Optical waveguide and method for manufacturing optical waveguide

Abstract

[Problem] To provide an optical waveguide having high reliability without changing a refractive index of a core / clad with the lapse of time in addition to transparency and lithography characteristics in an optical communication wavelength band. [Solution] Provided are an optical waveguide and a method for manufacturing the optical waveguide, wherein the optical waveguide includes: a core; a clad which surrounds the entire outer periphery of the core and has a refractive index smaller than that of the core; and a protective layer on at least a portion of the outer peripheral surface of the clad. In a high temperature durability test in which the optical waveguide is stored at 150°C for 1000 hours under the atmosphere, a change ratio of the value of a propagation loss of light having a wavelength of 1.31 μm after the test is 10% or less as compared with the value before the test.

Description

Optical waveguide and method for manufacturing the same

[0001] The present invention relates to an optical waveguide, and more particularly to an optical waveguide that exhibits little change in propagation loss even when used in a high-temperature environment and has high reliability.

[0002] In recent years, with technological advances such as autonomous driving and artificial intelligence and the expected technological innovation of 5G to 6G communications, the amount of data transmitted over communication lines has been increasing rapidly. Therefore, various research efforts are being conducted to realize energy-saving, large-volume information processing and ultra-high-speed, large-capacity communications. To achieve such high-speed, large-capacity communications with low power consumption, a shift from conventional electrical wiring using metal conductors to optical wiring is underway. For example, board-edge optical interconnection, which mounts an optoelectronic conversion unit on the edge of a substrate (board) and connects optical fibers, has already been put to practical use as an active optical cable (AOC), which uses optical fibers between connectors to improve cable performance. This trend continues with on-board optical interconnection, in which the optical-electrical conversion unit is placed on a substrate (board) near the processor as a small on-board optical module, then on-package optical interconnection, in which the optical-electrical conversion unit is made even smaller and mounted on a package substrate that mounts an LSI chip, and finally on-board optical wiring, in which an optical waveguide is formed on a substrate (board) to transmit optical signals on-board; opto-electrical hybrid boards, waveguide-type optical splitters, and integrated optical fiber / optical waveguide optical modules have already been put to practical use.

[0003] In the optical wiring described above, optical waveguides made of polymeric materials have attracted attention as optical transmission paths due to their ease of processing, low cost, high degree of wiring flexibility, and the possibility of high density. For example, organic polymer optical waveguides formed from photosensitive materials have been proposed, which use photolithography technology in all processes to form the underlying undercladding layer, the core layer that guides the light, and the top cladding layer that covers the core layer to complete the wiring within the package substrate. In addition to the desired high refractive index, photosensitive materials used to form optical waveguides are also required to have film-forming properties (such as film flatness), patterning properties (lithography characteristics), and high transparency in the communication wavelength band (e.g., the infrared region: 1.31 μm band) in order to form fine optical waveguides on the substrate.

[0004] For example, as a photosensitive material for forming the optical waveguide, a photosensitive epoxy resin composition for forming an optical waveguide containing a polyfunctional epoxy resin having a bisphenol A skeleton, a solid semi-aliphatic difunctional epoxy resin, or other difunctional epoxy resin as a resin component and containing a photocationic polymerization initiator has been proposed (see, for example, Patent Document 1). Also proposed is a composition for forming an optical waveguide containing a specific reactive silsesquioxane compound and a specific fluorene compound, aiming at low propagation loss and a high refractive index in the long wavelength range (see, for example, Patent Document 2), and a composition for forming an optical waveguide containing at least three epoxy compounds, namely, a naphthalene-containing difunctional fluorene epoxy compound, a difunctional or lower alicyclic epoxy compound, and another difunctional or lower aromatic epoxy compound other than the fluorene epoxy compound, aiming at patterning ability, film-forming ability, and a high refractive index (see, for example, Patent Document 3).

[0005] JP 2020-20927 A International Publication No. 2018 / 199305 International Publication No. 2023 / 277016

[0006] As mentioned above, photosensitive materials for forming optical waveguides are required to have patterning properties, film-forming properties, high refractive indexes, and high transparency. Furthermore, in view of recent trends toward high-speed communications and increased capacity, optical waveguides are required to have high reliability, i.e., the optical waveguide itself must have a uniform structure (uniform refractive index), be resistant to refractive index changes over time even in environments prone to high temperatures associated with high-speed communications, and ultimately exhibit small changes in propagation loss values.

[0007] The present invention aims to provide an optical waveguide that has high reliability, in addition to transparency and lithography properties in the optical communication wavelength band, in which the refractive index of the core / clad does not change over time in a high-temperature environment such as 150°C, and in which the propagation loss value changes little, i.e., the insertion loss value changes little.

[0008] In order to solve the above problems, the inventors conducted thorough research and found that in an optical waveguide having a core and a cladding that surrounds and covers the entire outer periphery of the core, the above problems can be solved by providing a protective layer on at least a part of the outer surface of the cladding, which led to the present invention.

[0009] That is, a first aspect of the present invention relates to an optical waveguide having a core, a cladding that surrounds and covers the entire outer periphery of the core and has a refractive index lower than that of the core, and a protective layer on at least a part of the outer periphery of the cladding, wherein, in a high-temperature durability test in which the optical waveguide is stored in air at 150°C for 1000 hours, the propagation loss value for light with a wavelength of 1.31 μm after the test changes by 10% or less compared to the same value before the test. A second aspect of the present invention relates to the optical waveguide according to the first aspect, in which the protective layer is a metal oxide-containing layer. A third aspect of the present invention relates to the optical waveguide according to the second aspect, in which the protective layer is a silicon dioxide-containing layer. As a fourth aspect, the present invention relates to the optical waveguide according to the first aspect, wherein the core comprises a cured product of a core-forming composition containing (A) a reactive silsesquioxane compound and (B) a fluorene compound, wherein the (A) reactive silsesquioxane compound is a polycondensate of an alkoxysilane compound A represented by the following formula [1] and an alkoxysilane compound B represented by the following formula [2], and the (B) fluorene compound is a compound represented by the following formula [3]: (In the formula, Ar１ represents a phenyl group having at least one group having a polymerizable double bond, a naphthyl group having at least one group having a polymerizable double bond, or a biphenyl group having at least one group having a polymerizable double bond; R １ represents a methyl group or an ethyl group.) (In the formula, Ar ２ represents a phenyl group which may be substituted with an alkyl group having 1 to 6 carbon atoms, a condensed polycyclic aromatic hydrocarbon group which may be substituted with an alkyl group having 1 to 6 carbon atoms, or a hydrocarbon ring assembly group in which a plurality of aromatic rings are directly bonded together via single bonds (which may be substituted with an alkyl group having 1 to 6 carbon atoms); R ２ represents a methyl group or an ethyl group.) (In the formula, R ３ and R ４ each independently represents a hydrogen atom or a methyl group; L １ and L ２ each independently represents a phenylene group which may have a substituent, or a naphthalenediyl group which may have a substituent; L ３ and L ４ each independently represent an alkylene group having 1 to 6 carbon atoms, and m and n represent 0 or a positive integer such that m+n is 0 to 40.) As a fifth aspect, the present invention relates to the optical waveguide according to the first aspect, wherein the cladding is made of a cured product of a cladding-forming composition containing (D) a fluorene skeleton-containing epoxy compound and (G) a photoacid generator, and the (D) fluorene skeleton-containing epoxy compound is a compound represented by the following formula [4]: (In formula [4], L ５ and L ６each independently represent a naphthalenediyl group which may have a substituent, and p and q each independently represent an integer of 0 to 10.) A sixth aspect relates to the method for manufacturing an optical waveguide according to any one of the first to fifth aspects, the method including: a first step of forming a lower clad; a second step of forming a patterned core on the lower clad; a third step of forming an upper clad so as to bond the upper clad to the lower clad and cover the core; and a fourth step of forming a protective layer on a necessary outer surface portion of the upper clad or the lower clad. A seventh aspect relates to the manufacturing method according to the sixth aspect, in which the fourth step is a step of forming a protective layer by a sputtering method. An eighth aspect relates to the manufacturing method according to the seventh aspect, in which the protective layer has a thickness of 0.1 to 0.5 μm.

[0010] The optical waveguide of the present invention exhibits a change in propagation loss value for light with a wavelength of 1.31 μm of 10% or less before and after a high-temperature durability test in which the optical waveguide is stored in air at 150° C. for 1,000 hours. In other words, a highly reliable optical waveguide can be provided in which the refractive index of the core / clad is unlikely to change over time in a high-temperature environment, the propagation loss value changes little, and ultimately the insertion loss value changes little. Furthermore, the optical waveguide manufacturing method of the present invention can manufacture a highly reliable optical waveguide in which the refractive index of the core / clad is unlikely to change over time in a high-temperature environment, the propagation loss value changes little, and as a result, the insertion loss value changes little.

[0011] FIG. 1 is a graph showing the change in insertion loss over time when optical waveguides 1 to 3 obtained in Examples 2-1 and 2-2 and Comparative Example 2-1 were kept at 150° C.

[0012] In evaluating the characteristics of an optical waveguide, it is desirable that the insertion loss, which is unavoidable when light passes through the optical waveguide, i.e., the coupling loss that occurs when light is introduced into and extracted from the optical waveguide, and the propagation loss that occurs when light passes through the optical waveguide (collectively referred to as insertion loss), be low. These insertion losses are affected by the transparency of the core / clad, the flatness of the core / clad interface, the uniformity of the refractive index, etc., but changes in the refractive index of the core / clad over time are one of the causes of changes in the propagation loss value and, ultimately, the insertion loss value, and therefore have a significant impact on the reliability of the optical waveguide.

[0013] In view of the problem of achieving high reliability in the optical waveguide, the inventors have investigated the constituent materials and the structure itself of the optical waveguide, focusing on the patterning properties, film-forming properties, high refractive index, and high transparency of the core and cladding materials, as well as the uniformity of the refractive index in the core and cladding and the change in the refractive index over time. With regard to the change in the refractive index of the core and cladding over time in a high-temperature environment, they have noticed that the cladding is particularly susceptible to oxidation, and have come to adopt a structure in which a protective layer, which is a barrier layer, is provided to suppress oxidation of the cladding.

[0014] The optical waveguide of the present invention comprises a core, a cladding that completely surrounds and covers the outer periphery of the core and has a refractive index lower than that of the core, and a protective layer on at least a portion of the outer periphery of the cladding. The optical waveguide of the present invention can be designed such that, after a high-temperature durability test in which the optical waveguide is stored in air at 150°C for 1000 hours, the propagation loss of light at a wavelength of 1.31 μm after the test changes by 10% or less, preferably 5% or less, compared to the same value before the test.

[0015] [Protective Layer] The optical waveguide of the present invention is characterized by having a protective layer. The protective layer may be, for example, a metal oxide-containing layer. The metal oxide may be, for example, silicon dioxide (SiO ２ ), titanium dioxide (TiO ２ ), tungsten trioxide (WO ３ ), zinc oxide (ZnO), zirconium oxide (ZrO ２ ), niobium oxide (Nb ２ O ５ ), aluminum oxide (Al２ O ３ Among them, the protective layer in the present invention is preferably made of silicon dioxide (SiO ２ The protective layer can be formed on at least a part of the outer circumferential surface of the cladding by, for example, sputtering, as will be described later.

[0016] [Core / Cladding] In the optical waveguide of the present invention, the core may be formed from a material having a refractive index greater than that of the formed cladding, and the material is not particularly limited. For example, in one embodiment, the core may be made from a cured product of a core-forming composition described below, and the cladding may be made from a cured product of a cladding-forming composition described below.

[0017] [Core Forming Composition] The core in the optical waveguide of the present invention is, for example, made of a cured product of a core forming composition containing (A) a reactive silsesquioxane compound and (B) a fluorene compound.

[0018] <(A) Reactive Silsesquioxane Compound> The (A) reactive silsesquioxane compound used in the core-forming composition is a polycondensate of an alkoxysilane compound A having a specific structure and an alkoxysilane compound B having a specific structure, which will be described later. More specifically, it is a compound obtained by polycondensing compound A and compound B in the presence of an acid or a base.

[0019] [Alkoxysilane Compound A] The alkoxysilane compound A is a compound represented by the following formula [1]. In the above formula [1], Ar １ represents a phenyl group having at least one group having a polymerizable double bond, a naphthyl group having at least one group having a polymerizable double bond, or a biphenyl group having at least one group having a polymerizable double bond; R １ represents a methyl group or an ethyl group.

[0020] Ar １Examples of the phenyl group having at least one group having a polymerizable double bond represented by Ar include a 2-vinylphenyl group, a 3-vinylphenyl group, a 4-vinylphenyl group, a 4-vinyloxyphenyl group, a 4-allylphenyl group, a 4-allyloxyphenyl group, and a 4-isopropenylphenyl group. １ Examples of the naphthyl group having at least one group having a polymerizable double bond represented by Ar include a 4-vinylnaphthalen-1-yl group, a 5-vinylnaphthalen-1-yl group, a 6-vinylnaphthalen-2-yl group, a 4-allyloxynaphthalen-1-yl group, a 5-allyloxynaphthalen-1-yl group, an 8-allyloxynaphthalen-1-yl group, a 5-vinyloxynaphthalen-1-yl group, a 4-allylnaphthalen-1-yl group, a 5-allylnaphthalen-1-yl group, and a 5-isopropenylnaphthalen-1-yl group. １ Examples of the biphenyl group having at least one group having a polymerizable double bond represented by the formula (I) include a 4'-vinyl-[1,1'-biphenyl]-2-yl group, a 4'-vinyl-[1,1'-biphenyl]-3-yl group, a 4'-vinyl-[1,1'-biphenyl]-4-yl group, a 4'-vinyloxy-[1,1'-biphenyl]-4-yl group, a 4'-allyl-[1,1'-biphenyl]-4-yl group, a 4'-allyloxy-[1,1'-biphenyl]-4-yl group, and a 4'-isopropenyl-[1,1'-biphenyl]-4-yl group.

[0021] Specific examples of the compound represented by the above formula [1] include, but are not limited to, trimethoxy(4-vinylphenyl)silane, triethoxy(4-vinylphenyl)silane, (4-isopropenylphenyl)trimethoxysilane, trimethoxy(4-vinyl-1-naphthyl)silane, and trimethoxy(4'-vinyl-[1,1'-biphenyl]-4-yl)silane.

[0022] [Alkoxysilane Compound B] The alkoxysilane compound B is a compound represented by the following formula [2]. In the above formula [2], Ar ２represents a phenyl group which may be substituted with an alkyl group having 1 to 6 carbon atoms, a condensed polycyclic aromatic hydrocarbon group which may be substituted with an alkyl group having 1 to 6 carbon atoms, or a hydrocarbon ring assembly group in which a plurality of aromatic rings are directly bonded together via single bonds (which may be substituted with an alkyl group having 1 to 6 carbon atoms); R ２ represents a methyl group or an ethyl group.

[0023] Ar ２ Examples of the phenyl group optionally substituted with an alkyl group having 1 to 6 carbon atoms represented by Ar include a phenyl group, an o-tolyl group, an m-tolyl group, a p-tolyl group, a 2,4,6-trimethylphenyl group, and a 4-tert-butylphenyl group. ２ Examples of the condensed polycyclic aromatic hydrocarbon group represented by the formula (I) include monovalent groups derived from naphthalene, phenanthrene, anthracene, triphenylene, pyrene, chrysene, naphthacene, biphenylene, and fluorene. Examples of hydrocarbon ring assembly groups in which multiple aromatic rings are directly bonded by single bonds include monovalent groups derived from biphenyl, terphenyl, quaterphenyl, binaphthalene, phenylnaphthalene, phenylfluorene, and diphenylfluorene. Examples of alkyl groups having 1 to 6 carbon atoms that may be substituted in the phenyl group, condensed polycyclic aromatic hydrocarbon group, and hydrocarbon ring assembly group include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, cyclopentyl, n-hexyl, and cyclohexyl. ２ Among these, a phenyl group which may be substituted with an alkyl group having 1 to 6 carbon atoms is preferred.

[0024] Specific examples of the compound represented by the above formula [2] include, but are not limited to, trimethoxy(phenyl)silane, triethoxy(phenyl)silane, trimethoxy(p-tolyl)silane, trimethoxy(1-naphthyl)silane, triethoxy(1-naphthyl)silane, trimethoxy(2-naphthyl)silane, triethoxy(2-naphthyl)silane, trimethoxy(2-phenanthryl)silane, trimethoxy(3-phenanthryl)silane, trimethoxy(9-phenanthryl)silane, triethoxy(9-phenanthryl)silane, [1,1'-biphenyl]-4-yltrimethoxysilane, [1,1'-biphenyl]-4-yltriethoxysilane, and the like.

[0025] Among these, the reactive silsesquioxane compound (A) is preferably a reactive silsesquioxane compound obtained by polycondensing a compound represented by the following formula [1a] and a compound represented by the following formula [2a] in the presence of an acid or a base: In the above formula [1a], R １ represents the same meaning as above. In the above formula [2a], R ２ represents the same meaning as above.

[0026] [Ratio of Alkoxysilane Compound A and Alkoxysilane Compound B] The molar ratio of alkoxysilane compound A represented by formula [1] to alkoxysilane compound B represented by formula [2] in the polycondensation reaction is not particularly limited. However, for the purpose of stabilizing the physical properties of the cured product (core), a range of 5:1 to 1:5 is usually preferred for alkoxysilane compound A:alkoxysilane compound B. A more preferred range is 3:1 to 1:3. By setting the molar ratio of alkoxysilane compound A to the number of moles of alkoxysilane compound B to 5 or less, a cured product with a higher refractive index can be obtained. Furthermore, by setting the molar ratio of alkoxysilane compound A to the number of moles of alkoxysilane compound B to 1 / 5 or more, sufficient crosslink density can be obtained and dimensional stability against heat can be further improved. The above-mentioned alkoxysilane compound A and alkoxysilane compound B can be appropriately selected and used as needed, and multiple compounds of each can also be used in combination. In this case, the molar ratio of the alkoxysilane compounds A to the alkoxysilane compounds B is also within the above range.

[0027] [Acid or Basic Catalyst] The polycondensation reaction between the alkoxysilane compound A represented by the formula [1] and the alkoxysilane compound B represented by the formula [2] is preferably carried out in the presence of an acid or basic catalyst. The catalyst used in the polycondensation reaction is not particularly limited in type as long as it dissolves or uniformly disperses in the solvent described below, and can be appropriately selected and used as needed. Examples of catalysts that can be used include: acidic compounds such as inorganic acids such as hydrochloric acid, nitric acid, sulfuric acid, and boric acid, and organic acids such as acetic acid and oxalic acid; basic compounds such as alkali metal hydroxides (sodium hydroxide, potassium hydroxide, etc.), alkaline earth metal hydroxides (magnesium hydroxide, calcium hydroxide, strontium hydroxide, barium hydroxide, etc.), ammonium hydroxide, quaternary ammonium salts (tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, etc.), amines (triethylamine, etc.); fluoride salts such as NH ４ F, NR ４F (tetramethylammonium fluoride, tetrabutylammonium fluoride, etc.). Here, R is one or more groups selected from the group consisting of a hydrogen atom, a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, and a cyclic alkyl group having 3 to 12 carbon atoms. These catalysts can be used alone or in combination.

[0028] Among the above catalysts, one or more selected from the group consisting of hydrochloric acid, acetic acid, potassium hydroxide, calcium hydroxide, barium hydroxide, and tetraethylammonium hydroxide can be preferably used. The amount of catalyst used is 0.01 to 10% by mass, preferably 0.1 to 5% by mass, based on the total mass of the alkoxysilane compound A and the alkoxysilane compound B. By using an amount of catalyst of 0.01% by mass or more, the reaction proceeds more smoothly. Furthermore, from an economical standpoint, use of 10% by mass or less is sufficient.

[0029] [Polycondensation Reaction] One of the characteristics of the (A) reactive silsesquioxane compound is the structure of the alkoxysilane compound A. The reactive group (polymerizable double bond) contained in the alkoxysilane compound A is easily polymerized by radicals or cations, and exhibits high heat resistance after polymerization (curing). The hydrolysis polycondensation reaction of the alkoxysilane compound A and the alkoxysilane compound B can be carried out without a solvent, but it is also possible to use a solvent inert to both alkoxysilane compounds (e.g., tetrahydrofuran (THF) described below) as the reaction solvent. Using a reaction solvent has the advantage that the reaction system is easily made uniform, allowing for a more stable polycondensation reaction.

[0030] The synthesis reaction of the (A) reactive silsesquioxane compound may be carried out without a solvent, as described above, but a solvent may be used to make the reaction more uniform. The solvent is not particularly limited as long as it does not react with both alkoxysilane compounds and dissolves their polycondensate. Examples of such reaction solvents include ketones such as acetone and methyl ethyl ketone (MEK); aromatic hydrocarbons such as benzene, toluene, and xylene; ethers such as tetrahydrofuran (THF), 1,4-dioxane, diisopropyl ether, and cyclopentyl methyl ether (CPME); glycols such as ethylene glycol, propylene glycol, and hexylene glycol; glycol ethers such as ethyl cellosolve, butyl cellosolve, ethyl carbitol, butyl carbitol, diethyl cellosolve, and diethyl carbitol; and amides such as N-methyl-2-pyrrolidone (NMP) and N,N-dimethylformamide (DMF). These solvents may be used alone or in combination.

[0031] (A) The reactive silsesquioxane compound is obtained by hydrolysis polycondensation of an alkoxysilane compound A represented by formula [1] and an alkoxysilane compound B represented by formula [2] in the presence of an acid or basic catalyst. The reaction temperature for the hydrolysis polycondensation is 20 to 150°C, more preferably 30 to 120°C. The reaction time is not particularly limited as long as it is at least the time required for the increase in molecular weight of the polycondensate to be completed and for the molecular weight distribution to be stabilized, and more specifically, it is several hours to several days. After completion of the polycondensation reaction, the resulting reactive silsesquioxane compound is preferably recovered by any method such as filtration or solvent distillation, and then appropriately purified as necessary.

[0032] Alternatively, (A) a reactive silsesquioxane compound can be obtained by polycondensing an alkoxysilane compound A represented by the above formula [1] with an alkoxysilane compound B represented by the above formula [2] in the presence of a base, followed by removal of the base using a cation exchange resin. The base and its amount can be one or more compounds selected from the group consisting of the basic compounds and fluoride salts described above, and the amount used can be the same. Preferably, one or more bases selected from the group consisting of potassium hydroxide, calcium hydroxide, barium hydroxide, and tetraethylammonium hydroxide can be used. The reaction conditions and reaction solvents used in the polycondensation reaction can be those described above. After completion of the reaction, an ion exchange resin having a sulfo group as the ionic group is preferably used as the cation exchange resin used to remove the base.

[0033] The polycondensate ((A) reactive silsesquioxane compound) obtained by such a reaction has a weight average molecular weight Mw of 500 to 100,000, preferably 500 to 30,000, as measured by GPC in terms of polystyrene, and a dispersity: Mw (weight average molecular weight) / Mn (number average molecular weight) of 1.0 to 10. The (A) reactive silsesquioxane compound is a compound having a molecular weight of [Ar １ SiO ３／２ ] and [Ar ２ SiO ３／２ The compound has a crosslinked structure and at least a siloxane unit represented by the formula:

[0034] <(B) Fluorene Compound> The (B) fluorene compound used in the core-forming composition is a compound represented by formula [3]. In the above formula [3], R ３ and R ４ each independently represents a hydrogen atom or a methyl group; L １ and L ２ each independently represents a phenylene group which may have a substituent, or a naphthalenediyl group which may have a substituent; L ３ and L ４ each independently represents an alkylene group having 1 to 6 carbon atoms, and m and n represent 0 or a positive integer such that m+n is 0 to 40.

[0035] L １ and L ２ Examples of the optionally substituted phenylene group represented by the formula (I) include an o-phenylene group, an m-phenylene group, a p-phenylene group, a 2-methylbenzene-1,4-diyl group, a 2-aminobenzene-1,4-diyl group, a 2,4-dibromobenzene-1,3-diyl group, and a 2,6-dibromobenzene-1,4-diyl group. １ and L ２ Examples of the optionally substituted naphthalenediyl group represented by the formula (I) include a 1,2-naphthalenediyl group, a 1,4-naphthalenediyl group, a 1,5-naphthalenediyl group, a 1,8-naphthalenediyl group, a 2,3-naphthalenediyl group, and a 2,6-naphthalenediyl group.

[0036] L ３ and L ４ Examples of the alkylene group having 1 to 6 carbon atoms represented by the formula (I) include a methylene group, an ethylene group, a trimethylene group, a 1-methylethylene group, a tetramethylene group, a 1-methyltrimethylene group, a 1,1-dimethylethylene group, a pentamethylene group, a 1-methyltetramethylene group, a 2-methyltetramethylene group, a 1,1-dimethyltrimethylene group, a 1,2-dimethyltrimethylene group, a 2,2-dimethyltrimethylene group, a 1-ethyltrimethylene group, a hexa Examples include a methylene group, a 1-methylpentamethylene group, a 2-methylpentamethylene group, a 3-methylpentamethylene group, a 1,1-dimethyltetramethylene group, a 1,2-dimethyltetramethylene group, a 2,2-dimethyltetramethylene group, a 1-ethyltetramethylene group, a 1,1,2-trimethyltrimethylene group, a 1,2,2-trimethyltrimethylene group, a 1-ethyl-1-methyltrimethylene group, and a 1-ethyl-2-methyltrimethylene group.

[0037] In the compound represented by formula [3], m and n are preferably such that m+n is 0 to 30, and more preferably m+n is 2 to 20.

[0038] Specific examples of the compound represented by the formula [3] include, but are not limited to, 9,9-bis(4-(2-(meth)acryloyloxyethoxy)phenyl)-9H-fluorene, OGSOL (registered trademark) EA-0200, EA-0300, EA-F5003, EA-F5503, EA-F5510, EA-F5710, and GA-5000 (all manufactured by Osaka Gas Chemicals Co., Ltd.), and NK Ester A-BPEF (manufactured by Shin-Nakamura Chemical Co., Ltd.). (Note that, in this specification, the term "(meth)acryloyl group" refers to both an acryloyl group and a methacryloyl group.)

[0039] In the core-forming composition, the content of component (B) is 10 to 500 parts by mass, preferably 30 to 250 parts by mass, per 100 parts by mass of component (A).

[0040] <(C) (Meth)acrylate Compound Not Belonging to the (B) Fluorene Compound> The core-forming composition may further contain, as component (C), a (meth)acrylate compound not belonging to the (B) fluorene compound. In this specification, (meth)acrylate refers to both acrylate and methacrylate. Among them, it is preferable that component (C) contains at least an aromatic ring-containing (meth)acrylate compound, or alternatively, it is preferable that component (C) contains at least a mono(meth)acrylate compound. In particular, it is preferable that component (C) contains at least an aromatic ring-containing mono(meth)acrylate compound.

[0041] Examples of such (meth)acrylate compounds of component (C) include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, tert-butyl (meth)acrylate, 2,2,2-trifluoroethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2,3-dihydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, phenyl (meth)acrylate, benzyl (meth)acrylate, 1-phenylethyl (meth)acrylate, 2-phenylethyl (meth)acrylate, 1-naphthyl (meth)acrylate, 1-naphthylmethyl (meth)acrylate, and 2-naphthyl (meth)acrylate. mono(meth)acrylate compounds such as o-phenylphenol (meth)acrylate, 2-naphthylmethyl (meth)acrylate, 9-anthryl (meth)acrylate, 9-anthrylmethyl (meth)acrylate, 9-phenanthryl (meth)acrylate, 9-phenanthrylmethyl (meth)acrylate, 1-phenoxyethyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, 2-phenoxybenzyl (meth)acrylate, 3-phenoxybenzyl (meth)acrylate, 4-phenoxybenzyl (meth)acrylate, 2-(2-biphenylyloxy)ethyl (meth)acrylate, 2-(3-biphenylyloxy)ethyl (meth)acrylate, 2-(4-biphenylyloxy)ethyl (meth)acrylate, and ethylene oxide-modified o-phenylphenol (meth)acrylate;Neopentyl glycol di(meth)acrylate, pentaerythritol tri(meth)acrylate, trimethylolethane tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, bisphenol A di(meth)acrylate, ethylene oxide-modified bisphenol A di(meth)acrylate polyfunctional (meth)acrylate compounds such as 2-(5-ethyl-5-hydroxymethyl-1,3-dioxan-2-yl)-2-methylpropan-1-ol di(meth)acrylate, ethylene oxide-modified 2-(5-ethyl-5-hydroxymethyl-1,3-dioxan-2-yl)-2-methylpropan-1-ol di(meth)acrylate, and propylene oxide-modified 2-(5-ethyl-5-hydroxymethyl-1,3-dioxan-2-yl)-2-methylpropan-1-ol di(meth)acrylate;

[0042] Among these, as the component (C), benzyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, 2-phenoxybenzyl (meth)acrylate, 3-phenoxybenzyl (meth)acrylate, 4-phenoxybenzyl (meth)acrylate, 2-(2-biphenylyloxy)ethyl (meth)acrylate, 2-(3-biphenylyloxy)ethyl (meth)acrylate, 2-(4-biphenylyloxy)ethyl (meth)acrylate, and ethylene oxide-modified o-phenylphenol (meth)acrylate are preferred, benzyl (meth)acrylate, 3-phenoxybenzyl (meth)acrylate, 2-(2-biphenylyloxy)ethyl (meth)acrylate, and ethylene oxide-modified o-phenylphenol (meth)acrylate are more preferred, and benzyl (meth)acrylate is even more preferred. Also preferred is 2-(5-ethyl-5-hydroxymethyl-1,3-dioxan-2-yl)-2-methylpropan-1-ol di(meth)acrylate.

[0043] These (meth)acrylate compounds are readily available as commercial products, and examples thereof include HEA, HPA, 4-HBA, AIB, TBA, Viscoat 3F, 4F, 8F, 8FM, #295, #300, #802, #160, #192, #700HV, and #540 (all manufactured by Osaka Organic Chemical Industry Ltd.); Light Acrylate NP-A, TMP-A, PE-3A, PE-4A, DPE-6A, PO-A, P2H-A, P-200A, BA-104, BP-4EAL, BP-4PA, and Light Acrylate NP-A. Ester E, NB, IB, TB, M-3F, HOA(N), HO-250(N), HOP(N), HOP-A(N), HOB(N), NP, TMP, BZ, PO, BP-2EMK [all manufactured by Kyoeisha Chemical Co., Ltd.]; NK Ester NPG, A-TMM-3, A-TMM-3L, A-TMM-3LM-N, A-TMPT, TMPT, A-TMMT, AD-TMP, A-9550, A-DPH, AMP-20GY, PHE-1G, A-LEN-10, ABE-300, A-BPE-4, A-BPE- 10, A-BPE-20, A-BPE-30, A-BPP-3, A-B1206PE, BPE-80N, BPE-100, BPE-200, BPE-500, BPE-900, BPE-1300N, A-9300, A-9300S, A-9300-1CL, A-DOG [all manufactured by Shin-Nakamura Chemical Co., Ltd.]; Aronix (registered trademark) M-309, M-306, M-305, M-303, M-452, M-450, M-408, M-403, M-400, M-402, M-404, M-406 , M-405, M-101A, M-102, M-106, M-110, M-111, M-113, M-117, M-5700, M-208, M-211B, M-215, M-313, M-315 [all manufactured by Toagosei Co., Ltd.]; Bremmer (registered trademark) Mark) AAE-300, PAE-100, 43PAPE-600B, ANP-300, 75ANEP-600, PDBE-200, PDBE-250, PDBE-450, PDBE-1300, PDBPE [all manufactured by NOF Corporation]; KAYARAD Examples of such polyols include NPGDA, TMPTA, PET-30, T-1420(T), D-310, DPHA, DPCA-20, DPCA-30, DPCA-60, DPCA-120, R-128H, R-551, and R-712 (all manufactured by Nippon Kayaku Co., Ltd.).

[0044] When (C) the (meth)acrylate compound (B) not belonging to the fluorene compound is added, the (meth)acrylate compound may be used alone or in combination of two or more. The amount of the (meth)acrylate compound added may be 1 to 50 parts by mass, for example, 10 to 40 parts by mass, or for example, 15 to 40 parts by mass, per 100 parts by mass of the total amount of the (A) component and the (B) component.

[0045] <Other Additives> In addition to the components (A) and (B), and optionally the component (C), the core-forming composition may optionally contain, as long as the effects of the present invention are not impaired, a polymerization initiator, a chain transfer agent, an antioxidant, an ultraviolet absorber, a light stabilizer, a leveling agent, a rheology modifier, an adhesion aid such as a silane coupling agent, a pigment, a dye, an antifoaming agent, etc. The core-forming composition may also contain other polymerizable compounds.

[0046] As the polymerization initiator, either a photopolymerization initiator or a thermal polymerization initiator can be used. Examples of the photopolymerization initiator include alkylphenones, benzophenones, acylphosphine oxides, Michler's benzoyl benzoates, oxime esters, tetramethylthiuram monosulfides, and thioxanthones. In particular, photocleavage-type photoradical polymerization initiators are preferred. Examples of photocleavage-type photoradical polymerization initiators include those described in "Latest UV Curing Technology" (page 159, published by Takasuki Kazuhiro, published by Technical Information Association, Inc., published in 1991). Commercially available photoradical polymerization initiators include, for example, OMNIRAD (registered trademark) (formerly IRGACURE (registered trademark)) 184, 369, 651, 500, 819, 907, 784, 2959, CGI1700, CGI1750, CGI1850, CG24-61, TPO, Darocur (registered trademark) 1116, 1173 [all manufactured by IGM Group B.V.], ESACURE KIP150, KIP65LT, KIP100F, KT37, KT55, KTO46, and KIP75 [all manufactured by Lamberti Co., Ltd.].

[0047] Examples of the thermal polymerization initiator include azo compounds, organic peroxides, etc. Commercially available azo-based thermal polymerization initiators include V-30, V-40, V-59, V-60, V-65, and V-70 (all manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. (formerly Wako Pure Chemical Industries, Ltd.)). Furthermore, examples of commercially available organic peroxide-based thermal polymerization initiators include, but are not limited to, Perkadox (registered trademark) CH, Perkadox BC-FF, Perkadox 14, Perkadox 16, Trigonox 22, 23, 121, Kayaester (registered trademark) P, Kayaester O, Kayabutyl B (registered trademark) [all manufactured by Kayaku Akzo Co., Ltd.], Perhexa (registered trademark) HC, Percumyl (registered trademark) H, Perocta (registered trademark) O, Perhexyl O, Perkadox Z, Perkadox O, Perkadox Z (registered trademark) [all manufactured by NOF Corporation], and the like.

[0048] When a polymerization initiator is added, the polymerization initiator may be used alone or in combination of two or more kinds, and the amount added is 0.1 to 20 parts by mass, more preferably 0.3 to 10 parts by mass, per 100 parts by mass of the polymerizable components, i.e., the total amount of the components (A) and (B), or per 100 parts by mass of the total amount of the components (A), (B), and (C) when the component (C) is included.

[0049] Examples of the chain transfer agent include thiol compounds such as methyl mercaptoacetate, methyl 3-mercaptopropionate, 2-ethylhexyl 3-mercaptopropionate, 3-methoxybutyl 3-mercaptopropionate, n-octyl 3-mercaptopropionate, stearyl 3-mercaptopropionate, 1,4-bis(3-mercaptopropionyloxy)butane, 1,4-bis(3-mercaptobutyryloxy)butane, and trimethylol. Ethane tris(3-mercaptopropionate), trimethylolethane tris(3-mercaptobutyrate), trimethylolpropane tris(3-mercaptopropionate), trimethylolpropane tris(3-mercaptobutyrate), pentaerythritol tetrakis(3-mercaptopropionate), pentaerythritol tetrakis(3-mercaptobutyrate), dipentaerythritol hexakis(3-mercaptopropionate) mercaptocarboxylic acid esters such as dipentaerythritol hexakis(3-mercaptobutyrate), tris[2-(3-mercaptopropionyloxy)ethyl]isocyanurate, and tris[2-(3-mercaptobutyryloxy)ethyl]isocyanurate; ethanethiol, 2-methylpropane-2-thiol, n-dodecanethiol, and 2,3,3,4,4,5-hexamethylhexane-2-thiol (tert-dodecanethiol); alkyl thiols such as benzenethiol, 3-methylbenzenethiol, 4-methylbenzenethiol, naphthalene-2-thiol, pyridine-2-thiol, benzimidazole-2-thiol, and benzothiazole-2-thiol; mercaptoalcohols such as 2-mercaptoethanol and 4-mercapto-1-butanol;Silane-containing thiols such as 3-(trimethoxysilyl)propane-1-thiol and 3-(triethoxysilyl)propane-1-thiol; disulfide compounds such as diethyl disulfide, dipropyl disulfide, diisopropyl disulfide, dibutyl disulfide, di-tert-butyl disulfide, dipentyl disulfide, diisopentyl disulfide, dihexyl disulfide, dicyclohexyl disulfide, didecyl disulfide, bis(2,3,3,4,4,5-hexamethylhexan-2-yl) disulfide (di-tert-dodecyl disulfide), bis(2,2-diethoxysilyl)disulfide, alkyl disulfides such as bis(2-ethyl)disulfide, bis(2-hydroxyethyl)disulfide, and dibenzyl disulfide; aromatic disulfides such as diphenyl disulfide, di-p-tolyl disulfide, di(pyridin-2-yl)pyridyl disulfide, di(benzimidazol-2-yl)disulfide, and di(benzothiazol-2-yl)disulfide; thiuram disulfides such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, and bis(pentamethylene)thiuram disulfide; and α-methylstyrene dimer.

[0050] When a chain transfer agent is added, the chain transfer agent may be used alone or in combination of two or more types, and the amount added is 0.01 to 20 parts by mass, more preferably 0.1 to 10 parts by mass, per 100 parts by mass of the polymerizable components, i.e., the total amount of the components (A) and (B), or per 100 parts by mass of the total amount of the components (A), (B), and (C) when the component (C) is included.

[0051] Examples of the antioxidant include phenolic antioxidants, phosphate antioxidants, and sulfide antioxidants, with phenolic antioxidants being preferred. Examples of the phenolic antioxidant include IRGANOX (registered trademark) 245, 1010, 1035, 1076, and 1135 (all manufactured by BASF Japan Ltd.), Sumilizer (registered trademark) GA-80, GP, MDP-S, BBM-S, and WX-R (all manufactured by Sumitomo Chemical Co., Ltd.), and Adekastab (registered trademark) AO-20, AO-30, AO-40, AO-50, AO-60, AO-80, and AO-330 (all manufactured by ADEKA Corporation).

[0052] When an antioxidant is added, the antioxidant may be used alone or in combination of two or more kinds, and the amount added is 0.01 to 20 parts by mass, more preferably 0.1 to 10 parts by mass, per 100 parts by mass of the polymerizable components, i.e., the total amount of the components (A) and (B), or per 100 parts by mass of the total amount of the components (A), (B), and (C) when the component (C) is included.

[0053] <Core-forming composition> The method for preparing the core-forming composition is not particularly limited. For example, the core-forming composition can be prepared by mixing the aforementioned components (A) and (B), and optionally the component (C), in a predetermined ratio, adding other additives as desired, and mixing to form a homogeneous solution; mixing at least a portion of at least two of these components, for example, components (A) to (C), to form a homogeneous solution, then adding the remaining components, and adding other additives as desired, and mixing to form a homogeneous solution; or by using a conventional solvent in addition to these components. When using a solvent, there are no particular restrictions as long as it is an organic solvent commonly used in the technical field. However, it is desirable to avoid using extremely high-polarity or low-polarity solvents, such as water or hydrocarbon solvents such as hexane, because they may cause precipitation or phase separation. Furthermore, care must be taken when adding a large amount of solvent, as this may prevent a sufficient film thickness from being achieved during film formation. When a solvent is used, the proportion of solids in the core-forming composition is not particularly limited as long as each component is uniformly dissolved in the solvent, but may be, for example, 1 to 90% by mass, 1 to 50% by mass, or 1 to 35% by mass. Here, the solids content refers to all components of the core-forming composition excluding the solvent component. In addition, the core-forming composition is preferably used for producing the optical waveguide described below after filtering using a filter with a pore size of 0.05 to 5 μm.

[0054] [Cladding-Forming Composition] The cladding in the optical waveguide of the present invention is, for example, made of a cured product of a cladding-forming composition containing (D) a fluorene skeleton-containing epoxy compound and (G) a photoacid generator.

[0055] <(D) Fluorene Skeleton-Containing Epoxy Compound> The fluorene skeleton-containing epoxy compound (D) used in the cladding-forming composition is a compound represented by the following formula [4]. In the above formula [4], L ５ and L ６ each independently represents a naphthalenediyl group which may have a substituent; p and q each independently represent an integer of 0 to 10;

[0056] L ５and L ６ Examples of the substituent on the naphthalenediyl group (on the naphthalene ring) in L include alkyl groups having 1 to 6 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, and t-butyl. ５ and L ６ The number of substituents in the naphthalenediyl group in each group is independently 0 to 6, preferably 0 to 2, more preferably 0 or 1, and most preferably 0. ５ and L ６ The types of the substituents in may be the same or different. When the same naphthalene ring has two or more substituents, they may be the same or different.

[0057] A specific example of the fluorene skeleton-containing epoxy compound (D) is a compound represented by the following formula [4a].

[0058] The (D) fluorene skeleton-containing epoxy compound can be a commercially available product. Examples include OGSOL (registered trademark) CG-500 and EG-280 (manufactured by Osaka Gas Chemicals Co., Ltd.). Such fluorene skeleton-containing epoxy compounds having a naphthalene ring can be used alone or in combination of two or more. Furthermore, from the viewpoint of the solubility and refractive index of the resin component, for example, OGSOL (registered trademark) CG-500 can be used alone.

[0059] When the cladding composition contains the <Other Epoxy Compounds> described below, the amount of the (D) fluorene skeleton-containing epoxy compound can be, for example, 5 to 50 parts by mass, or can be, for example, 10 to 40 parts by mass, relative to the total amount of epoxy compounds (100 parts by mass of the total amount of the (D) fluorene skeleton-containing epoxy compound and the <Other Epoxy Compounds>). In this specification, the epoxy compounds of the (D) component and the <Other Epoxy Compounds> described below are collectively referred to as the "resin component." Using the (D) fluorene skeleton-containing epoxy compound together with the <Other Epoxy Compounds>, ​​and using the (D) fluorene skeleton-containing epoxy compound in an amount of 5 parts by mass or more, can achieve a refractive index sufficient for the cladding. Using the same in an amount of 50 parts by mass or less makes the cladding composition less susceptible to deterioration in storage stability due to precipitation and to deterioration in film-formability, which are therefore preferred embodiments.

[0060] <Other Epoxy Compounds> The cladding composition may contain <other epoxy compounds> in addition to the fluorene skeleton-containing epoxy compound (D).

[0061] [(E) Monofunctional or Bifunctional Alicyclic Epoxy Compound] As the above-mentioned <Other Epoxy Compound>, a monofunctional or bifunctional alicyclic epoxy compound (E) can be used. The monofunctional or bifunctional alicyclic epoxy compound of component (E) is not particularly limited as long as it is a compound having one or two alicyclic epoxy groups. For example, the above-mentioned (E) alicyclic epoxy compound can be in a liquid form, and from the viewpoint of patterning properties (exposure sensitivity), it can be a compound having two epoxy groups introduced into an alicyclic skeleton. In this specification, "monofunctional or bifunctional" means containing one or two epoxy groups as functional groups.

[0062] Examples of the alicyclic epoxy compound (E) include compounds represented by the following formula [5]: In formula [5], R ５ and R ６each independently represents a hydrogen atom, a linear or branched alkyl group having 1 to 6 carbon atoms which may have an ester group or an ether group, or a cyclic alkyl group having 3 to 6 carbon atoms, or a combination of the linear or branched alkyl group and the cyclic alkyl group, in which the linear alkyl group having 2 or more carbon atoms, the branched alkyl group having 3 or more carbon atoms, or the cyclic alkyl group may combine with adjacent carbon atoms to form an epoxy ring, or R ５ and R ６ may be bonded to each other to form a ring having 4 to 6 carbon atoms, and in this case, adjacent carbon atoms constituting the ring may be joined together to form an epoxy ring.

[0063] Examples of the linear or branched alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, a 1-methylbutyl group, a 2-methylbutyl group, a 3-methylbutyl group, a 1,1-dimethylpropyl group, a 1,2-dimethylpropyl group, a 2,2-dimethylpropyl group, a 1-ethylpropyl group, an n-hexyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group, a 4-methylpentyl group, a 1,1-dimethylbutyl group, a 1,2-dimethylbutyl group, a 1,3-dimethylbutyl group, a 2,2-dimethylbutyl group, a 2,3-dimethylbutyl group, a 3,3-dimethylbutyl group, a 1-ethylbutyl group, a 2-ethylbutyl group, a 1,1,2-trimethylpropyl group, a 1,2,2-trimethylpropyl group, a 1-ethyl-1-methylpropyl group, and a 1-ethyl-2-methylpropyl group. Examples of the cyclic alkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group.

[0064] In a preferred embodiment, the alicyclic epoxy compound (E) can be a compound represented by the following formulas [5a], [5b], or [5c]. These are low-molecular-weight liquid compounds, and are suitable not only for patterning properties but also for adjusting the viscosity of the composition.

[0065] The alicyclic epoxy compound (E) can be a commercially available product. Commercially available bifunctional alicyclic epoxy compounds for component (E) include diepoxybicyclohexyl (e.g., Celloxide (registered trademark) 8000 and 8010, manufactured by Daicel Corporation), 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexenecarboxylate (e.g., Celloxide (registered trademark) 2021P, manufactured by Daicel Corporation), epsilon-caprolactone-modified 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate (e.g., Celloxide (registered trademark) 2081, manufactured by Daicel Corporation), bis(3,4-epoxycyclohexylmethyl)adipate, and diepoxidized tetrahydroindene (e.g., Epocalic (registered trademark) THI-DE, manufactured by ENEOS Corporation). Furthermore, for example, as the monofunctional alicyclic epoxy compound, 3,4-epoxycyclohexylmethyl methacrylate (e.g., Cyclomer (registered trademark) M-100, manufactured by Daicel Corporation), 3,4-epoxycyclohexylmethyl methacrylate, 1,2-epoxy-4-vinylcyclohexane (e.g., Celloxide (registered trademark) 2000, manufactured by Daicel Corporation), 1,2,8,9-diepoxylimonene (e.g., Celloxide (registered trademark) 3000, manufactured by Daicel Corporation), and the like can be used.

[0066] When an (E) alicyclic epoxy compound is used, the blending amount thereof can be, for example, 10 to 80 parts by mass, or can be, for example, 20 to 70 parts by mass, relative to the total amount of epoxy compounds (100 parts by mass of the total amount of the (D) fluorene skeleton-containing epoxy compound and <other epoxy compounds>). Blending 20 parts by mass or more of the (E) alicyclic epoxy compound makes it easier to obtain sufficient patterning properties, and blending 80 parts by mass or less makes it easier to obtain a sufficient refractive index.

[0067] [(F) Monofunctional or Bifunctional Aromatic Epoxy Compound] As the above-mentioned <Other Epoxy Compound>, a monofunctional or bifunctional aromatic epoxy compound (F) can be used. Here, the component (F) is a compound different from the fluorene skeleton-containing epoxy compound (D) represented by the above formula [4]. In a preferred embodiment, the aromatic epoxy compound (F) is a compound having two epoxy groups from the viewpoint of patterning properties (exposure sensitivity). Among them, an epoxy compound having a bisphenol A skeleton or a bisphenol F skeleton can be preferably used as the component (F).

[0068] Commercially available products can be used as the aromatic epoxy compound (F). Examples of the difunctional aromatic epoxy compound for component (F) include jER (registered trademark) 806, a bisphenol F type epoxy compound manufactured by Mitsubishi Chemical Corporation, and jER (registered trademark) 828, a bisphenol A type epoxy compound manufactured by Mitsubishi Chemical Corporation. Examples of monofunctional aromatic epoxy compounds include phenyl glycidyl ether (e.g., Denacol (registered trademark) EX-141, manufactured by Nagase ChemteX Corporation), phenol (EO) 5 glycidyl ether (e.g., Denacol (registered trademark) EX-145, manufactured by Nagase ChemteX Corporation), and p-tert-butylphenyl glycidyl ether (e.g., Denacol (registered trademark) EX-146, manufactured by Nagase ChemteX Corporation).

[0069] When an aromatic epoxy compound (F) is used, the blending amount thereof can be, for example, 5 to 60 parts by mass, or can be, for example, 10 to 50 parts by mass, relative to the total amount of epoxy compounds (100 parts by mass of the total amount of the fluorene skeleton-containing epoxy compound (D) and <other epoxy compounds>). Blending 5 parts by mass or more of the aromatic epoxy compound (F) makes it easier to obtain a sufficient refractive index and a uniform film, while blending 60 parts by mass or less makes it easier to obtain sufficient patterning properties.

[0070] [Other Epoxy Compounds] The cladding composition may also contain other epoxy compounds as "other epoxy compounds" other than the (D) fluorene skeleton-containing epoxy compound, (E) alicyclic epoxy compound, and (F) aromatic epoxy compound, as long as the effects of the present invention are not impaired. Examples of such epoxy compounds include heterocycle-containing epoxy compounds such as triglycidyl isocyanurate, aliphatic epoxy compounds, and alkoxysilanes having epoxy groups. Specific examples of the aliphatic epoxy compounds include monofunctional epoxy compounds such as glycidyl ethers of aliphatic alcohols and glycidyl esters of alkylcarboxylic acids, and polyglycidyl ethers of aliphatic polyhydric alcohols or their alkylene oxide adducts. Representative specific compounds of these include allyl glycidyl ether; glycidyl ethers of monoalcohols such as butyl glycidyl ether, 2-ethylhexyl glycidyl ether, and C12-13 mixed alcohol glycidyl ether; 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, glycerin triglycidyl ether, trimethylolpropane triglycidyl ether, sorbitol tetraglycidyl ether, dipentaerythritol hexaglycidyl ether, and polyethylene glycol diglycidyl ether. and polyglycidyl ethers of polyether polyols, which are adducts of one or more alkylene oxides with aliphatic polyhydric alcohols such as propylene glycol, trimethylolpropane, and glycerin; and alkoxysilanes having an epoxy group, such as 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltriethoxysilane, and 3-glycidoxypropyltrimethoxysilane. Such epoxy compounds can be contained, for example, in a proportion of 0 to 20 parts by mass relative to the total amount of epoxy compounds (100 parts by mass of the total amount of (D) fluorene skeleton-containing epoxy compound and <other epoxy compounds>).

[0071] [(G) Photoacid Generator] Specific examples of the (G) photoacid generator used in the cladding-forming composition include onium salts such as iodonium salts, sulfonium salts, phosphonium salts, and selenium salts, metallocene complex compounds, iron arene complex compounds, disulfone-based compounds, sulfonic acid derivative compounds, triazine-based compounds, acetophenone derivative compounds, and diazomethane-based compounds.

[0072] Among the onium salts, examples of iodonium salts include diaryliodonium salts such as chloride, bromide, mesylate, tosylate, trifluoromethanesulfonate, tetrafluoroborate, tetrakis(pentafluorophenyl)borate, hexafluorophosphate, hexafluoroarsenate, and hexafluoroantimonate of diaryliodonium such as diphenyliodonium, 4,4'-dichlorodiphenyliodonium, 4,4'-dimethoxydiphenyliodonium, 4,4'-di-tert-butyldiphenyliodonium, 4-methylphenyl(4-(2-methylpropyl)phenyl)iodonium, 3,3'-dinitrophenyliodonium, 4-(1-ethoxycarbonylethoxy)phenyl(2,4,6-trimethylphenyl)iodonium, and 4-methoxyphenyl(phenyl)iodonium.

[0073] Examples of the sulfonium salts include triarylsulfonium salts such as chlorides, bromides, trifluoromethanesulfonates, tetrafluoroborate, hexafluorophosphate, hexafluoroarsenate, hexafluoroantimonate, and tetrakis(pentafluorophenyl)gallates of triarylsulfonium such as triphenylsulfonium, diphenyl(4-tert-butylphenyl)sulfonium, tris(4-tert-butylphenyl)sulfonium, diphenyl(4-methoxyphenyl)sulfonium, tris(4-methylphenyl)sulfonium, tris(4-methoxyphenyl)sulfonium, tris(4-ethoxyphenyl)sulfonium, diphenyl(4-(phenylthio)phenyl)sulfonium, and tris(4-(phenylthio)phenyl)sulfonium.

[0074] Examples of the phosphonium salt include arylphosphonium salts such as chlorides, bromides, tetrafluoroborates, hexafluorophosphates, and hexafluoroantimonates of triarylphosphoniums or tetraarylphosphoniums such as tetraphenylphosphonium, ethyltriphenylphosphonium, tetra(p-methoxyphenyl)phosphonium, ethyltri(p-methoxyphenyl)phosphonium, and benzyltriphenylphosphonium.

[0075] The selenium salts include triarylselenium salts such as triphenylselenium hexafluorophosphate.

[0076] Examples of the iron arene complex compounds include bis(η5-cyclopentadienyl)(η6-isopropylbenzene)iron(II) hexafluorophosphate.

[0077] Among these, iodonium salts, sulfonium salts, etc. can be preferably used as the photoacid generator. Commercially available products can be used, and examples of such products include triarylsulfonium salts such as CPI-310FG and CPI-101A (both manufactured by San-Apro Co., Ltd.).

[0078] The (G) photoacid generator can be used alone or in combination of two or more. The (G) photoacid generator can typically be blended in an amount of, for example, 0.1 to 10 parts by mass, or 0.2 to 5 parts by mass, per 100 parts by mass of the total resin components, i.e., per 100 parts by mass of the fluorene skeleton-containing epoxy compound (D) and, if desired, <other epoxy compounds>. If the blending amount of the (G) photoacid generator is less than 0.1 parts by mass, the photocuring reaction may not proceed sufficiently. Furthermore, if the blending amount exceeds 10 parts by mass, the degree of polymerization of the polymer may decrease, making the polymer brittle and prone to cracking.

[0079] <Other Additives> In addition to the <other epoxy compounds> such as the above-mentioned components (D) and (G), and further, as needed, components (E) and (F), the cladding-forming composition may also contain, as needed, antireflection agents, ultraviolet absorbers, antioxidants, light stabilizers, sensitizers, surfactants, crosslinking agents, leveling agents, silane coupling agents, etc., within the scope of the present invention, so long as the effects of the present invention are not impaired. When these other additives are used, they are typically blended in at a ratio of 10 parts by mass or less per 100 parts by mass of the total mass of the resin components ((D) fluorene skeleton-containing epoxy compound and, as needed, <other epoxy compounds>).

[0080] <Cladding Composition> The method for preparing the cladding composition is not particularly limited. Examples include a method in which the aforementioned components (D) and (G), and optionally the <other epoxy compounds> (e.g., components (E) and (F)), and optionally other additives, are added and mixed to form a homogeneous solution, or a method in which a conventional organic solvent is used in addition to these components. When the prepared cladding composition has a low viscosity, good film formation is possible without the addition of an organic solvent. In this case, the solvent-free composition has the advantage of eliminating the need for a process to volatilize the organic solvent after film formation, such as by heat treatment. Furthermore, the absence of an organic solvent significantly reduces concerns about health hazards caused by worker inhalation during the evaporation of the organic solvent and corrosion of surrounding equipment. Because the cladding composition has a relatively low viscosity, the inclusion of an organic solvent is not essential. However, even if an organic solvent is included, it can be added in any proportion without impairing the above-described effects of the present invention. There are no particular limitations on the organic solvent that can be used in the cladding composition, as long as it is an organic solvent commonly used in the relevant technical field. However, it is desirable to avoid using extremely high-polarity or low-polarity solvents, such as water or hydrocarbon solvents such as hexane, because they may cause precipitation or phase separation. Furthermore, caution is required because adding a large amount of organic solvent may prevent a sufficient film thickness from being achieved during film formation. When an organic solvent is used, the solids content of the cladding composition is not particularly limited as long as each component is uniformly dissolved in the organic solvent, but may be, for example, 60% by mass or more, or 70% by mass or more. Preferably, the solids content of the composition can be, for example, 75% by mass to 100% by mass. Here, the solids content refers to all components of the cladding composition excluding the organic solvent component. Furthermore, the cladding composition is preferably filtered using a filter with a pore size of 0.05 to 5 μm before use in the fabrication of the optical waveguide described below.

[0081] The cladding composition preferably has a viscosity that allows for excellent workability in forming an optical waveguide. For example, the optical cladding composition may have a viscosity of 100 to 10,000 mPa·s at 25°C.

[0082] [Method for Manufacturing Optical Waveguide] The optical waveguide of the present invention can be manufactured by a manufacturing method including the following first to fourth steps (1) to (4): (1) a first step of forming a lower clad, (2) a second step of forming a patterned core on the lower clad, (3) a third step of forming an upper clad so as to bond the upper clad to the lower clad and cover the core, and (4) a fourth step of forming a protective layer on a necessary outer surface portion of the upper clad or the lower clad.

[0083] (1) Step 1: Step 1 is a process for forming a lower clad consisting of a cured product of the clad-forming composition, for example, using the clad-forming composition described above. In this process, for example, the clad-forming composition described above is applied to a substrate and dried to obtain a coating film, and the coating film is then exposed (photocured) to obtain a cured lower clad. Specifically, for example, the clad-forming composition described above (which may be dissolved or dispersed in an organic solvent, if necessary, to form a varnish (film-forming material)) is first applied to a suitable substrate using a coating method such as spin coating, blade coating, dip coating, roll coating, bar coating, die coating, inkjet printing, or printing (relief printing, relief printing, flat printing, screen printing, etc.), and then dried to form a coating film. The substrate on which the lower clad is formed is not particularly limited, but one with excellent flatness is preferred. Examples include metal substrates, silicon substrates, and transparent substrates, and can be selected appropriately depending on the shape of the optical waveguide. Preferred examples of metal substrates include gold, silver, copper, platinum, aluminum, chromium, etc., and preferred examples of transparent substrates include glass and plastic (e.g., polyethylene terephthalate) substrates. Furthermore, when a lower electrode is disposed between the substrate and the lower cladding, a known electrode can be used. The lower electrode may be a metal vapor deposition layer or a transparent electrode layer. Preferred examples of vapor-deposited metals include gold, silver, copper, platinum, aluminum, chromium, etc. Furthermore, preferred examples of transparent electrode layers include indium tin oxide (ITO), fluorine-doped tin oxide (FTO), antimony-doped tin oxide, etc. The method for drying the coating film is not particularly limited, and can be, for example, using a hot plate or oven under an appropriate atmosphere, i.e., air, an inert gas such as nitrogen, or a vacuum. The drying temperature is not particularly limited, but is, for example, 40 to 250°C. Examples of light rays to which the coating film is exposed include ultraviolet light, electron beams, and X-rays. Examples of light sources that can be used for ultraviolet irradiation include sunlight, chemical lamps, low-pressure mercury lamps, high-pressure mercury lamps, metal halide lamps, xenon lamps, UV-LEDs, etc. After exposure, the cured product may be post-baked to stabilize its physical properties.The post-baking method is not particularly limited, but is usually carried out using a hot plate, oven, or the like at 50 to 260° C. for 1 to 120 minutes.

[0084] (2) Step 2: Step 2 is a step of forming a patterned core on the lower clad formed in Step 1, for example, by photolithography of a coating film of the core-forming composition described above. In this step, for example, the core-forming composition described above is applied to the lower clad, followed by irradiation with ultraviolet light through a photomask and development to obtain a patterned core. Specifically, for example, the core-forming composition described above (which may be dissolved or dispersed in an organic solvent as needed to form a varnish (film-forming material)) is first applied to the lower clad using the coating method described above. Next, after irradiation with ultraviolet light through a photomask (pattern exposure), development is performed using an organic solvent, an alkaline aqueous solution, or the like. Examples of developers include isopropyl alcohol, propylene glycol monomethyl ether, ethylamine aqueous solution, n-propylamine aqueous solution, diethylamine aqueous solution, di-n-propylamine aqueous solution, triethylamine aqueous solution, methyldiethylamine aqueous solution, diethanolamine aqueous solution, triethanolamine aqueous solution, tetramethylammonium hydroxide aqueous solution, sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, sodium carbonate aqueous solution, sodium bicarbonate aqueous solution, sodium silicate aqueous solution, and sodium metasilicate aqueous solution. Development dissolves and removes the composition in unexposed areas. After development, post-baking may be performed as needed to stabilize the physical properties of the cured product. The post-baking method is not particularly limited, but is typically performed using a hot plate, oven, or the like at 50 to 260°C for 1 to 120 minutes.

[0085] (3) Step 3 Step 3 is a step of forming an upper clad by using, for example, the above-mentioned clad-forming composition so as to bond the upper clad to the lower clad and cover the core. This step can be carried out in the same manner as the above-mentioned (1) Step 1.

[0086] (4) Fourth Step The fourth step is a step of forming a protective layer, preferably a metal oxide-containing layer, on a necessary outer surface portion of the upper cladding or lower cladding. In this step, methods for forming the metal oxide-containing protective layer include sputtering, laser ablation, and electron beam evaporation. Among these, sputtering is preferred because it can form the protective layer at low temperatures and does not damage the upper / lower cladding layers. The protective layer can have a thickness of, for example, 0.1 to 0.5 μm. The protective layer may have a thickness of 0.5 μm or more, but a protective layer having a thickness of 0.5 μm or more does not affect the amount of change in propagation loss, as described below.

[0087] The optical waveguide of the present invention can take any of the following forms: a graded index (GI) type in which the refractive index of the core changes continuously in the radial direction; a multi-step index (MI) type in which the refractive index of the core changes stepwise in the radial direction; and a step index (SI) type in which the refractive index changes discontinuously only at the interface between the core and cladding.

[0088] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples. In the examples, the apparatus and conditions used for sample preparation and physical property analysis are as follows.

[0089] (1) Stirring deaerator Equipment: Rotating and revolving mixer ARE-310 (registered trademark) manufactured by Thinky Corporation (2) UV exposure Equipment: Batch type UV irradiation equipment (high pressure mercury lamp 2kW x 1 lamp) manufactured by iGraphics Co., Ltd. (3) Mask aligner Equipment: MA6 manufactured by SUSS MicroTec Lamp: high pressure mercury lamp Filter: i-line band pass filter Illuminance: 7mW / cm ２ (365 nm detection) (4) Dicing saw: DAD323 manufactured by Disco Corporation (5) Automatic alignment device: FCCB-253 automatic alignment device manufactured by Sigma Koki Co., Ltd.

[0090] CG-500: Oxol (registered trademark) CG-500, manufactured by Osaka Gas Chemicals Co., Ltd. CEL-8010: Celloxide (registered trademark) 8010, manufactured by Daicel Chemical Industries, Ltd. jER806: Bisphenol F type epoxy resin, manufactured by Mitsubishi Chemical Corporation M-100: Cyclomer (registered trademark) M-100 (3,4-epoxycyclohexylmethyl methacrylate), manufactured by Daicel Corporation EX-141: Denacol (registered trademark) EX-141 (phenyl glycidyl ether), manufactured by Nagase ChemteX Corporation STMS: Trimethoxy(4-vinylphenyl)silane [manufactured by Shin-Etsu Chemical Co., Ltd.] PTMS: Trimethoxy(phenyl)silane [manufactured by Shin-Etsu Chemical Co., Ltd.] TEAH: 35% by mass tetraethylammonium hydroxide aqueous solution [manufactured by Aldrich] FDA: bisarylfluorene diacrylate [Oxol (registered trademark) EA-F5503, manufactured by Osaka Gas Chemicals Co., Ltd.] BnA: benzyl acrylate [Viscoat #160, manufactured by Osaka Organic Chemical Industry Ltd.] I1010: pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] [IRGANOX (registered trademark) 1010, manufactured by BASF Japan Ltd.] O819: bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide [OMNIRAD (registered trademark) 819, manufactured by BASF Japan Ltd.] CPI-310FG: triarylsulfonium salt-type photoacid generator, manufactured by San-Apro Co., Ltd. Tinuvin 384-2: benzotriazole-based ultraviolet absorber, manufactured by BASF Japan Ltd. UVS-1331: sensitizer, manufactured by Kawasaki Chemical Industries, Ltd. IPA: isopropyl alcohol PGMEA: propylene glycol monomethyl ether acetate THF: tetrahydrofuran KBM-403: 3-glycidoxypropyltrimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.

[0091] [1] Preparation of Clad-Forming Material / Core-Forming Material [Example 1-1] Preparation of Clad-Forming Composition 20 parts by mass of CG-500, 35 parts by mass of jER806, 5 parts by mass of M-100, 8 parts by mass of EX-141, and 32 parts by mass of CEL-8010 were mixed, and to this was added 1 part by mass of photoacid generator CPI-310FG, 0.5 parts by mass of KBM-403, 1 part by mass of Tinuvin 384-2, and 0.2 parts by mass of UVS-1331. The mixture was stirred under heating at 110°C or less to completely dissolve the solid components, thereby preparing a liquid clad-forming composition.

[0092] [Example 1-2] Preparation of Core-Forming Composition According to the method described in WO2018 / 199305, a 200 mL reaction flask equipped with a condenser was charged with 2.97 g (7.1 mmol) of TEAH, 9.52 g (528 mmol) of ion-exchanged water, and 90 g of THF. The air in the flask was replaced with nitrogen using a nitrogen balloon. A mixture of 39.6 g (177 mmol) of STMS and 35.0 g (177 mmol) of PTMS was added dropwise over 10 minutes, and then stirred at 40 ° C for 16 hours. Next, 7.9 g of a cation exchange resin [Dow Chemical Company, Amberlyst (registered trademark) 15JWET] previously washed with THF was added to this reaction mixture, and the mixture was stirred for 1 hour to terminate the reaction. This mixture was then cooled to room temperature (approximately 23 ° C). The cation exchange resin was then filtered through a membrane filter with a pore size of 0.2 μm and further washed with 15 g of ethyl acetate. To the combined solution of the filtrate and washings, 9.3 g of BnA was added and mixed uniformly. Thereafter, using a rotary evaporator, THF, ethyl acetate, remaining water, and other volatiles were distilled off under reduced pressure to obtain a reactive silsesquioxane compound 1 (hereinafter sometimes abbreviated as SQ) / BnA solution. The weight average molecular weight Mw of SQ1 measured in polystyrene terms by GPC was 4,000, and the dispersity: Mw (weight average molecular weight) / Mn (number average molecular weight) was 1.8. Furthermore, the SQ content by GC quantitative analysis of the obtained solution was 75% by mass, and the BnA content was 25% by mass. 54.3 parts by weight of the SQ / BnA solution as a mixture of reactive silsesquioxane compound and (meth) acrylate compound (SQ 40.7 parts by weight, BnA 13.6 parts by weight), 31.6 parts by weight of FDA as a fluorene compound, 14.1 parts by weight of BnA as a (meth) acrylate compound (together with the BnA contained in the SQ / BnA solution 27.7 parts by weight), 0.25 parts by weight of I1010 as an antioxidant, and 2 parts by weight of O819 as a polymerization initiator were mixed, to which 18 parts by weight of PGMEA was added, and the mixture was heated and stirred at 50 ° C. for 8 hours. A core-forming composition was prepared by further stirring and degassing for 10 minutes.

[0093] [2] SiO ２Preparation of Optical Waveguide with Sputtered Film [Example 2-1] Production of Optical Waveguide 1 A PGMEA-diluted KBM403 solution was applied by spin coating (2,000 rpm x 30 seconds) and heated on a hot plate at 110°C for 10 minutes to prepare a silicon substrate that had been subjected to an adhesion treatment. The cladding composition prepared in Example 1 was applied to this silicon substrate by spin coating (1,800 rpm x 60 seconds) and heated on a hot plate at 60°C for 1 minute to obtain a coating film. This coating film was then exposed to 20 mW / cm using a batch-type UV irradiation device manufactured by Eye Graphics Co., Ltd. ２ The core-forming composition prepared in Example 2 was then applied onto the lower clad layer by spin coating (1,600 rpm x 60 seconds), and a mask aligner (mask width 15 μm) was used to apply a 7 mW / cm ２ The resulting composition was subjected to pattern exposure at 1000 rpm for 143 seconds. The unexposed composition was washed away with a PGMEA / IPA mixed solution (mass ratio 1:1), and then heated on a hot plate at 100°C for 2 minutes to obtain a linear core layer having a width of 12 μm, a height of 11 μm, and a length of 7 cm. The cladding composition prepared in Example 1 was applied onto the obtained core layer by spin coating (1,000 rpm x 60 seconds), and heated on a hot plate at 60°C for 1 minute to obtain a coating film. This coating film was then exposed to 20 mW / cm using a batch-type UV irradiation device manufactured by Eye Graphics Co., Ltd. ２ The resulting optical waveguide substrate was then exposed to light at 180° C. for 50 seconds, and finally heated on a hot plate at 180° C. for 20 minutes to form an upper clad layer, thereby obtaining an optical waveguide substrate. Finally, a 100-nm-thick SiO ２ A film was formed, and SiO ２ An optical waveguide 1 with a protective film was obtained.

[0094] [Example 2-2] Manufacturing of Optical Waveguide 2 After manufacturing an optical waveguide in the same manner as in Example 2-1, a 300 nm thick SiO ２ A film was formed, and SiO ２ An optical waveguide 2 with a protective film was obtained.

[0095] Comparative Example 2-1 Manufacture of Optical Waveguide 3 An optical waveguide 3 was manufactured in the same manner as in Example 2-1, except that the sputtering film formation step was not carried out.

[0096] The optical waveguides 1 to 3 obtained in Examples 2-1 and 2-2 and Comparative Example 2-1 were cut out to a waveguide length of 6 cm using a dicing saw (manufactured by Disco Corporation, product name "DAD323"), and the insertion loss at a wavelength of 1.31 μm was measured. The results are shown in Table 1.

[0097]

[0098] As shown in Table 1, SiO ２ No effect of sputtering on insertion loss was observed.

[0099] [3] High Heat Resistance Test Optical waveguides 1 to 3 obtained from Examples 2-1 and 2-2 and Comparative Example 2-1 were cut into waveguide lengths of 6 cm using a dicing saw (manufactured by Disco Corporation, product name "DAD323") and then placed in a 150°C thermostatic tester. Each waveguide was removed from the thermostatic tester every approximately 250 hours, and 0.25 cm lengths were cut from both end faces of the waveguide, and the insertion loss at a wavelength of 1.31 μm was measured. This procedure was repeated up to 1000 hours. The insertion loss measurement results for each elapsed time (test time) during the 150°C thermostatic test are shown in Tables 2, 3, and FIG. 1.

[0100]

[0101]

[0102] In the optical waveguide 3 of Comparative Example 2-1, the insertion loss increased significantly as the test time of the 150°C constant temperature test passed. ２ No increase in insertion loss was observed in the optical waveguide 1 of Example 2-1 and the optical waveguide 2 of Example 2-2, in which a film was formed by sputtering. Note that the loss decreased slightly over time, but this is thought to be due to the fact that the waveguide end face was cut out in 0.25 cm increments during the insertion loss evaluation. The result that the insertion loss was almost constant in the waveguides of the examples is due to the SiO ２ This can be said to be a protective effect provided by providing the sputtered film.

[0103] [4] Propagation Loss Evaluation For the optical waveguide obtained by the same operation as in Comparative Example 2-1, propagation loss was measured before the high heat resistance test using the method described in JPCA Standard (2008) 4.6.2.1 Cutback Method. The propagation loss at a wavelength of 1.31 μm was 0.31 dB / cm. Similarly, propagation loss was measured using the cutback method for the optical waveguides of Example 2-1 and Comparative Example 2-1 that had undergone the above-mentioned high heat resistance test (150°C, 1000 hours of constant temperature test). The propagation loss at a wavelength of 1.31 μm was 0.32 dB / cm (Example 2-1) and 2.03 dB / cm (Comparative Example 2-1), respectively. The propagation loss of the optical waveguide after the high heat resistance test at 150°C was measured using the SiO ２ Comparative Example 2-1, which does not have a sputtered film, showed a significant deterioration (from 0.31 dB / cm to 2.03 dB / cm), while the SiO ２ The results show that Example 2-1 having the sputtered film showed almost no change (from 0.31 dB / cm to 0.32 dB / cm, rate of change: 3.2%).

Claims

1. An optical waveguide having a core, a cladding that completely surrounds and covers the periphery of the core and has a smaller refractive index than the core, and a protective layer on at least a portion of the outer periphery of the cladding, in which, in a high-temperature durability test in which the waveguide is stored in air at 150°C for 1,000 hours, the propagation loss of light with a wavelength of 1.31 μm after the test has changed by 10% or less compared to the same value before the test.

2. The optical waveguide of claim 1, wherein said protective layer is a metal oxide-containing layer.

3. The optical waveguide of claim 2, wherein said protective layer is a silicon dioxide-containing layer.

4. The optical waveguide according to claim 1, wherein the core is made of a cured product of a core-forming composition containing (A) a reactive silsesquioxane compound and (B) a fluorene compound, the (A) reactive silsesquioxane compound being a polycondensate of an alkoxysilane compound A represented by the following formula [1] and an alkoxysilane compound B represented by the following formula [2], and the (B) fluorene compound is a compound represented by the following formula [3]. (In the formula, Ar １ represents a phenyl group having at least one group having a polymerizable double bond, a naphthyl group having at least one group having a polymerizable double bond, or a biphenyl group having at least one group having a polymerizable double bond; R １ represents a methyl group or an ethyl group. (In the formula, Ar ２ represents a phenyl group which may be substituted with an alkyl group having 1 to 6 carbon atoms, a condensed polycyclic aromatic hydrocarbon group which may be substituted with an alkyl group having 1 to 6 carbon atoms, or a hydrocarbon ring assembly group in which a plurality of aromatic rings are directly bonded together via single bonds (which may be substituted with an alkyl group having 1 to 6 carbon atoms); R ２ represents a methyl group or an ethyl group. (In the formula, R ３ and R ４ each independently represents a hydrogen atom or a methyl group; L １ and L ２ each independently represents a phenylene group which may have a substituent, or a naphthalenediyl group which may have a substituent; L ３ and L ４ each independently represents an alkylene group having 1 to 6 carbon atoms, and m and n each represent 0 or a positive integer such that m+n is 0 to 40.

5. The optical waveguide according to claim 1, wherein the cladding is made of a cured product of a cladding-forming composition containing (D) a fluorene skeleton-containing epoxy compound and (G) a photoacid generator, and the fluorene skeleton-containing epoxy compound (D) is a compound represented by the following formula [4]: (In formula [4], L ５ and L ６ each independently represents a naphthalenediyl group which may have a substituent, and p and q each independently represent an integer of 0 to 10.

6. A method for manufacturing an optical waveguide as claimed in any one of claims 1 to 5, comprising: a first step of forming a lower clad; a second step of forming a patterned core on said lower clad; a third step of forming an upper clad so as to bond it to said lower clad and cover said core; and a fourth step of forming a protective layer on a necessary outer surface portion of said upper clad or lower clad.

7. The manufacturing method according to claim 6, wherein the fourth step is a step of forming a protective layer by a sputtering method.

8. The method according to claim 7, wherein the protective layer has a thickness of 0.1 to 0.5 μm.

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