Self-written optical waveguide and its manufacturing method

Abstract

To provide a flexible self-forming optical waveguide with which a positional deviation, or breakage or separation subsequent thereto hardly occurs even under vibration states and it is possible to secure a sufficient connection state, and a manufacturing method for the same.SOLUTION: Provided is a method for manufacturing a flexible self-forming optical waveguide, the method including: a step A for preparing an admixture 12 that includes a photopolymerizable polymer gel material A that polymerizes upon irradiation of light of wavelength λA and a photopolymerizable polymer gel material B whose refractive index is lower than that of the photopolymerizable polymer gel material A and that polymerizes upon irradiation of light of wavelength λB (≠λA); a step B for holding the admixture 12 by a holding member 10; a step C for immersing one end of an optical fiber 14 in the admixture 12 held by the holding member 10; a step D for entering a laser beam of wavelength λA from the other end of the optical fiber 14, emitting it from one end of the optical fiber 14, and polymerizing and curing the photopolymerizable polymer gel material A epaxially in the optical axis direction of the optical fiber 14; and a step E for irradiating light of wavelength λB from the periphery of the admixture 12 and polymerizing and curing the photopolymerizable polymer gel material B.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a flexible self-written optical waveguide that can be used for connecting optical fibers, and a method for producing the same. [Background technology]

[0002] In recent years, there has been a need for faster, larger capacity communication between electronic devices in vehicles such as automobiles, and in order to meet this need, optical communication is becoming mainstream instead of electrical communication. Optical communication has the advantages of being more resistant to electromagnetic noise than electrical communication, and enabling faster, larger capacity communication. Electronic devices installed in vehicles can transmit and receive optical signals via optical fibers by using light-emitting elements such as laser diodes and light-receiving elements such as photodiodes.

[0003] In high-speed optical communication on board, for example, plastic optical fibers with a core diameter of 1 mm are used for gigabit speeds, and multimode optical fibers (glass, plastic) with a core diameter of about 50 μm are used for speeds of over 10 gigabits. In addition, since axis misalignment is likely to occur due to the influence of vibrations during driving, it is necessary to stabilize and highly reliable connectivity in vehicles. For this reason, it is necessary to consider and develop a method for connecting light-receiving and light-emitting elements and connecting relay connectors. In this situation, a method of inserting a gel film into the connector part has been proposed for transmission of gigabit Ethernet, since the core diameter is as large as 1 mm in the connection between plastic optical fibers for vehicle use (see Non-Patent Document 1). This method does not cause any problems in optical connection when the core size is large, but in the case of high-speed transmission of over 10 gigabits, an optical fiber with a core diameter of 50 μm is used, and there is a problem that the alignment between the cores is shifted due to vibrations in the vehicle environment.

[0004] Self-forming optical waveguides are promising as an automatic alignment technology between optical elements (see Patent Documents 1 and 2). Furthermore, self-forming optical waveguides would be useful if they could be applied to connections with light-receiving and light-emitting elements mounted on vehicles and to high-speed optical communications with relay connectors. Here, the term "self-forming optical waveguide" refers to an axial core formed by irradiating a photopolymerizable resin with light of a wavelength at which the photopolymerizable resin polymerizes, from an optical fiber or the like. However, in this specification, the combination of the core and cladding is called a self-forming optical waveguide. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2007-72129 A [Patent Document 2] JP 2008-83447 A [Non-patent literature]

[0006] [Non-Patent Document 1] M. Uchida, O. Sugihara, et al., “Temperature insensitive low-loss optical connection for automotive gigabit plastic optical fiber communication”, Jpn. J. Appl. Phys., Vol.57, No.8S2 (2018) 08PB03-1-08PB03-5. Summary of the Invention [Problem to be solved by the invention]

[0007] However, the self-written optical waveguides reported so far have been highly rigid because they use photocurable resins. If the core becomes misaligned due to vibration or other factors after connection, the core may break or peel off, making it impossible to ensure a sufficient connection.

[0008] The present invention has been made in consideration of the problems inherent in the conventional techniques, and an object of the present invention is to provide a flexible self-written optical waveguide that is unlikely to become displaced and is unlikely to break or peel off even under vibration conditions, and that can ensure a sufficient connection state, and a method for manufacturing the same. [Means for solving the problem]

[0009] The flexible self-forming optical waveguide according to the first embodiment of the present invention has a core formed from a polymer gel material A and a cladding formed from a polymer gel material B having a lower refractive index than that of the polymer gel material A.

[0010] A flexible self-forming optical waveguide according to a second aspect of the present invention relates to the flexible self-forming optical waveguide of the first aspect, in which the polymer gel material A is made of an acrylic gel, a urethane gel, or a silicone gel.

[0011] A method for producing a flexible self-written optical waveguide according to a third aspect of the present invention includes: A Photopolymerizable polymer gel material A is polymerized by irradiation with light of wavelength λ B (≠λ A A process A includes preparing a mixture containing a photopolymerizable polymer gel material B that is polymerized by irradiation with light of a wavelength λ; a process B includes holding the mixture with a holding member; a process C includes immersing one end of an optical fiber in the mixture held by the holding member; and a process C includes irradiating the other end of the optical fiber with light of a wavelength λ. A a step D of irradiating a laser beam having a wavelength of λ from the periphery of the mixture and emitting the laser beam from one end of the optical fiber located in the mixture to polymerize and harden the photopolymerizable polymer gel material A in an axial shape in the optical axis direction of the optical fiber; B and a step E of irradiating the photopolymerizable polymer gel material B with light to polymerize and harden the photopolymerizable polymer gel material B.

[0012] A fourth aspect of the present invention relates to a method for producing a flexible self-formed optical waveguide, and further includes a step of irradiating ultraviolet light towards the mixture between steps B and D. Effect of the Invention

[0013] According to the present invention, it is possible to provide a flexible self-written optical waveguide that is unlikely to become displaced and the associated breakage and peeling even under vibration conditions and that can ensure a sufficient connection state, and a method for manufacturing the same. [Brief description of the drawings]

[0014] [Figure 1] 1A to 1C are conceptual diagrams for explaining a series of steps in a method for manufacturing a flexible self-written optical waveguide according to the present embodiment. [Diagram 2] 3A to 3C are diagrams illustrating the formation of a core of the flexible self-written optical waveguide according to the present embodiment. [Diagram 3] 3A to 3C are micrographs showing the cores of flexible self-written optical waveguides formed using different laser powers in the configuration shown in FIG. 2. [Figure 4] 3A to 3C are diagrams illustrating the formation of a cladding of the flexible self-written optical waveguide of the present embodiment. [Diagram 5] 5 is a micrograph showing flexible self-written optical waveguides formed by varying the duration of light irradiation in the configuration shown in FIG. 4. [Figure 6] FIG. 2 is a diagram showing a schematic configuration of an apparatus for measuring and evaluating connection and insertion loss in the flexible self-written optical waveguide of the present embodiment. [Figure 7] 1 is a micrograph showing a state in which a flexible self-written optical waveguide according to the present embodiment is formed between optical fibers. [Figure 8] FIG. 13 is a plot showing an evaluation of insertion loss when the flexible self-written optical waveguide of the present embodiment is applied to optical fiber coupling. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] <Flexible self-written optical waveguide> The flexible self-forming optical waveguide of this embodiment (hereinafter also simply referred to as "self-forming optical waveguide") has a core formed from polymer gel material A and a cladding formed from polymer gel material B having a lower refractive index than polymer gel material A. In the self-forming optical waveguide of this embodiment, both the core and the cladding are formed from a flexible polymer gel material. Therefore, for example, when used to connect optical fibers, even if a positional shift is likely to occur under vibration conditions, it is possible to follow the positional shift displacement and prevent breakage and peeling of the core.

[0016] In the self-forming optical waveguide of this embodiment, polymer gel material B, which is the material from which the cladding is formed, has a lower refractive index than polymer gel material A, which is the material from which the core is formed, and the difference in refractive index between them is sufficient to establish a relationship between the core and the cladding, i.e., sufficient to confine the incident light within the core.

[0017] The polymer gel material A or B used in the self-forming optical waveguide of this embodiment may be (1) a copolymer of a polymerizable monomer and a crosslinking agent (multifunctional monomer), or (2) a crosslinking of a polymer chain using a multifunctional compound. An example of the above (1) is a copolymer of a (meth)acrylic monomer and a crosslinking agent. An example of the above (2) is a liquid acrylic polymer containing a polyhydric alcohol. Among them, the polymer gel material A is preferably an acrylic gel, a urethane gel, or a silicone gel. Details of these polymer gel materials will be described in detail in the manufacturing method of this embodiment described later.

[0018] As described above, the self-written optical waveguide of this embodiment can prevent breakage of the core even under vibration conditions, so that the core diameter can be set to 5 to 1000 μm in the self-written optical waveguide of this embodiment, for example. That is, the self-written optical waveguide of this embodiment can be applied to the connection of optical fibers with a core diameter of 50 μm, which are used for high-speed transmission of over 10 gigabits.

[0019] The self-written optical waveguide of this embodiment described above can be manufactured by the manufacturing method of the flexible self-written optical waveguide of this embodiment described below.

[0020] <Method of manufacturing flexible self-written optical waveguide> The method for producing a flexible self-written optical waveguide of this embodiment includes the following steps A to E. Process A: Wavelength λ A Photopolymerizable polymer gel material A is polymerized by irradiation with light of wavelength λ B (≠λ A ) and a photopolymerizable polymer gel material B that polymerizes when irradiated with light. Step B: The mixture is held by a holding member. Step C: One end of an optical fiber is immersed in the mixture held by the holding member. Step D: Wavelength λ from the other end of the optical fiber A The laser light is then incident on one end of an optical fiber located in the mixture, and the laser light is emitted from one end of the optical fiber, so that the photopolymerizable polymer gel material A is polymerized and hardened in an axial shape in the optical axis direction of the optical fiber. Step E: Wavelength λ from the surroundings of the mixture B The photopolymerizable polymer gel material B is polymerized and hardened by irradiating the photopolymerizable polymer gel material B with light.

[0021] The manufacturing method of the flexible self-written optical waveguide of this embodiment will be described with reference to Fig. 1. First, as shown in Fig. 1(a), A Photopolymerizable polymer gel material A is polymerized by irradiation with light of wavelength λ B (≠λ A ) and photopolymerizable polymer gel material B that polymerizes when irradiated with light of a different predetermined wavelength, a mixture 12 is prepared (Step A). ​​The prepared mixture is then held by a holding member 10 (Step B). Photopolymerizable polymer gel material A is a material that forms the core, and photopolymerizable polymer gel material B is a material that forms the cladding. Both are materials that polymerize and gel when irradiated with light of a different predetermined wavelength.

[0022] Next, as shown in FIG. 1(b), one end of an optical fiber 14 is immersed in the mixture 12 held by the holding member 10 (step C). Then, light having a wavelength λ is emitted from the other end of the optical fiber 14. A Then, as shown in FIG. 1(c), the laser light is introduced into the mixture 12, and the photopolymerizable polymer gel material A is polymerized and hardened in an axial shape in the optical axis direction of the optical fiber 14 to form a gel core 16 (step D). At this time, the photopolymerizable polymer gel material B is irradiated with a laser light having a wavelength of λ A However, the gel-like core 16 does not polymerize and harden by the irradiation of the laser light. The irradiation of the laser light is continued until the gel-like core 16 reaches the edge of the holding member 10 as shown in Fig. 1(d). In this manner, the gel-like core 16 is formed.

[0023] Furthermore, as shown in FIG. 1(e), from the outside of the holding member 10, B The photopolymerizable polymer gel material B is polymerized and hardened to gel by irradiation with light (step E).

[0024] Each step will be described in detail below.

[0025] [Process A] In step A, the wavelength λ A Photopolymerizable polymer gel material A is polymerized by irradiation with light of wavelength λ B (≠λ A A mixture containing a photopolymerizable polymer gel material A and a photopolymerizable polymer gel material B that is polymerized by irradiation with light having a wavelength λ of light for polymerizing the photopolymerizable polymer gel material A is prepared. A and the wavelength λ of light for polymerizing the photopolymerizable polymer gel material B. B is different.

[0026] Photopolymerizable polymer gel material A is a material that forms the core, and photopolymerizable polymer gel material B is a material that forms the cladding. Therefore, it is necessary to select a material such that the gel derived from photopolymerizable polymer gel material A has a higher refractive index than the gel derived from photopolymerizable polymer gel material B after gelation.

[0027] In this embodiment, a mixed liquid is used that contains a photopolymerizable polymer gel material A that has a relatively high refractive index after polymerization and hardening, and a photopolymerizable polymer gel material B that has a lower refractive index than the photopolymerizable polymer gel material A. The combination of the photopolymerizable polymer gel material A and the photopolymerizable polymer gel material B can be, for example, a combination in which the photopolymerizable polymer gel material A is a radical polymerization type acrylic monomer, and the photopolymerizable polymer gel material B is a cationic polymerization type epoxy monomer. Then, in order to form the core, a wavelength λ A and a radical polymerization initiator having sensitivity to the wavelength, and having no sensitivity to the wavelength, and having a wavelength λ B In this state, a predetermined amount of a cationic polymerization initiator having sensitivity to the wavelength λ A When the mixed liquid is irradiated with light of wavelength λ from an optical fiber, the photopolymerizable polymer gel material A in the mixed liquid is selectively polymerized and hardened in the optical axis direction of the optical fiber, and the core grows. B By irradiating the photopolymerizable polymer gel material B with this light, the photopolymerizable polymer gel material B is polymerized and hardened to form a cladding.

[0028] In this embodiment, both photopolymerizable polymer gel materials A and B contain raw materials capable of forming a polymer gel by light irradiation. In the following, a radical polymerizable material is used as the photopolymerizable polymer gel material A, and a cationic polymerizable material is used as the photopolymerizable polymer gel material B, but the present embodiment is not limited thereto.

[0029] (Photopolymerizable polymer gel material A) The photopolymerizable polymer gel material A contains at least a radically polymerizable monomer, a crosslinking agent, and a photopolymerization initiator.

[0030] As the radical polymerizable monomer, a monofunctional acrylate compound can be used. For example, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, myristyl (meth)acrylate, palmityl (meth)acrylate, and stearyl (meth)acrylate can be mentioned. In this specification, "(meth)acrylate" means both acrylate and methacrylate.

[0031] As the crosslinking agent, a polyfunctional compound having two or more functional groups in one molecule capable of forming a covalent bond with the photopolymerizable monomer by radical polymerization can be used. Examples of the polyfunctional acrylate include bifunctional: 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, ethylene oxide modified hexahydrophthalic acid di(meth)acrylate, neopentyl glycol modified trimethylolpropane di(meth)acrylate, adamantane di(meth)acrylate, 9,9-bis[4-(2-acryloyloxyethoxy)phenyl]fluorene, trifunctional: trimethylolpropane tri(meth)acrylate, diphenyl ether di(meth)acrylate, ethylene oxide modified hexahydrophthalic acid ... Examples of the functional groups include pentaerythritol tri(meth)acrylate, propionic acid modified dipentaerythritol tri(meth)acrylate, pentaerythritol tri(meth)acrylate, propylene oxide modified trimethylolpropane tri(meth)acrylate, tris(meth)acryloxyethyl isocyanurate, 4-functional: diglycerol tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, 5-functional: propionic acid modified dipentaerythritol penta(meth)acrylate, 6-functional: dipentaerythritol hexa(meth)acrylate, and caprolactone modified dipentaerythritol hexa(meth)acrylate. In addition, polyfunctional thiols may be used, and specific examples thereof include pentaerythritol tetrakis(3-mercaptobutyrate, 1,4-bis(3-mercaptobutyryloxy)butane, trimethylolpropane tris(3-mercaptobutyrate), 1,3,5-tris(2-(3-sulfanylbutanoyloxy)ethyl)-1,3,5-triazinane-2,4,6-trione, and the like.

[0032] Examples of the photopolymerization initiator include halogenated hydrocarbon derivatives (e.g., compounds having a triazine skeleton, compounds having an oxadiazole skeleton, etc.), aromatic ketones, α-aminoalkylphenones, α-hydroxyketones, acylphosphine oxides, oxime esters, aromatic onium salts, organic peroxides, thio compounds, hexaarylbiimidazole compounds, ketoxime ester compounds, borate compounds, azinium compounds, metallocene compounds, active ester compounds, compounds having a carbon-halogen bond, and alkylamine compounds. A When the wavelength of visible light or more, a sensitizer such as a dye having absorption at a predetermined wavelength may be added. Although there is no particular limitation on the dye that can be used, specific examples include cyanine dyes, rhodamine dyes, coumarin dyes, squarylium dyes, immonium dyes, phthalocyanine dyes, and porphyrin dyes.

[0033] (Photopolymerizable polymer gel material B) The photopolymerizable polymer gel material B contains at least a cationic polymerizable monomer, a crosslinking agent, and a cationic polymerization initiator.

[0034] The cationic polymerizable monomer may be a monofunctional monomer having an epoxy group or an oxetanyl group. Specific examples of the monofunctional epoxy monomer include ethyl glycidyl ether, butyl glycidyl ether, 2-ethylhexyl glycidyl ether, phenyl glycidyl ether, t-butylphenyl glycidyl ether, and glycidyl lauryl ether. Examples of the monofunctional oxetane monomer include 2-ethylhexyl oxetane, 3-hydroxymethyl-3-methyl oxetane, 3-hydroxymethyl-3-ethyl oxetane, 3-hydroxymethyl-3-propyl oxetane, 3-hydroxymethyl-3-normal butyl oxetane, 3-hydroxymethyl-3-phenyl oxetane, 3-hydroxymethyl-3-benzyl oxetane, 3-hydroxyethyl-3-methyl oxetane, 3-hydroxyethyl-3-ethyl oxetane, 3-hydroxyethyl-3-propyl oxetane, 3-hydroxyethyl-3-phenyl oxetane, 3-hydroxypropyl-3-ethyl oxetane, 3-hydroxypropyl-3-propyl oxetane, 3-hydroxypropyl-3-phenyl oxetane, and 3-hydroxybutyl-3-methyl oxetane.

[0035] Examples of the crosslinking agent include polyfunctional epoxies, bifunctional epoxies: ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1.6-hexanediol diglycidyl ether, glycerin diglycidyl ether, 2,2-bis(4-glycidyloxyphenyl)propane, and trifunctional epoxies: trimethylolpropane triglycidyl ether, tris(4-hydroxyphenyl)methane triglycidyl ether, glycerin triglycidyl ether, N,N,O-triglycidyl-p-aminophenol, N,N,O-triglycidyl-m-aminophenol, N,N,O-triglycidyl-4-amino-m-cresol, N,N,O-triglycidyl-5-amino-o-cresol, and 1,1,1-(triglycidyloxyphenyl)methane. In addition, polyfunctional oxetanes may be used. Specifically, bifunctional oxetanes such as xylylene bisoxetane, 3-ethyl-3{[(3-ethyloxetane-3 1,4-bis{[(3-ethyloxetan-3-yl)methoxy]methyl}oxetane, 1,4-bis{[(3-ethyloxetan-3-yl)methoxy]methyl}bene, bis[1-ethyl(3-oxetanyl)]methyl ether, 1,2-bis[(3-ethyloxetan-3-yl)methyloxy]ethane, 1,3-bis[(3-ethyloxetan-3-yl)methyloxy]propane, 1,4-bis[(3-ethyloxetan-3-yl)methyloxy]butane, 1,5-bis[(3-ethyloxetan-3-yl)methyloxy]pentane, 1,6-bis[(3-ethyloxetan-3-yl)methyloxy]hexane, 1,7-bis[(3-ethyloxetan-3-yl)methyloxy]heptane, 1,8-bis[(3-ethyloxetan-3-yl)methyloxy]octane, and the like.

[0036] Examples of the cationic polymerization initiator include sulfonium salt compounds, iodonium salt compounds, phosphonium salt compounds, ammonium salt compounds, antimony salt compounds, diazonium salt compounds, selenium salt compounds, oxonium salt compounds, and bromine salt compounds. B When the wavelength of visible light or more, a sensitizer such as a dye having absorption at a predetermined wavelength may be added. Although there is no particular limitation on the dye that can be used, specific examples include cyanine dyes, rhodamine dyes, coumarin dyes, squarylium dyes, immonium dyes, phthalocyanine dyes, and porphyrin dyes.

[0037] In step A, the photopolymerizable polymer gel material A and the photopolymerizable polymer gel material B are mixed and stirred according to a standard method to obtain a mixture.

[0038] [Process B] In step B, the mixture obtained in step A is held by a holding member. The holding member may be any member capable of holding the mixture for carrying out subsequent steps from step C onward, and examples of the holding member include a container and a formwork. For example, if the holding member is a container, a required amount of the mixture obtained in step A may be prepared and the mixture may be poured into the container.

[0039] [Process C] In step C, one end of an optical fiber is immersed in the mixture held by a holding member. In the subsequent step D, a laser beam is emitted from one end of the immersed optical fiber to form a core, so that only the vicinity of one end of the optical fiber needs to be immersed in the mixture. The optical fiber used is preferably a plastic optical fiber.

[0040] [Process D] In step D, the wavelength λ AThe laser light having a wavelength of λ is incident on the optical fiber and emitted from one end of the optical fiber located in the mixture, polymerizing and curing the photopolymerizable polymer gel material A in an axial shape in the optical axis direction of the optical fiber. Here, the other end of the optical fiber is the end opposite to the one end of the optical fiber immersed in the mixture in step C. As described above, the laser light having a wavelength of λ is incident on the optical fiber and emitted from one end of the optical fiber located in the mixture, polymerizing and curing the photopolymerizable polymer gel material A in an axial shape in the optical axis direction of the optical fiber. A By emitting the laser light from one end of the optical fiber, only the photopolymerizable polymer gel material A is selectively polymerized, and the material is polymerized and hardened in an axial direction along the optical axis of the optical fiber to form a core.

[0041] In step D, the wavelength λ of the laser light to be irradiated is set to 100 nm in order to copolymerize the polymerizable monomer and the crosslinking agent in the photopolymerizable polymer gel material A. A is a wavelength to which the polymerization initiator has sensitivity.

[0042] When the self-forming optical waveguide of this embodiment is used to optically connect a pair of optical fibers arranged so that their tips face each other, a core can be formed by irradiating a laser beam from the tip of one optical fiber toward the tip of the other optical fiber. Alternatively, a core may be formed by irradiating a laser beam from each of the optical fibers toward the tip of the other optical fiber.

[0043] [Process E] In step E, the wavelength λ B In other words, a clad is formed around the core formed in step D. In step E, in order to copolymerize the polymerizable monomer and the crosslinking agent in the photopolymerizable polymer gel material B, the wavelength λ of the laser light to be irradiated is B is a wavelength to which the polymerization initiator has sensitivity.

[0044] In this embodiment, it is preferable to further include a step of irradiating the mixture with ultraviolet light between step B and step D. If a thin core is formed in a liquid mixture, there is a concern that the core may easily bend due to the flow of the monomer. Therefore, by irradiating with ultraviolet light before forming the core and partially polymerizing the photopolymerizable polymer gel material A or B in the mixture to increase the viscosity, it is possible to prevent the core from bending. The irradiation time of ultraviolet light can be a time sufficient for the monomer to lose its fluidity, for example, 5 seconds or more. On the other hand, when the mixture is entirely surrounded by a holding member in step B, the holding member is preferably made of a material that transmits ultraviolet light.

[0045] [Test Example 1] In order to confirm whether a gel-like core can be formed in the photopolymerizable polymer gel material A by irradiating a laser beam from an optical fiber, the following test was carried out. First, the following components were prepared as the photopolymerizable polymer gel material A. Polymerizable monomer: AMP-20GY manufactured by Shin-Nakamura Chemical Co., Ltd. Crosslinking agent: Karenz MT (registered trademark) PE1, manufactured by Showa Denko K.K. Photopolymerization initiator 1: 2-(4-Methoxyphenyl)-4,6-bis(trichloromethyl)-1,3,5-triazine (TCT), manufactured by Tokyo Chemical Industry Co., Ltd. Photopolymerization initiator 2: Showa Denko Co., Ltd., product name P3B Near infrared absorbing dye: Showa Denko K.K., product name IRT These materials were mixed and stirred at room temperature for several hours to prepare photopolymerizable polymer gel material A. The mixing ratio of the materials was polymerizable monomer / crosslinking agent / photopolymerization initiator 1 / photopolymerization initiator 2 / dye = 2000 / 125 / 10 / 10 / 6.

[0046] Next, as shown in FIG. 2, a cover glass 22 was placed on a slide glass 20 in a U-shape, and the photopolymerizable polymer gel material A prepared as described above was dropped into the area surrounded by the cover glass 22. Then, using an alignment stage, one end of a plastic optical fiber (manufactured by AGC Corporation, FONTEX (registered trademark), core diameter: 55 μm, cladding diameter: 490 μm) was immersed in the photopolymerizable polymer gel material A. Next, a laser beam having a wavelength of 783 nm was incident from the other end of the plastic optical fiber to form a core. After the core was formed, the core was removed from the photopolymerizable polymer gel material A by the alignment stage, washed with ethanol, and observed with a CCD camera. The above operation was performed for each of the three laser powers of 5 mW, 500 μW, and 200 μW. The respective photographs are shown in FIG. 3. FIG. 3(a) shows a test when the laser power is 5 mW, (b) shows a test when the laser power is 500 μW, and (c) shows a test when the laser power is 200 μW. As shown in Fig. 3(c), the core of the self-written optical waveguide was formed when the laser power was 200 μW. The diameter of the self-written optical waveguide was about 50 μm.

[0047] [Test Example 2] The following test was conducted to confirm whether bending of the core could be prevented by partially polymerizing the material in advance through UV irradiation to increase the viscosity. As in Test Example 1, a cover glass 22 was placed in a U-shape on a slide glass 20 as shown in Fig. 4. The photopolymerizable polymer gel material A prepared as described above was dropped into the area surrounded by the cover glass 22. Furthermore, in order to prevent variation in the test results due to differences in material thickness, etc., a cover glass 28 was placed as a top cover. Next, power density 23mW / cm 2Afterwards, a laser beam with a wavelength of 853 nm was irradiated for 30 seconds to form a self-formed optical waveguide. The above operation was carried out twice, the first time with 6 seconds of UV irradiation, and the second time with 7 seconds of UV irradiation. Figure 5 shows the appearance of the self-formed optical waveguide formed. Figure 5(a) shows the appearance after 6 seconds of UV irradiation, and Figure 5(b) shows the appearance after 7 seconds of UV irradiation. As shown in Figure 5(b), that is, when UV irradiation was carried out for 7 seconds, a linear core was formed. In addition, it is considered that the inhibition of oxygen polymerization was reduced because the surface of the solution was not exposed to air due to the top cover glass. This makes it possible to form a core with a lower laser output.

[0048] [Test Example 3] In order to evaluate the connection performance of the self-written optical waveguide formed between plastic optical fibers, a test was carried out to measure the insertion loss. Fig. 6(a) shows a schematic diagram of an apparatus for measuring insertion loss. The apparatus shown in Fig. 6(a) includes a laser light source 40, a power meter 42 for measuring the output of the laser light, a pair of alignment stages 34 and 36 located between them, and a sample stage 30 on which a sample 32 for measuring insertion loss is placed. The alignment stage 34 holds an optical fiber 38 connected to the power meter 42, and the alignment stage 36 holds an optical fiber 38 connected to the laser light source 40. The sample stage 30 holds the sample 32 for measuring insertion loss. In this test example, a laser light having a wavelength of 1550 nm was used to measure the insertion loss at a wavelength to which the photopolymerizable polymer gel material A is not sensitive.

[0049] A self-forming optical waveguide was formed between the tips of a pair of optical fibers by assembling an apparatus configuration shown in Fig. 6(b). In Fig. 6(b), the same components as in Fig. 6(a) are given the same reference numerals. In Fig. 6(b), the laser light emitted from the laser light source 40 proceeds to the beam splitter 46 via the isolator 44, and is split into two directions at the beam splitter 46 with a splitting ratio of 1:1. The laser light split into two directions then merges on the sample stage 30, and the laser light is incident on the sample 32 from both directions. In this test example, a photopolymerizable polymer gel material A was used, and a power density of 23 mW / cm was set in advance. 2 The substrate was irradiated with UV of 1000 nm for 7 seconds, and then laser light of 853 nm wavelength was emitted from the laser light source 40 at an output of 2 μW to form a self-written optical waveguide. A microscope image after the self-written optical waveguide was formed is shown in Figure 7. As shown in Figure 7, it can be confirmed that a self-written optical waveguide has been formed between the tips of a pair of optical fibers 38.

[0050] On the other hand, the insertion loss was measured in the following three states A to C using the device shown in FIG. A: There is a gap between the tips of a pair of optical fibers 38. B: Photopolymerizable polymer gel material A is used as a sample, and the sample is not irradiated with laser light. C: The state in which the self-written optical waveguide is formed as described above. The measurement results were 5.68 dB for A, 3.82 dB for B, and 1.75 dB for C. The measurement results of the insertion loss are shown in a graph in Figure 8. It can be seen that the insertion loss is suppressed by forming a self-written optical waveguide.

[0051] Although the present embodiment has been described above, the present disclosure is not limited to this, and various modifications are possible within the scope of the gist of the present embodiment.

Claims

1. A self-forming optical waveguide having a core formed from a polymer gel material A obtained by polymerizing a radically polymerizable monomer which is a monofunctional acrylate compound and a crosslinking agent which is a polyfunctional acrylate or a polyfunctional thiol, and a cladding formed from a polymer gel material B which has a lower refractive index than the polymer gel material A and is obtained by polymerizing a cationic polymerizable monomer which is a monofunctional monomer having an epoxy group or an oxetanyl group and a crosslinking agent which is a polyfunctional epoxy or a polyfunctional oxetane.

2. 2. The self-forming optical waveguide according to claim 1, wherein the polymer gel material A is made of an acrylic gel.

3. A process A for preparing a mixture including: a photopolymerizable polymer gel material A which polymerizes when irradiated with light of wavelength λA, the photopolymerizable polymer gel material A including at least a radical polymerizable monomer which is a monofunctional acrylate compound, a crosslinking agent which is a polyfunctional acrylate or a polyfunctional thiol, and a photopolymerization initiator; and a photopolymerizable polymer gel material B which has a refractive index lower than that of the photopolymerizable polymer gel material A, the photopolymerizable polymer gel material B including at least a cationic polymerizable monomer which is a monofunctional monomer having an epoxy group or an oxetanyl group, a crosslinking agent which is a polyfunctional epoxy or a polyfunctional oxetane, and a cationic polymerization initiator ...; A step B of holding the mixture with a holding member; A step C of immersing one end of an optical fiber in the mixture held by the holding member; a step D of irradiating a laser beam having a wavelength λA from the other end of the optical fiber and emitting the laser beam from one end of the optical fiber located in the mixture, thereby polymerizing and curing the photopolymerizable polymer gel material A in an axial direction along the optical axis of the optical fiber; a step E of irradiating the mixture with light having a wavelength λB from around the mixture to polymerize and harden the photopolymerizable polymer gel material B; A method for producing a self-written optical waveguide, comprising:

4. The method for producing a self-written optical waveguide according to claim 3 , further comprising the step of irradiating the mixture with ultraviolet light between the step B and the step D.

Images