JP2023046799A - Optical waveguide manufacturing method and materials for optical waveguide - Google Patents

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

The present invention relates to an optical waveguide manufacturing method and an optical waveguide material.

Conventionally, optical fibers have been the main stream as a transmission medium in the field of FTTH (Fiber to the Home) and in-vehicle long-distance and medium-distance communications. In recent years, there has been a need for high-speed transmission using light over a short distance of 1 m or less. In this area, high-density wiring (narrow pitch, branching, crossing, multi-layering, etc.), surface mountability, integration with electric substrates, and optical waveguide type optical wiring boards that can be bent at small diameters, which cannot be done with optical fibers. is suitable.

As a material used for forming an optical waveguide, for example, an acrylic resin widely used for manufacturing optical fibers is known. However, an optical waveguide made of acrylic resin does not have the heat resistance to withstand the heating conditions for forming an electric circuit, for example, the high-temperature reflow conditions for lead-free solder. Therefore, when an optical waveguide is formed on a substrate using an acrylic resin, and 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 position the core of the optical waveguide on another substrate or the like on which various elements are mounted in advance, with precise position adjustment on the order of several tens of micrometers. Such a mounting process is very complicated and poor in mass productivity.

Therefore, it has been reported that a core layer and a clad layer of an optical waveguide are formed using a resin composition containing an epoxy resin and an ultraviolet curing initiator as a heat-resistant optical waveguide material (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, The content of the liquid bisphenol A type epoxy compound, the phenol novolac type epoxy compound, the cresol novolak type epoxy compound, and the solid alicyclic epoxy compound having three or more epoxy groups in the molecule, which contains a photocuring agent, is the epoxy compound. The optical waveguide composition is used in an amount of 5% by mass or less with respect to the total amount of .

JP 2020-184091 A

The epoxy-based raw material used in the invention described in Patent Document 1 is an aromatic or aliphatic polymer containing many epoxy groups. When a resin composition containing such an epoxy resin and an ultraviolet curing initiator is exposed to ultraviolet rays, the epoxy groups are easily reacted and cured by the acid generated by the ultraviolet rays, making it possible to form an optical waveguide. 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, there arises a problem 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 poses a problem in single-mode materials. In addition, since the variation in the refractive index is greater in the clad layer than in the core layer, there is also the problem that the numerical aperture (N/A) becomes small and the optical loss increases.

Therefore, the present invention solves the above problems and provides a stable optical waveguide material and an optical waveguide that can suppress a decrease in numerical aperture and an increase in optical loss even when used at high temperatures for a long time. The object is to provide a manufacturing method.

Means for Solving the Problems As a result of intensive studies aimed at solving the above problems, the inventors have found that the above problems can be solved by the following configuration.

That is, a method for manufacturing an optical waveguide according to one aspect of the present invention is a method for manufacturing an optical waveguide including a clad layer and a core layer overlapping the clad layer,
A step of laminating a clad dry film formed using a clad resin composition and a core dry film formed using a core resin composition having a higher refractive index than the clad resin composition. including
The refractive index n _crad 1 of the clad cured product and the refractive index n _core of the core cured product obtained by curing the clad dry film and the core dry film by UV treatment and heat treatment at 140° C. for 30 minutes, respectively. 1 and the numerical aperture NA1 calculated from 0.10 or more,
Calculated 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 obtained by further heat-treating the clad cured product and the core cured product at 175 ° C. for 177 hours. The numerical aperture NA2 to be used is 0.10 or more,
The difference 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 optical waveguide heat-treated product obtained by heat-treating the optical waveguide at 175° C. for 177 hours ( β-α) is 2.1 [db] or less,
It is characterized by

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a method for manufacturing an optical waveguide and an optical waveguide material that can keep the numerical aperture small and reduce the loss of light even when used at high temperatures.

FIG. 1 is a schematic diagram showing a manufacturing process for forming an optical waveguide on a substrate using a clad dry film and a core dry film according to one embodiment of the present invention.

EMBODIMENT OF THE INVENTION Below, although embodiment for implementing this invention is described concretely, this invention is not necessarily limited to these.

(Method for manufacturing optical waveguide)
The method for manufacturing an optical waveguide according to this embodiment is a method for manufacturing an optical waveguide including a clad layer and a core layer overlapping the clad layer.

The manufacturing method of the present embodiment includes a clad dry film formed using a clad resin composition, and a core resin composition formed using a core resin composition having a higher refractive index than the clad resin composition. and laminating a dry film.

In the present embodiment, the clad dry film and the core dry film are cured by ultraviolet treatment and heat treatment at 140 ° C. for ₃₀ minutes, respectively. and the numerical aperture NA1 calculated from the refractive index n _core 1 is 0.10 or more. Furthermore, the clad cured product and the core cured product are further heat treated at 175° C. for 177 hours, respectively, to obtain a heat-treated clad product with a refractive index n _crad 2 and a core heat-treated product with a refractive index n _core 2, The numerical aperture NA2 calculated from the above is 0.10 or more.

That is, in the present embodiment, in the cured products of the clad dry film and the core dry film, both the cured product before the heat treatment and the cured product after the heat treatment have a numerical aperture (NA) of 0.10 or more. It is characterized by As a result, it is possible to suppress a decrease in numerical aperture even when used at high temperatures, and to suppress variations in the refractive index in the 1.3 μm (1310 nm) band.

Furthermore, in the present embodiment, the optical loss α of the optical waveguide formed from the clad cured product and the core cured product, and the optical waveguide heat-treated product obtained by heat-treating the optical waveguide at 175° C. for 177 hours The loss fluctuation amount, which is the difference (β-α) from the optical loss β, is 2.1 [db] or less. In other words, the optical waveguide formed from the clad cured product and the core cured product of this embodiment has the advantage that the optical loss variation does not change significantly due to the heat treatment. Thereby, optical loss can be suppressed, and an optical waveguide with excellent reliability can be provided.

As the ultraviolet treatment performed on the clad dry film and the core dry film, specifically, ultraviolet irradiation is performed. The light source for the ultraviolet irradiation includes, for example, a low-pressure mercury lamp, a high-pressure mercury lamp, an extra-high pressure mercury lamp, and the like. The irradiation dose 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. is mentioned.

In this embodiment, the heat treatment after curing the dry film is heat treatment at 175° C. for 177 hours, which is equivalent to heat treatment at 150° C. for 1000 hours according to the Arrhenius definition.

In this embodiment, the numerical aperture is a value obtained as follows:
First, the refractive index of each cured product of the clad and the core is measured with an Abbe refractometer under conditions of a temperature of 25° C. and a wavelength of 1310 nm. Then, using the obtained value of each refractive index n, the numerical aperture (NA) is calculated by the following formula.
NA=((n _core )^2-(n _crad )^2)^(1/2))

In this embodiment, the loss variation is a value obtained as follows: First, an optical waveguide (5 cm square substrate, waveguide Length: 5 cm) before high temperature treatment, optical loss value α (average value of 36 total of 12 upper bundles, 12 middle bundles, and 12 lower bundles), and after treating the same sample at 175 ° C. for 177 hours (Average value of 36 total of 12 upper bundles, 12 middle bundles, and 12 lower bundles) is calculated (loss value after processing β−loss value before processing α).

The method for measuring the optical loss value is as described below. First, light from an LED light source of 1310 nm is passed through an optical fiber with a core diameter of 9 μm and an NA of 0.12, and is incident on the end of the optical waveguide via matching oil (refractive index: 1.505). Then, from the opposite side, an optical fiber with a core diameter of 50 μm and an NA of 0.21 is passed through the same matching oil and connected to a power meter to measure the power (P1) when an optical circuit is inserted. Furthermore, the power (P0) measured without the optical circuit is measured by abutting the two fibers, and the insertion loss of the optical circuit is calculated by the formula -10log(P1/Po).

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

In forming the optical waveguide of the present embodiment, a clad dry film and a core dry film are used to form the core and the clad, respectively. As the cladding dry film and the core dry film used in the present embodiment, it is preferable to use the dry film described in the later-described optical waveguide material.

First, as shown in FIG. 1(a), after the clad film 1 is laminated on the surface of the substrate 10 on which the electric circuit 11 is formed, the clad film 1 is cured by irradiation with light such as ultraviolet light or heating. Let As the substrate 10, for example, a flexible printed wiring board in which an electric circuit is formed on one side of a transparent base material such as a polyimide film, or a printed wiring board such as glass epoxy is used. Through such a process, the undercladding 3a is laminated on the surface of the substrate 10 as shown in FIG. 1(b).

Next, as shown in FIG. 1(c), after the core film 2 is laminated on the surface of the undercladding 3a, a mask having slits of a core pattern is superimposed, and light such as ultraviolet rays that can be photocured is passed through the slits. The optical film 2 for cores is exposed with a core pattern by irradiating with . As the exposure method, in addition to the method of selective exposure using a mask, a direct drawing method of scanning and irradiating laser light along the pattern shape may be used.

Next, after the exposure, the core optical film 2 is developed using a developer such as an aqueous flux detergent to remove the resin from the unexposed, uncured portions of the core optical film 2 . Thereby, as shown in FIG. 1(d), a core 4 having a predetermined core pattern is formed on the surface of the undercladding 3a.

Next, as shown in FIG. 1(e), the clad film 1 is laminated so as to cover the under clad 3a and the core 4. Then, as shown in FIG. Then, by curing the clad film 1 by light irradiation or heating, an over clad 3b as shown in FIG. 1(f) is formed. Thus, an optical waveguide A is formed on the surface of the substrate 10, in which the core 4 is embedded in the clad 3 composed of the under clad 3a and the over clad 3b.

In the optical waveguide A obtained in this way, by having the above-described configuration, it is possible to suppress the fluctuation of the refractive index in the 1.3 μm band due to high temperatures, reduce the optical loss, and achieve excellent optical communication even at high temperatures. can be realized. 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 in mobile phones, personal digital assistants, and the like, for example.

(Material for optical waveguide)
The optical waveguide material of the present embodiment is formed using a clad dry film formed using a clad resin composition and a core resin composition having a higher refractive index than the clad resin composition. Including dry film for the core.

Then, the clad dry film and the core dry film are cured by ultraviolet treatment and heat treatment at 140 ° C. for ₃₀ minutes, respectively. A clad heat-treated product obtained by further heat-treating the clad cured product and the core cured product at 175 ° C. for 177 hours, wherein the numerical aperture NA1 calculated from n _core 1 is 0.10 or more. The numerical aperture NA2 calculated from the refractive index n _crad 2 of the core heat-treated product and the refractive index n _core 2 of the core heat-treated product is 0.10 or more.

Further, in the optical waveguide material of the present embodiment, the optical loss α of the optical waveguide formed from the clad cured product and the core cured product, and the optical waveguide obtained by heat-treating the optical waveguide at 175° C. for 177 hours The loss fluctuation amount, which is the difference (β-α) from the optical loss β of the heat-treated optical waveguide, is 2.1 [db] or less.

In the optical waveguide material of the present embodiment, the ultraviolet treatment, numerical aperture, and loss variation are synonymous with the ultraviolet treatment, numerical aperture, and loss variation described in the manufacturing method.

By using such an optical waveguide material of the present embodiment, it is possible to obtain a highly reliable optical waveguide in which the numerical aperture can be kept small even when used at high temperatures, and the loss of light can be reduced. can.

The clad dry film and core dry film included in the optical waveguide material of the present embodiment will be described in more detail below.

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 numerical aperture specification and the loss fluctuation amount specification as described above, but will be described later. A cladding resin composition is used that has a lower refractive index at the transmission wavelength of guided light than the material of the core dry film. Specifically, a resin composition having a refractive index of, for example, about 1.5 to 1.57 at a transmission wavelength in the 1.3 μm band can be used. Examples of such resin compositions include curable resin compositions that are cured by energy rays such as light or heat. Examples thereof include resin compositions containing resins, silicone resins, and the like. Among these, epoxy resins are preferred, and bisphenol A type epoxy resins, fluorene skeleton-containing epoxy resins, phenol novolac type epoxy resins, and hydrogenated bisphenol A type epoxy resins are particularly preferred. These may be used individually by 1 type, or may be used in combination of 2 or more type.

In a particularly preferred embodiment, the use of a combination of a bisphenol A type epoxy resin and a hydrogenated bisphenol A type epoxy resin has the advantage of being able to suppress the occurrence of bleed-out caused by the antioxidant, which will be described later.

When the clad resin composition contains a bisphenol A type epoxy resin and a hydrogenated bisphenol A type epoxy resin, the blending ratio is 95: bisphenol A type epoxy resin:hydrogenated bisphenol A type epoxy resin by mass ratio. A range of 5 to 75:25 is preferred. When a bisphenol A type epoxy resin and a hydrogenated bisphenol A type epoxy resin are used in combination, the numerical aperture NA2 after the heat treatment can be maintained at 0.10 or more by setting the compounding ratio within the above range. It is considered that the optical loss in If the blending ratio of the hydrogenated bisphenol A type epoxy resin is too small, the antioxidant described below will bleed out and come out of the system, which is not preferable because there is a possibility that light loss will increase at high temperatures. On the other hand, if it is too large, there is a risk that light leakage will occur and the optical loss will increase, and that the numerical aperture after the high temperature treatment will be less than 0.10, which is not preferable. More preferably, the weight ratio of bisphenol A type epoxy resin:hydrogenated bisphenol A type epoxy resin is 95:5 to 85:15.

In a preferred embodiment, the clad resin composition contains an epoxy resin and an antioxidant. It is believed that this makes it possible to obtain a dry film for clad having more excellent heat resistance.

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

In the clad resin composition, 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 numerical aperture NA2 after heat treatment may become less than 0.10. Therefore, the lower limit of the antioxidant content is preferably 1.5 parts by mass or more, more preferably 2.0 parts by mass or more. On the other hand, if a large amount of antioxidant is contained, the antioxidant may bleed out. Therefore, the upper limit of the antioxidant content is preferably 5.0 parts by mass or less, and the bleed out is further suppressed. In order to suppress it, it is more preferably 3.0 parts by mass or less.

The clad resin composition preferably contains a photo-curing agent in addition to the resin and antioxidant described above.

The photo-curing agent is not particularly limited as long as it can accelerate curing of the clad resin composition by light. Photocuring agents include, for example, photocationic curing agents and photoanion curing agents.

A photocationic curing agent is a polymerization initiator for various resins, and is a compound capable of initiating a reaction by light. Examples of photocationic curing agents include CPI-101A, CPI-100P, and CPI-200K manufactured by San-Apro Co., Ltd., SP-170 manufactured by Adeka Co., Ltd., and B2380, C1390, and D2238 manufactured by Wako Pure Chemical Industries, Ltd. , D2960, I0591, M1209, N0137, T1608, etc. can be used. As the photocationic curing agent, the above-exemplified compounds may be used alone, or two or more of them may be used in combination.

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

The content of the photocuring agent is preferably 0.1 parts by mass or more and 1.0 parts by mass or less, and 0.2 parts by mass or more and 0.5 parts by mass or less with respect to 100 parts by mass of the epoxy resin. is more preferable. If the amount of the photocuring agent is too small, the clad resin composition will be difficult to cure. If the photocuring agent is too much, cations and anions are excessively generated. For this reason, for example, the resin composition for cladding may be too easily cured, and the storability and handleability may be deteriorated.

Additives such as a leveling agent and a coupling agent (silane coupling agent) can also be added to the clad resin composition of the present embodiment, in addition to the components described above.

The dry film for clad according to the present embodiment is not particularly limited as long as it has a layer of the resin composition for clad. Specifically, for example, the clad dry film includes a film substrate on one side of the layer of the clad resin composition and a protective film on the other side. The dry film for cladding may be provided with a resin composition layer for cladding, and may include other layers in addition to the film substrate and protective film, and the film substrate and protective film are not essential.

The film substrate is not particularly limited, but examples thereof include polyethylene terephthalate (PET) film, biaxially oriented polypropylene film, polyethylene naphthalate film, and polyimide film. Among these, a PET film is preferably used.

The protective film is also not particularly limited, and examples thereof include a polypropylene film.

The thickness of the clad dry film is not particularly limited, and can be appropriately set depending on the application.

The method for producing the dry film for clad is not particularly limited, but the following method may be mentioned, for example. First, a solvent or the like is added to the clad resin composition to form a varnish, and the varnish is applied onto a film substrate. This coating includes coating using a comma coater or the like. By drying this varnish, a clad resin composition layer is formed on the film substrate. Furthermore, a protective film is laminated on the clad resin composition layer. The lamination method includes, for example, a thermal lamination method.

・Dry film for core The material for forming the dry film for the core is not particularly limited as long as it is a resin composition that satisfies the numerical aperture and the loss fluctuation amount as described above, but the clad A material having a higher refractive index at the transmission wavelength of the guided light than the material of the dry film for the optical waveguide is used. Specifically, a resin material having a refractive index of, for example, about 1.55 to 1.6 at a transmission wavelength in the 1.3 μm band can be used.

More specifically, as with the dry film for the clad, the resin composition for the core includes a curable resin composition that is cured by energy rays such as light or heat. and resin compositions containing epoxy resins, acrylic resins, polycarbonate resins, polyimide resins, silicone resins, and the like. Among these, epoxy resins are preferable, and it is particularly preferable to use epoxy resins such as bisphenol A type epoxy resins, fluorene skeleton-containing epoxy resins, and phenol novolac type epoxy resins. These may be used individually by 1 type, or may be used in combination of 2 or more type.

In a preferred embodiment, the core resin composition contains an epoxy resin and an antioxidant. It is believed that this makes it possible to obtain a core dry film that is more excellent in heat resistance.

Although the antioxidant is not particularly limited, 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 as in the clad resin composition.

In the core resin composition, 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 numerical aperture NA2 after heat treatment may become less than 0.10. Therefore, the lower limit of the antioxidant content is preferably 1.5 parts by mass or more, more preferably 2.0 parts by mass or more. On the other hand, if a large amount of antioxidant is contained, the antioxidant may bleed out. Therefore, the upper limit of the antioxidant content is preferably 5.0 parts by mass or less, and the bleed out is further suppressed. In order to suppress it, it is more preferably 3.0 parts by mass or less.

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

Although the photo-curing agent is not particularly limited, for example, the same photo-curing agent as described above that can be used in the clad resin composition can be used.

The content of the photocuring agent is preferably 0.1 parts by mass or more and 1.0 parts by mass or less, and 0.2 parts by mass or more and 0.5 parts by mass or less with respect to 100 parts by mass of the epoxy resin. is more preferable. If the amount of the photocuring agent is too small, the core resin composition will be difficult to cure. If the photocuring agent is too much, cations and anions are excessively generated. For this reason, for example, the resin composition for the core becomes too easy to cure, and there is a risk that the storage stability and the handleability may deteriorate.

Additives such as a leveling agent and a coupling agent (silane coupling agent) can also be added to the core resin composition of the present embodiment, in addition to the components described above.

The dry film for core according to the present embodiment is not particularly limited as long as it has a layer of the resin composition for core. Specifically, for example, the core dry film includes a film substrate provided on one side of the layer of the core resin composition and a protective film provided on the other side. The core dry film only needs to include a core resin composition layer, and may include other layers in addition to the film substrate and protective film, and the film substrate and protective film are not essential.

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

The thickness of the core dry film is not particularly limited, and can be appropriately set depending on the application.

The method for producing the core dry film is not particularly limited, but for example, it can be produced by the same method as for the clad dry film described above.

The optical waveguide material of this embodiment includes the clad dry film and the core dry film as described above. A typical optical waveguide is formed of an upper clad layer, a core layer, and a lower clad layer. A dry film for 100% can be used to form the core layer.

The method of manufacturing an optical waveguide using the optical waveguide material of this embodiment has already been described.

The present invention also includes an optical waveguide formed from the optical waveguide material described above. That is, the optical waveguide of the present embodiment has a clad layer and a core layer surrounded by the clad layer, and the clad layer and the core layer are respectively for the optical waveguide of the present embodiment described above. It is characterized by being composed of a clad dry film and a core dry film included in the material. Since the optical waveguide of this embodiment has durability under high temperature, it is very useful for industrial use.

EXAMPLES The present invention will be described in more detail below with reference to examples. It should be noted that the present invention is by no means limited to the following examples.

First, the raw materials used for the preparation of the resin composition in this example are summarized below.

<Epoxy resin>
- "Epiclon 850S": bisphenol A type epoxy resin, manufactured by DIC Corporation (ACH number: 0.056, specific gravity: 1.15)
・ “VG3101M80”: Polyfunctional epoxy resin, manufactured by Printec 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)
- "Epikote 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

<Curing agent>
・ "CPI-101A": Photo cationic curing agent, manufactured by San-Apro Co., Ltd.

<Antioxidant>
・ “AO-60”: Phenolic antioxidant, manufactured by ADEKA Co., Ltd.

<Preparation of clad resin composition>
The components are blended according to the formulation (parts by mass) shown in Tables 1 and 2 below, and the mixed solvent of MEK and toluene is adjusted to 55 parts by mass with respect to 100 parts by mass of the resin. Mix while heating to 80°C. Next, the mixture was filtered through a membrane filter with a pore size of 0.5 μm and defoamed to prepare resin varnishes of the clad resin compositions of Examples 1 to 7 and Comparative Examples 1 to 6.

<Preparation of core resin composition>
The ingredients are blended according to the formulation (parts by mass) shown in Tables 1 and 2 below, and the mixed solvent of MEK and toluene is adjusted to 60 parts by mass with respect to 100 parts by mass of the resin. Mix while heating to 80°C. Next, the core resin compositions of Examples 1 to 7 and Comparative Examples 1 to 6 were prepared as resin varnishes by filtering through a membrane filter with a pore size of 0.2 μm and defoaming.

<Formation of dry film for clad>
The clad resin composition varnish of each example and comparative example is applied to a PET film (product number A4100) manufactured by Toyobo Co., Ltd. using a multi-coater with a comma coater head manufactured by HIRANO TECSEED Co., Ltd., dried to a predetermined thickness, and is a release film. By thermally laminating OPP-MA420 manufactured by Oji Specialty Paper Co., Ltd., a clad dry film having a resin layer thickness of 20 μm was obtained.

<Formation of dry film for core>
The core resin composition varnish of each example and comparative example is applied to a PET film (product number A4100) manufactured by Toyobo Co., Ltd. using a multi-coater with a comma coater head manufactured by HIRANO TECSEED Co., Ltd., dried to a predetermined thickness, and is a release film. By thermally laminating OPP-MA420 manufactured by Oji Specialty Paper Co., Ltd., a core dry film having a resin layer thickness of 7 μm was obtained.

<Evaluation method>
(refractive index)
The cladding dry film and the core dry film of each example and each comparative example were laminated together using a vacuum laminator so that the film thickness was 50 to 80 μm. The film was irradiated with ultraviolet rays, the PET film was peeled off, and the film was cured by heat treatment at 140° C. for 30 minutes to obtain a clad cured product and a core cured product.

The refractive index at a wavelength of 1310 nm was measured with an Abbe refractometer at a temperature of 25° C. for the clad cured product and the core cured product thus obtained.

Each clad cured product and core cured product were then heat treated at 175° C. for 177 hours. Specifically, each cured product was heat-treated by placing it in an oven at 175° C. for 177 hours in the atmosphere.

Then, the refractive index at a wavelength of 1.3 μm was measured with an Abbe refractometer for the clad cured product and the core cured product after the heat treatment.

Finally, from the refractive index n _crad 1 of the clad cured product and the core cured product before heat treatment (untreated) and the refractive index n _core 1 of the core cured product, the refractive index n _crad 2 of the clad heat treated product and the core heat treated product A numerical value obtained by subtracting the refractive index n _core 2 of was taken as the refractive index change amount.

Each value is shown in Table 1 and Table 2.

(numerical aperture NA)
From the refractive index values 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))
Further, the numerical aperture NA2 after heat treatment was calculated by the following formula.
NA2=((n _core 2)^2-(n _crad 2)^2)^(1/2))

Tables 1 and 2 show NA1 and NA2 obtained from the refractive indices of the clad cured products and the core cured products obtained in Examples and Comparative Examples.

(Loss fluctuation amount)
First, an optical waveguide was formed using the clad dry film and the core dry film of each example and each comparative example.

Specifically, using the core fud-dry film and the clad dry film, first, the clad dry film was laminated on the substrate (R-1515V, 0.8 mm thick, 125 cm square) as the under clad. Furthermore, a dry film for core is laminated on top of it, exposed using a mask capable of forming a pattern of 7 μm width and heat-treated, then the unexposed core material is removed by development, and the dry film for clad is used as an overclad. A single-mode waveguide sample with a waveguide length of 5 cm and a core size of 7 μm was prepared by lamination.

Then, the optical waveguide prepared on the substrate was cut into 5 cm squares (5 cm square substrate, waveguide length: 5 cm), and the optical loss value α before high temperature treatment (12 upper bundles, 12 middle bundles, 12 lower bundles, and the light loss value β after the same sample was treated at 175°C for 177 hours (average value of 36 total of 12 upper bundles, 12 middle bundles, and 12 lower bundles). The light from a 1310 nm LED light source is passed through an optical fiber with a core diameter of 9 μm and an NA of 0.12, and is incident on the end of the optical waveguide created above through matching oil (refractive index: 1.505). Power (P1) when an optical circuit is connected to a power meter through an optical fiber with a core diameter of 50 μm and an NA of 0.21 through the same matching oil, and the power (P1) when the above two fibers are butted against each other and measured without an optical circuit. The insertion loss of the optical circuit was calculated from the power (P0) at -10 log (P1/Po), and the difference between the values was calculated (loss value after processing β - loss value before processing α). The pass criteria for this test is that the loss variation is 2.0 dB or less.

Numerical values for each example and comparative example are summarized in Tables 1 and 2.

<Evaluation/Consideration>
From the results in Table 1, it was confirmed that according to the present invention, the numerical aperture NA can be maintained at 1.0 or more even after the heat treatment at high temperature for a long time. It was also shown that fluctuations in optical loss after heat treatment can be suppressed. It has been found that if the amount of the antioxidant is too large, the antioxidant bleeds out in the clad dry film and the core dry film.

On the other hand, as shown in Table 2, in the optical waveguides of Comparative Examples 2 to 6, which did not meet the requirements of the present invention, loss fluctuations exceeding 2.0 dB/cm were measured. In Comparative Example 1, since the oxidation progressed due to the long-time treatment at a high temperature and the numerical aperture NA greatly decreased, the light was not guided.

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.

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

1 clad film 2 core optical film 3 clad 3 a under clad 3 b over clad 4 core

Claims (8)

A method for manufacturing an optical waveguide comprising a clad layer and a core layer overlapping the clad layer,
A step of laminating a clad dry film formed using a clad resin composition and a core dry film formed using a core resin composition having a higher refractive index than the clad resin composition. including
The refractive index n _crad 1 of the clad cured product and the refractive index n _core of the core cured product obtained by curing the clad dry film and the core dry film by UV treatment and heat treatment at 140° C. for 30 minutes, respectively. 1 and the numerical aperture NA1 calculated from 0.10 or more,
Calculated 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 obtained by further heat-treating the clad cured product and the core cured product at 175 ° C. for 177 hours. The numerical aperture NA2 to be used is 0.10 or more,
The difference 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 optical waveguide heat-treated product obtained by heat-treating the optical waveguide at 175° C. for 177 hours ( β-α) is 2.1 [db] or less,
A method for manufacturing an optical waveguide. An optical waveguide comprising a clad dry film formed using a clad resin composition and a core dry film formed using a core resin composition having a higher refractive index than the clad resin composition. material for
The refractive index n _crad 1 of the clad cured product and the refractive index n _core of the core cured product obtained by curing the clad dry film and the core dry film by UV treatment and heat treatment at 140° C. for 30 minutes, respectively. 1 and the numerical aperture NA1 calculated from 0.10 or more,
Calculated 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 obtained by further heat-treating the clad cured product and the core cured product at 175 ° C. for 177 hours. The numerical aperture NA2 to be used is 0.10 or more,
The difference 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 optical waveguide heat-treated product obtained by heat-treating the optical waveguide at 175° C. for 177 hours ( β-α) is 2.1 [db] or less,
Materials for optical waveguides. The clad resin composition contains an epoxy resin and an antioxidant,
3. The optical waveguide material according to claim 2, wherein said epoxy resin contains a BisA type epoxy resin and a hydrogenated BisA type epoxy resin. 4. The optical waveguide material according to claim 3, wherein the BisA type epoxy resin and the hydrogenated BisA type epoxy resin contained in the clad resin composition have a mass ratio ranging from 95:5 to 75:25. 5. The optical waveguide material according to claim 3, wherein a ratio of said 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 said epoxy resin. 6. The optical waveguide material according to claim 2, wherein said core resin composition contains an epoxy resin and an antioxidant. 7. The optical waveguide according to claim 6, wherein a ratio of said antioxidant in said core resin composition is 1.5 parts by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of said epoxy resin. material. 8. The optical waveguide material according to claim 3, wherein said antioxidant is a phenolic antioxidant.

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