Materials for optical waveguides

Abstract

To provide materials for optical waveguides being stable even when used for a long period of time at a high temperature, and optical waveguide manufacturing method.SOLUTION: An optical waveguide manufacturing method includes a step of laminating a clad dry film and a core dry film with a high refractive index, where a numerical aperture NA1 calculated from a refractive index ncrad1 of a cured clad and a refractive index ncore1 of a cured core respectively obtained by subjecting the clad dry film and the core dry film to ultraviolet treatment and heat treatment is 0.10 or more, a numerical aperture NA2 calculated from a refractive index ncrad2 of a clad heat-treated product and a refractive index ncore2 of a core heat-treated product respectively obtained by further subjecting the cured clad and the cured core to the heat treatment is 0.10 or more, and a loss fluctuation amount between an optical loss of the optical waveguide formed from the cured clad and the cured core and an optical loss of an optical waveguide heat-treated product obtained by heat-treating the optical waveguide is 2.1 (db) or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing an optical waveguide and a material for an optical waveguide.

Background Art

[0002] Conventionally, optical fibers have been the mainstream transmission medium in the fields of long-distance and medium-distance communications such as FTTH (Fiber to the Home) and in-vehicle applications. In recent years, high-speed transmission using light has been required even at short distances within 1 m. In this area, optical waveguide type optical wiring boards that can perform high-density wiring (narrow pitch, branching, crossing, multi-layerization, etc.), surface mountability, integration with an electrical substrate, and bending with a small diameter, which cannot be achieved with optical fibers, are suitable.

[0003] As a material used to form an optical waveguide, for example, an acrylic resin widely used in the manufacture of optical fibers is known. However, an optical waveguide formed of an acrylic resin does not have heat resistance that can withstand the heating conditions when forming an electrical circuit, for example, the reflow conditions at a high temperature of lead-free solder. For this reason, when an optical waveguide is formed on a substrate using an acrylic resin and then various elements such as a photoelectric conversion element are to be mounted, a mounting process using a reflow process cannot be applied. Therefore, when such an optical waveguide is used, it is necessary to arrange the core of the optical waveguide on another substrate or the like on which various elements have been previously mounted with precise position adjustment on the order of several tens of micrometers. Such a mounting process is very complicated and has poor mass productivity.

[0004] Therefore, as a material for an optical waveguide having heat resistance, it has been reported that a resin composition containing an epoxy resin and a curing initiator by ultraviolet rays is used to form a core layer or a cladding layer of the optical waveguide (Patent Document 1). In Patent Document 1, a liquid aliphatic epoxy compound, a polyfunctional aromatic epoxy compound having three or more epoxy groups in the molecule, a solid bisphenol A type epoxy compound having an epoxy equivalent of 400 g / eq or more and 1500 g / eq or less, and a photocuring agent are included, and a liquid bisphenol A type epoxy compound, a phenol novolac type epoxy compound, a cresol novolac type epoxy compound, and a solid alicyclic epoxy compound having three or more epoxy groups in the molecule are contained in an amount of 5% by mass or less based on the total amount of the epoxy compounds. An optical waveguide composition is used.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The epoxy-based raw materials used in the invention described in Patent Document 1 above are aromatic or aliphatic polymers and contain many epoxy groups. When ultraviolet rays are applied to a resin composition containing such an epoxy resin and a ultraviolet curing initiator, the epoxy groups easily react and cure with the acid generated by the ultraviolet rays, so that an optical waveguide can be formed. However, it has been found that if there are unreacted epoxy groups in the resin composition, the epoxy groups will be oxidized by heat. Then, a problem occurs that the refractive index of the optical waveguide changes. In particular, since it affects the refractive index of light in the 1.3 μm band, it is a problem in single-mode materials. In addition, since the variation in the refractive index is larger in the cladding layer than in the core layer, there is also a problem that the numerical aperture (N / A) becomes smaller and the optical loss becomes larger.

[0007] Therefore, an object of the present invention is to provide a stable optical waveguide material and a method for manufacturing an optical waveguide that can improve the above problems and suppress a decrease in the numerical aperture or an increase in optical loss even when used at a high temperature for a long time.

Means for Solving the Problems

[0008] As a result of intensive studies to solve the above problems, the present inventor has found that the above problems can be solved by the following configuration.

[0009] That is, a method for manufacturing an optical waveguide according to an aspect of the present invention is a method for manufacturing an optical waveguide including a cladding layer and a core layer overlapping the cladding layer, including a step of laminating a cladding dry film formed using a cladding resin composition and a core dry film formed using a core resin composition having a refractive index larger than that of the cladding resin composition, the numerical aperture NA1 calculated from the refractive index n crad 1 of the cladding cured product and the refractive index n core 1 of the core cured product obtained by curing the cladding dry film and the core dry film by ultraviolet treatment and heat treatment at 140°C for 30 minutes respectively is 0.10 or more, the numerical aperture NA2 calculated from the refractive index n crad 2 of the cladding heat-treated product and the refractive index n core 2 of the core heat-treated product obtained by further heat-treating the cladding cured product and the core cured product at 175°C for 177 hours respectively is 0.10 or more, the loss variation amount, which is the difference (β-α) between the optical loss α of the optical waveguide formed from the cladding cured product and the core cured product and the optical loss β of the heat-treated optical waveguide obtained by heat-treating the optical waveguide at 175°C for 177 hours, is 2.1 [dB] or less. This is the gist of the present invention.

Advantages of the Invention

[0010] According to the present invention, it is possible to provide a method for manufacturing an optical waveguide and a material for an optical waveguide that can suppress a decrease in the numerical aperture and reduce light loss even when used at high temperatures.

Brief Description of the Drawings

[0011]

Figure 1

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments for carrying out the present invention will be specifically described, but the present invention is not limited thereto.

[0013] (Method for Manufacturing an Optical Waveguide) The method for manufacturing an optical waveguide according to the present embodiment is a method for manufacturing an optical waveguide including a cladding layer and a core layer overlapping the cladding layer.

[0014] The manufacturing method of the present embodiment includes a step of laminating a dry film for a cladding formed using a resin composition for a cladding and a dry film for a core formed using a resin composition for a core having a refractive index higher than that of the resin composition for a cladding.

[0015] In the present embodiment, the numerical aperture NA1 calculated from the refractive index n crad 1 of the cladding cured product and the refractive index n core 1 of the core cured product obtained by curing the dry film for a cladding and the dry film for a core by ultraviolet treatment and heat treatment at 140° C. for 30 minutes, respectively, is 0.10 or more. Further, the numerical aperture NA2 calculated from the refractive index n crad 2 of the cladding heat-treated product and the refractive index n core 2 of the core heat-treated product obtained by further heat-treating the cladding cured product and the core cured product at 175° C. for 177 hours, respectively, is 0.10 or more.

[0016] That is, in the present embodiment, in the cured products of the cladding dry film and the core dry film, the numerical aperture (NA) is 0.10 or more in both the cured product before heat treatment and the cured product after heat treatment. Thereby, even when used at high temperatures, it is possible to suppress a decrease in the numerical aperture, and it is possible to suppress fluctuations in the refractive index in the 1.3 μm (1310 nm) band.

[0017] Furthermore, in the present embodiment, the loss variation amount, which is the difference (β - α) between the optical loss α of the optical waveguide formed from the cladding cured product and the core cured product, and the optical loss β of the heat-treated optical waveguide obtained by heat-treating the optical waveguide at 175 °C for 177 hours, is 2.1 [dB] or less. That is, in the optical waveguide formed from the cladding cured product and the core cured product of the present embodiment, there is an advantage that the optical loss variation does not change significantly due to heat treatment. Thereby, it is possible to suppress optical loss and provide an optical waveguide with excellent reliability.

[0018] Specifically, ultraviolet irradiation is performed as the ultraviolet treatment on the cladding dry film and the core dry film. Examples of the light source for the ultraviolet irradiation include a low-pressure mercury lamp, a high-pressure mercury lamp, and an ultra-high-pressure mercury lamp. Also, the irradiation amount of ultraviolet rays is usually 10 mJ / cm 2 or more and 20000 mJ / cm 2 or less, preferably 100 J / cm 2 or more and 15000 mJ / cm 2 or less, more preferably 500 J / cm 2 or more and 10000 mJ / cm 2 or less.

[0019] In the present embodiment, as the heat treatment after curing the dry film, a heat treatment at 175 °C for 177 hours is performed, which is equivalent to a heat treatment at 150 °C for 1000 hours according to the definition of Arrhenius.

[0020] In the present embodiment, the numerical aperture is a value obtained as follows: First, measure the refractive indices of the cured products of the cladding and the core using an Abbe refractometer under the conditions of a temperature of 25°C and a wavelength of 1310 nm. Then, using the obtained values of the refractive indices n, calculate the numerical aperture (NA) using the following formula. NA = ((n core )^2 - (n crad )^2)^(1 / 2))

[0021] Also, in this embodiment, the loss variation amount is a value obtained as follows: First, the optical loss value α (the average value of a total of 36 channels including 12 upper channels, 12 middle channels, and 12 lower channels) of an optical waveguide (a 5 cm square substrate, waveguide length: 5 cm) fabricated on a substrate by a forming method as described later before high-temperature treatment, and the optical loss value β (the average value of a total of 36 channels including 12 upper channels, 12 middle channels, and 12 lower channels) of the same sample after being treated at 175°C for 177 hours are calculated (the loss value β after treatment - the loss value α before treatment).

[0022] Note that the method for measuring the optical loss value is as described below. First, light from a 1310 nm LED light source is incident on the end of the optical waveguide through an optical fiber with a core diameter of 9 μm and NA 0.12 via a matching oil (refractive index 1.505). Then, from the opposite side, a power meter is connected through an optical fiber with a core diameter of 50 μm and NA 0.21 via the same matching oil, and the power (P1) when an optical circuit is inserted is measured. Further, the power (P0) in a state where the optical circuit is not present and the two above-mentioned fibers are butted against each other is measured, and the insertion loss of the optical circuit is calculated using the calculation formula of -10log(P1 / Po).

[0023] Next, an embodiment of forming an optical waveguide on a substrate using a cladding dry film and a core dry film will be described with reference to FIG. 1.

[0024] In forming the optical waveguide of this embodiment, a cladding dry film and a core dry film are used to form the cladding and the core, respectively. Note that as the cladding dry film and the core dry film used in this embodiment, it is preferable to use the dry films described in the materials for optical waveguides described later.

[0025] First, as shown in Fig. 1(a), after laminating the clad film 1 on the surface of the substrate 10 on which the electric circuit 11 is formed, the clad film 1 is cured by irradiating light such as ultraviolet rays or heating. As the substrate 10, for example, a flexible printed wiring board having an electric circuit formed on one side of a transparent base material such as a polyimide film, a printed wiring board such as glass epoxy, or the like is used. By such a process, an underclad 3a is laminated and formed on the surface of the substrate 10 as shown in Fig. 1(b).

[0026] Next, as shown in Fig. 1(c), after laminating the core film 2 on the surface of the underclad 3a, a mask having slits of the core pattern is overlaid, and the core light film 2 is exposed with the core pattern by irradiating light such as ultraviolet rays that can be photocured through the slits. As the exposure method, in addition to the method of selective exposure using a mask, it may also be performed by a direct drawing method in which laser light is scanned and irradiated along the pattern shape.

[0027] Next, after exposure, the core light film 2 is developed using a developer such as an aqueous flux cleaning agent to remove the resin of the unexposed and uncured portions of the core light film 2. Thereby, as shown in Fig. 1(d), a core 4 of a predetermined core pattern is formed on the surface of the underclad 3a.

[0028] Next, as shown in Fig. 1(e), the clad film 1 is laminated and stacked so as to cover the underclad 3a and the core 4. Then, by irradiating light or heating to cure the clad film 1, an overclad 3b as shown in Fig. 1(f) is formed. In this way, an optical waveguide A in which the core 4 is embedded in the clad 3 composed of the underclad 3a and the overclad 3b is formed on the surface of the substrate 10.

[0029] In the optical waveguide A thus obtained, by having the above-described configuration, fluctuations in the refractive index in the 1.3-μm band due to high temperature can be suppressed, light loss can be reduced, and excellent optical communication can be realized even at high temperatures. Therefore, the substrate 10 on which such an optical waveguide A is formed is preferably used as a printed wiring board for optical transmission, and is preferably used, for example, in mobile phones, portable information terminals, and the like.

[0030] (Material for optical waveguide) The material for an optical waveguide according to the present embodiment includes a clad dry film formed using a resin composition for a clad, and a core dry film formed using a resin composition for a core having a refractive index higher than that of the resin composition for the clad.

[0031] Then, the refractive index n crad 1 of the clad cured product obtained by curing the clad dry film and the core dry film by ultraviolet treatment and heat treatment at 140°C for 30 minutes respectively, and the refractive index n core 1 of the core cured product, and the numerical aperture NA1 calculated therefrom is 0.10 or more. The refractive index n crad 2 of the clad heat-treated product obtained by further heat-treating the clad cured product and the core cured product at 175°C for 177 hours respectively, and the refractive index n core 2 of the core heat-treated product, and the numerical aperture NA2 calculated therefrom is 0.10 or more.

[0032] Furthermore, in the material for an optical waveguide according to the present embodiment, the loss variation amount, which is the difference (β - α) between the optical loss α of the optical waveguide formed from the clad cured product and the core cured product, and the optical loss β of the heat-treated optical waveguide obtained by heat-treating the optical waveguide at 175°C for 177 hours, is 2.1 [dB] or less.

[0033] In the material for an optical waveguide according to the present embodiment, ultraviolet treatment, numerical aperture, and loss variation amount have the same meaning as the ultraviolet treatment, numerical aperture, and loss variation amount described in the above manufacturing method.

[0034] By using the material for an optical waveguide of such an embodiment, even when used at a high temperature, it is possible to suppress the numerical aperture to a small value, reduce the optical loss, and obtain a highly reliable optical waveguide.

[0035] Hereinafter, the dry film for a cladding and the dry film for a core included in the material for an optical waveguide of this embodiment will be described in more detail.

[0036] · Dry film for cladding The material for forming the dry film for cladding is not particularly limited as long as it is a resin composition that satisfies the regulations on the numerical aperture and the amount of loss variation as described above. However, a cladding resin composition having a refractive index lower than that of the material for the dry film for core described later at the transmission wavelength of the guided light is used. Specifically, as the refractive index at the transmission wavelength in the 1.3 μm band, for example, a resin composition having a refractive index of about 1.5 to 1.57 can be mentioned. Examples of such resin compositions include curable resin compositions that are cured by energy rays such as light and heat, and resin compositions containing, for example, epoxy resins, acrylic resins, polycarbonate resins, polyimide resins, silicone resins, etc. having the refractive index as described above. Among these, epoxy resins are preferable, and in particular, it is preferable to use bisphenol A type epoxy resins, fluorene skeleton-containing epoxy resins, phenol novolac type epoxy resins, and hydrogenated bisphenol A type epoxy resins, etc. These may be used alone or in combination of two or more.

[0037] In a particularly preferred embodiment, by using a combination of bisphenol A type epoxy resin and hydrogenated bisphenol A type epoxy resin, there is an advantage that the occurrence of bleed-out by an antioxidant described later can be suppressed.

[0038] When the resin composition for the cladding contains bisphenol A type epoxy resin and hydrogenated bisphenol A type epoxy resin, the mixing ratio is preferably in the range of 95:5 to 75:25 in terms of mass ratio of bisphenol A type epoxy resin:hydrogenated bisphenol A type epoxy resin. When bisphenol A type epoxy resin and hydrogenated bisphenol A type epoxy resin are used in combination, by having the mixing ratio within the above range, it is considered that the number of apertures NA2 after heat treatment can be maintained at 0.10 or more, and light loss at high temperatures can be more suppressed. If the mixing ratio of the hydrogenated bisphenol A type epoxy resin is too small, the antioxidant described later will bleed out of the system, so there is a risk that the light loss at high temperatures will increase, which is not preferable. On the other hand, if it is too much, there is a risk of light leakage and an increase in light loss, and there is also a risk that the number of apertures after high-temperature treatment will be less than 0.10, so it is not preferable. More preferably, the mass ratio of bisphenol A type epoxy resin:hydrogenated bisphenol A type epoxy resin is 95:5 to 85:15.

[0039] Also, in a preferred embodiment, the resin composition for the cladding contains an epoxy resin and an antioxidant. Thereby, it is considered that a dry film for the cladding with more excellent heat resistance can be obtained.

[0040] The antioxidant is not particularly limited. For example, phenolic antioxidants, phosphite antioxidants, sulfur antioxidants, etc. can be used. Examples of phenolic antioxidants include AO-20, AO-30, AO-40, AO-50, AO-60, AO-80 manufactured by Adeka Corporation, and SUMILIZER GA-80 manufactured by Sumitomo Chemical Co., Ltd. Examples of phosphite antioxidants include PEP-8, PEP-36, HP-10, 2112, 1178, 1500 manufactured by Adeka Corporation, and JP-360, JP-3CP manufactured by Johoku Chemical Industry Co., Ltd. Examples of sulfur antioxidants include AO-412S, AO-503 manufactured by Adeka Corporation, and SUMILIZER TP-D manufactured by Sumitomo Chemical Co., Ltd. The antioxidant may be used alone or in combination of two or more of the above-exemplified compounds. Among these, preferably, a phenolic antioxidant is used.

[0041] In the resin composition for the cladding, the content of the antioxidant is preferably 1.5 parts by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the epoxy resin. If the antioxidant is less than 1.5 parts by mass, the number of openings NA2 after heat treatment may be less than 0.10. Therefore, the lower limit of the antioxidant content is preferably 1.5 parts by mass or more, and more preferably 2.0 parts by mass or more. On the other hand, if a large amount of antioxidant is contained, there is a possibility of bleed-out of the antioxidant. Therefore, the upper limit of the antioxidant content is preferably 5.0 parts by mass or less, and more preferably 3.0 parts by mass or less in order to further suppress bleed-out.

[0042] The resin composition for the cladding preferably contains a photo-curing agent in addition to the resin and antioxidant as described above.

[0043] The photo-curing agent is not particularly limited as long as it can promote the curing of the resin composition for the cladding by light. Examples of photo-curing agents include photo-cationic curing agents and photo-anionic curing agents.

[0044] The photo cationic curing agent is a polymerization initiator for various resins and is a compound that can initiate a reaction by light. As the photo cationic curing agent, for example, CPI-101A, CPI-100P, CPI-200K manufactured by San-Apro Ltd., SP-170 manufactured by Adeka Corporation, B2380, C1390, D2238, D2960, I0591, M1209, N0137, T1608, etc. manufactured by Wako Pure Chemical Industries, Ltd. can be used. The photo cationic curing agent may be used alone or in combination of two or more of the above-exemplified compounds.

[0045] The photo anionic curing agent is also a polymerization initiator for various resins and is a compound that can initiate a reaction by light. As the photo anionic curing agent, for example, A2502, N0528, O0396 manufactured by Wako Pure Chemical Industries, Ltd. can be used. The photo anionic curing agent may be used alone or in combination of two or more of the above-exemplified compounds.

[0046] The content of the photo curing agent is preferably 0.1 part by mass or more and 1.0 part by mass or less, and more preferably 0.2 part by mass or more and 0.5 part by mass or less with respect to 100 parts by mass of the epoxy resin. If the photo curing agent is too little, the clad resin composition will be difficult to cure. If the photo curing agent is too much, cations or anions will be generated excessively. For this reason, for example, the clad resin composition may become too easy to cure, resulting in a decrease in storage stability or handling properties.

[0047] In the clad resin composition of the present embodiment, in addition to the above-described components, additives such as a leveling agent and a coupling agent (silane coupling agent) can also be blended.

[0048] The dry film for cladding according to this embodiment is not particularly limited as long as it includes a layer of the resin composition for cladding. Specifically, for example, the dry film for cladding may include a film substrate on one surface of the layer of the resin composition for cladding and a protective film on the other surface. The dry film for cladding only needs to include a layer of the resin composition for cladding, and may include other layers in addition to the film substrate and the protective film, or the film substrate and the protective film are not essential either.

[0049] The film substrate is not particularly limited. For example, it includes a polyethylene terephthalate (PET) film, a biaxially oriented polypropylene film, a polyethylene naphthalate film, and a polyimide film. Among these, the PET film is preferably used.

[0050] Also, the protective film is not particularly limited. For example, it includes a polypropylene film and the like.

[0051] Note that the thickness of the dry film for cladding is not particularly limited and can be appropriately set according to the application and the like. For example, it is preferably about 10 μm or more and 30 μm or less.

[0052] The manufacturing method of the dry film for cladding is not particularly limited. For example, the following method can be mentioned. First, a solvent or the like is added to the resin composition for cladding to make it into a varnish state, and the varnish is applied onto the film substrate. This application includes application using a comma coater or the like. By drying this varnish, a layer of the resin composition for cladding is formed on the film substrate. Further, a protective film is laminated on the layer of the resin composition for cladding. As the lamination method, for example, a thermal lamination method can be mentioned.

[0053] · Dry film for core As a material for forming the core dry film, there is no particular limitation as long as it is a resin composition that satisfies the aperture ratio regulation and the loss variation regulation as described above. However, a material having a refractive index higher than that of the material of the clad dry film at the transmission wavelength of the light guiding wave is used. Specifically, as the refractive index at the transmission wavelength in the 1.3 μm band, for example, resin materials having a refractive index of about 1.55 to 1.6 can be mentioned.

[0054] More specifically, similar to the clad dry film, examples of the core resin composition include curable resin compositions that are cured by energy rays such as light or heat. For example, resin compositions containing epoxy resins, acrylic resins, polycarbonate resins, polyimide resins, silicone resins, etc. having the refractive index as described above can be mentioned. Among these, epoxy resins are preferred, and in particular, it is preferable to use epoxy resins such as bisphenol A type epoxy resins, fluorene skeleton-containing epoxy resins, and phenol novolac type epoxy resins. These can be used alone or in combination of two or more.

[0055] Also, in a preferred embodiment, the core resin composition contains an epoxy resin and an antioxidant. Thereby, it is considered that a core dry film having more excellent heat resistance can be obtained.

[0056] The antioxidant is not particularly limited, but for example, the same antioxidants as those described above that can be used in the clad resin composition can be used. Preferably, a phenolic antioxidant is used, similar to the clad resin composition.

[0057] In the resin composition for the core, the content of the antioxidant is preferably 1.5 parts by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the epoxy resin. If the antioxidant content is less than 1.5 parts by mass, the number of apertures NA2 after heat treatment may be less than 0.10. Therefore, the lower limit of the antioxidant content is preferably 1.5 parts by mass or more, and more preferably 2.0 parts by mass or more. On the other hand, if a large amount of antioxidant is contained, there is a risk of bleed-out of the antioxidant. Therefore, the upper limit of the antioxidant content is preferably 5.0 parts by mass or less, and more preferably 3.0 parts by mass or less in order to further suppress bleed-out.

[0058] The resin composition for the core preferably contains a photo-curing agent in addition to the resin and the antioxidant as described above.

[0059] The photo-curing agent is not particularly limited, and for example, the same photo-curing agents as those described above that can be used in the clad resin composition can be used.

[0060] The content of the photo-curing agent is preferably 0.1 part by mass or more and 1.0 part by mass or less, and more preferably 0.2 part by mass or more and 0.5 part by mass or less with respect to 100 parts by mass of the epoxy resin. If the photo-curing agent is too little, the resin composition for the core becomes difficult to cure. If the photo-curing agent is too much, cations and anions are generated excessively. For this reason, for example, the resin composition for the core may become too easy to cure, resulting in a decrease in storage stability or handling properties.

[0061] In the resin composition for the core of the present embodiment, additives such as a leveling agent and a coupling agent (silane coupling agent) can be blended in addition to the components described above.

[0062] The core dry film according to this embodiment is not particularly limited as long as it includes a layer of the core resin composition. Specifically, for example, the core dry film may include a film base material on one surface of the layer of the core resin composition and a protective film on the other surface. The core dry film only needs to include a core resin composition layer, and may include other layers in addition to the film base material and the protective film, or the film base material and the protective film are not essential.

[0063] Here, the film base material and the protective film are not particularly limited. For example, the same films as those described for the clad dry film above can be used.

[0064] Note that the thickness of the core dry film is not particularly limited and can be appropriately set according to the application, etc. For example, it is preferably about 3 μm or more and 10 μm or less.

[0065] The manufacturing method of the core dry film is not particularly limited. For example, it can be manufactured by the same method as the clad dry film described above.

[0066] The optical waveguide material of this embodiment includes the clad dry film and the core dry film as described above. A normal optical waveguide is formed of an upper clad layer, a core layer, and a lower clad layer. The clad dry film included in the optical waveguide material of this embodiment can be used for forming the upper clad layer and the lower clad layer, and the core dry film can be used for forming the core layer.

[0067] The method for manufacturing an optical waveguide using the optical waveguide material of this embodiment is as already described.

[0068] Note that the present invention also includes an optical waveguide formed from the above-described material for an optical waveguide. That is, the optical waveguide of the present embodiment has a cladding layer and a core layer surrounded by the cladding layer, and the cladding layer and the core layer are each composed of a dry film for cladding and a dry film for core included in the material for an optical waveguide of the present embodiment described above. Since the optical waveguide of the present embodiment has durability at high temperatures, it is very useful for industrial applications.

[0069] Hereinafter, the present invention will be described more specifically with reference to examples. Note that the present invention is not limited to the following examples at all.

Examples

[0070] First, the raw materials used for preparing the resin composition in the present embodiment are summarized below.

[0071] 〈Epoxy resin〉 · "Epiclon 850S": Bisphenol A type epoxy resin, manufactured by DIC Corporation (ACH number: 0.056, specific gravity: 1.15) · "VG3101M80": Multifunctional epoxy resin, manufactured by Printteck Co., Ltd. (ACH number: 0.048, specific gravity: 1.19) · "jER1001": Bisphenol A type epoxy resin, manufactured by Mitsubishi Chemical Corporation (ACH number: 0.050, specific gravity: 1.19) · "Epicoat 1006FS": Bisphenol A type epoxy resin, manufactured by Mitsubishi Chemical Corporation (ACH number: 0.048, specific gravity: 1.19) · "JER (registered trademark) YX8040": Hydrogenated bisphenol A type epoxy resin, manufactured by Mitsubishi Chemical Corporation

[0072] 〈Hardener〉 · "CPI-101A": Photo cationic curing agent, manufactured by San-Apro Ltd.

[0073] 〈Antioxidant〉 · "AO-60": Phenolic antioxidant, manufactured by ADEKA Corporation

[0074] <Preparation of Resin Composition for Clad> The components were blended with the blending compositions (parts by mass) shown in Tables 1 and 2 below, and the mixed solvent of MEK and toluene was adjusted to 55 parts by mass with respect to 100 parts by mass of the resin, and mixed while heating at 50 to 80°C. Next, after filtering with a membrane filter having a pore size of 0.5 μm, defoaming was performed to adjust the resin varnishes of the resin compositions for clad of Examples 1 to 7 and Comparative Examples 1 to 6.

[0075] <Preparation of Resin Composition for Core> The components were blended with the blending compositions (parts by mass) shown in Tables 1 and 2 below, and the mixed solvent of MEK and toluene was adjusted to 60 parts by mass with respect to 100 parts by mass of the resin, and mixed while heating at 50 to 80°C. Next, after filtering with a membrane filter having a pore size of 0.2 μm, defoaming was performed to adjust the resin varnishes of the resin compositions for core of Examples 1 to 7 and Comparative Examples 1 to 6.

[0076] <Formation of Dry Film for Clad> The resin composition varnishes for clad of each example and comparative example were applied to a PET film (product number A4100) manufactured by Toyobo Co., Ltd. using a multi-coater of a comma coater head manufactured by Hirano Texeed Co., Ltd., dried to a predetermined thickness, and heat-laminated with OPP-MA420 manufactured by Oji Special Paper Co., Ltd., which is a release film, to obtain a dry film for clad having a resin layer thickness of 20 μm.

[0077] <Formation of Dry Film for Core> The resin composition varnishes for core of each example and comparative example were applied to a PET film (product number A4100) manufactured by Toyobo Co., Ltd. using a multi-coater of a comma coater head manufactured by Hirano Texeed Co., Ltd., dried to a predetermined thickness, and heat-laminated with OPP-MA420 manufactured by Oji Special Paper Co., Ltd., which is a release film, to obtain a dry film for core having a resin layer thickness of 7 μm.

[0078] <Evaluation Method> (Refractive Index) For each of the clad dry films and core dry films in the examples and comparative examples, they were laminated using a vacuum laminator so as to be 50 to 80 μm each. The film was irradiated with ultraviolet rays, the PET film was peeled off, and it was cured by heat treatment at 140 °C for 30 minutes to obtain a clad cured product and a core cured product.

[0079] Regarding the obtained clad cured product and core cured product, at a temperature of 25 °C, the refractive index at a wavelength of 1310 nm was measured using an Abbe refractometer.

[0080] Next, each of the clad cured product and core cured product was heat-treated at 175 °C for 177 hours. Specifically, each cured product was put into an oven at 175 °C in the atmosphere for 177 hours for heat treatment.

[0081] Then, regarding the clad cured product and core cured product after heat treatment, the refractive index at a wavelength of 1.3 μm was measured using an Abbe refractometer.

[0082] Finally, the refractive indices n crad 1 of the clad cured product and core cured product before heat treatment (untreated) and the refractive index n core 1 of the core cured product were respectively subtracted from the refractive index n crad 2 of the clad heat-treated product and the refractive index n core 2 of the core heat-treated product, and the resulting values were taken as the refractive index change amounts.

[0083] Each value is shown in Table 1 and Table 2.

[0084] (Numerical aperture NA) From the values of each refractive index obtained above, the numerical aperture NA1 before heat treatment (untreated) was calculated by the following formula. NA1 = ((n core 1)^2 - (n crad 1)^2)^(1 / 2)) Furthermore, the numerical aperture NA2 after heat treatment was calculated by the following formula. NA2 = ((n core 2)^2 - (n crad 2)^2)^(1 / 2))

[0085] Table 1 and Table 2 show NA1 and NA2 obtained from the refractive indices of the clad cured product and the core cured product in each of the obtained examples and comparative examples.

[0086] (Loss variation amount) First, an optical waveguide was formed using the dry film for the clad and the dry film for the core of each example and each comparative example.

[0087] Specifically, using the dry film for the core and the dry film for the clad, first, as an underclad, the dry film for the clad was laminated on a substrate (R-1515V, 0.8 mm thick, 125 cm square). Further, the dry film for the core was laminated thereon, exposed using a mask capable of forming a pattern with a width of 7 μm, heat-treated, and then the unexposed core material was removed by development, and the dry film for the clad was laminated as an overclad, thereby creating a single-mode waveguide sample with a waveguide length of 5 cm and a core size of 7 μm.

[0088] Then, the optical waveguide fabricated on the substrate was cut into a 5 cm square (substrate of 5 cm square, waveguide length: 5 cm), and the optical loss value α before the high-temperature treatment (average value of 36 in total, 12 upper bundles, 12 middle bundles, and 12 lower bundles) and the optical loss value β after treating the same sample at 175 °C for 177 hours (average value of 36 in total, 12 upper bundles, 12 middle bundles, and 12 lower bundles) were measured. The light from a 1310 nm LED light source was incident through an optical fiber with a core diameter of 9 μm and NA of 0.12 to the end of the optical waveguide fabricated above through a matching oil (refractive index 1.505), and from the opposite side, through the same matching oil, through an optical fiber with a core diameter of 50 μm and NA of 0.21, connected to a power meter, and the insertion loss of the optical circuit was calculated using the formula of -10log(P1 / Po) when the optical circuit was inserted, and the difference between the values was calculated (loss value β after treatment - loss value α before treatment). The pass criterion in this test is that the loss variation amount is 2.0 dB or less.

[0089] The numerical values of each example and comparative example are summarized in Table 1 and Table 2.

[0090]

Table 1

[0091]

Table 2

[0092] <Evaluation and Discussion> From the results in Table 1, according to the present invention, it was confirmed that even after heat treatment at a high temperature for a long time, the numerical aperture NA can be maintained at 1.0 or more. It was also shown that the variation in optical loss after heat treatment can be suppressed. It was found that if the amount of the antioxidant is too large, bleed-out of the antioxidant occurs in the dry film for the cladding and the dry film for the core.

[0093] On the other hand, as shown in Table 2, in the optical waveguides of Comparative Examples 2 to 6 that do not satisfy the provisions of the present invention, a loss variation amount exceeding 2.0 dB / cm was measured. For Comparative Example 1, oxidation progressed due to treatment at a high temperature for a long time, and the numerical aperture NA decreased significantly, so light was not guided.

[0094] Furthermore, regarding the numerical aperture NA, in the optical waveguides of Comparative Examples 1 to 3 and 5, NA2 after heat treatment was less than 1.0.

[0095] From the above, it was confirmed that according to the material for an optical waveguide of the present invention, a highly reliable optical waveguide can be obtained even after treatment at a high temperature for a long time.

Explanation of Reference Numerals

[0096] 1 Film for cladding 2 Optical film for core 3 Cladding 3a Undercladding 3b Overcladding 4 Core

Claims

1. An optical waveguide material comprising a cladding dry film formed using a cladding resin composition and a core dry film formed using a core resin composition having a refractive index greater than that of the cladding resin composition, wherein the refractive index n ｃｒａｄ 1 of the cured cladding obtained by curing the cladding dry film and the core dry film by ultraviolet treatment and heat treatment at 140°C for 30 minutes, respectively, and the refractive index n ｃｏｒｅ 1, and the numerical aperture NA1 calculated therefrom is 0.10 or more, the refractive index n ｃｒａｄ 2 of the heat-treated cladding obtained by further heat-treating the cured cladding and the cured core at 175°C for 177 hours, respectively, and the refractive index n ｃｏｒｅ 2, and the numerical aperture NA2 calculated therefrom is 0.10 or more, the loss variation amount, which is the difference (β - α) between the optical loss α of the optical waveguide formed from the cured cladding and the cured core and the optical loss β of the heat-treated optical waveguide obtained by heat-treating the optical waveguide at 175°C for 177 hours, is 2.1 [dB] or less, and the cladding resin composition contains an epoxy resin and an antioxidant, the epoxy resin contains a BisA-type epoxy resin and a hydrogenated BisA-type epoxy resin, the mass ratio of the BisA-type epoxy resin to the hydrogenated BisA-type epoxy resin is in the range of 95:5 to 75:25, An optical waveguide material.

2. The proportion of the antioxidant is 1.5 parts by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the epoxy resin. The optical waveguide material according to claim 1.

3. The core resin composition contains an epoxy resin and an antioxidant. The optical waveguide material according to claim 1 or 2.

4. The proportion of the antioxidant in the resin composition for the core is 1.5 parts by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the epoxy resin. The optical waveguide material according to claim 3.

5. The optical waveguide material according to any one of claims 1 to 4, wherein the antioxidant is a phenolic antioxidant.

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