers include compounds having two or more ethylenically unsaturated groups, and difunctional, trifunctional, or higher functional (meth)acrylates. Specific examples include aliphatic (meth)acrylates, alicyclic (meth)acrylates, aromatic (meth)acrylates, heterocyclic (meth)acrylates, and their ethoxylated, propoxylated, ethoxylated propoxylated, and caprolactone-modified derivatives. Furthermore, the monomer may contain a bisphenol skeleton, urethane skeleton, or the like within the molecule.

Examples of epoxy-based monomers include alicyclic epoxy compounds, aromatic epoxy compounds, and aliphatic epoxy compounds.

The monomer may be a photopolymerizable monomer that reacts in the irradiated region to produce a reaction product upon irradiation with active radiation such as visible light, ultraviolet light, infrared light, laser light, electron beams, or X-rays. Furthermore, the monomer may be capable of migrating in the in-plane direction perpendicular to the film thickness in the core-forming layer 160 upon irradiation with active radiation, thereby generating a refractive index difference between the irradiated and non-irradiated regions of the resulting core layer 13.

The content of the monomer is preferably 1 part by mass or more and 70 parts by mass or less, and more preferably 10 parts by mass or more and 60 parts by mass or less, per 100 parts by mass of the polymer. This makes it possible to more reliably form the refractive index difference, i.e., refractive index modulation.

2.1.1.2.3 Polymerization Initiator The polymerization initiator is appropriately selected depending on the type of polymerization reaction or crosslinking reaction of the monomer. Examples of the polymerization initiator that can be used include radical polymerization initiators such as acrylic acid (methacrylic acid) monomers and styrene monomers, and cationic polymerization initiators such as epoxy monomers, oxetane monomers, and vinyl ether monomers.

Examples of radical polymerization initiators include benzophenones and acetophenones. Specific examples include Irgacure (registered trademark) 651, Irgacure 819, Irgacure 2959, and Irgacure 184 (all manufactured by IGM Japan LLC).

Examples of cationic polymerization initiators include Lewis acid generators such as diazonium salts, and Bronsted acid generators such as iodonium salts and sulfonium salts. Specific 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.).

The content of the polymerization initiator is preferably 0.01 to 5 parts by mass, and more preferably 0.05 to 3 parts by mass, per 100 parts by mass of the polymer. This allows the monomer to react quickly without degrading the optical and mechanical properties of the core layer 13.

2.1.1.2.4. Others The core-forming resin composition may further contain, for example, a crosslinker, a sensitizer (photosensitizer), a catalyst precursor, a cocatalyst, an antioxidant, an ultraviolet absorber, a light stabilizer, a silane coupling agent, a coating surface improver, a thermal polymerization inhibitor, a leveling agent, a surfactant, a colorant, a storage stabilizer, a plasticizer, a lubricant, a filler, inorganic particles, an antidegradant, a wettability improver, an antistatic agent, and the like.

2.1.1.2.5. Solvent The above-described components are added to a solvent and stirred to obtain a varnish-like core-forming resin composition. The resulting composition may be subjected to filtration, for example, using a PTFE filter with a pore size of 0.2 μm. Alternatively, the resulting composition may be subjected to mixing using various mixers.

Examples of solvents contained in the core-forming resin composition include organic solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, toluene, ethyl acetate, cyclohexane, heptane, cyclohexane, cyclohexanone, tetrahydrofuran, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, ethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, diethylene glycol dimethyl ether, ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether acetate, cellosolve-based solvents, carbitol-based solvents, anisole, and N-methylpyrrolidone, and these may be used alone or in combination.

2.1.2 Clad Film As described above, the clad film 401 is a laminate of the first cover layer 18 and the clad forming layer 170. As described above, the clad film 402 is a laminate of the second cover layer 19 and the clad forming layer 170. The clad films 401 and 402 are in the form of a film, and may be in the form of a sheet or a roll that can be wound up.

Methods for forming the cladding layer 170 include, for example, applying a varnish-like cladding resin composition onto the cover layer and then drying it, or laminating a resin film onto the cover layer.

Methods for applying the resin composition include, for example, coating using various coaters such as a spin coater, die coater, comma coater, or curtain coater, or printing methods such as screen printing.

Methods for laminating resin films include laminating a film-like resin film made from a varnish-like cladding-forming resin composition using, for example, roll lamination, vacuum roll lamination, flat lamination, vacuum flat lamination, atmospheric pressing, vacuum pressing, etc.

2.1.2.1 Cover Layer The thicknesses of the first cover layer 18 and the second cover layer 19 are not particularly limited, but are preferably about 1 to 200 μm, more preferably about 3 to 100 μm, and even more preferably about 5 to 50 μm. If the thickness of each cover layer is within the above range, the first cover layer 18 and the second cover layer 19 can ensure the ability to protect the core layer 13 and the like, while suppressing the adverse effects of an excessively thick optical waveguide 1, such as a decrease in the flexibility of the optical waveguide 1.

The film thicknesses of the first cover layer 18 and the second cover layer 19 may be different from each other, but are preferably the same. This helps prevent warping of the optical waveguide 1 due to differences in film thickness. Having the same film thickness means that the difference in film thickness is 5 μm or less.

The primary material of the first cover layer 18 and the second cover layer 19 may be, for example, a material containing various resins such as polyolefins such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethylene, and polypropylene, polyimide, polyamide, polyetherimide, polyamideimide, fluororesins such as polytetrafluoroethylene (PTFE), polycarbonate, polyethersulfone, polyphenylene sulfide, and liquid crystal polymers.

The main materials of the first cover layer 18 and the second cover layer 19 may be different from each other, but it is preferable that they are the same. This makes it possible to suppress warping of the optical waveguide 1 due to differences in the main materials.

The elastic modulus of the first cover layer 18 and the second cover layer 19 is preferably 1 to 12 GPa, more preferably 2 to 11 GPa, and even more preferably 3 to 10 GPa. Note that the above elastic modulus is the tensile modulus.

2.1.2.2. Clad-forming Resin Composition Examples of the clad-forming resin composition include compositions containing a polymer, a monomer, a polymerization initiator, and the like.

2.1.2.2.1 Polymers Examples of polymers include acrylic resins, methacrylic resins, polycarbonate, polystyrene, cyclic ether resins such as epoxy resins and oxetane resins, polyamide, polyimide, polybenzoxazole, polysilane, polysilazane, silicone resins, fluorine-containing resins, polyurethane, polyolefin resins, polybutadiene, polyisoprene, polychloroprene, polyesters such as PET and PBT, polyethylene succinate, polysulfone, polyether, cyclic olefin resins such as benzocyclobutene resins and norbornene resins, and phenoxy resins. One or more of these may be combined and used as a polymer alloy, polymer blend (mixture), copolymer, etc.

Among these, acrylic resins, phenoxy resins, or cyclic olefin resins are preferably used as polymers.

Examples of acrylic resins include polymers of acrylic compounds containing one or more compounds selected from the group consisting of monofunctional acrylates, polyfunctional acrylates, monofunctional methacrylates, polyfunctional methacrylates, urethane acrylates, urethane methacrylates, epoxy acrylates, epoxy methacrylates, polyester acrylates, and urea acrylates. Acrylic resins may also have a polyester skeleton, polypropylene glycol skeleton, bisphenol skeleton, fluorene skeleton, tricyclodecane skeleton, dicyclopentadiene skeleton, etc.

Examples of phenoxy resins include those containing bisphenol A, bisphenol A-type epoxy compounds, or derivatives thereof, and bisphenol F, bisphenol F-type epoxy compounds, or derivatives thereof as copolymerization component units.

The polymer may also contain a thermosetting resin, if necessary. Examples of thermosetting resins include amino resins, isocyanate compounds, blocked isocyanate compounds, maleimide compounds, benzoxazine compounds, oxazoline compounds, carbodiimide compounds, cyclocarbonate compounds, polyfunctional oxetane compounds, episulfide resins, and epoxy resins.

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

The total solids content of the cladding-forming resin composition refers to the non-volatile content in the composition, i.e., the remainder excluding volatile components such as water and solvents.

2.1.2.2.2 Monomer The monomer is not particularly limited as long as it is a compound having a polymerizable moiety in its molecular structure, but examples thereof include acrylic acid (methacrylic acid)-based monomers, epoxy-based monomers, oxetane-based monomers, norbornene-based monomers, vinyl ether-based monomers, styrene-based monomers, and photodimerization monomers, and one or more of these may be used in combination.

Among these, acrylic acid (methacrylic acid)-based monomers or epoxy-based monomers are preferably used as monomers.

Examples of acrylic acid (methacrylic acid)-based monomers include compounds having two or more ethylenically unsaturated groups, and difunctional, trifunctional, or higher functional (meth)acrylates. Specific examples include aliphatic (meth)acrylates, alicyclic (meth)acrylates, aromatic (meth)acrylates, heterocyclic (meth)acrylates, and their ethoxylated, propoxylated, ethoxylated propoxylated, and caprolactone-modified derivatives. Furthermore, the monomer may contain a bisphenol skeleton, urethane skeleton, or the like within the molecule.

Examples of epoxy-based monomers include alicyclic epoxy compounds, aromatic epoxy compounds, and aliphatic epoxy compounds.

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

2.1.2.2.3. Polymerization initiator The polymerization initiator is appropriately selected depending on the type of polymerization reaction or crosslinking reaction of the monomer. Examples of the polymerization initiator that can be used include radical polymerization initiators such as acrylic acid (methacrylic acid) monomers and styrene monomers, and cationic polymerization initiators such as epoxy monomers, oxetane monomers, and vinyl ether monomers.

Examples of radical polymerization initiators include benzophenones and acetophenones. Specific examples include Irgacure 651, Irgacure 819, Irgacure 2959, and Irgacure 184 (all manufactured by IGM Japan LLC).

Examples of cationic polymerization initiators include Lewis acid generators such as diazonium salts, and Bronsted acid generators such as iodonium salts and sulfonium salts. Specific 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.).

The content of the polymerization initiator is preferably 0.01 to 5 parts by mass, and more preferably 0.05 to 3 parts by mass, per 100 parts by mass of the polymer. This allows the monomers to react quickly without degrading the optical and mechanical properties of the first cladding layer 11 and the second cladding layer 12.

2.1.2.2.4. Others The cladding-forming resin composition may further contain, for example, a crosslinking agent, a sensitizer (photosensitizer), a catalyst precursor, a cocatalyst, an antioxidant, an ultraviolet absorber, a light stabilizer, a silane coupling agent, a coating surface improver, a thermal polymerization inhibitor, a leveling agent, a surfactant, a colorant, a storage stabilizer, a plasticizer, a lubricant, a filler, inorganic particles, a deterioration inhibitor, a wettability improver, an antistatic agent, and the like.

2.1.2.2.5. Solvent The above-described components are added to a solvent and stirred to obtain a varnish-like clad-forming resin composition. The resulting composition may be subjected to filtration, for example, using a PTFE filter with a pore size of 0.2 μm. Alternatively, the resulting composition may be subjected to mixing using various mixers.

Examples of solvents contained in the cladding-forming resin composition include organic solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, toluene, ethyl acetate, cyclohexane, heptane, cyclohexane, cyclohexanone, tetrahydrofuran, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, ethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, diethylene glycol dimethyl ether, ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether acetate, cellosolve-based solvents, carbitol-based solvents, anisole, and N-methylpyrrolidone, and these may be used alone or in combination.

The clad-forming resin composition for forming the first clad layer 11 and the clad-forming resin composition for forming the second clad layer 12 may be the same as or different from each other.

In the core layer forming step S104, the core layer 13 is formed from the core formation layer 160. Specifically, a part of the core formation layer 160 is irradiated with active radiation R to obtain the core layer 13 including a plurality of core portions 14 corresponding to the non-irradiated regions 302 and side cladding portions 15 located between the core portions 14 and corresponding to the irradiated regions 301.

To set the irradiation area 301 and non-irradiation area 302, for example, a method using a photomask 303 as shown in Figure 4(b) is used. By irradiating active radiation R through the photomask 303, the irradiation area 301 and non-irradiation area 302 can be set according to the mask pattern of the photomask 303.

Instead of using a photomask 303, a direct imaging exposure machine 304 may be used. In Figure 4(c), actinic radiation R is irradiated using the direct imaging exposure machine 304. Examples of the direct imaging exposure machine 304 include exposure machines that can select an irradiation area using various spatial light modulators, such as a reflective spatial light modulator like a digital micromirror device (DMD) or a transmissive spatial light modulator like a liquid crystal display (LCD). By using such a direct imaging exposure machine 304, it is possible to set the irradiation area 301 and non-irradiation area 302 without using a photomask 303. This allows the size of the irradiation area 301 and non-irradiation area 302 to be adjusted without changing the photomask 303, thereby reducing the manufacturing cost and improving efficiency of the optical waveguide 1.

Figures 4(b) and 4(c) show the polymer 131 and monomer 132 contained in the core-forming layer 160. In the core-forming layer 160 before irradiation with actinic radiation R, the monomer 132 is distributed almost uniformly in the polymer 131. Note that here, the monomer 132 and the structure derived from the monomer 132 have a lower refractive index than the polymer 131.

After irradiation with actinic radiation R, the core-forming layer 160 is heated. This heating activates the polymerization initiator present in the irradiated region 301, causing the reaction of the monomer 132 to proceed. This creates a concentration difference in the monomer 132, which in turn causes the monomer 132 to move. As a result, as shown in Figure 5(d), the concentration of the monomer 132 in the irradiated region 301 increases, while the concentration of the monomer 132 in the non-irradiated region 302 decreases. As a result, the refractive index of the irradiated region 301 decreases due to the influence of the monomer 132, and the refractive index of the non-irradiated region 302 increases due to the influence of the polymer 131. As a result, a core layer 13 including a core portion 14 and side cladding portions 15 is obtained, as shown in Figure 5(e).

The heating conditions for the core forming layer 160 include, for example, a heating temperature of 100 to 200°C and a heating time of 10 to 180 minutes.

Note that this heating may cause the monomer 132 to volatilize or the molecular structure of the polymer 131 to change, resulting in a change in refractive index.

While the method for forming the core layer 13 by irradiating the core-forming resin composition with active radiation R has been described above, the method for forming the core layer 13 is not limited to the above method. For example, photolithography, replication, etc. may also be used. Photolithography is a method that combines exposure, development, and etching techniques to form the core portion 14 and the side clad portion 15 using materials with different refractive indices. Replication is a method in which, for example, a mold having a core pattern is pressed against a resin film to form the core portion 14, and then the side clad portion 15 is formed. Furthermore, the core-forming layer 160 before or after irradiation with active radiation R may be subjected to a surface treatment, as necessary. Examples of surface treatments include plasma treatment, corona treatment, ultraviolet irradiation treatment, and electron beam irradiation treatment.

2.3 Clad Layer Forming Step In the clad layer forming step S106, the first clad layer 11 and the second clad layer 12 are laminated on the core layer 13, and the substrate 100 is peeled off, thereby obtaining the optical waveguide 1.

In this embodiment, as shown in FIG. 5(f), the clad film 402 is laminated on the top surface of the core layer 13. The resulting laminate is then heated. This bonds the core layer 13 and the clad film 402 together, as shown in FIG. 6(g). As a result, a second clad layer 12 is obtained that covers the core layer 13. Examples of heating conditions include a heating temperature of 100 to 200°C and a heating time of 10 to 180 minutes.

After peeling the substrate 100 from the core layer 13 as shown in FIG. 6( h), a clad film 401 is laminated on the lower surface of the core layer 13 as shown in FIG. 6( i). The resulting laminate is then heated. This bonds the core layer 13 and the clad film 401 together. As a result, a first clad layer 11 covering the core layer 13 is obtained. Heating conditions at this time include, for example, a heating temperature of 100 to 200°C and a heating time of 10 to 180 minutes. However, it is preferable to set the heating temperature to a higher temperature or for a longer time than the heating conditions used to form the second clad layer 12.
In this manner, the optical waveguide 1 shown in FIG. 2 is obtained.

2.4 Adjustment of Irradiated and Non-Irradiated Regions Adjustment of the irradiated and non-irradiated regions 301 and 302 in the core layer forming step S104 will now be described.

As mentioned above, in this embodiment, the size of at least one of the irradiated area 301 and the non-irradiated area 302 is adjusted depending on the time elapsed since the cladding forming layer 170 was manufactured.

The cladding layer 170 may be manufactured and stored in advance in the form of cladding films 401, 402. In this case, the required amount is cut out from the stored cladding films 401, 402 and used when the cladding layer formation process S106 is performed. In this case, the elapsed time since the time of manufacture of the cladding films 401, 402 used in the cladding layer formation process S106 is not constant, but since a large amount of cladding films 401, 402 can be manufactured in advance, it is easy to improve manufacturing efficiency.

However, it has been found that the pitch P of the core portions 14 changes as the time elapsed since the production of the clad films 401 and 402 changes. The pitch P of the core portions 14 refers to the distance between the optical axes of the core portions 14 when the core portions 14 are lined up along the Y axis, as shown in Figure 2.

The inventors therefore conducted extensive research into the relationship between the time T elapsed since the production of the clad films 401, 402 and the pitch P of the core region 14. They discovered that there is a correlation between the two, and that by setting the irradiation range of the active radiation R based on this correlation, the pitch P can be brought closer to the desired value, leading to the completion of the present invention.

Specifically, there is a negative correlation between the elapsed time T and the pitch P; as the elapsed time T of the clad films 401, 402 increases, the core layer 13 shrinks (deforms) along the Y axis due to the clad films 401, 402, and the pitch P decreases.

Therefore, in this embodiment, when manufacturing an optical waveguide 1 using clad films 401, 402 with a long elapsed time T, the size of at least one of the irradiated area 301 and non-irradiated area 302 is set large according to the elapsed time T, in anticipation of shrinkage of the core layer 13 caused by the clad films 401, 402. This allows the pitch P to approach the desired value. As a result, optical waveguides 1 with a highly accurate pitch P of the core portion 14 can be efficiently manufactured.

The relationship between the elapsed time T and the pitch P also changes depending on the temperature at which the clad films 401, 402 are stored. For example, when the clad films 401, 402 are stored at a low temperature below room temperature, the change in pitch P is likely to be kept within an acceptable range even if the elapsed time T is long. In contrast, when the clad films 401, 402 are stored at a temperature above room temperature, the change in pitch P becomes more apparent as the elapsed time T becomes longer.

Therefore, the elapsed time T may be the number of days stored at room temperature, which is the number of days the pitch P has been left at room temperature. In other words, given that the effect of the elapsed time T on the pitch P is small below room temperature, particularly at temperatures below 10°C, the number of days stored at room temperature may be particularly taken into consideration when determining the elapsed time T.

Figure 7 is a scatter plot showing the correlation between the number of days that a clad film 402 having a second clad layer 12 has been stored at room temperature and the pitch P of the core portion 14. In Figure 7, measured data is represented by dots. The number of days that a clad film 402 has been stored at room temperature is the number of days that have elapsed since the clad film 402 was removed from a refrigerator and began to be stored at room temperature. The temperature inside the refrigerator is 10°C or below. Room temperature refers to a temperature between 15 and 30°C.

As shown by the dashed line in Figure 7, there is a negative correlation between the number of days stored at room temperature and pitch P; the longer the number of days the clad films 401 and 402 are stored at room temperature, the shorter the pitch P. It is believed that if the storage temperature is lower than room temperature, the slope of the dashed line will be gentler than in Figure 7.

In this embodiment, when setting the irradiation area 301 and the non-irradiation area 302 in the core layer formation process S104, the size of at least one of these is corrected by multiplying the original size by a correction factor. By adjusting the size of the irradiation area 301, etc. using the correction factor, even if the core layer 13 is deformed due to the clad films 401, 402, the pitch P after deformation can be made closer to the target value.

Figure 8 is a scatter plot showing the correlation between the number of days x that a clad film 402 having a second clad layer 12 is stored at room temperature and the correction factor y required to correct the shrinkage of the core layer 13 shown in Figure 7. In Figure 8, the measured data is indicated by dots.

As shown in Figure 8, there is a positive correlation between the number of days x stored at room temperature and the correction factor y; the longer the number of days x stored at room temperature, the larger the correction factor y required for correction.

In this case, it is preferable to set the correction magnification y so as to satisfy the following correction formula (1).
y = x ^A (1)
[In the above correction formula (1), A is 0.00015 to 0.00045.]

The correction magnification y expressed by the above correction formula (1) is the magnification used to correct the length in the Y-axis direction for at least one of the illuminated area 301 and the non-illuminated area 302. Note that in Figure 8, the curve expressed by the above correction formula (1) when A = 0.00015 is shown by a dotted line, and the curve expressed by the above correction formula (1) when A = 0.00045 is shown by a dashed line.

As shown in Figure 8, the actual measurement data falls within the range of the above correction formula (1). Therefore, by using the above correction formula (1), the correction factor y can be determined more accurately, taking into account the effects of storage at room temperature. As a result, optical waveguides 1 with improved pitch P accuracy of the core portions 14 can be efficiently manufactured.

It is preferable to correct both the length of the illuminated area 301 along the Y axis and the length of the non-illuminated area 302 along the Y axis using a common correction magnification y, but they may also be corrected using different correction magnifications y, or only one of them may be corrected. Furthermore, in the above correction formula (1), it is particularly preferable that A be 0.00020 to 0.00040. Correction formula (1) is an example and is not limited to this. For example, instead of correction formula (1), an equation obtained by adding an arbitrary coefficient to formula (1) may be used.

The relationship between the time T elapsed since the production of the clad films 401 and 402 and the pitch P of the core portion 14 has been explained above. However, in the above-described production method, the impact of the number of days stored at room temperature on the clad film 401 is not as great as on the clad film 402. This is thought to be because the above-described production method employs a sequence in which the clad film 402 is first laminated onto the core layer 13, and then the clad film 401 is laminated thereon.

Therefore, if the number of days for which clad film 401 has been stored at room temperature differs from the number of days for which clad film 402 has been stored at room temperature, the number of days for which clad film 402 has been stored at room temperature should be given priority, and the size of irradiation area 301, etc. should be adjusted based on that.

Figure 9 is a graph showing how the pitch P of the core portion 14 changes when the number of days of room temperature storage of a clad film 401 having a first clad layer 11 and a clad film 402 having a second clad layer 12 are the same and different. In the example of Figure 9, the target value of the pitch P is 2750 μm.

Sample No. 1 is an example in which both clad films 401 and 402 have a short shelf life at room temperature.

Sample No. 2 is an example in which both clad films 401 and 402 were stored at room temperature for a long period of time.

Sample No. 3 is an example in which clad film 401 has a long room temperature storage period and clad film 402 has a short room temperature storage period.

Sample No. 4 is an example in which clad film 401 has a short room temperature storage period and clad film 402 has a long room temperature storage period.

When comparing the pitch P of these four samples, as shown in Figure 9, when clad film 402 is stored at room temperature for a long period of time, the amount of change in pitch P from the target value of 2750 μm is greater than when clad film 401 is stored at room temperature for a long period of time. In contrast, when clad film 402 is stored at room temperature for a short period of time, the amount of change in pitch P from the target value of 2750 μm is smaller, regardless of the number of days clad film 401 is stored at room temperature.

Taking these results into consideration, it can be seen that the influence of the clad film 402, which is laminated first onto the core layer 13, is more dominant than the influence of the clad film 401, which is laminated later.

Depending on the manufacturing method, it is possible that both clad films 401 and 402 may have a strong effect on pitch P. For example, this would occur when clad films 401 and 402 are simultaneously laminated to core layer 13. In such cases, any calculated value, such as the average number of days that clad films 401 and 402 are stored at room temperature, can be calculated and applied to the number of days that they are stored at room temperature.

As described above, in this embodiment, the irradiation area 301, etc. are adjusted based on the effect that the elapsed time T from the time of manufacture of the clad films 401, 402 has on the pitch P of the core portion 14. As such, there are several possible mechanisms by which the elapsed time T of the clad films 401, 402 affects the pitch P, but one mechanism is that the rate of the curing reaction in the clad forming layer 170 decreases as the elapsed time T increases.

Assuming that the rate of the curing reaction does not decrease even if the elapsed time T is long, when the cladding layer 170 laminated on the core layer 13 is heated, the cladding layer 170 quickly hardens and bonds to the core layer 13. This should suppress shrinkage of the core layer 13.

In contrast, if we assume that the rate of the curing reaction is slowing down, the curing of the cladding layer 170 is delayed, and it is thought that the core layer 13 shrinks due to heating before the cladding layer 170 is bonded to the core layer 13. Furthermore, it is thought that the longer the elapsed time T of the cladding films 401, 402, the greater the change in the pitch P of the core portion 14, which corresponds to the actual phenomenon.

As described above, the method for manufacturing an optical waveguide according to this embodiment includes a preparation step S102, a core layer formation step S104, and a cladding layer formation step S106. In the preparation step S102, the core-forming layer 160 and the cladding layer 170 are prepared. In the core-layer formation step S104, a portion of the core-forming layer 160 is irradiated with active radiation R to obtain a core layer 13 including multiple core portions 14 corresponding to the non-irradiated region 302 and side cladding portions 15 located between the core portions 14 and corresponding to the irradiated region 301. In the cladding layer formation step S106, the cladding layer 170 is laminated on the core layer 13 and heated to obtain an optical waveguide 1 including the core layer 13, the first cladding layer 11, and the second cladding layer 12. In the core layer formation step S104, the size of at least one of the irradiated region 301 and the non-irradiated region 302 is adjusted depending on the elapsed time T from the time of manufacturing the cladding layer 170.

With this configuration, the size of at least one of the irradiated area 301 and the non-irradiated area 302 can be appropriately set, taking into account deformation of the core layer 13 caused by the clad films 401, 402, including the clad forming layer 170. This allows for the efficient manufacture of optical waveguides 1 with a highly accurate pitch P of the core portions 14.

The optical waveguide 1 manufactured in this embodiment includes a core layer 13, and a first cladding layer 11 and a second cladding layer 12 laminated on both sides of the core layer 13. The core layer 13 is provided on a substrate 100 prior to the process of obtaining the optical waveguide 1, i.e., the cladding layer formation process S106. The cladding layer formation process S106 includes the steps of laminating a cladding layer 170 on the core layer 13 to obtain a laminate, peeling the substrate 100 from the laminate, and laminating the cladding layer 170 on the core layer 13 and heating the laminate to obtain the optical waveguide 1.

This configuration results in an optical waveguide 1 having a structure in which a core layer 13 is sandwiched between a first cladding layer 11 and a second cladding layer 12. In such an optical waveguide 1, the difference in refractive index between the core layer 13 and the first cladding layer 11 and second cladding layer 12 is stable, making it possible to efficiently manufacture an optical waveguide 1 with low transmission loss.

The optical waveguide 1 manufactured in this embodiment further includes a first cover layer 18 and a second cover layer 19. The first cover layer 18 is laminated on the first cladding layer 11 on the side opposite the core layer 13. The second cover layer 19 is laminated on the second cladding layer 12 on the side opposite the core layer 13.

With this configuration, the first cover layer 18 and the second cover layer 19 can protect the first cladding layer 11, the second cladding layer 12, and the core layer 13. This increases the durability of the optical waveguide 1. It also improves operability when laminating the first cladding layer 11 and the second cladding layer 12 onto the core layer 13. Specifically, even if the first cladding layer 11 and the second cladding layer 12 are very thin, supporting them with the first cover layer 18 and the second cover layer 19 improves grippability, portability, and other properties.

The method for manufacturing an optical waveguide according to the present invention has been described above based on the illustrated embodiments, but the present invention is not limited to these.

For example, the method for manufacturing an optical waveguide of the present invention may be obtained by adding any desired process to the above embodiment.

Next, specific examples of the present invention will be described.
3. Fabrication of Optical Waveguides 3.1. Fabrication of Core Film 3.1.1. Polymer Synthesis Hexylnorbornene (HxNB, 7.2 g, 40.1 mmol) and diphenylmethylnorbornenemethoxysilane (diPhNB, 12.9 g, 40.1 mmol) were weighed into a 500 mL vial in a dry box, and 60 g of dehydrated toluene and 11 g of ethyl acetate were added. The vial was then covered with a silicone sealer and sealed at the top.

Next, 1.56 g (3.2 mmol) of Ni catalyst and 10 mL of dehydrated toluene were weighed into a 100 mL vial, a stirrer tip was inserted, and the vial was sealed. The catalyst was thoroughly stirred to completely dissolve. 1 mL of this Ni catalyst solution was accurately measured with a syringe and injected into the vial containing the two norbornenes dissolved above. After stirring at room temperature for 1 hour, a significant increase in viscosity was confirmed. At this point, the vial was removed, and 60 g of tetrahydrofuran (THF) was added and stirred to obtain a reaction solution.

Next, 9.5 g of acetic anhydride, 18 g of hydrogen peroxide (30% concentration), and 30 g of ion-exchanged water were added to a 100 mL beaker and stirred to prepare an aqueous solution of peracetic acid. The entire amount of this solution was then added to the reaction solution and stirred for 12 hours to carry out the reduction treatment of Ni.

Next, the reaction solution after the treatment was completed was transferred to a separatory funnel, and after the lower aqueous layer was removed, 100 mL of a 30% aqueous solution of isopropyl alcohol was added and vigorously stirred. After allowing to stand and allowing for complete separation into two layers, the aqueous layer was removed. This water washing process was repeated a total of three times, after which the oil layer was dropped into a large excess of acetone to reprecipitate the produced polymer. The polymer was separated from the filtrate by filtration and then heated and dried for 12 hours in a vacuum dryer set at 60°C to obtain the polymer.

The molar ratio of each structural unit in the resulting polymer was identified by NMR measurement as 50 mol% hexylnorbornene structural units and 50 mol% diphenylmethylnorbornenemethoxysilane structural units.

3.1.2. Preparation of Core-Forming Resin Composition 10 g of the above polymer was weighed into a 100 mL glass container, and 40 g of mesitylene, 0.01 g of the antioxidant Irganox 1076 (manufactured by BASF), 2 g of cyclohexyloxetane monomer (2 g of CHOX, manufactured by Toagosei Co., Ltd.), and 0.0125 g of the polymerization initiator (photoacid generator) Rhodorsil (registered trademark) Photoinitiator 2074 (manufactured by Rhodia Chemicals, Inc.) in 0.1 mL of ethyl acetate were added thereto and dissolved uniformly. The mixture was then filtered through a 0.2 μm PTFE filter to prepare a varnish-like core-forming resin composition.

3.1.3. Preparation of Core-Forming Layer The core-forming resin composition was uniformly applied to a 100 μm-thick PET film that had been subjected to a release treatment using a doctor blade, and then placed in a dryer at 40°C for 5 minutes. The solvent was completely removed to form a coating. This resulted in a core film with a 40 μm-thick core-forming layer.

3.2. Exposure Treatment The core film was irradiated with ultraviolet light in a pattern including parallel linear irradiation regions using a direct imaging exposure machine. The core film was then placed in an oven and heated at 160°C for 60 minutes. This resulted in a core layer including linear core portions. The cumulative amount of ultraviolet light was 1,300 mJ/ ^cm² .

3.3. Fabrication of Clad Film 3.3.1. Preparation of Clad-Forming Resin Composition A varnish-like clad-forming resin composition was prepared by adding 2-undecylmethylimidazole (C11Z, Shikoku Chemicals Corporation, 0.06 g) to and mixing with a norbornene-based resin composition containing a cyclic olefin-based resin (10 g of a 20 wt % 2-heptanone solution of Avatrel (registered trademark) 2590, manufactured by Promerus).

The cladding resin composition was uniformly applied with a doctor blade to a 25 μm-thick polyimide film (Kapton 100ENC, manufactured by DuPont-Toray Co., Ltd.) and a 25 μm-thick polyimide film (Upilex 25SGA, manufactured by Ube Industries, Ltd.), and then dried for 15 minutes in a dryer at 45° C. This produced two cladding films each having a 6 μm-thick cladding layer.

3.4. Fabrication of Optical Waveguides Two clad films were cooled in a refrigerator with an internal temperature of 5°C, then placed at 22°C (room temperature) and left for a predetermined number of days. A clad film fabricated using a 25 μm-thick polyimide film (Kapton 100ENC, manufactured by DuPont-Toray Co., Ltd.) left at room temperature was adsorbed and fixed to a bonding device. Meanwhile, a core film with a core layer formed thereon was subjected to plasma treatment and then adsorbed and fixed to the bonding device. The plasma treatment involved exposing the core film to an atmosphere of 10 Pa, in which oxygen was introduced at 100 mL/min, using a plasma device. The clad-forming layer of the clad film was then laminated to the core film to obtain a laminate. The laminate was then thermocompressed using a laminator. The resulting bonded body was placed in an oven and heated at 160°C for 30 minutes. The bonded body was then slowly cooled to room temperature.

Next, a clad film made from a 25 μm thick polyimide film (Upilex 25SGA manufactured by Ube Industries) that had been left at room temperature was adsorbed and fixed to a lamination device. Meanwhile, the substrate was peeled off from the core film on which the core layer had been formed. The peeled surface was then subjected to a corona treatment, after which the clad-forming layer of the clad film was laminated onto the peeled surface of the core layer to obtain a laminate. The laminate was then thermocompressed using a laminator. The resulting pressed body was placed in an oven and heated at 180°C for 120 minutes to obtain an optical waveguide.

Several optical waveguides were then manufactured using the above method, while varying the number of days the clad film was stored at room temperature.

4. Evaluation of Optical Waveguides The core pitch of the manufactured optical waveguides was measured. The measured pitch and the number of days that the cladding film used to manufacture the optical waveguides had been stored at room temperature were plotted on an orthogonal coordinate system. This resulted in the scatter diagram shown in Figure 7.

As shown in Figure 7, a negative correlation was observed between the number of days the clad film was stored at room temperature and the core pitch, as indicated by the dashed line in Figure 7. Therefore, by utilizing this correlation, it was found that optical waveguides with highly accurate core pitch can be efficiently manufactured by adjusting the size of at least one of the irradiated and non-irradiated areas depending on the elapsed time since the production of the clad film comprising the clad-forming layer.

1 Optical waveguide 11 First cladding layer 12 Second cladding layer 13 Core layer 14 Core portion 15 Side cladding portion 18 First cover layer 19 Second cover layer 100 Substrate 101 End surface 102 End surface 131 Polymer 132 Monomer 160 Core forming layer 170 Cladding forming layer 200 Core film 301 Irradiated region 302 Non-irradiated region 303 Photomask 304 Direct imaging exposure machine 401 Cladding film 402 Cladding film P Pitch R Actinic radiation S102 Preparation step S104 Core layer forming step S106 Cladding layer forming step x Number of days of storage at room temperature y Correction magnification

Claims (6)

providing a core forming layer and a cladding forming layer;
irradiating a portion of the core-forming layer with active radiation to obtain a core layer including a plurality of core portions corresponding to non-irradiated regions and aligned in a predetermined direction , and side clad portions positioned between the core portions and corresponding to the irradiated regions;
a step of laminating the cladding layer on the core layer and heating the resulting layer to obtain an optical waveguide having the core layer and the cladding layer;
and
A method for manufacturing an optical waveguide, characterized in that the size of at least one of the irradiated area and the non-irradiated area in the direction in which the core portions are arranged is adjusted depending on the elapsed time from the time of manufacturing the cladding forming layer. The elapsed time is the number of days stored at room temperature,
2. The method for manufacturing an optical waveguide according to claim 1, wherein the correction factor when adjusting the size is y and the number of days of storage at room temperature is x, and the correction factor is set so as to satisfy the following correction formula (1):
y = x ^A (1)
[In the correction formula (1), A is 0.00015 to 0.00045.] The method for manufacturing an optical waveguide according to claim 1 or 2, wherein the cladding layer has a thickness of 1 to 200 μm. The optical waveguide is
the core layer;
a first clad layer and a second clad layer, which are the clad layers laminated on both sides of the core layer;
Equipped with
the core layer is provided on a substrate before the step of obtaining the optical waveguide;
The step of obtaining the optical waveguide includes:
laminating the cladding layer on the core layer to obtain a laminate;
peeling the substrate from the laminate;
laminating the cladding layer on the core layer and heating the cladding layer to obtain the optical waveguide;
The method for manufacturing an optical waveguide according to any one of claims 1 to 3, comprising: The optical waveguide is
a first cover layer laminated on the first clad layer on the opposite side of the core layer;
a second cover layer laminated on the second clad layer on the opposite side of the core layer;
The method for manufacturing an optical waveguide according to claim 4 , further comprising: The method for manufacturing an optical waveguide according to any one of claims 1 to 5, wherein the film thickness of the optical waveguide is 50 to 300 μm.